Glass Formation and Crystallization in Ternary Phosphate Systems Containing Al2O3

Abstract

Glass formation and crystallization were investigated in two types of three-component systems, M2O–Al2O3–P2O5 (M=Li, Na, and K) and MO–Al2O3–P2O5 (M=Mg, Ca, and Ba). In the Li2O–Al2O3–P2O5 and MO–Al2O3–P2O5 systems, wide regions of glass formation were found in compositions containing more than 50 mol% of P2O5. In the Na2O–Al2O3–P2O5 and K2O–Al2O3–P2O5 systems, the two peaks in Al2O3 content were found in the regions of glass formation corresponding to about 35 and 65 mol% of P2O5. In the devitrified products of the glasses with 60 and 70 mol% of P2O5, AlPO4, Al(PO3)3, and alkaline earth metaphosphate (in the MO–Al2O3–P2O5 system) were found by X-ray powder diffractometry. The crystalline phases in the samples obtained as mixtures of glass and crystal consisted of AlPO4 in the composition containing 60 mol% of P2O5, while those with a P2O5 composition of 70 mol% consisted of Al(PO3)3. By heating those samples at 700–900 °C, the X-ray diffractions of AlPO4 and Al(PO3)3 were intensified. On the other hand, in the samples with 37.5, 40, and 50 mol% of P2O5, all the crystalline phases consisted of AlPO4, and the intensities of these X-ray diffractions decreased after the samples were heated at 600–700 °C. Thus, there is a marked structural difference between the two peak-regions in the Na2O–Al2O3–P2O5 and K2O–Al2O3–P2O5 systems.