Chemistry of Engineering Materials PDF

Handout Chemistry of Engineering Materials Machine elements should be made of such a material which has properties suitable for the conditions of operation. Engineers must be familiar with the effects which the manufacturing processes and heat treatment have on the properties of the materi...

Handout Chemistry of Engineering Materials Machine elements should be made of such a material which has properties suitable for the conditions of operation. Engineers must be familiar with the effects which the manufacturing processes and heat treatment have on the properties of the materials. Classifications of Engineering Materials 1. Metal and their alloys, such as iron, steel, copper, aluminum, etc. 2. Non-metals such as glass, rubber, plastic, etc. The metals may be further classified as: a. Ferrous metals → Have iron as main constituent like cast iron, wrought iron and steel → Principal raw material for all ferrous metals is pig iron which is obtained by smelting iron ore with coke and limestone Types of ferrous metals: a) Cast iron – obtained by re-melting pig iron with coke and limestone known as cupola; carbon contents ranges from 1 to 4 percent b) Alloy cast iron – plain cast irons and is produced by adding alloying elements c) Wrought iron d) Steel – an alloy or iron and carbon (1 percent) e) Free cutting steels – contains Sulphur and phosphorous f) Alloy steel g) Stainless steel – it resists oxidation and corrosive attack h) High resisting steels – can resist creep and oxidations i) High speed tool steels – used for cutting metals j) Spring steels – can store up the maximum amount of work or energy without permanent deformation b. Non-ferrous metals → Have a metal other than iron as main constituent → Employed in industry due to its characteristics like ease of fabrication, resistance to corrosion, have electrical and thermal conductivity and weight Types of Non-ferrous a) Aluminum – white metal produced by electrical processes; prepared by mineral called bauxite; a light metal b) Aluminum alloys c) Copper - widely used non-ferrous metal, good conductor of electricity d) Copper alloys e) Gun metal – Admiralty metal f) Lead g) Tin Non-Metallic Materials → Used in engineering due to their low density, low cost, flexibility, resistance to heat and electricity Examples: 1. Plastics – synthetic materials which are molded into shape through pressure 2. Rubber – resists abrasion, heat, strong alkalis, and fairly strong acids Soft rubber – electric insulations Hard rubber – piping ang lining  3. Leather – flexible and can withstand considerable wear under suitable conditions; used for power transmission Selection of Materials for Engineering Purposes In engineering, selection of material is difficult for designers. Best material is one which serve the desired objective at minimum cost. Factors to consider in selecting material: 1. Availability of materials 2. Suitability of materials to the working condition in service 3. Cost Example of Valuable metals in Engineering → Copper → Aluminum → Iron → Zinc → Lead Metals Physical Properties of Metals a) Luster – the way light interacts with the surface of crystal, rock, or mineral b) Color – the sensation on the eye because of the way the object reflects of emits light c) Size – dimension or magnitude d) Shape – external form m) Hardness – has many properties such as resistance to wearing, scratching, deformation, machinability, ability to cut another metal etc. It can be determined by the following tests: 1. Brinell Hardness Test Brinell Tester – by Johann August Brinell (Swedish Metallurgist) which measures metal hardness precisely 2. Rockwell Hardness Test 3. Vickers Hardness Test or Diamond Pyramid Test 4. Shore scleroscope Chemical Properties a) Chemical Composition – indicates the elements which are combined to form that material b) Atomic bonding – represents how atoms are bounded to each other to form that material Types of Atomic bonds: o Ionic – metal to nonmetal; forms by exchanging valence electrons o Covalent – nonmetal to nonmetal: forms by sharing of electrons o Metallic - found in metals c) Corrosion Resistance - the ability to prevent environmental deterioration by chemical or electrochemical reaction; ability to resist oxidation d) Acidic or Alkalinity – indicates how they react with other materials Acetic material has pH value of below 7 Alkane Material has pH value of above 7