Effect of CaO and Al ₂ O ₃ addition on the properties of K ₂ O–Na ₂ O–P ₂ O ₅ glass system

Abstract

Abstract This work reports the effect of substituting Al 2 O 3 for P 2 O 5 and substituting CaO for (Na 2 O + K 2 O) in the ternary 0.46 (K 2 O + Na 2 O) 0.54 P 2 O 5 glass system, with certain of these compositions being eventually of interest for biomedical applications. Different properties are analyzed here. When CaO replaces (Na 2 O + K 2 O; constant O/P ratio) or when Al 2 O 3 replaces P 2 O 5 (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 behavior in water indicates that the dissolution rates decreased by orders of magnitude with the introduction of CaO or Al 2 O 3 , 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, that is, with the highest P 2 O 5 content. On another hand, when Al 2 O 3 was substituted for P 2 O 5 (ie, when P 2 O 5 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 Al 2 O 3 are proposed to explain these changes in properties with composition.