Effect of citric acid on the hydration process of colloidal silica-bonded magnesia gunning materials

Abstract

Abstract Magnesia gunning materials are widely used in the steel making process due to their high refractoriness and excellent corrosion resistance to alkaline slag. However, hydration of magnesia is still a key issue that needs to be settled in magnesia gunning materials. The citric acid can significantly inhibit hydration rate of magnesia in aqueous suspensions. In this paper, the performance of different citric acid contents on magnesia suspensions was evaluated by zeta potential and conductivity measurements, scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. And physical properties of magnesia gunning materials containing different citric acid contents were also obtained. The results showed that the citric acid, in the magnesia suspension, led to the formation of a complex structure layer, which was made of MgOH+ and Cit(n−) (n = 3, 2 or 1), thereby inhibiting the dissolution process of magnesia. However, this was only effective at low levels. When the content of citric acid in the suspensions was increased to 3 wt %, the magnesia still underwent significant dissolution due to a decrease in the formation of the [nMgOH+·Cit(n−)] (n = 3, 2 or 1) complexes. Moreover, the FTIR spectra suggested that the [nMgOH+·Cit(n−)] (n = 3, 2 or 1) complexes was unidentate coordination. In magnesia gunning materials, although the protective layer decomposed at about 500 °C, the decrease in sample strength was less than that caused by magnesia hydration. The optimal amount of citric acid in the magnesia gunning materials was 0.18 wt %.