Appendix Experimental Methods for In-situ Investigations

The following chapter has been included to emphasize that most of the experimental data on solid state kinetics have been obtained ex-situ and are correspondingly unreliable. Further progress will depend decisively on the invention and application of appropriate experimental in-situ methods. 

The unique mechanical and structural properties of crystals necessitate the application of special experimental methods for the investigation of thd chemical kinetics of solids. In principle, all the physical parameters of substances involved in a chemical process can be used to follow the kinetics. These processes normally occur at high temperatures since they need thermal activation. Conventionally, the outcome of a solid state reaction experiment is inspected only after quenching. However, the quenching process is prone to alter many properties of the system, which explains the ambiguous results often found in the studies of solid state kinetics. 

A kinetic measurement ideally determines the crystal structure, morphology, and concentrations of all structure elements as a function of locus and time. The appropriate experiment consists of 1) the question to the system in form of a known input, and 2) the response of the system to the question, which is the output to be measured and analyzed. In a thermodynamic measurement, a known probe which can register an intensive function of state (P, T,fx,) is often equilibrated with the system to be investigated. Thus, the question to the system is then answered by the probe. 

We will not discuss microscopy and structure determinations since special monographs are available. Let us mention, however, that hot stages are available these days which allow imaging and diffraction work to be done at high temperatures. The limits for high spatial resolution are often not set by the temperature but rather by the ambient atmospheres. For example, the electron probe beam requires vacuum, whereas the component chemical potentials of a sample are undefined in a vacuum. 

Various properties of crystals can be used to inspect c,( ,r), provided that appropriate detectors for the intensity of input and output signals are available. If the monitor response is sufficiently fast, one may determine the time dependence of solid state reactions. The monitoring of reactants and/or reaction products can serve this purpose, but the relation between signal intensity (property) and concentration Cj) must always be established first. Since functions of state are related to one another in a unique way, any equilibrium property can, in principle, be used to determine However, the necessary assumption of local equilibrium must still be 

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