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METALS AND ALLOYS
- METAL: opaque, closely packed crystalline structure,
- Conductors of heat and electricity
- Conductors of heat and electricity
- ALLOYS: Mix of 2 or more metals
- 2 metals - BINARY
- 3 metals - TERNARY
- 2 metals - BINARY
- Composed of many small crystals
- Form from molten metal
- As it cools impurities enable metal atoms to deposit upon them
- These Nucleat crystal growth
- Form from molten metal
- METALS
- ALLOYS
- Crystals termed GRAINS
- Grow until all melt metal is consumed
- where crystals abut their neighbour termed = GRAIN BOUNDARIES
- Grow until all melt metal is consumed
- NUCLEATION may be
- HETEROGENOUS- many sites of nucleation
- HOMOGENOUS- single site, metal is pure so requires 4 metal atoms
- to come together and requires specfial equipment
- HETEROGENOUS- many sites of nucleation
- GRAIN SIZE
- Influences physical properties
- TEMP OF MOULD - if similar to melt = slow cool and large grain size
- If different = rapid cooling and small grain size
- SHAPE OF MOULD - walls of mould intiate and influence crystal growth
- Influences physical properties
- VISUALISING GRAIN BOUNDARIES
- Light reflecting microscope
- Polished metal surface - irregularities scatter light
- app of suitable etching chemical
- Light reflecting microscope
- AMALGAMATION - MIX WITH Hg(mercury)
- plastic mass, hardening chemical reaction, Crystallisation
- plastic mass, hardening chemical reaction, Crystallisation
- DUCTILITY - max degree of extensionin response to tensile force
- MALLEABILITY - max degree of compression in response to an applied compressive force
- MALLEABILITY - max degree of compression in response to an applied compressive force
- On cooling from molten metals may :
- remain SOLUBLE in each other=SOLID SOLUTION
- be completely INSOLUBLE in each other
- be PARTIALLY SOLUBLE in each other
- form INTERMETALLIC COMPOUNDS if the metals have an AFFINITY for each other
- eg. Ag3Sn
- remain SOLUBLE in each other=SOLID SOLUTION
- SOLID SOLUTIONS
- 3 TYPES - ORDERED SOLID SOLUTION:
- metal atoms have specific site in common lattice
- metal atoms have specific site in common lattice
- If radii differ distortions of lattice
- RANDOM SOLID SOLUTION: Random sites in crystal lattice
- INTERSTITIAL SOLID SOLUTION: atoms of one lie within primarylattice
- 3 TYPES - ORDERED SOLID SOLUTION:
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