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MCE Clive 1 - Coggle Diagram
MCE Clive 1
Oxidation behaviour
Nucleation and growth of oxide 'islands' at discreet points on pure metal surface. Grow laterally until entire surface is covered in film
4 Stages:
- Exposure
- Molecular adsorption
- Dissociation and atomic adsorption
- Chemisorption
At high temps, O atoms can diffuse into metal lattice without forming oxide
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Electrons are being transported from metal, through oxide film to outside
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Assumptions:
- Cation diffusion controls rate of oxidation and therefore oxide layer thickness
- Thermodynamic equilibrium is established at the O-O and O-M interfaces
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Gibbs free energy
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Reaction is spontaneous if \(\Delta\)G is negative :heavy_minus_sign:
Reaction is non-spontaneous if \(\Delta\)G is positive** :heavy_plus_sign:
If \(\Delta\)H is positive :heavy_plus_sign: then reaction is endothermic (require heat)
If \(\Delta\)H is negative :heavy_minus_sign: then reaction is exothermic (release energy)
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