Reaction between silicon nitride and magnesium oxide during hot pressing

Conclusions Using the methods of microscopical examination, chemical and mass spectrometric analyses, electron probe microanalysis, and weight loss determination, astudy was made of the reaction between technical silicon nitride powder and magnesium oxide. It is shown that the reaction involves not only the formation of forsterite, enstatite, and variable-composition glasses but also diffusion of the main components, with a gradual fall in magnesium concentration over the whole length of the diffusion zone in a model system. In the temperature range 1600–1700°C magnesium atoms drive out of the silicon nitride lattice silicon atoms, which then react with oxygen from the magnesium oxide or air to form silicon monoxide ions in the gaseous phase. The evaporation of the silicon monoxide in the system results in loss of weight, which grows with rise in temperature. The processes of evaporation and dissociation of the starting components, which sharply increase in intensity at 1800°C, make a certain contribution to the loss of weight.Translated from Poroshkovaya Metallurgiya, No. 9(177), pp. 89–96, September, 1977.     

Effect of alloying method on sintering and physico-mechanical properties of Al-A.4% Cu-0.5% Mg powder alloy

Conclusions The method of alloying with copper and magnesium has a strong effect on compacting in sintering and on the physicomechanical characteristics of Al-4.4% Cu-0.5% Mg alloy.The alloy based on Al-0.5% Mg master alloy is characterized by the highest density but its sintering requires higher temperatures (615–635°C) and long holding times. This alloy produced in the optimum conditions is characterized by high physicomechanical properties in the sintered state but by low efficiency of heat treatment. The optimum physicomechanical properties were recorded for the alloy containing the elementary powders of copper and magnesium which was sintered at 595°C for 45 min.Translated from Poroshkovaya Metallurgiya, No. 10(310), pp. 37–41, October, 1988.     

Composition and thickness of surface oxide films on aluminum alloy granules

Conclusions The composition of oxide layers on granules is affected most by magnesium, the magnesium content of the layers being strongly dependent on the conditions of casting of granules. The thickness of surface oxide films on aluminum alloy granules produced by vibratory casting in water does not exceed 5–6 nm. In the casting of granules in water it is necessary to control the latter's impurity content. This applies particularly to closed water circulation systems, in which the degree of contamination of water increases with time.Translated from Poroshkovaya Metallurgiya, No. 8(260), pp. 4–9, August, 1984.     

Production of metal powders from melts by centrifugal atomization

Conclusions A study was made of centrifugal atomization of molten metals in argon at low argon consumption rates [(5.2–7.5) · 10^–3 NTP m³/kg]. Output with a single injector attained 30–40 kg/h. Increasing the molten metal head to 0.6–0.8 MPa and decreasing the nozzle diameter to 0.3 mm substantially increased the fineness of the powders. Raising the head still further influenced the effectiveness of atomization to a smaller extent, and decreasing the nozzle diameter to less than 0.3 mm coarsened the powders. Powders of magnesium, aluminum, and Br020 alloy. (20% Sn-Cu bronze) produced by centrifugal atomization of superheated (by about 30–50°K) melts in an inert atmosphere (argon) had spherical particle shapes, which imparted to them good flowability. The oxygen content of the powders was low (less than 0.08%).Translated from Poroshkovaya Metallurgiya, No. 12(276), pp. 5–10, December, 1985.     

Effect of sintering conditions on the structure and mechanical properties of P/M aluminum base alloys

Conclusions A magnesium addition promotes densification of Al-Cu alloy specimens sintered for short periods of time in the range 595–635C. Longer sintering at 615 and 635C results in higher specimen porosity. At a temperature above 595C Al-Cu alloys experience severe coarsening. Alloying with magnesium does not significantly affect the structure of the alloys. A magnesium addition improves the mechanical properties of an Al-Cu alloy. The extent to which magnesium alters the mechanical characteristics of heat-treated Al-Cu alloys depends on sintering conditions. The highest strength — 340 MPa and =6% — is exhibited by specimens sintered for 45 min at 595C.Deceased.Translated from Poroshkovaya Metallurgiya, No. 9(297), pp. 29–34, September, 1987.     

Elevated-pH bioleaching of a low-grade ultramafic nickel sulphide ore in stirred-tank reactors at 5 to 45 °C

This study is a continuation of previous work designed to assess the effect of elevated-pH bioleaching on a low-grade ultramafic nickel sulphide ore from Manitoba, Canada. The ore contains 21% magnesium and 0.3% nickel. Nickel is the only significant metal value, and is present primarily as pentlandite. A substantial fraction of the magnesium is present as lizardite, making processing of the ore difficult with conventional pyro- and biohydrometallurgical techniques. This work has two objectives: to maximize nickel extraction, and to minimize magnesium mobilization. Five-week stirred-tank bioleaching experiments were conducted with finely ground ore (− 147 µm) at three pH levels (3, 4 and 5) and five temperatures (5, 15, 22.5, 30, and 45 °C). The initial rate of nickel extraction from pentlandite was observed to be inversely correlated to acidity at all temperatures, while the final extraction of nickel after 5 weeks was determined to be moderately correlated to acidity at high temperatures and negatively correlated to acidity at low temperatures. The advantage of elevated-pH bioleaching was most evident at 5 °C, in which the final extraction of nickel at pH 5 was approximately 250% greater than at pH 3. Electron probe X-ray microanalysis of the post-leach residues revealed that the un-reacted lizardite was enriched with nickel during experiments conducted at pH 5, and that the extent of enrichment was a strong function of temperature. The undesirable extraction of magnesium exhibited a strong negative pH–temperature interaction and the consumption of sulphuric acid directly tracked the extraction of magnesium over all experimental conditions. Bioleaching at elevated pH substantially increased the ratio of nickel to magnesium in the leachate, and resulted in a substantial reduction in sulphuric acid consumption.     

Properties of electrolyte solutions relevant to high concentration chloride leaching I. Mixed aqueous solutions of hydrochloric acid and magnesium chloride

A computer code based on a Pitzer model has been developed for the comprehensive prediction of the thermodynamic properties of MgCl₂–HCl aqueous solutions over a wide range of conditions from 25 to 120 °C and from 0–350 g L^− 1 chloride. This code was applied to the calculation of (i) water activities and mean ionic activity coefficients for mixed aqueous solutions of hydrochloric acid and magnesium chloride over a wide range of concentrations and to 100 °C, (ii) solubilities of MgCl₂·6H₂O in MgCl₂–HCl solutions to 80 °C, (iii) partial pressures of HCl(g) and H₂O(g) over MgCl₂–HCl aqueous solutions at various temperatures and (iv) partial pressures of HCl(g) at the normal boiling point of these mixed electrolyte solutions. The model predictions are in excellent agreement with available experimental data and confirm evidence from the literature that MgCl₂(aq) and HCl(aq) mix almost ideally at constant water activity.     

Synthesis of the nitrides of Group II elements

Conclusions A study has been made, using kinetic, chemical, and x-ray diffraction methods, of the reactions of magnesium and zinc with ammonia. It has been established that the kinetics of magnesium and zinc nitride formation in ammonia is described by pseudotopokinetic equations. The reaction of magnesium takes place in the topokinetic range, with penetration into the diffusional range, while the reaction of zinc with ammonia is controlled by topochemical processes. In both cases surface activation is observed. The mechanism of formation of the nitrides of Group II elements is examined, ans suitable process parameters for the synthesis of the nitrides of Group II metals are indicated.Deceased.Translated from Poroshkovaya Metallurgiya, No. 2(206), pp. 57–62, February, 1980.     

Effect of Manganese and Niobium and Rolling Conditions on the Properties of Low-Alloy Steel

A series of studies was conducted to determine the optimum manganese and niobium contents in steels alloyed with the system C–Mn–Nb. Researchers also wanted to find the starting and finishing temperatures for rolling on a 2800 mill that would be best in order to obtain the necessary mechanical properties when the metal is deformed in the austenite range with small reductions.The studies established the following:– a greater improvement in strength properties is obtained from an increase in the mass content of manganese if the carbon content is reduced (0.09–0.10%) rather than increased (0.12–0.13%);– other conditions being equal, an increase in the niobium content of the steel from 0.02–0.03% to 0.04–0.06% leads to a substantial increase in strength and toughness properties and a decrease in ductility;– it was established that in terms of its effect on the yield point, microalloying steel with 0.01% niobium is equivalent to alloying with 0.30–0.40% manganese;– the percentage of the tough B component in the fracture of IPG specimens of low-alloy steel with a niobium content of 0.02–0.03 mass % can be increased from 30 to 100% by decreasing the temperature of the slab after the second pass through the two-high stand from 1020 to 980°C. For steels with a higher niobium content (0.05–0.06%), the temperature of the metal when it enters the roughing stand can be increased to 1010–1040°C without adversely affecting the standard characteristic B (%);– a decrease in the finishing temperature is accompanied by an increase in the strength and toughness properties of the metal and a decrease in ductility. Reducing the finishing temperature to below 760°C makes it possible to increase strength properties but does not change impact toughness.     

Thermal sprayed magnesium-aluminum protector alloy coatings

Conclusions Thermal spraying enables protector alloy coatings to be deposited possessing the required properties for the protection of low-carbon steel against corrosion. The optimum protector properties are exhibited by a coating containing aluminum and magnesium in the ratio 31.Translated from Poroshkovaya Metallurgiya, No. 1(265), pp. 45–48, January, 1985.     

Mechanism of ferrite formation in a mixture of metallic oxide powders

Conclusions It has been established that the mechanism of formation of new crystalline structures can be studied by determining the variation of the most probable crystallite size as a function of the ratio between the amounts of the starting phases. It is shown that magnesium and nickel ferrites with spinel structures form on the bases of the thermally-more-stable magnesium and nickel oxide lattices, with preferential diffusion of iron cations. To the initial stages of formation of these ferrites there will correspond a nonstoichiometric solid solution of increased divalent cation concentration. The crystal lattices of such spinel solid solutions are deficient in oxygen and contain interstitial cations.Translated from Poroshkovaya Metallurgiya, No. 7(163), pp. 79–82, July, 1976.     

Deformation behavior and dynamic recrystallization of Mg-Y-Nd-Gd-Zr alloy

The characteristics of dynamic recrystallization （DRX） in Mg-Y-Nd-Gd-Zr-RE magnesium alloy were investigated by compression tests at temperatures between 523 and 723 K and at strain rates ranging from 0.002 to 1 s^-1 with maximum strain of 0.693. The strainhardening rate can be obtained from true stress-true strain curves, plots of θ-σ, -（δθ/δσ-）-a and lnθ-σ in different compression conditions were obtained by further study. The critical condition of the onset of DRX process was determined as （（δ/δσ（ δθ/δσ））=0. In the range of the above deformation temperature and strain rate, the ratio of critical stress （σc） to peak stress （σm） and critical strain （εc） to the peak strain （εm） stood at σc/σm=0.62-0.89 and εc/εm=0.11-0.37, respectively. DRX could be observed during hot detormation process, microstructure evolution of the magnesium alloy at different temperatures and strain rates were studied with the aid of optical microscope（OM）, and the average recrystallized grain size was measured by means of intercepts on photomicrographs. It was shown that the average dynamically recrystallized grain size （drew） changed with different deformation parameters, the natural logarithm of the average recrystallized grain size varied linearly with the natural logarithm of Zener-Hollomon parameter; the peak stress changed with the average recrystallized grain size, and the natural logarithm of the average recrystallized grain size varied linearly with the natural logarithm of the peak stress.     

Phase Equilibria in the Mg – Al – Ca System (Region 50-100 mass% Mg)

Phase equilibria in the ternary system Mg – Al – Ca in the composition range 50-100 mass% Mg were studied by the methods of differential thermal, xray diffraction, electron-probe and microscopic analysis. The projection of the liquidus surface on the concentration triangle, isothermal section at 150°C and polythermal sections at 4.5, 8.5, and 16 mass% Al were constructed. It was determined that additions of Al and Ca decrease the liquidus temperature of magnesium alloys (from 650 to 438°C). It is shown that the three-phase region + 2Ca> + 17Al₁₂> exists at 150°C with the corresponding two-phase fields. The temperature dependence of the homogeneity range of the Mgbased solid solution was determined, and also the temperatures of the phase transformations which occur in the investigated range of compositions in the system.     

Porous metallic elements for the lubrication of yarn

The properties of porous permeable lubricating elements fabricated from sintered metal powders were studied. It was shown that the working properties of the material are determined by its pore structure. Tests on type V TS-07/2 twisting machines revealed that the newly developed lubricating elements increase the degree of lubrication ten fold, and decrease thread breakage by 13–30%. Use of these elements permitted an increase in spindle rotation rate, leading to a 7–9% increase in machine productivity, and also decreased the extent of dusting by 57–76%.Materials Science Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5–6, pp. 15–20, May–June, 1996. Original article submitted October 18, 1994.     

Mechanism of additional reduction of metallic powders in a falling layer

Conclusions The specific rate of additional reduction of the oxides films on the particles of iron in a falling layer of the powder in the temperature range 800–1000°C calculated for the initial specific surface was 0.036–0.078 g[O]/m²· sec. The activation of the reduction process was equal to 54.16 kJ/mole.The rate of additional reduction of the iron powder in the falling layer is high. For example, in the temperature range 800–1000°C it is 1.2–3.1% [O]/sec.The experimental results as well as the comparison with the available data make it possible to conclude that the process of reduction of the surface oxides in the falling layer in the temperature range 800–1000°C takes place in the kinetic range of reaction and is limited by the reaction of interaction of hydrogen with the surface oxides of iron.Translated from Poroshkovaya Metallurgiya, No. 9-(345), pp. 1–5, September, 1991.     

A model investigation of the sintering of zirconium

Summary A study was made of the welding of iodide zirconium spheres of 2-ram diameter in a purified helium atmosphere (3 atm gauge) and in a vacuum (10^–4–10^–5 mm Hg). It is shown that welding in helium (1265–1810°C occurs mainly as a result of diffusion material transport, whereas welding in a vacuum (1500–1800°C is controlled primarily by an evaporation-condensation mechanism. The data obtained are used to evaluate the self-diffusion and evaporation parameters and to derive equations expressing the self-diffusion coefficient and vapor pressure of zirconium as functions of temperature over the range investigated.Translated from Poroshkovaya Metallurgiya, No. 6(66), pp. 41–46, June, 1968.The authors are indebted to V. V. Khromonozhkin for helpful discussion and to V. G. Osintsev for making available the test materials.     

Effect of porosity and grain size on the mechanical properties of hot-pressed boron carbide

Conclusions An investigation was carried out into the effect of porosity in the range 2–46% and grain size in the range (5–140)·10^–6 m on the mechanical properties of boron carbide. It is shown that the level of mechanical properties of boron carbide produced by hot pressing from powders synthesized from the elements is 1.5 times higher than that of boron carbide produced by other methods. Increasing the porosity of boron carbide to 46% decreases its strength by a factor of six or seven. Increasing the grain size to 140·10^–6 m has the same effect. An analysis is made of equations describing the dependence of the mechanical properties of boron carbide on porosity and grain size. The constants of these equations have been determined.Translated from Poroshkovaya Metallurgiya, No. 1(229), pp. 63–67, January, 1982.     

Comparative leaching of minerals by sulphuric acid in a Chinese ferruginous nickel laterite ore

The Yuanjiang nickel laterite ore containing mainly maghemite, goethite and lizardite was leached by sulphuric acid at atmospheric pressure and the residues were characterized using X-ray diffraction and scanning electron microscopy/X-ray energy dispersive spectroscopy. The relationship was discussed between the extraction of nickel, cobalt, iron, magnesium, aluminum, and the dissolution behaviour of the laterite minerals; as well as the extent of congruency of nickel, cobalt and iron extraction. The results show that the solubility of the laterite minerals in sulphuric acid decreases in the following order: lizardite > goethite > maghemite > magnetite ≈ hematite > chromite ≈ ringwoodite. Lizardite dissolved rapidly in 0.6 mol/L sulphuric acid at 60 °C whilst goethite dissolved completely in 2.5 mol/L sulphuric acid at 80 °C. The dissolution of the primary mineral maghemite was slow, but increased with increasing acid concentration and leaching temperature. Magnetite dissolved more slowly than maghemite; and hematite was only dissolved in > 6.2 mol/L sulphuric acid at 105 °C. Chromite and ringwoodite were not dissolved. The leaching behaviour of the laterite minerals may be explained by the bond strength differences of Me–O and the substitution of metal cations in the mineral structure.     

Dielectric characteristics of silicon nitride powders in the SHF range

Conclusions The dielectric properties of silicon nitride are strongly affected by the presence of impurities, in particular oxygen. The dielectric permittivity of silicon nitride, calculated from data yielded by measurements at a frequency of 9.5 GHz, is 6.3–7.1, and the tangent of its dielectric loss angle, (5.3–9.7) · 10^–3.Translated from Poroshkovaya Metallurgiya, No. 9(213), pp. 62–70, September, 1980.     

Chemical reaction of aluminum alloy powders with water

Conclusions As a result of an investigation into the reaction of powders of several aluminum alloys with water it was established that the most active with respect to water are aluminum alloys containing magnesium, lithium, zinc, and other active elements. The rates of the reactions of these alloy powders with water are determined by the following factors: alloy composition, water and powder temperatures, and suspension concentration (s1). The highest rate of reaction with water (of the three industrial powders investigated — AMLD, PV-90, and SAS-1) is exhibited by the AMLD alloy powder, which contains lithium. The reaction of such alloy powders with water can be retarded or even completely prevented by the introduction of inhibitors — a measure permitting safe handling (e.g., hydrostatic pressing) of all aluminum alloy powders.Translated from Poroshkovaya Metallurgiya, No. 8(308), pp. 15–19, August, 1988.