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Thesis (M.S.)--Ohio University, August, 1989. / Title from PDF t.p.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: compaction; powder; ejection. Includes bibliographical references (p. 117-119).

Thesis (M.S.)--University of Wisconsin--Madison, 1982. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 70-74).

Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 120-129).

The contribution of plastic flow to overall densification of a powder compact during hot-pressing has been analysed. The basis of this analysis is the incorporation of hot-working characteristics of materials at elevated temperatures into an equation applicable to hot-pressing conditions. The empirical equation relating steady state strain rate to stress is ἐ = Aσn and for the densification of a powder compact, the strain rate [formula omitted] The particles are assumed to be spheres and four different packing geometric configurations: cubic, orthorhombic, rhombic dodecahedron and b.c.c. are considered. Taking into consideration the effective stress acting at the points of contact, the equations for the strain rate can be combined and arranged into another equation which is shown below:[formula omitted] where α₁ and ϐ are geometric constants and can be calculated from the packing geometry. 'A' and 'n' are material constants. D is the relative density of the compact, and ‘R’ is the radius of sphere at any stage of deformation in arbitrary units. Computerized plots of D vs t were obtained for lead-2% antimony, nickel and alumina. Experimental verification of these plots was carried out using hot-pressing data for lead-2% antimony, nickel and alumina spheres. The hot-compaction experiments were carried out over a range of temperatures for each material and under different pressures. The experimental data fitted well with the theoretical prediction for the orthorhombic model. However, a deviation at the initial stage of compaction was encountered in most cases. This deviation was explained on the basis of the contribution to densification by particle movement or rearrangement at the initial stage, which could not be taken into account in the theoretical derivation. The stress concentration factor i.e., the effective stress acting at necks between particles has been calculated. This was found to be very much higher than that previously used by other workers. The theoretical equation for the effective stress is [formula omitted]. This equation predicts an effective stress, which is more than an order of magnitude higher than that predicted by several empirical equations used previously. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Submitted in fulfillment of the requirements for the Degree of Master of Technology: Chemical Engineering, Durban University of Technology. Durban. South Africa, 2015. / Cobalt powder is a grey metallic powder that is produced by the thermal decomposition and reduction of a cobalt compound. The challenge faced by Shu Powders Africa was that sub-micron cobalt powder had never been produced in a two-step furnace by any manufacturer in the cobalt powder industry. Hence there was no prior information to guide this type of processing. Therefore this research set out to investigate the production of sub-micron cobalt powder through a two-step furnace to determine the optimum parameters for this process. For the company to remain competitive, it was imperative to begin producing sub-micron cobalt powder. Sub-micron cobalt powder is much more valuable and profitable to produce. The second production line would be operational due to the production of sub-micron cobalt powder hence creating job opportunities for the local community. Sub-micron cobalt powder shares the same chemical composition and physical characteristics as cobalt powder. The only differences are particle size (0.60 - 0.90 µm), oxygen content (0.30 - 0.80%) and the microscopic structure which is the particle size distribution d90 (7 - 10 µm). The approach taken was to understand the variables that had a large effect on the powder. The effects needed to be established by determining how it impacted on the quality of the powder which is pertinent to making sub-micron cobalt powder. Due to the experience in producing cobalt powder, variables that had a large effect on normal cobalt powder production were assumed to be the same variables that would impact the production of sub-micron cobalt powder. Some of these effects were also confirmed by literature. A strategy of statistical design of experiments was used to evaluate the conditions for sub-micron cobalt powder production. Design of experiments assisted in planning the experimental design matrices for both experiments. For the furnace experimentation a 24 factor design was selected. For the jet mill experimentation a 23 factor design was selected. Response surface methodology was used to determine optimum ranges of the variables at various process conditions. The central composite rotatable design laid out the design in which the variables interacted with one another at different process conditions. Evaluation of results was based on the generated model. Models such as the 3D surface model, cubic model and the contour model were generated to graphically illustrate the effects that the variables have on the response. Analysis of furnace data indicated that the optimal response was achieved at a temperature range (445 - 460)°C, hydrogen gas range (225 - 250) Nm3/h, belt speed (80 - 90) mm/min, and carbon dioxide gas range (80 - 90) Nm3/h. Analysis of the jet mill experimental data indicated that the optimal response particle size distribution, was achieved at a classifier speed range of (5500 - 6000) rpm, AFG grinding bin range (30 - 35) kgs and grinding gas pressure of (4.0 - 4.5) bar. The study confirms the efficiency of a two-step furnace to produce sub-micron cobalt powder at high volumes. The advantage of the two-step furnace was the increased throughput of 2.3-2.7 tons/day whilst in industry furnace throughputs are 1.3-1.6 tons/day. This represented a 60% increase in productivity over conventional furnaces. The response surface methodology also proved to be a suitable technique for process optimization.

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