Activation of Zr, ZrVHf and TiZrV Non-Evaporative Getters Characterized by In Situ Synchrotron Radiation Photoemission Spectroscopy

The activation process of Zr, ZrVHf and TiZrV non-evaporative getter (NEG) thin films, prepared by direct current magnetron sputtering, is investigated by in situ synchrotron radiation photoemission spectroscopy. The activation temperatures of Zr and ZrVHf films are found to be 300 °C and 200 °C, respectively, and the activation temperature of TiZrV film is 120 °C—the lowest activation temperature reported on TiZrV. As the heating temperature increases, the transformation of metal-C bond follows the orders of V–C, Ti–C, Zr–C, Hf–C. It is found that the order of reduction difficulty of the same element oxides, that is, Zr oxide and V oxide in different films follows Zr film > ZrVHf film > TiZrV film. The order of difficulty in the reduction of oxides in the same alloy NEG films follows HfO2 > ZrO2 > TiO2 > V2O5. We propose that the above phenomena can be explained by interstitial diffusion, grain boundary diffusion of residual gas atoms and grain boundary precipitation of V and Ti in the solid solution of the NEG films.

Biochemical and artificial pathways for the reduction of carbon dioxide, nitrite and the competing proton reduction: effect of 2nd sphere interactions in catalysis

Reduction of oxides and oxoanions of carbon and nitrogen are of great contemporary importance as they are crucial for a sustainable environment.

Carbothermal and boron carbide reduction of oxides of some transition metals

The study presents a possible mechanism to produce carbides and diborides of transition metals, such as titanium, vanadium, chromium and zirconium. The carbothermal synthesis of transition metal carbides has defined the direct dependence between the thermodynamic stability of oxides and the temperature range of the reduction onset (the stronger the oxide, the higher the value of the temperature is). It reaches 2000-2100, 1500-1600, 1300-1400 and 2100-2200°C for such carbides as TiC, VC0,88, Cr3C2 and ZrC respectively. The same dependence has not been found for the diborides of these metals. Optimum synthesis temperatures for all these compounds lie in the range of 1600-1700 °C. This viable method to produce transition metal carbides consists in the transfer of vaporous higher and lower oxides. Diborides preparation involves the transfer of oxides and boron vapors onto the surface of the carbon material with the subsequent chemical interaction. In the case of carbide-boron reduction of zirconium oxide in excess of boron carbide, the reaction product will be a composite material (B4C – ZrB2). The ceramics based on this composite possesses high performance properties.

THERMODYNAMIC LAWS OF CHROMIUM REDUCTION BY MIXTURES OF СН4 + Н2О AND СН4 + СО2

The development of a physico-chemical model of methane behavior in the processes of solid-phase reduction of chromium-containing raw materials will allow us to create the technological basis for the production of multicomponent sponge ligatures. The reduction of oxides with methane is accompanied by the deposition of soot carbon. The negative effect of carbon black, which is blocking the reaction surface, can be eliminated by adding carbon dioxide or water vapor to methane. A thermodynamic analysis of the reduction of chromium oxide with mixtures of CH4-CO2, CH4-H2O was carried out. The effect of the partial replacement of methane by carbon on the thermodynamic preferences of the process is analyzed. A physicochemical model of the behavior of the CH4 molecule in the recovery process is proposed. The thermodynamic features of reduction at various ratios of СН4 are considered: (Н2О, СО2, О2), as well as the composition of the mixture (Н2О+СО2+О2), which ensure the conditions of solid-phase reduction of oxides and the product of carbide destruction. The use of CH4 + H2O + O2 mixtures in the reduction of chromium oxide is thermodynamically less effective. The use of a mixture of СН4 + Н2О + СО2 has a very insignificant effect on the conversion of methane, and also reduces the thermodynamic preference for the reduction of Cr2O3 in comparison with СН4 + Н2О + О2 and СН4 + Н2О. However, it should be noted that in addition to CO and H2, carbon can be present in the reduction products, so the high reduction potential in this process variant (C+CO+H2) can be used to reduce oxides. The reduction of chromium oxide with mixtures of СН4 + Н2О + О2, СН4 + Н2О, and СН4 + Н2О + СО2 can be thermodynamically realized in the temperature range excluding the melting of the charge. As a result of this process, a carbide phase is formed, as well as a gas phase, which has a high reduction potential and can be used in further technological schemes. Meanwhile, it seems possible to control the carbon content in the sponge ligature by selecting the optimal composition of the source gas mixture.

TiC plasma spray cermets

The microstructure and microhardness of eleven volumetric cermets based on TiC carbide with nickel and cobalt based matrices after liquid-phase sintering at a temperature of 1400 °C were studied. It is supposed to use the research results for the subsequent formation of a powder for plasma spraying of coatings. The compositions of the matrix, additional hardening phases, and carbon were selected taking into account the specific features of the formation of plasma coatings: a decrease in the carbon content and high solidification rates of the sprayed particles with the formation of additional nanosized carbides and an increase in the volume fraction of carbides from 70 % to 88 %. As the matrix, we used the traditional composition for cermets with TiC carbide, NiCr – Mo, and industrial powders, PGSR brands, Ni – 13.5 Cr – 2.7 Si – 4.5 Fe – 0.37 C – 1.65 B, and TAFA 1241F Co – 32 Ni – 21 Cr – 8 Al – 0.5 Y. The ring zone on TiC carbide is formed with the participation of WC, Cr3C2, TiN, matrix phases and additional carbon in the composition of cermets, 1 – 2.8 %, as a result, the initial volume fraction of TiC carbide increases 70 to 88 %. Additional carbon is consumed to reduce oxygen content at the stage of sintering (reduction of oxides). After sintering, cermets have high microhardness values at a load on an indenter of 20 G, 1940 – 3210 kgf/mm2, and lower values at a load on an indenter of 200 G, which was explained by a scale factor. The maximum calculated contribution of the hardness of the hardening phases to the hardness of the cermet was established for cermets with a Co matrix of 3681 kgf/mm2.