Fabrication and analysis of lightweight magnesia based aggregates containing nano-sized intracrystalline pores

To efficiently reduce heat loss in high-temperature furnaces, the use of a working lining with low thermal conductivity, in lightweight refractories is a significant development. Conventional lightweight refractories focus on the fabrication of Al2O3-based, spinel-based, or Al2O3-spinel based refractories with micro-sized closed pores. In this study, lightweight magnesia-based aggregates with smaller nano-sized pores were fabricated by the decomposition of magnesite by using nano-sized Al2O3 and ZrO2 as additives. The lightweight magnesia containing nano-sized intracrystalline pores (100-300 nm) had a relatively low thermal conductivity of 4.539 W.m(-1)K(-1) at 500 degrees C with a bulk density of 3.37 g/cm(3) and a closed porosity of 4.3%. Moreover, the formation mechanism of nano-sized intracrystalline pores was proposed, and the effect of nano-sized additives on the sintering properties was discussed. We concluded that nano-sized Al2O3 and ZrO2 raise the number of nano-sized intracrystalline pores by increasing their migration distance required to separate from the magnesia grains. With the joint addition of nano-sized Al2O3 and ZrO2, the light weight magnesia possessed the lowest thermal conductivity, as well as excellent strength, owing to the generation of intergranular MgAl2O4 spinel. Furthermore, the nano-sized Al2O3 and ZrO2 also promoted the sintering of magnesia resulting in the formation of cation vacancies (V(M)g). (c) 2019 The Authors. Published by Elsevier Ltd.