Thorium hydride, decomposition

Layers of uranium or thorium hydrides ignited spontaneously after exposure to ambient air for a few min [1], Thermal decomposition yields pyrophoric uranium [2],... 

A further study of the decomposition kinetics of thorium hydride has been made (314). 

The decomposition of thorium hydride is controlled by kinetic rather than diffusion parameters [14]. The value of is 58 kJ mol for the decomposition of TI1H3 between 483 and 663 K and is 137 kJ mol" for the decomposition of ThH, 5 in the interval 873 to 1073 K. Reaction orders were reported to be 0.34 and 0.25, respectively. The evolution of hydrogen from PbH j proceeds [15] at about 463 K in steps during an increasing temperature programme and the apparent magnitude of , increases from 6.7 to 15 kJ moT as the hydrogen content decreases. 

These methods deal with specific cases. The list of examples is not exhaustive. The low-T (200-300°C) decomposition of the transition-metal borohydrides M(BH4> , e.g., leads to titanium, zirconium, halfnium, uranium and thorium borides . Alternatively, the uranium diboride may be obtained by reacting uranium hydride with diborane in hydrogen at 200-400°C. 

Thorium.—The production of nearly comparable quantities of propene and propane on photolysis of [Th(PrO( -C 5H 5)3] contrasts with the results of thermal decomposition studies and suggests that -hydride elimination pathways become available on photochemical excitation. The weakening of the metal-cyclopentadienyl ligand bonding e.g. promotion to 7 or ri excited states) and consequent reduction of metal co-ordinative saturation is a possible explanation for this change in behaviour. 

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