Vitrification (from Latin vitrum 'glass', viaFrenchvitrifier) is the full or partial transformation of a substance into aglass,[1] that is to say, a non-crystalline oramorphous solid. Glasses differ from liquids structurally and glasses possess a higher degree of connectivity with the sameHausdorff dimensionality of bonds as crystals: dimH = 3.[2] In the production ofceramics, vitrification is responsible for their impermeability towater.[3]
Vitrification is usually achieved by heating materials until they liquify, then cooling the liquid, often rapidly, so that it passes through theglass transition to form a glassy solid. Certain chemical reactions also result in glasses.
In terms ofchemistry, 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.[4] Thermal fluctuations break the bonds; therefore, the lower thetemperature, the higher the degree of connectivity. Because of that, amorphous materials have a characteristic threshold temperature termed glass transition temperature (Tg): belowTg amorphous materials are glassy whereas aboveTg they are molten.
The most common applications are in the making ofpottery, glass, and some types of food, but there are many others, such as the vitrification of an antifreeze-like liquid incryopreservation.
In a different sense of the word, the embedding of material inside a glassy matrix is also calledvitrification. An important application is the vitrification of radioactive waste to obtain a substance that is thought to be safer and more stable for disposal.
One study suggests[5][6][7][8] that, during theeruption of Mount Vesuvius in 79 AD, a victim'sbrain was vitrified by the extreme heat of thevolcanic ash; however, this has been strenuously disputed.[9]
Vitrification is the progressive partial fusion of aclay, or of a body, as a result of afiring process. As vitrification proceeds, the proportion of glassy bond increases and the apparent porosity of the fired product becomes progressively lower.[3][10] Vitreous bodies have open porosity, and may be eitheropaque ortranslucent. In this context, "zero porosity" may be defined as less than 1% water absorption. However, various standard procedures define the conditions of water absorption.[11][12][13] An example is byASTM, who state "The term vitreous generally signifies less than 0.5% absorption, except for floor and wall tile and low-voltageelectrical insulators, which are considered vitreous up to 3% water absorption."[14]
Pottery can be made impermeable to water byglazing 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.[15][3][16]
Whensucrose is cooled slowly it results in crystalsugar (orrock candy), but when cooled rapidly it can form syrupycotton candy (candy/fairy floss).
Vitrification can also occur in a liquid such as water, usually through very rapid cooling or the introduction of agents that suppress the formation ofice crystals. This is in contrast to ordinaryfreezing which results in ice crystal formation. Vitrification is used incryo-electron microscopy to cool samples so quickly that they can be imaged with an electron microscope without damage.[17][18] 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.[19]
Ordinarysoda-lime glass, used in windows and drinking containers, is created by the addition ofsodium carbonate and lime (calcium oxide) tosilicon dioxide. Without these additives, silicon dioxide would require very high temperature to obtain a melt, and subsequently (with slow cooling) a glass.
Vitrification is used in disposal and long-term storage ofnuclear waste or other hazardous wastes.[20] 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 resemblesobsidian 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 forair orgroundwatercontamination. Bulk vitrification useselectrodes to melt soil and wastes where they lie buried. The hardened waste may then be disinterred with less danger of widespread contamination. According to thePacific Northwest National Labs, "Vitrification locks dangerous materials into a stable glass form that will last for thousands of years."[21]
Vitrification in cryopreservation is used to preserve, for example, human egg cells (oocytes) (inoocyte cryopreservation) and embryos (inembryo cryopreservation). It prevents ice crystal formation and is a very fast process: -23,000 °C/min.
Currently, vitrification techniques have only been applied to brains (neurovitrification) byAlcor and to the upper body by theCryonics Institute, but research is in progress by both organizations to apply vitrification to the whole body.
Manywoody plants living in polar regions naturally vitrify their cells to survive the cold. Some can survive immersion inliquid nitrogen andliquid helium.[22] Vitrification can also be used to preserve endangered plant species and their seeds. For example,recalcitrant seeds are considered hard to preserve. Plant vitrification solution (PVS), one of application of vitrification, has successfully preservedNymphaea caerulea seeds.[23]
Additives used incryobiology or produced naturally by organisms living inpolar regions are calledcryoprotectants.
| Formula | Tg (Mid, °C) |
| 1M sucrose | -30.9 |
| 1M glucose | -41.3 |
| 1M trehalose | -68.0 |
| 50% sucrose + 50% glycerol (PVS3) | -90.7 |
| 50% sucrose + 50% (ethylene glycol) EG | -101.1 |
| 50% sucrose + 50% (propylene glycol) PG | -89.1 |
| 75% sucrose + 25% glycerol | -81.2 |
| 75% sucrose + 25% EG | -80.7 |
| 75% sucrose + 25% PG | -63.6 |
| 25% sucrose + 75% glycerol | -91.3 |
| 25% sucrose + 75% EG | -108.9 |
| 25% sucrose + 75% PG | -98.0 |