Solid state reaction kinetic

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. 

Nuclei provide a large number of spectroscopic probes for the investigation of solid state reaction kinetics. At the same time these probes allow us to look into the atomic dynamics under in-situ conditions. However, the experimental and theoretical methods needed to obtain relevant results in chemical kinetics, and particularly in atomic dynamics, are rather laborious. Due to characteristic hyperfine interactions, nuclear spectroscopies can, in principle, identify atomic particles and furthermore distinguish between different SE s of the same chemical component on different lattice sites. In addition to the analytical aspect of these techniques, nuclear spectroscopy informs about the microscopic motion of the nuclear probes. In Table 16-2 the time windows for the different methods are outlined. 

It is not accidental that the consideration bears a polemic character. It was not my intention merely to give a number of ready mathematical formulae for the experimentalists to treat their data and to obtain some constants, although such a work is clearly also necessary and useful and must therefore be welcomed. However, it seemed to be far more important to show that, firstly, not all has yet been done in the field of theory of solid-state reaction kinetics and, secondly, some of wide-spread views should be modified or even rejected as contradicting not only the available experimental data but the common sense as well. 

The unjustified neglect of a chemical interaction step in analysing the process of compound-layer formation appears to be the main source of discrepancies between the diffusional theory and the experimental data. The primary aim of this book is, on the basis of physicochemical views regarding solid state reaction kinetics, to attempt... 

Role of Intermolecular Vibrations in Solid-State Reaction Kinetics... 

ROLE OF INTERMOLECULAR VIBRATIONS IN SOLID-STATE REACTION KINETICS... 

Epple, E. Cammenga, H.K. Temperature resolved x-ray diffractometry as a thermoanalytical method a powerful tool for determining solid state reaction kinetics. J.Therm. Anal. 1992, 38, 619-626. 

The theory of solid state reaction kinetics includes no consideration of surface properties other than the recognition that crystal faces are the most probable location for nucleation in many reactions. Dehydration studies have provided evidence that, in many such processes, all surfaces are modified soon after the onset of chemical change [20,21], This is ascribed to a surface reaction that is limited in extent and can continue only at local sites of special reactivity where the recrystallization required for nucleation is possible. In other decompositions there is evidence that the modified reactivity associated with surfaces may influence the overall reaction [11] and may also preserve the identity of crystals. This, incidentally, masks the occurrence of melting during decomposition [22],... 

The mathematical kinetic models proposed by Korobov. Korobov [96] has discussed the limitations of the traditional geometric-probabilistic approach to describing solid state reaction kinetics. He proposes that some of the more recently developed mathematical techniques (see Section 6.8.5.) should be used to provide improved descriptions of the advance of the reaction fi"ont within the structural symmetry of an individual reactant. 

Introduction to the Theory of Solid-State Reaction Kinetics.179... 

A very recent article concerning methodology to record solid-state reaction kinetics by in situ time-resolved NMR at very high temperatures (> 1,000 K) is worth quoting despite the absence of phase transitions because the method may be useful. It was applied to monitor the kinetics of the reaction of powdered Na2C03 with Si02 with static 23Na NMR.192... 

No doubt that the progress in both sensitivity and methodology will increase the range of applicability of time-resolved in situ NMR studies, which are important for the comprehension of first-order and reconstructive phase transitions, but also in solid-state reaction kinetics. 

The decay of trapped radicals in polyethylene has been studied by many workers in recent years [226—242]. The usual pattern of step-like decay is observed below room temperature. The radicals studied, the experimental conditions and the measured reaction orders are given in Table 12. This clearly shows that disagreement exists between the results obtained by the various workers. The general problems of solid state reaction kinetics and the problems related to inter- and intraspur recombination have been discussed in section 3. It must be remembered, however, that usual kinetic analyses cannot be applied to step-like reactions and that the determination of the order of reaction by the integration method requires very accurate analytical methods. A strong dependence of the rate of radical decay on the crystallinity of the sample was nevertheless clearly demonstrated by Charlesby et al. [228] the specific rate... 

Solid State Reactions.—Kinetic and mechanistic studies of substitutions in the solid state, which are of some relevance to mechanisms of substitution in solution, include those of [Cr(NH3)5(OH2)]X3, where there seems to be some associative character to the mechanism for X = Br, SOg - or S042- 13 of [Cr(NH3)6]Cl3, [CrCl(NH3)5]Cl2, and c -[CrCl2(NH3)4]Cl, for which rates and activation parameters were determined of [Cren3](NCS)3 and of the racemisation of K3[Cr(oxalate)3]. ... 

The two following examples will show how galvanic cells can be used in the direct study of diffusion-controlled solid state reactions and phase boundary reactions. These examples are illustrative of a large number of possible applications in the field of solid state reaction kinetics. Emphasis here will be placed upon the principles of the methodology. Further examples can be found in the literature cited above. 

The solid state reaction kinetic model mentioned above is based on such an assumption that the rate determined step in chemical interaction between solid states is the formation and growth of crystal nucleus of products on the active sites. The active site can be the defects of surface and point or the outcrop moved to the crystal surface. As the volume of the original material and products varies, the generation process of crystal nuclei will be accompanied by the lattice deformation, that is, the speed of the process depends not only on chemical factor but also depends on the nucleation chemistry. 

J. Sestak, Z. Chvoj Irreversible thermodynamics and true thermal dynamics in view of generalized solid-state reaction kinetics Thermochim. Acta 388(2002)427... 

A deeper insight into electrochemical reaction mechanisms is possible by electrochemical studies employing solid electrolyte instead of liquid electrolyte With a solid electrolyte having preponderantly only one mobile ionic species electrode polarization can be studied under thermodynamically well-defined conditions without superimposed side effects by solvents and without the complications created by the presence of hydrated films or hydrolytic layers. Such measurements can be used, for instance, for the study of electrodeposition, formation of monolayers or of dendrites due to nucleation, for the study of polarization phenomena in ionic solids, solid-state reaction kinetics, transport phenomena, thermodynamics or constitutional diagrams, and for the development of practical devices. 

Similarly, sample packing could affect solid-state reaction kinetics where loosely packed powders have large gaps that may reduce thermal conductivity or trap evolved gases compared to a more densely packed powder, which would minimize these effects. Uncontrolled experimental conditions could cause a thermogram to be altered such that it falls above or below its expected location for a non-isothermal study. This results in errors in the calculation of the activation energy by isoconversional methods, which are manifested by a false or artifactual variation in activation energy. 

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