A Laser Flash Technique for Determining Thermal Diffusivity of Liquid Metals at Elevated Temperatures

The laser flash technique has been frequently employed in many laboratories as a relatively fast and easy technique of modest accuracy for measuring the thermal diffusivity of solids at ordinary and elevated temperatures. We have refined this technique and extended it to measurements of the thermal diffusivities of liquid metals. In both solid and liquid metallic specimens we have found, on both experimental and theoretical grounds, that the accuracy of the results is very sensitive to the degree of uniformity of the laser pulse. By introducing appropriate optics between the laser and the specimen we have been able to obtain a very uniform laser pulse and thus considerably enhance the accuracy of our measurements. In particular in measuring the thermal diffusivity of liquid mercury at temperatures from 13 to 300°C the difference between our values and values derived from published results of steady state measurements was never more than 5%. A cinematographic study of the impact of the laser beam on the surface of the liquid mercury was also carried out.