Uranium hydride

The rather narrow two-phase fields such as the delta hydride +c -uranium in the 627° section, and the corresponding delta hydride +/ -uranium in the 675° and 750° sections have somewhat uncertain limits. Other two-phase fields are well defined. 

Both zirconium hydride and zirconium metal powders compact to fairly high densities at conventional pressures. During sintering the zirconium hydride decomposes and at the temperature of decomposition, zirconium particles start to bond. Sintered zirconium is ductile and can be worked without difficulty. Pure zirconium is seldom used in reactor engineering, but the powder is used in conjunction with uranium powder to form uranium—zirconium aUoys by soHd-state diffusion. These aUoys are important in reactor design because they change less under irradiation and are more resistant to corrosion. 

The corrosion behavior of plutonium metal has been summarized (60,61). a-Plutonium oxidizes very slowly in dry air, typically <10 mm/yr. The rate is accelerated by water vapor. Thus, a bright metal surface tarnishes rapidly in normal environments and a powdery surface soon forms. Eventually green PUO2 [12059-95-9] covers the surface. Plutonium is similar to uranium with respect to corrosion characteristics. The stabilization of 5-Pu confers substantial corrosion resistance to Pu in the same way that stabilization of y-U yields a more corrosion-resistant metal. The reaction of Pu metal with Hquid water produces both oxides and oxide-hydrides (62). The reaction with water vapor above 100°C also produces oxides and hydride (63). 

Hydrocarbyl Complexes. Stable homoleptic and heteroleptic uranium hydrocarbyl complexes have been synthesized. Unlike the thorium analogues, uranium alkyl complexes are generally thermally unstable due to P-hydride elimination or reductive elimination processes. A rare example of a homoleptic uranium complex is U(CH(Si(CH2)3)2)3, the first stable U(I11) homoleptic complex to have been isolated. A stmctural study indicated a triganol... 

Carbides of the Actinides, Uranium, and Thorium. The carbides of uranium and thorium are used as nuclear fuels and breeder materials for gas-cooled, graphite-moderated reactors (see Nuclearreactors). The actinide carbides are prepared by the reaction of metal or metal hydride powders with carbon or preferably by the reduction of the oxides uranium dioxide [1344-57-6] UO2 tduranium octaoxide [1344-59-8], U Og, or thorium... 

The mechanisms of corrosion by steam are similar to those for water up to 450°C, but at higher temperatures are more closely related to the behaviour in carbon dioxide. Studies at 100°C have demonstrated that uranium hydride is produced during direct reaction of the water vapour with the metal and not by a secondary reaction with the hydrogen product. Also at 100°C it has been shown that the hydride is more resistant than the metal. Inhibition with oxygen reduces the evolution of hydrogen and does not involve reaction of the oxygen with the uranium . Above 450°C the hydride is not... 

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. 

Hartmann, I. et al., Rept. Invest. No. 4835, Washington, US Bur. Mines, 1951 Thorium hydride explodes on heating in air [1], and the powdered hydride readily ignites on handling in air [2], Layers of thorium or uranium hydrides ignited spontaneously after exposure to ambient air for a few min [3],... 

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

Sodium hydride ignites in oxygen at 230°C, and finely divided uranium hydride ignites on contact. Lithium hydride, sodium hydride and potassium hydride react slowly in dry air, while rubidium and caesium hydrides ignite. Reaction is accelerated in moist air, and even finely divided lithium hydride ignites then [1], Finely divided magnesium hydride, prepared by pyrolysis, ignites immediately in air [2], See also COMPLEX HYDRIDES... 

Storage of uranium foil in closed containers in presence of air and water may produce a pyrophoric surface [1], Uranium must be machined in a fume hood because, apart from the radioactivity hazard, the swarf is easily ignited. The massive metal ignites at 600-700°C in air [2]. The finely divided reactive form of uranium produced by pyrolysis of the hydride is pyrophoric [3], while that produced as a slurry by reduction of uranium tetrachloride in dimethoxyethane by potassium-sodium alloy is not [4],... 

Benzopinacol contains two acidic hydrogens which could account fpr the greater yield of TPA. When benzopinacoRL was reacted with U, >73% of the deuterium was incorporated into the TPA. This clearly shows that the benzylic hydrogens of TPA may originate from a uranium hydride. 

However, the soqrce of the uranium hydride in the reaction of benzophenone with U wasn t clear. When the reaction was worked up with D90, no deuterium incorporation in TPA or DPM was seen, nor was any seen when using toluene-dg as a solvent. All of the naphthalene could be recovered, which led us to conclude that TMEDA (presumably coordinated to uranium) was reacting with the low valent uranium generating a uranium hydride which became incorporated into the TPA or DPM. 

This reaction with TMEDA is temperature dependent. When the reaction of U with benzophenone is carried out at 70 °C, TPE is produced exclusively, with no TPA or DPM seen. As the reaction temperature is increased above 70 °C, the amounts of TPA and DPM produced increase. It appears that th hydrogenated products TPA and DPM arise when benzophenone reacts with U containing uranium hydrides. These hydrides may be formed from either substrates containing acidic hydrogens, or by thermal reaction of the low valent uranium species with coordinated TMEDA. 

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