【作者】 陈智慧；

【导师】 李江涛；

【作者基本信息】 中国科学院研究生院（理化技术研究所） ， 物理化学， 2007， 博士

【摘要】 钇铝石榴石(Y₃Al₅O₁₂, YAG)具有良好的光学性能,是一种重要的激光基质材料。与YAG单晶相比,YAG多晶陶瓷的优势在于可制备出满足大功率激光器所需的大尺寸样品并实现高浓度的掺杂。1995年日本Krosaki公司首次制备出了高质量的Nd:YAG透明陶瓷并实现了激光输出,这充分证明了采用合适的工艺制备透明陶瓷,并以之取代单晶的可行性。目前美国已经开发出激光输出功率达67kW的固体激光器,我国对固体激光器的研究与国外存在巨大差距。面对全球的竞争,我们必须以创新的思维和技术推动国内透明陶瓷的快速发展,使Nd:YAG陶瓷激光器逐步实现kW级激光输出,并实现大尺寸和大规模的生产,进而使我国在工业应用激光材料上占有一席之地。要实现以上目标,必须对YAG粉体制备技术和透明陶瓷材料的烧结制备技术进行深入的研究和开发。本文重点研究利用改进的共沉淀法制备YAG纳米粉体的工艺,并以制备的YAG纳米粉体为原料制备高透过率的YAG透明陶瓷。改进的共沉淀法制备YAG纳米粉体的研究表明,以正戊醇为脱水剂,用减压蒸馏沉淀法可以避免颗粒间的硬团聚,合成分散均匀的YAG纳米粉体。1100℃煅烧2 h后YAG的平均粒径为50nm。通过研究YAG纳米粉体的真空烧结致密化行为和晶粒生长行为,得到了YAG坯体密度与烧结温度的烧结回归方程以及YAG的等温烧结动力学方程。动力学方程结果表明:YAG的烧结和晶粒生长动力学受晶界扩散控制。在1750℃真空烧结5¹8小时制备的YAG透明陶瓷,经过1450℃流动空气氛下热处理2小时后,对800nm波长的中波红外光的透过率为54⁷9.7%。热处理可以使YAG样品的透过率较热处理前提高19³2%。首次采用两步真空烧结工艺制备了YAG透明陶瓷。两步烧结工艺的技术思路:以工艺手段促进晶界扩散,抑制晶界迁移。本文采用的具体工艺条件是将试样首先加热到1750℃¹800℃的高温,然后,不经保温即快速降温至第二阶段的烧结温度1550℃¹600℃,在第二烧结温度下继续保温10小时。用这种两步真空烧结制备的YAG透明陶瓷在可见光下透过率最高可达到74%。当两步烧结的最高温度为1800℃,保温温度为1550℃时可有效抑制晶界迁移,避免晶粒异常长大,致密YAG陶瓷的平均晶粒度为6μm,对可见光的透过率达到71%。采用热压烧结工艺在1650℃制备了可见光下半透明的YAG陶瓷。该部分工作的意义在于:发现了以微米级的Al2O3和Y2O3为原料,采用固相反应热压烧结工艺同样可以制备YAG透明陶瓷,而且平均晶粒度仅为2.2μm,较之以纳米级YAG粉体为原料以真空烧结工艺所制得的透明YAG陶瓷的晶粒尺寸降低约1²倍。这表明透明多晶YAG陶瓷的制备并非必须以纳米粉末为原料。而最终获得的YAG陶瓷的微观结构特征是决定其透光性的根本因素。更多还原

【Abstract】 Yttrium aluminum garnet (Y3Al5O12, YAG) is an important laser material due to its excellent optical properties. Comparing with single crystal YAG, polycrystalline YAG ceramic exhibits many advantages. The ability of polycrystalline YAG ceramic incorporated with very high concentrations of Nd provides the possibility of high power laser. The first transparent Nd: YAG ceramic with nearly equivalent refractive index and thermal conductivity with that of a YAG single crystal was reported in 1995 by Ikesue et al, who demonstrated the potential of substituting YAG single crystal with polycrystalline YAG ceramic if proper synthesis methods are adopted. Although polycrystalline Nd:YAG laser ceramic has been produced and 67kW continuous wave laser operation was obtained in America, the fundamental relationship among the sintering process, microstructure and the optical properties of transparent laser ceramics has not been systematically studied yet.In this dissertation, YAG nanopowders were synthesized by a modified co-precipitation technique, and the fabrication of transparent YAG ceramics using the as synthesized nanopowders was investigated. A hydrate precursor of yttrium aluminum garnet (YAG) was synthesized by the co-precipitation method, in which a distillation process was used with n-amyl alcohol as dehydration solvent. By preventing the connection among particles, hard agglomerates were avoided and well dispersed nanopowders were obtained. The average particle size of the nanocrystalline YAG powders calcined at 1100℃was about 50nm. The sintering regression equation and the kinetic equation for the densification of YAG ceramic were obtained by manipulate the densification behavior and the grain growth behavior of YAG compacts during the sintering process. The kinetic equation revealed that both the sintering mechanism and the grain growth of YAG ceramic were dominated by grain boundary diffusion. Transparent YAG ceramics were prepared by vacuum sintering at 1750℃for 5~18hours. The transmittance of the YAG ceramics heated at 1450℃for 2 hours under flowing air reached 54~79.7% at a wavelength of 800nm, which was 19~32% higher than that without the heat-treatment.A two-step sintering method was used to fabricate transparent YAG ceramics, the YAG pellets were rapidly heated to a peak temperature (1750℃or 1800℃) without holding time, and then immediately cooled down to a lower temperature (1550℃or 1600℃) and held for 10 hours. The maximum transmittance of the YAG ceramics by the two step sintering method can reach 74%. When the sample was sintered at 1800℃as the first sintering step and held at 1550℃for 10 hours as the second step, the grain-boundary migration was effectively suppressed while the grain-boundary diffusion was enhanced. The mean grain size of the densified YAG ceramic was 6μm and the transmittance was 71%.Translucent YAG ceramics were fabricated by reactive hot pressure sintering at 1650℃for 90 minutes using micro-sized Al2O3 and Y2O3 powders as reactants. The grain size of the hot- pressed YAG ceramic is much smaller than that of the samples prepared by vacuum sintering. This work reveals that YAG nanopowder is at least not the exclusive starting material for preparing transparent YAG ceramic. In contrast, the final microstructure is the most important factor to determine the transmittance of the YAG ceramic.更多还原