Irreversible expansion of silica-gel beads and quantification of pore structure made by silica-gel bead infiltration method

Abstract

The irreversible expansion of silica-gel beads upon heating makes the silica-gel bead infiltration method a novel method for manufacturing Cu-based shape-memory foams with adjustable pore structures. The mechanism of silica-gel bead expansion, however, is not clear, making control and prediction of the pore structure difficult. This paper investigated the expansion mechanism of silica-gel beads by measuring expansion ratios and observing microstructural changes during heating. The irreversible and non-uniform expansion was caused by high-pressure steam generated from water confined in the nano-pores of the silica-gel beads. A geometrical model was developed to calculate the pore structures and the influences of expansion ratio and bead indentation on pore structure were discussed. The calculated values for pore size, porosity and specific surface area agreed well with the experimental results with small relative errors of 0.1% ~ 5.2%. The model will help to control the pore structure manufactured by the silica-gel bead infiltration method more precisely.