NEW DATA-PROCESSING FOR THE SESSILE DROP TECHNIQUE AND THE APPLICATION TO CU-20 MASS-PERCENT NI/AL2O3 SYSTEM

A new method of data processing for the sessile drop technique was developed. The principle of this method is based on the Laplace equation in consideration of hydrostatic pressure in a sessile drop. This method consists of several procedures as follows. (1) The contour of the sessile drop was taken into an image processor by a CCD camera. (2) The principal curvatures and normal angle at many points on this contour are calculated numerically. (3) The sum of principal curvatures at each point is plotted as a function of the vertical distance from the top of the sessile drop. (4) The value of surface tension can be determined from the slope of the regession line obtained above. (5) The value of contact angle can be also obtained from the normal angle at the contact point of both sessile drop and substrate. The experiment was undertaken on Cu-20 mass%Ni alloy in Ar-7 vol%H-2, Ar atmosphere purified by Ti, and Ar atmosphere at 1523-1623 K. The surface tension of this alloy decreased with increasing temperature in the Ar-7 vol%H-2 atmosphere. In both the Ar atmosphere purified by Ti and the Ar atmosphere, however, the reverse took place. It can be ascribed to adsorbed oxygen onto the sessile drop surface. This data processing method can be applied to the real alloy system successfully. It was named "Curvature plotting method".