Electroless coating of Fe3Si on steel in the molten salt

The corrosion-resistive intermetallic compound Fe3Si could non-electrolytically coat pure iron and mild steel. The disproportional reaction between Si and Si4+ ions deposited the homogeneous Fe3Si layer on the Fe substrates, by using solid silicon and the molten salt composed of NaCl-KCl-NaF-Na2SiF6-SiO2. SiF4 gas evaporation prevented from continuous siliconization, when only Na2SiF6 was used as Si4+ ion source. By adding SiO2 into the salt as another source, the molten salt became endurable for repeated usage in air. The layer of Fe3Si single phase with silicon mole fractions of 24 +/- 1 % grew thicker than 200 mu m by immersing for a few hours at 973 - 1173K.