a H°k,GL = standard enthalpy of component k in the glassy state; Hk,1300 = enthalpy of k in the liquid state at 1300 °C; cP,k,L = isobaric heat capacity of liquid k; m(k) = equilibrium amount of k in the multicomponent phase diagram; H°GLASS = standard enthalpy of the resulting glass; H1300,MELT = enthalpy of the melt at 1300 °C; ΔH1300 = heat content of the melt at 1300 °C relative to the glass at 25 °C.
b hm = FeO·Fe2O3, F = Fe2O3, M = MgO, C = CaO, N = Na2O, K = K2O, S = SiO2.
A better understanding of redox and acid base reactions in real furnaces is also desired. Although these reactions are well understood at the laboratory scale, the transfer to a real production situation is still set by experience rather than by scientific principles. In view of the large impact of these reactions on glass quality, progress in this area would be highly appreciated.
Finally, the glass industry is engaged in a quest to lower its overall energy consumption to decrease its operating costs and to satisfy increasingly stringent legislation imposed on high‐temperature industrial processes. The design of faster conversion batches is becoming important in this respect. Conventional glass formulae and batch recipes are no longer taken for granted. Efforts are in particular made to design batches that would melt along reaction pathways ensuring higher turnover rates than current randomly mixed batches. Progress may be achieved with selective batching, granulation processes bringing the reaction partners into close contact at the μm scale, preparation of core‐shell type pellets, or selective preheating of specific raw‐material combinations of the batch. In each case, of course, a prerequisite would be that the obtained energy savings are not offset by increased batch costs.
Appendix
The results plotted in Figure 7 for the dissolution of an ensemble of grains have been obtained from the analytical solution to the integral A(t) of Eq. (6) given by:
(18)
Here, erfc(z) denotes the complementary Gaussian error function of argument z, while y and s are used as abbreviations in the formula. It is true that sand dissolution does not proceed isothermally at a constant diffusion coefficient D in a real fusion process, but the utmost importance of the grain‐size distribution for a successful fusion process is nonetheless demonstrated clearly.
References
1 1 Cable, M. (1998). A century of development in glass melting. J. Am. Ceram. Soc. 81: 1083–1094.
2 2 Simpson, W. and Myers, D.D. (1978). The redox number concept and its use by the glass technologists. Glass Technol.
