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High-Temperature Modifications of Thorium Dicarbide

  • P. K. Gantzel (a1), S. Langer (a1), N. L. Baldwin (a1) and F. L. Kester (a1)

Abstract

Thermal analyses of samples of thorium dicarbide in equilibrium with graphite show arrests which indicate phase transitions at 1427 ± 21°C arid 1481 ± 28°C. These thermal effects have been observed on heating and cooling both in standard thermal analysis and in differential thermal analysis using graphite as a reference material. The microstructure of thorium dicarbide samples shows the characteristic “herringbone” pattern of a material which has undergone a martensitic-type transition.

A high-temperature X-ray investigation has revealed that the observed thermal arrests correspond to erystallographic transformations. The monodinic modification found at room temperature is stable to 1427°C, at which temperature a tetragonal modification with a 0 = 4.235 ± 0.002Å and c 0 = 5.408 ± 0.002Å is formed. At 1481°C, the tetragonal is transformed to cubic with a 0 = 5.809 ± 0.002 Å. The best agreement between observed and calculated intensities has been obtained with C-C units of 1.5-Å assumed bond length in space groups P42/mmc and Pa3 for the tetragonal and cubic modifications, respectively.

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References

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