以反應燒結法制備多晶釔鋁石榴石陶瓷

Abstract

釔鋁石榴石(YAG)由於具備出色的物理、化學性質以及立方體結構，故其一直以來為製備光學透明陶瓷的理想材料。本實驗採用氧化釔與氧化鋁搭配燒結助劑二氧化矽，比較兩種不同固態燒結路徑:(1)典型固相燒結:先高溫(1500°C)煅燒形成均相YAG再行燒結; (2)固相反應燒結: 混和氧化物在升溫過程中，燒結伴隨著生成YAG反應。在本研究中，在空氣氣氛下進行燒結，最高溫度為1650°C。使用傳統固相燒結法時，煅燒生成之YAG粉末即使透過長時間球磨細化，仍會有輕微燒結現象而成硬凝團，故粉末之燒結活性較差，進而造成燒結後密度過低。本實驗中透過反應燒結法省略了高溫煅燒步驟，進一步探討不同製程參數如:粉末粒徑、升溫速率、燒結溫度以及持溫時間對於YAG反應燒結之影響。此外，本實驗亦探討添加燒結助劑二氧化矽的影響，燒結緻密速率及晶粒成長皆隨著添加二氧化矽量越多而顯著提升。然而，過多的燒結助劑會造成二次相或析出物產生。本實驗中，最佳製程條件為: 採用反應燒結法，當添加0.14 wt% 二氧化矽時，使用升溫速率10°C/min，在1650°C持溫兩小時得到相對密度約97.4%，晶粒大小約4.9 um且無二次相析出之YAG多晶陶瓷。

Y3Al5O12 (YAG) has been seen as an ideal candidate for optical transparent ceramics due to its highly symmetries garnet structure. The solid state processing is popular in ceramic processing due to its feasibility for the fabrication of ceramic products. There are two approaches adopted in the present study: (1) traditional solid state sintering and (2) solid state reaction sintering. The major difference between these two processes involves a reaction at elevated temperature. The calcined YAG powder is used as the starting material for traditional sintering, while the Y2O3-Al2O3 powder mixture for reaction sintering. Two processing routes are conducted in air with a maximum sintering temperature at 1650°C. For the traditional sintering, some hard agglomerates are formed during the calcination of YAG powder at 1500°C. The sinterability is thus poor due to the presence of these hard agglomerates. As a consequence, the density of traditional sintered YAG is low, less than 91.8% when the sintering temperature is 1650°C. The reaction sintering avoids the use of calcination process. The formation of YAG is taken place at the same time with the densification process. In the present study, several processing parameters such as particle size, sintering temperatures, heating rates and dwell time, are evaluated. Moreover, the use of a sintering additive, silica, is also investigated. Increasing the doping level of SiO2 would facilitate both densification and grain growth. However, some precipitations or inclusions are observed when the doping level of SiO2 is higher than the solubility limit (<0.1 wt%). The optimum amount of silica is 0.14 wt%. The density of the reaction sintered YAG reaches 97.4% after sintering at 1650°C for 2h and no second phase particle or inclusion was observed.