Metals

Properties of metalSolidification of a substance

Modification of grain size

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Today’s Lesson• You are going to work in pairs and download this slide show

from the server• AllStaff• jc• jcStudR• Year 12• Topic 4 Metals.ppt

• You are going to go through the slide show and complete the tasks on each of the slides (in red) it may be necessary to add slides, do not change the font or the look of the slides but do add images and add to the bibliography page

• Remove red tasks as you complete them and save regularly and finally add your names and save, and email back to jc@shatincollege.edu.hk

Commonly available metal forms

• The basic elements of all metals are found naturally occurring within the earth. After they are extracted in the from of ore they are refined and processed in a variety of ways to produce usable materials. Metals are commonly available for manufacturing use in a wide range of forms and sizes.

www.afcd.gov.hk/.../cou_vis_cou_mos.html Mining for Iron Ore in Ma On Shan until 1981

www.ferretrollforming.com/aboutus.htm

http://thomonthenet.com/ContemporaryGlass/JoshSimpson_Megaworld13_large.jpg

Types of metal

• Two significant groups• Ferrous metals – contains iron• Non-ferrous metals – do not contain iron

• Alloys • The process of bringing together two or more

metals, often with other elements• Define the above and add examples

Heat Treatment of Metals

• The process of heating and cooling metal can be used to change its properties and characteristics

• Watch the Material Bonding PowerPoint , and describe and add images to show the metallic bonding of metal

• What makes metals such good electrical and thermal conductors, explain your answer

• What are free electrons?

Solidification of a substance

Liquid metal solidifies when cooled (except mercury)• Minute nuclei (crystals) of a solid form when a

pure, molten metal is cooled to just below its freezing temperature. Impurities in the molten material provide the centre for growth for the nuclei.

• All metals (except mercury) are solid at room temperature.

• A process of nucleation & growth achieves solidification.

• ‘Dendrites’ grow out from the nuclei forming a tree-like structure in the direction of the fastest heat loss.

Solidification of a substance

• Show some images which illustrate the previous slide

• The atoms arrange themselves in a regular pattern or lattice structure. Most metals form one of three types of lattice structure

Close packed hexagonal (CPH)

• Images and examples

Face-centred cubic (FCC)

• Images and examples

Body-centred cubic (BCC)

• Images and examples and don’t forget to add the source of the images to the bibliography

Metallic Structures

• This crystalline structure gives metals their properties (strength, stiffness, ductility, conductivity & toughness).

• Each dendrite grows in a geometric pattern consistent with the lattice structure until each one touches its neighbour. At this point the dendrites begin to thicken to form a totally solid grain of metal.

• The grain boundaries between are visible under a microscope, each grain having the same structure but a different orientation. This boundary is a narrow zone (perhaps three atoms) in which the atoms are not properly spaced according to the lattice structure.

Metallic Structures

Growth of metal dendrite

Copper dendrites

Modification of grain size• The rate of cooling and the amount of impurities in the molten

metal will affect grain size:• Gradual cooling - a few nuclei are formed - large grain size• Rapid cooling - many nuclei formed - small grain size.• Reheating a solid metal / alloy allows the grain structure to

re-align itself.• Directional cooling in a structure is achieved by selectively

cooling one area of a solid.• The effect of impurities (or additives) in a molten metal can

induce a large number of fine grains that will give a stronger and harder metal. This addition must be carefully controlled as too many impurities may cause an accumulation at the grain boundaries, which will weaken the material.

Keywords & Terminology

• Make a list of all the keywords and terminology used in your powerpoint

BibliographyBOOKS• Carbon, Mould, Cave, Design and Technology, Nelson International Editions,1996• Chapman C, GCSE D&T Resistant Materials, Total Revision, Collins Revision Guides, Collins, 2003• Cresswell, Lambert, Goodier, Product Design: Resistant Materials Technology, Second Edition, Heinemann, 2003,INTERNET

• Metallic Bonding, BBC Bitesize, Chemistry, Classifying Materials, http://www.bbc.co.uk/schools/gcsebitesize/chemistry/classifyingmaterials/bonding_higherrev5.shtml, 13/11/2007

• Metal Basics, Martin Tarr, www.ami.ac.uk/courses/topics/0131_mb/index.html , 13/11/2007• NASA, Sampson, Leidecker, nepp.nasa.gov/WHISKER/dendrite/index.html , 13/11/2007• Ferret Inc., http://www.ferretrollforming.com/index.htm, 13/11/2007• Sha Tin College, Technology Faculty, Jutka Czirok, https://msc-technology.wikispaces.com/IB+Design+Technology,

13/11/2007OTHER• Material bonding Powerpoint.ppt, Sha Tin College, 2006