Neck growth kinetics during microwave sintering of nickel powder

Model experiments on initial stage of microwave sintering of nickel powder showed anomalous neck-growth rate during isothermal soaking, which is not the case for conventional sintering. Neck growth was determined as a function of time. Values for the neck growth exponent in the neck growth equation, (x/a)(n) = Bt, of 5.2, 5.4, 5.8, and 5.9 were found for within the temperature range 700-950 degrees C, respectively. The evidences of formation of liquid phase during microwave sintering have been revealed, that may support enhancement of mass transfer during sintering process. The activation energy of 48 kJ mol(-1) was found for microwave sintering of nickel, according to sphere-to-sphere model. Value revealed is significantly lower then values for conventional sintering (136 kJ mol(-1)), and is on same level with activation energy for diffusion of metals in liquid state. An explanation and analysis of this phenomenon has been attempted. (C) 2010 Elsevier B.V. All rights reserved.