Kinetics of Reactions in the Solid State

House, J. E. (2007). Principles of Chemical Kinetics, 2nd ed. Academic Press/Elsevier, San Diego, CA. A kinetics book that presents a discussion of several types of reactions in the solid state as well as solvent effects. 

There are approximately 20 rate laws that have been found to provide the kinetic description of reactions in the solid state. These rate laws have widely differing mathematical forms, and they are derived starting with certain models. Some of the most important rate laws will now be described and derivations shown to illustrate how the principles are applied. After doing this, we will show how the models are applied by considering a few case studies. 

Exothermic Decompositions These decompositions are nearly always irreversible. Sohds with such behavior include oxygen-containing salts and such nitrogen compounds as azides and metal styphnates. When several gaseous products are formed, reversal would require an unlikely complex of reactions. Commercial interest in such materials is more in their storage properties than as a source of desirable products, although ammonium nitrate is an important explosive. A few typical exampes will be cited to indicate the ranges of reaction conditions. They are taken from the review by Brown et al. ( Reactions in the Solid State, in Bamford and Tipper, Comprehensive Chemical Kinetics, vol. 22, Elsevier, 1980). 

Kinetic curves relative to polymerization reactions in the solid state commonly show a sigmoidal shape with a slow initiation step followed by a steep increase, even by two orders of magnitude, of the reaction rate. A reaction with this kind of kinetic curve is said to have an autocatalytic behavior. 

Two reasons are responsible, for the greater complexity of chemical reactions 1) atomic particles change their chemical identity during reaction and 2) rate laws are nonlinear in most cases. Can the kinetic concepts of fluids be used for the kinetics of chemical processes in solids Instead of dealing with the kinetic gas theory, we have to deal with point, defect thermodynamics and point defect motion. Transport theory has to be introduced in an analogous way as in fluid systems, but adapted to the restrictions of the crystalline state. The same is true for (homogeneous) chemical reactions in the solid state. Processes across interfaces are of great... 

In 1937, dost presented in his book on diffusion and chemical reactions in solids [W. lost (1937)] the first overview and quantitative discussion of solid state reaction kinetics based on the Frenkel-Wagner-Sehottky point defect thermodynamics and linear transport theory. Although metallic systems were included in the discussion, the main body of this monograph was concerned with ionic crystals. There was good reason for this preferential elaboration on kinetic concepts with ionic crystals. Firstly, one can exert, forces on the structure elements of ionic crystals by the application of an electrical field. Secondly, a current of 1 mA over a duration of 1 s (= 1 mC, easy to measure, at that time) corresponds to only 1(K8 moles of transported matter in the form of ions. Seen in retrospect, it is amazing how fast the understanding of diffusion and of chemical reactions in the solid state took place after the fundamental and appropriate concepts were established at about 1930, especially in metallurgy, ceramics, and related areas. 

There are a number of references on gas-solid noncatalytic reactions, e.g., Brown, Dollimore, and Galwey ["Reactions in the Solid State, in Bamford and Tipper (eds.), Comprehensive Chemical Kinetics, vol. 22, Elsevier, 1980], Galwey (Chemistry of Solids, Chapman and Hall, 1967), Sohn and Wadsworth (eds.) (Rate Processes of Extractive Metallurgy, Plenum Press, 1979), Szekely, Evans, and Sohn (Gas-Solid Reactions, Academic Press, 1976), and Ullmann (Enzyk-lopaedie der technischen Chemie, Uncatalyzed Reactions with Solids, vol. 3, 4th ed., Verlag Chemie, 1973, pp. 395-464). 

The kinetics of an addition of oxygen to macroradicals in polymer systems performs the stepwise character which is caused by the kinetic non-equivalency of reactants in the solid state [4]. Achieving a certain conversion, the process ceases and may be reinitiated by a temperature increase. The carbon macroradicals begin to react already at 90 K. The resulting extent of transformation towards peroxyl radicals does not depend on the way how the temperature increase has been performed (i.e. whether all at once or in steps), which indicates that the stepwise character of a reaction may be attributed to the existence of discrete subsystems... 

There have been studies of polyanion unit isomerization in the solid state but such isomerizations are more problematical to quantify and unequivocal inferences from them are harder to come by than from the analogous studies in solution. The difficulty derives in part because high-quality kinetics data are hard to obtain for reactions in the solid state. Nonetheless, some reports on solid-state POM isomerization in the time period of this review afford valuable insights. 

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