triple point

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triple point

Chem the temperature and pressure at which the three phases of a substance are in equilibrium. The triple point of water, 273.16 K at a pressure of 611.2 Pa, is the basis of the definition of the kelvin
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Triple Point

 

in thermodynamics, the point on a phase diagram at which three different phases of a substance can coexist in equilibrium.

It follows from the phase rule that there cannot be more than three phases in equilibrium in a substance consisting of one chemical element or compound, that is, a one-component system. The three phases may be, for example, the solid, liquid, and gas phases or, as in the case of sulfur, the liquid phase and two al-lotropes of the crystalline phase. The phases can coexist only for specific values of temperature T and pressure p, which determine the coordinates of the triple point on the p-T diagram.

For example, for carbon dioxide the triple-point temperature Ttp = 216.6°K, and the triple-point pressure ptp = 5.12 atmospheres. At the triple point of water, which is the fundamental fixed point of the absolute thermodynamic temperature scale, Ttp = 273.16°K (exactly), and ptp = 4.58 mm Hg.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

triple point

[′trip·əl ′pȯint]
(physical chemistry)
A particular temperature and pressure at which three different phases of one substance can coexist in equilibrium.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
The pressure [p.sub.v] is lower than the triple-point pressure of C[O.sub.2] if the upstream pressure [p.sub.in] varies from 8 MPa (1160 lbf x [in..sup.-2]) to 12 MPa (1740 lbf x [in..sup.-2]).
A new equation of state for carbon dioxide covering the fluid region from the triple-point temperature to 1100 K at pressure up to 800 MPa.
Strouse, Effects of Different Methods of Preparation of Ice Mantles of Triple Point of Water Cells on the Temporal Behaviour of the Triple-Point Temperatures, Metrologia 34, 215-233 (1997).
Thornton, Determination of the Triple-Point Temperature of Gallium, Metrologia 15, 201-215 (1979).
Ferri, The Triple-point Temperature of pure Equilibrium Deuterium, Metrologia 24, 107-120 (1987).
Illumination Effect on Temperature Measurement in Water Triple-Point Cells Packed in Crushed Ice, Can.
Mangum, Standard Reference Material 1972, 1,3-Diox olan-2-one (Ethylene Carbonate) Triple-Point Standard, NIST SRM Certificate (1994) 4 p.
Mangum, Standard Reference Material 1969, Rubidium Triple-Point Standard, NIST SRM Certificate (1991) 4 p.
Mangum, Standard Reference Material 1973, n-Docosane Triple-Point Standard, NIST SRM Certificate (1994) 3 pp.
El-Sabban, SRM 1970: Succinonitrile Triple-Point Standard-A Temperature Reference Standard Near 58.08 [degrees]C.
Mangum, Standard Reference Material 1970, Succinonitrile Triple-Point Standard, NIST SRM Certificate (1991) 4 p.