Transformation without formation of a new solid phase

Two main families appear first transformations without formation of a new solid phase (such as anatase grain growth mentioned earher) and transformations that lead to a new solid phase (such as decarbonizing described previously). 

The first family is divided into two classes transformations that modify phase composition and transformations with only textnral change. 

The second family is also divided into two classes. In the first one, the initial solid is the single reactant. In the second one, the transformation involves several reactants. Some subclasses will precisely describe these two classes. 

In this transformation, the initial solid phase surrounded by a gaseous phase is preserved, but the rise in temperature induces a change in the composition of the sohd, or a textural modification due to grain growth (which can lead to densification and sintering). 

Stoichiometric change due to reaction of gas with a solid belongs to this class of transformation, such as the stoichiometric variation in cerium oxide under oxygen pressiue, which can be expressed as 

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