LOI
Simplistically, LOI is the amount of weight a material loses on firing. LOI is usually crystal-bound water or carbon material that burns away. However in raw clays it is also common to see SO3 content (which can be as high as 5%).
However LOI can also be other things (e.g. sulfur, chlorine, oxygen). It is also more complex for many materials since they go through a number of changes during temperature rise and these changes may involve weight loss or even weight gain (e.g. for non-oxide materials that capture oxygen from the atmosphere or other materials). Some of these changes may occur at a temperature higher than that at which they are being used. In addition, some materials that might otherwise break down quickly and form gases of decomposition may linger when they are in a glaze or frit that is being fired quickly (e.g. fluorine).
LOI is important in ceramic chemistry, especially with INSIGHT. The primary purpose of recipe calculations is to derive the formula for the glass that comes out of the kiln, from the mix of recipe materials that go into the kiln. A fired glass has no organics or carbonates; so it always has zero LOI. This means that LOI is never shown for a glaze formula and you will never need to worry about it for any batch-to-formula or analysis calculations.
However, many raw materials that go into the kiln do lose weight during firing; so they are not sourcing as many oxide molecules as a calculation might suggest. If a raw material loses weight on firing, it must be accounted for in calculations. You can think of LOI as being like the shells which we throw away from a bag of nuts. We compensate for anything lost during firing by increasing the formula weight. For example, 100 grams of kaolin going into a kiln produce only 88 grams of oxides for glass making. By increasing the formula weight of the kaolin by the correct amount, a full calculated oxide yield will result. The INSIGHT software stores a material’s formula in its MDT (materials database) exactly as you enter it. It requires a formula weight for each material; so when needed it can calculate the material’s LOI as the difference between the recorded weight and the actual sum of the weights of the oxides in the formula.
Since INSIGHT knows the LOI for each material in a recipe, it can calculate the LOI of the raw recipe as a whole. This can be very useful. For example, if you are blending materials to create a composite material that will be used in recipes, you need to know its LOI when you add it to INSIGHT's materials database.
If you have an analysis lacking an LOI figure or suspect the accuracy of the analysis delivered by a lab, then you can weigh, fire, and weigh again to derive the LOI and compensate the analysis. Following is mathematical method of applying a 5% measured LOI to an existing analysis. This is called "LOI Compensating an Analysis".
100 - 95 = 5 / 100 = 0.95
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K2O 7.3% x 0.95 = 6.9%
CaO 9.4% x 0.95 = 8.9%
MgO 1.0% x 0.95 = 1.0%
ZnO 1.0% x 0.95 = 1.0%
Al2O3 11.8% x 0.95 = 11.2%
SiO2 69.5% x 0.95 = 66.0%
LOI 5.0%
--------------------------
100.0% 100.0%
Out Bound Links
In Bound Links
- (Glossary)
Formula Weight
Quite simply, the weight of a formula. Typically, ... - (Project)
Stains
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