1 / 32

Durability of Lead Glasses in Extreme Environments: Research Findings and Methodology

Study on alteration processes in lead glasses for conservation in museums. Experimental protocols and results for glass leaching in acidic medium. Analytical techniques used include SEM, RBS, and Raman spectroscopy.

jude
Download Presentation

Durability of Lead Glasses in Extreme Environments: Research Findings and Methodology

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related