The effect of NiO on the phase formation, thermo-physical properties and sealing behaviour of lithium zinc silicate glass–ceramics

Abstract

We have prepared lithium zinc silicate (LZS) glasses of compositions (mol%) 17.83Li₂O–17.73ZnO–(53.52 − x)SiO₂–5.25Na₂O–1.25P₂O₅–4.31B₂O₃–x-NiO, where 0.5 ≤ x ≤ 2.0, by the melt quench technique. The effect of NiO on the phase formation, thermo-physical properties and sealing behaviour of LZS glass–ceramics was studied using X-Ray diffraction (XRD), thermo-mechanical analysis (TMA) and microhardness (MH) measurements. It is found that NiO incorporation leads to a change in the role of ZnO from network modifier to intermediate oxide. The intermediate network forming Zn²⁺ ions would find it more difficult to diffuse and initiate the transformation of Li₃Zn_0.5SiO₄ to Li₂ZnSiO₄. Thus Li₃Zn_0.5SiO₄ is formed instead of Li₂ZnSiO₄ on addition of 2 mol% NiO. Scanning electron microscopy (SEM) and energy dispersive analysis of X-rays (EDAX) measurements at the glass–ceramic-to-metal interface reveal a change in the microstructure commensurate with the changing role of ZnO. Addition of NiO favoured interdiffusion of species at the interface leading to better sealing.