Melting, viscosity and structure of lithium-free CaO-SiO2 based melt: Substituting Li2O with Na2O and B2O3

Abstract

Lithiation-free mold fluxes with excellent performances are urgently needed to be developed, due to the desire for Li2CO3 (Li2O) from the lithium battery industry. So, in this study, the melting, viscosity and structure of the CaO-SiO2 based flux melt, with the aim to replace Li2O by Na2O and B2O3, were investigated. Results show that the melting temperature decreased from 1258.1-1651.9 K to 1245.3–1632.5 K, and the viscosity at 1573 K decreased from 0.310 to 0.098 Pa s, when the ratio of Li2O/(Na2O + B2O3) decreased from 0.38 to 0.00. Meanwhile, the break temperature reduced from 1475.3 to 1451.4 K, and the activation energy of viscous flow also decreased from 181.44 to 55.39 kJ/mol, with the decease of Li2O/(Na2O + B2O3) ratio. Melt structure analyses indicate that the simpler structural units, such as Q0(Si), Q1(Si), [AlO4]5- tetrahedral and B-O- in [BO3] increased, while the more complex structural units, like Q2(Si), Q3(Si), bending vibration of Si-O-Al and boron ring in borate reduced, when Li2O was replaced by Na2O and B2O3. These changes suggest that the DOP of the flux melt was reduced and the melt structure was simplified during the lithiation-free process.