NATURE OF ALUMINA IN PHOSPHATE-GLASS .1. PROPERTIES OF SODIUM ALUMINOPHOSPHATE GLASS

Glasses along four compositional tie lines, I: xAl(PO3)3.(1 - x)NaPO3, II: xAlPO4.(1 - x)NaPO3, III: xAl2O3.(1 - x)NaPO3, and IV: xNaAlO2.(1 - x)NaPO3, have been prepared and a number of their properties evaluated. In general, Al2O3 additions increase the glass transition temperature, decrease thermal expansion, and improve aqueous durability. However, the composition/property relationships are strongly influenced by relative cation ratios and thus the overall O/P ratio. The nature of these glasses undergoes significant transformations at both the pyrophosphate (O/P = 3.5) and the orthophosphate (O/P = 4.0) compositions, producing significant changes in the property behavior. Spectroscopic analyses of glass structure, described in part II of this report, reveal that changes in Al coordination coincide with the breaks in the property behavior.