Continuous ceramic foam production through direct gas injection technology for high temperature refractory materials

Porous alumina is widely used as thermal insulation in high-temperature furnaces due to its desirable characteristics, including a high specific surface area, good permeability, low density, and low specific heat. Among the various fabrication routes, direct gas injection is considered one of the most cost-effective methods for producing alumina insulation foams. In this study, the properties of a commercial Goodfellow alumina insulation component were first examined as a reference to guide the development of a comparable product. A stable alumina slurry was prepared using Dolapix CE64 as the dispersant, and its stability was assessed. The optimal dispersant level was found to be 0.5 wt% relative to the solid content. The stabilized slurry, prepared with different solid loadings, was then introduced into the foaming device and aerated. Through a separate inlet, silica sol (4 wt%) and magnesium oxide (0.6 wt%) were added until the generated foam transitioned into a wet gel, which was subsequently dried and fired. The resulting porous bodies were sintered at 1400 °C for 2 hours and characterized using SEM, compressive strength testing, density measurements, and porosity analysis. The best foam properties were obtained from the slurry containing 78% solids, yielding a density of 0.92 g/cm³, compressive strength of 30 MPa, porosity of 78%, and thermal conductivity of 0.7 W/m·K—values that closely matched those of the reference material.