Nature of Alumina in Phosphate Glass: I, Properties of Sodium Aluminophosphate Glass

TLDR

Glasses were synthesized along four compositional tie lines varying Al and Na content and their properties were evaluated. Al₂O₃ additions raise Tg, lower thermal expansion, and improve aqueous durability, yet property trends are strongly influenced by cation ratios and O/P ratio, with pronounced changes at pyrophosphate and orthophosphate compositions linked to shifts in Al coordination.

Abstract

Glasses along four compositional tie lines, I: xAl(PO 3 ) 3 ’(1 – x)NaPO 3 , II: xAlPO 4 ′(1 – x)NaPO 3 , III: xAl 2 O 3 ′(1 – x)NaPO 3 , and IV: xNaAlO 2 ,(1 – x)NaPO 3 , have been prepared and a number of their properties evaluated. In general, Al 2 O 3 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.