Thermo-optische analyse/untersuchungen von festkörperreaktionen

Abstract

Based on the fact that structural and optical properties in solid-state materials are interrelated, a thermo-optical analysis (TOA) may be used to investigate the course of solid-state reactions. An automated measuring process is possible, where use is made of the changes in light intensity that occur as a result of the temperature-dependent double refraction properties in crystallographically oriented intersection surfaces. This phenomenon is accessible to relatively simple and reliable measurement. When measurements were carried out with cleavage platelets of glauberite crystals [CaNa 2(SO 4) 2], the change in the orientation of the optical axes could be observed up to the point of decomposition. It has been shown in an experiment with decomposition reactions of gypsum that light intensity measurements at one cut surface, in the two positions of bright and dark field, will simultaneously yield quantitative information on changes in optical orientation and on the formation of nuclei in the early stage. The method also works in investigating phase conversions of the first order in cases where the conversion is accompanied by a change in optical properties. Thermooptical analyses of KCIO 4 and K 2CrO 3 (ICTA temperature standards) shows that this method may be used as an effective tool in investigating .χ-β conversions.