All Glossary

LOI-Adjust

LOI adjustment of the weight of a material is done to compensate for the weight loss when it is calcined. And to correct a chemical analysis (by weight) of a material.

Key phrases linking here: loi-adjusted, loi-adjust - Learn more

Details

LOI adjustment is needed in the following cases:

1. Adjusting a recipe (compensating for the weight lost when a clay is calcined, preserving its contribution to fired chemistry) Calcined kaolin is the most typical material. Consider this glaze recipe containing 30 parts #6 Tile Kaolin. We want to replace 10 parts of the raw kaolin with calcined kaolin. Assuming an LOI of 12%, the calcined equivalent is 10 x 0.88 = 8.8 parts.

   Material	Original	Adjusted
   Ferro Frit 3195	20.0	20.0
   Wollastonite	29.0	29.0
   Nepheline Syenite	4.0	4.0
   #6 Tile Kaolin (raw)	30.0	20.0
   Calcined Kaolin	-	8.8
   Silica	17.0	17.0
   Total	100.0	98.8

   The adjusted recipe totals 98.8 rather than 100 because 1.2 parts of material that would have been lost during firing have already been removed by calcination. The calculated fired chemistry remains unchanged, assuming no other constituents are lost during calcination.

   Note: Others might point out that LOI-adjustment preserves the calculated fired oxide contribution, not necessarily all the physical properties of the original recipe. Remember, however, that was the point of this: a mix having less plastic and therefore lower drying shrinkage.



2. Adjusting a material analysis. Correcting the oxide percentages when a measured LOI differs from the value recorded in the analysis. A material analysis may have no LOI specified, or its reported LOI may be inaccurate. In either case, the actual LOI can be measured by firing a weighed sample and weighing it again. The oxide percentages must then be adjusted to accommodate the measured LOI. Consider two versions of the same analysis. In the first, no LOI was specified. In the second, a 2% LOI was specified. Testing now establishes that the actual LOI is 5%.

   Oxide	Original No LOI	Original 2% LOI	Corrected 5% LOI
   K2O	7.300	7.154	6.935
   CaO	9.400	9.212	8.930
   MgO	1.000	0.980	0.950
   ZnO	1.000	0.980	0.950
   Al2O3	11.800	11.564	11.210
   SiO2	69.500	68.110	66.025
   LOI	0.000	2.000	5.000
   Total	100.000	100.000	100.000

   Where no previous LOI was specified, multiply each oxide percentage by 0.95:

   (100 - 5) / 100 = 0.95

   Where the previous analysis specified a 2% LOI, multiply each oxide percentage by 0.969388:

   (100 - 5) / (100 - 2) = 0.969388

   The general formula is:

   Multiplier = (100 - New LOI) / (100 - Old LOI)

   In both cases, the corrected analysis totals 100%, including the new 5% LOI. The relative proportions of the oxides are unchanged.

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