Preparation Of Nano-powder And Transparent Ceramic Of Yttrium Aluminum Garnet By Single Step Co-precipitation Method

Yttrium aluminum garnet (YAG) is a kind of high performance transparent ceramic material. It has not only the inherent qualities of ceramic, but the excellent optical properties of glass. So it has a broad application prospects in the special window materials, lighting materials, as well as high-performance laser ceramic materials. In this thesis YAG nano-powder was synthesed by one step co-precipitation method. Effects of precipitant concentration, feeding method and reaction temperature on the properties of YAG powder and calcination temperature of YAG powder, forming pressure and holding time on YAG ceramics were researched.When the concentration of Al3+and Y3-were0.15and0.09mol/L respectively, and the mole ratio of was8, the chemical composition of the precursors obtained by forward-titration, reverse-titration and one-step injection at room temperature (25℃) were10[8.9A1(OH)3+1.1NH4Al·(OH)2CO3]·3[Y2(CO3)3·3H2O]、10[7.3Al(OH)3+2.7NH4Al·(OH)2CO3]·3[Y2(CO3)3·3H2O] and10[Al(OH)3]·3[Y2(CO3)3·3H2O] respectively. The YAG nano-powders were obtained by calcining the precursors at900℃for2h. The powders obtained by forward-titration and reverse-titration were of major-phase YAG and a trace amount of YAP, while the powder by one-step injection was of pure-phase YAG. The precursors prepared by different feeding methods were calcined at1000℃for2h, the size of powders obtained by forward-titration, reverse-titration and one-step injection were about85,75and65nm in average diameter respectively. In the meantime, the reaction temperature had a greater influence on the preparation of YAG powders. When the low temperature was not enough to provide the energy for homogeneous chemical reaction, but the high temperature would lead to a complex reaction environment, so it was difficult for low or high reaction temperature to obtain highpurity of YAG powders.In vacuum sintering process,1000℃was a cut-off point ofpowder calcinations. When the powder calcination temperature was1050℃, which would lead to the decrease of sintering activity, it wasdifficult to obtain dense ceramic samples. The forming pressure ofYAG green body also directly affected the ceramic densification. Thehigh forming pressure would not only hinder the mass transfer andmigration process, also reduce the driving force of sintering process, soit was difficult to obtain dense ceramic material. The green dody wasprepared under100MPa and sintered at1750℃for10h, the relativedensity and linear shrinkage reach the maximum value99.45%and32.32%. At the same time, when the holding time was extendedappropriately, it would help improve the transparency of ceramics.In the optimized experimental conditions, the pure cubic YAGpowder with average particle size of about65nm was obtained bycalcining the precursor prepared by one-step injection at roomtemperature（25℃）.With the prepared YAG powders as raw materialand tetraethyl orthosilicate as sintering additive, the YAG green bodyswere formed under100MPa, and then transparent YAG ceramics wereprepared by sintering YAG green dody at1750℃for15h in vacuum.Therelative density and transmittance spectra of transparent YAG ceramicsreach the maximum value99.65%and11.6%.