EFFECTS ON THE THERMAL-PROPERTIES AND BIOACTIVITY OF SUBSTITUTION OF CAO BY M2O3 (M = LA, Y, AL) IN WOLLASTONITE GLASS

The effects on the thermal properties and bioactivity of the substitut ion of CaO by La2O3, Y2O3 and Al2O3 in a glass of composition CaO.SiO2 were studied and compared. The trivalent metal oxides were all effect ive in raising the glass transformation and softening temperatures whe n they replaced CaO in the glass of composition CaO.SiO2. The experime ntal results suggest that Al2O3 plays the role of a glass-former, whil e La2O3 and Y2O3 behave as glass-modifiers. The tendency to devitrify appears to be the lower, the farther the glass composition is from tho se of the crystalline phases, owing to the need for diffusion over lon ger distances, the greater the composition difference. The substitutio n with the trivalent metal oxides is detrimental to the bioactivity, w hich is preserved only in the event of very small degrees of substitut ion. The most negative role appears to be played by Al2O3.