Microwave Processing Of Electronic Oxide Ceramics

According to the principle of microwave heating, the main interest of this dissertation is to systematically investigate the microwave processing of electronic ceramic materials, including microwave sintering of NTC thermistor ceramics, PTC thermistor ceramics, ZnO varistor ceramics, and BST pyroelectric ceramics, and microwave synthesis of fine ceramics powders, microwave annealing of PZT ferroelectric thin films, with comparison to the conventional heating process. The mechanism of microwave sintering in ceramic materials is analyzed according to thermodynamics. The main works of this dissertation are as follows.In the study of microwave sintering technology, a kind of MgACVLaCrO3 insulator is designed, which solve the problem of thermal cracks easily occurred in the rapid heating and cooling of electronic oxide ceramics during the microwave sintering process, produced a homogeneous heating for the samples in the microwave sintering, and improve the production rate of electronic oxide ceramics by microwave sintering. This insulator solve a key problem which obstacle the application of microwave sintering to the production of electronic ceramics. The NTC thermistor ceramics in diameter of 50 mm are successfully microwave sintered without thermal crack by the adoption of this kind insulator which has been granted with China patent.A kind of microwave shielded thermocouple was made for temperature measurement in microwave field. The thermocouple is sheathed with NiCrAl alloy tube to avoid the arcing in the microwave field, and has been applied for temperaure measurement up to 1350. This temperature measuring system has higher accuracy than the infra optic and pyrometer in the applied temperature range.In the research of microwave sintering of Y3+ doped (Bao.eSro.TiO3 PTC ceramics, the results showed that microwave sintering reduced the sintering temperature and total time to 1150 and 4 hrs to obtain the near characteristic parameters of materials, comparing to 1350 and 28 hrs in conventional sintering. In the study of microwave sintering of BaTiO3 PTC ceramics, when the applied microwave power are above than a certain value , the abnormal axial shrinkage of the sintered sample will occur, by the analysis of SEM and XRD, it is found the micro structure and phase are different with conventionally sintered sample, the reason for this phenomenon is due to orientational grain growth by the action of electric field in the microwave sintering process.The ZnO pellets from nanopowders are microwave sintered with comparison to conventional sintering, the microstructure and electrical properties of sintered sampleare analyzed .The results showed that the ZnO varistor materials can be densified by microwave sintering in lower temperature and shorter time, with same grain size as conventional sintered samples. The microwave sintered varistor samples displayed superior electrical properties than conventionally sintered sample, e.g., the ZnO sample microwave sintering at 1100 720 min showed excellent I-V characteristics than the conventionally sintered samples at 1100/120 min, with nonlinear coefficient value, a =46 and leakage current li=Q.3 uA, comparing to conventionally sintered samples, a =35 and Ii=0.9 uA.The (Ba,Sr)TiO3 (BST) powder were prepared by sol-gel processing and microwave sintering technique , their properties were studied and compared with identical powder prepared by conventional technique. The results showed that the synthetic temperature of the BST powder can be reduced from 1100 to 900, The grain size of BST powder can be reduced from 320nm to 50nm. and the BaQ 65Sr0 35TiO3 ceramic with fine grain size (-1 um) can be obtained at 1310/25 min by microwave sintering .The volatility of lead in Pb(Zr,Ti)O3 (PZT) thin films can be avoided by microwave annealing , which is of benefit to the control of lead content and the microstructure of PZT films ,the annealing temperature are lowered in microwave annealing and the micro-cracks are avoided comparing to conventional annealing. Microwave ann...