Metal dioxides

Ruthenium—Titanium Oxides. The x-ray diffractioa studies of mthenium—titanium oxide coatiags show that the coatiag components are preseat as the metal dioxides, each ia the mtile form as weU as ia soHd solutioa with each other (13). The developmeat of the crystal stmcture begias to occur at a bake temperature of about 400°C. By foUowiag the diffractioa line for the mtile stmcture, an iacrease ia crystallinity can be seen as temperatures are iacreased to the 600—700°C range. Above these temperatures, the peak begias to separate iato two separate peaks, iadicative of phase separatioa iato iadividual mtile oxides, oae rich ia mthenium and one rich ia titanium. 

Another significant comparison between the two systems concerns the partial pressures of the metal dioxide molecules. These pressures are relatively insensitive to the condensed-phase composition and are quite similar in the plutonia and urania systems. Calculated metal dioxide vapor pressures are compared in Table V for 0/M = 1.96. 

Borides and Tetrahydroborate Compounds.—ZrB2, HfB2, and the mixed diboride TiB2-ZrB2 have been prepared by heating a stoicheiometric mixture of boron and the metal dioxides (1600—1900 C 10 mmHg). The phases of the Hf-B and I f-M-B (M = Mo or W) systems have been studied by X-ray diffraction techniques. 

Table 6.4. Properties of transition-metal dioxides with rutile-type structure ...

Solid superacids may be made by treating ordinary solid add catalysts with strong Br0nsted or Lewis acids. For example, if freshly precipitated titanium hydroxide or zirconium hydroxide is treated with sulfuric acid and calcined in air at 500 °C. a very active solid acid catalyst results. The solids consist mainly of the metal dioxides with sulfate ions coordinated to the metal ions on the surface. Likewise, a superacid solid catalyst can be made by treating these metal oxides with antimony penlafluonde. Both catalysts contain both Br nsted and Lewis acid sites, and they arc sufficiently active to catalyze the isomerization of n-butane at room temperature.26... 

Kulhenwm-Titanium Oxides. Ihc x-ray diffraction studies of rmhe-nium-liianium oxide coalings show that the dialing components are present as the metal dioxides, each in the rutile form as well as in solid solution with each other. 

Single-crystal precession data indicate orthorhombic symmetry with the crystallographic space group Fddd. This system is not isostructural with any other known metal oxyfluoride or metal dioxide. The cell dimensions, determined from Guinier data, are a = 8.370 1 A. b = 10.182 1 A. and c = 7.030 1 A. The indexed powder data are given in reference 6. 

The reaction of platinum dioxide with other metal dioxides can be separated into three groups—i.e., compounds with metal-oxygen coordination numbers of 4 2, 6 3, and 8 4. We have investigated only a single... 

Several high-temperature procedures have been described in the literature for the preparation of the transition-metal dioxides. Direct oxidation of the metals, lower oxides, chlorides, or nitrate precursors provides a convenient route to the dioxides of several metals Ti, Mn, Ru, Rh, Os, Ir, and Pt.1,3-5 (Syntheses of the rutile forms of rhodium and platinum dioxides by direct oxidation requires application of high pressures.5) Reduction of higher oxides is the most common method of synthesis for these dioxides V02, Nb02, Mo02, W02, and /3-Re02.4,6-8 Stoichiometry in these reactions is most readily controlled by use of the respective metal or a lower oxide as reductant. Chromium dioxide is normally synthesized by hydrothermal reduction of the trioxide.9... 

McNutt patented a noncorrosive priming composition composed of mercury fulminate, a metal dioxide (barium peroxide), and a ailicide such as that of calcium. 

Hewett et al. (9) have reviewed the spectroscopic studies on Mo02(g). In addition they have studied spectroscopically M0O2 in neon and argon matrices at 4 K. The adopted bond distance and angle and two stretching frequencies are derived from this study. Brewer ( ) adopted the same values. The bending frequency (300 cm ) is estimated by comparison with other transition metal dioxides. 

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