Metals and their Properties Resistant Materials

Learning objectives By the end of this unit, you will: Know more about the properties of metals and the categories into which metals are separated. Learn about the process by which metal ores are taken from the Earth and converted to metals. Understand some of the tools that are used with metals and some metalwork industrial processes. Learning objectives The key concepts covered are: Designing and making Creativity

Heavy metal? Photo credit: © John Wollwerth, Shutterstock.com

Categories of metal Metals can be broken down into two main categories: ferrous metals and non-ferrous metals. Ferrous metals all have certain properties: they contain iron they will corrode unless protected they are attracted by magnets. Non-ferrous metals also have certain unique properties: they do not contain iron they are not magnetic they are mostly pure metals. Teacher’s note: There are a wide variety of metals that the students could cite as examples. They should be able to list the metals that were shown as examples in the previous activity. A sample list of some metals they may know are: steel, aluminium, brass, copper, iron, stainless steel, bronze. You may also wish to discuss ferrous and non-ferrous metals at this stage in more depth. Some points that you may wish to mention include: The Periodic table - do students recognize Fe? Fe = ferrous = containing iron Iron is the basis for all ferrous metals but as a material in its own right (in today’s terms) it has little practical use. To make it suitable for use in today’s demanding environments, we combine it with other materials (alloying) to enhance its properties. Carbon is one of the main materials which is combined with iron ore to make useful materials. Photo credits: Ferrous © David Burden, Shutterstock.com Non-ferrous © Terry Davis, Shutterstock.com How many different metals can you think of?

Metalwork Photo credits: Pure metals © Steffen Foerster Photography, Shutterstock.com Alloys © Ford Photography, Shutterstock.com

Examples of metals Teacher’s note: The more carbon that is added to steel, the harder the alloyed steel. Unfortunately, when we add carbon to steel, this reduces the ductility and malleability of the material. There will always be a trade-off between hardness and brittleness when combining carbon with steel. However, there are several processes such as case-hardening, hardening, tempering, normalizing and annealing which can be employed to counteract some of these properties. Photo credits: Can © Galayko Sergey, Shutterstock.com Cutlery © Robyn Mackenzie Image of drill bits courtesy of Middlesex University Teaching Resources (www.mutr.co.uk).

Examples of metals Photo credits: Can and trumpet © 2009 http://www.sxc.hu Photo credit: Pipe © Gordon Ball LRPS, Shutterstock.com

Where do they come from? Teacher’s note: This is a good opportunity to explore how other metals are extracted from the Earth. Students could be asked to conduct online research to try and find out how different metals are extracted from the Earth and also what some of the problems are with these methods of extraction. As we moved towards the Iron Age, the ease and strength with which metals could be shaped made them invaluable. Initially small pieces of gold and copper were found and could be used without much processing but these were used mainly for decorative purposes. To gather any significant amounts of metals, mining was needed. For example, copper was extracted from the mixture of minerals, rocks and dirt known as copper ore. This meant that lots of copper could be used in the production of household products such as pans and spears. Stages in mining copper: 1) Extract the ore. 2) Wash it to remove gangue (rocks dirt etc) leaving pure ore. 3) Smelt (heat) the ore in a blast furnace with carbon and air. 4) Copper flows out.

Properties of metals Teacher’s note: There are various other properties of metals that you may wish to let your students know about. Some of these are included here: Hardness – ability to withstand indents, abrasive wear and deformation Durability – ability to withstand wear and tear Strength – ability to withstand force without breaking or permanently bending (tensile, compressive, bending, shear and torsional strength) Plasticity – ability to be changed permanently in shape (deformed) by an external force without breaking Elasticity – ability to bend and flex when subjected to a force and then return to its original shape when the force is removed (like an elastic band) Brittleness – opposite of toughness. Photo credit: © Mircea BEZERGHEANU, Shutterstock.com