Thorium carbide ThC

Thorium carbides (ThC, ThC2) and uranium carbides (UC, UC2) exhibit metallic properties, but in other properties differ significantly from the carbides of the subgroups of the IVth, Vth and Vlth groups of the periodic table. Their hardnesses are substantially lower (see Table 5.6-1), they are pyrophoric and are easily hydrolyzed in water or weak aeids. Their only economic importance is as carbidie fuels in nuelear technology, particularly for high temperature and breeder reactors which are currently in the evaluation phase. 

Conversion of thorium nitrate. The conversion consists in producing a thorium nuclear fuel required in power reactors. Five thorium compounds can be used as nuclear fuel thorium metal, thorium dioxide (ThO ), thorium carbide (ThC ), thorium fluoride (ThF,), and thorium chloride (ThClJ. 

Thorium combines with nitrogen at elevated temperatures to form nitrides ThN and Th2N3. Reaction with carbon at elevated temperatures forms the carbides ThC and ThC2. 

Thorium Carbides. Two carbides are known ThC, m.p. 2625°C ThC2, m.p. 2700°C. Monoclinic ThC2 inverts to the tetragonal form at 1410 + 20°C and from tetragonal to cubic at 1500° 20°C. These special carbides are of potential interest in nuclear engineering. 

In the actinide system, the heat of formation as a function of composition has been measured recently for ThC and UC. A single value is available for PuC, but this is apparently much too positive. The thorium carbides... 

The effective charge on the thorium atom is found to be 1.66 for ThC2(g) and 1.60 for ThC4(g). For this reason, [2008KOV/KON] used the electronic levels of ThO(g), where the thorium atom is divalent, in calculating the thermal functions of the carbide molecules, and we have followed the same procedure, as discussed in sections XL 1.2.1 and XL 1.2.2. However, as noted there, the calculated entropies of the reactions Th(g) + C(cr) ThC (g), = 2, 4 are noticeably different (by ca. 30 and -17 J-K -moL respectively) from those derived from the vaporisation experiments of [1964JAC/BAR] and [1974KOH/STE]. 

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