Zirconium compounds-—continued

Concomitant with continued olefin insertion into the metal-carbon bond of the titanium-aluminum complex, alkyl exchange and hydrogen-transfer reactions are observed. Whereas the normal reduction mechanism for transition-metal-organic complexes is initiated by release of olefins with formation of hydride followed by hydride transfer (184, 185) to an alkyl group, in the case of some titanium and zirconium compounds a reverse reaction takes place. By the release of ethane, a dimetalloalkane is formed. In a second step, ethylene from the dimetalloalkane is evolved, and two reduced metal atoms remain (119). 

Biomimetic oxidations of alcohols and amines to carbonyl compounds continue to attract attention. Whilst methods are not yet of significant synthetic value, advances have been made in the development of oxidation catalysts. The isoalloxazine (1), when complexed with zirconium(iv), acts as an efficient catalyst for the oxidation of alcohols by oxygen, and the pyrimidopteridines (2) show high autorecycling efficiency in the oxidation of cyclopentanol. The deazatoxoflavin derivatives (3) oxidize primary amines to imines with high turnover of the catalyst. Subsequent hydrolysis liberates the carbonyl compound. 

Early waterproofing treatments consisted of coatings of a continuous layer impenetrable by water. Later water-repellent fabrics permitted air and moisture passage to improve the comfort of the wearer. Aluminum and zirconium salts of fatty acids, siUcone polymers, and perfluoro compounds are apphed to synthetic as well as natural fibers. An increase in the contact angle of water on the surface of the fiber results in an increase in water repeUency. Hydrophobic fibers exhibit higher contact angles than ceUulosics but may stiU require a finish (142). 

Zirconium and hafnium are separated by fractional distillation of the anhydrous tetrachlorides in a continuous molten solvent salt KCl—AlCl system at atmospheric pressure (56,57). Zirconium and hafnium tetrachlorides are soluble in KCl—AlCl without compound formation and are produced simultaneously. 

Zirconium tetrafluoride [7783-64-4] is used in some fluoride-based glasses. These glasses are the first chemically and mechanically stable bulk glasses to have continuous high transparency from the near uv to the mid-k (0.3—6 -lm) (117—118). Zirconium oxide and tetrachloride have use as catalysts (119), and zirconium sulfate is used in preparing a nickel catalyst for the hydrogenation of vegetable oil. Zirconium 2-ethyIhexanoate [22464-99-9] is used with cobalt driers to replace lead compounds as driers in oil-based and alkyd paints (see Driers and metallic soaps). 

Precipitation of the coating from aqueous solutions onto the suspended Ti02 particles. Batch processes in stirred tanks are preferred various compounds are deposited one after the other under optimum conditions. There is a very extensive patent literature on this subject. Continuous precipitation is sometimes used in mixing lines or cascades of stirred tanks. Coatings of widely differing compounds are produced in a variety of sequences. The most common are oxides, oxide hydrates, silicates, and/or phosphates of titanium, zirconium, silicon, and aluminum. For special applications, boron, tin, zinc, cerium, manganese, antimony, or vanadium compounds can be used [2.40], [2.41],... 

Three classes of hybrid HPA are known to be stable to hydrolysis 1. Organometallic derivatives of the type RM (M = Si, Ge, Sn, Pb and R = alkyl or aryl). 2. Cyclopentadienyl-titaninm derivatives. 3. Zirconium alkoxide or phosphate derivatives, all of which are illustrated in Figure 2. We have tested phenyl model compounds of all of these for stability by boiling them in 6M HCl or H2O2 solution. This study showed that only PhP-O-HPA moieties are stable under conditions likely to be encountered in a fuel cell. Never the less we continue to study model compounds of the type RSi-O-HPA due to the large diversity of available ethoxy- and chloro- silanes. 

ZIRCAT (7440-67-7) Finely divided material is spontaneously flammable in air may ignite and continue to bum under water. Violent reactions with oxidizers, alkali hydroxides, alkali metals (and their compounds), carbon tetrachloride, cupric oxide, lead, lead oxide, lead peroxide (combined material can burn explosively, and is sensitive to friction and static electricity), nitryl fluoride, oxygen difluoride, phosphoms, potassium, potassium compounds (potassium chlorate, potassium nitrate), sodium borate, sodium hydroxide. Explodes if mixed with hydrated borax when heated. Contact with lithium chromate may cause explosion above 752°F/450°C. Forms explosive mixture with potassium chlorate. Dusts of zirconium ignite and explode in a carbon dioxide atmosphere. Contact with ammonium-V-nitrosophenylhydroxylamine above 104°F/40°C forms an explosive material. Incompatible with boron, carbon, nitrogen, halogens, lead, platinum, potassium nitrate. In case of fire, use approved Class D extinguishers or smothering quantities of dry sand, crushed limestone, clay. 

Monocyclopentadienylzirconium trichloride has been prepared from zirconium tetrachloride by reaction with cyclopentadienylmagnesium chloride in toluene/diethyl ether solution 240, 241). Both the chloride and bromide have been prepared from the corresponding tetrahalides and magnesium cyclopentadienide in xylene at 100°-110°C 451), or by continuous recirculation of cyclopentadiene vapor upward through a bed of zirconium trihalide (250°-300°C) resting on a glass sinter. The products were purified by sublimation. Yields were only about 15% compared to the 60-70% obtained from syntheses carried out in solution. The melting points and colors for the monocyclopentadienyl metal trihalides and for other cyclopentadienyl metal halide compounds are tabulated in Table I. 

The bis(77-cyclopentadienyl)zirconium dichloride has been synthesized by a variety of routes and a variety of authors. It can be recovered from reaction systems of zirconium tetrachloride and sodium cyclopentadienide in tetrahydrofuran or ethyleneglycol dimethyl ether 89, 194, 343, 471) or with lithium cyclopentadienide 472) in place of the sodium compound. The hafnium compound was prepared in a similar manner 343, 471). In general, the residue obtained upon evaporation of the solvent is extracted with chloroform and the product from the extraction is recrystallized from benzene. The dichloride was also prepared 451) by the continuous recirculation of cyclopentadiene vapor through a bed of ZrCl2 at 270°-350°C. Another route to the chloride is the reaction of zirconium tetrachloride with cyclopentadienylmagnesium chloride 559) in benzene yet another involves the reaction of zirconium tetrachloride and cyclopentadiene in ethylamine as the solvent at room temperature 367). 

With the stoichiometry ZrSej 94, zirconium diselenide is a semiconductor with an empty tjg band ( 16.4.3.1). The LijZrSej 94 intercalation compounds show a phase transition when x reaches 0.40. A continuous filling of the octahedral sites of the van der Waals gap (see Fig. 1, 16.4.3.1.) is observed over the whole composition domain (0 < X < 1) according to a classical CdIj-NiAs transition. Electrical, electrochemical, magnetic, NMR and EPR measurements affirm that it is a purely electronic transition. Below X = 0.40 the electrons are localized on zirconium centers, reducing Zr ions Zr above x = 0.40 a metallic behavior is observed. 

According to the thermodynamic calculations performed by Besmann and Lin-demer (1978), the presence of pure H2O vapor in the gap does not effect an oxidation of UO2+X to U4O9 (UO2.25). This oxidation step, which is accompanied by a phase transformation of the uranium oxide, should only be possible in the presence of oxygen in the steam. However, as a consequence of radiolytic reactions the steam in the gap will contain oxygen in any case so that continued oxidation of the UO2-1-X should be possible. Under such conditions, the Csl assumed to be present as the most stable iodine compound in the gap of an intact fuel rod will become thermodynamically unstable in favor of elemental I2 and, in contact with zirconium metal, of Zrh or Zrh, with the rate of oxidation and its extent depending on the concentration of oxygen present in the steam. These oxidized iodine species have a measurable vapor pressure under the prevailing conditions. 

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