Identification of MgO·Al₂O₃ Spinel on MgO Refractory for Aluminum Deoxidation Process of Stainless Steel Using Cathodoluminescence and X-ray Excited Optical Luminescence Imaging

MgO·Al₂O₃ spinel particles adhered to MgO refractory become a source of inclusions in stainless steel during the aluminum deoxidation process. In contrast, the MgO·Al₂O₃ spinel layer formed on MgO refractory can protect it from further dissolution and spalling. Thus, identifying the MgO·Al₂O₃ spinel particles and layer is critical for locating areas on the refractory that require repair and replacement. In this study, the author demonstrates that the MgO·Al₂O₃ spinel particles and layer on MgO refractory for aluminum deoxidation process of stainless steel are distinguishable from their luminescence colors in cathodoluminescence (CL) and X-ray excited optical luminescence (XEOL) images at wavelengths of 420 to 680 nm, 650 to 680 nm, and 350 to 1000 nm, respectively. The CL and XEOL images can be acquired within 2 seconds and 1 minutes, respectively. Surface examination of the MgO refractory aids in more precise identification. XEOL imaging, in particular, is promising because it can perform a nondestructive onsite evaluation of the MgO refractory.