Presentation on theme: "APPLICATION OF LOW TEMPERATURE PLASMAS FOR THE TREATMENT OF ANCIENT ARCHAEOLOGICAL OBJECTS František Krčma Faculty of Chemistry Brno University of Technology."— Presentation transcript:
APPLICATION OF LOW TEMPERATURE PLASMAS FOR THE TREATMENT OF ANCIENT ARCHAEOLOGICAL OBJECTS František Krčma Faculty of Chemistry Brno University of Technology Czech Republic
Outline Excavated ancient objects and goals of conservation Corrosion layers Conventional conservation technique Plasmachemical reduction of corrosion layers Deposition of protective coatings
Present state of ancient metallic objects Materials: iron and its alloys copper silver, gold, etc. alloys – bronze (Cu + Sn), brass (Cu + Zn),… The objects are commonly affected by various corrosion kinds with different intensity. The given corrosion state of object depends on: artifact material artifact manufacturing technology time of storing before excavation composition of corrosive surrounding storage between excavation and conservation precedent conserving procedures
medieval horse shoe???????????? Goals of conservation elimination of the corrosive agents to remove different stimulators of corrosion (mainly chlorine ions) from corrosion layers to remove or reduce the corrosion layers (Bronze, copper – patina layer???) to protect object from further corrosion during its storage
Structure of corrosion layer A – incrustation layers B – corrosion layers C – metal core Cut of a medieval “silver” coin Klíma, M., Ptáčková, M., Soudný, M. and Rusnák, V., Metodical Paper –Proc. of Symposium of conservation and restoration of the national cultural heritage, , Luhačovice 1994.
-FeOOHgeotite β-FeOOHakaganeite -FeOOHlepidokrocite -Fe 2 O 3 hematite Fe 2 SiO 4 fayalite Fe 3 (PO 4 ) 2 8H 2 Ovivianite FeCO 3 siderite Fe(OH)SO 4 2H 2 O FeOCl FeCl 2 Internal corrosion layers – mainly consist of magnetite Fe 3 O 4 Outer layers – composition depends on the surrouding, usually contain oxides, oxide-chlorides and oxide-hydroxides of iron Corrosion layers of iron and its alloys medieval iron axe
Corrosion layers of copper and bronze ???????????? Cu (I) complexes – colourless, except chalcocite (black), cuprite (red) Cu (II) complexes – red and blue colour Cu 2 Ocuprite Cu 2 CO 3 (OH) 2 malachite CuCl 2 2H 2 Oeriochalcite CuFeS 2 chalcopyrite CuO, Cu(OH) 2 Cu 2 Cl(OH) 3 CuS, Cu 2 S Cu 4 (OH) 6 SO 4 2H 2 O
Corrosion layers of silver -Ag 2 S Ag 2 O AgCl Ag 3 CuS 2 AgCuS Medieval “silver” coin Klíma, M., Ptáčková, M., Soudný, M. and Rusnák, V., Proc. of Symposium of conservation and restoration of the national cultural heritage, Metodical Paper, , Luhačovice 1994.
Mechanical cleaning sanding, ultrasonic needle, dental drill, etc. „Desalination“ dipping the metal artifact in: distilled water (1 – 4 months), sodium sulphite (cca 6 months) Drying Fine mechanical cleaning Final conservation tanate, varnish, wax,… Conventional conservation procedure
Veprek, S., Patscheider, J. and Elmer, J., Plasma Chemistry and Plasma Processing 5, (1985). Veprek, S., Eckmann, Ch. and Elmer, J., Plasma Chemistry and Plasma Processing 8, (1988). Plasma chemical reduction of corrosion layers - mid 80's
Contemporary plasmachemical process Real application in Technical Museum in Brno Museum of Central Bohemia in Roztoky Swiss National Museum Contemporary conservation technology using plasma: Vacuum drying (80 C, 15 hours) Plasma cleaning in 1 or more cycles (T 200 C, 2-6 hours, H 2 or H 2 /Ar mixture) Mechanical/chemical cleaning between the cycles (sanding, ultrasonic bath, Chelaton3, citric acid, etc.) „Desalination“ Fine mechanical cleaning and final conservation Havlínová, A., Perlík, D., Proc. of Conservator and Restorer Symposium, 65-69, Teplice Perlík, D., Proc. of Conservator and Restorer Symposium, 89-95, České Budějovice Schmidt-Ott, K. and Boissonnas, Studies in Conservation 31, (2002).
Advantages of plasmachemical treatment Dry removal of chlorine ions Easier removal of the incrustation and corrosion layers Shorter desalination procedure Possibility of full reduction of some corrosion kinds up to the pure metal Applicability for the hollow or very broken objects Full excavation of the surface relief with many details Passivation and stabilization of object
Disadvantages of plasmachemical treatment Method is not applicable for the fully corroded samples (anisotropic stress at elevated temperature) Patina removal on copper and bronze object (esthetic as well as historical problem) T 200 C changes in iron crystallography, lost of manufacturing information, lost of metal hardness T 150 C changes in copper alloys composition and crystallography, lost of manufacturing information, lost of metal hardness Financial expenses of experimental device Optimal conditions are unknown How to measure the real temperature of object
Our experimental set up
Plasma process monitoring
Treatment time end of plasma treatment I max /10 Rašková, Z., Krčma, F., Klíma, M., Kousal, J., Czechoslovak Journal of Physics 52, Suppl. E (2002).
Plasma process monitoring – multiphase treatment Rašková, Z., Krčma, F., Klíma, M., Kousal, J., Czechoslovak Journal of Physics 52, Suppl. E (2002).
Chemical composition of the surface layers SEM-EDX “silver” coin Klíma, M., Ptáčková, M., Soudný, M. and Rusnák, V., Proc. of Symposium of conservation and restoration of the national cultural heritage, Metodical Paper, , Luhačovice 1994.
SiO 2 2,32 % Cu 2 (OH) 2 (CO) 3 56,36 % Cu 2 O 12,61 % Ag 2 S 7,12 % AgCl 21,59 % SiO 2 0,57 % Cu(CO) 3 4,93 % Cu 2 O 3,74 % Ag 2 S 0,17 % AgCl 0,59 % Ag 36,56 % Cu 53,44 % After 16 hours of plasma treatment “silver” coin Chemical composition of the surface layers Klíma, M., Ptáčková, M., Soudný, M. and Rusnák, V., Proc. of Symposium of conservation and restoration of the national cultural heritage, Metodical Paper, , Luhačovice 1994.
Chemical composition of the surface layers medieval iron axe
Chemical composition of the surface layers Before FeO(OH), Fe 2 O 3, H 2 O, FeOCl After Fe 3 O 4, Fe 2 O 3, CaFe 3 O 5 RBS diagnostics
Chemical composition of the surface layers
Application on various objects Stud – silver (9 th century)??? - silver (9th century)
Application on various objects ??? - silver stirrup - silver
Application on various objects ??? -silver ear-ring - silver
Optimization for the most abundant metallic objects (iron, copper, bronze, brass ) using model samples with identical material and corrosion – it allows to compare different treatment conditions Temperature measurement directly inside the model sample Decrease of the mean energy using plasma in pulsed regime New approaches
continuos X pulsed Pulsed regime duty cycle = 100 % t ON / (t ON + t OFF ) P eff = P total t ON / (t ON + t OFF ) High energy in pulse but the mean energy is significantly lower and sample temperature is also lower. Moreover the process kinetics is different.
Preparation of model samples Surface with defined roughness - sanding Material characterization of metal (SEM-EDX) Preparation of corrosive layers (HCl, HNO 3 and H 2 SO 4 ) Storage for 7 days in dessicator SEM-EDX analyzes of surface corrosion bronze HCl HNO 3 H 2 SO 4
Monitoring at different conditions – iron + HCl
Bronze before (left) and after (right) plasma treatment HClHNO 3 H 2 SO 4
Surface analyses before and after plasma treatment HCl ironbronze
Surface analyses before and after plasma treatment brass 400 W, 25%400 W, 75%
Temperature monitoring during the plasma treatment brass 300 W – 50% 300 W – continuous Plasma temperature is nearly independent on conditions but sample temperature is significantly different.
Temperature monitoring during the plasma treatment Temperature is measured by thermocouple inside the brass sample.
Temperature monitoring during the plasma treatment brass
Temperature monitoring during the plasma treatment brass 100 W200 W300 W400 W 100% % % %
Visual results – iron, HCl 25% 75% 100 W300 W
Visual results – copper, HCl, 200 W 25%75%50%original
Deposition of the protective thin layers - HMDSO
Oxygen Transmission Rate measurements
Oxygen Transmission Rate measurements - HMDSO
Application of parylene (poly-para-xylylene) layers Parylene coatings are chemically inert, conformal transparent with excellent barrier properties relatively small adhesion Preparation by classical CVD from dimer
Comparison of parylene layers with standard application of Paraloid B44 varnish Parylene Used modification Parylene C Thickness 10 microns Paraloid B44 Samples dried at 100°C for 4 hours under vacuum 2 layers of varnish (delay 6 hours), dried at ambient air Solution of 4% for iron samples 3% of benztriazole in ethanol added for other materials Test According to ISO 9227 in salt chamber Ascot hours Temperature of 25°C
Comparison of parylene layers with standard application of Paraloid B44 varnish - iron 0 hours 300 hours Paraloid Parylene
Comparison of parylene layers with standard application of Paraloid B44 varnish - brass 0 hours 300 hours Paraloid Parylene
Future research Application of gas mixtures at low pressure RF discharge Application of sample bias at low pressure RF discharge Combination of active discharge with post-discharge Construction of underwater plasma jet based on capillary discharge Deposition of diamond like carbon thin layers Deposition of gradient thin layers and multilayer systems Study of thin layers stability Colorimetry of protecting layers Study of protecting coatings removal Verification of all processes and their transfer to the technology
Research staff and students Assoc. Prof. František Krčma Dr. Zdenka Kozáková Dr. Věra Mazánková Dr. Radek Přikryl Dr. Martin Zmrzlý Dr. Lukáš Richtera Karel Štefka Ing. Drahomíra Janová - FMI Dr. Hana Grossmannová -TM Dr. Martin Hložek - TM Ing. Alena Selucká - TM Ing. Jitka Slámová - TM Ing. Věra Sázavská Ing. Michal Procházka Ing. Lucie Hlavatá Ing. Lenka Hlochová Ing. Petra Fojtíková Ing. Lucie Řádková Ing. Radka Balaštíková Ing. Lucie Němcová Ing. Přemysl Menčík Ing. Ondřej Sedláček Bc. Adam Kujawa Bc. Lucie Blahová Bc. Jakub Horák Finished students Dr. Zuzana Rašková Ing. Kamil Brandejs Ing. Marek Cihlář Ing. Nikola Zemánek Ing. Tereza Šimšová Ing. Osvald Kozák Main collaboration Technical Museum, Brno Faculty of Mechanical Eng., BUT, Brno Comenius University, Bratislava Inst. of Nuclear Physics, CAS, Řež
All this work is supported by Czech Ministry of Culture National Identity Research Program Plasma Chemical Processes and Technologies for Conservation of Archaeological Objects – €
Thank you for your attention
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