Towards new temperature standards for contact thermometry above 660 C

In the course of a study on the behaviour of coupled heat pipes, perfect agreement has been obtained for the first time between measurements on the immersion characteristics in a mercury heat pipe and the Clausius-Clapeyron profile. This result opens up the perspective of using coupled heat pipes to relate thermodynamically two different temperature ranges, with the possibility of redefining one temperature range in terms of another. As a consequence, using sodium for the second heat pipe, the very high reproducibility of standard platinum resistance thermometers (SPRTs) below 400 °C can be transferred to the temperature range above 660 °C, surpassing the characteristics of high-temperature standard platinum resistance thermometers (HTSPRTs).