triple point
Noun
Meaning
(physics) The unique temperature and pressure at which the solid, liquid and gas phases of a substance are all in equilibrium.
A pressure vs. temperature diagram showing phases of matter and the triple point
(physics) A point where the incident shock wave, the reflected shock wave, the Mach stem, and one slipstream meet.
(mathematics) A point where a curve or surface intersects itself along three arcs.
Boy's surface, showing the triple point where it intersects itself
(meteorology) The intersection of an occluded front, cold front, and warm front.
(meteorology) The point where two boundaries, such as a dry line, outflow boundary, or cold front, intersect.
(plate tectonics) A point where three plates intersect.
Source: en.wiktionary.orgExamples
Above the triple point, CO 2 goes through the more familiar transitions via a liquid phase.
Even if the total pressure of a system is well above triple point of water, provided the partial pressure of the water vapor is 611.657 pascals then the system can still be brought to the triple point of water.
For example, the triple point at 251 K (−22 °C) and 210 MPa (2070 atm) corresponds to the conditions for the coexistence of ice Ih (ordinary ice), ice III and liquid water, all at equilibrium.
At temperatures just below the triple point, compression at constant temperature transforms water vapor first to solid and then to liquid (water ice has lower density than liquid water, so increasing pressure leads to a liquefaction ).
At this time, the triple point still had no formal definition for its equivalent kelvin value, which the resolution declared "will be fixed at a later date".
Beyond its triple point, a compound's normal boiling point, if any, is higher than its melting point.