The analysis of XRD indicates that slag is similar with minerals in the initial sediments. However, the proportion of bauxite A12O3, hematite Fe2O3 has a big difference. The electric structure, elastic constants of A12O3 and Fe2O3 were calculated using the ultra soft pseudo-potential plane-wave method based on the first-principles. The results show that from the structure of material, the accumulation mode of Al3+ and O2- in A12O3 crystal is sparser than that of Fe3+ and O2 in Fe2O3, which is the reason for their different properties. For their chemical bonds in the direction of < 100 > and in tangential, Fe-0 is more easy to deformate and fracture than Al-O, leading to Fe2O3 deposition in the clean water wall. For Fe2O3, tangential surface plays a key role for its deposit.%选取矾土Al2O3和赤铁矿Fe2O,,对这两种矿物做弹性常数的微观分析、对比,X射线衍射分析表明,煤灰与初始沉积层中的矿物种类相同,但两者中矾土Al2O,和赤铁矿Fe2O,的含量相差很大.采用第一性原理(fu-st-principles)的超软赝势平面波方法,对Al2O3和Fe2O3的电子结构、弹性常数进行了计算.结果表明,从两种物质的结构角度分析,Al2O3晶体中Al3+、O2-的堆积排列相对于Fe2O,中Fe3+、O2-要稀疏,这是它们性质不同的结构原因；对于两晶体在＜100＞方向和切向上的化学键,Fe-O键比Al-O键更容易变形或者断裂,从而导致Fe2O,极易沉积在清洁水冷壁上；对Fe2O,,切向面对其沉积起了关键性的作用.
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