Qualitative analysis of the growth

To ensure that this last effect is not a rate-determining step and to reach the tme reaction speed, we can carry out the experiments either on very thin powder beds or out of agitated engine (fluidized bed, rotary furnaces). Note that many authors observe an influence of the mass of the sample on the thermogravimetric speed. This influence is normal because this speed is an extensive property. If we consider the rate, brought back to the unit of initial amount of matter, in a fixed-bed, this influence of the initial amormt and the influence of the thickness of the bed are generally the proof of the intervention of the inter-granular diffusion in the speed. 

In what follows, we will assume a veiy fast intra-granular diffusion compared with the other phenomena. 

In both cases, we will have an inward development of the new solid phase. 

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After a qualitative analysis of the growth, we can examine two models that are used ... 

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