Effect of CaO and Al2O3 addition on the properties of K2O-Na2O-P2O5 glass system
Résumé
This work reports on the effect of substituting Al2O3 for P2O5 and substituting CaO for (Na2O+K2O) in the ternary 0,46 (K2O + Na2O) 0,54 P2O5 glass system, certain of these compositions being eventually of interest for bio-medical applications. Different properties are analysed here. When CaO replaces (Na2O+K2O) (constant O/P ratio) or when Al2O3 replaces P2O5 (increasing O/P ratio), it is shown that the density of the glasses increased, the coefficient of thermal expansion decreased and the glass transition temperature increased. A partial and limited study of dissolution behaviour in water indicates that the dissolution rates decreased by orders of magnitude with the introduction of CaO or Al2O3, in agreement with the trends reported in the literature. The pH values of the dissolution solutions were also measured. The pH quickly decreased and saturated to around 2.5 for glasses with no alumina, i.e with the highest P2O5 content. On another hand, when Al2O3 was substituted for P2O5 (i.e. when P2O5 content decreased and O/P increased), the pH initially increased to more basic values (around 7) and always remained above 5. Some interpretation of the structural role of CaO and Al2O3 are proposed to explain these properties change with composition.