Oxygen generation in anodized Ta–Cu alloys

Comparison is made of the influences of copper in the development of amorphous anodic films on Ta-Cu alloys, containing up to 57 at.%Cu, in ammonium pentaborate electrolyte at 293 K. The various films are based on tantala, with low concentrations of copper, relative to those of the alloys, since copper species migrate through the films more rapidly than Ta⁵⁺ ions and are lost to the electrolyte on reaching the film surface. Of particular interest, film growth on Ta-1.5at.% Cu alloy at 1, 0.1 and 0.01 mA cm^?2 proceeds with generation of oxygen, which is contained in nanoscale bubbles within the oxide. Bubbles are more numerous as the current density decreases. In the case of Ta-12at.% Cu and Ta-57at.%Cu alloys, the films are flawed extensively by more numerous oxygen bubbles, which are present mainly in the outer parts of the anodic films; oxygen production and film damage due to the bursting of bubbles limit the anodizing voltage to relatively low values. It is suggested that copper species modify the electron levels, and possibly structure, of the tantala-based films, thereby facilitating oxygen generation within the bulk film by oxidation of O^2- ions of the oxide.     

Excess molar enthalpies of the ternary system MTBE+ethanol+octane

Excess molar enthalpies of the ternary mixture {x ₁ tert-butyl methyl ether (MTBE)+x ₂ ethanol+(1–x ₁–x ₂) octane} and the involved binary mixture {x ethanol+(1–x) octane} have been measured at 298.15 K and atmospheric pressure, over the whole composition range, using a Calvet microcalorimeter. The results were fitted by means of different variable degree polynomials.     

Experimental and predicted excess molar volumes of the ternary system.

Summary Experimental excess molar volumes for the ternary system x₁MTBE+x₂1-propanol+(1-x₁-x₂) heptane and the three involved binary mixtures have been determined at 298.15 K and atmospheric pressure. Excess molar volumes were determined from the densities of the pure liquids and mixtures, using a DMA 4500 Anton Paar densimeter. The ternary mixture shows maximum values around the binary mixture MTBE+heptane and minimum values for the mixture MTBE+propanol. The ternary contribution to the excess molar volume is negative, with the exception of a range located around the rich compositions of 1-propanol. Several empirical equations predicting ternary mixture properties from experimental binary mixtures have been applied.     

Excess molar enthalpies at 298.15 k of the binary mixtures

We have determined the excess molar enthalpies H _m ^E at 298.15 K and normal atmospheric pressure for the binary mixtures containing tert-butyl methyl ether (MTBE)+(methanol, ethanol, 1-propanol, 1-pentanol) using a Calvet microcalorimeter. This revised version was published online in July 2006 with corrections to the Cover Date.     

Temperature dependence of volumetric behaviour for methyl tert-butylether+1-butanol system

Excess molar volumes and excess isoentropic compressibilities of methyl tert-butylether (MTBE)+1-butanol at 288.15, 293.15, 298.15, 303.15 and 308.15 K and atmospheric pressure have been studied. In order to analyse the temperature dependence of this mixture, isobaric expansibility a, (dV _m ^e dT) _P,xand (dH _m ^e dP ) _T,x, were computed by analytical differentiation of the density and excess molar volume fitting equations. Cubic equation of state (Soave-Redlich-Kwong) has been applied to excess molar volume correlation obtaining binary interaction parameters using different mixing rules. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ternary mixture MTBE+1-pentanol+nonane at 298.15 K and atmospheric pressure

Densities at 298.15 K and atmospheric pressure have been measured, using a DMA 4500 Anton Paar densimeter, for the ternary mixture methyl tert-butyl ether (MTBE)+1-pentanol+nonane and for the involved binary mixture 1-pentanol+nonane. In addition, excess molar volumes were determined from the densities of the pure liquids and mixtures. Suitable fitting equations have been used in order to correlate adequately the excess molar volumes. Experimental data were also used to test several empirical expressions for estimating ternary properties from experimental binary results.     

Temperature dependence of thermophysical properties of octane+1-butanol system

The aim of this work is to complete our studies on physical properties of binary mixtures of alkane+1-alkanols. This work reports densities, refractive indices, speeds of sound and isentropic compressibilities of the mixture octane + 1-butanol at different temperatures, from 288.15 to 308.15 K. From the experimental values, the corresponding excess and deviation values were computed (excess molar volumes, changes of refractive index on mixing, changes of speed of sound on mixing and changes of isentropic compressibilities on mixing). The results were fitted to variable-degree polynomials. Excess molar volumes were compared with the predictions of Nitta-Chao Group Contribution Model. This revised version was published online in July 2006 with corrections to the Cover Date.     

Modulation of the Activity of Gold Clusters Immobilized on Functionalized Mesoporous Materials in the Oxidation of Cyclohexene via the Functional Group. The Case of Aminopropyl Moiety

Gold nanoclusters and isolated gold atoms have been produced in a two-liquid phase procedure that involves a solution of gold in aqua regia and rosemary essential oil as organic layer. These gold entities have been immobilized on the ordered mesoporous silica material SBA-15 functionalized with different amounts of aminopropyl groups. The resulting materials have been characterized by XRD, N₂ adsorption, chemical analysis, TGA, ²⁹Si MAS NMR, ¹³C CP/MAS NMR, UV-vis spectroscopy, XPS, and STEM. The Au-containing materials retain the ordering and porosity of the pristine support. Gold content varies in the range of 0.07–0.7 wt% as a function of the specific immobilization conditions, while STEM evidences the presence of isolated gold atoms. XPS shows a shift of the Au 4f BE toward values lower than those of metallic gold. The catalytic activity in the oxidation of cyclohexene with molecular oxygen at atmospheric pressure parallels the Au content of the aminopropyl-SBA-15 supports. This activity is higher than that of analogous Au entities immobilized on SBA-15 functionalized with thiol or sulfonate groups, the activity decreasing in the order Au-NH₂ > Au-SO₃⁻ > Au-SH. This behavior has been attributed to differences in the interaction strength between the functional group and the Au entities, which is optimum for the aminopropyl groups.