5 LOOKING INSIDE MATERIALS Determining atomic and molecular dimensions oExplain how an STM, AFM and SEM work oDetermine resolution, magnification and atomic dimensions from microscope data oEstimate molecular size from experimental data

Cotton wool SEM 150x Space shuttle tile SEM 2000x

World’s smallest advertisement: STM of xenon atoms

STM of iron on copper

STM of iron on copper: “The atomic corral”

Making the corral

STM of metal surface showing instrumentally-induced distortion of atom shapes

AFM

AFM image of gold 111

AFM of rhodium screw dislocations

Say hallo to “carbon monoxide man” (STM image)

AFM of DNA strand

SEM

SEM of fruit fly head. Be afraid Be very afraid

SEM of solar spiderWill he catch the fruit fly?

SEM of ant

SEM of snowflake

Fracture behaviour oLearn how to calculate fracture energy oDistinguish between strength and toughness in terms of fracture behaviour of materials oExplain why metals are tough

Energy stored in stretched material Energy stored = area under graph = ½ x F x e = ½ x (k x e) x e = ½ x k x e 2

Fracture surfaces in metals Which shows ductile fracture, and which shows brittle fracture?

Fracture of CFRP in a tennis racquet

Composite materials Know the meaning of the term composite material For a range of composite materials (ferroconcrete, bone, CFRP etc.), explain how creating a composite can improve on the properties of the individual components

Composite materials Investigate properties of composite materials based on ice and/or jelly

Metal microstructures Recognise the various atomic-level structural features present in metals

Grain boundaries

A dislocation: an incomplete row of atoms

Metal microstructures Explain the effects that micro structural features have on the properties of metals

Questions on modifying the properties of metals 1. Draw diagrams to illustrate the following: (a) the pinning of a dislocation by a foreign atom (b) a large substitutional impurity atom in a crystal (c) an interstitial atom 2. What common effect(s) on the metal’s properties do all of the modifications described in Q1 have? 3. How can excessive work hardening of a metal be reduced? 4. A metal contains large crystal grains. How could you change the crystal grain size to create smaller grains? 5. Now try Questions 70X from Folio Views

Heat treatment of steel Investigate and explain how various heat treatments of steel can affect its properties

Stiffness and elasticity Explain stiffness and elasticity in metals, ceramics and polymers

Comparisons of materials of different classes(metals, ceramics, polymers) See p112-3 Give an example of a material with (a) giant covalent structure; (b) an ionic structure; (c) metallic structure Explain why ceramics, salts and metals are all stiff, but only metals are ductile and tough Why are polymers generally much less stiff than metals? How can some polymers be made stiffer? Why does rubber get stiffer the more it is stretched?

Electrical conductivity Investigate and explain the temperature dependence of the conductivity in metals, semiconductors and insulators

copper.swf nichrome.swf