Effects of SiO2, CaO2, and MgO Additions on the Grain Growth of Alumina
Effects of SiO2, CaO2, and MgO Additions on the Grain Growth of Alumina
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DOI：
10.1111/j.1151-2916.2000.tb01596.x
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发表时间：
2004-12
影响因子：
3.9
通讯作者：
C. Park;D. Yoon
中科院分区：
文献类型：
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作者：
C. Park;D. Yoon
当纯氧化铝在1620°C下烧结时，发生正常的晶粒生长，具有等轴晶粒和弯曲的晶界。当100 ppm的SiO2与50 ppm的CaO一起添加时，发生异常晶粒生长（AGG），大晶粒在基面方向上以直晶界段拉长。一些细小的基体颗粒也具有直的晶界，并且当通过透射电子显微镜（TEM）观察时，基体颗粒的大约10%的晶界是刻面的。预计这些晶界中的一些是奇异的，具有对应于晶界能量对倾斜角的极坐标图中的尖点的低能结构。透射电镜观察表明，在晶界和晶界处没有发现冻结液。当600ppm的MgO与100ppm的SiO2和50ppm的CaO一起加入时，发生正常生长。当通过光学显微镜和TEM观察时，晶界是弯曲的，并且显示所有的晶界都是小面化的，表明它们变得原子级粗糙。当添加150、300或500 ppm的SiO2后在1900°C下烧结时，AGG出现直的和刻面的晶界，类似于添加CaO和SiO2后在1620°C下烧结的试样。当MgO与SiO2一起加入并在1900°C下烧结时，发生正常晶粒生长并具有粗糙的晶界。高分辨率TEM观察显示在晶界处没有冻结液体层。结果表明，在Al2O3和SiO2以及Al2O3和CaO的混合物中，AGG的发生与小平面和平直（原子尺度上）晶界的形成有关。这些晶界具有奇异的有序结构，具有低的边界能，它们通过横向台阶运动的生长可以引起AGG。MgO的加入导致晶界粗糙化，从而导致正常的晶粒生长。纯氧化铝中的晶界也显得粗糙，因此发生正常的晶粒生长。
When pure alumina is sintered at 1620°C, normal grain growth occurs with equiaxial grains and curved grain boundaries. When 100 ppm of SiO 2 together with 50 ppm of CaO is added, abnormal grain growth (AGG) occurs with large grains elongated with straight grain-boundary segments in the direction of the basal planes. Some of the fine matrix grains also have straight grain boundaries, and ∼10% of the grain boundaries of the matrix grains are faceted when observed by transmission electron microscopy (TEM). Some of these grain boundaries are expected to be singular with low-energy structures corresponding to the cusps in the polar plot of the grain-boundary energy against the inclination angle. No frozen liquid is found at the grain triple junctions and grain boundaries by TEM. When 600 ppm of MgO is added together with 100 ppm of SiO 2 and 50 ppm of CaO normal growth occurs. The grain boundaries are curved when observed via optical microscopy and TEM and show that all the grain boundaries are defaceted, indicating that they become atomically rough. When sintered at 1900°C after adding 150, 300, or 500 ppm of SiO 2 , AGG occurs with straight and faceted grain boundaries, similar to the specimens sintered at 1620°C after CaO and SiO 2 are added. When MgO is added together with SiO 2 and sintered at 1900°C, normal grain growth occurs with rough grain boundaries. High-resolution TEM observation shows no frozen liquid layer at a grain boundary. The results indicate that the occurrence of AGG in alumina with SiO 2 or together with CaO is correlated with the formation of faceted and straight (on large and atomic scales) grain boundaries. It is proposed that these grain boundaries have singular ordered structures with low boundary energies and their growth by lateral step movement can cause the AGG. The addition of MgO causes grain-boundary roughening and, thus, normal grain growth. The grain boundaries in pure alumina also appear to be rough, and, hence, normal grain growth occurs.