0.0020
The results of the considered raw‐material analysis is reported in the shaded gray area of the matrix.
Table 3 Redox factors R(i) of selected active raw materials i; these factors refer to batch compositions normalized to a sand amount of 2000 kg.
| Raw material i | Chemical formula | R(i) per 2000 kg sand |
|---|---|---|
| Carbon | C : 100, 85, 65% | −6.70 |
| Iron sulfide | FeS | −1.60 |
| Pyrite | FeS2 | −1.20 |
| Fluorspar | CaF2 | −0.10 |
| Calumite | Multicomponent slag | −0.073 |
| Iron red | Fe2O3 | +0,25 |
| Chili saltpeter | NaNO3 | +0.32 |
| Heavy spar | BaSO4 | +0.40 |
| Gypsum | CaSO4·2 H2O | +0.56 |
| Potassium dichromate | K2Cr2O7 | +0.65 |
| Salt cake; sulfate | Na2SO4 | +0.67 |
| Gypsum anhydrite | CaSO4 | +0.70 |
| Sodium dichromate | Na2Cr2O7 | +0.77 |
| Manganese oxide | MnO2 | +1.09 |
Final adjustment of the batch composition still requires allotments of the appropriate agents for controlling glass color, fining (as described in Section 5.2), redox conditions, and, thus, valence states and oxygen complex formation of polyvalent ions (cf. Chapter 5.6) at the industrial scale. For adjustment of the redox state, the so‐called redox number concept [2] is widely accepted and empirically applied in industry. This incremental system assigns a specific redox factor Ri to every member of a set of redox‐active ingredients i (Table 3). In the example of Table 4, the batch composition from Table 2 is complemented by 4 kg of sulphate (the amount of soda ash being reduced accordingly to maintain an identical amount of Na2O in the glass). Then the batch composition is normalized to amounts mIII(i) per 2000 kg of sand, and the total redox number of the batch is calculated from the weighted sum R = ∑ Ri·mIII(i). It is true that this number R does not have a straightforward scientific meaning but it allows one to set in a well‐defined way the redox state to a desired level. For redox numbers in the interval −25 < R < 25, a fair estimate of the Fe2+/Fetotal ratio for is given by 0.4 – 0.015·R. Because the chemical composition of the batch can no longer be corrected after charging, these rather simple calculations are mandatory for any successful melting process.
Finally,
