含锰的花岗岩土层，表层多孔使排水性良好。
Granite with manganese. Porous top layer provides good drainage.
结果表明：膜层表面微观形貌呈网状多孔结构，不同时间和终止电压下，膜表层结构区别较大；
The results show that the film surface morphology is reticular porous structure, at different time and termination voltage, there is large difference between membrane surface structure;
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