Papers by Keyword: Rutile

Abstract: Chemical synthesis of nanocomposite particles based on titanium dioxide modified with iron and gold was carried out. It was shown that, depending on the mass content of the doping species, the phase transformation of titanium hydroxide at T = 700 °C proceeds with the formation of either anatase (2 wt.%) or anatase and rutile (8 wt.%). The doping species form a hematite phase and gold clusters on the metal-oxide surface. A weakly crystalline anatase obtained by the transformation of metatitanic acid (MTA), with a particle size of 8 nm and a sulfur content of 0.036%, was selected as the co-catalyst. The anatase co-catalyst exhibits photocatalytic activity in the destruction of organic dyes. Its introduction into the TiO₂&Fe₂O₃&Au nanocomposite suspension promotes the catalytic degradation of cationic and anionic dyes at temperatures ranging from 35 to 60 °C. It was observed that the degradation degree of the solutions after 150 min of catalytic process is the following: Methyl Orange (MO) – 72 %, Methylene Blue (MB) – 71.5 %, Rhodamine B (RhB) – 63.5 %, and Orange G (OG) – 47 %. The reaction rate constant depends on the composition of the dye, varying from 6.5·10^-4 min^-1 for OG to 2.56·10^-3 min^-1 for MB. The prospect of creating heterostructures based on TiO₂ modified with hematite and gold, and their further adaptation for photocatalytic hydrogen production, is considered.

Abstract: Due to its to its optical, thermal, photocatalytic and electrophysical properties, nanocrystalline titanium oxide (TiO₂) is widely used in various fields. In the present work, a series of pure and Gd-modified (0.5, 5, 50 mol%) TiO₂ nanocrystalline powders were prepared by a novel synthesis approach – extraction-pyrolytic method (EPM). Metal containing extracts on the basis of valeric acid were used as precursors. Thermal behavior of produced individual and mixed precursors were investigated by thermogravimetric analysis (TGA) and high temperature differential scanning colometry (HDSC). Phase composition of pure and Gd-modified TiO₂ powders were studied as a function of pyrolysis temperature (450^o -850°C ) and gadolinium content by X-ray diffraction (XRD) method. Photocatalytic activity of produced powders was studied by photocatalytic degradation of methylene blue (MB) under UV/VIS light irradiation.

Abstract: The purpose of the plasma oxidation process is to increase the hardness, corrosion resistance and to improve the biocompatibility properties of Ti6Al4V alloys by thickening the natural oxide in the material, which is produced by this treatment. The aim of this work is to verify the effect of temperature on the thickness, hardness and wear resistance of the Ti6Al4V alloy treated with plasma oxidation. The treatment was performed using a Pulsed DC vacuum reactor, with a gas ratio of 60% Ar and 40% O₂ and 1.65 torr pressure for 1 hour of treatment, at temperatures of 480°C, 520°C, 670°C and 705°C. In regards to the multilayer formation of anatase and rutile, it was observed that the layer thickness increased as the treatment temperature increased. The increase of surface hardness provided by the treatment caused a considerable increase in the wear resistance of the studied material. The greatest layer thickness and surface hardness were obtained for the material treated at 705°C, but the lowest wear volume was obtained for the material treated at 520°C.

Abstract: Titanium dioxide has a special feature: anatase, to rutile transformation which was considered in our investigations. It is especially important to keep anatase form of titanium dioxide for photocatalytic materials, different ceramics with tribo-chemical properties, self-cleaning coatings and self-sterilizing coatings. For that only one of the titanium dioxide forms is more suitable – anatase, which is more active but not stable, because it transforms to rutile during the time or with the temperature increase loses its activity. Different methods of stabilising anatase have been considered in the paper. Several doping agents have been determined and it was chosen fluorine ion to modify titanium dioxide. Stabilization of anatase is achieved by preparing the reaction mixture by a sol-gel method with hydrofluoric acid. It has shown thermodynamic data, results of experiment, temperatures of anatase to rutile transformation of non-doped and doped titanium dioxide, its X-Ray diffraction and TGA. It is proved that titanium dioxide doped by fluorine ion keeps anatase form till the temperature is more than 1000 °C.

Abstract: Nanodispersed rutile with rod-like particles is synthesized by hydrolysis of TiCl₄ in hydrochloric acid - ethanol alcohol aqueous solution. It is found that the specific surface area, crystallite size and degree of agglomeration are determined by molar ratio of ethanol in reaction medium. According to HR-TEM images and XRD data rutile crystallites are preferred oriented along the [001] axis. The analysis of the Raman spectra for samples with different morphology is performed. The model of rutile nanorods nucleation and growth is proposed.

Abstract: The use of titanium dioxide is so diverse that varies from food to heavy industry and it is the main substance in the titanium industry. Over 90% of the world's mined titanium concentrates are processed to produce pigments. The sources for the production of titanium dioxide are the typically used titanium-containing ores including minerals rutile, ilmenite, and others. The volume of world production of titanium dioxide pigment exceeds 5 million tons per year and it is carried out in two ways: sulphate and chlorine (in approximately equal volumes). The changed approach to the green production processes requires the improvement of existing technologies and the development of new methods for processing titanium-containing raw materials. The authors have experimentally confirmed the high efficiency of complex, waste-free processing of titanium-containing raw materials developed by hydrofluoride. Creating pigment production on the basis hydrofluoride method will meet not only the domestic needs but also offer thepigment for export, as its parameters will surpass those of the best world analogues.

Abstract: The titanium dioxide phase formation is dependent on the synthesis method, temperature of calcination and modifiers insertion. By using chemical methods, such as Polymeric Precursor Method, the organic impurities or extrinsic defects caused by doping play an important rule on the formation of precursor structure before the phase crystallization above 500 oC. Some dopants can change the decomposition mechanism of the precursor, which affects the anatase-rutile phase transition. In this work, the Polymeric Precursor Method was used to synthesize titanium dioxide powder samples in order to investigate the effects of iron (III) and vanadium (V) dopants on the phase formation. Through thermal analysis of polymeric precursors and X-ray diffractometry for calcined powder samples it was possible to show the existence of antagonistic effects for both investigated dopants. While the iron doping reduces the anatase phase tetragonality and delays the rutile phase conversion, the vanadium one changes the mechanism of decomposition of polymeric precursor and leads to more amount of rutile phase.

Abstract: This review focuses on the recent developments of high temperature stable anatase TiO₂ photocatalyst. Eventhough TiO₂ exists in different forms anatase, rutile and brookite, anatase phase stabilization is often the key to obtain the highest photocatalytic performance for TiO₂, particularly for the use as an antibacterial and self-cleaning coatings in high temperature processed ceramics. Different methods available for the anatase stabilization in literature are critically reviewed and emphasis is placed on relatively recent developments. Currently available methods of anatase stabilizations are classified in to four categories viz (i) doping with metal ions (ii) doping with non-metal ions (iii) co-doping with metal and non-metal ions and (iv) dopant free stabilization by oxygen richness. Further to this, the application of these high temperature stabilized anatase TiO₂ photocatalyst on various ceramics substrates such as tile, glass and sanitary wares as self-cleaning and antibacterial coatings are also been briefly discussed.

Abstract: The possibility of production of white cover glass-enamel coatings for steel products has been considered. A number of compositions of glass-enamel coatings has been worked out. The obtained samples have been subjected to tests for corrosion resistance, temperature resistance and whiteness index. The peculiarities of crystallization in white cover glass-enamel coatings have been revealed. It is shown that the produced cover glass-enamel coatings for steel products conform to all requirements of GOST R 52569-2006. The application of RGB color model has been considered to determine the color hues of the white enamel coatings.

Abstract: This paper studied the high temperature creep properties of high-alumina bauxite (the mass fraction of Al₂O₃ in the new ore is about 78, the following abbreviations for Al₂O₃~78). The results indicated that the Al₂O₃~78 high-alumina bauxite mainly are corundum phase after high temperature sintered.When the temperature is 1100°C, corundum exists as crystal phase and the connections between grains are directly. The creep resistance of samples is very good at this temperature and the creep rate of 50 hours heat preservation is-0.266%. When the temperature is 1200°C, liquid phase starts to produce in a large number and the creep rate in 50 hours heat preservation is-1.589%. When the temperature is 1300°C, because of the further increase on the amount of liquid phase and wetting coated corundum particle, the direct connections between corundum particles are broken and the creep resistance is greatly reduced, the creep rate in 50 hours heat preservation is-4.088%. The creep curve fitting after 25 hours indicated that the creep property shows linear relations in three different temperatures after 25 hours. When the temperature is 1200°C and 1300°C, the creep variables arise rapidly in linear which declare the creep resistance of corundum is poor and increasing with temperature go up, more corundum phase is covered by glass phase and the creep resistance reduces dramatically.