Measurement of contact angle in systems involving liquid metals

A technique has been developed for measurement of the contact angle of liquid metals with solid materials. The liquid metal, when contained in a small cup (inner diameter < 4 mm) forms a concave or convex mirror surface. For the present technique, an optical method was devised to measure the radius of curvature of this mirror surface, from which the contact angle can be determined. The surface of the liquid metal approaches sphericity as the diameter of its container is decreased. The optical system formed in this method is non-paraxial. An analytical formula, Valid for a spherical non-paraxial mirror, for calculation of image size was deduced. The technique has been demonstrated using the mercury-graphite (15.9% total porosity) system at room temperature and the contact angle was determined to be 152.5 +/- 2 degrees.