Fine-structure of the dehydration boundary diaspore = corundum + H2O as indication of a system of PVT-anomalies

Abstract

Abstract The study presents a re-examination of the dehydration reaction diaspore to corundum + H2O between 450° − 600° C in the pressure range 1 to 3 GPa. The high-pressure study bases on differential pressure analysis and simultaneous monitoring of piston displacement performed in a piston-cylinder apparatus. In quasi-isobaric runs the reaction of dehydration and re-hydration is documented by a temperature interval of about 30° width indicating that the reaction is affected by kinetics. In contrast to previous studies which explored the pressure range up to 5 GPa, the re-examined boundary is not presented by a smooth curve, but is structured by pressure anomalies at 1.0, 1.8 and 2.75 GPa. Literature data suggest further anomalies in the pressure range below 1.0 GPa, at 200 and 400 MPa. Comparison with earlier dehydration studies shows a striking similarity in this respect, and suggest a largely temperature independent general system of high-pressure anomalies. Literature examples show that these anomalies are also to be found in other materials of very divers composition.