Showing papers on "Mixed oxide published in 1989"

Influence of the Valve Metal Oxide on the Properties of Ruthenium Based Mixed Oxide Electrodes II . Coatings

Abstract: Depth profiling of RuO{sub 2}/TiO{sub 2} mixed oxide coatings supported on titanium foil, was performed by means of Rutherford backscattering spectrometry and x-ray photoelectron spectroscopy. Results of the two techniques indicate the occurrence of surface segregation of the valve-metal oxide and a general enrichment with it across the first 100-150 nm. The segregation phenomenon takes place for all of the coating compositions investigated. However, it seems less pronounced for Ru contents higher than 60/ac. The nature of the ruthenium salt used in the coating preparation seems to affect the extent of the surface enrichment.

Catalytic oxidation of sulfur compounds

Abstract: Sulfur containing organics, e.g., carbon disulfide carbon oxysulfide, or a mercaptan, are oxidized to sulfur dioxide in gaseopus phase, whether alone or conjointly with hydrogen sulfide and/or elemental sulfur, per se, by passing a gaseous stream thereof, at elevated temperature, over a catalyst composition which comprises (i) a carrier substrate comprising titanium oxide, silica, zirconium oxide, silica-magnesia, silica-zirconia, silica-titanium oxide, zirconia-titanium oxide, or a zeolite, or admixture thereof, and (ii) a catalytically effective amount of at least one catalytically active element of Group Ib, IIb, IIIb, Vb, VIb, VIIb, VIII or Va of the Periodic Table, e.g., copper, silver, zinc, cadmium, yttrium, a lanthanide, chromium, molybdenum, tungsten, manganese, iron, cobalt, rhodium, iridium, nickel, palladium, platinum, tin and/or bismuth, but said catalyst composition being devoid of mixed oxide of spinel type.

Selective Formation of Ethene from CO Hydrogenation Reaction over In2O3–CeO2, –La2O3, and –Y2O3 Mixed Oxide Catalysts

Abstract: CO hydrogenation over mixed oxides of 3A and 4A Groups (Y2O3, La2O3, CeO2, and ZrO2) with 3B Group (Al2O3, Ga2O3, and In2O3) was carried out. The addition of Ga2O3 or In2O3 to Y2O3, La2O3, and CeO2 enhances the formation of light alkenes. An In2O3–CeO2 catalyst shows the highest selectivity (43%) for ethene with the lowest selectivity (0.5%) for ethane in total hydrocarbons produced. The addition of In2O3 to CeO2 results in an increase in activity for the CO hydrogenation reaction. From the results of an ethene hydrogenation reaction over mixed oxide catalysts, the high selectivity for alkene formation over In2O3-containing catalysts is due to a suppression of alkene hydrogenation by the addition of In2O3. Indium in CeO2 is highly dispersed while keeping an oxidation state of +1 or +3 under the reaction conditions.

Oxidation processes in silicon-nitride-based ceramics

Abstract: The oxidation of silicon nitride ceramics densified with mixed oxide additives has been investigated using thermogravimetric techniques. The majority of experiments were conducted with a ceramic containing 17 mol.% of an equimolar mixture of magnesia and neodymia. After initial film formation by direct chemical reaction between the ceramic and air the oxidation reaction continues by a diffusion-controlled process, demonstrated by a parabolic relationship between weight gain per unit area and time. Furthermore there is an enrichment in the oxide scale of additive and impurity cations with a corresponding depletion in the surface layers of the bulk ceramic. Thus, the oxidation reaction is controlled by the rate of diffusion of cations from the amorphous grain boundary phase to the ceramic-scale interface. At longer times, there is a deceleration in the oxidation rate to less than the value which the parabolic relationship would predict, and this is due to the devitrification of the amorphous grain boundary phases, resulting in the formation of more oxidation-resistant intergranular phases. Mechanisms of oxidation are discussed with reference to data obtained for similar ceramics which have been heat treated in nitrogen after sintering in order to encourage devitrification. Comparisons are also made with β′-SiAlON systems where the volume of amorphous phase in the fired ceramic is considerably lower than that obtained with the magnesia-neodymia densified silicon nitride.

Vehicle exhaust gas catalysts

Abstract: A method for the catalytic oxidation of carbon monoxide and unburnt hydrocarbon components of vehicle exhaust gas streams is disclosed. The method comprises using as the catalyst a mixed oxide catalyst composition consisting essentially of tin (IV) oxide (SnO 2 ), chromium (VI) oxide (CrO 3 ) and copper (II) oxide (CuO) free from platinum and other noble metals or noble metal oxides, and containing an Sn:Cr weight ratio (calculated as SnO 2 :CrO 3 ) in the range 99:1 to 1:99, and copper (II) oxide (CuO) in an amount of from 0.5 to 100% by weight, based on the combined weight of SnO 2 and CrO 3 . The catalyst composition having been prepared by impregnating tin(IV) oxide (SnO 2 ) with chromium(VI) oxide (CrO 3 ) and copper oxide (CuO) and calcining the resulting product.

Electrochemical characterisation of BaSn1–xSbxO3 perovskites

Abstract: The electrochemical properties of the sintered pellets of the mixed oxide perovskite system BaSn1–xSbxO3 have been investigated by cyclic voltametry and a.c. impedance measurements. The solid-state properties and morphology of the materials have also been investigated and the information used to interpret the electrochemical behaviour. The conductivity of the samples increases with antimony content and for x > 0.05 the oxides behave essentially as porous metal electrodes, exhibiting a relatively wide range of electrochemical stability.

Structural investigation on a spinel-related Zn/Cr = 1 mixed-oxide system

Abstract: A Zn–Cr mixed oxide of 1/1 composition has been characterized by powder X-ray diffraction infrared spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy, differential thermal analysis–thermal gravimetry, surface-area determination and chemical analysis. The behaviour of the system has been studied over a large temperature range and under different activation atmospheres. In addition to the model involving a single non-stoichiometric spinel phase, already proposed in the literature, a model involving a shell rich in ZnCrO4 and a core constituted by ZnCr2O4 and ZnO is discussed and shown to be consistent with the experimental evidence.

Tg, UV-transparency and mixed oxide effect of ultrapure ternary alkaline earth-metaphosphate glasses

Abstract: Five CaBa-metaphosphate glasses were prepared from high-purity raw materials of “Optipur” and “Ultrapur” quality in silica crucibles. While density, molar volume, refractive index and molar refraction are linear functions of molar fraction x = Ca/(Ca + Ba), the glass transition temperature Tg and UV absorption show pronounced minima at x = 0.45 and 0.6 , respectively. The thermal expansion coefficients are a nonlinear but monotonic function of the molar fraction x. These results are interpreted as mixed oxide effect for which an increase of the cooperative bonding strength within the very local regions of the coordination spheres of network modifying cations takes place if two different network modifying cations with large enough field strength difference are adjacent, in agreement with Dietzel's model. This increase in local cooperative bonding strength has consequences primarily on energetic-dynamic but much less on geometrical-static properties. Thus, the UV absorption is connected with local energetic conditions for electron transition and Tg with energetic-dynamic processes. As a practical consequence it is possible to improve UV transmission not only by decreasing impurity content but also by choosing kind and ratio of certain cations according to the oxide effect.

Mixed oxide catalyst and coating or porous material comprising the same

Abstract: A mixed oxide comprising oxides of Ce, Cu and Mn wherein an atomic ratio of Ce to a total atom number of Cu and Mn is from 1:2 to 2:1 and the metals are present in the mixed oxide in the oxide forms of CeO 2 and Cu x Mn 3-x O 4 wherein x is a number larger than 0 (zero) and less than 3, which can catalyze the oxidation of organic materials.

Adsorption characteristics of organic dyes in aqueous solutions on mixed-oxide gels: II. Alumina-containing mixed-oxide gels

Abstract: Five alumina-containing gels were investigated on the adsorption characteristics for four types of organic dyes (acidic, basic, reactive, and direct dyes). Alumina-magnesias exhibited the properties as strong solid bases and adsorbed effectively three dyes except for the acidic dye. While, alumina-silicas, strong solid acids, showed the high ability only for the acidic dye.

Method of producing mixed metal oxide material, and of producing a body comprising the material

Abstract: A novel method of producing mixed metal oxide powder (e.g., ferrite powder, or high temperature superconductor powder such as YBa₂Cu₃Ox powder) is disclosed. The method comprises forming an intimate mixture of appropriate metal salts (e.g.., nitrates and acetates), at least one of which is an oxidizing agent with respect to at least one of the others, and heating the mixture to a reaction temperature such that an exothermic redox reaction occurs. Appropriate choice of oxidizing and reducing agents permits control of heat of reaction and reaction temperature. The product of the reaction typically is a precursor of the desired mixed oxide, the precursor typically consisting essentially of the metal constituents of the mixed oxide and oxygen. Heat treatment in an O₂-containing atmosphere transforms the precursor into the desired mixed oxide powder. The thus produced powder can then be used in conventional fashion, e.g., to produce bodies therefrom by pressing and/or sintering.

Conductive articles and intermediates containing heavy pnictide mixed alkaline earth oxide layers

Abstract: Articles are disclosed in which an electrically conductive layer on a substrate exhibits a superconducting transistion temperature in excess of 90° K. Conductive layers are disclosed comprised of a crystalline heavy pnictide mixed alkaline earth copper oxide. Processes of preparing these articles are disclosed in which a mixed oxide precursor composition is coated and heated to its thermal decomposition temperature to create an amorphous mixed metal oxide layer. The amorphous layer is then heated to its crystallization temperature.