Self-propagating High Temperature Synthesis of Pink Corundum

Pigments based on pink corundum have been obtained by self-propagating high temperature synthesis in Cr2O3-Al2O3-Al system using a small amount of chromium oxide (up to 0.5 wt %) in the composition of the green mixture. Absorption bands of pink corundum in visible reflectance spectrum at λ=560 nm (17850 cm−1) and 400 nm (25000 cm−1) correspond to electron transitions 4А2g→4T2g(4F) and 4А2g→4T1g(4F). Increasing chrome oxide content to 5 wt.% in initial charge mixture leads to pigment darkening due to inclusions of Cr2O3. Synthesized pigments can be used as a component of glaze ceramic colors for porcelain

Self-propagating high temperature synthesis of pink corundum

Pigments based on pink corundum have been obtained by self-propagating high temperature synthesis in Cr2O3-Al2O3-Al system using a small amount of chromium oxide (up to 0.5 wt %) in the composition of the green mixture. Absorption bands of pink corundum in visible reflectance spectrum at λ=560 nm (17850 cm−1) and 400 nm (25000 cm−1) correspond to electron transitions 4А2g→4T2g(4F) and 4А2g→4T1g(4F). Increasing chrome oxide content to 5 wt.% in initial charge mixture leads to pigment darkening due to inclusions of Cr2O3. Synthesized pigments can be used as a component of glaze ceramic colors for porcelain

Surface properties of metal hydroxide microparticles in the ambient air

The adsorption and photoadsorption properties of Mg(OH)2 and Ca(OH)2 microparticles in the ambient air were investigated. The compositional analysis of an adsorption layer of microparticles was carried out. The kinetics of photodesorption of molecules from microcrystal surfaces and the interaction of HCFC-22 (CHF2Cl) in the dark and under light were studied. Quantum yields and their spectral dependencies were determined for CO2 photodesorption, O2 and CO photoadsorption. The effect of weakly bound CO displacement from the surface of microparticles was revealed during dark adsorption of HCFC-22. It is supposed that adsorbed CO is formed as a result of atmospheric CO2 reduction after the break of Mg—OH bonds. In case of calcium hydroxide, CO is generated during the interaction of calcium hydroxide with carbon dioxide in the presence of water

Structure and phase composition of material based on vanadium alloy V-4.9Ti-4.8Cr and ferrite steel 17Cr-12Ni-Fe

Three-layer materials consisting of the V-4.9Ti-4.8Cr/ferrite steel 17Cr-12Ni-Fe /V-4.9Ti-4.8C

The influence of scandium on the composition and structure of the Ti-Al alloy obtained by "Hydride Technology"

In this study the influence of scandium on the structural and phase state of the Ti-Al alloy obtained by the method of “Hydride Technology” (HT). The Rietveld method has allowed for determining the content of basic phases of the 49at.%Ti-49at.%Al-2at.%Sc system. By means of the methods of transmission electron microscopy (TEM) and X-ray spectral microanalysis, it has been established that scandium additives into the Ti-Al system result in the change of the quantitative content of phases in local regions of the structure. The Ti2Al5 phase has been found, and Ti2Al has been absent. In the morphology of substructures Ti-Al and Ti-Al-Sc there are lamellar structures or lamellae; the peculiarities of the distribution, fraction and size of which are influenced by scandium additives. The average width of Al-rich lamellae has been 0.85 U+03BCm, which is four times greater than that for the Ti-Al system (0.21 U+03BCm). For Ti-rich lamellae of the sample of the Ti-Al-Sc alloy, the average width of the lamellae has been 0.54 U+03BCm, and for Ti-Al it has been 0.34 U+03BCm. Based on the obtained data, a scheme of the distribution of phases in the composition of the Ti-Al-Sc alloy in the lamellar structures has been proposed. It has been established that in the Ti-Al-Sc system there is growth of the near-surface strength relative to Ti-Al. In this way, the microhardness of the Ti-Al-Sc alloy has amounted to 1.7 GPa, that is of the Ti-Al alloy which is 1.2 GPa

Structure peculiarities of binary state diagrams of vanadium with neighboring elements of Mendeleev’s periodic table

Data on search for correlations between a structure of state diagrams of binary systems based on V-Me (Me = Ti, Zr, Hf, Nb, Ta, Cr, Mo, W) and crystal-geometric and crystal-chemical parameters were presented. Manifestation of both positive and negative deviations in experimental concentration dependences of the atomic volume in solid solutions in systems V-Me (Me = Ti, Nb, Ta, Cr, Mo) from Zen's law was established. It was found that in the systems with unbounded regions of solid solutions, the deviation from Zen's law is insignificant. A correlation was found between the types of state diagrams and the difference in atomic volumes of alloy-forming elements in systems V-Me (Me = Ti, Nb, Ta, Cr, Mo)

Peculiarities of structure and phase composition of V-Ti-Cr alloy obtained by sintering technique

Abstract Alloy of the V-Ti-Cr system is a promising material exploited under high radiation and in corrosion environment. We sintered V-4.9Ti-4.8Cr alloy from particles with original average size of 30, 280 and 200 μm, respectively for vanadium, titanium and chromium powders, by pressing of the powder mixture and its further sintering. The studies were undertaken using the methods of X-ray structural analysis, scanning electron microscopy with an energy dispersive analyzer and transmission electron microscopy. It was established that the structure of the alloy represented matrix grains (BCC solid solution), along the boundaries and at junctions of which the groups of oxycarbonitride particles of V, Ti, Cr (C,N,O) type of the variable elemental composition were arranged. The particles possessed a plate-like (0.4 x 2.0 μm) and rounded (0.5 μm) shape. The solid solution of the alloy was heterogeneous by concentration. This was evidenced by the complications of the diffraction patterns obtained from the corresponding sections of the structure. These were cords of main reflexes, satellites and emergence of a moire banded contrast in separate sections of the sample. Inside the matrix grains, there were nanoparticles (15 μm) of carbide V55Cr25C20, being a source of elastic internal local stresses

Corrosion resistance of neodymium and dysprosium hydrides

This paper describes the methods of obtaining hydrides of rare earth elements such as dysprosium and neodymium. The properties and corrosion resistance of these elements are investigated. A synthesis method of monophasic dysprosium and neodymium dihydrides is presented. Synthesized dihydrides are agglomerates with an average size of 3-50 µm and are formed by crystalline grains of a nanometer size. BET specific surface area, morphology, elemental analyses and composition of samples have been studied. Corrosion stability in aqueous solutions of hydrochloric acid and sodium hydroxide were studied. It was determined that both hydrides undergo hydrolysis in acid and alkaline mediums. Neodymium hydride is more stable to corrosion than dysprosium hydride, which is proved by its longer exposure to aggressive medium to hydrides. The formation of insoluble /poorly soluble products of corrosion can make a significant contribution to the process of powder dissolution

Structure and phase composition of material based on vanadium alloy V-4.9Ti-4.8Cr and ferrite steel 17Cr-12Ni-Fe

Three-layer materials consisting of the V-4.9Ti-4.8Cr/ferrite steel 17Cr-12Ni-Fe /V-4.9Ti-4.8Cr were obtained in the paper. Phase composition and microstructure of the transition zone of the three-layer material of vanadium alloy V-4.9Ti-4.8Cr and ferrite steel 17Cr-12Ni-Fe were considered. The use of the method of direct laser growing allowed obtaining a three-layer material with qualitative interconnection of layers, as well as decreasing a multistage nature of deformation and thermal operations used when obtaining a three-layer material in earlier works. Additional thermal treatment of a three-layer alloy led to growth of matrix grains up to 100 μm of the vanadium alloy. A uniform distribution of main elements V, Ti, Cr was observed in the transition zone both before and after annealing. A zone of interdiffusion of the metals amounted to 250-350 μm