The excellent emissive and protective properties of magnesium oxide are deteriorated by Mg (OH)2 formation through chemisorption of water. To address this issue, pure MgO powder has been first synthesized by a sol-gel process involving gel formation from solutions of magnesium nitrate hexahydrate and oxalic acid in ethanol, drying at 100℃ for 24 h to form magnesium oxalate dihydrate and decomposition at 600℃. The product is then subjected to grinding, sieving through a 240 mesh, pelletization and sintering at 1000℃ for 2 h. The resulting MgO target has then been used to prepare thin films over a glass substrate by e-beam evaporation under vacuum ～10-5 mbar. The MgO films as such and after annealing at 450℃ have been characterized for (a) phase and preferred orientation, (b) surface morphology, (c) optical trans- mittance, and (d) OH bond. They are shown to (I) possess an f. C.c. (NaCl-type) structure with lattice parameter a ～ 4. 2165±0.005A and (ii) have preferred orientation along＜100 and ＜110. The films exhibit (I) pyramidal columnar morphology, (ii) high optical transmittance ( 88～92%) in visible re-gion, and (iii) no signature of -OH bond. Further the hydration is effectively controlled if neutral planes like {100} and {110} bound the grains of MgO films.%MgO 优异的发射和保护性能会由于水吸附作用形成 Mg(OH)2而变差.为了证明这一点,实验首先采用 Sol-gel 法合成了纯净的 MgO 粉末:将硝酸镁六水合物和草酸溶解在乙醇中形成凝胶体,接着将该凝胶体在 100℃时烘 24 h以形成草酸镁,然后升温到600℃使之裂解,将其磨碎,再使用240 mesh 筛分,最后再在1000℃时烧结 2 h,形成 MgO.该法制成的MgO 在气压为 10-5 mbar的气氛中通过电子束蒸发到玻璃衬底上形成薄膜.以上方法制成的 MgO 薄膜和在450℃直接退火的 MgO 薄膜在以下几点做了对比:(a)生长过程和结构;(b)表面形貌;(c)透光度;(d)OH键.以上对比结果表明前者:(i)具有 fcc 结构,其晶格常数 a 为 4.216±0.005A,(ii)具有在＜100和＜110之间的择优取向.另外前者还有以下特征;(i)表面形貌呈锥柱状、(ii)可视光范围的高透光度( 88～92%)、(iii)无OH键.此外,如果 MgO 薄膜的晶粒取向{100}和{110}之类的中性面,那么其水合作用就可以得到有效的控制.
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