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Old 03-31-2005, 11:38 AM
Dave Bross Dave Bross is offline
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Random bits from the Lithium chapter in Volf's "Chemical Approach to Glasses':

"It's low ionization energy is indicative of the strongly ionic nature of it's bonds. Lithium differs from the other alkalai metals in the properties of it's compounds and it's behavior in glass.

In its behavior in glass,Li is more similar to Mg than to Na or K. Lithium and magnesium have similar effective radii,and are functionally substitutable, in particular in glasses with low dielectric losses, and both decrease the liquidus temperature of basic silicate glasses in the range between 2 and 4% of the oxide."

(My note here: lowering the liquidus temp. lowers the annealing point that Lani is talking about up above, and in what I've been melting, way less than 2-4% lithium will drop the anneal temp.)

"Li2O is the lightest oxide component of glasses, being twice as light as Na2O. Replacement of Li2O for Na2O or K2o, or assesment of the effect of Li2O on the physical properties of glasses, should therefore be considered on a molar basis only. The effect of Lithium in glasses is first of all given by its small effective radius, which is the smallest among the monavelent metals. "

" The small size of the lithium ion also facilitates diffusion into the glass by substitution for Na and K both below and above the transformation interval. The process results in a permanent compressive tension in the surface, which has become the basis of chemical strengthening of glass products."

( my note here: You have to wonder if this wasn't in Nick Labino's mind when he suggested the lithium to Tom and family for tuning up the final version of Spruce Pine. Nick knew that studio artists would be attempting to combine all sorts of odd glasses and may have figured some " permanent compressive tension in the surface" would be a very good thing.)

"As a result of a strong attraction to oxygen, lithium tends to contract the free spaces in the silicate network. This contraction, for example, leads to a greater effect of Li on the density of glass than would be expected theoretically.

Owing to its small ionic radius the field strength of Li is the greatest among the alkalai metals. Li is therefore strongly bound in the silicate network, as indicated by its improving effect on the chemical durability with respect to water and acids in both glass and enamels. The properties that increase with increasing bond strength (such as viscosity) thus follow the sequence Li - Na - K, whereas the properties that increase with the loosening of the structure (such as thermal expansion) follow the opposite sequence K Na Li."

" Lithium raw materials generally improve the melting properties of glasses, which is a result of the low melting point of Lithium compounds, of the formation of eutectics and the mobility of the lithium ion."

" The lithium ion resembles in some respects a proton, which has the ability to penetrate deeply into the electron envelope of anions and neutral molecules. In this way, Fajans and Kreidl explain the outstanding efficiency of Li as a flux and its effect on decreasing the viscosity, in spite of it not being an element with a high deformability of its ion. The meltability is likewise contributed to by the great mobility of the small Li ion."
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Last edited by Dave Bross; 03-31-2005 at 11:46 AM.
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