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Durability of lead glasses in extreme environments

Durability of lead glasses in extreme environments. Anne BOUQUILLON UMR-CNRS 171 C2RMF – 6 rue des pyramides – 75041 Paris cedex 01. Collaborations. University of Lille I – LASIR (Raman spectroscopy) : Pr . Turrell. University of Poitiers – ESIP – Pr . Thomassin.

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Durability of lead glasses in extreme environments

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  1. Durability of lead glasses in extreme environments Anne BOUQUILLON UMR-CNRS 171 C2RMF – 6 rue des pyramides – 75041 Paris cedex 01 ICF 2003 – A.Bouquillon

  2. Collaborations University of Lille I – LASIR (Raman spectroscopy) : Pr. Turrell University of Poitiers – ESIP – Pr. Thomassin Centre de Recherche et de Restauration des Musées de France Commissariat à l’Energie Atomique : Pr. Trocellier Ecole Polytechnique (Paris) : Pr. Barboux - Pr. Devreux ICF 2003 – A.Bouquillon

  3. Origin of the research • Problems of alteration of archaeological objects and of artefacts in the museums • Comprehension of the processes involved • Evaluation of the development of the alteration • Proposal for a curative or a preventive treatment ICF 2003 – A.Bouquillon

  4. Some examples of Renaissance lead glazed on terracotta Palissy wares Della Robbia’s sculpture ICF 2003 – A.Bouquillon

  5. Example of a weathered renaissance lead glaze Very deeply altered glaze Alternance of lead-enriched layers with silicon-enriched ones Probable surface gel layer with processes of auto-organization with time How to prove this hypothesis ? Experimental alteration ICF 2003 – A.Bouquillon

  6. Protocol of the experimental alteration of lead glasses • Choice of the glasses : glasses with high Pb contents (25 to 66 weight% PbO) • Choice of the alteration medium : basic, neutral and acid leaching solutions • Choice of the parameters studied : leached elements, evolution of the glass structure and of the altered surface layer ICF 2003 – A.Bouquillon

  7. Methodology • Analysis of the leaching solution : ICP-AES • Structure of the altered glass ( altered layer): • Scanning electron microscopy (SEM) • Rutherford backscattered spectrometry (RBS) • Raman spectroscopy • «  XPS », « TEM » ICF 2003 – A.Bouquillon

  8. Information recorded SEM : Aspect of the leached glass – on surface and in depth (cross section) RBS : Thickness of the leached layer, evolution of the chemical composition from the surface to the unaltered glass Raman : Structure of the leached layer – Kinetic evolution of the structure of alteration ICF 2003 – A.Bouquillon

  9. Raman spectra of glass surface Evolution of the glass in a basic medium The dissolution is congruent : all the elements go into solution The surface is very « eaten » and covered with lead-rich needles (here hydrocerusite) Raman spectrometry does not show any change in the molecular structure ICF 2003 – A.Bouquillon

  10. Basedon these results : The basic medium is not interesting for the reproduction of the alteration processes observed in archaeological glasses So the work should be focused on alterations in acid media ICF 2003 – A.Bouquillon

  11. Glass G 28% SiO2 ; 66% PbO 4,1% BaO ; 1,3% ZrO2 Glass A 59,3% SiO2 ; 25,2% PbO, 9,3% K2O ; 3,1% Na2O Glass K 45,7% SiO2 ; 45,3% PbO, 3,9% K2O ; 5,1% Na2O Lead as modifier and network former Lead as modifier Intermediate glass Experimental Composition of the glasses Experimental • Monoliths 1 cm3, polished with diamond powder to 1/4 m, annealed at 400°C • Teflon-walled autoclaves • Leaching solutions : HNO3 and CH3COOH - (pH = 2) • S/V = 0,5 cm-1 • T° = 90°C • Duration of leaching experiments between 1 hour and 3 months ICF 2003 – A.Bouquillon

  12. Profiles for leaching solutions – Glass G (66%PbO)– HNO3 Second phase 1 day to 3 months “stabilization” with evident fluctuations First phase 1h to 1day Diffusion law (t 1/2) ICF 2003 – A.Bouquillon

  13. Acid medium = HNO3 Example of the lead-rich glass G • Observation of the evolution of the surface • between 1hour and 1 day 2)Between 1 day and 5 weeks ICF 2003 – A.Bouquillon

  14. Unaltered Si Pb Si • Formation of a cracked layer, enriched in Si (thickness 3 to 6 m) O Unaltered glass Energie (keV) • Initial growth of the Si-layer , followed by formation and partial detachment of scales 1 hour Si Pb O O • Apparent homogenisation of layer Pb Energie (keV) Energie (keV) Si-rich surface layer 7 hours 10 hours 1 day Underlying zone Verre G / HNO3: from 1hour to 1 day ICF 2003 – A.Bouquillon

  15. depth of the reclusion = f (t) Creation of a Si-rich layer. The evolution of the thickness follows a t 1/2 law (maximum thickness = 3 m) RBS spectra • Regular reclusion of the Pb edge ICF 2003 – A.Bouquillon

  16. Important regions in Raman spectra TOT 450 cm-1 D1 480 cm-1 • CH • 1400 cm-1 v 2900 cm-1 OH 3200-3600 cm-1 NBO 900-1100 cm-1 PbO 350 cm-1 intensité (ua) medium : CH3COOH ICF 2003 – A.Bouquillon nombre d’ondes (cm-1)

  17. Evolution of Raman spectrum in HNO3 1 hour to 1 day Unaltered glass Ga1h Evolution of -OH intensity shows that hydration of the gel layer follows a t 1/2 law Ga7h Ga10h Ga1j intensité (ua) nombre d’ondes (cm-1) OH regions (water and silanols) ICF 2003 – A.Bouquillon

  18. Acid medium = HNO3 Example of the lead-rich glass • Observation of the evolution of the surface • between 1hour and 1 day 2) Between 1 day and 3 months ICF 2003 – A.Bouquillon

  19. 7 jours 7 days 14 days 21days • From 7 to 21 days, increase of the surface porosity • at about 1 month, re- homogenisation of the surface • At 5 weeks, increase of the surface roughness 5 weeks 1 month Glass G / HNO3 7 days to 3 months • Apparent homogenisation of the Si-enriched layer ICF 2003 – A.Bouquillon

  20. Apparent « structuration” of the silicon-rich layer Lead migration to the surface ? Precipitation of a lead component on the surface ? • From 1to 7 days,re-emergence of the Pb-edge. Then stabilization • Appearance of a small lead peak at the extreme surface ; this peak fluctuates slightly in intensity over the period 7 days to 3 months ICF 2003 – A.Bouquillon

  21. Raman spectroscopy : HNO3 A: increase in the ratio D1/TOT Indication of increasing porosity A 35 days B 7 days 1 day 10 hours B : * Decrease in intensity of the region of the 900-1000 cm-1 bands with respect to the T-O-T bands destructuration of the network 7 hours 1 hour unattacked * Changes in numbers of NBO  Change in the density of the « gel »?? Wavenumber (cm-1) ICF 2003 – A.Bouquillon

  22. Raman spectroscopy : acetic acid medium Increase in Si-OH and water Evolution of the organic components Evolution of the density Increase of porosity Destructuration of the matrix Glass G : 35 days Glass G : unaltered ICF 2003 – A.Bouquillon

  23. Synthesis of the alteration in an acid medium First phase : * Creation of a silicon-enriched layer at the surface, more or less thick depending on the nature of the acid used. * Increase of the porosity, increase of the NBO * Origin of the phenomenon : Diffusion processes 2 (Si-O)-Pb + 2H+ 2 (Si-OH) + Pb2+ Second phase : * Stabilization with HNO3. With CH3COOH, only a decrease in the rate of lixivation * Stabilization leads to repolymerization of the gel andprecipitation of secondary phases enriched in heavy elements (Pb, Ba..) ICF 2003 – A.Bouquillon

  24. Influence of the nature of the glass Glass A (25% PbO) : Absolutely no evolution of the glass characterized bythe techniques used Only a lixiviation of K No regular reclusion of the Pb edge ICF 2003 – A.Bouquillon

  25. Influence of the nature of the glass (glass K) The thickness of this layer increases with the leaching time up to 2 leaching days. Then it stops at a layer thickness of 500 nm A very thin (4nm thick) Pb-enriched outer layer is present, too. It increases up to 2 days then, then, it disappears Therefore, the Pb content affects the leaching mechanism ICF 2003 – A.Bouquillon

  26. PROTOCOL 1 Influence of phosphate and organic acids Medium with sand, phosphate, humic acid T° : 90°C Static conditions 3 weeks of alteration PROTOCOL2 More simplified system Sand or clay T° : 40°C Static conditions 4 weeks of alteration Preliminary studies on glass alteration in a simplified soil medium ICF 2003 – A.Bouquillon

  27. First protocol Crystal (25%PbO) + Apatite+ Sand 3 weeks - 90°C - in water * Glass very altered : surface completely porous * Presence of a gel structure and appearance of undetermined small lead-rich crystals (probably lead phosphate = pyromorphite) * Features are too complex Simplified protocol 2 ICF 2003 – A.Bouquillon

  28. Second protocol Clay (kaolinite) + water T° = 40°C 7days RBS H+ On the surface, creation of a Pb-depleted gel 14days Simultaneously, appearance of Al, Si and Pb deposits Densification of these deposits with time 28days ICF 2003 – A.Bouquillon

  29. Conclusion Alteration in acid solution • Rapid creation of a Si-enriched layer • Diffusion processes at the beginning • Leached elements, hydration of the gel, thickness of the • gel layer follow a t 1/2 law • Intensity of the processes depends on the chemical • composition of the glass, on the structure of the glass • and on the medium • The gel layer seems to stabilize but fluctuations with time • Are observed for Pb leaching rate ICF 2003 – A.Bouquillon

  30. Conclusion In the simplified soil media : • Processes are much more complicated • Evidence of Si-rich layer + deposits of Pb enriched crystals • (pyromorphyte or lead alumino-silicates) • These observations are close to the features identified on • archaeological glazes BUT • For the moment, no periodical structures observed, only • one alternation between a silica-rich layer and a lead-rich layer ICF 2003 – A.Bouquillon

  31. Perspectives • Pursue of the studies in soils • More complex media by addition of organic compounds • More complex aging protocols : cycles of wet/dry conditions, • cycles of cold/warm temperatures to simulate as accurately as • Possible, the real conditions of a buried environment ICF 2003 – A.Bouquillon

  32. Have contributed to this research Ph-D thesis : D.Chaulet and C.Bonnet DEA : C.Bonnet, A.Guéguan, V.Deram, S. Vialle Italian collaboration (Ph-D) : L. Milanese (univ. of Padova) Acknoledgements : Many thanks to Arc’International R &D team, especially Mr D.Lalart and Mr S.Donze ICF 2003 – A.Bouquillon

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