Thermal Diffusivity and Conductivity with a Dilatometer

Abstract

Quartz based differential dilatometers are commonly used to measure thermal strain and coefficients of linear thermal expansion of solid materials. With modifications they can be adopted to perform additional measurements of thermal diffusivity and thermal conductivity. This paper outlines the experimental and analysis approach to achieving a versatile instrument for the simultaneous measurement of all three properties. Design goals included minimal sample preparation, size or shape restrictions, no attachments or reference materials, potentially rapid operation from 77 to 2000K and extension to the measurement of liquids, powders and foams. Sample temperature uniformity is most readily achieved with a horizontal system—hence the most common dilatometer design. Diffusivity and conductivity were determined through formation of short term thermal gradients and by sensing the temperature changes of the sample ends. Heat flow models were evaluated in terms of their compatibility with the boundary conditions. Semi-infinite and finite length models were found adequate depending on the sample dimensions and diffusivity/conductivity ranges. A constant temperature front surface model, which also takes the lateral heat transfer into account was found suitable for high diffusivity materials. Data are included for graphite, Pyroceram and steel.