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 CO,.Almost all the (C,O,)" decomposed sharply over a small temperature range near 300 OC. 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 a t 360 O C . was Tho, with a trace of carbonate and water. X-ray analysis, however, showed it to be a mixture of Tho, and a second substance whose identity is unknown.I n the electron microscope the hydrated oxalate and the thoria produced from it were httle different in appearance. Both appeared as relic crystals which were square prisms about l y across and 0 . 2 y thick, with a characteristic central aperture which exposed a large area of surface.* Total thorium was known from the weight and composition of the sample before heating.

ThO2-based pellet fuels - their properties, methods of fabrication, and irradiation performance: a critical assessment of the state of the technology and recommendations for further work

“…With a decomposition temperature of 350 0 C, the results of Breysse et ale (1965) showed that the larger the particle size of the Th0 2 powder, the larger the surface area. Although this result seems a paradox, it is compatible with the oxalate decomposition work done by Becket and Winfield (1951) in which they showed the larger Th0 2 particles to be composed of laminae of oxide crystallites with a central hole whose surface is not smooth like the exterior but is broken by very thin projecting laminae. In the work of Allred et a1.…”

“…The thermal decomposition mechanism for thorium oxalate has been extensively investigated (Becket and Winfield 1951;D'Eye and Sellman 1955;Wendlandt et ale 1961;Moorehead and McCartney 1976). The amount of water, both chemically combined and adsorbed, varies depending upon the age and storage condition of the oxalate.…”

The Chemistry of the Metal Oxalato Complexes.

“…are 42 and 24, respectively. They are in remarkably good agreement considering the various approximations made at each stage in the treatment, which is based entirely on classical electrostatistics.…”

“…Detailed kinetic studies have been made of only a few compounds: the oxalates of silver(I), mercury®, mercury (II), nickelfll), and lead(II). In recent years new techniques, particularly that of thermogravimetry, have been applied, and reports have appeared on many bivalent metal oxalates (146,233,234,378,421), a few rare earth oxalates (70,433,434), and two actinide oxalates, thorium(IV) (42,111,322), and americium-(III) (273). An interesting isotope-effect study has been made of the pyrolysis of lead oxalate (451).…”