A novel low thermal conductivity refractory aggregate for high-temperature applications: Lightweight microporous alumina-rich spinel (Mg0.4Al2.4O4)

Abstract

This study aimed to develop lightweight refractory aggregates with high closed porosity and low thermal conductivity. We report the preparation of a series of lightweight microporous alumina-rich spinel (Mg0.4Al2.4O4) aggregates with low open porosity, high closed porosity, small intragranular pore size, and low thermal conductivity. The sintering activity of the nano-zirconia sol increased the grain boundary migration rate under the action of surface tension during sintering; therefore, the pores were closed before they were eliminated. Simultaneously, Zr4+ replaced Mg2+ and Al3+, which increased the number of cation vacancies in the crystal and accelerated the ion migration, resulting in a faster formation of Mg0.4Al2.4O4. When 0.75 wt% nano-zirconia sol was added, it increased the diffusion rate of ions and the migration rate of grain boundary, which improved the sintering reactivity. The pores were mainly small-sized intragranular pores (median size: 1.89 μm), which reduced the thermal conductivity (2.5 W•m−1K−1 at 1000 °C).