Modifier effects on the properties and structures of aluminophosphate glasses

Properties and structures of potassium, barium and magnesium alumino-metaph osphate glasses (O/P approximate to 3) have been investigated. Adding Al(PO 3)(3) to an alkali or alkaline earth metaphosphate glass improves the chemi cal durability, increases the glass transition temperature and reduces ther mal expansion and residual OH-content. Infrared spectra are dominated by me taphosphate vibrational modes, the frequencies of which are dependent on th e field strengths of the modifying cations. Al-27 MAS NMR spectroscopy indi cates that aluminum ions are incorporated into the aluminophosphate network primarily in octahedral sites, although tetrahedral and pentahedral sites are also present. The average aluminum co-ordination number decreases in th e series K+ > Ba2+ > Mg2+ and this is related to a reduction in the basicit y of glasses with higher field strength modifiers. (C) 2001 Published by El sevier Science B.V.