Thermodynamic Prediction for Glass Properties (with a special focus on Pb-containing glasses)

1. ICF 2005 Thermodynamic Prediction for Glass Properties (with a special focus on Pb-containing glasses) Reinhard Conradt XVII ICF Technical Exchange Conference Telfs-Buchen, October 8th-11th, 2005 conradt@ghi.rwth-aachen.de

2. CONTENTS • energy of glass formation • heat demand of melting • batch melting • evaporation • hydrolytic stability

3. GA GB GC G A + B  C GLASS Ox|in glass + B  C (ox) = G°(ox) + RT ln c(ox)· ƒ(ox)

4. glasses, melts, and the crystalline reference system „c.r.s.“

5. thermochemical models: 1. the cell model (Gaye 1984) 2. the quasi-chemical model (Pelton & Blander 1986)  F*A*C*TSage 3. the model of ideal mixing of complex components (Bonnel & Hastie 1990)  statistical mixing of oxide components on the g-atom level = „ideal“; deviations decribed by adjustable interaction parameters 4.the associated liquid model(Shakhmatkin & Vedishcheva 1994)  statistical mixing of oxide components on the g-atom level = „ideal“; deviations described by the evaluation of formation equilibria of all known compounds in a given system 5.the constitutional model(own work 1996)  no statistical mixing of oxide components on the g-atom level; deviations described by the evaluation of known constitutional relations in a given system

6. data set for a one-component system: crystal - melt - glass: solid melt glass Today, such data are available!

7. Exploite the principles of majority partition, parsimony, HMIX, and SMIX minimization

8. successful prediction of activities in Na2O-SiO2 melts:

9. prediction of Gibbs energies of formation of 4 mineral fibre compositions: experiments by Richet et al. 2003

10. Conventional industrial melts We need to analyse phase diagrams!

11. liquidus temperatures and viscosities for PbO-SiO2:

12. K2O-PbO-SiO2 liquidus temperatures

13. liquidus temperatures

14. K2O-PbO-SiO2 phase relations acidic glasses; stable against crystallization extremely PbO-rich glasses; less stable against crystallization poor chemical durability phase separation below this line no glass formation 30 % PbO

15. Lead Crystal Let us keep it simple!

16. simplified phase relation: SiO2-PbO·SiO2-K2O·2SiO2 K2O-PbO-SiO2 acidic glasses; stable against crystallization extremely PbO-rich glasses; less stable against crystallization poor chemical durability phase separation below this line no glass formation 30 % PbO

17. CONTENTS • energy of glass formation • heat demand of melting • batch melting • evaporation • hydrolytic stability

18. heat input (in) offgas (off) q = H · r [kW/m²] = [kWh/t]·[t/(m²·h)] recovered (re) set free (sf) exchanged (fire) transferred (ht) wall losses, heat exchanger (wx) exploited heat (ex) exchanged in the heat exchanger (exch) wall losses, basin (wu) stack losses (stack) wall losses, upper structure (wo)

20. H°chem= - 2893.6 kWh - 202.4 kWh + 3172.5 kWh ___________________ + 76.5 kWh HT,melt = + 322.7 kWh ,, Hex = (1 - yC) · H°chem +HT,melt

21. CONTENTS • energy of glass formation • heat demand of melting • batch melting • evaporation • hydrolytic stability

22. Hex does not yet give the full picture of glass melting:

23.  = max; but  long process time very fast process;   0 finite time heat transfer: chemical efficiency: Hin = Hex + (qloss / r) · Kquality Nemec et al. 2005 thermal efficiency: Curzon & Ahlborn, 1963 optimum efficiency ex

24. 4 3 2 1 sensors batch heap (4 kg) 5 cm glass melt (7 kg)

25. primary melt formation (779 °C) granular bulk solid

26. 1 batch 1 primary melt formation 0 -1 water release -2 log ,  in -1·cm-1 W = 1150 s reaction foam -3 -4 foam = 2330 -2700 s -5 -6 1 batch 2 Zeit in s primary melt formation 0 -1 water release -2 W = 1880 s log ,  in -1·cm-1 reaction foam -3 -4 foam = 1420 s -5 -6 0 2000 4000 6000 8000 time in s

27. conventional batch fast conversion batch

28. CONTENTS • energy of glass formation • heat demand of melting • transport properties • evaporation • hydrolytic stability

29. (T) Avramov Adam-Gibbs, for specific SC the structure parameter describes the dependence of (T) on chemical composition

30. exp: Seward & Vascott, 2005; PTB 1974; Lakatos et al.1976; Richet et al. 1995

31. exp. data by Seward & Vascott, 2005 low  E fibre TV panel log  log  log  log ,  in dPa·s; - log ,  in ohm-1·cm-1 - log  - log  - log  Tg / (T·SC) in (g·K) / J

32. CONTENTS • energy of glass formation • heat demand of melting • batch melting • evaporation • hydrolytic stability

33. partial pressure Pi

34. mass balance in terms of total shares of oxides j:

37. 16 K2O + 20 PbO + 64 SiO2 Pb + PbnOn + Pb(OH)2 K + KOH 

38. CONTENTS • energy of glass formation • heat demand of melting • batch melting • evaporation • hydrolytic stability

39. old paradigm: network modifiers are depleted, network formers are enriched new paradigm: incongruent dissolution according to the solubility of individual oxides

40. solution altered zone (gel layer) bulk glass intrinsic Na+ mobilization surface equilibrium fast exchange of H+, Na+, H2O condensation of OH groups (gel formation) breaking of HOSi bonds (dissolution) low density, high connectivity, H2O percolation

41. Use formn. properties, i.e., Ggl= Gƒ(glass), Gaq = Gƒ(soln.)

42. the dissolution rate is a combined effect of • hydrolytic stability, • surface charging

43. the dissolution rate is a combined effect of • hydrolytic stability, • surface charging • (as varified for many different glasses)

44. silica

45. hydrolytic stability of the pure oxides:

46. Pb(OH)2 Pb(OH)3-  PbOOH-  HPbO2- Pb++

47. Mg++ Ca++ Zn++ Fe++

49. the presence of organic species has a high impact on hydrolytic stability

50. the presence of organic species has a high impact on hydrolytic stability