Zirconium dioxide formation

Another study on the preparation of supported oxides illustrates how SIMS can be used to follow the decomposition of catalyst precursors during calcination. We discuss the formation of zirconium dioxide from zirconium ethoxide on a silica support [15], Zr02 is catalytically active for a number of reactions such as isosynthesis, methanol synthesis, and catalytic cracking, but is also of considerable interest as a barrier against diffusion of catalytically active metals such as rhodium or cobalt into alumina supports at elevated temperatures. 

Zirconium Arsenite.—A hydrogel of zirconium dioxide forms true adsorption complexes with arsenious oxide, but there is no evidence of the formation of an arsenite.13... 

The results of fundamental investigations of the formation of hydrated zirconium dioxide are reported in [41]. The oxidation degree of zirconium ions is -t4 in nearly all its compounds. Possessing rather large radius (0.092 nm) and rather low ion potential, it forms sterically maximal number of bonds. Accordingly, in the major part of its compounds, Zt ions exhibits coordination number 8. 

For the preparation of sol, 25% solution of NH3 was added in small portions (2 mL) to 1 L of 1 M solution of ZrOCU while heating under mechanical stirring. The temperature of solution did not exceed 90°C. Each following portion of NH3 solution was added only after complete dissolution of the zirconium hydroxide precipitate. The addition of the NH3 solution was terminated once the zirconium hydroxide precipitate did not dissolve within 20 min. The raw sol obtained was boiled using a reflux condenser for 25 h to allow the formation of the crystalline strucmre. Thereafter the sol was cooled to ambient temperature and filtered. Ceramic materials were immersed in 1 M sol of zirconium dioxide that was prepared as described... 

Burukina G. V., Vitkovsky G. E. and Ryabchuk V. K. (1990a), The estimate of the quantum yield of colour-centre formation in dispersed zirconium dioxide under the action of UV light , Vestnik LGU (Fizika, khimia), Ser. 4 (Iss. 4), No. 25, pp. 92-95. 

Blesa, M.A. et al.. Hydrous zirconium dioxide Interfacial properties, the formation of monodisperse spherical particles, and its crystallization at high temperatures, 7. Mater. Sci., 20, 4601, 1985. 

The Cr203/Zr02 catalysts showed activity in the SCR of NO by a propane-butane mixture, which depended on the means of preparation of the zirconium dioxide. Thus, the conversion of NO to N2 was 13-17% at 350 °C on 5-10 wt.% Cr203/Zr02 catalysts obtained by precipitation, while the conversion of NO to N2 was 54% at 300 °C on catalysts with analogous composition obtained through an alcogel step. This more active sample was also tested in the presence of SO2 (0.02%) in the reaction mixture. The conversion of NO in this case was also enhanced and reached 60% at 300-350 °C. This increase in activity by the action of sulfur dioxide may be attributed to the formation of sulfate since sul ted zirconium dioxide is a solid superacid and catalyzes the SCR of NO by hydrocarbons [11]. 

Cr2O3/ZrO2 may indicate the formation of new metal-oxygen bonds of the Zr-O-Cr type in the zirconium dioxide surface layer. 

Fig 1 gives IR spectra for pyridine adsorbed on previously dehydrated samples. The spectrum of starting zirconium dioxide obtained through an alcogel step lacks the band eharacteristic for Brdnsted acid sites. The addition of Cr203 into zirconium dioxide leads to acidic B-sites characteristic for pyridinium ions with a band at 1540 cm". This may be related to formation of structure such as [3] ... 

The activation of carbon dioxide was studied over a zirconium dioxide catalyst via infrared spectroscopy and 0-labeled reactants. The carbon dioxide adsorbed on the surface as either a carbonate or a bicarbonate species. The carbonate species formed as a result of CO2 Interaction with lattice oxygen. The bicarbonate species formed from CO2 interaction with a hydroxyl group. There was no direct interconversion between the carbonate and the bicarbonate. It is proposed that the bicarbonate can be converted to the formate via molecular CO. 

The most stable solid oxide phase corresponds to the stoichiometry Zr02. Oxygen deficient Zr02 x or zirconium-oxygen alloys exist only under extremely reducing conditions. Reduction of zirconium dioxide by carbon at 1610 to 1680 K leads to the formation of ZrO 95 [78KUT/ZHE]. Amorphous hydrous oxides and basic salts are known to precipitate from aqueous solution. 

K using an oxygen bomb calorimetric technique. The formation of zirconium dioxide was studied by eombustion of the metal in oxygen. The purity of the zirconium metal used was 99.967%, with the contaminants being C, H and O. The completeness of the combustion varied from 99.30 to 99.95%. Examination of the product formed using X-ray diffraction indicated monoclinic zirconium dioxide. 

Makarenko A.N., Belous A.G., Pashkova Y.V. Structure Formation and Degradation Partially Stabilized Zirconium Dioxide, J. Europ. Ceram. Soc., 1999, V.19, p. 945-947. 

Nanocrystalline powders of stabilized by scandium(III) zirconium dioxides was produced by us a sol-gel method. It was investigated the optimal conditions and mechanism of a collateral deposition of Zr(IV) and Sc(III) cations in their chloride solutions. It is shown, that the essential influence on formation of scandium (III) solid solutions in a matrix of zirconium dioxide and degree of its stabilization has a requirements of preparation of initial solutions, receptions and requirements of their coprecipitation, dehydration and calcination. 

The phase analysis of zirconium dioxide, which was obtained with the various content of SC2O3, has shown that the preparation of solid solutions with a fluorite phase is observed already at adding of 2 % (mol) Sc(III) in initial solutions. With increasing of scandium concentration in a solution the amount of the fluorite phase in synthesis products is incremented. For zirconium dioxide with more than 12 %(mol) SC2O3 it was found the formation of phases with structure which most close to structure of fluorite (Fig. 3). It is necessary also to note that in comparison with solid phase method of synthesis the sol-gel procedure of synthesis allows to obtain the solid solutions of scandium in ZrOi at considerably lower temperatures (750-900 °C). 

Zirconium dioxide shows specific catalytic actions for the cleavage of a C-H bond (ref.8) and the hydrogenation of buta-1,3-diene by a molecular hydrogen and hydrogen donor molecules such as cyclohexadiene (refs.9-11) and high selectivities for the formation of 1-olefins from secondary alcohols (ref.12) and of isobutane in CO + H2 reaction (ref.l3). Recently decomposition of triethylamine to yield acetonitrile, in which both dealkylation by acidic sites and dehydrogenation by basic sites were involved, was reported (ref.14). These characteristic behaviors of Zr02 are considered due to the acid-base... 

The possible employment of beryllium in nuclear engineering and in the aircraft industry has encouraged considerable investigation into its oxidation characteristics. In particular, behaviour in carbon dioxide up to temperatures of 1 000°C has been extensively studied and it has been shown that up to a temperature of 600°C the formation of beryllium oxide follows a parabolic law but with continued exposure break-away oxidation occurs in a similar fashion to that described for zirconium. The presence of moisture in the carbon dioxide enhances the break-away reaction . It has been suggested that film growth proceeds by cation diffusion and that oxidation takes place at the oxide/air interface. ... 

Table 1(c) on the formation or removal in vacua of carbon dioxide by reaction of the surface oxides with carbon in the metal shows the results of these calculations. The reactions are feasible for tungsten and iron but not for zirconium and magnesium. Chromium presents an intermediate case with an equilibrium pressure of 10-12-46 at 800°C., 10-9,88 at 1000°C., and 10 768 at 1200°C. The reverse reaction is feasible for zirconium and magnesium and for chromium at low temperatures. From a kinetic viewpoint the probability that this reaction will occur is small compared to the reaction to form carbon monoxide gas. In this case zirconium will act as a getter for carbon dioxide, while tungsten, iron, and chromium will be relatively inert to carbon dioxide molecules. 

The thermodynamic equilibria for the reactions of zirconium with oxygen, water vapor, carbon monoxide, carbon dioxide, and nitrogen have been discussed elsewhere (27). All these reactions can occur in the temperature range of 800° to 1200°C. and down to pressures of 10-8 mm. of mercury. In this range the rate of solution of the compounds formed is sufficient to maintain the zirconium surface in a film-free condition provided the reaction rate is maintained below the rate of solution. At very low pressures the reaction rate is probably proportional to the pressure of the gases present. The critical conditions for the reactions are the pressure and temperature at which the rate of formation of the compound equals the rate of solution in the metal. Although we have not determined these conditions precisely, experience has shown that the metal remains in the proper film-free condition at 800° to 1200°C. at pressures of the order of 1 X 10 mm. of mercury and less. 

Bigger clusters have been formed, for instance, by the expansion of laser evaporated material in a gas still under vacuum. For metal-carbon cluster systems (including M C + of Ti, Zr and V), their formation and the origin of delayed atomic ions were studied in a laser vaporization source coupled to a time-of-flight mass spectrometer. The mass spectrum of metal-carbon cluster ions (TiC2 and Zr C j+ cluster ions) obtained by using a titanium-zirconium (50 50) mixed alloy rod produced in a laser vaporization source (Nd YAG, X = 532 nm) and subsequently ionized by a XeCl excimer laser (308 nm) is shown in Figure 9.61. For cluster formation, methane ( 15% seeded in helium) is pulsed over the rod and the produced clusters are supersonically expanded in the vacuum. The mass spectrum shows the production of many zirconium-carbon clusters. Under these conditions only the titanium monomer, titanium dioxide and titanium dicarbide ions are formed. 

Nano-grained Ni/ZrOj and Ni/ZrOj-Sm Oj catalysts were prepared from amorphous Ni-Zr and Ni-Zr-Sm alloys by oxidation-reduction treatment. Their catalytic activity for methanation of carbon dioxide was examined as a function of precursor alloy composition and temperature. The addition of samarium is effective in enhancing the activity of the nickel-rich catalysts, but not effective for the zirconium-rich catalysts. The surface area and hydrogen uptake of the nickel-rich catalysts are increased by the samarium addition. In addition, tetragonal zirconia, the formation of which is beneficial to the catalytic activity, is stabilized and formed predominantly by the addition of samarium to the nickel-rich catalysts, although monoclinic zirconia is also formed in the zirconium-rich catalysts. As a consequence, the higher conversion of carbon dioxide is obtained on the Ni-Zr-Sm catalysts with relatively high nickel contents. 

The conversion of carbon dioxide on the catalysts prepared from nickel-rich amorphous Ni-Zr alloys is improved by the addition of samarium. On the other hand, the activity of the zirconium-rich catalysts is not influenced by the addition of samarium. The predominant formation of tetragonal zirconia in the nickel-rich Ni-Zr-Sm catalysts, in contrast to the formation of two types (monoclinic and tetragonal) of zirconia in the zirconium-rich Ni-Zr-Sm catalysts, appears to be responsible for the higher catalytic activity of the nickel-rich catalysts in addition to their higher surface area than the corresponding samarium-free Ni-Zr catalysts. 

Aqueous solutions of zirconium or hafnium compounds may be obtained by dissolving the conesponding hydrous dioxide in the appropriate strong acid. Because zirconium and hafnium oxides are such weak bases, these aqueous solutions tend to hydrolyze, with formation of zirconyl salts such as Zr0(N03)2. 

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