unit 4 1. classification of materials can be classified into two main categories: raw materials:...

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UNIT 4 1 Slide 2 Classification of materials Can be Classified into two main categories: Raw materials: they are substances extracted directly from natural resources. They can be, according to their origin: Animal: wool, silk, hide Vegetable: wood, rubber, cotton Mineral: copper, gold, iron, coal, marble Technical materials: the raw materials are transformed by physical and chemical processes into technical materials, that can be used for making different products. E.g. plastic, paper 2 Slide 3 Raw materials 3 Slide 4 4 Natural resources Raw materials Materials or technical materials Manufactured goods TreeWoodPlancks, plywoodsShelf, table SheepWoolWoolen threadsScarf, sweater Petroleum wellPetroleumPlasticsPen, bottle, toy Slide 5 5 Technical materials Slide 6 Material Raw materials of mineral origin: marble, clay, iron. A processed raw material that is ready for making any type of product. What have we learned? First think about the answers, then click the mouse Raw materials Are classified into: Raw materials of animal origin: wool, silk, hides. Raw materials of vegetable origin: cotton, wood, cork, linen. Unprocessed substances in their natural state. Slide 7 Properties of materials Physical properties: related to how materials react to external stimuli, e.g. light, forces Chemical properties: related to the changes in the chemical composition of a material because it interacts with other substances. Ecological properties: related to the impact they have on the environment. 7 Slide 8 Physical properties (1) Electrical Thermal Optical Acoustic 8 Electrical properties: what happens when an electric current is passed through a material? Conductor: it transmits electricity. E. g. metals Insulator: it does not. E.g plastic, porcelain Magnetic Mechanical Others Slide 9 9 Thermal properties (1): what happens when a material is heated? Thermal conductor / thermal insulator: It conducts the heat (iron) / It does not (wood) Expansion / contraction: When the temperature increases /decreases, the material expands / contracts (iron in the railways). Physical properties (2) insulatorconductor Slide 10 10 Thermal properties (2): Fusibility: it melts (=it changes from solid to liquid) when the temperature is increased. E. g. glass, some plastics, metals. Welding: it can be welded with a different material or with another piece of the same material (this property implies fusibility). E. g. some metals: iron, aluminium, gold. Physical properties (2) Slide 11 11 Optical properties: can you see through a material? Opaque: wood, metals Translucent: some types of glass, plastic Transparent: glass, some plastics Acoustic properties: can you hear sound through a material? Acoustic conductors (iron) / acoustic insulators (cork, polyurethane) Magnetic properties: Does a material react to a magnet? Magnetism: some metals attract other metallic materials (iron) Physical properties (3) Slide 12 12 Mechanical properties (1): what happens to a material when external forces are applied? Mechanical strength: it depends on the type of force that acts upon them. There are several types of strength: Tensile strength Compressive strength Physical properties (4) Shear strength Torsional strength Flexural strength Slide 13 13 Mechanical properties (2): Malleability: it allows a material to be spread into sheets (malleable material). Ductility: it allows a material to be formed into filaments or wires (ductile material). Elasticity: it allows a material to return to its original form after a force that has changed its shape is removed. Plasticity: it allows a material to be permanently deformed. Physical properties (5) Slide 14 14 Mechanical properties (2): Hardness: what happens to a material when it is scratched by another material? This property is measured using the Mohs scale: The diamond is the hardest material. The softest one is the talc. Toughness versus brittleness: Does it break easily when it is hit? E.g. Iron Warning! Iron is tough, but not hard. Physical properties (6) Slide 15 15 Density: it is the quotient between the mass of an object and its volume. A block of lead has more density that a sponge of the same size. Porosity: capability of absorb or release liquids or gases, e.g. volcanic rocks. Permeability and impermeability: some materials allow liquids to filter through them (an earthenware), others dont (glass, cork, plastics...) Other physical properties Slide 16 Chemical properties Related to the changes in the chemical composition of a material because it interacts with other substances. Oxidation: it happens when a mineral reacts to oxygen in the air or water(e.g. metals). The reddish-brown substance produced is called rust. 16 Slide 17 Ecological properties Materials are classified according to their impact on the environment: 17 Recyclable materials: they can be reused. This avoid the accumulation of waste products. Eg: some plastics (bottles...) Toxic materials: they are harmful to the environment and can be poisonous for living things. (E.g. Mercury, in the batteries) Biodegradable materials: they decompose naturally and do not damage the environment. (paper, water-soluble plastics) Slide 18 Properties of a material Properties of a material These are classified as: These properties relate to how the material reacts to external stimuli, e.g. electricity, light, heat or the applying of various forces. Chemical properties: rusting or oxidation. Ecological properties: recyclable materials, biodegradable materials and toxic materials. Physical properties: electrical, acoustic, optical, thermal, magnetic, mechanical, density, porosity, permeability and impermeability. Manufactured goods Products made by humans to help satisfy their needs and improve their standard of living. What have we learned? First think about the answers, then click the mouse Slide 19 Homework 1 JK: Activities 1 to 9, page 47 textbook 1 L: Activities 1 to 4 (corrected), 5 to 9 and 2 to 17 in the textbooks Optional: you can listen to the new words, paying attention to the pronunciation in this website: www.howjsay.com This presentation will be available in: www.larratecnologia.wordpress.com 19