Solid-state reactions theory

Fej04 . A similar correspondence between theory and practice has been found for growth of Fej04 by the solid state reactions from FeO and Fe, , between 600 and 1 200°C. The growth rate of FeO is within 10% of the theoretical rate expected from Fe lattice diffusion, calculated according to the Wagner theory . 

It is appropriate to terminate this section, concerned with the formal theories of solid state reactions, with a table summarizing those a—time... 

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. 

An appreciable number of special monographs on metal oxidation are available. These presentations normally start with Wagner s theory of scale formation [C. Wagner (1933), (1951)], which represented the first consistent and quantitative treatment of a solid state reaction model. As Figure 7-1 shows, metal oxidation has quite... 

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... 

See also Retro-Hantzsch Hard acid or base, see HSAB theory Heating curves, in solid-state reactions,... 

The evaluation made in the preceding section shows the possibility of a natural explanation of the regulation of low-temperature solid-state reactions in a model accounting for barrier parameter oscillations resulting from intermolecular vibrations. A consistent analysis of such a model is required. A mathematical body used for this purpose is, conceptually, close to the common theory of nonradiative transitions, but unlike the latter it enables us to exceed the limits of the one-dimensional Franck-Condon approximation which is inapplicable in treatment of heavy-particle transfer. 

Studies of dehydrations continue to contribute much to the theory of solid state reactions. 

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],... 

Reports of compensation behaviour appear to have been mainly empirical findings which have not contributed much to the theory of solid state reactions. Identification of the effect as a direct consequence of isokinetic behaviour [57,58] does, however, offer a theoretical foimdation for interpretation of the observed correlated changes in apparent Arrhenius parameters. The fit of Arrhenius parameters for crystolysis reactions to the expression ... 

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

INTRODUCTION TO THE THEORY OF SOLID-STATE REACTION KINETICS... 

The summary of the theory of kinetics of solid-state reactions given here is applicable to TG investigations and also equally to rate measurements by other methods of thermal analyses. For more extensive treatments and further background information see References 4,5,10,29,71,76,103. 

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