Zirconium, elemental hydride

Toxicity Variable. The hydrides of phosphorus, arsenic, sulfur, selenium, tellurium and boron which are highly toxic, produce local irritation and destroy red blood cells. They are particularly dangerous because of their volatility and ease of entry into the body. The hydrides of the alkali metals, alkaline earths, aluminum, zirconium and titanium react with moisture to evolve hydrogen and leave behind the hydroxide of the metallic element. This hydroxide is usually caustic. See also sodium hydroxide... 

Zirconium hydride, ZrH2, finds application as an antioxidant for rubber, in addition to being a moderator for nuclear fuel elements, and as a hydrogenation catalyst. Zirconium hydroxide, best formulated as Zr02 hH20 because of its variable water content, is used as a drying agent and absorbent and also has deodorant properties.19... 

Analytical Chemistry of the Transition Elements Coordination Numbers Geometries Coordination Organometallic Chemistry Principles Hydride Complexes of the Transition Metals Oxide Catalysts in Sohd-state Chemistry Periodic Table Trends in the Properties of the Elements Sol Gel Synthesis of Solids Structure Property Maps for Inorganic Solids Titanium Inorganic Coordination Chemistry Zirconium Hafnium Organometallic Chemistry. 

The atomic density of hydrogen in many metal hydrides is greater than that in liquid H2 or in H20. Metal hydrides are efficient moderators (Fig. 1) and neutron shielding materials, and help to minimize the core shield volume. Metal-clad yttrium hydride moderators capable of operation at 1000°C in air, uranium-zirconium hydride rods as a combination fuel-moderator element are examples, and metal-clad zirconium hydride units as moderator elements for operation up to 600°C° °. The hydrogen atom density in hydrides, Ah, the number of hydrogen atoms per cubic centimeter of hydride X 10 , is calculated from the hydrogen-to-metal atom ratio, H/M, the density of the hydride p, and the molecular weight W by ... 

The hydriding in a furnace of zirconium hydride moderator parts of 90 cm long by 10 cm in diameter (weighing 27 kg) lasts 1 week . The H/Zr ratio can be controlled to within 0.02, with a yield of 95%. In most cases, the hydrogen content is mostly 62 64 atom%. Stainless steel or nickel alloys are used for cladding zirconium hydride shielding elements. 

A. F. Lillie, D. T. McClelland, W. J. Roberts, J. H. Walter, Zirconium Hydride Fuel Element Performance Characteristics, U.S. AEC Report Al-AEC-13084, Atomics International, Canoga Park, CA, June 1973. 

The major use for zirconium is in the nuclear industry. Zirconium alloys (zircaloys) are used extensively as a cladding for nuclear (uranium oxide) fuel rods in water cooled reactors. Zircaloys were favoured over stainless steel cladding because they had a considerably lower neutron cross-section, appropriate thermal conductivity and both corrosion and mechanical resistance. As indicated, hafnium is an impurity in nearly all zirconium ores. Hafnium, however, has a much higher neutron cross-section than zirconium and, as such, the two elements must be separated prior to using zirconium in fuel rod cladding. For many years the separation was very difficult due to the chemical similarity of the two elements. Zirconium hydride is used as a moderator in nuclear reactors. 

All of the members of the final review team contributed, if not text, then comments to all of the chapters of the book. Their primary responsibilities for the different sections/chapters were divided as follows. Paul Brown prepared the introduction, and the sections on elemental zirconium, the zirconyl ion, the gaseous zirconium oxides, zirconium hydride, the halogen compounds and complexes, the chalcogen compounds and complexes, the Group 15 compounds and complexes, zirconium carbides and silicates. He was assisted by Christian Ekberg in the interpretation of aqueous zirconium complexes in these sections. Some initial work was done by Ken Jackson on the zirconium sulphate, nitrate and phosphate compounds and complexes. Bernd Grambow was responsible for the drafting of the sections on zirconium hydrolysis, the ion and the section on crystalline and amorphous zirconium oxides. Enzo Curti drafted the section on the zirconium carbonates. 

The conversion of CO + H2 (syn-gas) to hydrocarbons and oxygenates (Fischer-Tropsch chemistry)" is of considerable industrial importance and recently the activation and fixation of carbon monoxide in homogeneous systems has been an active area for research. The early transition elements and the early actinide elements, in particular zirconium and thorium," " supported by two pentamethylcyclopentadienyl ligands have provided a rich chemistry in the non-catalytic activation of CO. Reactions of alkyl and hydride ligands attached to the Cp M centers with CO lead to formation of reactive -acyl or -formyl compounds." " These may be viewed in terms of the resonance forms (1) and (2) shown below. 

When zirconium is oxidized in water, a considerable fraction of the corrosion product hydrogen enters the metal. There is evidence that the oxide recrystallization and the transition in kinetics that were shown in Figure 19 are related to a buildup of hydrogen in the surface of the metal. It has been suggested that at that time some zirconium hydride forms beneath the film. The addition of alloying elements which form active cathodes for hydrogen liberation have reduced hydrogen uptake, have delayed transition, and have resulted in the formation of more coherent oxide after transition. There has been no clear resolution as to mechanisms (29). 

Yttrium hydride or zirconium hydride may be used as a moderator. Boron carbide or alloys of rare earth elements (Eu, Gd, Hf) serve as absorbing elements in control drums. The beryllium reflector is sectional (at high temperatures, beryllium oxide maybe also employed). 

The in situ formed basic cyclopentadienyl complex of titanium, ethylene-bis( f-tetrahydroindenyl)-titanium hydride (EBTHI)TiH) containing a planar element of chirality, is active for the reduction of a C=N double bond of both N-aryl-imines (Schiff bases) and unsubstituted imines (108,109). (EBTHl)TiX2 derivatives are used as precursors of the hydride analogue. The chiral zirconium analogues of the above-mentioned complexes provided a breakthrough in asymmetric polymerization of terminal oleflns (110). 

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