0000000000073196
AUTHOR
Ernst-michael Sipple
Electronic microdiffraction study of structural modifications resulting from the dehydration of gypsum. Prediction of the microstructure of resulting pseudomorphs
Abstract Endothermic decomposition reactions (solid 1→solid 2+gas) generally affect only part of the inter-atomic bonds of the solid 1 structure. In consequence, the morphology and external dimensions of particles remain unchanged (the particles of solid 2 are referred to as pseudomorphs of those of solid 1). The gas release normally leads to a decrease of the molar volume of the precursor solid, resulting in cracking and formation of intra-particle porosity. This work deals with such a reaction: the dehydration of gypsum into sub-hydrated and anhydrous phases. Ultrathin (010) gypsum cleaved plates have been dehydrated under controlled conditions and studied by electron microdiffraction. Al…
Microstructural modifications resulting from the dehydration of gypsum
Various faces of dehydrated gypsum-cleaved blocks and single crystals have been investigated using optical microscopy, SEM, and TEM. The orientation of the cracks with respect to the initial gypsum structure and the Miller indices of all possible crack planes have been determined. These crack planes have been found to be few and to correspond to planes of high atomic density in the initial and final structures, therefore characterised by a low surface tension. These observations allow us to propose cracking criteria based on general concepts of crystal growth. The cracks' dimensions measured on different faces of the pseudomorph are distributed over several orders of magnitude and seems to …