以往使用微米級Al2O3+Y2O3原料粉末，以固態反應法製備YAG (Y3Al5O12)粉末的過程中，一般歸咎於粉末的合成受限於成分的擴散距離，使煅燒溫度需至1600℃始可得單相YAG，而藉由降低起始反應物之粒徑，使反應物表面積增加，可提高反應物彼此接觸點，促使反應發生，降低活化能，因此原料粉末的尺寸必為合成材料的一項重要因素。然以不同粒徑之原料粉末合成YAG的系統研究尚未被提出，本研究以改變原料粉末之粒徑，觀察其對YAG生成過程的影響。實驗擬使用三種不同粒徑：100 nm (S)，400 nm (M)，700 nm (L)之氧化釔(Y2O3)，分別與固定粒徑(150 nm)之氧化鋁(α-Al2O3)混合為起始粉末，並分別以從室溫升溫與直接置入高溫之快速升溫兩種方式進行煅燒，之後觀察比較YAG合成過程的差異，並計算三系統之YAG生成活化能。實驗結果得知，隨氧化釔粒徑變小，YAM、YAP及YAG之合成溫度亦隨之降低；由定量分析結果並配合YAG生成活化能計算結果可發現，YAG 之生成於不同溫度範圍有不同來源：< 1150℃主要為氧化釔與氧化鋁直接成YAG，生成活化能約100 kJ/mol，為介面控制(Interface control)生成機制；1150-1200℃為YAM及YAP轉換而來，活化能約400 kJ/mol，為擴散控制(Diffusion control)生成機制；> 1200℃則為YAP的轉換或剩餘大粒子之氧化釔反應而來，此部分之活化能於本實驗中不易觀察故無法得知。另外本實驗亦發現使用奈米級起始粉末合成YAG，YAM、YAP、YAG三相均可於快速置入高溫熱處理後瞬間合成，其中生成速率與消失速率均以YAM為最快。

Due to micron-scaled Al2O3+Y2O3 starting powders for synthesizing YAG (Y3Al5O12) powder using via solid state reaction, the temperature for pure YAG formation usually performed above 1600℃. Lowering the particle sizes of reactants could raise contact points, so as to promote the reaction to occur. Therefore, the size of starting powders must be one of crucial factors for material synthesis. However, a systematic research on YAG formation by using different size of starting powders has not be done so far. In this study, the difference in the process of YAG formation caused by reactant particle sizes was observed. The starting powders were mixed respectively from α-Al2O3 (150 nm) and Y2O3 with three different sizes ( 100 nm (S), 400 nm (M), and 700 nm (L)) , then calcined by two ways:(1) treating with a heating rate of 10℃/min from R.T to specific temperatures and (2) placing in high temperatures rapidly. After heat treatment, the comparison of YAG formation processes occurred in three systems was made and YAG formation activation energies (Ea) for three systems were calculated by the isothermal kinetics.
The results are showed as following. The smaller the size of Y2O3 was, the lower temperatures of YAM, YAP and YAG phases formed. Three mechanisms should be existed in three different temperature ranges in the process of YAG formation. (1) Below 1150℃, YAG was formed from reaction between Al2O3 and Y2O3 directly, and the Ea of YAG formation was about 100 kJ/mol caused by interface-control mechanism; (2) between 1150-1200℃, YAG was formed from YAM or YAP reacted with Al2O3, and the Ea of YAG formation was about 400 kJ/mol attributed to diffusion-control mechanism; (3) above 1200℃, YAG was transformed from YAP or the residual Y2O3 reacted with Al2O3, and the mechanism was difficult to be observed in this study. The YAG, YAM, and YAP could be synthesized instantaneously as the samples were subjected to high temperatures rapidly, while nano-scaled powders were used as starting materials. Among these phase, YAM showed the fastest formation rate and disappearing rate.

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