In this paper, we report an improved torsion pendulum method for the viscosity measurement on molten K_2O-Nb_2O_5 system and BaB_2O_4 melts, with and without flux, at high temperature in air ambient atmosphere. In K_2O-Nb_2O_5 molten system, the viscosity shows time-dependence, indicating that the annealing process of the liquid is useful for crystal growth from the liquid. The viscosity of BaB_2O_4 melt has a different property between the normal and supercooling region. For the purpose of comparison, the viscous property of fluid Hg from the reference from the normal to expanded region has been discussed. The improved torsion pendulum method shows high potential to the study of the relationship between the viscosity and composition, atmosphere, temperature and history of a liquid.
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