Example Calculation
An example batch calculation may be demonstrated here. The desired glass composition in wt% is: 67 SiO2, 12 Na2O, 10 CaO, 5 Al2O3, 1 K2O, 2 MgO, 3 B2O3, and as raw materials are used sand, trona, lime, albite, orthoclase, dolomite, and borax. The formulas and molar masses of the glass and batch components are listed in the following table:
Formula of glass component | Desired concentration of glass component, wt% | Molar mass of glass component, g/mol | Batch component | Formula of batch component | Molar mass of batch component, g/mol |
---|---|---|---|---|---|
SiO2 | 67 | 60.0843 | Sand | SiO2 | 60.0843 |
Na2O | 12 | 61.9789 | Trona | Na3H(CO3)2*2H2O | 226.0262 |
CaO | 10 | 56.0774 | Lime | CaCO3 | 100.0872 |
Al2O3 | 5 | 101.9613 | Albite | Na2O*Al2O3*6SiO2 | 524.4460 |
K2O | 1 | 94.1960 | Orthoclase | K2O*Al2O3*6SiO2 | 556.6631 |
MgO | 2 | 40.3044 | Dolomite | MgCa(CO3)2 | 184.4014 |
B2O3 | 3 | 69.6202 | Borax | Na2B4O7*10H2O | 381.3721 |
The batching matrix B indicates the relation of the molarity in the batch (columns) and in the glass (rows). For example, the batch component SiO2 adds 1 mol SiO2 to the glass, therefore, the intersection of the first column and row shows "1". Trona adds 1.5 mol Na2O to the glass; albite adds 6 mol SiO2, 1 mol Na2O, and 1 mol Al2O3, and so on. For the example given above, the complete batching matrix is listed below. The molarity matrix NG of the glass is simply determined by dividing the desired wt% concentrations by the appropriate molar masses, e.g., for SiO2 67/60.0843 = 1.1151.
The resulting molarity matrix of the batch, NB, is given here. After multiplication with the appropriate molar masses of the batch ingredients one obtains the batch mass fraction matrix MB:
or
The matrix MB, normalized to sum up to 100% as seen above, contains the final batch composition in wt%: 39.216 sand, 16.012 trona, 10.242 lime, 16.022 albite, 4.699 orthoclase, 7.276 dolomite, 6.533 borax. If this batch is melted to a glass, the desired composition given above is obtained. During glass melting, carbon dioxide (from trona, lime, dolomite) and water (from trona, borax) evaporate.
Another simple glass batch calculation can be found at the website of the University of Washington.
Read more about this topic: Glass Batch Calculation
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