Heat-loss modified Angstrom method for simultaneous measurements of thermal diffusivity and conductivity of graphite sheets: The origins of heat loss in Angstrom method

• Simultaneous measurements of thermal diffusivity and conductivity.
• Heat loss is taken into account to achieve high accuracy.
• The origins of heat loss parameter are also discussed.

Angstrom method is a steady-state measurement for thermal diffusivity αα using ac heating. Since thermal conductivity λλ is a better-known quantity, measured diffusivity αα is sometimes transformed into λλ based on relation λ=Cvαλ=Cvα using recorded or DSC measured CvCv. However, Angstrom method itself is principally possible to extend to specific heat measurements, yet the accuracy is not promising due to the complexity of heat loss. Here we present a modified method for simultaneous measurements of thermal diffusivity and thermal conductivity with high accuracy by taking heat loss into account. A linear heat loss term m2Tm2T is introduced into the diffusion equation and the thermal conductivity λλ can be directly measured instead of specific heat. The measured thermal properties of commercial graphite sheets agree well with their nominal value. The origins of m2m2 are also discussed. m2m2 can be divided into amplitude independent and dependent part. From the basics of radiation and convection, the first-order radiation and convection comprise the amplitude independent part, while the dependent part includes higher order (dominated by second-order) radiation. Although the amplitude independent part agrees well with the extrapolated value of m2m2 at zero amplitude, the second-order radiation cannot fully cover the measured amplitude dependent part. This discrepancy is further explained by floating temperature baseline variation due to residual heat during heat oscillation.