Melting Properties and Viscosity of SiO2-CaO-Al2O3-B2O3System

This paper investigated melting properties and viscosity of SiO 2 ‐CaO‐Al 2 O 3 ‐B 2 O 3 fluxes with a mass ratio of CaO/SiO 2 from 0.83 to 1.5 and B 2 O 3 content from 5 to 9 wt%. Melting properties of these fluxes were studied using the hot stage microscopy method; viscosity was measured using the rotating cylinder method. Break temperature was also determined from the viscosity change with temperature in flux cooling process. Equilibrium liquidus temperature was calculated using FactSage. Increase in CaO/SiO 2 ratio was found to decrease hemispherical temperature and viscosity. The addition of B 2 O 3 did not significantly affect hemispherical temperature but decreased the flux viscosity. Viscosity was analyzed in relation to the flux structure. The increase of the CaO/SiO 2 ratio reduced the degree of flux polymerization, and B 2 O 3 apparently acted as a weak network modifier under the low concentration of B 2 O 3 . The experimental viscosity was in a good agreement with calculated viscosity using the modified NPL model.