EFFECT OF MO MICROSTRUCTURE ON THE CRITICAL VOLUME FRACTION FOR CONDUCTION IN MO-ALUMINA CERMETS

The microstructure of Mo in an alumina/frit matrix was found to be dep endent on the initial particle sizes of the alumina and Mo powders, th e glass content in the matrix ceramic, and the amount of moisture in t he firing atmosphere. The Mo microstructure had a significant influenc e on the critical volume fraction for conductivity in these cermets. C oarser alumina powder, finer Mo powder, and higher glass content promo ted coalescence of Mo into conductive networks at lower metal contents . Drier firing atmospheres produced a more coarsened Mo microstructure with a slight decrease in the amount of network contiguity, causing a n increase in the amount required for electrical percolation.