Mechanism of gel-to-crystallite conversion process in the synthesis of nanocrystalline multinary oxides

Description of gel-to-crystallite conversion process is made towards the synthesis of nanocrystalline titanates and aluminates. Thermodynamic and kinetic factors governing the conversion of a gel to meta-stable and stable nanocrystalline products(s) are discussed. Correlations between these factors and the preparative conditions employed for the syntheses of titanates and aluminates are arrived at.

Thermodynamic Properties of Niobium Oxides

Thermodynamic properties of three oxides of niobium have been measured using solid state electrochemical cells incorporating yttria-doped thoria (YDT) as the electrolyte in the temperature range T = (1000 to 1300) K. The standard Gibbs energies of formation of NbO, NbO2, and NbO2.422 from the elements can be expressed as: Delta(f)G(NbO)(o) +/- 547/J . mol(-1) = -414 986 + 86.861(T/K) Delta(f)G(NbO2)(o) +/- 548/J . mol(-1) = -779 864 + 164.438(T/K) Delta(f)G(NbO2.422)(o) +/- 775/J . mol(-1) = -911 045 + 197.932(T/K) The results are discussed in comparison with thermodynamic data reported in the literature. The new results refine data for NbO and NbO2 presented in standard data compilations. There are no data in thermodynamic compilations for NbO2.422 (Nb12O29). In the absence of the heat capacity and enthalpy of formation measurements, only the Gibbs energy of formation of NbO2.422 can be assessed. The free energy of formation of stoichiometric Nb2O5 is evaluated on the basis of measurements on NbO2.422 and information available in the literature on phase boundary compositions and isothermal variation of nonstoichiometric parameter with oxygen potential for Nb2O5-x. The results suggest a minor revision of data for Nb2O5. A minimum in the Gibbs energy of mixing for the system Nb-O occurs in the nonstoichiometric domain of Nb2O5-x with x = 0.036.

XPES and UVPES studies of iron oxides

X-Ray and uv photoelectron spectra of FeO, Fe2O3, and Fe3O4 have been studied along with those of a few model compounds. It has been possible to assign distinct bands due to Fe2+ and Fe3+ in the 3d, 3p, 3s, and 2p bands of Fe3O4. The spectra of Fe3O4 do not show major changes through the Verwey transition.

Platinum particles supported on titanium nitride: an efficient electrode material for the oxidation of methanol in alkaline media

In the present study, titanium nitride which shows exceptional stability, extreme corrosion resistance, good electronic conductivity and adhesion behaviour is used to support platinum particles and then used for methanol oxidation in an alkaline medium. The catalyst shows very good CO tolerance for the electrochemical oxidation of methanol. In situ infrared spectroelectrochemical data show the remarkable ability of TiN to decompose water at low over potentials leading to -OH type functional groups on its surface which in turn help in alleviating the carbon monoxide poisoning associated with methanol oxidation. TiN supported catalysts are found to be very good in terms of long term stability, exchange current density and stable currents at low over voltages. Supporting evidence from X-ray photoelectron spectroscopic data and cyclic voltammetry clearly demonstrates the usefulness of TiN supported Pt catalysts for efficient methanol oxidation in alkaline media.

A2MoTiO7−x (Atriple bond; length as m-dashrare earth or Y): a new series of oxide pyrochlores prepared by topochemical reduction of A2MoTiO8 scheelites

A series of anion-deficient pyrochlore oxides of the formula A2MoTiO7−x (xless-than-or-equals, slant0.5), where Atriple bond; length as m-dashSm, Gd, Tb, Dy, Ho, Er, Lu and Y, has been prepared by reduction of A2MoTiO8 scheelites. The scheelite-to-pyrochlore conversion is reversible, indicating that the reaction is likely to be topochemical. The oxidation states of molybdenum and titanium are most probably Mo(III) and Ti(IV) for the limiting composition of the pyrochlores A2MoTiO6.5. The new pyrochlores are non-metallic and paramagnetic as expected.

Photocatalytic inactivation of Escherischia coli and Pichia pastoris with combustion synthesized titanium dioxide

The photocatalytic inactivation of Escherischia coli and Pichia Pastoris was studied with combustion synthesized titanium dioxide photocatalysts Three different combustion synthesized (CS) catalysts were used viz CS-TiO2 1% Ag substituted in TiO2 and 1% Ag impregnated in TiO2 All the combustion synthesized catalysts showed higher activity as compared to the activity observed with commercial Degussa P-25 TiO2 The effect of various parameters like catalyst loading different catalysts and initial cell concentration was studied At the optimum loading 1% Ag impregnated TiO2 showed the maximum efficiency and complete inactivation of both the microorganisms was observed within an hour of irradiation The morphology of inactivated cells was studied by inverted microscope and SEM From the images obtained it was hypothesized that damage to the cell wall was the main cause of cell inactivation The initial cell concentration had a prominent effect on the inactivation At a low initial cell concentration the complete inactivation of E cob and P pastoris was observed within 10 and 20 min respectively This shows that P pastoris has a stronger resistance towards photocatalytic inactivation than E cols The inactivation reactions were modeled with power law kinetics The order of reaction in case of E colt and P pastoris were determined as 1 20 and 1 08 respectively (C) 2010 Elsevier B V All rights reserved

dc reactive magnetron sputtering of titanium‐structural and optical characterization of TiO2 films

This paper deals with the reactive sputtering of titanium in an argon and oxygen mixture. The variation in cathode potential as a function of oxygen partial pressure has been explained in terms of cathode poisoning effects. The titania films deposited during this process have been studied for their structural and optical characteristics. The effect of substrate temperature (from 25 to 400 °C) and annealing (from 250 to 700 °C) on the packing density, refractive index, extinction coefficient, and crystallinity has been investigated. The refractive index varied from 2.24 to 2.46 and extinction coefficient from 2.6 × 10-3 to 10.4× 10-3 at 500 nm as the substrate temperature increased from 25 to 400 °C. The refractive index increased from 2.19 to 2.35 and extinction coefficient changed from 3.2× 10-3 to 11.6 × 10-3 at 500 nm as the annealing temperature was increased from 250 to 700 °C. Anatase and rutile phases have been observed in the films deposited at 400 °C substrate temperature and annealed at 300 °C. The changes in the optical constants at higher substrate temperature have been attributed to an increase in packing density, oxygen content, and crystallinity of the films.

An unusual anti-markovnikov hydration of alkenes with titanium(III) tetrahydroborates

Titanium(III) tetrahydroborate formed by the reaction of titanium tetrachloride and benzyltriethylammonium borohydride (1:4) reacts with alkenes in dichloromethane (-20-degrees-C) very readily to yield directly the corresponding alcohols in excel lent yields after a simple aqueous work up.

Bridging the Ruddlesden–Popper and the Dion–Jacobson series of layered perovskites: synthesis of layered oxides, A2–xLa2Ti3–xNbxO10(A = K, Rb), exhibiting ion exchange

Solid solutions of the formula, A2–xLa2Ti3–xNbxO10(A = K, Rb), exist for the range 0[less-than-or-eq]x[less-than-or-eq]1.0, bridging n= 3 members of the Ruddlesden–Popper series (A2La2Ti3O10) and the Dion–Jacobson series (ALa2Ti2NbO10). For 0[less-than-or-eq]x[less-than-or-eq]0.75, the phases possess body-centred structures characteristic of the Ruddlesden–Popper phases, while the x= 1 members are isostructural with KCa2Nb3O10(A = K) and CsCa2Nb3O10(A = Rb). Protonated derivatives, H2–xLa2Ti3–xNbxO10, which are prepared by ion exchange, retain the structural difference of the parent phases. A difference in the Brønsted acidity of the protonated derivatives revealed by intercalation experiments with organic bases seems to be related to this structural difference.

Microstructural features of flow instability in α-titanium cylinders under high strain rate compression at 25°C to 400°C

Cylindrical specimens of commercial pure titanium have been compressed at strain rates in the range of 0.1 to 100 s-1 and temperatures in the range of 25-degrees-C to 400-degrees-C. At strain rates of 10 and 100 s-1, the specimens exhibited adiabatic shear bands. At lower strain rates, the material deformed in an inhomogeneous fashion. These material-related instabilities are examined in the light of the ''phenomenological model'' and the ''dynamic materials mode.'' It is found that the regime of adiabatic shear band formation is predicted by the phenomenological model, while the dynamic materials model is able to predict the inhomogeneous deformation zone. The criterion based on power partitioning is competent to predict the variations within the inhomogeneous deformation zone.