Trace elements in gas-solid reactions

Considerable interest in the partitioning of trace elements in gas-solid reactions has been generated recently. To a large 

In the present section we shall present a discussion of gas-solid eq iilibria pertinent to the interpretation of such rare-earth element anomalies, but which will also serve as a general approach to the thermodynamics of gas-solid reactions involving trace elements. The treatment here is somewhat different to that of Boynton (1975), but employs essentially the same basic thermodynamic data. 

In calculating the distribution of rare-earth elements, or indeed any other trace elements, between a gas of solar composition and condensing crystalline phases there are two basic steps. Firstly, the distribution of rare-earth species in the nebula must be estimated and secondly, the partition of the REE between the gas and solid phases calculated. In the ensuing discussion it is ass amed following Grossman (197 ) and Boynton (1975), that equilibrium was achieved in the condensing solar nebula. 

In the nebula gas finite amounts of many REE species will exist, but studies of vapours in equilibrium with REE oxides suggest that M and MO species will be the most important. 

For a particular REE the proportions of these two species in the nebula are governed by 

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