Study On The Preparation And Mechanical Properties Of AlN/C Composite Prepared By Gelcasting Method With Environmental Protection System

In this paper, the surface water-resistance treatment of high purity AlN powder was firstly carried out with stearic acid and tween 80. Infrared spectroscopy,differential thermal analysis, XRD analytical method were used to study the surface modification mechanism of AlN powder. The effect of stearic acid content and ball milling time on the stability of modified AlN powder was discussed.AlN/C composite green body was prepared by the gelcasting method with the modified AlN powder and C powder as the main raw material, with the agarose and gelatin-urea as environmentally friendly gelcasting system, and then the sintering process was carried with the vacuum pressureless sintering method. The stability and rheological behavior of slurry was studied by the viscometer, the curing mechanism of agarose gel system and the gelatin-urea gel system was investigated using infrared spectroscopy analysis method, the microstructure of ceramic green body and sintered body was observed by the scanning electron microscopy(SEM), the material phase composition was investigated by the XRD analysis, the mechanical properties of green body and sintered body were measured by the three point bending test method.The effect of temperature, p H value, organic monomer content and solid content on slurry properties, gelation time, relative density, microstructure and mechanical properties of the green and sintered body was investigated.Experimental results show that the surface modification effect of the AlN powder is the best when the content of stearic acid is 10 wt.% and the content of tween 80 is 3 wt.%. The surface modified AlN powder has strong warer-resistance property, good chemical stability in warm water from 20 to 60oC, and the p H value of the solution is stable. The main phased is AlN crystal phase and there is not other crystalline phase in the surface modified AlN powder soaking in water for 24 hours.The modified AlN powder has strong stability in aqueous ball milling medium, thenitrogen content of modified AlN powder remains stable under the high shear stress of 3 h.When the AlN/C composite green body is prepared by the gelcasting method with agarose as the gelcasting system, the three-dimensional net structure forms through abundant hydrogen bonds, and the raw powders solidify in situ with temperature decreasing. The viscosity of slurry increases, sedimentation increases,and stability decreases with the agarose and solid content increasing. The agarose and solid content have influence on the relative density, microstructure and mechanical properties of the green and sintered body. When the solid content in the slurry is 50 vol. %, agarose content is 0.5 wt. %, the flexure strength of green body reaches the highest value, and 24.6 MPa, and the flexure strength of sintered body reaches the highest value, 46.78 MPa.When the AlN/C composite green body was prepared by the gelcasting method with gelatin-urea as the gelcasting system, urea in the slurry was decomposed by the initiator urease, the gelatin can form hydrogen bonds, the stable netwok structure is formed, then the raw powder solidity. The viscosity of slurry increases, gelation time decreases with the gelatin and solid content increasing. The gelatin and solid content have influence on the relative density, microstructure and mechanical properties of the green and sintered body. When the solid content of the slurry was 50 vol. %, the mass fraction of gelatin was 10 wt. %, the flexure strength of green and sintered body reaches the highest value, and the microstructure is uniform. The property of AlN/C composite with gelatin-urea as the gelcasting system is lower than that of the composite with agarose as the gelcasting system.