Position of the problem and experimental approach

Reactions between solids proceed basically via the two processes of surface nucleation and growth and thus their study is based on the assumptions and methods developed in Chapters 8 to 11. 

For the reaction between massive solids, from the experimental knowledge of the kinetic law, it is theoretically possible to deduce the specific nucleation frequency and the growth reactivity, with the condition of having modeled the space function. 

In the case of reactions between powders, the problems of relative placement of grains of the initial solid in the space (design of the powder) seriously complicate the obtained laws and the total rate is not always separ le. 

For the reaction mechanism, that is, to study the reactivity, we can use a method that fixes in a simple way the space functions. For this, we carry out the reaction between two plates A and C (for this, we press each of the two initial powder pellets slightly to assemble two cohesive pellets). Then, these two assembled pellets are placed in contact in a matrix imder high pressine to carry ont the leactioa 

If the experiment thus carried out leads to a rate independent of time, this means that an interface step is rate determining at interface AvB or B/C whose areas are invariable. If the rate is a function of time, this means that diffusion through the formed solid B is the rate determining step. 

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