29 Oxidation - 530.352 Materials Selection Lecture #28 -...

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Unformatted text preview: 530.352 Materials Selection Lecture #28 - Oxidation Monday November 21 st , 2005 What materials oxidize ?? Material + Oxygen +Energy --> Oxide of Material Do the following materials oxidize and if so - how ?? Metals Ceramics Polymers ??? ??? ??? Energy of formation of oxides: Materials that are unstable in Oxygen Materials that are stable in Oxygen E for Oxide Formation (kJ/mol) What materials oxidize ?? Material + Oxygen +Energy --> Oxide of Material Do the following materials oxidize and if so - how ?? Metals Ceramics Polymers YES NOT MANY YES (all but gold) (most are oxides) (they burn) Rates of Oxidation Linear m = k L t Parabolic ( m) 2 = k P t Linear gain Linear loss m t Ta, Nb W, Mo m t Fe, Ni, Cu Al, Co, Si Relative rates of different metals Time (hrs.) for 0.1mm of oxide at 0.7 T m : Au infinite ? Ni 600 Ag very long Cu 25 Al very long Fe 24 Sn very long Co 7 Pt >100,000 Ti <6 Zn >10,000 Ta very short Cr 1,600 Nb very short Mo very short W very short Stages of Oxide Growth metal Air oxide M ++ + O---> MO metal oxide Air Growth at surface Diffusion through film M ++ 2e- O- - Cracking, Spalling, Evaporation Linear loss m t W, Mo Linear gain m t Ta, Nb Diffusion Controlled Growth...
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29 Oxidation - 530.352 Materials Selection Lecture #28 -...

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