Improved Thermal Model for the Realization of the Triple Points of Cryogenic Gases as Temperature Fixed Points

The realization of the triple points of the cryogenic gases hydrogen, neon, oxygen, and argon as temperature fixed points at the highest level of accuracy requires consideration of the special properties of these fixed-point substances, as done in a general measurement protocol published elsewhere. The protocol is applied to the apparatus and methodology used for an international star intercomparison of sealed fixed-point cells. A generalized thermal model is developed to include the coexistence of different solid?Cliquid interfaces and various thermal resistances. This results in further components in the detailed uncertainty budget for the correction of the measuring power of the thermometer and for the extrapolation to the liquidus point. As a basis for an optimum fixed-point realization, especially an explanation is given why extremely long time periods may be necessary for the thermal recovery after pulses of the intermittent heating used for the calorimetric method.