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NIST
Sealed-Cell Fixed Point Development
Goals: Develop, maintain
and disseminate ITS-90 primary and secondary fixed points using sealed-cell
devices for triple point realizations.
Applications:
- International Fixed Point Comparisons for gas-based triple points
- Reference Material development
- Fixed Point Dissemination to Secondary Standards Laboratories
- Temperature Scale Research
Advantages:
- Compact and robust fixed point devices
- Easily Transportable
- Minimum chance of contamination
- Long term stability
Range: T=161.406 K
to 13.8 K
NIST Sealed Triple Point
Cells currently in place or under development:
|
Material
|
Triple
Point
|
Status
|
Purity
|
Melting
Range
|
| e-H2 |
13.8033 K |
ITS-90 |
99.9999% |
- |
| e-D2* |
18.689 K |
secondary |
99.995% |
- |
| Ne |
24.5561 K |
ITS-90 |
99.9995% |
0.27 mK |
| O2 |
54.3584 K |
ITS-90 |
99.9999+% |
0.06 mK |
| Ar |
83.8058 K |
ITS-90 |
99.9999% |
0.18 mK |
| Xe |
161.406 K |
secondary |
99.999% |
0.5 mK |
* In collaboration with the
IMGC, Turin, Italy
Techniques:
- Melting plateau
- Pulsed heating
- Adiabatic re-equilibration
Cell Designs:
- AR and O2: All Stainless Steel, Types 316L and 304L
- NE and H2: Type 316L SS with OFHC copper inserts, electron-beam
welded (see Figure 1)
- D2: Type 316L Vacuum-Arc-Remelt
- Xe: All OFHC copper (NRC type)
Figure 1. A Ne TP cell and
wiring platform.
For more information, contact
Weston Tew at weston.tew@nist.gov
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