Influence of glass composition on the properties of glass polyalkenoate cements. Part I: influence of aluminium to silicon ratio.

Hydrolysis of aluminium-oxygen-silicon bonds is thought to be the first step in the setting reaction of polyalkenoate cements and the aluminium to silicon ratio of the glass is widely believed to be a dominant factor determining cement properties. The properties of glass polyalkenoate cements based on the generic glass composition (6 + X)SiO2 x (4 - X)Al2O31.5P2O5 x 4CaOCaF2 with varying aluminium to silicon ratio were studied. Setting and working times of the cement pastes, compressive strength, un-notched fracture strength, Young's modulus, fracture toughness and toughness were evaluated for the cements. In contrast to previous studies the aluminium to silicon ratio was not found to influence the cement properties significantly. The high phosphorus content of the glasses studied is thought to reduce the influence of the aluminium to silicon ratio of the glass, as a result of phosphorus locally charge balancing four coordinate aluminium ions in the glass network, as well as providing an additional mechanism of degradation in the form of hydrolysable phosphorus-oxygen bonds.