Hydrothermal-carbothermal Synthesis Of AlON Powders And Sintering Of Its Transparent Ceramics

AlON ceramics are widely used in military fields due to their excellent light transmission and corrosion resistance.At present,most methods for synthesizing AlON powders and ceramics require a high temperature,and the particle size of the obtained powders is large,which is not conducive to the development of AlON transparent ceramics.Hydrothermal-carbonthermal method can reduce the reaction temperature and synthesize ceramic powders with smaller particle size,such as AIN powders,etc,but it hasn’t been applied to the synthesis of AlON powders.This project aims to synthesize nano-sized AlON powders at a relatively low temperature by hydrothermal-carbonthermal method,and sinter AlON transparent ceramics with this powders as raw material.Precursor powders containing the aluminum source and the carbon source was first synthesized by hydrothermal reaction,and the precursor powders were synthesized into nano-sized high-purity AlON powders by carbothermal reduction reaction.Second,the micron-sized high-purity AlON powders were synthesized by the direct nitridation method;Finally,AlON transparent ceramics were synthesized by two kinds of high-purity AlON powders,which were formed by cold isostatic pressing and sintered by high temperature.The effects of raw material ratio and hydrothermal reaction process on the composition and morphology of precursor powders and AlON powders,the effects of carbothermal reduction process and direct nitriding process on the composition and morphology of AlON powders and the effects of sintering process and powder types on transmittance of AlON transparent ceramics were all investigated.The main research conclusions are as follows:1)The precursors which had C-coated AlOOH structure were synthesized by hydrothermal method,As the temperature rose,AlOOH decomposed into Al2O3.C-coated structure can reduce the diffusion distance of C and Al2O3.It’s not need excessive temperature to provide kinetic energy,which made C and Al2O3 close to each other for reaction.So carbothermal reaction temperature was reduced.High-purity hexagonal AlON powders with a polyhedral morphology can be synthesized by hydrothermal-carbonthermal method at 1500℃-1700℃ and the powder particle size is 300nm-500nm.2)When the sintering temperature was the same,high-purity AlON powders which were synthesized by hydrothermal-carbothermal method can sinter transparent ceramics with less porosity.So the transmittance of ceramics was relatively high because of less reflection and refraction of incident light.High-purity AlON powders which were synthesized by hydrothermal-carbonthermal method can sinter AlON transparent ceramics with a transmittance of 71%at 1750℃.But AlON transparent ceramics which sintered at the same temperature by AlON powders synthesizing by the direct nitridation had a transmittance of only 50%.HIP can promote the venting of pores in the ceramics,which can greatly increase the ceramic transmittance with relatively low density.The AlON transparent ceramics which sintered at 1850℃ by high-purity AlON powders synthesizing by hydrothermal-carbonthermal method had a transmittance of only 19%,and the transmittance increased to 53%after HIP.