THE THERMAL DISSOCIATION OF OXIDES

This chapter is concerned with the thermal decompositions of oxides and peroxides. There are obviously very important connections with the reactions of hydroxides (Chapter 8) and so-called peroxysalts, which contain hydrogen peroxide of crystallization (included in Chapter 7 on hydrates). Hydrated oxides vary from compounds accurately represented by the stoichiometric formula M(OH) , to phases which contain discrete HjO molecules. The chemistry of oxides should also be considered in the context of the other binary compounds (e.g. hydrides, nitrides, carbides, sulphides etc.) dealt with in Chapter 10. 

The mechanisms of dissociation of sohd oxides may include one or more of the following steps (some or all of which may be at least partially reversible)  

This step may be accompanied by, or followed by, the transfer of electrons to acceptor sites, ultimately leading to cation reduction  

The reverse of these reactions is chemisorption and oxidation. Such chemical processes (in either direction) may also involve the transient formation of such intermediates [1] as O, O, etc., perhaps localized at specific sites. Alternatively, 

Oxides can be classified into two groups [2] (i) those which dissociate to yield molecular oxygen only, and (ii) those that yield a mixture containing both atomic and molecular oxygen (Table 9.1.). Other oxides melt unchanged at temperatures below the onset of dissociation, and sublimation may also occur. 

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