The Effects Of Additive On Preparation Of α-Al₂O₃ Powers By Hydrothermal Synthesis

α-Al₂O₃ has super performance of physical chemistry:the hardness of diamond,the low friction factor,the low conductivity,the high temperature conductivity.α-Al₂O₃ can be used in laser host material,semiconducting material,high voltage device,optics device and various precision mechanical accessory.This dissertation studies the technology and performance of synthesisα-Al₂O₃ by addingα-Al₂O₃ and NH₄HCO₃ during alkoxide-hydrolysis.XRD,SEM,size analysis and the analysis of specific surface area are used to characterize the samples and to study the effects of different synthesis conditionds on the properties ofα-Al₂O₃.The results indicate that,α-Al₂O₃ as crystal seed added to synthesizeα-Al₂O₃,can reduce the transformation temperature ofαphase from above 1200℃to 1100℃;the maximal merit of the way is that the way can reduce the transformation temperature of a phase by the condition of no reducing purity;the quantity of crystal seed,the dispersing time of crystal seed,hydro-thermal condition can have effect on microcosmic morphology ofα-Al₂O₃;when the temperature of hydro-thermal is 200℃,there is optimal condition of dispersing;at the same time,the diameter of particle is 200nm;PEG2000 has great effect on granularity,but has no effect on microcosmic morphology.NH₄HCO₃ as modifying agent is added to synthesize mid-product NH₄Al(OH)₂CO₃ (AACH);AACH can be decomposed under high temperature getting the gas of NH₃,CO₂,H₂O, and which can make the power ofα-Al₂O₃ loose comparatively;the results indicate that,as the condition of n(NH₄HCO₃)/n(Al³⁺)=3.0,140℃of hydro-thermal temperature,α-Al₂O₃ has been dispersed well;at the same time,the diameter of particle is 250nm;PEG2000 has no effect on granularity and microcosmic morphology.