MATERIAL STRUCTURE AND ALLOY BINARY SYSTEM

A. MATERIAL STRUCTURE AND ALLOY BINARY SYSTEM

1.1 Material Structure And Period Table

The ionic bonding

In ionic bonding, metal atoms lose electrons and non-metal atoms gain electrons to form ions, which are then held together by strong electrostatic interactions. An ionic bond involves the transfer of electrons. When sodium reacts with chlorine, sodium chloride is formed. Sodium is a metal and chlorine is a non-metal. Sodium atom has the following arrangement of electrons, the electrons are shown as crosses.

2, 8, 1

It loses the electron in the outer shell easily to form an ion with a charge of +1. It is stable now because it has a full outer shell.

[ ]⁺ 2, 8

A Chlorine atom has the following arrangement of electrons, the electrons are shown as open circles.

2, 8, 7

It needs to gain one electron to form an ion with a full outer shell, and gets this electron from the sodium atom to form an ion with a charge of -1.

[ ]^- 2, 8, 8

So the dot and cross diagram for sodium chloride is

[ ]⁺ [ ]^-

The covalent bonding

In covalent bonding, non-metal atoms share electrons to form molecules, each atom making up the covalent bond has a full outer shell giving it more stability. A covalent bond involves the sharing of electrons.

Most gases exist as molecules, where two atoms share electrons by covalent bonding. Chlorine gas for example is made up of two chlorine atoms each with seven electrons in their outer shell.

Both atoms need to gain one electron to get a full outer shell so their shells overlap to make a covalent bond sharing a pair of electrons.

Instead of drawing the electrons in their shells a short hand version acceptable for A level Chemistry is shown below:

The metallic bonding

Metallic bonding in sodium

Metals tend to have high melting points and boiling points suggesting strong bonds between the atoms. Even a metal like sodium (melting point 97.8°C) melts at a considerably higher temperature than the element (neon) which precedes it in the Periodic Table.

Sodium has the electronic structure 1s²2s²2p⁶3s¹. When sodium atoms come together, the electron in the 3s atomic orbital of one sodium atom shares space with the corresponding electron on a neighbouring atom to form a molecular orbital - in much the same sort of way that a covalent bond is formed.

The difference, however, is that each sodium atom is being touched by eight other sodium atoms - and the sharing occurs between the central atom and the 3s orbitals on all of the eight other atoms. And each of these eight is in turn being touched by eight sodium atoms, which in turn are touched by eight atoms - and so on and so on, until you have taken in all the atoms in that lump of sodium.

All of the 3s orbitals on all of the atoms overlap to give a vast number of molecular orbitals which extend over the whole piece of metal. There have to be huge numbers of molecular orbitals, of course, because any orbital can only hold two electrons.

The electrons can move freely within these molecular orbitals, and so each electron becomes detached from its parent atom. The electrons are said to be delocalised. The metal is held together by the strong forces of attraction between the positive nuclei and the delocalised electrons.

This is sometimes described as "an array of positive ions in a sea of electrons".

If you are going to use this view, beware! Is a metal made up of atoms or ions? It is made of atoms.

Each positive centre in the diagram represents all the rest of the atom apart from the outer electron, but that electron hasn't been lost - it may no longer have an attachment to a particular atom, but it's still there in the structure. Sodium metal is therefore written as Na - not Na⁺.

Unit Cells

We will focus on the cubic category, which includes the three types of unit cellssimple cubic, body-centered cubic, and face-centered cubicshown in the figure below.

These unit cells are important for two reasons. First, a number of metals, ionic solids, and intermetallic compounds crystallize in cubic unit cells. Second, it is relatively easy to do calculations with these unit cells because the cell-edge lengths are all the same and the cell angles are all 90°.

The simple cubic unit cell is the simplest repeating unit in a simple cubic structure. Each corner of the unit cell is defined by a lattice point at which an atom, ion, or molecule can be found in the crystal. By convention, the edge of a unit cell always connects equivalent points. Each of the eight corners of the unit cell therefore must contain an identical particle. Other particles can be present on the edges or faces of the unit cell, or within the body of the unit cell. But the minimum that must be present for the unit cell to be classified as simple cubic is eight equivalent particles on the eight corners.

The body-centered cubic unit cell is the simplest repeating unit in a body-centered cubic structure. Once again, there are eight identical particles on the eight corners of the unit cell. However, this time there is a ninth identical particle in the center of the body of the unit cell.

The face-centered cubic unit cell also starts with identical particles on the eight corners of the cube. But this structure also contains the same particles in the centers of the six faces of the unit cell, for a total of 14 identical lattice points.

The face-centered cubic unit cell is the simplest repeating unit in a cubic closest-packed structure. In fact, the presence of face-centered cubic unit cells in this structure explains why the structure is known as cubic closest-packed.

The Period Table

IIIb

IVb

VIb

VIIb

VIIIb

IIb

III

VII

La*

Ac**

Lanthanides *

Actinides **

How to read?

Example: Al - Aluminum

A common metal comprising nearly ten percent of the crust of the earth, aluminum has been known since its preparation by Hans Oerstead 1825. Reactions of aluminum are investigated in fundimental and general chemistry.

Atomic number	-	13		Density	g/mL	2	.7
Atomic weight	u	26	.98154	Melting point	K	933	.25
Bonding radius	A	1	.18	Boiling point	K	2740
Atomic radius	A	1	.82	Heat of vaporization	kJ/mol	293	.4
Ionization Potential	V	5	.986	Heat of fusion	kJ/mol	10	.79
Electronegativity	-	1	.61	Specific heat	J/gK	0	.9
The oxide is amphoteric.				Crystal are face centered cubic.

1.2 Solidification Of Metal Alloy

Microporosity Formation in Alloy Solidification

Y. Sun and C. Beckermann

The single most important feature of the research is that it focuses solely on the microscopic scale (on the order of microns) where nucleation, interfaces, growth morphologies, and micro-flows can be directly observed. Previous studies of microporosity formation have only been concerned with larger length scales, and have not resolved the actual solid and pore microstructures. The present study will provide valuable knowledge of pore nucleation and growth rates, microscopic flow and solute fields in the solid-liquid-gas system present during pore formation, and the interactions between the pores and the evolving microstructure. This information can then be used to develop improved averaged descriptions of microporosity formation for use in macro-scale casting simulations. It also allows for the prediction of the exact characteristics of the pores in a fully solid microstructure as a function of the alloy composition and processing conditions.

The research will be accomplished through the combined use of novel modeling, numerical simulation, and experimental techniques. A phase-field method will be developed to model the complex phase transformation and transport phenomena present, including multi-component thermodynamics, curvature effects, and convection. Modern numerical techniques, such as deforming finite element meshes and highly efficient parallel solvers, will be employed to solve the model equations. The experiments will use transparent model alloys inside a Hele-Shaw cell under a high-resolution microscope. In the experiments, the initial gas content and the solidification conditions will be carefully controlled. The model predictions will be validated by the experimental measurements.

Figure: SCN-acetone dendrites growing around an artificially introduced bubble. Picture taken by Ahmet Guner.

Phase-Field Simulations with Convection

J. Ramirez, X. Tong, Yili Lu, H.J. Diepers (Aachen), I. Steinbach (Aachen), A. Karma (NEU), and C. Beckermann

The present work finds application in nearly every metal casting process. The problem of microporosity is of renewed interest because of the dramatically increased use of castings in the automotive and aerospace industries. Only the detailed prediction of microporosity can aid in its prevention and in assessing its influence on the strength and fatigue life of cast components. The transfer of the knowledge obtained through the proposed project will take place through continued collaboration with the casting industry, the development of improved microporosity models for use in casting simulation software, and the education of students. From a more fundamental point of view, the project will advance a largely uncharted area of research that is concerned with micro-scale, multi-component, multi-phase systems with phase change. Such systems are important not only in metal casting, but also in other materials processing operations, in nature, and in living organisms.

Figure: Porosity in an Al-10%Cu alloy.

B. FERROUS METAL

Iron and steel are the world's cheapest and most useful metals. These hard, durable metals are used in making thousands of products, from paper clips to automobiles. Machines made of iron and steel help produce almost everything we use, including our clothes, our homes, and even our food.

The word iron can refer to both an element and a number of alloys (mixtures) of iron and other metallic elements. As an element, iron is one of the most common chemical substances in the earth's crust, but it is never found in pure form there. Almost all iron occurs in ores, though some meteorites also contain iron. Manufacturers use iron alloys in the manufacture of so-called iron products.

Steel is produced by refining (purifying) iron and alloying it with other metals. Iron may be thought of as the basic material of steel, and steel may be considered the refined product of iron. Similarly, gasoline can be thought of as refined oil. However, the properties (characteristics) and uses of iron and steel differ as widely as do those of gasoline and oil.

Iron ores are mineral or rock deposits in which iron was concentrated by natural forces during the formation of the earth's crust. Steel manufacturers crush and process these ores to produce high-grade iron concentrates. The concentrates are turned into metallic iron by heating them with other raw materials in huge furnaces. Most metallic iron is used in manufacturing steel, but some is made into iron products. Steelmakers convert metallic iron into liquid steel by refining it in furnaces with recycled iron and steel scrap. The liquid steel is then formed into sheets, beams, rods, wire, tubing, and other shapes used in making various products. Most modern steel mills perform all the steps in steelmaking, from smelting iron ore to producing steel in useful shapes and forms.

As early as 4000 B.C., people used iron from meteorites to make ornaments, weapons, tools, and utensils. However, no one knows when or where people first made iron from iron ore. This process developed independently in several parts of the world, including the Middle East, China, and India. It spread quickly to other regions. By about 1000 B.C., most advanced civilizations had mastered the art of ironmaking. Early ironmakers produced small quantities of tough, elementary forms of steel. However, steel could not be manufactured cheaply in large quantities until the late 1800's. The technology of steelmaking has developed most rapidly during the second half of the 1900's.

Today, the production of iron and steel is one of the world's most vital industries. Throughout the world, millions of workers are employed in steel-manufacturing plants. Millions of additional workers provide machinery, raw materials, and energy to iron and steel companies or manufacture consumer products from iron and steel.

Kinds of iron and steel

The metals called iron and steel are alloys of the element iron. In general, steel is any alloy of the elements iron and carbon that contains less than 2 per cent carbon. Almost all types of steel also contain some manganese, and many kinds also include other elements. The properties of any kind of iron or steel depend largely on the chemical composition of the alloy. Heating and working (shaping) the metal can greatly change its physical properties.

There are thousands of kinds of iron and steel. But all types of iron can be classified as (1) pig iron, (2) cast iron, or (3) wrought iron. All kinds of steel can be grouped as (1) carbon steel, (2) alloy steel, (3) stainless steel, or (4) tool steel.

Sources of iron ore

The term iron ore commonly refers to any rock or mineral that contains enough iron to make it possibly worth mining. The location and characteristics of an ore deposit may at first make it undesirable as a source of iron. However, improvements in transportation, mining techniques, or mineral processing may later make a deposit commercially valuable. Increased demand for iron, or changes in government policies or world trade, can also lead to the opening of new mines.

The supply of iron ore in the world remains plentiful even though the steel industry continually uses huge amounts of it. In the United States and some other countries, much of the richest ore has been used up. As a result, steel companies have developed manufacturing techniques that enable them to use lower-grade ores. The United States also imports iron ore from Canada and various other nations.

Kinds of iron ore

In nature, iron always occurs in chemical combination with other elements, especially oxygen, carbon, sulfur, and silicon. The many kinds of iron ores thus contain chemical compounds made up of iron and one or more other elements. The principal ores from which iron is obtained include hematite, magnetite, limonite, pyrite, siderite, and taconite.

Hematite and magnetite are the richest iron ores. They are iron oxides (compounds of iron and oxygen) and contain about 70 percent iron. Hematite may occur as shiny crystals; grainy rocks; or a loose, earthy material. It may be black, brownish-red, or dark red. Magnetite is black and has magnetic properties.

Limonite has an iron content of about 60 percent. It is yellow-brown and consists of iron oxide and water.

Pyrite is about half iron and half sulfur. It has a shiny, metallic appearance and looks like gold.

Siderite is a gray-brown compound that contains about 50 percent iron, plus carbon and oxygen. In the past, it served as an important source of iron in Britain and Germany. However, those two nations have largely used up their deposits of siderite.

Taconite is a hard rock that contains about 30 percent iron. The iron occurs in the form of fine specks of magnetite or, in some cases, hematite. Taconite has increased in importance as deposits of richer iron ores have been used up.

Iron ore deposits. The world's largest deposits of iron ores were formed by a process that began more than 2 billion years ago. This process took place in areas then covered by shallow seas. Iron compounds in the water gradually settled to the bottom of the seas. There, together with sand and a fine-grained material called silt, they were formed into rock. Earthquakes and the shrinking of the earth's crust later raised this rock above the level of the water. In some areas, extremely rich concentrations of ore were left behind as water trickled through the rock, dissolving much of the sand.

Other iron ore deposits were formed in different ways. For example, the slow cooling of molten volcanic rock produced iron ore deposits in Sweden and some other areas. Elsewhere, tiny organisms in the water caused iron oxide to form. Today, iron oxides accumulate in marshy areas and on beaches.

The most important iron ore deposits in the United States lie near Lake Superior in Minnesota and Michigan. The Mesabi Range in Minnesota has produced more ore than any other area in the nation. California, Missouri, and Wyoming also have major deposits of iron ore. Canada's chief deposits occur along the border between Quebec and Newfoundland and north of Lake Superior in Ontario. Other nations that have large deposits of iron ore include Australia, Brazil, China, Russia, Sweden, and Ukraine. One of the world's richest deposits is Cerro Bolivar, a mountain of iron ore in Venezuela.

Mining and processing iron ore

There are two basic methods of mining iron ore, open-pit mining and underground mining. After the ore has been removed from the earth, it must be processed to make it suitable for use in making iron.

Open-pit mining is used to dig out deposits of iron ore that lie near the surface of the earth. First, bulldozers and other earthmoving equipment remove the soil and rocks that cover the deposits. This material is called the overburden. Next, miners use explosives to break up the mass of ore. Huge power shovels then scoop the ore into trucks and railroad cars for delivery to a central processing station.

Most of the world's iron ore comes from open-pit mines. These mines provide about 96 percent of the supply produced in the United States. The largest open-pit mines extend over several square miles or square kilometers and may measure more than 500 feet (152 meters) deep.

Underground mining, also known as shaft mining, involves digging tunnels into an ore deposit. Miners then go into the tunnels to remove the ore. To mine iron ore far below the surface, they dig a shaft into the rock next to the deposit. From this shaft, the miners drill horizontal tunnels into the ore at various levels. Conveyor belts or special railroad cars transport the ore to the shaft, where it is hoisted to the surface in buckets.

Underground mining is much more expensive and hazardous than open-pit mining. Today, this method is rarely used except to mine extremely high-grade ore and ore that lies near a steelmaking center. Miners also go underground to remove iron ore from inside a mountain. They reach such deposits by drilling horizontal tunnels into the side of the mountain. This method of underground mining brings much iron ore from the mountains of western Australia.

Processing. Ores with a high iron content may need only to be crushed, screened, and washed to remove particles too small for use. However, the United States and most other nations rely heavily on the use of taconite and other ores that require much processing. These ores must be broken down so that the particles of rich ore can be separated from worthless sand and rock. The rich ore is called concentrate, and the waste materials are referred to as tailings. Taconite must be crushed and ground to free the crystals of iron oxide from the surrounding material. Chunks of taconite are crushed to fine powder by tumbling them with steel rods or balls in large, rotating barrels. Powerful magnets then remove particles of magnetite from the powder. If the taconite contains hematite, which is not magnetic, workers must put the crushed ore into a chamber containing a mixture of liquids. The waste particles remain suspended in the liquid. But the particles that contain iron are denser and so settle to the bottom. This concentrated iron oxide is then removed from the chamber and dried.

Iron oxide produced from taconite must be converted into a form suitable for shipping and for use in making iron. In the most widely used process, the concentrate is moistened and combined with clay in rotating drums to form small pellets. The pellets, which measure1/2 inch to 1 inch (1.25 to 2.5 centimeters) in diameter, are dried and baked to a hard finish.

Taconite produces about 2 short tons (1.8 metric tons) of tailings for every 1 short ton (0.9 metric ton) of iron-oxide pellets. Therefore, iron ore is processed near the mine to save the cost of transporting huge quantities of waste material. Most of the pellets made in the United States come from the Lake Superior area. They are transported by ship to iron and steel plants on the southern shores of the Great Lakes.

In the past, processors dumped the tailings into Lake Superior. However, a federal court ordered an end to this dumping because it was creating pollution in the lake. Processors now dispose of such tailings in large artificial basins.

2.1 Iron Production

Blast Furnace.

A blast furnace is a huge cylinder made of steel and lined with firebrick (heat-resistant brick). Some blast furnaces stand more than 100 feet (30 meters) tall and measure over 30 feet (9 meters) wide at the base. Structures for loading raw materials and recovering waste gases are on top. Blast furnaces operate continuously until their brick lining wears out. A furnace may function for more than two years before being shut down for repairs.

The term blast furnace came from the blast of hot air that is constantly forced into the lower part of the furnace. This air is heated by two or more giant stoves as tall as 125 feet (38 meters). Air is blown through a stove into the furnace. The blast of air enters the furnace through pipes called tuyeres at between 1400 and 2100 °F (760 and 1150 °C). While air is blown through one stove, the other stove or stoves are being heated.

Workers load iron ore, coke, and limestone into the top of the blast furnace. These materials are called the charge, and the loading process is known as charging. The charge is carried to the top of the furnace by open cars that move up and down tracks on a ramp called a skip hoist. At the bottom of the ramp, each skip car is filled with a carefully weighed load of ore, coke, and limestone. At the top of the ramp, the skip car dumps its load into the furnace. In Germany and some other countries, almost all plants use a continuous conveyor belt rather than a skip hoist to load the furnace.

As the materials in the charge go down in the furnace, they contact the blast of hot air. The hot air causes the coke to burn. Oxygen in the air combines rapidly with the coke to produce carbon monoxide gas. This gas is the reducing agent that removes oxygen from the ore. The burning of the coke also produces intense heat, which melts the iron. Temperatures rise above 3000 °F (1600 °C) at the bottom of the furnace. In this area, called the hearth or crucible, the molten (liquid) iron forms a pool 4 to 5 feet (1.2 to 1.5 meters) deep. Molten slag floats on top of this pool. Waste gases rise to the top of the furnace. After devices called gas scrubbers clean these gases of dust and other impurities, the gases are burned as fuel in the stoves.

Molten iron is tapped from the furnace every four or five hours. Workers burn out a plug called the iron notch, and a white-hot stream of iron rushes through the hole. The iron flows into a hot-metal car, which holds more than 150 short tons (136 metric tons) of iron.

The slag is tapped more often than the iron. Workers remove it through a slag notch located above the level of the iron. The slag flows into a slag ladle, a container mounted on a railroad car. Manufacturers use some slag in making cement and other products but dispose of most of it as waste. Some producers convert slag into sandlike grains called slag granules.

Copula furnance

Direction reduction

Direct reduction converts iron oxide into solid iron called directly reduced iron. There are several methods of direct reduction, but the main ones all use reducing gases obtained from natural gas. Each process combines iron ore and reducing gases in a large furnace.

Direct reduction is a major method of producing iron in Mexico, Venezuela, and other nations that have a plentiful supply of cheap natural gas. This method will not become important in the United States and Canada until ironmakers can use gases produced from coal rather than gases obtained from natural gas. Several processes involving coal are being developed.

Furnaces used in direct reduction can be built much more quickly and cheaply than blast furnaces and coke ovens. Direct reduction also causes much less air pollution because coke ovens are a principal source of pollution in ironmaking. But metallic impurities in iron ore are not removed in a direct reduction furnace as they are--by the formation of slag--in a blast furnace. Therefore, the solid iron produced in a direct reduction system must be screened and magnetically cleaned before being charged into a steelmaking furnace.

2.2 Steel Production

There are three chief methods of making steel: (1) the basic oxygen process, (2) the electric furnace process, and (3) the open-hearth process. In each of these processes, charge materials are placed in a furnace, where the necessary reactions are carried out to produce a heat (batch) of refined steel. The rate of steel production varies greatly among the three processes. A basic oxygen furnace produces a heat of steel in about 45 minutes. An electric furnace does the job in about four hours, and an open-hearth furnace takes about eight hours. Steelmaking furnaces range in capacity from less than 50 short tons (45 metric tons) to more than 500 short tons (450 metric tons).

A steelmaking furnace has a control panel lined with dials, gauges, and other instruments. Workers use these instruments to adjust the temperature, pressure, and other conditions inside the furnace. Workers also take samples of molten steel from the furnace. Each plant has a laboratory with such instruments as spectroscopes and electron microscopes to analyze samples.

The basic oxygen

The basic oxygen process (BOP) produces steel by blowing oxygen at high pressure into molten iron and scrap. This method has become increasingly important ever since it was introduced into the United States from Austria in 1954. During the mid-1980's, about 60 per cent of the nation's steel was produced by the basic oxygen process.

A basic oxygen furnace, usually called a BOF, is a pear-shaped steel vessel with an open top and heat-resistant lining. The furnace is mounted on trunnions (pivots) so it can be tilted for charging and emptying. Basic oxygen furnaces are generally operated in pairs. While one produces steel, the other is being charged.

The usual charge in a BOF consists of about three-fourths molten iron and one-fourth scrap steel. After tilting the furnace and charging it with scrap, workers add a ladle of molten iron and return the furnace to its upright position. Then they lower an oxygen lance (pipe) into the furnace to blow pure oxygen onto the charge. The lance operates at a rate of up to 30,000 cubic feet (850 cubic meters) of oxygen per minute. The oxygen penetrates into the molten charge and reacts rapidly with the iron and impurities. These reactions create the heat necessary for the refining process. Fluxes are then added, and a slag soon forms.

As the blowing continues, oxygen combines with carbon and other impurities, converting the charge into steel. The waste gases are trapped by a smoke hood on top of the furnace. The BOF is then tilted to pour the molten steel out through a taphole near the top. The molten steel flows into a ladle, to which workers add alloying materials.

During the 1970's, some steelmakers began to use a new type of oxygen process in which oxygen is blown into the charge through tuyeres at the bottom of the furnace. This process, called Q-BOP, originated in Europe and was further developed in the United States. The Q stands for the German word Quell, which means fountain and refers to the manner in which the oxygen enters the charge. Any fluxes used are in powdered form and are blown in along with the oxygen. A Q-BOP unit has no overhead oxygen lance, and so it can be housed under a much lower roof than a basic oxygen furnace. In addition, Q-BOP produces steel faster than BOP.

Both BOP and Q-BOP produce steel at relatively low cost, largely because they require no electricity or fuel oil to create heat. The two processes also produce steel rapidly. In addition, steel produced by these methods is low in nitrogen. Nitrogen reduces the toughness of certain kinds of steel. However, BOP and Q-BOP do not permit as much precision as other processes do in the control of the chemical composition of steel. They also can use only a limited amount of scrap.

The electric furnace

The electric furnace process uses electric current to produce the heat needed to make steel. There are several types of electric furnaces, but the most widely used one by far is the electric arc furnace. During the mid-1980's, electric arc furnaces produced approximately 35 per cent of the steel manufactured in the United States. Their use is increasing steadily because they operate more efficiently and cost less to build than basic oxygen or open-hearth furnaces.

An electric arc furnace consists of a shallow steel cylinder lined with firebrick. The roof has holes through which three carbon rods called electrodes are inserted. A powerful electric current arcs (jumps) from each electrode to the charge material and then to another electrode. This arcing produces intense heat, which quickly melts the charge and promotes chemical reactions that produce steel.

The charge in an electric arc furnace consists mostly of scrap steel and alloy materials. Steelmakers rarely use pig iron in this type of furnace. But directly reduced iron is used wherever available at an economical price. The furnace roof is raised and swung to one side so the charge can be dumped in. After the charge has melted, fluxes and alloying material are added through a charging door on the side. The furnace stands on rockers and so can be tilted to pour off the slag through the charging door. Later, it is tipped in the opposite direction to pour out the molten steel through the taphole.

Electric arc furnaces are ideal for making certain alloy steels and tool steels. These steels require the addition of alloying elements that readily combine with oxygen. Such elements, which include chromium and vanadium, would be oxidized rapidly in an open-hearth or basic oxygen furnace and thus lost in the slag. The slag in an electric arc furnace contains so little oxygen that alloying elements are not oxidized.

The open-hearth furnace

The open-hearth process got its name because the hearth of the furnace is open directly to the flames that melt the charge. The furnace has a lining of firebrick, and a low, arched roof covers the hearth. An open-hearth furnace measures about 90 feet (27 meters) long and about 30 feet (9 meters) wide. Most open-hearth plants have several furnaces end to end in one long building. Workers fill the furnaces through doors on one side. They tap the steel on the opposite side, where the floor of the building is one story lower.

Each end of an open-hearth furnace has a fuel burner and a chamber called a checker chamber. These chambers contain firebricks arranged in a checkered pattern that provides many passages through which air and waste gases can flow. While the burner at one end is burning, the exhaust gases are drawn off through the checker chamber at the other end. These hot gases heat the checker chamber. The furnace automatically switches burners about every 15 minutes, and the flow of gases through the furnace is reversed. Thus, the air on its way to the hearth is preheated by passing through the hot checker chamber. Most open-hearth furnaces also have an oxygen lance in the roof. Pure oxygen is forced through this pipe into the furnace to increase the temperature and so speed the melting process.

Open-hearth furnaces can melt pig iron and scrap in varying proportions, but most steelmakers use about equal amounts of each. First, a charging machine dumps limestone and scrap steel into the furnace. After they have melted, molten iron is poured into the furnace. As the heating continues, most of the carbon from the iron is driven off in the form of carbon monoxide gas. Other impurities are oxidized and become part of the slag. Workers take a sample of the molten steel and may add materials to obtain the desired composition.

To tap the steel, workers blow out the tap-plug with a small explosive. The steel flows into a large ladle. Workers may then add alloying materials or substances to remove oxygen from the steel. When the slag appears, it overflows from the ladle into a smaller container called a slag thimble.

The open-hearth process uses expensive fuel oil and makes steel much more slowly than other methods do. It also produces large volumes of waste gases that must be cleaned to reduce air pollution. For these reasons, use of the open-hearth method has declined steadily since 1950, when it was the chief steelmaking process. By the mid-1980's, open-hearth furnaces produced only about 5 per cent of the steel made in the United States.

Special refining processes. Steel tapped from a furnace may require additional refining and alloying. In the simplest case, excess oxygen may be removed from molten steel in the transfer ladle by adding silicon, manganese, and aluminum. More complicated operations involve transferring the molten steel to a special refining vessel. For example, molten steel may be poured into a pear-shaped vessel equipped with tuyeres underneath. A mixture of argon and oxygen is blown through the pipes into the metal. This process removes excess carbon from the steel without oxidizing the chromium. Steelmakers also use various types of vacuum systems to remove dissolved hydrogen, oxygen, carbon, and nitrogen from molten steel.

Several complicated and expensive refining processes involve remelting steel after it has hardened into solid metal. These processes improve the purity of steel and help ensure the same quality throughout the product. However, their high cost restricts their use to the production of small amounts of specialty steels.

2.3 Carbon Steel

Carbon steel is by far the most widely used kind of steel. The properties of carbon steel depend primarily on the amount of carbon it contains. Most carbon steel has a carbon content of less than 1 per cent. Carbon steel is made into a wide range of products, including structural beams, automobile bodies, kitchen appliances, and cans.

Type of carbon steel;

a) low carbon steels - below 0.3 % carbon.

b) medium carbon steel – between 0.3 % to 0.8 % carbon.

c) high carbon steel – more than 0.8 % to 2.0 % carbon.

2.4 Alloy Steel

Alloys of iron. Iron is the most important industrial metal. Manufacturers have almost always used it as an alloy rather than as a pure metal. Iron-based alloys are called ferrous alloys.

The most widely used ferrous alloys are the steels. Steels vary both in the way people make them and in their composition. All steels, however, contain small amounts of carbon and manganese and large amounts of iron.

Each variety of steel has certain advantages. Carbon steels rank as the most widely used steels. Most carbon steels contain less than 1 percent carbon. Their strength and durability make them popular materials for structural beams, automobile bodies, and food cans. Alloy steels contain nickel, chromium, and molybdenum. They are strong enough for such products as bicycle frames and aircraft landing gear. Stainless steels contain more than 12 percent chromium, and many varieties also use nickel. Stainless steels can resist corrosion (rust and other chemical damage) extremely well. They are common materials for kitchen utensils, pots and pans, and hospital equipment. Tool steels are ferrous alloys used to work and shape other materials. They contain such components as tungsten, chromium, and molybdenum. Machines used to shape metal are made with special tool steels that keep their hardness and sharp cutting edges, even when they become red-hot in use.

2.5 Cast Iron

Cast iron is a hard, brittle form of iron made by casting. Casting is a process in which metal that has been melted is poured into molds and allowed to harden. Cast iron is often made by remelting a form of iron called pig iron. Solid cast iron is inexpensive and easy to make. It is known for its strength, density, and ability to absorb shock and vibration. All these qualities make cast iron especially useful in producing engine blocks, machinery frames, pipes, fire hydrants, and construction materials.

Cast iron is an alloy (mixture of metals) that contains about 90 percent iron, 2 to 4 percent carbon, 1 to 3 percent silicon, and smaller amounts of manganese, phosphorus, and sulfur. The high carbon content of cast iron contributes to its brittleness. This condition makes cast iron impossible to shape at any temperature below its melting point and requires the use of molds.

Contributor: James A. Clum, Ph.D., Prof. of Mechanical Engineering and Associate Dean for Research and External Affairs, State Univ. of New York, Binghamton.

C. METAL WORK, CASTING AND HEAD TREATMENT

3.1 Cold Work

Typical applications include:

· All severe cold heading applications

· Self-tapping screws

· Roofing bolts

· Machine screws

· Bolts

· Set screws

· Blind rivets

Cold rolling

Cold rolling is a process by which the sheet metal or strip stock is introduced between rollers and then compressed and squeezed. The amount of strain introduced determines the hardness and other material properties of the finished product.

The advantages of cold rolling are good dimensional accuracy and surface finish.

In general, manufacturers are interested in the final dimensions of the products; therefore, the angle after unloading is the main parameter to control in sheet metal bending. The major methods used to reduce springback or control the unloaded bend angle can be listed as follows:

Bendings

3.2 Hot Work

Liquid steel is useless when it comes from the furnace. It must be cast into a solid form before it can be made into useful objects. Steelmakers cast most steel by means of ingot casting or strand casting. These processes produce solid steel that must be further formed by rolling, forging, extruding, or other processes. Some types of steel also receive a special finish or coating. A process called mold casting is used for a small amount of steel. This method involves casting steel in a mold that gives it the shape of a finished product.

The various shaping and finishing processes are carefully controlled from elevated platforms. Steel mills have laboratories that test the finished products to assure their high quality.

Ingot casting. Much steel is cast into blocks called ingots. Steel ingots vary widely in size, depending on the type of steel and the kind of product to be made. For example, ingots of tool steel may weigh only a few hundred pounds or kilograms. In contrast, huge ingots weighing up to 300 short tons (270 metric tons) are made into parts for enormous industrial machines. Most ingots weigh between 2 and 40 short tons (1.8 and 36 metric tons).

To cast ingots, workers pour liquid steel from a ladle into molds made of cast iron. Most of these molds have a tapered, rectangular shape and are open at both ends. The molds are placed on special railroad cars, and steel is poured in from above. After the steel hardens, the mold is lifted off by giant tongs that grip it by handles on the sides. The ingots are then placed in a heated pit called a soaking pit, where they remain until they have a temperature of about 2200° F. (1200° C) throughout.

The heated ingots travel to a roughing mill, a machine that squeezes them between heavy rollers into longer and thinner shapes. Roughing mills produce three semifinished forms of steel: (1) blooms, (2) billets, and (3) slabs. Blooms have a square cross section, and slabs are rectangular in cross section. Billets are square like blooms but have a smaller cross section. Most billets are much longer than blooms.

Strand casting produces blooms, billets, or slabs directly from molten steel. Strand-casting machines make it possible for steelmakers to avoid the costly and time-consuming processes of casting, heating, and rolling ingots.

In strand casting, workers pour liquid steel from a ladle into a tundish (flow control dish) at the top of the machine. The steel flows at a controlled rate from the tundish through a mold that forms the metal into the desired shape. Cold water quickly cools the steel, causing it to harden as it continues to move through the caster. As the steel leaves the caster, a moving torch cuts it into the desired lengths.

Rolling is the most commonly used method of shaping steel products. In this process, billets, blooms, or slabs pass between heavy rollers that squeeze them into the desired size and shape. The major products made by rolling include (1) sheet and strip, (2) bars, (3) railroad rails and structural beams, and (4) plates.

Sheet and strip are flat products, generally less than 1/4 inch (6.4 millimeters) thick. Strip is much narrower than sheet, which may be up to 100 inches (250 centimeters) wide. Sheet and strip are the main products of the steel industry. Together, they account for more than a third of the steel produced in the United States.

Steelmakers produce most sheet and strip in the form of large coils that the user can cut into pieces of any desired length. However, some comes from the steel plant cut into specified lengths. Most sheet and strip is used in automobile bodies, but thousands of other products also contain these forms of steel.

Machines called hot-rolling mills produce sheet and strip from slabs and billets. The process is known as hot rolling because the steel is reheated to about 2200° F. (1200° C) before being rolled. A hot-rolling mill has many sets of rollers called roll stands arranged in a long line. In each roll stand, the rollers are closer together than in the preceding stand. As a result, the steel is squeezed thinner and thinner as it travels through the mill. As the thickness decreases, the length increases.

A hot-rolling mill can convert a slab 5 inches (13 centimeters) thick and 8 feet (2.4 meters) long into a sheet 1/16 inch (1.6 millimeters) thick and 1,400 feet (430 meters) long. The process takes only a few minutes. A hot-rolling mill may be housed in a building up to 1 mile (1.6 kilometers) long. This great length is necessary because of the large number of roll stands and the tremendous increase in the length of the steel. As the hot-rolled steel comes out of the last stand, the steel is wound into large coils.

After being cooled, the coils of steel may be shipped to customers or may be processed further. Much hot-rolled sheet and strip is pickled and then cold-rolled. Pickling involves passing the steel through vats of acid to remove the oxide that formed on it during hot rolling. In a cold-rolling mill, the steel travels rapidly at room temperature through a series of roll stands and then is recoiled. Cold rolling gives steel the ability to be stretched and shaped without cracking. It also makes steel thinner and smoother and gives it a bright finish.

Bars are the second leading product of the steel industry. Products made from steel bars include hand tools and automobile parts. Steel companies make bars in many sizes and in such shapes as round, square, oval, and hexagonal. Bars are hot rolled by bar mills, which resemble the machines used for sheet and strip. However, a bar mill has grooved rolls that squeeze a hot billet into the desired shape. Many bars receive further processing after being hot rolled. They are pulled at room temperature through an opening in a tool called a die. This process strengthens the steel and gives it a bright, smooth finish.

Railroad rails and structural beams are hot-rolled into long lengths in the same way as bars. But steelmakers produce many structural shapes, such as I-beams and H-beams, according to the instructions of a specific customer. Most railroad rails and structural beams are made from blooms.

Plates are flat and measure more than 1/4 inch (6.4 millimeters) thick. They are used in the construction of ships and bridges and in many kinds of industrial and scientific equipment. Steel plants roll most plates from slabs, but some come directly from ingots. Machines called reversing mills produce the majority of plates. The heated steel passes back and forth between the rollers of a single roll stand. The distance between the rolls decreases each time until the steel reaches the desired thickness. Some plates are made by continuous rolling mills like those that produce sheet and strip.

Forging

Forging is the process by which metal is heated and is shaped by plastic deformation by suitably applying compressive force. Usually the compressive force is in the form of hammer blows using a power hammer or a press.

Forging refines the grain structure and improves physical properties of the metal. With proper design, the grain flow can be oriented in the direction of principal stresses encountered in actual use. Grain flow is the direction of the pattern that the crystals take during plastic deformation. Physical properties (such as strength, ductility and toughness) are much better in a forging than in the base metal, which has, crystals randomly oriented.

Forgings are consistent from piece to piece, without any of the porosity, voids, inclusions and other defects. Thus, finishing operations such as machining do not expose voids, because there aren't any. Also coating operations such as plating or painting are straightforward due to a good surface, which needs very little preparation.

Forgings yield parts that have high strength to weight ratio-thus are often used in the design of aircraft frame members.

A Forged metal can result in the following

•	Increase length, decrease cross-section, called drawing out the metal.
•	Decrease length, increase cross-section, called upsetting the metal.
•	Change length, change cross-section, by squeezing in closed impression dies. This results in favorable grain flow for strong parts

Extruding involves forcing heated steel through an opening in a die. A ram at one end of a cylinder pushes the steel through a die at the other end. Molten glass serves as a lubricant to help the hot steel slip through the die. The steel comes out shaped like the die opening. Steel firms use extrusion for seamless tubing and products of various complicated shapes.

Other shaping processes are used in making a variety of small steel products. Automatic machines stamp, hammer, and press steel into such products as bolts, nails, screws, and tools. Wire is made by drawing steel rods through a series of successively smaller dies.

Finishing. Many types of steel receive a special finish or coating. For example, some stainless steel goes through special grinding and polishing. The most important coating processes include (1) galvanizing and (2) electroplating.

Galvanizing is the process of coating steel with a thin layer of zinc. The zinc coating makes the steel highly resistant to corrosion. Each year, millions of tons of galvanized steel sheet are made into such products as heating ducts and storage tanks. The most widely used method of galvanizing, called hot-dip galvanizing, starts with coils of steel sheet. The steel is annealed (heated and then cooled slowly) to make it more flexible. Next, rollers carry the steel into a pot of molten zinc. The steel then travels through a cooling tower, where the zinc coating hardens. The finished product is wound into coils or cut into sheets.

Electroplating puts a coating of another metal on steel by means of electric current. Steel companies use this process in producing huge quantities of tin-plated steel, which is made into tin cans. Steel is electroplated with chromium in making so-called tin-free steel. This metal can be used instead of tin-plated steel in manufacturing cans and other containers.

3.3 Casting Process

3.4 Heat Treatment

Different heat treatments have significant effects on the microstructure and mechanical properties of a material. Heat treatment processes include annealing, normalizing, and quenching and tempering. In the lab, specimens are heated in the furnaces and given different heat treatments. The effects of each heat treatment are determined using diverse equipment in the lab: microstructure by the video microscope, hardness by the Rockwell hardness tester, and tensile tests (data for stress-strain curves).

D. MATERIAL TESTING

4.1 Material Defects – failure material.

· Fracture – frature is the separation of a solid under stress into two or more parts. In general metal fractures can be classified as ductile or brittle but can be a mixture of two.

The ductile fracture of metal accurs after entensive plastic deformation and is

characterized by slow cract propagation.

The brittle fracture, in contras, usually proceeds along characteristic

crystallographic planes called cleavage planes and has rapid crack propagation.

· Creep – when a metal or an alloy is under costant load or stress, it may undergo progressive plastic deformation over a period of time. This time-dependent strain is called creep. The creep of metals and alloys is very important for some type of engineering design, particularly those operating at evevated temperatures.

· Fatiq – In many type of servive applications metal part subjected to repetitive or cylic stress will fail at a much lower stress than that which the part can witstand under the application of single static stress. These failures which accur under repeated or cyclic stressing are called fatique failures.

4.2 Properties of metal (Hardness, Toughness, Elastice Of Material, Ductile)

4.3 Destructive And Non-Desstructive Test

Destructive test

· Hardness test

· Tensile test

· Creep test

· Impact test

· Fatig test

· Metallugraphy experiment

Non-Desstructive Test

· Ultra sonic test

· Dye peneterant test

· Magnetic particle test

· Identification and selection of material

· Heat test

E. CORROSION

5.1 Defination

Corrosion, pronounced kuh ROH zhuhn, is the destruction of a material caused by the chemical action of a gas or liquid. Corrosion occurs chiefly in metals, but it may also affect ceramics. Rust is the most familiar form of corrosion. This reddish-brown substance forms on iron and steel that are exposed to moist air or to water containing impurities.

In most cases, corrosion involves two related chemical reactions--oxidation and reduction. In oxidation, the atoms of a metal give up electrons to a liquid or a gas. In reduction, part of the same metal or an adjoining metal captures these electrons from the liquid or gas. The electrons that flow from one metal to the other form an electric current. In this sense, corrosion is an electrochemical process.

There are many types of corrosion. One kind, called localized attack, occurs on small areas of bare metal and produces holes or cracks. Another type, uniform corrosion, attacks much larger areas, such as the surface of an aluminum pot or a copper roof. It can be beneficial. On copper roofs, for example, such corrosion produces a thin, greenish film called patina that protects the surface against further rapid corrosion.

The type of corrosion and its severity depend on the chemical makeup of the metal and of the corrosive agent. Other major factors include stresses in the metal, the temperature of the corrosive agent, and the speed at which the agent moves against the metal. Corrosion tends to be more severe if the corrosive agent hits the metal at a high speed. If the agent contains solid particles, the corrosion is even worse and is called erosion-corrosion.

Contributor: Cathleen J. Hapeman, Ph.D., Research Chemist, U.S. Department of Agriculture- Agriculture Research Service.

5.2 Type of corrosion

· Uniform or general attact corrosion

· Galvanic or two-metal corrosion

· crevice corrosion

· pitting corrosion

· intergranular corrosion

· stress corrosion

· erosion corrosion

· cavitation damage

· fretting corrosion

· selective leaching or dealloying

5.3 Electrochemical series

Table 1. Relative position of common metals in the electrochemical series

Metal / Alloy	Potential (Volts)	Reactivity
Magnesium	-1.55	More Reactive
Zinc	-1.10
Aluminium	-0.86
Cadmium	-0.77
Cast Iron	-0.68
Carbon Steel	-0.68
Stainless Steel	-0.61
Lead	-0.57
Solder	-0.52
Tin	-0.49
Copper	-0.43
Aluminium Bronze	-0.41	Less Reactive

5.4 Prevention of corrosion

· Material selection

· Coating

· Design

· Cathodic and anodic protection

· Environmental control (cleaning,volocity,oxygen)

STAINLESS STEEL

A. STAINLESS STEEL

1.1 Mechanic Properties Of Stainless Steel

Stainless steel is the name of a family of alloy steels that resist corrosion (rust). As a family, the stainless steels have an easily maintained, attractive appearance. They show remarkable strength and ductility and are unique in their general resistance to weather and to most corrosives. Most stainless steels used in the home are highly polished, with a silvery appearance, but they do not need this finish to resist corrosion. Stainless-clad steel is commonly ordinary steel to which a thin layer of stainless steel has been bonded on one or both sides.

The most familiar use of stainless steel in the home is in kitchen knives, flatware, sinks, pots and pans, and other places where cleanliness and easy maintenance are essential. Stainless-steel equipment is used in hospitals, restaurants, chemical industries, dairies, and food-processing plants. Engineers use stainless steel parts for automobiles, aircraft, and railroad passenger cars. Scientists use microporous stainless steel, made with a nickel alloy, to filter gases, liquids, and small particles.

1.2 Chromium Additive

Chromium is the chief metal alloyed with iron, carbon, manganese, and silicon in making stainless steel. Chromium helps steel resist corrosion. However, the carbon in the steel reduces the ability of chromium to provide corrosion resistance. As a result, most stainless steels are improved by reducing the amount of carbon in them to very low levels. Nickel ranks as the second most important alloy in most stainless steels. One or more of the following elements also may be added to iron to make stainless steel: molybdenum, titanium, columbium, aluminum, nitrogen, phosphorus, sulfur, and selenium. Each element modifies stainless steel so it can be used for a specific purpose.

Contributor: James A. Clum, Ph.D., Prof. of Mechanical Engineering and Associate Dean for Research and External Affairs, State Univ. of New York, Binghamton.

B. COPPER ALLOY

Copper has been one of the most useful metals for over 7,000 years. Today, the uses of this reddish-orange metal range from house gutters to electronic guidance systems for space rockets.

Copper is the best low-cost conductor of electricity. As a result, the electrical industry uses about 60 percent of the copper produced, chiefly in the form of wire. Copper wire carries most of the electric current inside homes, factories, and offices. Large amounts of copper wire are used in telephone systems, as well as in television sets, motors, and generators.

Combined with other metals, copper forms such alloys as brass and bronze. Copper and its alloys can be made into thousands of useful and ornamental articles. In the home, copper serves as a basic material for locks, pipe, plumbing fixtures, doorknobs, and drawer pulls. Other commonly used copper products include lamps, pots, pans, roofing, and jewelry.

Chemical compounds of copper help improve soil and destroy harmful insects. Copper compounds in paint serve as pigments and help protect materials against corrosion. Also, copper in small amounts is vital to all plant and animal life.

In ancient times, one of the chief sources of copper for the peoples near the Mediterranean Sea was the island of Cyprus. As a result, the metal became known as Cyprian metal. Both the word copper and the chemical symbol for the element, Cu, come from cuprum, the Roman name for Cyprian metal.

Properties of copper

The physical properties of copper make the metal valuable to industry. These properties include (1) conductivity, (2) malleability, (3) ductility, and (4) resistance to corrosion.

Conductivity. Copper is perhaps best known for its ability to conduct electric current. Silver is the only better conductor, but silver is too expensive for common use. Copper alloys do not conduct current nearly as well as pure copper.

Impurities in refined copper greatly reduce electrical conductivity. For example, as little as 5/100 percent arsenic cuts the conductivity of copper by 15 percent. Copper is also an excellent conductor of heat. This property makes it useful in cooking utensils, radiators, and refrigerators.

Malleability. Pure copper is highly malleable (easy to shape). It does not crack when hammered, stamped, forged, or spun into unusual shapes. Copper can be worked (shaped) either hot or cold. It can be rolled into sheets less than 1/500 inch (0.05 millimeter) thick. Cold rolling changes the physical properties of copper and increases its strength.

Ductility. Copper possesses great ductility, the ability to be drawn into thin wires without breaking. For example, copper rod that is 7/16 inches (1 centimeter) in diameter can be heated, rolled, and drawn into a wire that is thinner than a human hair.

Resistance to corrosion. Copper is quite resistant to corrosion. It will not rust. In damp air, it turns from reddish-orange to reddish-brown. After long exposure, copper becomes coated with a green film called patina, which protects it against further corrosion.

Other properties. Cold-rolled copper has a tensile strength from 50,000 to 70,000 pounds per square inch (3,500 to 4,900 kilograms per square centimeter). A material's tensile strength is the maximum stress it can withstand before breaking. Copper keeps its strength and toughness up to about 400 °F (204 °C).

2.1 Phase Diagram Of Copper Alloy

2.2 Brass

Brass is an alloy (mixture) of copper and zinc. Other elements may be added to the alloy for special uses. Brass is widely used in making hardware, electrical fixtures, inexpensive jewelry, metal decorations, military supplies, and musical instruments.

The amount of copper used in brass ranges from 55 percent to more than 95 percent. The color and properties of brass vary with its composition. When the alloy contains about 70 percent copper, it has a golden yellow color and is known as yellow brass, high brass, or cartridge brass. When it contains 80 percent or more copper, it has a reddish copper color and is known as red brass or low brass. Muntz metal contains 60 percent copper and 40 percent zinc. Alloys that have a high copper content are almost as soft as pure copper. But as zinc is added, they become stronger and tougher. Compositions of 55 percent copper and 45 percent zinc are hard and somewhat brittle.

To obtain special properties, brass makers often add other elements to the copper-zinc alloy. Lead is added to improve machinability (ease of cutting). The result is called leaded brass. Brass that contains 1 percent to 3 percent lead can be machined easily and is often used to make parts for clocks and other precision equipment. Tin and nickel are often added to increase the alloy's resistance to corrosion or wear. Naval brass contains 1 percent tin. Nickel can be added to obtain a silvery-white color that makes the alloy a more suitable base for silver plating. Silver-plated flatware and hollowware often have a brass base. Other elements added to brass are iron, aluminum, and manganese. Aluminum helps prevent seawater from corroding brass.

Making brass. The first step in making brass is to melt copper in an electric furnace. Solid pieces of zinc are then added to the melted copper. The zinc melts rapidly. A covering of charcoal is often placed over the liquid metals to reduce the loss of heat and to prevent an excessive loss of zinc by vaporization (see VAPOR). After the copper and zinc have been melted and thoroughly mixed, the brass is ready for pouring. It can be poured directly into forms to cast the wanted articles, or it can be made into bars called billets. Such bars make it easier to work with the brass or to store it. Workers may cut off the top of the brass bar. This portion, which became solid last, contains impurities and is porous. The billet is then placed in another furnace and reheated until it reaches the proper temperature for working.

After the reheating process, the brass can be rolled while it is still hot, and formed into the desired shape. A milling machine removes surface imperfections. The brass is then cold-rolled.

Almost any method for shaping metal can be used to shape brass. It can be rolled into sheets and plates; drawn or extruded (squeezed out) into rods, tubes, and wire; forged or pressed into complicated shapes; and spun to form deep receptacles (containers).

Brass articles are free from dirt, gas, and other defects, so they can be polished to a brilliant finish. Brass objects often are electroplated (see ELECTROPLATING). Their surfaces are easily treated to obtain beautiful and useful effects.

History. Both brass and bronze, the alloy of copper and tin, were probably first made accidentally when people heated copper ores that contained the alloying metals. But brass did not have the importance of bronze in ancient times. Brass was harder to produce because the zinc in brass, unlike the tin in bronze, evaporates soon after melting and is lost.

Contributor: Sara Steck Melford, Ph.D., Associate Prof. of Chemistry, DePaul Univ.

2.3 Usage Of Copper Alloy In Engineering

· Electrical equipments ( bell, cabel, plug,… etc)

· Air condition tube

· Electrical conductor

C. ALUMINIUM ALLOY

Aluminum, pronounced uh LOO muh nuhm, is a lightweight, silver-colored metal that can be formed into almost any shape. It can be rolled into thick plates for armored tanks or into thin foil for chewing gum wrappers. It may be drawn into wire or made into cans. Aluminum does not rust, and it resists wear from weather and chemicals. Aluminum is called aluminium ( pronounced al yuh MIHN ee uhm) in English-speaking countries outside North America.

Pure aluminum is soft and has little strength. Thus, aluminum producers almost always alloy (mix) it with small amounts of copper, magnesium, zinc, and other elements to form aluminum alloys. The added elements give aluminum strength and other properties that make it one of the most useful metals. The world uses more aluminum than any other metal except iron and steel.

The largest share of aluminum alloy production goes to the packaging industry for use in such items as beverage cans, bottle caps, foil pouches, foil wrappers, and food containers. The construction industry uses aluminum alloys in such items as gutters, panels, residential siding, roofing, tubes for electric wires, and window frames. Manufacturers of transportation equipment use huge amounts of aluminum in airplanes, automobiles, boats, railroad cars, and trucks. Aluminum is used in much electrical equipment, including light bulbs, power lines, and telephone wires. Thousands of other products also contain aluminum. These products include air conditioners, cookware, golf clubs, knitting needles, lawn furniture, license plates, paints, refrigerators, rocket fuel, and zippers.

Aluminum is the most plentiful metallic element in the earth's crust and the third most common of all the elements, after oxygen and silicon. Aluminum makes up about 8 percent of the earth's crust. But unlike some other metals, such as gold and silver, aluminum never occurs free (uncombined) in nature. It is always chemically combined with other elements. People had no way of separating aluminum from these elements until the 1800's. Scientists then developed processes for separating the elements and producing aluminum. These processes have been used to make aluminum ever since.

Properties of aluminum alloys

Only a small percentage of aluminum is used in pure form. It is made into such items as electrical conductors, jewelry, and decorative trim for appliances and cars.

Almost all aluminum is used commercially in alloy form with up to 15 percent of one or more other elements. The chief elements are copper, magnesium, manganese, silicon, tin, and zinc. Copper and magnesium increase the strength and hardness of aluminum. Magnesium also makes aluminum easier to weld. Manganese helps aluminum resist corrosion and also provides strength. Silicon lowers the melting point of aluminum and makes it easier to cast. Tin makes aluminum easier to shape with metalworking tools. Zinc, especially when combined with magnesium, gives added strength. Other elements may also be alloyed with aluminum for special purposes. These elements include bismuth, boron, cadmium, chromium, cobalt, iron, lead, lithium, nickel, sodium, titanium, vanadium, and zirconium.

Aluminum, with its alloys, has many valuable properties that make it an exceptionally useful metal. These properties include (1) light weight, (2) strength, (3) corrosion resistance, (4) electrical conduction, (5) heat conduction, and (6) light and heat reflection.

Light weight. Aluminum is one of the lightest metals. It weighs about 170 pounds per cubic foot (2,720 kilograms per cubic meter)--about a third as much as steel. As a result, aluminum has replaced steel for many uses. For example, some parts of airplanes, automobiles, and trucks are now made of aluminum rather than of steel because lighter vehicles use less fuel. Products packed in aluminum containers cost less to ship because the containers weigh less than those made of other metals. To make aluminum alloys even lighter, the lightest metal, lithium, is added to the aluminum.

Strength. Although pure aluminum is weak, certain aluminum alloys are as strong as steel. Such alloys are used in airplanes and trucks, in guardrails along highways, and in other products that require strength. Aluminum alloys lose some strength at high temperatures. But unlike many other metals, they get stronger at extremely low temperatures. Aluminum alloys are widely used in equipment for processing, transporting, and storing liquefied natural gas, which can have a temperature of -260° F (-162° C).

Corrosion resistance. Some metals corrode (wear away) if exposed to oxygen, water, or various chemicals. A chemical reaction occurs that causes the metals to rust or become discolored. When aluminum reacts with oxygen, however, the metal forms an invisible layer of a chemical compound called aluminum oxide. This layer protects aluminum from corrosion by oxygen, water, and many chemicals. It makes aluminum especially valuable for use outdoors, where the metal resists the effects of wind, rain, and pollution.

Electrical conduction. Aluminum and copper are the only common metals suitable for use as electrical conductors. Aluminum conducts electricity about 62 percent as well as copper. But aluminum weighs a third as much. Aluminum wire can therefore carry the same amount of electric power as copper wire that weighs twice as much. In addition, aluminum is more ductile than copper, which means it can more easily be drawn into wires. Aluminum wire is used for nearly all high-voltage power lines in the United States.

Heat conduction. The first large commercial use of aluminum was in cookware. Aluminum cookware heats up quickly and evenly. Aluminum also cools quickly, which helps make it popular for such items as beverage cans and ice cube trays.

Light and heat reflection. Aluminum reflects about 80 percent of the light that strikes it. This property has made the metal widely used in lighting fixtures. Aluminum also reflects heat well. Buildings with aluminum roofs reflect much of the sun's heat and so stay cooler in hot weather. When fire fighters must walk through flames, they wear special suits coated with aluminum.

Other properties. Aluminum is nonmagnetic, which makes it valuable for protecting electrical equipment from magnetic interference. Aluminum does not produce sparks when struck and can therefore be used near flammable or explosive materials. The metal is not poisonous, and so food can be safely wrapped in aluminum foil and cooked in aluminum pots. Aluminum can be shaped by almost any metalworking process. It can also be bolted, glued, riveted, soldered, welded, and otherwise joined by most methods used for other metals. Finally, aluminum can be recycled.

Sources of aluminum

Most minerals, rocks, and soils contain aluminum compounds. But aluminum can be made economically only from bauxite. Bauxite is the name for any ore that has a large amount of aluminum hydroxide--a chemical combination of aluminum oxide and water. Aluminum oxide, also called alumina, is the compound from which aluminum is made.

Most bauxite consists of 30 to 60 percent alumina and 12 to 30 percent water. It also contains iron oxide, silica, and titanium oxide. The color of bauxite depends chiefly on how much iron oxide the ore contains. The more iron oxide it has, the darker the color. Bauxite may be white, cream, gray, pink, yellow, red, or brown. Most bauxite is as hard as rock, but some is as soft as clay.

The richest deposits of bauxite lie in tropical and near-tropical regions. Enough bauxite deposits have been found to last several hundred years. The leading bauxite-mining countries include Australia, Guinea, Jamaica, and Brazil.

Most bauxite deposits lie near the surface of the earth and are mined by the open-pit method. In this process, bulldozers and other earthmoving machines first clear away the overburden--the soil, rocks, and trees that cover the deposits. Next, explosives blast the ore loose. Huge power shovels scoop up the bauxite, and trucks or railroad cars carry it to a processing plant.

At the processing plant, the bauxite is crushed and then washed to remove clay and dirt. Some of the water in the bauxite is removed by drying the ore in kilns (ovens). The bauxite is then ground into a powder and shipped to a refining plant.

How aluminum is produced

There are two chief steps in producing aluminum: (1) refining the bauxite to obtain alumina and (2) smelting the alumina to obtain aluminum. After smelting, the molten aluminum is cast into blocks called ingots or other forms that will be shaped into finished products. It takes 4 to 6 pounds of bauxite to make 1 pound of aluminum.

Refining the bauxite separates the alumina in the ore from the iron oxide, silica, and titanium oxide. To separate the alumina, aluminum producers use the Bayer process. This technique was patented by Karl Joseph Bayer, an Austrian chemist, in 1888.

The first step of the Bayer process is mixing powdered bauxite with a solution of caustic soda (sodium hydroxide). Machines pump the mixture into large tanks called digesters. The digesters heat the mixture under pressure at 300 to 480 °F (150 to 250 °C) for about 30 minutes. The alumina dissolves in the caustic soda, forming a solution of sodium aluminate. The other materials in the bauxite remain as solids and are called red mud because of their color.

The mixture of sodium aluminate solution and red mud next passes through a series of tanks in which cloth filters separate the liquid from the solids. The red mud is discarded. The sodium aluminate solution is cooled slightly and sent to tanks called precipitators. Crystals of aluminum hydroxide are then added to the solution, which is agitated (stirred) for several days. This process causes most of the alumina in the solution to precipitate (come out of solution) and collect on the crystals.

After the precipitation is complete, the solution is filtered to separate the aluminum hydroxide crystals from the liquid. The crystals are washed to remove any impurities and then heated at 2000 to 2200 °F (1090 to 1200 °C). The heat drives out water, leaving a fine white powder of alumina. The alumina is composed of aluminum and oxygen. To recover the alumina that did not precipitate, manufacturers take the liquid and refine it with a new batch of bauxite and caustic soda. Small amounts of lime and soda ash may also be added.

Smelting the alumina separates the aluminum from the oxygen. The smelting is done by the Hall-Heroult process. This method was developed independently in 1886 by two scientists. They were Charles Martin Hall of the United States and Paul L. T. Heroult of France.

Aluminum producers begin the Hall-Heroult process by dissolving the alumina in a chemical bath composed mainly of cryolite (sodium aluminum fluoride). The bath also contains a little aluminum fluoride and calcium fluoride. The bath is held in large rectangular steel containers and heated to about 1740 °F (950 °C). The containers, called pots or cells, have a carbon lining.

In a process called electrolytic reduction, one or more carbon blocks suspended in each pot send an electric current through the bath. The current flows to the carbon lining, completing the electric circuit. The blocks act as the anode, or positive pole of the circuit, and the lining acts as the cathode, or negative pole. As the current flows through the bath, the alumina breaks apart. The oxygen in the alumina combines with the carbon in the anode and is released as carbon dioxide gas. The aluminum metal collects at the cathode at the bottom of the pot. See ELECTROLYSIS.

An aluminum plant may have as many as 200 pots electrically connected to one another in long rows called potlines. The reduction of alumina to aluminum goes on continuously. Alumina is added to the pots regularly, and the electric current keeps the bath at the proper temperature. A large pot may produce more than 2 short tons (1.8 metric tons) of aluminum daily.

Casting the molten aluminum. About once a day, molten aluminum from the potlines is drawn off into pots called crucibles. Each crucible holds 4,000 to 8,000 pounds (1,800 to 3,600 kilograms) of aluminum. Most of the aluminum is cast into ingots. There are two types of ingots: (1) fabricating ingots and (2) foundry ingots. Aluminum is also cast into forms called billets.

Fabricating ingots, or rolling ingots, are used by aluminum producers to make plates, sheets, and foil. The ingots may be 30 feet (9 meters) long, 6 feet (1.8 meters) wide, and 2 feet (0.6 meter) thick. They may weigh up to 18 short tons (16 metric tons). To make fabricating ingots, producers alloy other metals with the molten aluminum in a furnace and then purify the mixture. Scrap aluminum and recycled aluminum may also be added. The purification process, called fluxing, consists of pumping nitrogen, argon, or other gases through the liquid. The gas causes impurities to float to the surface, where they are skimmed off. During fluxing, chemical reactions cause some hydrogen gas to be trapped in the liquid. In a process called degassing, chlorine or some other gas is added to remove the hydrogen.

After fluxing and degassing, the molten aluminum alloy is filtered to remove solid impurities. Then it is cast into ingots, usually by the direct chill method. In this process, the alloy is poured into a mold, which is then passed through a spray of cold water. The water quickly cools and freezes the alloy.

Foundry ingots, also called alloy ingots or remelt ingots, weigh 4 to 50 pounds (1.8 to 23 kilograms). In most cases, the molten aluminum is poured from the crucibles directly into molds, where it cools and hardens gradually. Aluminum producers sell foundry ingots to plants called foundries. The foundries remelt the ingots with scrap and recycled aluminum and perform the alloying, fluxing, and degassing operations themselves. The alloyed aluminum is then recast and turned into parts for appliances, automobiles, and other products. Aluminum producers supply some foundry ingots in alloy form. Foundries near aluminum plants may buy molten aluminum that comes directly from the potlines to eliminate the need for remelting.

Billets are made either in long rectangular shapes that look like railroad ties or in the shape of thin poles. They are produced in the same way as fabricating ingots. Billets can be made into bars, rods, and parts for thousands of items. Bars look like small rectangular billets. Bars may also be hexagonal or octagonal. Rods look like small pole-shaped billets. Bars and rods are made into tubing, wire, and various other products.

How aluminum is shaped and finished

Aluminum ingots and billets can be shaped by any of the metalworking processes. These processes include (1) rolling, (2) casting, (3) extruding, (4) drawing, (5) forging, and (6) machining. After the aluminum is shaped, various finishes may be applied.

Rolling consists of reducing the thickness of fabricating ingots by squeezing them between pairs of heavy rollers. The ingots are heated and then rolled to a thickness of 1 to 3 inches (2.5 to 7.6 centimeters). After cooling, the metal is rolled again to form plates, sheets, or foil. Aluminum plates are 1/4 inch (6.4 millimeters) thick or more. They are used in such things as railroad cars, ships, and storage tanks. Aluminum sheets measure 6/1,000 to 1/4 inch (0.15 to 6.4 millimeters) thick. They are used for the "skins" of airplanes and in such products as awnings and cooking utensils. Aluminum foil is less than 6/1,000 inch (0.15 millimeter) thick. It has many household uses, especially in cooking and in wrapping food. Rolling may be used to shape aluminum billets into bars and rods.

Casting is a process in which alloyed foundry ingots are melted and then poured or forced into molds of a desired shape. The aluminum is removed from the molds after it hardens. Casting is used to make parts of particular items, such as the bottoms of electric irons or parts for automobile engines. See CAST AND CASTING.

Extruding consists of forcing a heated billet through an opening in a tool called a die. A ram at one end of a cylinder forces the billet through a die opening at the other end. The aluminum comes out shaped like the die opening. The extrusion process is used to make rods and tubing, trim for automobiles, and frames for doors and windows. See EXTRUSION.

Drawing is used to produce aluminum wire and tubing. To make wire, a pointed aluminum rod is pulled through a series of successively smaller dies. The rod becomes wire when it reaches a diameter of less than 3/8 inch (9.5 millimeters). Tubing is made by pulling an aluminum rod through one die. A steel bar called a mandrel extends through the center of the die and hollows out the rod.

Deep drawing forms aluminum into beverage cans, beer barrels, pots and pans, and various other containers. In this process, a ram forces aluminum plate or an aluminum sheet into a cavity of the desired shape.

Forging is the process of hammering or pressing heated aluminum ingots or billets into the desired shape. Forging produces exceptionally strong parts for use in aircraft landing gear, truck wheels, tools, and various other items. See FORGING.

Machining. Aluminum can be shaped with a variety of machine tools, including drills, grinders, saws, and shears. Such tools shape aluminum bars and rods into bolts, screws, and other small items. Machining may also be used to put final touches on products that have been cast or forged. See MACHINE TOOL.

Other shaping processes produce aluminum in such forms as powders and pastes. Powders and pastes consist of finely ground particles of aluminum. Aluminum powder goes into such products as explosives and inks. In paste form, aluminum is used in paints and in metallic finishes for automobiles.

Aluminum powder is also used to produce gears and other small parts by a process called powder metallurgy. In this process, the aluminum powder is pressed into the desired shape and then heated to bond the particles together. Powders of other metals also may be mixed with the aluminum. Powders of aluminum alloys also may be used. The item is further shaped by forging or some other process. See POWDER METALLURGY.

Finishing aluminum. Aluminum has an attractive natural appearance and so is often used without a special finish. However, various finishes may be used for decoration or to improve resistance to corrosion and wear. More kinds of finishes can be applied to aluminum than to any other metal. There are four types of finishes. They are (1) mechanical, (2) chemical, (3) electrochemical, and (4) applied.

Mechanical finishes include such processes as embossing and polishing. In embossing, a raised pattern is made on aluminum sheets by passing them between rollers that have been engraved with a design. A method called barrel burnishing polishes aluminum articles in a revolving or vibrating barrel that contains an abrasive (gritty) substance.

Chemical finishes include acid and alkaline etches, which eat designs into aluminum. Acid etches are also used to remove stains from the metal and to prepare it for further finishing. Alkaline etches may be used to give aluminum a dull finish.

Electrochemical finishes include anodizing and electroplating. Anodizing thickens aluminum's natural coating of aluminum oxide and thus increases resistance to corrosion, scratching, and wear. It also makes aluminum easy to dye. Electroplating involves coating aluminum with another metal. Certain coatings improve aluminum's corrosion resistance, electricity conduction, or other properties. See ANODIZING; ELECTROPLATING.

Applied finishes include such coatings as enamel, lacquer, paint, and plastic film. They may be applied by dipping, spraying, or other methods.

The aluminum industry

About 50 countries produce aluminum. The world's annual aluminum production totals about 23 million short tons (21million metric tons). The United States is the leading aluminum producer, accounting for about 20 percent of the world total.

The primary aluminum industry consists of companies that produce aluminum ingots and billets and shape them into such forms as plates, sheets, foil, bars, rods, and wires. The firms also sell the ingots and billets to foundries in the secondary aluminum industry, which specializes in shaping aluminum. Specialized workers in the primary aluminum industry include engineers, geologists, and metallurgists.

In the United States, the primary aluminum industry produces about 4 million short tons (3.6 million metric tons) of the metal yearly. The leading aluminum companies in the country are the Aluminum Company of America (Alcoa), Alumax Incorporated, Reynolds Metals Company, and Kaiser Aluminum and Chemical Corporation. Two labor unions--the Aluminum, Brick and Glass Workers International Union (ABGWIU) and the United Steelworkers of America (USWA)--represent most of the workers in the aluminum industry.

Aluminum producers in the United States use about 11 million short tons (10 million metric tons) of bauxite annually. They import all of this bauxite, chiefly from Brazil, Guinea, Guyana, and Jamaica. Aluminum producers also import alumina.

In Canada, the primary aluminum industry produces about 21/2 million short tons (2.3 million metric tons) of the metal yearly. About 90 percent of Canada's aluminum is made in Quebec. The country's leading aluminum manufacturers are Alcan Aluminum Limited and Canadian Reynolds Metals Company. Canada produces no bauxite. It imports most of this ore from Guinea, Guyana, and Suriname.

In other countries. Only about a third of the aluminum-producing countries perform each step in aluminum production--mining the bauxite, refining the ore, and smelting the alumina. In some countries, such as Guinea and Jamaica, the industry mines and refines bauxite for export but produces no aluminum. Other countries, including Germany and Japan, import bauxite and then refine it and smelt the alumina. Some countries, such as Norway and Tajikistan, import alumina but not bauxite. Countries that perform each step in the production process include Australia, Brazil, China, Russia, and Suriname. Several bauxite-mining countries have joined together to form the International Bauxite Association (IBA).

Recycling

Recycling has become a very important aspect of the aluminum industry in many countries. In the United States, scrap makes up about 30 percent of the total aluminum supply. Heavily recycled items include used beverage cans, parts from old automobiles, and scrap accumulated during the manufacture of aluminum products. Beverage cans represent the leading product made from aluminum by volume. More than half the beverage cans used in the United States are recycled.

One benefit of recycling aluminum is that it conserves natural resources. The most important natural resource saved is energy. Recycling saves about 95 percent of the energy required to make aluminum from bauxite. One recycled aluminum can saves enough energy to keep a 100-watt light bulb burning for about 31/2 hours. In addition, recycling preserves natural beauty. It also reduces the amount of garbage sent to sanitary landfills.

History

The word aluminum comes from the term alumen. Alumen is the Latin name for alum, a group of aluminum compounds that occur in nature and which ancient peoples used in dyeing textiles. In 1746, Johann Heinrich Pott, a Prussian chemist, prepared alumina from alum. Scientists believed that alumina was a chemical compound that consisted of oxygen and an unknown metal. The British chemist Sir Humphry Davy called this metal alumium and later changed the name to aluminum. In 1809, Davy formed an alloy of iron and aluminum by electrically melting alumina with iron and carbon.

The first aluminum. In 1825, Hans Christian Oersted, a Danish scientist, produced the first aluminum. Oersted prepared aluminum chloride from alumina. He then heated the aluminum chloride with an alloy of potassium and mercury, and a small lump of impure aluminum formed in the alloy.

In 1827, Friedrich Wohler, a German chemist, produced aluminum as gray powder by heating aluminum chloride with potassium. In 1845, Wohler produced aluminum particles large enough to be weighed. He discovered that aluminum was lightweight. Wohler was the first scientist to describe several other properties of aluminum.

In 1854, Henri Etienne Sainte-Claire Deville, a French chemist, improved on Wohler's method. Deville used sodium instead of potassium to break down aluminum chloride. This process produced larger quantities of aluminum. Commercial aluminum plants using Deville's method soon opened in France. The price of aluminum dropped from $115 a pound ($254 a kilogram) in 1855 to $17 a pound ($37 a kilogram) in 1859. However, it was still too costly for widespread use.

The growth of the aluminum industry increased greatly following two important developments in the 1880's. They were the invention of the Hall-Heroult process and of the Bayer process.

In 1886, two scientists--Charles Martin Hall of the United States and Paul L. T. Heroult of France--developed an inexpensive way to make aluminum. Neither scientist knew that the other was working on the problem. However, each thought of dissolving alumina in the mineral cryolite and separating aluminum from the mixture by electrolytic reduction. Today, the Hall-Heroult process is used to produce nearly all the aluminum in the world.

Karl Joseph Bayer, an Austrian chemist, further reduced the cost of aluminum production. In 1888, he patented an inexpensive method for obtaining alumina from bauxite. The aluminum industry still uses the Bayer process to produce alumina. The Hall-Heroult and Bayer processes are described in the section How aluminum is produced.

Hall and several business associates organized the Pittsburgh Reduction Company in 1888. The company began producing 50 pounds (23 kilograms) of aluminum a day. The firm changed its name to the Aluminum Company of America (Alcoa) in 1907. By 1909, Alcoa was producing 16,500 short tons (14,970 metric tons) a year. The price of aluminum dropped to less than 30 cents a pound (66 cents a kilogram). Heroult formed a Swiss aluminum company in 1888, but it did not begin production immediately. In 1902, the Northern Aluminium Company, Limited (now Alcan Aluminium Limited), was founded in Canada.

Aluminum production soared during World War I (1914-1918) as the fighting nations increased output to help fill their military needs. During the 1920's, the development of new aluminum alloys and of improved methods of turning aluminum into useful products continued to boost production. The Great Depression of the 1930's cut world aluminum output almost in half. But the start of World War II (1939-1945) brought tremendous expansion in production. In 1941, Reynolds Metals Company became the second producer of primary aluminum in the United States.

After World War II, the aluminum industry developedmany products that have become commonplace. The first successful aluminum foil wrap appeared in 1947. Also in the 1940's, aluminum began to replace brass in the base of light bulbs. High-strength aluminum wire for power lines was introduced in 1957. Aluminum cans became popular in the 1960's. Today, nearly all beverage cans are made completely of aluminum.

Recent developments. The demand for aluminum has grown steadily with the continuing development of new uses for the metal. For example, the auto industry has used increasing amounts of aluminum in cars to lessen their weight and so improve fuel efficiency.

During the late 1900's, several aluminum producers began to sell aluminum to any customer who would buy it. This practice led to aluminum's becoming an international commodity (product of trade). In 1978, aluminum appeared on the London Metal Exchange (LME). In 1983, it was listed on the Commodities Exchange (COMEX) in the United States. Only a small amount of aluminum is sold through these markets. But the published market prices are used to set the price of aluminum when it is sold by a producer to a customer who will fabricate the metal into products.

The collapse of the Soviet Union in 1991 led to a sharp drop in the world price of aluminum. The Soviet Union had developed a huge defense industry that required massive amounts of aluminum. After the collapse, the newly independent former Soviet republics maintained their own defense industries. However, the total size of these industries was much smaller than the Soviet industry had been. As a result, the demand for aluminum in the former Soviet Union was much decreased.

The republics also needed money badly. To raise money, they began to export aluminum to countries outside the former Soviet Union. Because of the resulting oversupply, the price of aluminum plunged. The aluminum industry throughout the world responded by closing relatively old and inefficient smelters.

Contributor: Kenneth A. Bowman, Ph.D., Technical Specialist, Alcoa Laboratories.

3.1 Usage Of Aluminium alloy in engineering

· Parts of engine

· Piston

· Parts of furnitur

· Sport rim

· Cooking equipments

D. ZINC ALLOY

4.1 Properties Of Zinc Alloy

Zinc, a chemical element, is a shiny, bluish-white metal. It is important in industry. Zinc can be worked into almost any shape using conventional metalworking methods. Such metals as iron and steel can be galvanized--that is, coated with zinc--to prevent rusting. Galvanized metal is used in such products as roof gutters and tank linings. Zinc is also used in electric batteries. Plants and animals require zinc for normal growth and healing. Zinc is also a component of the hormone insulin.

Zinc can be combined with other metals to form many alloys (mixtures). For example, brass is an alloy of copper and zinc. Bronze is copper, tin, and zinc. Nickel silver is copper, nickel, and zinc. Zinc is also used in solders (easily melted alloys used for joining metals). Zinc and its alloys are used in die-casting (forming objects from liquid metal in molds), electroplating (coating an object by using an electric current), and powder metallurgy (forming objects from metal powder). Since 1982, United States pennies have been made from a predominantly zinc alloy coated with a thin layer of copper.

Moist air tarnishes (discolors) zinc with a protective coating of zinc oxide. Once a thin layer of this coating forms, air cannot tarnish the zinc below it. White, powdery zinc oxide is used in making cosmetics, plastics, rubber, skin ointments, and soaps. It is also used as a pigment in paints and inks. Zinc sulfide, a compound of zinc and sulfur, glows when ultraviolet light, X rays, or cathode rays (streams of electrons) shine on it. It is used on luminous dials for clocks and to coat the inside of television screens and fluorescent lamps. When mixed with water, zinc chloride, a compound of zinc and chlorine, protects wood from decay and insects.

Zinc is never found in a pure state in nature. It occurs combined with sulfur in a mineral called sphalerite or zinc blende. Other zinc-containing minerals are calamine, franklinite, smithsonite, willemite, and zincite. Zinc is hard and brittle at room temperature. It is taken from its ores by heating them in air to convert them to zinc oxide. The oxide is heated with carbon to produce zinc.

Zinc's chemical symbol is Zn. Its atomic number is 30, and its atomic weight is 65.39. Zinc melts at 419.58 °C and boils at 907 °C. Alloys containing large amounts of zinc have been found in prehistoric ruins. In the 100's B.C., the Romans made brass coins from ores containing zinc and copper. The first complete study of zinc was published in 1746 by Andreas Sigismund Marggraf, a German chemist.

Contributor: Raymond E. Davis, Ph.D., Prof. of Chemistry, Univ. of Texas, Austin.

4.2 Usage Of Zinc Alloy

· Parts of Television

· Parts of Radio

· Parts of automotif industrial

· roofs

E. POLYMER

5.1 Polymerization

Polymerization, pronounced pahl ih muhr uh ZAY shuhn, is a chemical process important in the production of plastics, artificial fibers, synthetic rubber, and paints. In this process, many small molecules called monomers combine to build much larger molecules called polymers. If only one kind of monomer is used, the process is called homopolymerization. If more than one kind of monomer is used, it is called copolymerization. The homopolymerization of the gas vinyl chloride produces polyvinyl chloride, a solid plastic commonly called vinyl. The copolymerization of vinyl chloride with vinylidene chloride forms the plastic used in food wrap.

Chemists also classify polymerization processes by the chemical reactions that occur. In addition polymerization, entire monomer molecules bond to form the growing polymer. In condensation polymerization, small pieces of the monomers split off, usually as water molecules, as the polymer forms.

Contributor: Dorothy M. Feigl, Ph.D., Vice President and Dean of Faculty and Prof. of Chemistry, Saint Mary's College.

5.2 Properties Of Polymer

Polymer, pronounced PAHL ih muhr, is a large molecule formed by the chemical linking of many smaller molecules into a long chain. The small molecular building units are called monomers. Monomers are joined into chains by a process of repeated linking known as polymerization. A polymer may consist of thousands of monomers. Some polymers occur naturally. Others are synthetic.

Many common and useful substances are polymers. For example, starch and wool are naturally occurring polymers. Starch is formed by plants from a simple sugar called glucose, and wool is a variety of protein. Nylon and polyethylene, a tough plastic material, are examples of synthetic polymers. Rubber, another polymer, occurs naturally and is also made synthetically.

A chain molecule has a definite length, but, like a piece of string, it can assume a variety of shapes. This combination of molecular length and flexibility gives polymers many useful and unique properties. For example, rubber and many other polymers can be stretched to several times their normal length without breaking. The chains simply straighten into more extended shapes. Because of the large size of the molecules, polymers do not dissolve easily. They also have high viscosity (resistance to flowing).

Contributor: William W. Graessley, Ph.D., Prof. of Chemical Engineering, Princeton Univ.

5.3 Usage Of Polymer In Engineering

· The housing for a computer – polyethylene, polypropylene, ABS, PVC.

· A self-lubrication gear that is no exposed to moisture – polyethylene, ABS, nylon.

· An electrical insulator at room temperature – polyethylene, PVC, ABS.

· A gasket exposed to fuel and oils – SBR, NBR.

F. ENVIRONMENT EFFECT

6.1 Impact

6.2 Creep

Creep is a measure of a material's resistance to gradual deformation under a constant force. At room temperature, creep is almost nonexistent in many metals, including aluminum and steel. However, manufacturers of metal parts such as jet engine turbine blades that operate at high temperatures must consider creep.

6.3 Degradation

G. ELECTRICAL PROPERTIES OF MATERIAL

7.1 Condoctor

A good electrical conductors depend to the properties of the metal usage. In engineering, engineers have developed two kinds of cables that can carry especially large quantities of messages at once. They are (1) coaxial cables and (2) fiber-optic cables.

Coaxial cables are made up of two conductors. The outer conductor is a rigid or flexible metal tube, and the inner conductor is a wire running through its center. Insulation holds the wire in place. The tube and the wire have the same axis (center) and are therefore called coaxial. A typical coaxial cable has about the same diameter as a pencil, and as many as 22 cables may be bundled together to make a larger cable.

A coaxial cable's outer conductor shields the electric signals it carries from outside interference and helps prevent the signals from escaping. In addition, special amplifiers called repeaters are installed at various points along many coaxial cable systems to strengthen the signals. These amplifiers help prevent cable loss. Cable loss is the gradual weakening of signals as they travel along a cable. Repeaters consist of such electronic devices as transistors.

Many telephone calls, especially long-distance calls, travel over coaxial cables. When used for telephone conversations, coaxials work in pairs. One coaxial carries signals in one direction, while the other handles signals from the other direction. A pair of coaxials may handle as many as 13,200 telephone conversations at once.

Cable television systems use coaxial cables to transmit TV programs. A single cable can carry as many as 100 television signals at once. As a result, cable TV systems can transmit regular network programs as well as a variety of special features. See TELEVISION (Cable television systems).

Fiber-optic cables carry messages in the form of light. Such cables consist of a bundle of glass optical fibers, which look somewhat like transparent threads. Coded light signals travel through the core of the fibers. A thin layer of glass called cladding surrounds the core and helps prevent the light from escaping.

Special lasers are used to transmit the coded light signals through fiber-optic cables. The lasers flash on and off at extremely high speeds. Electronic devices at the receiving end of fiber-optic cables decode the light signals.

The largest fiber-optic cables can carry hundreds of thousands of telephone conversations or hundreds of television channels. Many communications companies have begun using fiber-optic cables instead of coaxial cables. No electrical interference occurs in fiber-optic cables, and there is less cable loss than there is in coaxial cables. Fiber-optic cables measure only 1/25 to 1/2 inch (1 to 13 millimeters) in diameter and thus take up much less space than coaxial cables.

7.2 Semi Conductor

Semiconductor is a material that conducts electricity better than insulators like glass, but not as well as conductors like copper. Such materials have made possible modern computers and other important electronic devices. The transistors used in tiny pocket radios are semiconductor devices. So are the solar cells that provide electric power in artificial satellites.

Silicon is the most widely used semiconductor material. Other important semiconductor materials include cuprous oxide, germanium, gallium arsenide, gallium phosphide, indium arsenide, lead sulfide, selenium, and silicon carbide.

Electronic devices made of semiconductor materials can perform many functions, including those of vacuum and gas-filled tubes. However, semiconductor devices have a number of advantages over these tubes. Semiconductor devices use much less power than tubes, they last longer, and they can be built much smaller. One example of a tiny semiconductor device is the silicon chip used in computers and calculators.

Like tubes, semiconductor devices can rectify (change alternating current to direct current). They can also amplify weak electric signals. In addition, these devices can oscillate (make alternating current or radio waves) at frequencies from a few hertz to over 100,000 megahertz. Radios, television sets, and other electronic devices depend on rectifiers, amplifiers, and oscillators. Some semiconductor devices can make light, and others can detect light. Most television camera tubes are semiconductor devices.

Basic principles. In ordinary copper wire, the copper atoms have electrons that are free to move from atom to atom. Such a flow of electrons makes up an electric current. In an ideal state, semiconductor materials would be insulators because they would have no free electrons. But if very small amounts of certain impurities such as antimony, arsenic, or phosphorus are present, a few free electrons are produced that can move and form an electric current. These semiconductors are known as n-type semiconductors.

Another type of semiconductor, called p-type, is formed by adding small quantities of other impurities such as aluminum, boron, or gallium. These impurities take electrons away from a few atoms of the semiconductor. This lack of an electron in an atom is called a hole. A hole can pass from one atom to another. A flow of such holes passing from atom to atom also forms an electric current.

The abbreviation n means negative, referring to the negative charge of the electrons in n-type materials. Similarly, p means positive, referring to the positive charge associated with holes in p-type materials.

Semiconductor materials must be exceptionally pure to work properly. Scientists have developed special techniques to obtain pure crystals of semiconductor materials and to add the right amounts of impurities.

Semiconductor devices include semiconductor diodes, semiconductor lamps, semiconductor lasers, semiconductor radiation detectors, solar cells, and transistors. These devices are formed by making certain regions in a semiconductor either p- or n-type.

Semiconductor diodes allow current to flow in only one direction and are used as rectifiers. They have a piece of gallium arsenide, germanium, or silicon with an n-type region and a p-type region. The area where the two regions touch is called a p-n junction. When the p-type region has a positive charge and the n-type region has a negative charge, the p-type attracts electrons from the n-type, and the n-type attracts holes from the p-type. Thus, electric current flows across the p-n junction. If the p-type region is made negative and the n-type region is positive, almost no current will flow across the junction. The p-type then repels electrons in the n-type, and the n-type repels holes in the p-type.

Other semiconductor diodes, such as the Esaki or tunnel, Gunn, IMPATT, and LSA diodes can oscillate. They generate extremely high frequency radio waves that are used for communications, radar, or other purposes.

Semiconductor lamps include tiny gallium phosphide diodes that produce light with little electric power. These lamps are used in some telephone sets.

Semiconductor lasers produce narrow beams of intense light. They are efficient lasers, but their light covers a wider frequency range than light from other lasers.

Semiconductor radiation detectors indicate the presence and intensity of gamma rays and X rays. These devices are widely used in scientific research.

Solar cells change sunlight into electricity. They are made of slabs of silicon with a p-n junction near the surface. Light knocks electrons out of the atoms, producing electrons and holes that flow to make an electric current.

Transistors are used to amplify electric signals, act as oscillators, or make circuits that perform arithmetic and logic operations. Some transistors have more than one p-n junction.

Contributor: Vijai K. Tripathi, Ph.D., Prof. of Electrical and Computer Engineering, Oregon State Univ.

7.3 Magnetic Properties

7.3.1 Paramagnetic

7.3.2 Diamagnetic

mechanical engineering polisas