Key Engineering Materials Vols. 280-283

Abstract: In the industrialization of gelcasting, storage of ceramic slurry has been one of the key problems that must be solved. Except for sedimentation of ceramics particle, solidification properties of slurries were also affected after long-term storage. In this article, some factors in the process of slurry were discussed, and corresponding solution methods were put forward.

Abstract: Gelcasting is a novel ceramic forming process for fabricating products of complex-shaped ceramics. In this contribution, the gelcasting process is applied to manufacture green body of microwave ceramic components for resonators, oscillators and antennas. Calcined powders, dispersant and organic monomers are mixed together by ball-milling to acquire high solid loading slurry with low viscosity. After addition of initiator and catalyst, the slurry is cast into a non-pours mold and then polymerized. The slurry is thus solidified in situ and the green bodies with the desired shapes are obtained. The dried body is rather strong and can be machined so as to get more precise or complex-shaped components. Then the green bodies are sintered at high temperature. The microwave properties (εr, Q, τf) and microstructures of the ceramics prepared by gelcasting are compared with those of die-pressed ones.

Abstract: A novel process, gel-tape-casting, is employed to fabricate LSGM thin dense sheets in aqueous AM system. The influences of powder properties, dispersant and other additives were discussed and relevant processing parameters were also explored. The slurry of LSGM with a high solid loading about 33 vol.% was successfully obtained.

Abstract: As a good binder for aqueous Al2O3 suspensions tape-casting process, a commercial styrene-acrylic latex binder had been investigated. This paper studied on the rheological behaviors of the suspensions and drying process of aqueous slurries with latex binder system, and the research results indicated the rheological behaviors was affected by pH value, solid loading and dispersant (PAA-NH4) additives; and the drying speed of slurries was most decided by drying temperature and slurry coating thickness.

Abstract: Tape-casting technology is introduced to fabricate metal-arrayes patterned ceramic substance containing periodic multilayer silver wire structure in the low dielectric constant ceramic matrix for microvave bandgap materials and left hand material application. One important advantage of the metal patterned ceramic substance comparing with the periodic structures fabricated on the printed circuit boards (PCB) using a shadow mask/etching technique is that complex multilayer structure can be designed and fabricated in the ceramic body as well as on the surface by the tape-casting process, while the shadow mask/etching technique technology can only design patterns on the surface of printed circuit boards. An Hp8720ES network analyzer was used to measure the transmission properties of the metal patterned ceramic substance. The experimental result shows some novel properties at X-band microwave frequencies. The metal patterned ceramic substance can be used in the microwave communication, such as microwave antenna.

Abstract: Solid oxide fuel cell positive-electrolyte-negative (SOFC PEN) structures were fabricated by complex tape casting and co-firing technologies. La0.8Sr0.2FeO3 (LSF20) powders for cathode and 8 mol% yttria-stabilized zirconia (YSZ) powders for electrolyte were synthesized through glycine-nitrate process (GNP). The slurries for cathode, electrolyte and anode (NiO-YSZ) were cast in sequence to form green PEN structures. Co-fired at 1200oC for 6 h, there were no delamination, crack or curl occurred in PEN structures. SEM analysis showed that YSZ electrolyte film had been sintered to full dense and the interface combinations were compact. No evident reaction product between YSZ and LSF20 was detected by XRD.

Abstract: PZT-based slurry with Newtonian behavior was prepared for tape casting. The viscoelasti cproperties of the slurry were studied. High quality of green tape and well sintered of PZT-based thick films are obtained using the PZT-based slurry with Newtonian behavior.

Abstract: Pure Strontium barium niobate, Sr0.5Ba0.5Nb2O6 (SBN50), was synthesized successfully by spark plasma sintering from two mixtures: SrCO3/BaCO3/Nb2O5 mixtures and the mixtures calcined at 800oC. The phase identification of the SBN crystalline grains was evaluated by X-ray diffraction analysis, and the formation mechanism was discussion based on the XRD results at various temperatures. They are different when SrCO3/BaCO3/Nb2O5 powder mixtures and the mixtures calcined at 800oC was chosen as the raw materials.

Abstract: NiAl2O4-metal composite material is an effective candidate for anodes used in industrial production of aluminium as a substitute for graphite anodes. NiAl2O4-Cu-Ni anode was prepared by spark plasma sintering in present paper. According to the density and electrical conductivity of the anodes, the optimal process parameters were given and the result showed that sintering temperature had the most significant influence on the properties of the inert anodes. Moreover, NiO was added to the inert anodes. The results showed that adding NiO will highly increase electrical conductivity of the inert anodes. SEM and optical microscope were applied to study the mechanism of the effect of NiO on the inert anodes.

Abstract: Fine grained and dense dielectric ceramics of the BaO-Nd2O3-TiO2 system have been fabricated by the most advanced Spark Plasma Sintering (SPS) technology, whose average grain size is about 100nm as determined by SEM. XRD showed that the diffractive peak of the sample was broadened clearly. The nano-ceramic microstructure formed by SPS is due to the high pressure up to 50 MPa, low temperature (1000°C) and fast sintering (1 minute). The BaO-Nd2O3-TiO2 ternary nanoceramic sample, which consists of the main phase Nd2Ti2O7 with perovskite-like layer structure (PLS) and the secondary phase BaNd2Ti4O12（Ba4.5Nd9Ti18O54）with perovskite-like tungsten bronze structure, was prepared for the first time by rapidly sintering nano-particles of the xBaO×(0.35-x)Nd2O3×0.65TiO2 compound. Those two phases are formed in BaO-Nd2O3-TiO2 micron-grained ceramics prepared by normal sintering of the nano-particles at 1300°C, resulting in good dielectric characteristics for microwave ceramics; however, dielectric characteristics are significantly degraded in the SPS-sintered samples probably due to the carbon contamination from the graphite SPS dies.