Modification of interface chemistry and slag structure by transition element Cr

A comparative study on CaO-MgO-Al2O3-SiO2 slag and CaO-MgO-Al2O3-SiO2-Cr2O3 slag was conducted to investigate the distribution of the elements at the gas-slag interface. The effect of redox states of chromium on the distribution of sulfur and oxygen at the interface was revealed by gas-slag equilibrium method using X-ray photoelectron spectroscopy at 1873K. From the analysis of the S2p core-level spectra, the negative divalent sulfur (S-2) was detected at the interface in the Cr-bearing slag, which directly proved that sulfur exists in the form of S2- in the slag for the first time. However, the S2- peak is very weak at the interface of Cr-free slag. The reason for the difference between the two slags may be due to chromium changing the interface structure. According to the O1s and Cr2p core-level spectra, non-bridged oxygen(O-) increased, while bridged oxygen(O-0) decreased with the etching depth deepened. The increase of NBO/BO and Cr2+/Cr3+ elucidates that Cr3+ can modify the structure of the slag as basicity substance, but its effect is weaker than that of Cr2+. Meanwhile, due to the affinity of sulfur and chromium, the addition of chromium may also lead to the enhancement of the S2- peak at the gas-slag interface. Gradient change of elements at the interface proved the existence of the boundary layer.