Regulatory issues pertaining to the use of elemental mercury and technology barriers pertaining to the use of certain non-metal substitutes have created a need for new temperature reference cells to support International Temperature Scale (ITS) below 273 K. New research on non-metal triple point realizations and the development of practical reference cells for that purpose are needed. Two main thrusts are being pursed with this aim. One strategy involves the development of 'drop-in' replacement cells to substitute either sulfur hexafluoride or carbon dioxide triple points for those legacy types using mercury. That strategy focuses on temperatures in the range between 200 K and 234 K. NIST was the first lab to demonstrate the precise realization of the SF6 TP using immersion-type cells [1] and has also conducted preliminary research with CO2 cells. Advances are being made in other laboratories using CO2 immersion cells. [2] A second thrust area is focused on use of the xenon triple point, but in that case new technologies are needed to support the use of xenon immersion-type cells at lower temperatures (161.406 K). To date, progress has been limited to the use of small xenon cells [3] that are not compatible with the more prevalent immersion-type thermometric systems. NIST has a patented design combines the latest in closed-cycle compact Sterling-based coolers and multi-zone architecture to support the realization of any elemental or molecular species triple-point in the range 70 K and 200 K using immersion cells. New research and development efforts to leverage these advances are of the greatest interest to NIST and our stakeholders. Proposals that take advantage of state-of-the-art thermodynamic methodologies in physical chemistry and chemical engineering are encouraged.

1. W.L. Tew and K.N. Quelhas, Realizations of the Triple Point of Sulfur Hexafluoride in Transportable and Refillable Cells, J. Res. NIST, 123, Article No. 12013 (2018)
2. Y. Liang, J.T. Zhang, X.J. Feng, P. Qiu, Realization of the triple point of carbon dioxide in a transportable cell using long-stem SPRTs, Metrologia 60 015006 (2023)
3. P.P.M. Steur, P.M.C. Rourke, D. Giraldi, Comparison of xenon triple point realizations, Metrologia 56(1) 015008 (2019)

key words

Temperature; Triple Point; non-metal solid; ITS-90; Fixed-point cells; argon; xenon; carbon dioxide; sulfur hexafluoride;

Citizenship:  Open to U.S. citizens

Level:  Open to Postdoctoral applicants