Advanced Materials Research Vols. 941-944

Abstract: 0.95MgTiO₃-0.05CaTiO₃ (95MCT) microwave dielectric ceramics was prepared solid-state reaction method. Effect of H₃BO₃ additive and forming pressure on sintering process, microstructure and microwave dielectric properties of 95MCT were investigated. The result showed that the additive of H₃BO₃ can lower the sintering temperature of 95MCT, and improve the densification of 95MCT. MgTi₂O₅ was found as mesosphere, which can be effectively suppressed through the additive of H₃BO_3. Excellent microwave dielectric properties of ceramics was obtained when the H₃BO₃ additive was 0.50wt%. The best value of dielectric constant (ε_r), quality factor (Q×f) and temperature coefficient of resonant frequency (τ_f ) of 21.54, 67,286GHz and-4.1ppm/^oC was obtained for the ceramics with sintering 1220^oC for 2h.

Abstract: The structure material corrosion in liquid lead or lead-bismuth eutectic (LBE) is a tremendous limitation of the development of lead cooled fast reactors and accelerator driven sub-critical system (ADS). Keeping a certain oxygen concentration can prevent the steel pipe from corrosion by LBE. Through dissolution and precipitation of PbO ceramic has been found to control the oxygen concentration successfully. This paper presents research on a new technology of processing lead oxide ceramic. The raw material, pure lead oxide powder and deionized water, without any other chemical substances, were dry-pressed, placed in sample holder and heated in household microwave oven. Compare with conventional sintered ceramics, the microwave sintered lead oxide ceramics show better density, greater hardness. The results show that this promising technique has distinguished characteristics of energy-saving, rapid processing and better hardness and microstructure.

Abstract: This paper introduces a kind of rotary surface processing technique which is realized through installing a main shaft on common digital control wire-electrode cutter to drive rotary workpiece. Then the discharge machining test is conducted to study the surface roughness which is the main factor influences the surface quality, and then it comes to a test conclusion that installing electrode wire restrainer and auxiliary electrode device can improve the machining surface quality of rotary surface discharge. It has also provided the basis for further optimizing machining parameters in later study.

Abstract: It was investigated that the effect of wear resistance of high-alumina ceramic with a series of Tb₄O₇ additives. It showed that wear resistance of ceramic firstly increased and then decreased with increasing of Tb₄O₇ doped. And we found that microscopic played the vital role to affect wear resistance of alumina ceramic, decreasing grain sizes would improve the wear resistant. Terbium ions dissolved in liquid phases and the second phase of Tb₃Al₅O₁₂ appeared would improve microscopic of ceramic, taken grain sizes small and made ceramic density. Doped 0.2wt% Tb₄O₇, alumina ceramic with small grain sizes had better wear resistance than other ceramic.

Abstract: As for the liquid-phase sintered (LPS) Al₂O₃ based on the CaO-MgO-Al₂O₃-SiO₂ (CMAS) system, we found a strange phenomenon. It is commonly acknowledged that, the sintering temperature should be high corresponding with the increase of the content of Al₂O₃ in a special system. However, when the content of Al₂O₃ is limited within 95-98wt%, the conclusion is opposite. It means that there is a low-temperature sintering-tunnel. What’s more, as wear resistant materials, the wear rate of alumina ceramics reduces with the increasing of the content of Al₂O₃ among 95-98wt%. In this paper, taking industrial alumina as raw material, we obtain low-wear-rate high-alumina ceramics by conventional sintering in CMAS system. We explain and analyze the condition from the perspective of crystalline phase and microstructure by XRD and FESEM. The results show that the 98 porcelain is of better wear resistance and indicate excellent prospect in the fabrication of lower wear rate of high-alumina ceramics.

Abstract: In order to improve the wear resistance and reduce the sintering temperature of alumina ceramics, Y₂O₃ powder added in the system of MgO-CaO-SiO₂-Al₂O₃ alumina ceramics were prepared by the technique of pressureless sintering. The properties of the ceramic samples were investigated by the measurements of bulk density, wear rate, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the wear rate of alumina ceramic contenting Y2O3 of the 0.8wt% is 0.041‰. Adding the yttrium oxide to the raw materials and then calcine them to ceramics, which can reduces the sintering temperature, promote the densification and improve wear-resistant property of alumina ceramics.

Abstract: A analytic method for the calculation of the electrical characteristics of semiconducting ceramics is suggested. This paper put forward the concept of effective carrier concentration. Electrical characteristics under extra electric field have been calculated by the method of tilted energy band. The non-linear current-voltage characteristics with different grain sizes has been obtained. The results pointed out that the current-voltage characteristics divide into three regions: Linear region before breakdown field, nonlinear region near breakdown field and upturn region after breakdown field; The grain boundary barrier leads to the strong non-linear characteristics, which has nothing to do with the grain size. With the grain size decreasing, the breakdown field increases. The results are compared with experimental data.

Abstract: As a new promising integrating and packing technology, the low temperature co-fired ceramic (LTCC) technology shows great potential in the microelectronics field and attracts great attentions for the scholars at home and abroad. In this paper, the practical application of LTCC is introduced and the emphasis is focused on the ways to the main problems in the application. As to this point, some advices are also given for the future development.

Abstract: Al₂O₃–ZrO₂ ceramic composite samples were prepared using Al₂O₃–ZrO₂ composite powder synthesized by sol-gel processing as the main starting material and zirconia gel as the binder. Then the mineral phases were analyzed by X-ray diffraction (XRD) and the crystal bonding mechanism was analyzed by scanning electron microscopy (SEM). The results show that: 1) the mineral phases were monoclinic zirconia, tetragonal zirconia and corundum. The microstructure shows an alumina-zirconia diffusion mosaic structure and the grain boundary interface with direct bonding state. 2) The crystal growth model was the Ostwald dual growth model of the alumina and zirconia grains, and the crystal bonding mechanism was that the intragranular zirconia grain exited within the alumina grain and the intergranular zirconia grain exited during the alumina grain boundaries.

Abstract: According to the characteristics that purple red of nixing pottery contains an amount of calcite; different samples were fired with different content of calcite in the mud and varying temperature under oxidizing conditions. The phase composition and microstructure were analyzed. The results show that number and size of pores in the sintered samples increased and pore morphology changed from irregular closed hole to round closed then converted to irregular inter-connected one along with the increase of calcite content. As calcite content in the mud increases the viscosity of liquid phase decreases while the crystalline phase gradually increased as sintering, thus wollastonite phase transformed into eutectic phase of aluminum scapolite and wollastonite, and quartz content gradually reduced. Higher sintering temperatures and content of calcite were helpful to the reduction in viscosity, as calcite content increased gradually, the amount of liquid phase increased at first then decreased.