Oxidation Processes for Alloys in the Ni – Zr System. Part 1. Structure of Ni – Zr Alloys. Oxidation Kinetics for Ni7Zr2

We have studied the synthesis conditions and crystal structures for one-phase intermetallic alloys Ni₅Zr, Ni₇Zr₂, and NiZr. We used the continuous weighing method to study the oxidation kinetics in air for the alloy Ni₇Zr₂ in the range 500-1000°C. We have shown that the oxidation process is described mainly by a parabolic law. The kinetic isotherms for the change in mass suggest that over time, the rate constant for parabolic oxidation K _p decreases due to improvement in the protective properties of the scale. The temperature dependence of the oxidation rate suggests a change in the oxidation mechanism for T > 800°C, due to changes in the defect structure of the ZrO₂ lattice.     

Oxidation of porous nanocrystalline titanium nitride. II. Scale structure and composition

We have used x-ray phase analysis to study the composition of the products of reaction between oxygen and nanocrystalline powders with particle sizes 15, 40, 55, and 80 nm, and also specimens pressed (and sintered) from them. The powders were oxidized in air at 100°C (400 h) to 500°C (5 min), while the sintered specimens were oxidized at 600–900°C for 15, 120, and 240 min. In all cases, in the initial oxidation step the oxynitride Ti(O_xN_y) is formed, which over time is oxidized to TiO, Ti₂O₃, Ti₃O₅, TiO₂ (anatase) and TiO₂ (rutile). In the range 600–800°C, formation of a continuous oxide layer and conversion of anatase to rutile slows down diffusion of oxygen in the scale. We have established that at 900°C, the growth rate of the scale thickness increases and so the reflections from the oxynitride are barely noticeable on the diffraction patterns taken from the surface of the oxidized specimen. In these diffraction patterns, along with strong reflections from the rutile, we also observed weak reflections from lower oxides and anatase, which may be due to reaction between oxygen and the titanium ions diffused to the scale surface. We have concluded that at T > 850°C, the mechanism for oxidation of TiN changes. This is due to superposition of counterdiffusion of titanium ions on the diffusion of oxygen. __________ Translated from Poroshkovaya Metallurgiya, Nos. 3–4(448), pp. 72–78, March–April, 2006.     

Specific features of obtaining molybdenum-nickel coatings on diamonds

Conclusions Formation of the molybdenum-nickel coatings is determined mainly by the reactions occurring between carbon and molybdenum oxides developed during the reduction process of nickel oxide in the presence of molybdenum. In contrast to the metallizing process of diamonds in the oxidized molybdenum powder, metallizing in a NiO + Mo mixture is distinguished by the fact that all other things being equal, a continuous thick layer forms earlier and the active process of its weight increment continues for a longer time. This can be attributed to the catalytic effect of active (reduced) nickel on the reactions of reduction and carbide formation. Reduction reactions of molybdenum in the presence of active carbon (forming due to the dissociation of CO at the surface of the finely dispersed nickel) are assumed to occur. They are expected to contribute to the weight increment of the coating. During the stage of oxygen loss in the metallizing agent ( > 2 h), this becomes the main process and is determined mainly by the carbide composition of the external layers of the coating.Translated from Poroshkovaya Metallurgiya, No. 6(354), pp. 23–28, June, 1992.     

High-temperature oxidation of titanium carbide in oxygen

The kinetics of titanium carbide oxidation in oxygen over the temperature range of 600–1200°C and oxygen pressure from 0.1 to 740 Torr have been studied with a vacuum microbalance. Layer-by-layer x-ray analysis, petrography, metallography, and gas chromatography have been used to analyze the oxidation products. A paralinear nature of the oxidation of material was established, and the rate constants of the process were calculated for the corresponding parabolic and linear portions of the kinetic curves. It was shown that a gaseous product, CO₂, formed, as well as a solid product, TiO₂ (rutile), both stoichiometric and nonstoichiometric. The lower oxides, Ti₃O₅, Ti₂O₃, TiO, were noted in the scale at temperatures from 700 to 800° and low oxygen pressures, their relative quantity rising with decreasing pressure. Based on x-ray analysis and microhardness measurements, it was concluded that titanium oxicarbides formed in the TiC, directly adjacent to the scale. A possible oxidation mechanism of titanium carbide is proposed.     

X-ray diffraction investigation of Ni-Mn-Sn-Ti coatings applied to diamond

Conclusions At the boundary with diamond there forms a carbide interlayer consisting mainly of Mn₇C₃, which ensures a strong bond between the coating and diamond. In the case of a titanium-containing coating, titanium carbide and oxycarbides forming as a result of the dissolution of oxygen adsorbed on the surfaces of metal powder particles do not occur at the boundary of the coating, but are distributed within it. This helps purify the system from oxygen and intensifies the reaction of the melt with the diamond.Translated from Poroshkovaya Metallurgiya, No. 1(253), pp. 40–44, January, 1984.     

Depolarization of light in SnO2:In2O3 layers

Electric current pulses passing through conducting SnO₂:In₂O₃ (ITO) layers (used as electrodes in optoelectronic devices) on plane-parallel glass substrates produce depolarization of the transmitted light. This effect, which is probably related to changes in the structure of ITO layers as a result of Joule heating, can lead to distortions of the information field in the course of optical data transmission.