Surface tension of molten bismuth at different oxygen partial pressure with the sessile drop method

The surface tension of molten bismuth has been analyzed and determined by the sessile drop method at temperatures ranging from 573 to 973 K and in the oxygen partial pressure (Po2) range from 8.56 × 10−16 to 8.37 × 10−6 MPa. At Po2= 8.56 × 10−16 and 5.23 × 10−13 MPa, the surface tension decreases linearly with the increase in temperature and its temperature coefficients are −0.087 and −0.064 mN/m/K, respectively. However, at high Po2 in argon gas (8.37 × 10−6 MPa, not deoxidized with magnesium chips), the surface tension values and the absolute value of its temperature coefficient are both smaller than that at low Po2 ranging from 8.56 × 10−16 to 5.23 × 10−13 MPa. Based on the review of the surface tension and the temperature coefficient of molten bismuth reported by various investigators, the surface tension obtained by our research is recommended as σ (mN/m) = 382 − 0.076 (T− 544 K). The effect of oxygen in the measurement atmosphere is considered from thermodynamics and kinetics on the basis of a model, and the experimental results can be explained qualitatively.