The triple point of sulfur hexafluoride (SF6) has been precisely determined to be 223.555 23 Kelvin (K), with an uncertainty of 0.000 49 K (for a coverage factor k=1). This exact value is established on the full low-temperature e-H2–TPW subrange of the International Temperature Scale of 1990 (ITS-90).
Understanding the Triple Point
A triple point is a specific temperature and pressure at which three phases (solid, liquid, and gas) of a substance coexist in thermodynamic equilibrium. It represents a unique and invariant state, making it an extremely valuable fixed point for calibrating thermometers and defining precise temperature scales.
Determining the SF6 Triple Point
The accurate determination of sulfur hexafluoride's triple point involved a meticulous process. Researchers utilized a method based on analyzing the melt plateau of SF6. This technique involved creating a linear fit of the experimental data versus the melted fraction of the substance. This fitted line was then carefully extrapolated to the liquidus point, which signifies the state where the substance is entirely liquid. This analytical approach allowed for a highly accurate measurement of the triple point temperature.
Key Data for SF6 Triple Point
For clarity and quick reference, the precise details of the sulfur hexafluoride triple point are summarized below:
| Property | Value |
|---|---|
| Triple Point Temperature | 223.555 23 K |
| Uncertainty (k=1) | 0.000 49 K |
| Temperature Scale | ITS-90 (e-H2–TPW subrange) |
Significance and Applications
The precise measurement of the SF6 triple point is crucial for various scientific and industrial applications, particularly in the fields of metrology (the science of measurement) and the development of highly accurate temperature standards. Its invariant nature makes it an ideal fixed point for:
- Thermometer Calibration: Ensuring the accuracy and reliability of temperature measuring devices.
- Defining Temperature Scales: Contributing to the fundamental definition of temperature, especially within the low-temperature range of the International Temperature Scale of 1990 (ITS-90).
- Scientific Research: Providing a stable reference for experiments requiring precise temperature control and measurement.
This exact value ensures consistency and comparability in temperature measurements across different laboratories and systems worldwide.
