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Li2O (Lithium Oxide, Lithia)
Notes-Lithium is the lightest, smallest, and most reactive flux. Adding small amounts by weight introduces disproportionately large amounts to the glaze formula (because of its low molecular weight).-Together with boron and sodium, it acts as a melter at lower temperatures. Together with sodium and potassium oxides, it is classified as one of the Alkaline group. -Lithium Carbonate, its main source, has a very low melting point and is a very active and powerful flux. -In frits and glazes, lithia is used to reduce the viscosity and thereby increase the fluidity of the coatings. This reduces maturing times and lowers firing temperatures. -1% additions can increase glaze gloss to a marked degree and slightly greater amounts (3%) can reduce melting temperature by several cones and affect surface tension of the melt. -High cost limits its use in larger amounts, but in small amounts it acts as a powerful auxiliary alkaline flux with welcome thermal expansion lowering effects. However in large amounts lithia can drastically increase the thermal expansion of a glass. -Calculated expansion projections tend to break down with all but low additions of lithium to glazes (less than 5%). Its contribution in nonlinear, especially in high sodium and potassium glazes. Often high lithium glazes appear to shiver whereas the calculated expansion does not indicate a sufficiently low expansion. It is known that molten lithia is mobile (diffuses into the surrounding matrix because of its small ionic radius and low charge). It can also diffuse into the body and create a low expansion glaze interface. One theory proposes that glazes with more than about 5 mol% Li2O could develop a lithium-rich interface (this could be coupled with a lithium-deficient upper glaze layer). The result could be crystallization of a spodumene layer thereby introducing its inversion and associated sudden expansion at 1082 C during cooling. -Its expansion is much lower than soda or potash, and it is used to produce special low-expansion bodies and glazes which are resistant to heat-shock. When used as a partial substitute for sodium and potassium oxides, it produces glazes of lower expansion. -Lithia gives the most intense colors in low alumina high alkali glazes. -The alkalis can increase lead solubility. -It can promote textural or variegated effects in the glaze surface because it promotes devitrifaction in glass systems. -Lithia can promote bubble defects in glazes if used in isolation from the other alkalis. -In some systems small additions of lithium will react with quartz during firing and can eliminate the alpha-beta quartz transition in the cooling cycle. Mechanisms
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