Measurements of the thermal expansion and heat capacity of metals by electromagnetic levitation

Abstract

Electromagnetic levitation is a very useful non-contact melting technique that can be exploited for measurements of thermophysical properties of many reactive metals and alloys. This study focused on thermal expansion and heat capacity measurements based on digital image processing and the modulated power method using the electromagnetic levitation technique (EML). An improved pixel threshold method was developed for accurate determination of the thermal expansion of an axisymmetrically levitated droplet.The modulated power method, originally proposed by Fecht and Johnson (1991), was exploited for measuring the heat capacity of metals in the temperature range of around 1300 to 1800 K. Moffat’s uncertainty estimation procedure (Moffat, 1998) was used to theoretically analyzethe various contributions to the experimental uncertainty. A numerical model was developed to examine the sample modulated movement and non-uniform temperature distribution effects during the modulated heating process. The experimental work used different materials including nickel, titanium, zirconium and nickel-based superalloy IN718. The experiments were performed with the electromagnetic levitator of Auburn University.