Synthsis of nano-structured ceramics by electromagnetic-assisted processing

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Electromagnetically-assisted effects on the materials characters in the consolidation of powder materials were investigated in the millimeter-wave and pulsed high current (or SPS) heating processes and it was tried to develop nano-structured ceramics with the two processes. The following results were obtained ;1) It was found that ytterbia-base sintering aids are very effective for low temperature rapid sintering of A1N and Si3N4. Especially, A1N with higher thermal conductivity than 200W/(m・K) was successfully synthesized in the conditions of one-order shorter sintering time and 200cC lower temperature than those in conventional method.2) In the millimeter-wave sintering of A1N arid Si3N4, it was found that the composition of sintering aid should be designed so as to correspond the composition of intergranular phase in the sintered A1N to eutectic one in the system of Al2O3-Yb2O3. Further, successful synthesis of the A1N with about 150W/(nr K) at 1500°C using a aid of CaO-Al2O3-Yb2O3 … More system shows high possibility of producing a cheep A1N.3) It was succeeded to produce dense nano-structured anatase with grain size less than 300nm by using pulsed high current heating (SFS) process. Further, z-axis directional preferential orientation can be generated by consolidating at a temperature below the temperature of anatase-rutile transition, and the degree of preferential orientation can be controlled by the change of current and pressure.4) Formation of solid solution between strontium and barium titanates by pulsed high current heating (SPS) method was detected at 200°C lower temperature than that in the conventional method, resulting in verification of the enhanced mass transfer under the pulsed high current filed.5) Dense nano-structured alumina with the grain size less than 300nm was successfully synthesized by sintering alumina nano-powder of 100nm at the low temperature (1150°C) and a short time (10 min) using pulsed high current heating (SPS) method. In the use of alumina nano-powder of 230nm, dense nano-structured alumina with the grain size less than 500nm could be also synthesized at 1200°C using the same method. Less