Investigation of the sintering kinetics of lead powders. Final technical report

An analysis of the parameters involved in the sintering of lead powders under vacuum has been made. Sintering was accomplished at temperatures between 250/sup 0/ and 280/sup 0/C. Evaluation of surface area reduction data results in values of the mechanism exponent N between 5.3 and 6.7. Lack of shrinkage and the low vapor pressure of lead at the experimental temperatures lead to the conclusion that surface diffusion is the rate-controlling sintering mechanism. However, comparison of the experimentally measured activation energy, 170 kJ/mol (40.7 Kcal/mol), to that reported in the literature for surface self-diffusion of lead showed a significant discrepancy. Effects of pore isolation and surface oxide layers are proposed as possible explanations for this discrepancy as well as the deviation in the N values from those obtained theoretically. An attempt to isolate the effect of the oxide layer was made by sintering lead in a hydrogen atmosphere. Under these conditions, sintering is accompanied by shrinkage, thus indicating the presence of bulk-transport process. A mechanism exponent corresponding to viscous flow sintering was obtained. Furthermore, the calculated activation energy for this process was in good agreement with that reported for creep in lead.