Reference Points on the ITS-90 Temperature Scale

Major update of Reference Points on the ITS-90 Temperature Scale... 

SECONDARY REFERENCE POINTS ON THE ITS-90 TEMPERATURE SCALE (continued)... 

This table summarizes the significant points on the phase diagrams for the elements for which data are available. Values are given for the solid-liquid-gas triple point normal melting point t, normal boding point and critical temperature all are on the lTS-90 scale. An sp notation indicates a sublimation point, where the vapor pressure of the solid phase reaches 101.325 kPa (1 atm). Transition temperatures between allo-tropic forms are included for several elements. The major data sources are listed below values from Reference 1, which deals with reference points on the ITS-90 scale, were adopted when applicable. 

The following data were obtained by a critical evaluation of all existing experimental measurements on liquid helium, using a fitting procedure described in the reference. All values refer to liquid helium at saturated vapor pressure temperatures are on the ITS-90 scale. Several properties show a singularity at the lambda point (2.1768 K). 

This table gives Vcilues of the melting temperature of ice at various pressures, as calculated from the equation for the ice 1 -liquid water phase boundary recommended by the International Association for the Properties of Steam (LAPS). Temperatures are on the ITS-90 scale. See the Reference for information on forms of ice that exist at higher pressures. The transition points for transformations of the various forms of ice (in each case in equilibrium with liquid water) are ... 

Note that the lUPAC values refer to the IPTS-68 temperature scale, while the NIST values are based on the ITS-90 scale (where the normal boiling point is 99.974°C). The conversion between these scales can be found in Sec. 1. The difference between the scales leads to a difference in the density of water of about 20 ppm in the neighborhood of 100°C and much less at lower temperatures. 

This table gives properties of compressed water and superheated steam at selected pressures and temperatures. The properties included are density p, enthalpy//, entropy S, heat capacity at constant pressure C, and static dielectric constant (relative permittivity). The table was generated from the formulation approved by the International Association for the Properties of Water and Steam for general and scientific use. The reference state for this table is the liquid at the triple point, at which the internal energy and entropy are taken as zero. A duplicate entry in the temperature column indicates a phase transition (liquid-vapor) at that temperature property values are then given for both phases. In the 100 MPa section of the table, an entry is given at the critical temperature, 647.10 K. Temperatures refer to the ITS-90 scale, on which the normal boiling point of water is 373.12 K (99.97°C). 

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