2 Alloys To know what alloys are, and how their properties are useful Saturday, April 01, 2017To know what alloys are, and how their properties are useful
3 RomansWhy were the Romans so successful at fighting?!
4 RomansApart from excellent tactics one clear advantage the Roman’s had over most of their enemies was technological excellence, specifically in their weaponsThey originally used iron swords, but during the Republic period they advanced their manufacture – these new swords were still made from iron ores, but had bands of steel within their bladesThe steels added superior strength and meant opposition soldiers often found their swords to be weaker, often shattering (leading to their death)!
5 IronPure iron is soft and easily shaped because its atoms are arranged in a regular way that lets layers of atoms slide over each otherPure iron is too soft for many usesLayers of atoms slide over each other when metals are bent or stretched
6 IronIron from the blast furnace is an alloy of about 96% iron with carbon and some other impurities – it is hard, but too brittle for most usesSo, most iron from the blast furnace is converted into steel by removing some of the carbon (adding just 1% impurities makes the iron much stronger)Adding just 1% impurities makesthe iron much stronger
7 SteelCarbon is removed by blowing oxygen into the molten metal – it reacts with the carbon producing carbon monoxide and carbon dioxideThese escape from the molten metal – enough oxygen is used to achieve steel with the desired carbon contentOther metals are often added, such as vanadium and chromiumThere are many different types of steel, depending on the other elements mixed with the iron…
8 Resistant to corrosion SteelType of steelIron alloyed withPropertiesTypical useLow carbon steelAround 0.25% carbonEasily shapedCar body panelsHigh carbon steelUp to 2.5% carbonHardCutting toolsStainless steelChromium and nickelResistant to corrosionCutlery and sinks
9 Making SteelDifferent amounts of carbon (and other impurities) are added to make steel, stopping the atoms from sliding over one another as easily…StrongStrengthHardnessWeak0.5% 1% %Amount of carbon added
10 Steel Steel with a low carbon content is easily shaped Steel with a high carbon content is strong, but brittleStainless steel contains chronium and nickel
11 AlloysSteel is an alloy – a mixture of two or more elements, where at least one element is a metal, is called an alloyThe properties of a metal are changed by including other elements, such as carbonAlloys contain atoms of different sizes, which distort the regular arrangements of atoms making it more difficult for the layers to slide over each other, so alloys are harder than the pure metalIn alloys it is more difficult for the layers of atoms to slide over one another
12 AlloysCopper, gold and aluminium are too soft for many uses, but they can be mixed with other metals to make them harder for everyday use…Brass – used in electrical fittings is 70% copper and 30% zinc18 carat gold – used in jewellery is 75% gold and 25% copper and other metalsDuralumin – used in aircraft manufacture is 96% aluminium and 4% copper and other metals
13 Smart AlloysSmart alloys (shape memory alloy (SMAs)) can return to their original shape after being bentThey are useful for spectacle frames and dental braces (e.g. Nitinol)
14 Summary QuestionsComplete the sentence below using the key words: aluminium; brass; bronze; smart; soft; and thousandsCopper has been used by people for ______ of years. Like pure iron, pure copper is too ______ to be very useful. Copper can be alloyed with tin to make ______, and with zinc to make ______.There are over 300 alloys of ______. Some alloys can ‘remember’ their shape when they are heated after they have been bent – they are called ______ alloys.Explain the advantage of a dental brace made of a smart alloy over one made from a conventional alloy
15 Summary QuestionsCopper has been used by people for thousands of years. Like pure iron, pure copper is too soft to be very useful. Copper can be alloyed with tin to make bronze, and with zinc to make brass. There are over 300 alloys of aluminium. Some alloys can ‘remember’ their shape when they are heated after they have been bent – they are called smart alloys.The smart alloy can be cooled and shaped into the patient’s mouth. When the alloys warms up it will push the teeth into the correct position and hold them there!