Processing, sintering, and properties of foamed cellular silica.

摘要

One possible method for making cellular lightweight ceramics is to apply the polymer foaming technique which utilizes gas evolution by decomposition or evaporation of foaming agents followed by a rapid polymerization reaction to stabilize the unstable foam structure. In this study, a silica hydrosol was used as a foaming host material and liquid freon was employed as a foaming agent. Liquid freon was dispersed in the sol by use of surfactants and the dispersion was heated at temperatures above the boiling point of freon to foam the silica sol. The foamed sol became gelled a few minutes after bubble formation to fix the foamed structure. When sintered at 1000;The sintering behavior of the silica gel matrix followed Scherer's gel sintering model. Total foam density change was also explained by Scherer's model assuming that the cell shrunk at the same rate as the matrix. Mechanical strength of sintered foam was tested by three-point bending and ranged from 0.75 to 8.5 MPa for the specimens with relative densities of 14 to 40%. Dielectric permittivity of sintered foam ranged from 1.5 to 2.5 with loss less than 0.001 at 20