Metals Flashcards
Body Centred Cubic (BCC)
More open structure
Coordination number- 8
Packing Density- 68%
Slip systems- 48 (planes are not close packed needing high temp. or force to activate)
Hexagonal Close Packing (HCP)
Each atom is surrounded by 6 more
Coordination number- 12
Packing Density- 74%
Slip systems- 3 (brittle)
How do you reduce slip in metals and why?
- Alloying
- Decrease grain size
Makes a metal harder/stronger or more brittle
Elastic Deformation
Stress is proportional to strain, is reversible
Malleability
The ability of a solid material to deform under compression
Types of Alloys
- Interstitial- Alloying atoms fit between metal atoms (Carbon in Steel)
- Substitutional- Alloying atoms replace other metal atoms (Brass with Copper and Zinc)
How does Grain Size affect the mechanical properties of metals?
Less slip across grain boundaries
Smaller grain means more boundaries which means harder to slip which means harder/stronger metal
Small grains are obtained by fast cooling, use of chemical agents, or application of physical treatment
Coordination Number?
Amount of neighbour atoms
Suitability of a metal
CASE
Cheap
Abundant
Suitable for the task
Easy to extract
Brittle
Materials considered this if they fracture at less than 5% strain
Ductility
A measure of the extent of plastic deformation a material can sustain before fracturing. Can be drawn into wires
Metallic Glass
Disordered structure like a liquid
High strength and elastic limit
Resistant against corrosion/scratches/dents/wear
Brittle
Cubic Close Packing (CCP)
Each atom is surrounded by 6 others in each layer
Coordination number- 12
Packing Density- 74%
Slip systems- 12 (4 slip planes, 3 directions) (ductile)
How do Metallic Grains form?
- As a metal solidifies, crystals start to grow in all different directions
- These merge to give a grain structure where each grain has its own crystalline orientation
Where are small grains not wanted?
High temp. strength
Temp-induced slip/failure more likely along the grain boundaries
Jet Turbines
Plastic Deformation
Deformation in which stress and strain are no longer proportional, not reversible
Anode and Cathode (metal corrosion)
The anode defines the area at which oxidation takes place
The cathode defines the area at which reduction takes place (where oxide layer forms)
This is always true!
Example of REDOX reactions
- Corosion
- Extraction of metals
- Batteries/Fuel Cells
- Burning of fuels
Transistion Metals
d-block elements lose the valence s-electrons when they form compounds but most can also lose a variable number of d-electrons. Explains mulitiple oxidation states
Trends across a Period
Atomic Radius- Increases
Ionisation energy- Decreases
Oxidising Strength- Decreases
Reducing Strength- Increases
Ionisation energy
The energy required to remove one electron from an atom of the element in the gas phase
Metals in Nature
Generally form positive ions which combine non metal negative ions, forming ores
Electrochemical Potential
It is a measure of the chemical potential of compounds which takes electrostatic forces into account
