Papers by Author: Satoru Ishihara

Abstract: Lead-free Li_0.06(Na,K)_0.94NbO₃ (LNKN) piezoelectric ceramics were sintered by a new process, “two-step mixing process”, in which a part of alkali source powders (R_A) was initially preserved and mixed with the rest matrix powders after the calcinations step, in order to improve bulk density. Sintering of the LNKN ceramics was improved by this process, and the sample with R_A = 5% had the highest bulk density of 4.34 g/cm³ (ca. 95%TD). The pore shape and the fracture morphology of the samples suggested the formation of a liquid phase. The present results indicated that the two-step mixing process was an universal approach for improvement in the densification of alkali niobate ststem.

Abstract: Consolidation of pyrolyzed powders has been tried by hot isostatic pressing (HIP) without sintering additives, in order to obtain dense non-oxide ceramic bulk materials derived from polymer precursors. Si1.0C1.6N1.3 ceramic powders were derived from a polyvinylsilazane polymer. The polymer was thermally crosslinked at 250oC and pyrolyzed at 1050oC under Ar atmosphere. The pyrolyzed powders were die-pressed into rectangular bars at room temperature and densified by HIP at 1400oC-900 MPa and 1500oC-950 MPa. Dense ceramic monolith, in which pores were not observed by optical microscopy, was obtained by the HIP consolidation at 1500oC-950 MPa. The microstructure of the ceramic monolith was a nano-composite structure consisted of α-Si3N4 and graphite phases. In the compression tests of the HIP-treated sample, slight plastic deformation was observed at 1400 and 1500oC in spite of high compressive stress over 1000 MPa. On the other hand, the sample showed a compressive strain of about 7% at 1000 MPa at 1600oC. The compressive strain of about 11% was achieved at 1700oC.