Influence of K and Mg substitutions on the synthesis and the properties of CaO-MgO-SiO2/Na2O, P2O5, CaF2 bioactive glasses

Novel glasses in CaO-MgO-SiO2 system with Na2O, P2O5, and CaF2 additives were produced by melting/quenching technique. The influence of K2O and MgO on glass structure, the thermal properties (of major importance for evaluating the crystallization mechanism), and properties related to their potential in biomedicine (bioactivity, machinability), was investigated. According to Raman spectra, K2O for Na2O substitution favors the formation of Q(0) and Q(1) silicate units at the expense of Q(2) and Q(3) ones, whereas substitution of MgO for CaO increases the Q(2) and Q(3) units at the expense of Q(1) ones. The presence of K2O caused the increase of T-g and of the crystallization temperature as well as of the E-a of crystallization. A weaker influence on the above magnitudes was recorded in glasses with MgO substitution. The produced glasses are generally prone to 3-dimensional crystallization, display bioactivity in SBF testing, and manifest positive value of the machinability parameter n.