Papers by Author: Xiaogang Shang

Abstract: The spreading of a liquid on a solid surface is very important in a number of practical applications. Many interesting physical phenomena can be observed when a small drop of a fluid spreads on a solid surface. These phenomena are related to spreading dynamics, which can be classified as spontaneous and forced wetting. In this work spreading dynamics of liquid metals and solders alloys were established to determine the mechanism of spreading. The spreading dynamics of bismuth, tin, 99.3wt%Sn-0.7wt%Cu alloy, 99.8 wt%Bi-0.2wt%Cu alloy and 60wt%Sn-40wt%Pb were studied by using sessile droplet method. Tests were carried out at a temperature range from 280oC to 350oC over a copper substrate. Results showed a discontinuous decrease of spreading velocity as a function of time. For example, spreading velocity of liquid tin at 320oC decreased from 234.86 mm/s at 0.0025 s to 4.62 mm/s at 0.0225 s, after that increased up to 9.24 mm/s at 0.025 s, then down back to 6.07 mm/s at 0.03 s, and finally reached to the end of spreading after 0.04 s.

Abstract: In this work an applicable mathematical method is described in the analysis and description of the profile of the drop obtained in the sessile droplet test. The proposed method bases on the study of the differential geometry of surfaces and in the analysis of phenomena related with the creation, expansion and contraction of interfaces to calculate the surface tension of metals. Liquid vapor surface energy of tin and indium were calculated by using sessile droplet method. Tests were carried out at 280 and 350oC temperature over a titanium nitride substrate. Results showed a very good agreement between both methodologies. For example, Sn at 280oC presented a surface tension of 545 mN/m, which is closer to the value reported in the literature (550 mN/m).