Download
1 / 16
200 likes | 664 Vues
Alloys. Noadswood Science, 2012. Alloys. To know what alloys are, and how their properties are useful. Romans. Why were the Romans so successful at fighting?!. Romans.
E N D
Alloys Noadswood Science, 2012
Alloys • To know what alloys are, and how their properties are useful
Romans • Why were the Romans so successful at fighting?!
Romans • Apart from excellent tactics one clear advantage the Roman’s had over most of their enemies was technological excellence, specifically in their weapons • They 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 blades • The steels added superior strength and meant opposition soldiers often found their swords to be weaker, often shattering (leading to their death)!
Iron • Pure iron is soft and easily shaped because its atoms are arranged in a regular way that lets layers of atoms slide over each other • Pure iron is too soft for many uses Layers of atoms slide over each other when metals are bent or stretched
Iron • Iron 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 uses • So, 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 makes the iron much stronger
Steel • Carbon is removed by blowing oxygen into the molten metal – it reacts with the carbon producing carbon monoxide and carbon dioxide • These escape from the molten metal – enough oxygen is used to achieve steel with the desired carbon content • Other metals are often added, such as vanadium and chromium • There are many different types of steel, depending on the other elements mixed with the iron…
Making Steel • Different amounts of carbon (and other impurities) are added to make steel, stopping the atoms from sliding over one another as easily… Strong Strength Hardness Weak 0.5% 1% 1.5% Amount of carbon added
Steel Stainless steel contains chronium and nickel Steel with a low carbon content is easily shaped Steel with a high carbon content is strong, but brittle
Alloys • Steel is an alloy – a mixture of two or more elements, where at least one element is a metal, is called an alloy • The properties of a metal are changed by including other elements, such as carbon • Alloys 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 metal In alloys it is more difficult for the layers of atoms to slide over one another
Alloys • Copper, 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% zinc • 18 carat gold – used in jewellery is 75% gold and 25% copper and other metals • Duralumin – used in aircraft manufacture is 96% aluminium and 4% copper and other metals
Smart Alloys • Smart alloys (shape memory alloy (SMAs)) can return to their original shape after being bent • They are useful for spectacle frames and dental braces (e.g. Nitinol)
Summary Questions • Complete the sentence below using the key words: aluminium; brass; bronze; smart; soft; and thousands • Copper 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
Summary Questions • Copper 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!
