Bio-Inspired Hydro-Pressure Consolidation of Silica

Abstract

Room-temperature hydro-pressure-driven densification of amorphous silica (nanoparticles and microbeads) is developed. This technique is inspired by biological silicification with reference to dissolution, precipitation, and hardening mechanisms. Cold sintering based on uniaxial pressure is taken as a benchmark. Starting from a green-body relative density of 70%, densification exceeding 99% is achieved by adding distilled water or caustic solution to an amorphous powder under a hydrostatic pressure of 450–600 MPa for 5–30 min. Translucent samples are obtained. Silica microbeads are employed as a model system to define the effect of the sintering parameters: pressure, pH, and soaking time. Densification is attained through a preferential precipitation of a second phase from silica dissolution under hydro-pressure. Precipitation is governed by minimization of the surface energy (Ostwald ripening). Transmission electron microscopy, NMR, thermal gravimetric analysis/differential scanning calorimetry, and Fourier transform infrared spectroscopy reveal the mechanisms of the process and the analogies with biosilicification.