Solids decomposition

Measurements [113,368] of interfacial (contact) potentials or calculated values of the relative work functions of reactant and of solid decomposition product under conditions expected to apply during pyrolysis have been correlated with rates of reaction by Zakharov et al. [369]. There are reservations about this approach, however, since the magnitudes of work functions of substances have been shown to vary with structure and particle size especially high values have been reported for amorphous compounds [370,371]. Kabanov [351] estimates that the electrical field in the interfacial zone of contact between reactant and decomposition product may be of the order of 104 106 V cm 1. This is sufficient to bring about decomposition. 

Experimental techniques used in the kinetic investigation of solid decompositions (described in Chap. 2) may need modification for the study of rate processes which yield no gaseous products. Measurements... 

This solid decomposition product of tetraperchloratosilicon was so explosive, even in small amounts, that work was discontinued. 

Figure 8.1 Typical solid decomposition curve showing fraction decomposed, a, as function of time, t.

This assumption however is not true, for powder which contains nitroguanidine produces a gray smoke consisting of solid decomposition products and yields gases which smell of ammonia. 

Potassium nitrate (together with sulfur and charcoal) is used in the manufacture of gunpowder (black powder). When such a mixture is ignited by means of a spark, both gaseous and solid decomposition products are produced in the resulting explosive reaction, which is quite complex. Black powder is used in the manufacture of ammunition for small firearms, in the production of time fuses, and as a blasting powder in mining operations. 

The CVD process involves the reaction of a mixture of gases with a heated substrate. Due to the thermoshock at the substrate s interface, the gases decompose and solid decomposition products deposit at the surface. 

It should be noted that over the past 50 years studies of solid decomposition kinetics have progressed from the application of equations which were originally derived for gases to more and more detailed studies on molecular events occurring at the reactant-product interface. This point has been emphasized by Boldyrev28 who, with his co-workers, has amassed a large body of evidence that shows the importance of defect structure on kinetics. This structure may be affected by radiation or by mechanical forces, such as grinding, which affect both the surface and the internal structure of crystals. 

The ratio of the experimental flow J to. /lllM, the decomposition coefficient, may be useful in assessing the decomposition mechanism. However, account must be taken of formation of the solid product in a metastable state. The formation of this material may be the rate-limiting step. Beruto and Searcy3334 have carried out a study of CaC03 decomposition using these principles. They have also studied the nature of the CaO formed. Thus, the field of solid decomposition kinetics seems to be moving toward a detailed examination of the products formed, with less emphasis on the overall kinetic equations. 

Reactions of solids are typically feasible only at elevated temperatures. High temperatures are achieved by direct contact with combustion gases. Often, the product of reaction is a gas. The gas has to diffuse away from the reactant, sometimes through a solid product. Thermal and mass-transfer resistances are major factors in the performance of solids reactors. There are a number of commercial processes that utilize solid reactors. Reactor analysis and design appear to rely on empirical models that are used to fit the kinetics of solids decomposition. Most of the information on commercial reactors is proprietary. 

Finally, the diffusion coefficients can also be estimated using alternative techniques, such as the analysis of Hall effect, electrode reaction kinetics, or solids decomposition rate. 

The range of melting is 210 -253oC. At 253°C the submitters observe solid decomposition. The checkers observed an mp range of 222-238°C (dec.). 

Weiss, V., Fett, F. N., Helmrich, H., and Janssen, K. Mathematical modelling of circulating fluidized bed reactors by reference to a solids decomposition reaction and coal combustion, Chem. Eng. Process, vol. 22, No. 2, pp. 79-90 (1987). 

Carbon, silica, and siliconcarbid were detected as solid decomposition products by X-ray dififracto-metry of the layers deposited at various amount of substance flow rate relations and temperatures. The carrier material was graphite, therefore the detection of carbon can not be traced back to the decomposition reaction clearly. 

Ammonium azide, solid. Decomposition, explosion, and combustion data (Ref 99). See also Vol 1, p A521-L... 

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