Fundamentals of Hydrogen Solubility in Calcium-Alumino-Silicate Molten Fluxes Containing NaF

The effect of the NaF and CaO/SiO₂ ratio (mass percentage ratio) on hydrogen solubility in a CaO-SiO₂-Al₂O₃-NaF system was studied and correlated to the structural units of the molten flux. Fourier transformed infrared, Raman, and X-ray photoelectron spectroscopy analyses were used to evaluate the structural units with NaF additions and various CaO/SiO₂ ratios. At a CaO/SiO₂ ratio of 0.8, the incorporated-hydroxyl dissolution mechanism is dominant, whereas the free-hydroxyl mechanism is pronounced at higher CaO/SiO₂ ratio. At low NaF contents, the hydrogen solubility as a function of the CaO/SiO₂ ratio showed a parabolic trend with a minimum typical of a change from incorporated- to a free-hydroxyl dissolution mechanism. The addition of network-modifying NaF depolymerizes the structural units of the flux, reducing the available sites for incorporated-hydroxyl groups. The hydrogen solubility behavior in the flux system correlates well with the structural analysis, where a high NaF content and CaO/SiO₂ ratio are shown to depolymerize the complex structural units of the molten flux.