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11 Cards in this Set
- Front
- Back
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Alloy |
Alloy is a mixture of two or more metals or of one or more metals with certain non-metallic elements. |
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Fusible alloy |
An alloy melting in the range of about 51-260°C ,usually contains bismuth , lead , tin , etc. These alloys are called visible alloys. |
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Alloy steel |
A steels containing up to 10% of elements such as chromium , molybdenum , nickel , etc., usually with a low percentage of carbon is known as alloy steel. These added elements improve hardness , toughness , wear resistance and other properties. |
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Amalgam |
A mixture or an alloy of mercury with a number of metals or alloys such as sodium zinc , gold and silver as well as with some non-metals is known as amalgam. |
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Dental amalgam |
A mixture of mercury and silver-tin alloy. |
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Reasons for alloying: |
1. to modify appearance and colour 2. to modify chemical activity 3. to modify casting ability 4. to lower the melting point 5. to increase hardness and tensile strength 6. to increase resistance to electricity |
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Method of making alloys |
1. by fusing the metals together 2. by compressing dinely divided metals |
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quenching of steel |
when the steel is heated red hot at temperature above 800°C and immediately plunged into cold water or oil , it become hard and more brittle . this process is called quenching (hardening) of steel. |
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annealing of steel |
If quenched steel is reheated carefully to a temperature of 220 - 300°C and then allowed to copl slowly , it retains its hardness but its brittleness vanishes. this process is known as annealing of steel. |
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galvanisation |
zinc is mostly used for coatinf iron and steel sheets to prevent them from rusting . this process is known as galvanisation. Coating is either done by spraying molten zinc on the surface of iron or by immersing the iron object in a bath containing molten zinc. |
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Aluminothermy |
Aluminium isa powerful reducing agent . When a mixture of aluminium powder and iron oxide is ignited, the latter is reduced to metal. This process is called aluminothermy. |
