Effect of FeO_2 Content and CaO/SiO_2 Ratio on Hydrogen Dissolution in CaF_2-CaO-SiO_2-Based Welding Fluxes

摘要

The solubility of hydrogen in the CaF_2-CaO-SiO_2-FeO_t slag system was studied to characterize the dependence of hydrogen dissolution behavior on the CaO/SiO_2 ratio and the Fe3+/Fe2 + redox equilibrium at 1823 K. In an acidic slag composition, the dissolved hydrogen seems to exist as an incorporated hydroxyl, where the supplied water vapor reacts with the bridged oxygen (O°) of the slag network. In a basic slag composition, hydrogen dissolves as a free hydroxyl in the molten slag by reacting with the free oxygen (O ). Using FTIR (Fourier transform infrared) and Raman spectroscopy, the addition of FeO_t depolymer-ized the slag structure in an acidic slag system, but polymerized the slag structure in a basic slag system as the FeO_t content increased. Furthermore, the formation of γ- and δ-FeO(OH) was controlled by the amount of Fe2O_3 present in the flux and increased at higher concentrations of Fe_2O_3. At a fixed Fe_2O_3 content and with CaO/SiO_2 ratios varying from 0.7 to 1.3, the hydrogen solubility curve was parabolic as a function of CaO/SiO_2, with a minimum near the CaO/SiO_2 ratio of 1.0 and rapidly increasing at CaO/SiO_2 ratios above 1.0.