Search Results
Abstract
The possibility of concentrating Pt, Ir, Au, Ag, Re and some other elements from samples of chromites, sulfide ores, laterites, shales, titanium magnetites, and ultrabasic rocks was studied. A new simple procedure is based on sublimation of elements to be determined in air stream at 1200 °C in the presence of some powdered reagents /e.g., TiO2, Nb2O5, Nb/ to enhance the yield, and on the use of chemical filters /CaO, MgO, TiO2, Al2O3, Nb2O5/ absorbing the interfering volatile elements from the gas phase. Neutron activation and X-ray fluorescence isotopic excitation were used to analyze the obtained concentrates.
. A DAMS , L. K. , L YON , D. Y. & A LVAREZ P. J. J. , 2006 . Comparative eco-toxicity of nanoscale TiO 2 , SiO 2 , and ZnO water suspensions . Water Research . 40 . 3527 – 3532
Abstract
Results of Carr and Galwey [1] concerning copper malonate (CM) decomposition in vacuo at 510 K prompted present studies on the utility of CM as a low-temperature precursor of oxide-supported copper catalysts. CM deposited upon metal oxides has been converted to copper particles by vacuum thermal decomposition or reduction with aqueous hydrazine. Using the dehydrogenation of isopropanol to acetone as a catalytic probe reaction, comparisons are made between levels of catalytic activity and selectivity induced in TiO2, MgO and Ca(OH)2 supports by copper deposited thereon. Effects of particle size, prereduction temperature, and support reducibility are described and evidence is given for a strong metal support interaction (SMSI)-like inhibition of activity of Cu/TiO2 by prior high temperature reduction.
Abstract
Mesoporous titanium-containing silicas with TiO2 contents from 1 up to 70 mol% were prepared. The obtained samples have been characterized by the powder X-ray diffraction data, the diffuse reflectance infrared Fourier transform method, and nitrogen adsorption at 77 K. Specific surface area, total pore volume, distribution pore volume on pore sizes were determined from nitrogen adsorption isotherm for synthesized titanosilicas.
Abstract
The changes of physico-chemical properties of mechanochemically pretreated (BaCO3 +TiO2 +PbO) powders were investigated. The values of apparent activation energy of BaTiO3 formation calculated by the Freeman and Carroll method decrease with milling time. The changes of precursors density may be interpreted as a consequence of mechanochemical reactions during milling.
Abstract
Differential thermal analysis was carried out on the self-propagating high-temperature synthesis reaction 3TiO2+4Al+3C→3TiC+2Al2O3. The results allow the ignition temperature of the reaction to be estimated and the reaction mechanism to be identified. The ignition temperature was 900°C and the results suggest that the reaction proceeds by an initial reaction between titania and aluminium (3TiO2+4Al→3Ti+2Al2O3) and the titanium formed reacts with the carbon (Ti+C→TiC).
Abstract
The conditions to fabricate the bulk porous specimens have been studied on account of sodium borosilicate (NBS) glasses. Glass composition, heat treatment at phase separation and TiO2 addition have been considered in this study. Original glass samples of composition in mol%: sample A: 9.19 Na2O - 23.58 B2O3 - 67.23 SiO2, sample B: 9.29 Na2O - 3.17 TiO2 - 23.82 B2O3 - 63.72 SiO2 were prepared by melting reagent grade chemicals (Na2CO3, HBO3, SiO2 and AgNO3) in platinum crucibles at 1480C for 1 h in air. The melts were poured onto stainless steel plates and were annealed at 500C for 0.5 h after cooling. Thus, obtained samples were phase separated at 700C for 2, 15, 25 and 50 h to study their microstructure by scanning electron microscope (SEM). Besides the direct study of the microstructure by SEM, information on glass structural changes of samples are provided by measuring in situ changes by the optical transmittance thermal analysis. The isothermal measurements were carried out at 700, 720 and 740C. The temperature of phase separation, the leaching and nucleator addition (TiO2), significantly influence the microstructure of the resulting leached product. TiO2 additive seems to suppress crystallization of cristobalite: especially at the extended above heat treatment phase separation runs. The phase-separated domains of glasses containing above 80 moles of SiO2 are so small that it is very hard to observe them by SEM. The glass composition in our case was selected in a way to have relatively large phase separated areas easily observed by SEM at magnification 20 000. The influence of TiO2 is not too pronounced. It seems to suppress the cristobalite crystallization, especially of longer heating runs. The image analysis of leached glasses shows the prevailing content of the skeletal phase in a comparison to pores. The TiO2 content diminishes the content of the skeletal phase.
Abstract
Emanation thermal analysis (ETA) was used in the characterization of microstructure changes during heating ofprecursors for the titania based materials: hydrous titania, TiO2
nH2O (n=0.58) and hydrous titania containing 10% ruthenia,(TiO2)0.9(RuO2)0.1
nH2O (n=1.5). The precursors were heated at the constant rate 6 K min–1 in argon flow in the range 20–1000°C. ETA results were compared with the theoretical curves simulating the temperature dependences of radon release rate, E(T). Two mathematical models were used in the simulation. The models considered either subsequent or simultaneous solid state processes (i.e. dehydration, crystallization orphase transition, resp.) during thermal treatment of titania based materials. A good agreement was found between experimental and the simulated ETA curves. The results of ETA were confirmed by XRD patterns of intermediate products of thermal treatment of the precursors.
Abstract
To evaluate the thermal stability of oxide glasses, various criteria have been used. Not only the simple parameters, as characteristic temperatures and values of activation energy and enthalpy changes, but also the combined criteria E/RTp and kf(T) have been taken into account. Three glasses with the composition of Li2O·2SiO2 (a), Li2O·2SiO2·0.03TiO2 (b) and Li2O·2SiO2·0.1TiO2 (c) were prepared and the validity of the criteria was tested by applying them to these glasses. The results indicate that the sequence thermal stability of the studied glass system vs. crystallization depends not only on their composition but also on the used criteria.
A series of coprecipitates of basic cobalt carbonate and hydrated titanium oxide were investigated by TG and DTA up to 1000°. In the absence of water and CO2, an oxide system is obtained consisting of Co3O4 and TiO2, from which cobalt metatitanate is first formed; from the latter, depending on the presence of TiO2 or Co3O4 in the system, the dititanate or the orthotitanate is formed. IR absorption and X-ray spectra and TG and DTA curves prove that the double oxides of cobalt and titanium are obtained in this manner at temperatures lower than in other methods; this gives them useful properties for practical applications.
