Electrical behavior of oxidized metal powders during and after compaction

The electrical behavior during compaction of tantalum and aluminum powders was characterized before and after thermal oxidation. The resistivity of unoxidized powders decreased by >10⁶ over a narrow range of stress between 1 and 10 MPa. Thermal oxidation of the powders to produce submicrometer thick oxide layers on the particles increased the precompaction electric breakdown strength from <0.2 to >5 kV/cm but did not have a significant effect on the low field resistivity of the powders during compaction. At higher fields, the decrease in resistivity during compaction occurred at lower stresses and over a much narrower stress range since catastrophic electrical breakdown occurred once a certain level of stress was reached. The breakdown field at constant stress also decreased as the stress was increased for the oxidized powders. These effects are caused by the cracking of the brittle oxide coatings at the contact points between the particles during compaction.