Electrodeposition of finely divided copper of uniform structure

Conclusions In the potentiostatic deposition of finely divided copper on a rod cathode in the over-voltage range 0.3–0.5 V the best approximation to the shape of the current vs time function is provided by a straight line. At overvoltages of 0.6 and 0.7 V an exponential and a power-type function, respectively, represent more closely experimental plots. The structure of the dendrites is determined by the magnitude of the overvoltage, and remains uniform over the whole thickness of the loose deposit, as is evidenced by micrographs of transverse sections through the cathode with the deposit. The particle size distribution, apparent density, and flowability of the electrodeposited powder are determined by the overvoltage of the cathodic process, and can be regulated by varying the parameters of galvanodynamic electrolysis.Translated from Poroshkovaya Metallurgiya, No. 8(308), pp. 5–11, August, 1988.     

Structure of particles of very finely divided electrolytic iron

Conclusions X-ray structural analysis and electron microscopy have been employed to study the sizes and crystalline structures of particles of very fine iron powders produced in a two-layer bath using direct and pulsed currents and in a bath with an ultrasound-emitting cathode. The study has demonstrated that the superposition of an additional perturbance (an ultrasonic field or a pulsed current supply) on the electrolysis process restricts the growth of microcrystals and decrease their size variation compared with particles produced by electrolysis using a direct current. The character of curves of some structural characteristics of very fine iron powders plotted against the parameters of electrolysis in a two-layer bath with the use of a direct current, an ultrasound emitting cathode, and a pulsed current is evidence that iron particle formation in these variants of the electrolytic process occurs through different mechanisms.Translated from Poroshkovaya Metallurgiya, No. 5(257), pp. 1–6, May, 1984.     

Manufacture of composite electrophoretic coatings using very finely divided Mo and Mo2C powders

An electroplating-electrophoretic procedure for producing composite coatings using a combination of electroplating and electrophoretic methods, followed by liquid phase sintering at the eutectic formation temperatures, has been studied. Finely divided Mo and Mo₂C powders produced by low-temperature catalytic reduction of molybdenum trioxide and subsequent molybdenum carbiding were employed, and the main electrophoretic deposition mechanisms have been estabished. Electrophoresis parameters have been examined in terms of their effect on the precipitates formation rate and their structure. This procedure enables components operating under corrosion-erosion wear conditions to be protected and their service life increased by a four or fivefold factor.Translated from Poroshkovaya Metallurgiya, No. 12 (360), pp. 21–25, December, 1992.     

Sintering kinetics of finely divided molybdenum-copper composites

Conclusions The highest activity in solid- and liquid-phase sintering was exhibited by the specimens from the mixtures with the matrix-type distribution of the copper relative to the molybdenum and a low-melting-point component content of 40%. The specimens from the industrial powders exhibited no volume shrinkage during solid-phase sintering. In these specimens zonal segregation and ruptures between individual blocks were observed. A nonuniform structure formed in the pseudoalloys affected their liquid-phase sintering and inhibited free regrouping. After low-temperature (1150°C) liquid-phase sintering a solid pseudoalloy could be obtained only at a low-melting-point component content of 40 wt.%.Translated from Poroshkovaya Metallurgiya, No. 9(309), pp. 13–16, September, 1988.     

Kinetics of densification and growth of refractory phase grains in the liquid-phase sintering of very finely divided tungsten-copper materials

Conclusions The kinetics of tungsten grain growth during the LPS of a very finely divided W-20% Cu mixture and of densification of the composite in the middle stage of LPS is determined by a process of transport of the refractory component through the liquid phase. Under conditions of full separation of the refractory grains by the second phase the character of the variation of the viscosity and rate of local nonuniform deformation of the two-phase material indicates that the densification of such a composite is due to a superplasticity mechanism. An expression has been derived, taking into account the kinetics of refractory phase grain growth, relating the porosity ofa very finely divided composite to time of LPS under conditions of superplastic flow.Translated from Poroshkovaya Metallurgiya, No. 9(285), pp. 30–37, September, 1986.The authors wish to thank V. V. Skorokhod and V. V. Panichkina for helpful discussion.     

Model systems for dissolution of finely divided (multisized) drug powders

Several reports have dealt with model systems for the dissolution of log-normally distributed powders. A numerical solution is presented for the previously published Higuchi-Hiestand equations for a log-normal particle-size distribution. This solution was realized via an application of the System 360 Continuous System Modeling Program (CSMP). The resulting computer-aided calculations were utilized in the comparisons between the Higuchi-Hiestand model and other existing models. These comparisons provided a basis for the development of an adaptation of the Nielsen moving sphere model for log-normally distributed powders. The adaptation of the Nielsen equation for multisized particle systems is suggested as being potentially useful for treating experimental data where hydrodynamic effects must be considered.