The thermal and electrical conductivities of a sample of acheson graphite from 0 C. to 800 C

Abstract

Determinations have been made of both the thermal and the electrical conductivities of a sample of Acheson graphite over the temperature-range from 0°C. to 800°C. The thermal conductivity K is found to decrease from a value of 0.40 unit at 0°C. to 0.16 at 800°C., the rate of decrease being greater at lower temperatures. The electrical conductivity σ has at 0°C. a value of 1218 Ω-1.-cm-1., which increases to a maximum value of 1518 at 450°C. and decreases to 1444 at 800°C. The corresponding Lorenz function Kσ-1T-1 has a value of 121×10-8 at 0°C., which is more than 200 times the value indicated by the electronic theory and possessed by most well-conducting metals. With increase in temperature the value of the Lorenz function decreases rapidly, its value being given by the equation Kσ-1T-1=0.0294T-1.8. Thus the Wiedemann-Franz-Lorenz law does not hold for the present sample of graphite, but is replaced by the equation Kσ-1T0.8=a constant. The power to which the absolute temperature is raised is different, as well as the constant value of the expression.