The characterisation of Manganese (IV) compounds and the study of the thermal decomposition of Potassium Chlorate alone and with Mn(IV) and other oxides and salts

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Manganese dioxide compounds are preferred curing agents for Polysulphide resins used as sealants in industry. These are required to have consistent setting characteristics and the investigation was initiated to characterise a number of proffered compounds of this type an to establish criteria by which an informed choice could be made of an optimum curing ages for a specific set of conditions. Several different chemical and physical properties were examined and critical parameters were established. A compound - sodium birnessite- was identified as a significant agent in the determination of curing properties. It was synthesised and its curing properties alone and in combination with other manganese dioxide compounds was evaluated. In an effort to find a specific reaction which might be used to characterise manganese dioxide curing agents it was decided to examine the classical reaction between these compounds and potassium chlorate. A literature search revealed major contradictions in the reported conditions under which potassium chlorate undergoes thermal decomposition as result of which it was decided to study the decomposition of potassium chlorate alone and in the presence of manganese dioxide and other catalysts. During this investigation a hitherto unreported high temperature structural change in potassium chlorate at 341° C was identified. The existence of this reversible change was confirmed by Powder Diffraction X-Ray analysis and an orthorhombic (near tetragonal) more open structure was assigned to it. It is suggested that the rapid decomposition of potassium chlorate in the solid state presence of catalysts is related to this change to a more open structure