Structure and Viscosity of CaO–Al₂O₃–B₂O₃ Based Mould Fluxes with Varying CaO/Al₂O₃ Mass Ratios

Abstract

The effect of CaO/Al₂O₃ ratio on the structure of CaO–Al₂O₃–B₂O₃ based glassy mould fluxes was investigated by employing ²⁷Al and ¹¹B Triple Quantum Magic-angle spinning nuclear magnetic resonance (3QMAS-NMR) and Raman spectroscopy. ²⁷Al and ¹¹B 3QMAS-NMR spectrums showed that Al³⁺ mainly forms [AlO₄] as a network former and B³⁺ mainly forms [BO₃] groups in CaO–Al₂O₃–B₂O₃ based glasses. Raman spectrum showed existences of different [AlO₄] structure units and BO₃ pyro-borate units. In addition, deconvolution results on Raman spectrums indicate that the degree of polymerization of aluminate network in CaO–Al₂O₃–B₂O₃ based glasses decreases with the increase of CaO/Al₂O₃ ratio. The effect of CaO/Al₂O₃ ratio on viscosity of CaO–Al₂O₃–B₂O₃ based glassy mould fluxes was investigated by employing the rotating-cylinder method. The viscosity decreases with increasing CaO/Al₂O₃ ratio in CaO–Al₂O₃–B₂O₃ based mould flux. Correlation between viscosity and structural information of investigated mould fluxes was explored.