Decomposition of Solids [antikvár]

PREFACE Whilst subject to the normal laws of chemistry, kinetic studies of the thermal and photolytic decomposition of solids have imposed on them powerful geometric factors which tend in practice to dominate the interpretation. Furthermore, the absence of the principal adjustable parameters of classical chemical kinetics can make development of decomposition mechanisms in terms of chemical reactions an unrewarding task. One notes that chemically dissimilar substances such as nickel oxalate, potassium azide, barium permanganate, ammonium di-chromate, lead styphnate, mercury fulminate, lithium aluminium hydride and lead oxalate all decompose with similar, if not identical, kinetics, whereas the azides, most of which decompose simply to give a metal and nitrogen gas, encompass a wide range of kinetic forms. Clearly the link is not one of chemical stoichiometry. A unifying theme is found in the topochemistry of the reaction-product interface. The location and characterisation of this interface by the determination of rates, kinetic forms and energies is thus a primary objective which normally takes priority over mechanistic speculations. However, the usually capricious behaviour of nominally identical materials reminds us that first we have to investigate the nature and distribution of non-equilibrium imperfections in the reaction matrix. At this stage invention fails. There simply do not exist adequate non-destructive methods for characterising imperfections in reactive microcrystals, extrapolations from single crystal data proving often disappointing. Accordingly, solid state chemists are driven to deduce the nature of the imperfections from the kinetics of the decomposition. The inferential arguments which have to be used are not to everybody's taste, nevertheless real progress has been made by these means. It is the purpose of this book to chart the development of reaction topochemistry and, by highlighting unsolved problems, to indicate fields for further research. In order to compare and contrast kinetic data obtained over a period of 40 years, I have reluctantly accepted the convention that a transition state exists. It has a lifetime which is long compared with lattice relaxation times. A free energy of formation can be defined. Thus where