Experimental highlighting of electric field effects with pulsed and continuous currents during resistance sintering of a silver-based matrix composite Ag-SnO2

Abstract

The aim of this work is to compare the effects of two kinds of current on the sinterability of the silver-based matrix composite Ag-SnO2 during resistance sintering. For this, comparative sintering tests are performed on a same apparatus. The samples are directly heated by Joule effect, with pulsed or continuous current at same IRMS values. During the tests, temperatures and electrical potentials are recorded at different points on tools and on the sample. The shrinkage of the sample is also measured with a displacement sensor. The final relative density and electrical conductivity are determined and used for comparison. The final properties are found to depend mainly on the maximum temperature reached in the sample, which is always higher in continuous current configuration. These results are explained through the effect of the external electrical contact resistances, between the sample and the punches, which are here the main Joule heating source. With pulsed currents, because of the high peak current value reached during the first pulse, the external contact resistances decrease more abruptly. The interfacial power heating is consequently lower, which leads to lower maximal temperatures in the sample and lower final values of electrical conductivity and density. Because of the high effective electrical conductivity of green Ag-SnO2 samples, local Joule heating inside the porous structure is weak either with pulsed or with continuous currents. Finally, results suggest that, in these conditions, the sinterability of the porous cermet Ag-SnO2 is better by using continuous electric currents.