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Chemistry
 

Chemistry

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    Chemistry Chemistry Document Transcript

    • CHEMISTRY FORM 4NAME:
    • INTRODUCTION o Pure metals usually have high densities; high melting and boiling points are good conductors of heat and electricity, shiny, malleable and ductile. o Pure metals are composed of the same type of atoms and are of the same size. o In the solid state, the atoms are closely packed in an orderly manner. o This arrangement of atoms in metals gives the metals their ductile and malleable properties when a force is applied. o Ductility of metals The layers of atoms can slide over one another when a force is applied. Therefore, metals are ductile or can be stretched. o Malleability of metals There are some imperfections in the orderly arrangement of atoms. When a metal is knocked, atoms slide into new positions. Therefore, metals are malleable (can be hammered into different shapes without cracking) or can be shape o Alloys may contain mixtures of metals or mixture of metals and non metals. o Foreign atoms added may be larger or smaller than the atoms of the pure metal.Arrangement of atom in alloy o The presences of foreign atoms that are of different sizes disturb the orderly arrangement of metal atoms. o This reduces the layers of atoms from slidingover one another. Thus, an alloy is stronger and harder than its pure metal.
    • OBJECTIVETo know more about alloy and their important.
    • WHAT ARE ALLOYS?1.Pure metal are usually too soft for most uses. They also have a lowr e s i s t a n c e t o corrosion. They rush and tarnish easily.2.To improve the physical properties of metal, a small amount of anothere l e m e n t (usually metal) is added to form another alloy.3.An alloy is a mixture of two or more metals (something non -metal) in as p e c i f i c proportion. For example a) Bronze (90% of copper and 10% of tin) b) b.Steel (99% of iron and 1% of carbon)4.The purposes of making alloys include the following:a)Increase the strength i. Pure iron is soft and vary malleable. When a small amount of carbon is added to iron, an alloy, steal is formed. The more carbon is added, the stronger the steel becomes. ii. ii.Pure aluminium is light but not strong. With a small amount of copper andmagnesium are added to aluminium , a strong, light and d u r a b l e a l l o y c a l l duralumin is produced.b)Improving the resistance to corrosion i. Iron rust easily but stainless steel which contains 80.6% of iron, 0.4% of carbon, 1 8 % of chromium and 1% of nickel does not rush. These properties m a k e stainless steel suitable for making surgical instrument and cutlery. ii. Pure copper tarnish easily. When zinc (30%) is added, the yellow alloy which isknown as brass develops a high resistance to corrosionc)Enhancing the appearance i. Pewter, an alloy of tin (97%), antimony and copper is not only hard but also hasa more beautiful white silvery appearance. ii. When copper is mixed with nickel to form cupronickel, an alloy t h a t h a s a n attractive silvery, bright appearance is formed which is suitable for makingcoins
    • EXAMPLES OF ALLOYALLOY COMPOSITIONS PROPERTIES USESDuralumin Al 94% Light and strong Aeroplane part, Cu 4% electric cables Mg 1% racing bicyclesSteel Fe 99% Hard, strong and Vehicles, bridges C 1% cheap and buildingsStainless steel Fe 73% Hard, rust and Kitchen Cr 18% resistant appliances, Ni 8% watches, knifes, C 1% fork, spoon, machine partsBronze Cu 90% Hard, strong and Decorative items, Sn 10% shining medals, artworksBrass Cu 70% Harder and Musicals Zn 30% cheaper than instrument, bells, copper nails, screw potsPewter Sn 91% Malleable, ductile, Decorative items, Sb 7% rust resistant souvenirs Cu 2%
    • DISCUSSIONAn alloy is a mixture or metallic solid solution composed of two or more elements. Completesolid solution alloys give single solid phase microstructure, while partial solutions give two ormore phases that may or may not be homogeneous in distribution, depending on thermal (heattreatment) history. Alloys usually have different properties from those of the componentelements.Alloy constituents are usually measured by mass. Alloys are usually classified as substitution orinterstitial alloys, depending on the atomic arrangement that forms the alloy. They can befurther classified as homogeneous, consisting of a single phase, heterogeneous, consisting oftwo or more phases, or intermetallic, where there is no distinct boundary between phases.
    • CONCLUSIONSWe must appreciate these various synthetic industrial materials. One of the ways is bydoingcontinuous research and development (R&D) to produce better materials used toimprove ourstandard of living. As we live in a changing world, our society is gettingmore complex. Newmaterials are required to overcome new challenges and problems weface in our daily lives.Synthetic materials are developed constantly due to the limitationand shortage of naturalmaterials. New technological developments are used by scientiststo make new discoveries. New materials for clothing, shelter, tools and communication to improve our dailylife aredeveloped continuously for the well-being of mankind. New needs and new problem willstimulate the development of new synthetic materials. For example, the newuse of plasticcomposite material will replace metal in the making of a stronger andlighter car body. This willsave fuel and improve speed. Plastic composite materials mayone day used to make organs fororgan transplant in human bodies. This will becomenecessity with the shortage of human organdonors.The understanding of the interaction between different chemicals is important for both thedevelopment of new synthetic materials and the disposal of such syntheticmaterials as waste. Aresponsible and systemic method of handling the waste of syntheticmaterials and their by-product is important to prevent environmental pollution. The recycling and development ofenvironmental friendly synthetic material should beenforced.
    • REFERENCES 1. Spotlight SPM Chemistry, Ooi Yong Seang, Darric Lim, Pan Asia Publications SDN BHD, 2009. 2. www.scribd.com