Silica sols as refractory fibre binders

Four different colloidal silica sols with different specific surface areas (from 80 up to 360 m2/g) and particle sizes have been examined in an application as refractory fibre binders. The fibrous materials were fabricated using a vacuum-forming technique, and a cationic starch was used as flocculent to obtain high retention of silica. The starch molecule also works as a temporary binder in the fibre product. Optimum retention and, hence, the most homogeneous fibre bodies were obtained at a constant ratio between the starch addition and the total surface area of the added silica, regardless of the type of silica sol used. The compressive strength of the fibre products depended mainly on the density of the fibrous materials. The density increased with increased starch content. The green strength was higher than the strength of the sintered samples, as starch is an effective binder. The sol with the best overall properties had a particle size of about 15 nm and an intermediate specific surface area (220 m2/g).