Vitrification
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Image:Vitrification1.jpg Vitrification is a process of converting a material into a glass-like amorphous solid which is free of any crystalline structure, either by the quick removal or addition of heat, or by mixing with an additive. Solidification of a vitreous solid occurs at the glass transition temperature (which is lower than melting temperature, Tm, due to supercooling).
When the starting material is solid, vitrification usually involves heating the substances to very high temperatures. Many ceramics are produced in such a manner. Vitrification may also occur naturally when lightning strikes sand, where the extreme and immediate heat can create hollow, branching rootlike structures of glass, called fulgurite.
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Examples
When sucrose is cooled slowly it results in crystal sugar (or "rock candy"), but when cooled rapidly it can form syrupy "cotton candy".
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 other reptiles naturally produce glycerol or glucose in their livers to reduce ice formation. When glucose is used as a cryoprotectant by artic 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 in the Spring, the extra glucose must be rapidly eliminated, but stored. Arctic insects also use sugars as cryoprotectants.
Applications
Ordinary soda-lime glass, used in windows and drinking containers, is created by the addition of soda and lime (calcium oxide) to silicon dioxide. Without these additives silicon dioxide will (with slow cooling) form sand or quartz crystal, not glass.
Vitrification is a proven technique in the disposal and long-term storage of nuclear waste or other hazardous wastes. Waste is mixed with glass-forming chemicals to form molten glass that then solidifies, 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. According to the Pacific Northwest National Labs, "Vitrification locks dangerous materials into a stable glass form that will last for thousands of years."Template:Ref.
Ethylene glycol is used as automotive antifreeze and propylene glycol has been used to reduce ice crystals in ice cream, making it smoother.
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 currently 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. At the July, 2005 annual conference of the Society for Cryobiology Template:Ref Twenty-First Century Medicine announced the vitrification of a rabbit kidney to -135ºC with their proprietary vitrification cocktail. The kidney was successfully transplantated upon rewarming to a rabbit, with complete functionality and viability.
In the context of cryonics, especially in preservation of the human brain, vitrification of tissue is thought to be necessary to prevent destruction of the tissue or information encoded in the brain. 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 vitrication to the whole body.
Notes
References
- Steven Ashle, Divide and Vitrify, June 2002, Scientific American
- Stefan Lovgren, Corpses Frozen for Future Rebirth by Arizona Company, March 2005, National Geographic
- Vitrification: Putting the Heat on Waste