Study On Microstructures And Properties Of AlN And AlN/C Composites Prepared By Gel Casting

AlN ceramic material have high thermal conductivity, good insulationproperties, low dielectric constant, which are mainly applied to the substrate in themicroelectronics industry and electronic device, so it possesses broad applicationprospect. Because of high sintering temperature, it is difficult to prepare complexshape product and realize industrialization production. AlN/C composite materialshave good corrosion resistance, light weight, good heat conduction performance,which are mainly applied to microelectronic field of radiation, and it has extensiveattention of many researchers.AlN ceramic and AlN/C composite materials were prepared by gelcastingtechnology, with AlN powder and AlN plus C powder as main raw material, chitosanas the organic monomer, acetic acid as dispersing agent, glutaraldehyde as initiator.The reaction mechanism of gelation were determined by Fourier infraredspectroscopy, the rheological property of slurry was studied with digital viscometer,the bending strength of green body was measured with universal mechanical testingmachine. Microstructures of ceramic body were observed by scanning electronmicroscope (SEM). The effects of temperature, pH value, content of chitosan,proportion of raw materials, acetic acid content and solid content et al on the slurryrheological property, properties and microstructures of green body and gelation timeof AlN ceramic and AlN/C composite are studied.The results show that, using acetic acid as dispersant, when pH=3, AlN ceramicslurry dispersant effect is great. With increasing solid content, decreasing acetic acidcontent, the viscosity of slurry increases. The temperature, pH value, glutaraldehydecontent, solid content et al have important impact on the gelation time. Under thecondition of pH=3and solid content reaches to52vol.%, the bending strength ofAlN ceramic body prepared by gel casting technology can reach18MPa. Organicmonomer forms long chain and cross-links with each other, then AlN ceramicpowders are fixed in situ to form three-dimensional network structure. With increasing solid content, green body density increase. AlN ceramic body is pressureless sintering at1750oC with vacuum condition. The materials realize liquid phasesintering mechanism, and solid content has effect on the microstructure uniformity ofAlN ceramic.When the content of acetic acid is1vol.%, glutaraldehyde content is0.7vol.%,AlN and C powder ratio is1:4, with increasing solid and chitosan content, AlN/Ccomposite slurry viscosity increases, the gelation time decreases. With increasingproportion of C, the viscosity of the slurry increases and the gelation time decreasesbecause of big diameter and lamellar structure of C particle. Imide bond (-C=N-)forms through shrinkage of polymerization between carbonyl groups (-C=O) ofglutaraldehyde and amine groups (-NH2) on the chitosan, then certain strength of thegel generates. Chitosan content, acetic acid content, solid content and glutaraldehydecontent have significant effects on the relative density and bending strength of AlN/Ccomposite green body. When the AlN and C powder ratio of1:4, the solid content is50vol.%, the density of AlN/C composite green body is64%and the bendingstrength is15.5MPa. With increasing chitosan content, porosity decreases and thedensity increases of material.