Thermal behaviour and excess entropy of bioactive glasses and Zn-doped glasses

Bioactive glasses prepared in SiO₂–CaO–Na₂O and P₂O₅ system are used as biomaterials in orthopaedic and maxillofacial surgery. Zn presents high physiological interest. It enhances physiological effects of implanted biomaterials. In this work, the thermal characteristics (T _g, T _c and T _f) of pure bioactive glass elaborated with different amounts of CaO, Na₂O in pure glass and with different amounts of introduced Zn in glass (ranging from 0.1 to 10 in mass%), were studied. The excess entropy was calculated for different compounds. Glasses were prepared by the melting process. The thermal behaviour of obtained bioactive glasses was determined using differential thermal analysis. Therefore, the glass transition (T _g), the crystallization (T _c) and the melting temperatures (T _f) were revealed. Moreover, according to Dietzel formula, the thermal stability (TS) of the studied bioactive glasses has been calculated. The first results concerning the impact of different oxides, revealed a decrease of the TS, T _g, T _c and T _f when the SiO₂/CaO increases and revealed an increase of these thermal characteristics when the SiO₂/Na₂O and CaO/Na₂O ratios increase. Introducing Zn into the bioactive glasses induces a decrease of T _f and an increase of TS. Contrary to crystals, prepared glasses have entropy different to zero at T = 0 K and vary versus T _f. The excess entropy of pure glasses and Zn-doped glasses were calculated. The significant variations were registered.