Alternate Names: Lith Carb, Li2CO3
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|SLBY - Solubility||1.3 g/100ml at 20 deg C|
Lithium Carbonate is the best source of lithium oxide for glazes. It is slightly soluble. It is unusual to see more than 5% lithium carbonate in glaze. Because of the low expansion of Li2O, high lithium glazes tend to shiver.
There are certain basic properties of lithium which are of interest in ceramics. Since lithium has a very small ionic radius in comparison to the other alkali metals, it has a higher field strength. Low expansion coefficients are generally imparted to ceramic compositions containing lithia. Lithium carbonate is a very strong flux (also true of lithium fluoride). In contrast, other lithium compounds may be quite refractory: lithium zirconate and lithium aluminum spinel are examples.
There is comparatively little published information on the use of lithia compounds in ceramics. Laboratory investigations indicate that small additions of lithium will react with quartz during firing and eliminate the alpha-beta quartz transition in the cooling cycle. Lithia imparts low thermal expansion coefficients to glasses and also promotes devitrification in glass systems. Smaller amounts act to smooth the glass surface.
Lithium exhibits many properties that are similar to the more common alkali metals sodium and potassium. In many respects is also shows similarities to the elements of the alkaline earth group, especially magnesium.
In addition to being soluble, lithium carbonate produces gases as it decomposes and these can cause pinholes or blisters in glazes. There are insoluble lithium frits available (e.g. Fusion F-493 has 11%) and incorporating one of them to source the Li2O instead is a classic application of glaze chemistry calculations (however for glazes with very high amounts of lithium, like 10%+, it will be difficult to source the Li2O using a frit because significant amounts will be required and this will likely oversupply the other oxides the frit brings). The resultant glaze will be more fusible and will have better clarity and fewer defects.
This is 85% Alberta Slip, 11% lithium and 4% tin fired at cone 6 in oxidation. Like the original Albany version, it has a very low thermal expansion (because of the high lithium content) and likes to shiver on many bodies.
This is one of the issues with using the material. These have to be screened out from time to time, if not they produce defects in fired ware. Better to employ a lithium frit to source Li2O.
10% lithium carbonate and 4% tin.
Crystals found growing in a glaze containing 7% lithium carbonate, 7% titanium dioxide and 6% cadycal. Also had wollastonite, silica, koalin and nepheline syenite. Courtesy of Mark Rossier Pottery.
Lithium carbonate is now incredibly expensive. The glaze on the left employs it. But I was able to source the Li2O from spodumene instead. Spodumene has a complex chemistry, but the oxides that it contains (other than Li2O) are those common to glazes anyway. Using my account at insight-live.com, I did the calculations and got a pretty good match in the formulas (lower section in the green boxes). Then I made 10 gram balls and did a melt flow test at 2200F (notice the long crystals in the pools of glass below the runways). And I glazed buff stoneware test (below the flow tests). Not surprisingly, this glaze is very runny. That's why the tiny yellow crystals grow during cooling, they produce the gold effect this recipe is known for. The spodumene version is very similar, perhaps better. Notice my calculated cost: $15.47/kg vs. $8.12/kg.
These materials have many issues. They can create problems in your glaze slurries (like precipitates, higher drying shrinkage), cause issues with laydown and dried surface and cause fired surface defects (like pinholes, blisters, orange peeling, crystallization). And lithium and barium have toxicity issues (as raw materials). And the lithium, barium and strontium are carbonates, that means carbon burns off during firing (with lithium, for example, 60% of its weight is lost). Yet the oxides that these materials source to the glaze melt, ZnO, Li2O, BaO and SrO can be sourced from frits. In doing that you can solve almost all the problems and get better glaze melting. Fusion Frit F 493 has 11% LI2O, F 403 has 35% BaO, F 581 has 39% SrO and FZ 16 has 15% ZnO. Of course, these frits source other oxides (but these are common in most glazes). Using glaze chemistry you can often duplicate the chemistry of a glaze while sourcing these oxides from frits.
Out Bound Links
The toxicity of lithium in ceramics is a hotly debated subject, especially with regards to handling raw lithium carbonate, but also with reference to leaching from glazes.
Hazards of lithium carbonate in the ceramic industry and process and in ceramic products containing it
Fusion Frit F493
In Bound Links