Influence of glass composition on the properties of glass polyalkenoate cements. Part II: influence of phosphate content

The influence of phosphate content of the glass on the formation of glass p olyalkenoate cements was investigated. Glasses were synthesised based on (4 .5 - 2X)SiO2-3.0 Al2O3-(3.0 - X)CaO-(1.5 + X)P2O5-2.0 CaF2 and X was varied from -1.5 to 0.8. The setting and working time of the cement pastes increa sed with the phosphate content of the glass (X). Increasing the phosphate c ontent resulted in an initial increase in compressive strength followed by a sharp reduction in strength. Young's modulus and un-notched fracture stre ngth exhibited a maximum at intermediate phosphate contents. Fracture tough ness reduced at high phosphate contents, whilst toughness increased. Phosph ate in the glass is thought to aid glass degradation by providing additiona l phosphorus-oxygen bonds for hydrolysis, but may also reduce the amount of aluminium released by reducing the susceptibility of aluminium-oxygen-sili con bonds to acid hydrolysis. The released phosphate may also compete with the carboxylate groups in the polysalt matrix cement for cations inhibiting the crosslinking reaction. (C) 2000 Elsevier Science Ltd. All rights reser ved.