Preparation of lightweight corundum-mullite thermal insulation materials by microwave sintering

Lightweight corundum-mullite thermal insulation materials were successfully prepared by microwave sintering at low temperature. The effects of sintering temperatures, PMMA microspheres and SiC particles on structure and properties of as-prepared corundum-mullite materials were investigated. The SiC became a hot spot under the action of microwave field, and these local high temperature areas promoted the formation and growth of mullite whiskers. The PMMA microspheres were burn out, leaving pores which could provide space for the growth of mullite whiskers. It was found that the optimal sintering temperature was 1400?C and corresponding porosity, density and bending strength of the samples were 71.2%, 0.99 g/cm3 and 3.85MPa, respectively. The thermal conductivity was from 0.201 to 0.313W/(m?K) between 30?C and 950?C. This work demonstrated that lightweight corundum-mullite materials with low density, high porosity, good thermal shock resistance and excellent thermal insulation properties could be successfully prepared by microwave sintering.

Influence of Contents of Pre-Synthesized Spinel on the Microstructures and Mechanical Properties of the Lightweight Corundum-Spinel Refractory Castables

Five kinds of lightweight refractory castables were prepared by using lightweight corundum-spinel aggregates (LCSA), pre-synthesized spinel (PSS), magnesia and corundum powders as raw materials. Effects of the PSS contents on the microstructures and mechanical properties of the refractory castables were studied by means of X-ray diffractometer (XRD), elastic modulus tester and scanning electron microscopy (SEM), etc. It is found that with the PPS content increase from 0 to 15.3 wt %, the permanent linear change (PLC) of castables sintered at 1600 °C decreases from 1.02% to -0.56%; the bulk density (BD) and apparent porosity (AP) are in the range of 29.6 %~27.8 % and 2.71~2.79 g/cm3, respectively, changing a little; the cold compressive strength (CCS) decreases from 106.0 MPa to 94.4 MPa; the thermal shock resistance improves; the hot modulus of rupture (HMOR) decreases from 6.7 MPa to 4.3 MPa. Considering these aspects, sample with 7.6 wt% PPS (LA7.6) has the best performance.