AQA GCSE Design and Technology 8552 Metals and alloys Unit 3 Materials and their working properties 3
Objectives Know the primary sources of materials for producing metals and alloys Be able to recognise and characterise different types of metals and alloys Understand how the physical and working properties of a range of metals and alloys affect their performance
Metal Metals have been essential in the development of civilisation The word metal comes from the ancient Greek word metallon which means to mine, excavate or extract from the ground Prehistoric man used metals to make tools and weapons Which common metals would you find in a domestic kitchen?
Ore The Earth s crust contains many types of rock Metallic minerals are found naturally in rock or ore Ore is obtained by mining and the metals within it are extracted The method used for extraction depends on the metal s reactivity with air, water or acids The more reactive the metal, the more expensive it is to extract
Finding metal Some naturally occurring metals are found as lumps in the rock and don t require a chemical extraction Why is gold expensive in comparison to aluminium?
Extraction processes Some metals exist as oxides Metals such as copper, iron and zinc are oxides. These are heated with carbon to extract the metal Electrolysis is used to extract metals such as aluminium Are metals a renewable resource? How can man reduce the speed at which we will run out of natural resources?
Iron ore Iron can be extracted from iron ore by using a blast furnace and the process of smelting Smelting extracts common industrial metals such as iron The extreme heat draws off the metals in a liquid state called hot metal The impurities are removed and the iron mixed or alloyed with a small amount of carbon to create steel The amount of added carbon affects the strength of the steel
Ferrous metals Ferrous metals contain iron and may rust Iron and steel can corrode this is known as rust Rust is a compound called iron oxide and is formed when iron and oxygen react in the presence of moisture or water Most ferrous metals are magnetic Name two types of protective layer that could be added to metal to help prevent rust
Ductility and malleability Ductile metals Will stretch without being damaged Can be drawn or stretched out into long wires Copper is highly ductile and can be drawn into long, thin wires Malleable metals Can be hammered into a shape without breaking Can be rolled or pressed into sheets Will deform under compression
Hard or tough? Hardness a material s ability to withstand abrasion A very hard metal is likely to crack or shatter upon impact or force. Cast iron would be described as hard and brittle Toughness metal requires strength and ductility This is how well a metal can absorb energy and resist fracturing without deforming
Tensile strength Tensile strength is the amount of tensile stress (stretching) a material can withstand before breaking or failing Testing for tensile strength is crucial in industry Suggest two uses for metals with high tensile strength Why is destructive testing so important?
Hard as nails Steel is a ferrous metal available in different forms Steel has a high resistance to corrosion, staining and friction which makes it suitable for a wide range of uses These elements give steel its characteristic properties of hardness and toughness High speed steel is formed by alloying elements of carbon, tungsten, vanadium, cobalt, chromium or molybdenum Name three everyday applications of stainless steel
Material selection Ferrous metals have varying properties making them suitable for different uses Low carbon steel is tough, ductile and easily welded High carbon steel is very hard wearing, but less ductile or malleable Cast iron is hard and easily cast into shapes, but brittle Suggest two items made from each of these metals?
Non-ferrous properties Non-ferrous metals don t contain iron They are often more expensive than ferrous metals owing to their desirable properties which include: Lightweight Good conductivity Ductile and malleable Resistant to corrosion The process of galvanising adds a protective coat of zinc to iron and steel to help prevent rusting
Electrical conductivity Conductivity is how easily an electrical current can flow through a metal As copper is such an efficient conductor, it s most common use is in electrical cabling
Thermal conductivity Thermal conductivity measures the ability of a metal to conduct heat Copper is also an excellent conductor of heat and is commonly used in air conditioning, water tanks, saucepan bases and water heaters In what environment would it be more appropriate to use steel than copper?
Non-ferrous metals Aluminium, copper, tin and zinc are all non-ferrous metals List a selection of household items that may be made from non-ferrous metals In what way do non-ferrous metals differ from ferrous metals?
Tin Tin is commonly associated with a tin can In fact, the can is steel, with a thin coating of tin, tin plating, which helps preserve the contents Tin is soft, ductile and malleable Alloys of tin include pewter, copper, bronze and soft solder What other non-ferrous metal is associated with the production of cans?
Alloys Metals are rarely used in their pure form. Alloys are made by combining two or more elements This helps improve the working properties and appearance Brass and steel are common alloys Stainless steel is made by combining iron, with a small amount of carbon and chromium This protects the alloy from oxygen what will this help prevent? What are the advantages of creating alloys?
Worksheet Complete Tasks 1 and 2 on your worksheet
Uses of metals Given the various properties of metals, list as many metals as you can that are used to make this bicycle
Uses of metals Answers A vast range of metals may be used to create a single product Twisted strands of steel in the brake cables, aluminium and steel in the brake handle Aluminium or stainless steel shopping basket Steel or aluminium spokes Steel wire in the tyres, zinc in the manufacture of rubber Fused or welded joints are usually brass (a copper / zinc alloy) Frame could be low carbon steel, aluminium alloy Aluminium alloy in the pedals Steel springs Aluminium mud guards Chain made of carbon steel High speed steel in ball bearings, pedals, wheel hubs, headstocks, cranks
Worksheet Complete Task 3 of the worksheet
Everything but tin? Tin probably didn t feature in your bicycle list Working with recycled cans is a technique called Kapoaka Used in Madagascar by small scale workshops, crafters make decorative objects and toys for sale It has created sustainable employment and helps the poorest in Africa attain a living from the profits
Oxidisation Non ferrous metals such as copper and bronze, don t rust, but may oxidise Oxidising can be caused by corrosion or weather exposure over a period of time A thin layer of tarnish that appears on the surface of the metal is known as a patina A natural patina occurring on copper is called Verdigris The green hue can be manufactured by adding acetic acid to copper and is often used in architecture for aesthetic purposes
Plenary What are metals commonly extracted from? Name three ferrous metals Which metal would you select for high conductivity? Explain the term alloy Describe the difference between hard and tough How can you protect metal from oxidisation? Justify one metal used to manufacture cutting tools
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