Study On The Process And Mechanism Of Microwave Sintering Preparing ZTA Ceramics

Zirconia-toughened-alumina(ZTA) ceramics were used widely due to perfect properties, which were mechanical strength at high temperatures, thermal shock resistance, wear and oxidation resistance, low thermal conductivity, and the close match between their thermal expansion coefficients. Microwave sintering promoted the density of materials by materials dielectric loss absorbing microwave. The special heating mode that was the combining of thermal effect and non-thermal effect could improve the materials performances. Meanwhile, microwave sintering included these advantages such as efficient, energy saving and environmental protection. Firstly, this topic prepared the raw materials of ZTA ceramics, then prepared ZTA ceramics and special shape ZTA products by microwave sintering. Meanwhile, this subject designed special auxiliary-heating insulation device for microwave sintering of special shape ZTA products. The thesis explored the effect of microwave pyrolysis and silica carbide on the characteristic of raw materials by the analysis of matter phase, particle size distribution and micrograph. The effect of silicon carbide on microwave heating process was researched by the curve of power and temperature. In addition, this paper explored the effect of microwave and silica carbide particle on the structure and properties of ZTA ceramics by analyzing XRD, SEM, density, bending strength, and Vickers-hardness. The mechanism of action of microwave and material was revealed.Partially stabilized zirconia(3Y-ZrO2)/SiC and α-Al2O3 powders were produced by microwave pyrolysing related precursor with α-AlOOH, zirconium oxychloride and yttrium nitrate as raw materials. The research results showed that pure α-Al2O3 powder could be produced by microwave pyrolysing α-AlOOH, silicon carbide formed the microwave heating spot that promoted pyrolysis progress when3Y-ZrO2/SiC powder was prepared by microwave heating. 3Y-ZrO2/SiC powder contained more tetragonal phase than 3Y-ZrO2 powder. The average particle size of3Y-ZrO2/SiC powder gradually increased with the increase of microwave pyrolysistemperature(700o C, 50nm; 900 o C, 200nm).The powders which were produced by microwave pyrolysis were used. ZTA ceramics were prepared by microwave sintering with self-made auxiliary-heating insulation device. The results proved that density, bending strength, and hardness respectively reached to 97% of theoretical density, 452 MPa and 13.3GPa at 1500 oC with holding 30 min. Large size special-shape ZTA ceramics(seal valves) were successfully speedy sintered using microwave with self-design special auxiliary-sintering insulation device in this topic. Density, bending strength and hardness were respectively 99%, 435 MPa and 13.9GPa at 1500 oC with holding30 min. The sintering time of special shape ZTA ceramics ring was 250 min. By contrast, the sintering time of traditional using resistance furnace was 24*7h.The particle size of zirconia was smaller by microwave pyrolysing precursor containing silica carbide, this phenomenon was related to shorter pyrolysis time due to the heating spot effect of silicon carbide. The ladder type heating mode of microwave sintering ZTA ceramics reduced relatively sintering time by 20 min due to the addition of silica carbide. Silica carbide absorbed microwave firstly that made more uniform sintering of ZTA ceramics and caused local oriented growth of zirconia increasing the bending strength. This subject proposed local heat compensation principle by the successful sintering of industrial ZTA ceramic eccentric rings.