Search Results
Abstract
DTA, TG, XRD and IR methods were used to study the formation of solid solutions in the selected subsolidus range of the PbZrO3-K0.5Bi0.5TiO3 system by heating mixtures prepared using oxide substrates, i.e. PbO, Bi2O3, ZrO2, TiO2 and K2CO3. It was found that solid solutions are formed in the reaction of PbO and ZrO2 with intermediate compound, i.e. K0.5Bi0.5TiO3. PbZrO3 was not found to be formed as an intermediate phase.
Abstract
Samples with various amounts of tin oxide were prepared by impregnating γ-Al2O3, TiO2(anatase), SiO2, ZrO2 and MgO with tin tetrachloride or tributyltin acetate solutions. After drying and calcination, the samples were characterized by chemical analysis, XRD and BET measurements. Ammonia adsorption microcalorimetry was used in order to determine the number, strength and strength distribution of surface acid sites. The influence of the adsorption temperature, evacuation temperature, amount of SnO2 deposited and of the nature of the support on the adsorption properties were studied.
Abstract
Standard entropies of adsorption (Δs 0) of CO on different materials (Cu catalysts, Au catalysts, ZnO and to TiO2) are obtained from static adsorption microcalorimetry, adsorption isobars and temperature-programmed desorption, based on the thermodynamics of adsorption on energetically heterogeneous surfaces. Vibrational entropies of the surfaces s vib α are normally between the rotational and the standard translational entropy of CO in gas phase, and decrease with increasing adsorption energy, which agrees with the explanation of statistical thermodynamics. Δs 0 reflects both the mobility of adsorbates and the specific adsorbate-adsorbent interaction. Limits for reasonable values of the entropy of adsorption are proposed.
The intrinsic kinetics, unaffected by diffusional and mass transfer effects, of the air oxidation of Na2TiF6 and Na3TiF6 were determined by using a nonisothermal technique. The oxidation of these sodium fluorotitanates proceeds through two-step reactions involving the formation of oxyfluorotitanate, i.e. Na3TiOF5, as the intermediate. The oxidation rate shows a first-order dependence on the amount of the unreacted solids for each of the two-step reactions for both fluorotitanates. The activation energy for the further oxidation of Na3TiOF5 to a mixture of NaF + TiO2 was determined to be 52.4 kJ/mol and 55.3 kJ/raol for Na2TiF6 and Na3TiF6 as reactants, respectively.
Abstract
The aim of this work is the synthesis and the characterization of a microporous material obtained from gels with titanium and silicon: NTS (titanosilicate). The structure of NTS zeotype is similar to that of AM-1 and JDF-L1 (titanosilicates). The synthesis were carried out with gels of composition: 3.5Na2O–yTiO2–4.48HCl–xSiO2–110H2O with 1.0≤x≤12.0 and 0.2≤y≤0.7. The temperature of reaction was 1902C. In most of the cases NTS was prepared in a pelletted form. NTS pellets are produced at TiO2 content higher than 0.3 moles and SiO2 comprised between 3 and 7. NTS in a powder form is produced for TiO2<0.3 and SiO2 between 3 and 5 moles. It describes crystallization field and the kinetic curves of the titanosilicate. The samples are characterized by X-ray diffraction (XRD), thermogravimetry (TG), derivative thermogravimetry (DTG), differential scanning calorimetry (DSC), nuclear magnetic resonance spectroscopy-high resolution solid state MAS 29Si-NMR, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) X-ray microanalysis.
Abstract
Degradation of ethylenediaminetetraacetic acid (EDTA) present in the liquid waste was demonstrated by photocatalytic oxidation route by using nanoparticles of anatase titania. Nano sized titania photocatalyst was synthesized using sol–gel method coupled with ultrasonication mode and characterized using X-ray diffraction, transmission electron microscope, BET, Fourier transform infrared spectroscopy and TG–DTA. A cylindrical photoreactor was employed for the degradation studies. Five milligram of the nano anatase TiO2 + 0.5 ml of 30% H2O2 were employed as catalysts for the degradation studies of 1,000 mg/L EDTA. EDTA degradation was followed by a complexometric titration method. Complete degradation of 1,000 mg/L EDTA could be achieved in 90 min and the photocatalytic efficiency of the synthesized titania photocatalyst was higher than that of P-25 TiO2 for EDTA degradation. The influence of pH on the degradation of EDTA follow the order acidic > neutral > alkaline. More than ten fold increases in the decontamination factors were obtained for the chemical precipitation step for the liquid waste containing degraded EDTA compared to liquid waste without EDTA degradation.
Introduction TiO 2 and Fe 2 O 3 can be found in wide applications, such as catalysts [ 1 ] and gas sensors [ 2 , 3 ]. Recently, binary mixed oxides were reported to be good catalysts with improved photocatalytic properties
Abstract
Thermogravimetry-differential thermal analysis, emanation thermal analysis, mass spectrometry detection, Fourier transform infrared and XRD were used to characterize thermal behaviour of titanium dioxide photocatalyst precursors prepared by precipitation at various conditions from peroxotitanic acid sols. The transmission electron microscopy HRTEM technique was used to characterize the surface microstructure. The sols contained TiO2 anatase particles of approximately 10 nm in diameter. During heating of the air dried samples, their chemical degradation took place giving rise to anatase. On further heating, the crystallization of anatase and formation of rutile phase was observed. To test the photocatalytic activity of the samples, the decomposition of 4-chlorophenol (4-CP) under ultraviolet and visible irradiation was monitored. It was shown that photocatalytic activities of the samples are comparable to the Degussa P25 photocatalyst reference material.
Abstract
Polycrystalline titanium samples were oxidized in pure oxygen under a 75 torr pressure, at temperatures ranging from 400°C to 500°C, and for times up to 2 hrs. A similar treatment was applied to some single crystal samples, so as to show the relationship between the crystallite orientation and the oxidation rate. The oxide films were studied by means of radioanalytical techniques, such as nuclear microanalysis, electron diffraction and ESCA, in addition to most classical techniques such as optical and electron microscopy. The complementary side of these methods is showed. They permit us to determine the contamination of the metallic surface introduced by the polishing treatments, the oxidation rate at constant temperature, and the structure of the oxides which exists in the films. These ones are especially TiO2, Ti3O5, Ti2O3 and TiO.
Abstract
Thermochemistry and structural mechanism of crystallization of MgO-Al2O3-SiO2 glasses with TiO2 as crystallization activator were studied. Thermal and HREM investigation proved that near the T g temperature crystallization is going by rearrangement of glass structure elements and part of its components redistribution like at disorder — order phase transition in solid bodies. Nanocrystals of Mg-titanate and high quartz structure solid solution are formed then. Next enstatite and cordierite are crystallizing. Thermochemical and chemical bonds strength analysis indicate that during multistage crystallization of glasses, kind and order of crystal phase formation, is determined by the glass structure decomposition progress and its particular components release accompanying increase of temperature. It has been proved that molar heat capacity change (ΔC p) accompanying the glass transition is the significant measure of degree of changes in the structure of glass preceding crystallization.
