1. Is lead part of the glass network in lead glasses
Is lead part of the glass network in lead glasses? Recent insights and practical consequences
L.Montagne and G.Palavit
Ecole Nationale Superieure de Chimie de Lille -France
XVI ICF Technical Exchange Conference Karlovy Vary 9-12 th october 2004

2. Pb environment in PbO
PbO
litharge
massicot a b c
Pb+2
O-2

3. Low field strength (z/ri2) Large size
Specificities of Lead
free 6s2 electron pair
Low field strength (z/ri2)
Large size
PbO3 /PbO4 environments are prefered in crystals

4. Main techniques for the examination of the local environment of lead in glasses
207Pb Solid-state NMR
X-Rays and neutrons diffraction
Pb-LIIIedge XAFS
X-ray photoelectron spectroscopy (XPS): binding energies from Pb 4f7/2, Pb 4f5/2..
Vibrational spectroscopies

5. Outline NMR, basics and scales Lead in binary glasses PbO-SiO2
Comparative studies: PbO-SiO2, PbO-P2O5
Lead in complex glasses:
PbO-B2O3-Al2O3-SiO2 glasses
PbO-P2O5-SiO2 glasses
PbO-P2O5-Na2O-CaO-Al2O3-SiO2 glasses

6. Nuclear Magnetic Resonance ?b
Bo > 0
Bo = 0
DE = h n
Access to chemical informations:
bonding, geometry,...
29Si, 207Pb, 31P, ...

7. NMR of glasses: the scales
Phase separation: Demixion, crystallisation
SiO4
Na+
Nucleus 207Pb, 29Si,...
1st-2nd neighbours:
Coordinence,
Former/modifier
Connectivity :
SiOSi, SiOPb,BOSi,...
PbO4

8. Outline NMR, basics and scales Lead in binary glasses PbO-SiO2
Comparative studies: PbO-SiO2, PbO-P2O5
Lead in complex glasses:
PbO-B2O3-Al2O3-SiO2 glasses
PbO-P2O5-SiO2 glasses
PbO-P2O5-Na2O-CaO-Al2O3-SiO2 glasses

9. 207Pb NMR spectra of PbO-SiO2 glasses
PbO w.% 90 72 61
ppm
Covalent (former)
SiOPb
ionic (modifier)
SiO...Pb

10. lead environment in PbO-SiO2 glasses
Pb 2+ appears to be more donating than cationic potential predicts  large involvement of the inert pair of electrons
Larger coordinence in glasses
than in crystals
Current model proposes a disproportionation :
2 Si-O-Pb  Si-O-Si + Pb-O-Pb
I.A.Gee, 2001

11. Outline NMR, basics and scales Lead in binary glasses PbO-SiO2
Comparative studies: PbO-SiO2, PbO-P2O5
Lead in complex glasses:
PbO-B2O3-Al2O3-SiO2 glasses
PbO-P2O5-SiO2 glasses
PbO-P2O5-Na2O-CaO-Al2O3-SiO2 glasses

12. Structure of lead phosphate glasses
Chemical shift / ppm
-4500
-3000
-1500
1500
3000
60.2
42.2
34.4
32.1
27.6
51.8
mol% P2O5
207Pb NMR
ionic (modifier)
Covalent (former)
Chemical shift / ppm 20 10
-20
-30
-40
-50
-10
21.4
27.6
32.1
34.4
42.2
51.8
60.2
mol% P2O5
31P NMR
Depolymerisation
We have also described the local environment of lead cations in these lead and cadmium phosphate glasses using NMR.
We can observe that the chemical shift of the resonance shifts towards more positive ones as the amount of modifying oxides increases. We associate this chemical shift evolution to an increase of the lead-oxygen bond covalency.
The structural modifications of the lead and cadmium phosphate glasses observed by phosphorus NMR and lead NMR can be correlated to the increase of the glass temperature as P2O5 content decreases .
Then we can conclude that the excess of lead chloride and cadmium chloride in the batch to be converted induces the reticulation of the depolymerised phosphate network by P-O-Pb bonds.
Increasing lead in PbO-P2O5 glasses :
31P indicates a depolymerisation of the phosphate network
207Pb indicates a transition from network modifier to former
S. Donze, L. Montagne, G. Palavit, Phys. Chem. Glasses (2001)

13. Geometries of oxygen environments of Pb 2+ cations in PbO-SiO2 and PbO-P2O5 glasses
Neutron diffraction
Distance and number of Pb-O bonds
PbO-SiO2
PbO-P2O5
Shortest bonds
3 x nm
5 x nm
Additional oxygen neighbours
1 x nm
3 x 0.28nm
total 4 8
Do not depend on the PbO content, but on the nature of the network-forming oxide
(U. Hoppe, J. Non-cryst. solids 328, 1-3 (2003)146)

14. Outline NMR, basics and scales Lead in binary glasses PbO-SiO2
Comparative studies: PbO-SiO2, PbO-P2O5
Lead in complex glasses:
PbO-B2O3-Al2O3-SiO2 glasses
PbO-P2O5-SiO2 glasses
PbO-P2O5-Na2O-CaO-Al2O3-SiO2 glasses

15. Pb environment in complex oxide glasses?
What is the influence of another network former, like P2O5, B2O3 or Al2O3 in lead silicate glasses?
(1) PbO-B2O3-Al2O3-SiO2 glasses
- addition of B2O3 to lead silicate glasses
- substitution of B2O3 by Al2O3
(2) PbO-P2O5-SiO2 glasses
- Effect of P2O5 doping in lead silicate and aluminosilicate glasses

16. (1) PbO-B2O3-Al2O3-SiO2 glasses
- Addition of B2O3 to lead silicate glasses:
The covalent character of Pb-O increases
with the amount of PbO (similar to PbO-SiO2)
stabilisation of BO3 units at the expense of BO4.
- Substitution of B2O3 by Al2O3 :
PbO[(B2O3)1-z(Al2O3)Z] SiO2 glasses
promotion of BO3 species
at the expense of BO4.
BO3 induces a decrease of surface tension
s. Fujino, J. Am. Ceram. Soc. 87(2004)10
Sawvel, S.Chinn, W.Bourcier, R.Maxwell,Chem. Mater., in press (2004)

17. (2) Effect of phosphate doping in lead silicate glasses
Why P2O5 ?  P2O5 increases the chemical durability of lead silicate glasses
Effect of phosphate addition on lead release
(24h exposure, 4% acetic acid)
Base glass
Phosphate doped
Na2O-CaO-PbO-SiO2
Glasses+1mol%P2O5
R.L. Lehman, J. Am. Ceram. Soc., 65 (1982) 410 and 75 (1992) 2194.

18. (2) Effect of phosphate doping in lead silicate glasses
Is the reduction of lead release due to:
- Surface crystal formation (5PbO-P2O5-SiO2) ?
Complexing of Pb2+ by the phosphate into the glass structure ?
R.L. Lehman (1992)
 Need for a structural approach

19. (2) Effect of phosphate doping in lead silicate glasses
Strategy of the structural approach :
P2O5 in Na-silicate glasses
PbO-P2O5 in Na-Ca-Al silicate glasses

20.  Isolated phosphate anions
P2O5 in Na-silicate glasses
31P MAS-NMR :
 No P-O-Si bonds,
 Isolated phosphate anions
sodium
orthophosphate
Na3PO4
sodium
pyrophosphate
Na4P2O7
67SiO2 - 33Na2O + 1,3 mol.% (P2O5 ; Na2O)
L. Montagne, G.Palavit et al., Glastech. Ber. Glass Sci. Technol. 71C (1998) 204

21. P2O5 in Na-silicate glasses
The influence of P2O5 on the silicate network depends on how P2O5 is introduced :
silicate network polymerisation increased
P2O5 + 4Si-O-Na Na4P2O7 + 2Si-O-Si
P2O5 + 6Si-O-Na Na3PO4 + 3Si-O-Si
29Si NMR
+ P2O5
silicate network polymerisation unchanged
+ Na3PO4
Dissolution of Na3PO4
L. Montagne, G.Palavit et al., J. Non-Cryst. Solids, 263&264 (2000)

22. P2O5 in Na-silicate glasses
Viscosity at 1250°C
silicate network polymerisation increased
+ P2O5 1
1,4
1,8
2,2
2,6
5,7
6,1
6,5
6,9 10 4
.1/T(K -1 )
log h
(P)
silicate network polymerisation unchanged
+ Na3PO4 1
1,4
1,8
2,2
2,6
5,7
6,1
6,5
6,9 10 4
.1/T(K -1 )
log h
(P)
L. Montagne, G. Palavit et al., Glastech. Ber. Glass Sci. Technol. 73 (12) (2000)

23. P2O5 in Na-silicate glasses
Liquidus temperature
silicate network polymerisation increased
+ P2O5 T L
(°C)
Phase
Si60Ca20Na20
1181
Silica
Si60Ca20Na20+1,3(M +
;PO 4 x- )
1161
Si60Ca27Na13
1264 a
- CS
Si60Ca27Na13+1,3(M
1230 CS
Si60Ca34Na6
1380
Si60Ca34Na6+1,3(M
1360
silicate network polymerisation unchanged
+ Na3PO4

24. PbO-P2O5 in Na-Ca-Al silicate glasses
(ppm)
-120
-110
-100
-90
-80
-70
-60
-50
Base glass
+10%
+5%
+20%
29Si NMR
Polymerization of the silicate glass network, which depends on the proportion of PbO-P2O5
L. Montagne, G. Palavit et al., in preparation

25. PbO-P2O5 in Na-Ca-Al silicate glasses
(ppm)
-60
-50
-40
-30
-20
-10 10 20 30
PbO-P2O5
31P NMR
Depolymerization of the phosphate chains
Dissociation of lead phosphate into Ca,Na monomers
(Ca,Na)PO4

26. PbO-P2O5 in Na-Ca-Al silicate
1) Na2O-CaO-Al2O3-SiO2 glass

27. PbO-P2O5 in Na-Ca-Al silicate
2) Addition of P2O5 to Na2O-CaO-Al2O3-SiO2 glass

28. PbO-P2O5 in Na-Ca-Al silicate
3) Addition of PbO-P2O5 in Na2O-CaO-Al2O3-SiO2 glass

29. (2) Effect of phosphate doping in lead silicate glasses
Is the reduction of lead measured in solution due to:
- Surface crystal formation (5PbO-P2O5-SiO2) ?
Complexing of Pb2+ by the phosphate into the glass structure ?
R.L. Lehman (1992)

30. Conclusions The local structure around lead depends :
1) on its quantity in the glasses:
High: covalent bonding (network former),
low: ionic bonding (network modifier).
2) on the nature of the network former(s)
Structural informations from other nuclei (29Si, 31P) are as important as that from lead (207Pb)
The consequence on properties depends on indirect effect of lead on the other network formers (Al2O3, B2O3, P2O5).