Preparation and characteristic of a temperature resistance buoyancy material through a gelcasting process

A novel temperature resistance buoyancy material with hollow glass microspheres (HGMs) as the filler and borosilicate glass (BG, similar chemical composition to the HGMs) as the high temperature matrix was prepared by a tert-butyl alcohol based on gelcasting process. The effect of solid loading and sintering temperature on microstructure and mechanical properties were investigated. The results showed that HGMs were bonded together by borosilicate glass and 45 wt.% solid loading and 700 °C were the optimal processing parameters to fabricate the samples with the best mechanical and thermal properties, and the corresponding bulk density, compressive strength, thermal conductivity and Young's modulus were 0.92 g/cm3, 14.46 MPa, 0.15 W/m K and 1.24 GPa, respectively. The exponent m value for the samples fabricated in this work was 1.18, lower than that of open- or closed-cell foams, because the sample possess both the closed and open pores. The experimental values of thermal conductivity from 0.07 to 0.16 W/m K were lower than the prediction with the Hashin-Shtrikman upper bound and almost close to that predicted by the Landauer's relation. Only modulus value of SSL45 sample which possessed the maximum value was closer to Hashin-Shtrikman upper bound, while the modulus value of other samples agreed well with Ashby-Gibson model applied for a porosity ranging from 65% to 89%. The HGMs/BG composite exhibited a low density, low thermal conductivity and excellent temperature resistance, and can be used as the thermal insulation for undersea pipeline or submarine.