本文探討採用粒徑 100 nm 原料粉末製成之 α(+θ)-Al2O3 生坯，以二階段燒結法製備微奈米級高純度氧化鋁於異常晶粒成長前的燒結行為與機械特性。
採用的原料粉末係以晶徑 25 nm θ-Al2O3 粉末，以之壓坯，於溫度 1200°C下，不同持溫時間進行相變煅燒，生成 65-80% α-Al2O3 含量及剩 20-35% θ-Al2O3之 α(+θ)-Al2O3 生坯。此生坯中 α-Al2O3 及 θ-Al2O3 之晶徑分別為 50-100 nm 及30 nm。生坯密度接近 60% T.D.。之後摻雜 1000 ppm 的 Mg2+進行燒結，再進行 SEM、燒結體密度及硬度分析。異常晶粒成長建立在燒結體內直線晶界的比例(Straight edge percent, SEP)接近 100%及平均每顆晶粒的直線晶界數量(Straight edges/Grain, SEG)接近 6 條。確認燒結體皆在異常晶粒成長前的階段。
結果顯示於不同二階段燒結條件下晶粒尺寸、相對密度與生坯的 α- Al2O3含量有關。相同燒結條件下，相對密度於 α- Al2O3 含量為 75±2.5%時會有最大值。於真空條件下以 T1 (1500℃)- T2 (1420℃)/ 6h 二階段燒結，相對密度為 99.9%，晶粒尺寸為 1.13 μm。此時燒結體內直線晶界的比例(SEP)< 100%及平均每顆晶粒的直線晶界數量(SEG)<6 條。
機械特性僅探討燒結體的硬度(Vicker’s hardness)，密度大於 95%T.D 硬度均可超過 25 GPa。當晶徑大於 0.4μm 後，同一晶徑下，提高陶瓷體的密度可使其硬度略升。對應於此，同一密度陶瓷體晶粒越小硬度越高。當密度大於 98.5%後，以硬度而言，微結構之完整性影響不彰，能維持細晶粒比再提高燒結體之相對密度，更具實質意義。.

In this paper, the sintering behavior and mechanical properties of α(+θ)-Al2O3 green body made of starting powder with a particle size of 100 nm were investigated by a two-stage sintering method to prepare micro-nano-scale high-purity alumina before abnormal grain growth.
The raw material powder is the θ-Al2O3 powder with a crystal diameter of 25 nm, which is compacted and subjected to phase transformation calcination at a temperature of 1200°C., the α(+θ)-Al2O3 green body with 65-80% α- Al2O3 content and remaining 20-35% θ-Al2O3 was produced. The crystal diameters of α- Al2O3 and θ-Al2O3 in this green body are 50-100 nm and 30 nm. The green density is close to 60% T.D. After that, doped 1000 ppm of Mg2+ for sintering, and then SEM, density and hardness analysis were performed. The abnormal grain growth is based on the straight edge percent (SEP) in the sintered body being close to 100% and the straight edges/Grain (SEG) being close to 6. It was confirmed that the sinter bodies were all at the stage before abnormal grain growth.The results show that the grain size and relative density are related to the α-Al2O3 content of the green body under different two-stage sintering conditions. Under the same sintering conditions, the relative density will have a maximum when the content of α- Al2O3 is 75±2.5%. It was sintered in two stages of T1 (1500℃)-T2 (1420℃)/6h under vacuum conditions, the relative density was 99.9%, and the grain size was 1.13 μm. At this time, the proportion of SEP is < 100% and the the SEG is< 6.The mechanical properties only discuss the Vicker's hardness of the sintered body, the density is greater than 95% T.D hardness can exceed 25 GPa. When the crystal diameter is greater than 0.4 μm, under the same crystal diameter, increasing the density of the ceramic body can slightly increase the hardness. Corresponding to this, the smaller the grain size of the ceramic body with the same density, the higher the hardness. When the density is greater than 98.5%, in terms of hardness, the integrity of the microstructure is not significantly
affected, and it is more meaningful to maintain the fine grain ratio.

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