Thermal Conductivity of a Glass: I. Measurement by the Glass–Metal Contact

Abstract

The thermal (phonon) conductivity of glass has been measured by contacting the sample with a metal at a different uniform initial temperature. The subsequent temperature response in the metal is measured by a tiny thermocouple just underneath the (contact) surface. The coefficient of heat penetration λρcp follows directly from the fitted asymptotic temperature jump or drop for long times. Division by the separately measured heat capacity ρcp yields the thermal conductivity λ. The conductivity measurement reproducibility was σ = 3%. The standard deviation between validation measurements and round robin test results on Pyrex glass was σ = 5.8%, somewhat more than the accuracy σ = 5.2% of the round robin test results. The measurement method is insensible for slight imperfections of the thermal contact and infrared radiation diffusion (photon conductivity) in a hot glass. The method has been used with minor modifications for solid and molten samples at temperatures of 50–850°C and conductivities of 0.1–25 W/(m K). The thermal (phonon) conductivity of the investigated soda-lime silicate glasses increases slightly (∼27–30%) with temperature from ambient up to around the glass transition.