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Concept
Amorphous ice
Summary
Amorphous ice (non-crystalline or "vitreous" ice) is an amorphous solid form of water. Common ice is a crystalline material wherein the molecules are regularly arranged in a hexagonal lattice, whereas amorphous ice lacks long-range order in its molecular arrangement. Amorphous ice is produced either by rapid cooling of liquid water (so the molecules do not have enough time to form a crystal lattice), or by compressing ordinary ice at low temperatures.
Although almost all water ice on Earth is the familiar crystalline ice Ih, amorphous ice dominates in the depths of interstellar medium, making this likely the most common structure for H2O in the universe at large.
Just as there are many different crystalline forms of ice (currently more than seventeen are known), there are also different forms of amorphous ice, distinguished principally by their densities.
Amorphous ices have the property of suppressing long-range density fluctuations and are, therefore, nearly hyperuniform. Despite the epithet "amorphous", artificial intelligence has shown that amorphous ices are glasses.
Amorphous ice may be formed when liquid water is cooled to its glass transition temperature (about 136 K or −137 °C) in milliseconds to prevent the spontaneous nucleation of crystals.
Pressure is another important factor in the formation of amorphous ice, and changes in pressure may cause one form to convert into another.
Cryoprotectants can be added to water to lower its freezing point (like antifreeze) and increase viscosity, which inhibits the formation of crystals. Vitrification without addition of cryoprotectants can be achieved by very rapid cooling. These techniques are used in biology for cryopreservation of cells and tissues.
Low-density amorphous ice, also called LDA, vapor-deposited amorphous water ice or amorphous solid water (ASW) is usually formed in the laboratory by a slow accumulation of water vapor molecules (physical vapor deposition) onto a very smooth metal crystal surface under 120 K.
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