Thorium Monocarbide Research Articles

Thermodynamic properties of non-stoichiometric thorium monocarbide

Thermodynamic information on nonstoichiometric thorium monocarbide was obtained from measurements on solid electrochemical cells. The cells were of the type Th, ThF 4 | CaF 2 | ThF 4, ThC 1−x. Measurements were made at temperatures of 800–950°C. Partial molar free energies of thorium and carbon were calculated from the data. The monocarbide phase was found to be stable from a composition of ThC 0·66 to ThC 0·96 from measurements of the variation of lattice parameter with composition. The results are discussed in connection with theories of chemical bonding which have been proposed for transition metal and actinide metal carbides. A qualitative picture of the bonding in nonstoichiometric thorium carbide is presented in which it is assumed that thorium and carbon form covalent bonds which increase in strength when some of the carbon is removed from the lattice.

Hydrolysis of thorium carbides between 25 and 99°C

The reactions with water of arc-cast thorium carbides with total-C/Th atom ratios varying from 0·8 to 2·1 were investigated. Thorium monocarbide produced mostly methane (and also hydrogen if carbon-deficient). Thorium dicarbide yielded C 2 to C 8-hydrocarbons, hydrogen, and a nonvolatile wax. Varying the reaction temperature between 25 and 99°C caused no change in the hydrolysis products, although the reactions were considerably faster at the higher temperatures. Hydrolysis of monocarbide-dicarbide mixtures gave the products expected from simple ThC-ThC 1·95 binaries. Tungsten (2·4 atom%) as an impurity in thorium dicarbide catalysed the polymerization of the C 2 units to wax which markedly changed the gas composition. The maximum combined-C/Th atom ratio obtainable by arc-melting with graphite electrodes was 1·95 rather than the theoretical 2·00. There was no indication of any significant range of composition for the dicarbide. The lattice parameter for ThC 1·0 was 5·346Å, and for the carbon-deficient ThC 0·81 5·340 Å.

Ternary compounds between thorium monocarbide and thorium dihydride

The thorium-hydrogen-carbon system was studied by measuring hydrogen equilibrium pressures at various compositions and temperatures. Two compounds, ThC·ThH 2 and ThC·2ThH 2, were found and characterized. ThC·ThH 2 has a hexagonal closest-packed lattice with a o = 3·816 A ̊ and c o = 6·302 A ̊ . ThC·2ThH 2 has a monoclinic lattice with a o = 6·50 A ̊ , b o = 3·80 A ̊ , c o = 10·91 A ̊ and β = 119°. The enthalpies of formation for each compound were determined.