Solid-state reactions first-order

We have presented two methods useful in following solid state reactions. In order to completely classify a reaction, we need to obtain an estimate of the reaction kinetics and order of the solid state reaction. Both DTA and TGA have been used to obtain reaction rate kinetics. But first, we must refixamlne Mnetic... 

Spectroscopic analyses of solid-state reactions must first use solid-state techniques (IR, UV/Vis, Raman, luminescence, NMR, ESR, CD, X-ray powder diffraction, DSC, etc.) in order to secure the solid-state conversion, before the solution techniques (detection of minor side products, specific rotation, etc.) are applied. 

Dinuclear dihydroxo-bridged complexes can often be obtained from the parent mononuclear complexes by the solid-state reaction Eq. (7). This was first reported by Werner (7, 11) and Dubsky (18), and it is generally the most convenient method for the preparation of dihydroxo-bridged complexes of Cr(III), Co(III), Rh(III), and Ir(III) with L4 = (NH3)4 or (en)2 [and (tn)2 in the case of chromium(III)] (67, 131, 133, 214 219). With the exception of the ammonia chromium(III) complex, these reactions are essentially quantitative and the rate of reaction follows the order chromium(III) > cobalt(III) > rhodium(III) >... 

The kinetics of many solid state reactions have been reported as being satisfactorily represented by the first-order rate equation [70] (which is also one form of the Avrami-Erofeev equation (n = 1)). Such kinetic behaviour may be expected in decompositions of fine powders if particle nucleation occurs on a random basis and growth does not advance beyond the individual crystallite nucleated. 

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. 

There are several well known examples of photochemical reactions which exhibit a discontinuous change in rate constants and quantum yields when they are carried out in solid matrices and not in solution (see Table 2.5). The deviation from first-order kinetics for a reaction carried out in a matrix below its glass transition temperature is a characteristic feature of solid-state reactions. 

Thus, ideally, the total number of acid sites is equal to the total number of A1 atoms on framework tetrahedral (T) sites. Because the acidity of zeolites is adversely affected by a small amount of residual Na", Na must be exhaustively removed in order to obtain a highly active solid acid catalyst. Removal of Na from zeolites usually requires repeated ion-exchange steps combined with calcination, in the temperature range of 823-1050 K. Only about 70% of the Na ions are replaced by NH4 ions during the first exchange. It is assumed that as a result of calcination Na atoms, which were not accessible for ion exchange, are redistributed over the zeolite surface and made accessible. Simultaneously, solid-state reactions occur in the zeolite, and framework aluminum is removed. This phenomenon results in stabilization of the zeolite structure the acid forms of low-silica zeolites are inherently unstable. 

Epstein (1990) also considers a model (Allnatt and Jacobs, 1968) for nucleation in solid-state reactions that is equivalent to a set of coupled first-order rate equations. He shows that by introducing delays to account for the fact that an n-particle nucleus cannot grow until an (n — l)-particle nucleus is formed, the model can be made more physically realistic with relatively little increase in computational effort. 

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