Vitrification (from Latin vitreum, "glass" via French vitrifier) is the transformation of a substance into a glass, that is to say, a non-crystalline amorphous solid. In the production of ceramics, vitrification is responsible for its impermeability to water.
Vitrification is usually achieved by heating materials until they liquidize, then cooling the liquid, often rapidly, so that it passes through the glass transition to form a glassy solid. Certain chemical reactions also result in glasses.
In terms of chemistry, 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.
In a different sense of the word, the embedding of material inside a glassy matrix is also called vitrification. An important application is the vitrification of radioactive waste to obtain a substance that is hopefully safer and more stable for disposal.
Vitrification is the progressive partial fusion of a clay, or of a body, as a result of a firing process. As vitrification proceeds, the proportion of glassy bond increases and the apparent porosity of the fired product becomes progressively lower. Vitreous bodies have open porosity, and may be either opaque or translucent. In this context 'zero porosity'; may be defined as less than 1% water absorption. However, various standard procedures define the conditions of water absorption. An example is by ASTM, who state "The term vitreous generally signifies less than 0.5% absorption. except for floor and wall tile and low-voltage electrical insulators which are considered vitreous up to 3% water absorption."
Pottery can be made impermeable to water by glazing or by vitrification. Porcelain, bone china and sanitaryware are examples of vitrified pottery, and are impermeable even without glaze. Stoneware may be vitrified or semi-vitrified; the latter type would not be impermeable without glaze.
Vitrification can also occur in 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. Vitrification is used in cryo-electron microscopy to cool samples so quickly that they can be imaged with an electron microscope without damage. In 2017, the Nobel prize for chemistry was awarded for the development of this technology, which can be used to image objects such as proteins or virus particles.
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 used in 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. It is widely assumed that such 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 lie 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
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.
- 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
- Varshneya, A. K. (2006). Fundamentals of Inorganic Glasses. Sheffield: Society of Glass Technology.
- Dodd, Arthur; Murfin, David (1994). Dictionary of Ceramics (3rd ed.). London: The Institute of Minerals. ISBN 0901716561.
- Ojovan, M. I.; Lee, W. E. (2010). "Connectivity and glass transition in disordered oxide systems". Journal of Non-Crystalline Solids. 356: 2534–2540.
- 'Role Of Accessory Minerals On The Vitrification Of Whiteware Compositions.' N.M.Ghoneim; E.H.Sallam; D.M. Ebrahim. Ceram.Int. 16. No.1. 1990.
- Whitewares: Production, Testing and Quality Control. William Ryan & Charles Radford. Institute of Materials, 1997
- 'Methods Of Extending The Narrow Vitrification Range Of Clays.' E.V. Glass & Ceramics 36, (8), 450, 1979.
- 'Control Of Optimum Vitrification In Vitreous And Porcelain Bodies.' E.Signorini. Ceram.Inf. 26. No.301. 1991
- ASTM C242-01. 'Standard Terminology Of Ceramic Whitewares and Related Products'.
- 'Body Builders.' J.Ahmed. Asian Ceramics. June 2014
- 'An Introduction To The Technology Of Pottery.' Paul Rado, Institute of Ceramics. 1988.
- Dubochet, J.; McDowall, A.W. (December 1981). "Vitrification of pure water for electron microscopy". Journal of Microscopy. 124 (3): 3–4. doi:10.1111/j.1365-2818.1981.tb02483.x.
- Dubochet, J. (March 2012). "Cryo-EM-the first thirty years". Journal of Microscopy. 245 (3): 221–224. doi:10.1111/j.1365-2818.2011.03569.x.
- "Nobel Prize in Chemistry Awarded for Cryo-Electron Microscopy". The New York Times. October 4, 2017. Retrieved 4 October 2017.
- Ojovan, Michael I.; Lee, William E. (2011). "Glassy wasteforms for nuclear waste immobilization". Metallurgical and Materials Transactions A. 42 (4): 837–851. Bibcode:2011MMTA...42..837O. doi:10.1007/s11661-010-0525-7.
- "Waste Form Release Calculations for the 2005 Integrated Disposal Facility Performance Assessment" (PDF). PNNL-15198. Pacific Northwest National Laboratory. July 2005. Retrieved 2006-11-08.