Synthesis of molten-electrolyte corrosion resistant MgAl2O4[sbnd]MgAlON sidewall materials by pressureless sintering

Abstract

MgAl2O4MgAlON materials as potential candidate sidewalls were prepared by using AlN, MgO, Al2O3, and nanosized MgAl2O4 powder as starting materials. The reaction sintering of the MgAl2O4MgAlON materials was investigated by means of X-ray diffraction and scanning electron microscope. All the specimens were corroded in a Na3AlF6AlF3CaF2Al2O3 bath to assess the electrolyte corrosion resistance. The results show that reaction sintering occurs in the MgAl2O4MgOAl2O3AlN system at 1830 °C and 5 MPa in flowing nitrogen for 5 h. The MgAl2O4MgAlON specimens are obtained and have high bulk density. The flexural strength increases from 202 ± 6 MPa to 248 ± 8 MPa and the Vickers hardness increases from 9.5 ± 0.2 GPa to 12.6 ± 0.4 GPa with increasing MgAlON content from 10 wt% to 40 wt%. The MgAl2O4MgAlON materials exhibit a good corrosion resistance to the Na3AlF6AlF3CaF2Al2O3 bath owing to their high-density and the formation of the composite spinel in the specimens. The corrosion mechanisms of MgAl2O4MgAlON composites in molten electrolyte are mainly proposed by the dissolution of MgAl2O4 and the diffusion of fluoride. Corrosion kinetic obeys a nearly parabolic law and the corrosion rate decreases with increasing MgAlON content.