3. Non-reproducible experiments

The stall method can also be used to determine variations in surface reactivity, particularly in the case of non-reproducible experiments. In general, thermogravimetry poses no particular problem of experimental repeatability when the sample, temperature and composition of the gaseous atmosphere are well controlled. However, despite these precautions, it is sometimes impossible to reproduce kinetic curves from one experiment to the next. Since the thermodynamic variables are fixed, the surface reactivity is also fixed, the non-repeatability can only come from the S _m function. This can be a sampling problem, given the small amount of solid introduced into the crucible (a few milligrams for split solids). It may also be the case when a limited number of random processes occur during the reaction:

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