Influence of magnesium-aluminum hydrotalcite on the microstructure and mechanical properties of magnesia castables

Abstract

The stability of the thermo-mechanical properties of magnesia castables is critical for both the service life of castables and the steel cleanliness. In this study, simultaneous use of magnesium-aluminum hydrotalcite and hydratable alumina was determined to improve the mechanical strength and volume stability of magnesia castables. Hydrotalcite was decomposed to magnesium aluminate spinel and reactive MgO below the medium temperature, which accelerated sintering reactions in magnesia castables and further promoted the formation of spinel and forsterite at high temperature. Suitable volume stability was presented as a consequence of the improved sinterability. The thermo-mechanical properties of magnesia castables were also enhanced. A modified three-dimensional microstructure with the fewer and smaller pores in this optimized magnesia castable at the same time was verified by X-ray micro-computed tomography technology. A correlation analysis identified bending strength and compressive strength of castables having the strongest relationship with the spatial porosity and the number of pores in a diameter range of 0.3–0.5 mm.