Surface energies and thermodynamic phase stability in nanocrystalline aluminas
Surface energies and thermodynamic phase stability in nanocrystalline aluminas
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DOI：
10.1126/science.277.5327.788
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发表时间：
1997-08-08
期刊：
影响因子：
56.9
通讯作者：
Navrotsky, A
中科院分区：
文献类型：
--
作者：
McHale, JM;Auroux, A;Navrotsky, A
刚玉，α-Al_2O_3，是粗晶氧化铝的热力学稳定相，但纳米晶Al_2O_3的合成通常会产生伽马-Al_2O_3。吸附微量热分析、热重分析和Brunauer-Emmett-Teller吸附实验，再加上最近报道的高温溶液量热数据，证明了伽马-Al_2O_3比α-Al_2O_3具有更低的表面能，在每克大于125平方米的表面积上变得能量稳定，在更小的表面积上热力学稳定(例如，在800开尔文时，每克75平方米)。结果与最近的分子动力学模拟结果一致，并提供了确凿的实验证据，表明表面能的差异有利于特定多晶型的形成。
Corundum, alpha-Al2O3, is the thermodynamically stable phase of coarsely crystalline aluminum oxide, but syntheses of nanocrystalline Al2O3 usually result in gamma-Al2O3. Adsorption microcalorimetry, thermogravimetric analyses, and Brunauer-Emmett-Teller adsorption experiments, coupled with recently reported high-temperature solution calorimetry data, prove that gamma-Al2O3 has a lower surface energy than alpha-Al2O3 and becomes energetically stable at surface areas greater than 125 square meters per gram and thermodynamically stable at even smaller surface areas (for example, 75 square meters per gram at 800 kelvin). The results are in agreement with recent molecular dynamics simulations and provide conclusive experimental evidence that differences in surface energy can favor the formation of a particular polymorph.