Laser interferometric measurement of the surface tension of Ni in a vacuum

The zero creep method of surface tension measurement has been utilized in conjunction with laser interferometry to measure the surface tension ('y) of Ni at 1040 K, 1090 K, and 1 140 K in a vacuum. The sample strains can be measured in-situ,without disturbing the sample. This method utilizes foils 25 tm thick which are cylindrically configured (1.25 cm inside diameter) and are stressed by a load at the bottom of the sample cylinder. Through a stress analysis on the sample, the stress in the downward direction can be related to the surface tension of the sample. The stress (as) at the zero creep point, where the forces due to the surface tension of the sample are balanced by the force due to the load on the sample, is determined by linear interpolation of several differently loaded samples (1 .5-15 g 0.001 g) which result in positive or negative strain rates, depending on that load. Prior techniques utilized to measure the sample strains are not accurate at temperatures less than 85 % Tm. The application of laser interferometry to the measurement of sample strain allows the metal surface tension to be measured at temperatures less than 85 % Tm, possibly as low as 45 % Tm. The surface tension of Ni was measured to be 3 155 dynes/cm at 1040 K (60 % Tm), 3085 dynes/cm at 1090 K (63 % T.), and 2933 dynes/cm at 1 140 K (66 % T).