The Thermal Decomposition of Thorium Oxalate

Abstract

The thermal decomposition of hydrated thorium oxalate was followed by determining weight loss, change in electrical conductivity, and chemical composition of products. At temperatures below 200°C. the weight-loss curve indicated the existence of a tri- and a dihydrate and possibly a pentahydrate of thorium oxalate as stages m the dehydration. At higher temperatures dehydration was accompanied by loss of CO and CO₂. Almost all the (C₂O₄)⁼ decomposed sharply over a small temperature range near 300°C. Although some carbonate was formed, it did not exceed a concentration of 0.076 mole per mole of total thorium. According to chemical analysis the residue after heating at 350°C. was ThO₂ with a trace of carbonate and water. X-ray analysis, however, showed it to be a mixture of ThO₂, and a second substance whose identity is unknown. In the electron microscope the hydrated oxalate and the thoria produced from it were little different in appearance. Both appeared as relic crystals which were square prisms about l μ across and 0.2 μ thick, with a characteristic central aperture which exposed a large area of surface.