CHARACTERISTICS OF PORE AND CAPACITANCE OF POROUS TANTALUM COMPACT SINTERED IN CAPSULE FREE HOT ISOSTATIC PRESSING OR VACUUM

Recently, electrolytic capacitor of tantalum have been demanded to be smaller in size and higher in performance. But there is few reports ab out sintering of tantalum. Then, in this work, the tantalum was sinter ed by hot isostatic pressing (HIP ping) without capsule, so-called a c apsule-free HIP (CFHIP), under the high pressure of argon gas and was sintered also in vacuum furnace at 1523 and 1623 K for 1 h. The volume shrinkage with sintering was measured and the properties of pore of t he sintered tantalum were measured by a mercury pressure porosimeter, too. The surface was observed by SEM and capacitance was measured. The sintering behavior and characteristics of pores of the porous tantalu m compact sintered under CFHIP and in vacuum were investigated. The re sults obtained are as follows. The shrinkage of volume under both sint ering conditions became larger with the higher sintering temperature. The volume shrinkage of tantalum sintered under CFHIP was samller than by sintering in vaccum. From the SEM image, it was obviously clear th at tantalum powder was lumped larger by sintering in vaccum as compare d with under CFHIP. The pore of these sintered compacts, in this exper imental region, was open. The mean diameter of pores of the sintered c ompacts with CFHIP was smaller as compared with those sintered in vacc um and the specific surface area of the sintered compact with CFHIP wa s larger than that sintered in vacuum. The capacitance of the sintered compact increased with increase of its specific surface area and the capacitance of the specimen treated at 1623 K was larger.