Study of Al sub(2)O sub(3) effect on structural change and phase separation in Na sub(2)O-B sub(2)O sub(3)-SiO sub(2) glass by NMR

• Published in: Journal of materials science Vol. 35; no. 19; pp. 4865 - 4871
• Main Authors: Du, W-F, Kuraoka, K, Akai, T, Yazawa, T
• Format: Journal Article
• Language: English
• Published: 01.10.2000
• ISSN: 0022-2461

The effect of Al sub(2)O sub(3) on the structure change and the phase separation in Na sub(2)O-B sub(2)O sub(3)-SiO sub(2) glass was investigated using super(11)B nuclear magnetic resonance (NMR), super(29)Si MAS NMR, and super(27)Al MAS NMR together with infrared absorption spectroscopy and field emission scanning electron microscopy (FE-SEM). The results show that the structure change from the introduction of Al sub(2)O sub(3) contributes greatly to the inhibition of phase separation. First, the introduction of Al sub(2)O sub(3) imparts an ionic character to the boron-oxygen network, resulting in the formation of B-O-Al-O-Si bonds and thus increases the compatibility of the silicon network with the boron-oxygen network. Second, the addition of Al sub(2)O sub(3) causes the sodium ion to transfer from the boron-oxygen network to AlO sub(4) tetradedra, changing a number of four-coordinated borons into three-coordinated borons. As the bond energy of the four-coordinated boron is weaker than that of the three-coordinated boron, the -B-O-Si-bond with the four-coordinated boron in Na sub(2)O-B sub(2)O sub(3)-SiO sub(2) glasses is easily broken and results in severe phase separation during heat treatment. However, the -B-O-Al-bond with the three-coordinated boron formed in Na sub(2)O-B sub(2)O sub(3)-SiO sub(2)-Al sub(2)O sub(3) glasses is difficult to be broken due to the high bond energy. In addition, the silicon network in Na sub(2)O-B sub(2)O sub(3)-SiO sub(2)-Al sub(2)O sub(3) glasses is also strengthened by the addition of Al sub(2)O sub(3), which prevents [BO] groups from further aggregation. As a result, the tendency of the glass towards phase separation is greatly suppressed in the Na sub(2)O-B sub(2)O sub(3)-SiO sub(2)-Al sub(2)O sub(3) system.