One of the key actions in freeze drying is triple point. People are a bit confused with how this happens and why, and there is also a misconception that this is sublimation. The fact is that triple point is a stage you must achieve for the sublimation phase to start. Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase.
Triple Point Explained:
In physics and chemistry, the triple point of a substance is the temperature and pressure at which three phases (gas, liquid, and solid) of that substance may coexist in thermodynamic equilibrium.
Scientific explanation: The single combination of pressure and temperature at which pure water, pure ice, and pure water vapour can coexist in a stable equilibrium occurs at exactly 273.16 kelvins (0.01 °C) and a pressure of 611.73 pascals (ca. 6.1173 millibars, 0.0060373057 atm).
Simply put, the triple point of water is the only temperature at which water can exist in all three states of matter; solid (ice), liquid (water), and gas (water vapour). This temperature is 0.01°C.
At that point, it is possible to change all of the substance to ice, water, or vapour by making infinitesimally small changes in pressure and temperature.
To help explain this futher, here is a video which shows how one small change affects the equilibrium. (soruce:Science Channel)
The image shows at what stage the triple point happens and how it will react when the equilibrium is changed.
In chemistry and physics, the triple point is the temperature and pressure at which solid, liquid, and vapor phases of a particular substance coexist in equilibrium. It is a specific case of thermodynamic phase equilibrium. The term "triple point" was coined by James Thomson in 1873.
Simply put, the triple point of water is the only temperature at which water can exist in all three states of matter; solid (ice), liquid (water), and gas (water vapour). This temperature is 0.01°C.
where δ V = M ( 1 / d l − 1 / d s ) where M is the molecular weight and d the densities of liquid and solid. T 1 and P 1 are temperature and pressure at the triple point. Thus you have to iterate T 1 and P 1 by fitting (say by least squares) to the calculated curves to whatever data you have to find the triple point.
At the triple point, all three phases (solid, liquid, and gas) are in equilibrium. Since the triple point is a point, there is only one temperature and one pressure where the three phases will exist. This fact often helps in identifying compounds or in problem solving.
It's called the Triple Point of Water. Put simply, it's the point at which water, subject to the right temperature and pressure, can exist as a solid, liquid and gas at once. In more technical terms, water at this point is referred to as existing in thermodynamic equilibrium.
Triple point on a phase diagram is indicated by the point where all three equilibrium lines meet. This is the temperature and pressure combination that allows for all three phases of a substance to occur simultaneously. There will be solid, liquid and gas molecules all existing in a state of equilibrium.
Triple point of water is the temperature where all the three states of water – liquid, gas and solid co-exist in equilibrium with each other and it's value is 0.01 degree Celcius.
The thermodynamic temperature of the triple point of water was defined for many years to be exactly 273.16 kelvins (where 0 K is the absolute zero of temperature).
The triple point for water occurs at a pressure of 4.6 torr and 0.01oC. Click on the diagram to see a microscopic view of the phase(s) that exist for a given temperature and pressure. At this temperature and pressure, liquid and gaseous water exist in equilibrium. A microscopic view is shown below.
For a “usual” triple point we therefore have to go to the element with the second lowest melting temperature: hydrogen with melting point 13.99 K, it has its triple point at 13.84 K and 7 kPa.
Therefore sign (or ∴), a shorthand form of the word "therefore" or "thus" U+20DB ◌⃛ COMBINING THREE DOTS ABOVE character is a combining diacritical mark for symbols. When used after U+0020 SPACE, it is used in mathematical notations (and represented with the "tdot" or "TripleDot" entities in HTML 5.0 and MathML 3.0)
The triple point is the pace on a phase diagram where all three lines converge. At that point the substance exists as a mixture of gas, liquid, and solid all in equilibrium with one another. An increase in temperature will move the substance to the right on the phase diagram into the gas portion of the diagram.
In thermodynamics , the triple point of a substance is the temperature and pressure at which the three phases ( gas , liquid , and solid ) of that substance coexist in thermodynamic equilibrium . For example, the triple point of mercury occurs at a temperature of −38.83440 °C and a pressure of 0.2 m Pa .
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