Sol-gel derived silicate-phosphate glass SiO2–P2O5–CaO–TiO2: The effect of titanium isopropoxide on porosity and thermomechanical stability

Abstract

Despite of several decades lasting extensive research of bioactive and bioresorbable glasses the systematic parametrization and determination of the key factors affecting porosity and thermomechanical characteristics still remains challenging. Here, we present silica-phosphate glasses, with the composition 70SiO₂–20P₂O₅–(10-x)CaO–xTiO₂ (mol%; x = 0, 2.5, 5, and 7.5), prepared by sol-gel method and reinforced by titanium dioxide via titanium isopropoxide (TTIP) incorporation which demonstrated tunable variation of porosity from micro-to macro-region and superb mechanical integrity during the calcination process. The presence of 7.5 mol% TiO₂ promotes dimensional stability up to 1000 °C as investigated by thermomechanical analysis. The XRD showed the dominant presence of silicon phosphate [Si(P₂O₇)], titanium phosphate [Ti(P₂O₇)] and calcium phosphates [β-Ca(P₂O₆) and γ- Ca₂(P₂O₇)]. The effect of TiO₂ doping on the multiscale morphology and porosity was investigated by means of SEM, MIP, μCT, N₂ adsorption and USAXS/SAXS. Increasing TiO₂ content leads to the formation of open porosity up to 70 vol% and drives the formation of a refined interconnected macroporosity of 2–30 μm. In contrast, mesoporosity with a dominance of 3–6 nm pores decreases in all samples with increasing TiO₂ content. USAXS/SAXS revealed an increase in primary particle size with increasing TiO₂ content which is in good agreement with the nitrogen physisorption analysis showing that microporosity decreases with increasing TiO2 content.