Vitrification is characteristic for amorphous materials or disordered systems and occurs when bonding between elementary particles (atoms, molecules, forming blocks) becomes higher than a certain threshold value. Thermal fluctuations break the bonds; therefore, the lower the temperature, the higher the degree of connectivity. Because of that amorphous materials have a characteristic threshold temperature termed glass transition temperature (Tg): below Tg amorphous materials are glassy whereas above Tg they are molten.
Usually, it is achieved by rapidly cooling a liquid through the glass transition. Certain chemical reactions also result in glasses. An important application is the vitrification of an antifreeze-like liquid in cryopreservation.
In a wider sense, the embedding of material in a glassy matrix is also called vitrification. An important application is the vitrification of radioactive waste to obtain a stable compound that is suitable for ultimate disposal.
"Vitrification is the process of melting that clays and glazes go through as they are fired to maturity. In a fully matured clay body, the spaces between refractory particles are completely filled up with glass, fusing the particles together and making the clay body impervious to water."
- The maximum Cone rating of a stoneware or porcelain clay is the temperature at which it vitrifies. This is the hardening, tightening and finally the partial glassification of the clay. Vitrification results from fusions or melting of the various components of the clay. The strength of fired clay is increased by the formation of new crystalline growth within the clay body, particularly the growth of mullite crystals. Mullite is an aluminum silicate characterized by a long needle-like crystal. These lace the structure together, giving it cohesion and strength.
Glazing alone does not make pottery vitrified or impermeable to water. High fire clay and, if used, high temperature glaze are required, which must be heated sufficiently to fuse into glass. Porcelain and Bone china are examples of vitrified pottery; stoneware may be vitrified or semi-vitrified. All are impermeable to water.
When sucrose is cooled slowly it results in crystal sugar (or rock candy), but when cooled rapidly it can form syrupy cotton candy (candyfloss). In the process of vitrification the solid waste is exposed to heat and is converted into a sort of glass-like substance.
Vitrification can also occur when starting with a liquid such as water, usually through very rapid cooling or the introduction of agents that suppress the formation of ice crystals. This is in contrast to ordinary freezing which results in ice crystal formation. Additives used in cryobiology or produced naturally by organisms living in polar regions are called cryoprotectants.
Arctic frogs and some other ectotherms naturally produce glycerol or glucose in their livers to reduce ice formation. When glucose is used as a cryoprotectant by arctic frogs, massive amounts of glucose are released at low temperature and a special form of insulin allows for this extra glucose to enter the cells. When the frog rewarms during spring, the extra glucose must be rapidly eliminated, but stored. Arctic insects also use sugars as cryoprotectants. Arctic fish use antifreeze proteins, sometimes appended with sugars, as cryoprotectants.
Ordinary soda-lime glass, used in windows and drinking containers, is created by the addition of sodium carbonate and lime (calcium oxide) to silicon dioxide. Without these additives silicon dioxide will require very high temperature to obtain a melt and subsequently (with slow cooling) a glass.
Vitrification is a proven technique in the disposal and long-term storage of nuclear waste or other hazardous wastes in a method called geomelting. Waste is mixed with glass-forming chemicals in a furnace to form molten glass that then solidifies in canisters, thereby immobilizing the waste. The final waste form resembles obsidian and is a non-leaching, durable material that effectively traps the waste inside. The waste can be stored for relatively long periods in this form without concern for air or groundwater contamination. Bulk vitrification uses electrodes to melt soil and wastes where they lay buried. The hardened waste may then be disinterred with less danger of widespread contamination. According to the Pacific Northwest National Labs, "Vitrification locks dangerous materials into a stable glass form that will last for thousands of years."
Vitrification in cryopreservation is used as a common method to preserve, for example, human egg cells (oocytes) (in oocyte cryopreservation) and embryos (in embryo cryopreservation). For years, glycerol has been used in cryobiology as a cryoprotectant for blood cells and bull sperm, allowing storage at liquid nitrogen temperatures. However, glycerol cannot be used to protect whole organs from damage. Instead, many biotechnology companies are researching the development of other cryoprotectants more suitable for such uses. A successful discovery may eventually make possible the bulk cryogenic storage (or "banking") of transplantable human and xenobiotic organs. A substantial step in that direction has already occurred. Twenty-First Century Medicine has vitrified a rabbit kidney to -135 °C with their proprietary vitrification cocktail. Upon rewarming, the kidney was successfully transplanted into a rabbit, with complete functionality and viability, able to sustain the rabbit indefinitely as the sole functioning kidney.
Currently, vitrification techniques have only been applied to brains (neurovitrification) by Alcor and to the upper body by the Cryonics Institute, but research is in progress by both organizations to apply vitrification to the whole body.
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- Vitrification of pottery
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- Clay vitrifying temperatures
- What is China? As with stoneware, the body becomes vitrified; which means the body fuses, becomes nonabsorbent, and very strong. Unlike stoneware, china becomes very white and translucent.
- Arthur Dodd & David Murfin. Dictionary of Ceramics; 3rd edition. The Institute of Minerals, 1994.
- M.I. Ojovan, W.E. Lee. Glassy wasteforms for nuclear waste immobilisation. Metallurgical and Materials Transactions A, 42 (4), 837-851 (2011).
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- Steven Ashle (June 2002). "Divide and Vitrify" (PDF). Scientific American. Retrieved May 10, 2015.
- Stefan Lovgren, "Corpses Frozen for Future Rebirth by Arizona Company", March 2005, National Geographic