Solid-state decomposition process

The stability of suspensions, emulsions, creams, and ointments is dealt with in other chapters. The unique characteristics of solid-state decomposition processes have been described in reviews by D. C. Monkhouse [79,80] and in the monograph on drug stability by J. T. Carstensen [81]. Baitalow et al. have applied an unconventional approach to the kinetic analysis of solid-state reactions [82], The recently published monograph on solid-state chemistry of drugs also treats this topic in great detail [83],... 

Maciejewski M, Reller A (1987) How unreliable are kinetic data of reversible solid-state decomposition processes Thermochim Acta 110 145-152... 

The process of calculation becomes more complicated on adding further terms. Coats and Redfem [555] effectively put (U-2)/U equal to a constant value and the relationship is equivalent to that already given for In g i/T2 from the single term expansion. They assumed that f(q) = (1 — q)" and determined n by testing values which have significance in solid state decomposition reactions (i.e. n = 0, 0.5, 0.67 and 1.00). Sharp [75,556] has shown that the approach may be applied to other functions of g(q). If it is assumed that the zero-order equation applied at low a, as q -> 0, then g(q) == a. 

The catalytic activity of doped nickel oxide on the solid state decomposition of CsN3 decreased [714] in the sequence NiO(l% Li) > NiO > NiO(l% Cr) > uncatalyzed reaction. While these results are in qualitative accordance with the assumption that the additive provided electron traps, further observations, showing that ZnO (an rc-type semi-conductor) inhibited the reaction and that CdO (also an rc-type semi-conductor) catalyzed the reaction, were not consistent with this explanation. It was noted, however, that both NiO and CdO could be reduced by the product caesium metal, whereas ZnO is not, and that the reaction with NiO yielded caesium oxide, which is identified as the active catalyst. Detailed kinetic data for these rate processes are not available but the pattern of behaviour described clearly demonstrates that the interface reactions were more complicated than had been anticipated. 

OH- HB. One can assnme that these dihydrogen bonds play a principal role in the formation of these dimer structures. Finally, the authors demonstrated that these dihydrogen bonds provide preservation of crystallinity during O-H H-B conversion into O-B bonds with H2 elimination. In fact, solid-state decomposition of NaBHt THEC and other systems leads to a crystalline covalent product by a crystal-to-crystal process. 

Reviews of the application of electrical measurements in solid state decompositions have been given by Kabanov [52]. Electrical conductivity measurements, both a.c. and d.c. studies, have been used to characterize the species that participate in the thermal decomposition of ammonium perchlorate [53,54] (this reaction is discussed in Chapter 15). Other studies have been concerned with the mechanisms of oxide decompositions [55,56]. Torkar et al. [56] conclude from electrical conductivity evidence that the decompositions of alkali oxides are more complicated than exciton formation processes. 

It would be experimentally very difficult to measure amounts of liquid present (including variations with a and temperature) in mixtures that have undergone partial melting. The kinetics of processes that demonstrably involve the participation of a liquid phase often resemble those for solid state decompositions, as illustrated by the following examples. 

Representations of the textural and chemical changes that may accompany a solid state decomposition [8]. Contributions from these processes must be considered in formulating a reaction mechanism. 

This reaction has been studied in considerable detail and is mentioned here as providing a link between the nucleation and growth mechanisms characteristic of solid state decompositions and surface processes of the type discussed in heterogeneous catalysis. 

Maciejewski and Reller confirm [6] that (as yet) there is no experimental evidence for the existence of an amorphous or metastable intermediate in the dissociation of calcite. They show that the CaO formed by CaCOj dissociation under high vacuum reacts relatively rapidly at low temperatures (below 320 K) in the reverse process on CO2 readmission. Carefully controlled conditions are required to isolate and to study any highly active phases that may be formed during solid state decompositions. 

The solid state decomposition of Ba(Br03)2 has been described [34] as proceeding through (i) an initial fast process followed by (ii) a short induction period (iii) a slow linear reaction (iv) an acceleratory stage and finally (v) a deceleration to completion. The activation energy during nucleation (159 kJ mol ) was smaller than that for the main reaction (191 kJ mol ). Irradiation increased the values of the rate coefficients. 

Solid state reactions discussed here refer to the reactions which have at least one solid as reactants or products. Both the preparation and reduction of fused iron catalyst are solid state reaction processes, but the role of solid reaction has never been studied thoroughly yet, although there are few reports in literatme and textbooks on the preparation and reduction of fused iron catalyst. There is no doubt that the basic reactions during preparation and reduction of fused iron catalysts belong to orderliness of solid state reactions. The reduction and oxidation of solid oxide, the decomposition of carbonates and hydrates, and the oxidation of sulfides etc belongs to solid state reaction. The solid state reaction follows its imique law, and it must be considered in the analysis and interpretation of preparation and reduction of fused iron catalyst. Therefore, it should be understood on the basic law of solid state chemical reactions. 

Silicon is prepared commercially by heating silica and carbon in an electric furnace, using carbon electrodes. Several other methods can be used for preparing the element. Amorphous silicon can be prepared as a brown powder, which can be easily melted or vaporized. The Gzochralski process is commonly used to produce single crystals of silicon used for solid-state or semiconductor devices. Hyperpure silicon can be prepared by the thermal decomposition of ultra-pure trichlorosilane in a hydrogen atmosphere, and by a vacuum float zone process. 

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