Sintering kinetics of niobium carbide powders of nonstoichiometric composition

Conclusions The sintering densification kinetics of NbC_x powders depends to a large extent on their degree of dispersion and nonstoichiometry; a characteristic feature of the densification kinetics is that the main contribution to densification, which grows further with increasing degree of dispersion and defectiveness (activity) of NbC_x phases, is made by the initial stage of sintering, apparently involving threshold mechanisms of mass transport, which are activated by oxycarbide decomposition processes in the temperature range 1600–2420°K. Because of this, in the sintering of NbC_x and ZrC_x phases the principal mechanisms of mass transport change in different temperature ranges.Translated from Poroshkovaya Metallurgiya, No. 5 (185), pp. 47–50, May, 1978.     

Sintering of aluminum with additions of nickel

The sintering of aluminum with substantial additions of nickel was investigated. It was determined that within the temperature range (700–750°C) and concentration range (10–17.5 at. % Ni) it was possible by the sintering of pressed powder compacts to obtain alloys with densities approaching the theoretical. The hardness and tensile strength of the alloys increased and the ductility decreased with increasing nickel concentration and increasing temperature. The curves of yield, tensile strength, and ductility vs nickel concentration exhibited maxima.     

氧化镍中三价镍含量的测定

用碘量法测定了氧化镍中三价镍的量,然后用EDTA络合滴定法测定了氧化镍中的总镍量,从而计算出氧化镍中三价镍的百分含量。碘量法测定氧化镍中三价镍的原理为:首先将氧化镍溶解在含KI的酸中,然后以淀粉为指示剂,用Na2S2O3标准溶液滴定;滴定条件为:碘量法中所用的酸应为pH 1.11~1.19的盐酸,KI的加入量应为0.1 g左右,KI与三价镍的反应时间为2~3 min,氧化镍的加入量为0.02 g左右,常温下测定。EDTA络合滴定法的原理为:在氨性溶液中,二价镍与其络合形成络合物,以紫脲酸铵为指示剂,用已标定的EDTA溶液滴定,即可得出二价镍的量,即为总镍量;滴定条件为:pH 9~11,紫脲酸铵的量为0.05~0.06 g,温度略高于34℃。三价镍在总镍量中百分含量测定结果的相对标准偏差小于5%,能很好的满足液相法制备氧化镍的分析需要。     

Electrochemical reduction of nickel from oxide melts

The electrochemical behavior of nickel ions in melted sodium borosilicate and calcium alumino-silicate with NiO additions (0.25–4 wt %), which cover the entire solubility region, is studied using I-V characteristics and an electrolytic method.     

Sintering of dispersed oxide composites for high-temperature protective coatings

Conclusions A method is proposed for the continuous study of sintering processes under nonsteady-state temperature conditions. Activating factors in the sintering of oxide powders were investigated. A study was made of the effectiveness of activating additions as a function of their physicochemical properties.Translated from Poroshkovaya Metallurgiya, No. 7 (127), pp. 18–21, July, 1973.     

Mechanically activated reduction of nickel oxide with graphite

The reduction of nickel oxide with graphite during ball milling at both ambient and elevated temperatures was investigated using X-ray diffraction (XRD), simultaneous thermogravimetry and differential thermal analysis (TG/DTA), and electron microscopy. It was found that milling at ambient temperature did not result in the reduction of nickel oxide to nickel. However, milling significantly reduced the critical reaction temperature for the reduction, from 1350 K for the unmilled sample to ∼650 K for samples milled for 12 hours or longer. This reduction in reaction temperature is rationalized in terms of the microstructural refinement observed in the milled samples. The reduction of nickel oxide to nickel was observed to occur at elevated temperatures during milling. The thermodynamics and kinetics of the reduction reaction are discussed.     

Anode dissolution of nickel in segregating oxide systems

The kinetics of anode dissolution of nickel in molten sodium borosilicate and calcium aluminosilicate containing 0.5?C3 wt % NiO is studied. Data on the current efficiency of nickel during its anode dissolution under various experimental conditions are obtained. The steady-state current-voltage characteristics of a nickel electrode are analyzed.     

The concentration-dependent diffusion of chromium in nickel oxide

A theory has been developed to describe the diffusion of trivalent impurities in a divalent metal oxide and has been evaluated for the diffusion of trivalent chromium in NiO. The theoretical model developed by Lidiard to describe the diffusion of divalent impurities in alkali halides was revised to describe the migration of chromium-vacancy complexes in the divalent NiO crystal. A radioactive⁵¹Cr tracer and NiO single crystals were used and the concentration profiles were analyzed by sectioning and counting. The diffusion coefficient of chromium as a function of chromium concentration was determined at 1000°, 1100°, 1200°, and 1300°C and at oxygen pressures of 1.0, 10^-2, and 10^-5 atm using a modified Matano analysis of the concentration profiles. A reasonable fit of the theory to the experimental concentration dependence of chromium diffusion was obtained which indicates that, at 1000°C and above, chromium diffuses in NiO by a mechanism involving chromiumvacancy two-member complexes. The energy of association of a chromium-vacancy couple was found to increase from approximately -3000 cal at 1000°C to about -600 cal at 1300°C. The diffusivity of chromium (Dcr) in NiO saturated with chromium increases from approximately 2 x 10^-12 cm²/s at 1000°C to 2 x 10^-10 cm²/s at 1300°C.     

Sintering composites made of plasticized W-Mo powders and hafnium oxide

Conclusions The compactibility in uniaxial compacting of plasticated granules of tungsten-molybdenum mixtures and also of multilayer composites of films of the powders of hafnium and tungsten oxides and their cermets, cast using a rubber binder, is considerably higher than that of the dry tungsten powders. The density of the compacted composite specimens increases and linear shrinkage decreases with the increase of pressure to the critical value (500–600 MPa) and then remains unchanged but the final density after sintering at 2000°C does not depend on the compacting pressure.The concentration dependences of shrinkage of the granulated W-Mo powders contain a deep minimum determined evidently by Frenkel's effect caused by the differences in the partial coefficients of heterodiffusion of the components and by the larger interphase surface.Translated from Poroshkovaya Metallurgiya, No. 3(303), pp. 51–57, March, 1988.     

Effects of oxide particles on properties of sintered nickel

Conclusions The effect was investigated of the addition of aluminum, zirconium, silicon, and hafnium oxides on the hot hardness and rupture strength of nickel at temperatures of 600–800°C. The rupture strength of nickel is shown to increase with increasing amount of oxide introduced into it and with decreasing oxide particle size. In tests below the temperatures at which transformations take place, the nature of the oxides investigated does not affect the properties of nickel.Translated from Poroshkovaya Metallurgiya, No. 6 (78), pp. 81–86, June, 1969.     

Equilibrium relations in the system nickel oxide-copper oxide

Phase relations in the system Cu-Ni-0 were studied atPo ₂ = 0.21 atm using DTA and quenching techniques. Results were expressed in the form of a NiO-CuO “binary” in which a eutectic occurs at 1090°C and 6 mol pct NiO. The activities of CuO in (Ni,Cu)O solid solutions were determined at 1024°C by establishing the oxygen partial pressures at which Cu₂O precipitates from members of this solution series.