The effects of plasma treatment on the microstructure of metals
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Published
Nov 12, 2021
Abstract
Plasma treatment became an established method for the treatment of corroding metals, particularly iron, in the 1990s. There seemed to be a general assumption that the treatment had little significant effect on the microstructure of the metals and this has never been seriously challenged. Although under the less extreme conditions now adopted in some laboratories gross phase changes may not happen, more subtle changes are very likely to be taking place, as exemplified here by a series of test pieces of iron and silver metallographically examined before and after plasma treatment. These tests are described and some of the changes in structure that
are likely to occur in metals in the temperature range 100–300°C are outlined. These changes are significant and are often the result of deliberate heat treatments during the original manufacture of the artefacts. Once they have been modifi ed by subsequent heating much of the fabrication history will have been lost. Other structural changes occur over long periods of time and these are also vulnerable to quite modest heating, thereby compromising future authentication examinations.
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References
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Archer P J and Barker B D 1987, ‘Phase changes associated with the hydrogen reduction conservation process for ferrous artefacts’, Historical Metallurgy 21(1), 86–91.
Arnould-Pernot C, Forrières C, Michel H and Wéber B 1994, ‘Optimisation d’un traitment de dechloruration d’objets ferreux par plasma d’hydrogene’, Studies in Conservation 39(4), 232–40.
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Bradley S, Newey H, Lee L, Lang J, Craddock P, Watkins S, Shearman F and Thickett D 1997, ‘Assessment of the plasma treatment for archaeological iron objects in the collections of the British Museum’, in N Oswald (ed), Conservation of Metal Objects in Low-Pressure Hydrogen Plasma (Proceedings of the International Symposium held at the Swiss National Museum, Zurich) = Zeitschrift für Schweizerische Archäologie und Kunstgeschichte 54(1), 54–58.
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Daniels V D, Holland L and Pascoe M W 1979, ‘Gas plasma reactions for the conservation of antiquities’, Studies in Conservation 24(2), 85–92.
Ehrenreich R M and Strahan D K 1987, ‘The Effects of Boiling on the Quenched Steel Structure of Martensite’, in J Black (ed), Recent Advances in the Conservation of Artifacts (London), 86–89.
Fell V 1993, ‘Examination of four Iron Age ferrous hammer heads from Bredon Hill (Hereford and Worcester), England’, Historical Metallurgy 27(2), 60–70.
Fell V 1995, ‘Metallographic examination of Iron Age tools from Somerset’, Historical Metallurgy 29(1), 1–11.
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Havlinová A, Perlík D and Sankot P 1998, ‘Integration of hydrogen plasma into the traditional conservation process of metal’, in W Mourey and L Robbiola (eds), Metal 98 (London), 209–14.
Hombeck F and Bell T 1991, ‘Environmentally harmless plasma thermochemical process’, Surface Engineering 7(1), 45–52.
Jakobsen T 1988, ‘Iron corrosion theories and the conservation of archaeological iron objects in the 19th century with emphasis on Scandinavian and German sources’, in V Daniels (ed), Early Advances in Conservation (London), 51–58.
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Scott B 1989, ‘The retrieval of technological information from corrosion products on early wrought iron artefacts’, in R C Janaway and D Scott (eds), Evidence Preserved in Corrosion Products: New Fields in Artifact Studies (London), 8–14.
Sjøgren A and Buchwald V F 1991, ‘Hydrogen plasma reactions in a d.c. mode for the conservation of iron meteorites and antiquities’, Studies in Conservation 36(2), 161–71.
Smith C S 1967, ‘The Interpretation of Microstructures of Metallic Artifacts’, in W J Young (ed), Application of Science in Examination of Works of Art (Boston), 20–52.
Speich G R 1969, ‘Tempering of Low-carbon Martensite’, Transactions American Institute of Mining and Metallurgical Engineers 245, 2553–64.
Staines A M 1990, ‘Trends in Plasma-assisted Surface Engineering Processes’, Heat Treatment of Metals 4, 85–92.
Swiss A J and McDonnell J G 2003, ‘Evidence and interpretation of cold working in ferritic iron’, in A Giumlia Mair (ed), Archaeometallurgy in Europe I (Milan), 209–17.
Thompson F C and Chatterjee A K 1952–4, ‘The Age-Embrittlement of Silver Coins’, Studies in Conservation 1(3), 115–26.
Turgoose S 1982, ‘Post-excavation changes in iron antiquities’, Studies in Conservation 27(2), 97–101.
Tylecote R F and Black J W 1980, ‘The effect of hydrogen reduction on the properties of ferrous materials’, Studies in Conservation 25(2), 87–96.
Vepřek S 1993, ‘A new method for the restoration of archaeological metallic artefacts by means of low pressure plasma treatment: the development and the present status’, in S Aoki (ed), Current Problems in the Conservation of Metal Antiquities (Tokyo), 71–87.
Vepřek S, Patscheider J and Elmer J 1985, ‘Restoration and Conservation of Ancient Artifacts: A New Area of Application of Plasma Chemistry’, Plasma Chemistry and Plasma Processing 5(2), 203–09.
Voute A 1997, ‘The Plasma Equipment at the Swiss National Museum – Observations and improvements’, in N Oswald (ed), Conservation of Metal Objects in Low-Pressure Hydrogen Plasma (Proceedings of the International Symposium held at the Swiss National Museum, Zurich) = Zeitschrift für Schweizerische Archäologie und Kunstgeschichte 54(1), 41–44.
Wanhill R J H, Steljaart J P H M, Leenheer R and Koens J F W 1998, ‘Damage assessment and preservation of an Egyptian silver vase’, Archaeometry 40(1), 123–37.
Wanhill R J H 2003, ‘Brittle archaeological silver: a fracture mechanisms and mechanics assessment’, Archaeometry 45(4), 625–36.
Wayman M L and Bringas J E 1995, The Metals Black Book 1: Ferrous Metals (Edmonton, Canada).
Werner A E 1967, ‘Two Problems in the Conservation of Antiquities: Corroded Lead and Brittle Silver’, in W J Young (ed), Application of Science in Examination of Works of Art (Boston), 96–104.
Williams A 2003, The Knight and the Blast Furnace (Leiden).
Aoki S, Hirao Y, Hirai S and Kubota H 1993, ‘Stabilization of archaeological iron’, in S Aoki (ed), Current Problems in the Conservation of Metal Antiquities (Tokyo), 91–97.
Archer P J and Barker B D 1987, ‘Phase changes associated with the hydrogen reduction conservation process for ferrous artefacts’, Historical Metallurgy 21(1), 86–91.
Arnould-Pernot C, Forrières C, Michel H and Wéber B 1994, ‘Optimisation d’un traitment de dechloruration d’objets ferreux par plasma d’hydrogene’, Studies in Conservation 39(4), 232–40.
Barker B D, Kendell K and O’Shea C 1982, ‘The hydrogen reduction process for the conservation of ferrous objects’, in R W Clarke and S M Blackshaw (eds), Conservation of Iron (Greenwich), 23–27.
Bradley S, Newey H, Lee L, Lang J, Craddock P, Watkins S, Shearman F and Thickett D 1997, ‘Assessment of the plasma treatment for archaeological iron objects in the collections of the British Museum’, in N Oswald (ed), Conservation of Metal Objects in Low-Pressure Hydrogen Plasma (Proceedings of the International Symposium held at the Swiss National Museum, Zurich) = Zeitschrift für Schweizerische Archäologie und Kunstgeschichte 54(1), 54–58.
Cohen M 1937, ‘Aging Phenomena in a Silver-rich Copper Alloy’, Transactions American Institute of Mining and Metallurgical Engineers 124, 138–57.
Daniels V D, Holland L and Pascoe M W 1979, ‘Gas plasma reactions for the conservation of antiquities’, Studies in Conservation 24(2), 85–92.
Ehrenreich R M and Strahan D K 1987, ‘The Effects of Boiling on the Quenched Steel Structure of Martensite’, in J Black (ed), Recent Advances in the Conservation of Artifacts (London), 86–89.
Fell V 1993, ‘Examination of four Iron Age ferrous hammer heads from Bredon Hill (Hereford and Worcester), England’, Historical Metallurgy 27(2), 60–70.
Fell V 1995, ‘Metallographic examination of Iron Age tools from Somerset’, Historical Metallurgy 29(1), 1–11.
Greiff S and Bach D 2000, ‘Eisenkorrosion und Natriumsulfitensalzung: Theorie und Praxis’, Arbeitblätter für Restauratoren 2, 319–39.
Havlinová A, Perlík D and Sankot P 1998, ‘Integration of hydrogen plasma into the traditional conservation process of metal’, in W Mourey and L Robbiola (eds), Metal 98 (London), 209–14.
Hombeck F and Bell T 1991, ‘Environmentally harmless plasma thermochemical process’, Surface Engineering 7(1), 45–52.
Jakobsen T 1988, ‘Iron corrosion theories and the conservation of archaeological iron objects in the 19th century with emphasis on Scandinavian and German sources’, in V Daniels (ed), Early Advances in Conservation (London), 51–58.
Keene S and Orton C 1985, ‘Stability of treated archaeological iron: an assessment’, Studies in Conservation 30(3), 136–42.
Knight B 1997, ‘The Stabilisation of Archaeological Iron: Past, Present and Future’, in I D MacLeod, S L Pennec and L Robbiola (eds), Metals 95 (London), 36–40.
Lacoudre N nd, Elecricité et Archéologie (Paris).
Norbury A L 1928, ‘The Effect of Quenching and Tempering on Standard Silver’, Transactions of the Institute of Metals 39, 45–61.
Oswald N 1997, ‘In Search of the Lost Surface: 10 Years of Active Hydrogen Research. An Attempt to Convert Destructive Criticism into Improvements of the Plasma Method’, in I D MacLeod, S L Pennec and L Robbiola (eds), Metals 95 (London), 133–37.
Patscheider J and Vepřek S 1986, ‘Application of low-pressure hydrogen plasma to the conservation of ancient iron artefacts’, Studies in Conservation 31(1), 29–37.
Pearson C 1972, ‘The preservation of iron cannon after 200 years under the sea’, Studies in Conservation 17(2), 91–110.
Perlík D 2004, ‘The infl uence of low-pressure hydrogen plasma on changes in the metallographic structure of iron objects’, in I D MacLeod, J M Theille and C Degrigny (eds), Metal 2001 (Perth, Australia), 12–18.
Petrie W M F 1888, ‘The treatment of small antiquities’, Archaeological Journal 45, 85-89.
Rinuy A and Schweizer F 1981, ‘Méthodes de conservation d’objets de fouiles en fer. Etude quantitative compare de l’elimination des chlorures’, Studies in Conservation 26(1), 29–41.
Samuels L E 1980, Optical Microscopy of Carbon Steels (Clevland).
Schmidt-Ott K 1997, ‘Applications of low pressure plasma treatment at the Swiss National Museum and assessment of the results’, in N Oswald (ed), Conservation of Metal Objects in Low-Pressure Hydrogen Plasma (Proceedings of the International Symposium held at the Swiss National Museum, Zurich) = Zeitschrift für Schweizerische Archäologie und Kunstgeschichte 54(1), 45–50.
Schmidt-Ott K 2004, ‘Plasma Reduction; its Potential Use in the Conservation of Metals’, in J Ashton and D Hallam (eds), Metal 2004 (Canberra), 235–46.
Schmidt-Ott K and Boissonnas V 2002, ‘Low-pressure hydrogen plasma: an assessment of its application on archaeological iron’, Studies in Conservation 47(1), 81–87.
Schwab R 2002, ‘Evidence for carburized steel and quench-hardening in the “Celtic” oppidum of Manching’, Historical Metallurgy 36(1), 6–16.
Schweizer F and Meyers P 1979, ‘Authenticity of ancient silver objects: a new approach’, MASCA Journal 1(1), 9–11.
Scott B 1989, ‘The retrieval of technological information from corrosion products on early wrought iron artefacts’, in R C Janaway and D Scott (eds), Evidence Preserved in Corrosion Products: New Fields in Artifact Studies (London), 8–14.
Sjøgren A and Buchwald V F 1991, ‘Hydrogen plasma reactions in a d.c. mode for the conservation of iron meteorites and antiquities’, Studies in Conservation 36(2), 161–71.
Smith C S 1967, ‘The Interpretation of Microstructures of Metallic Artifacts’, in W J Young (ed), Application of Science in Examination of Works of Art (Boston), 20–52.
Speich G R 1969, ‘Tempering of Low-carbon Martensite’, Transactions American Institute of Mining and Metallurgical Engineers 245, 2553–64.
Staines A M 1990, ‘Trends in Plasma-assisted Surface Engineering Processes’, Heat Treatment of Metals 4, 85–92.
Swiss A J and McDonnell J G 2003, ‘Evidence and interpretation of cold working in ferritic iron’, in A Giumlia Mair (ed), Archaeometallurgy in Europe I (Milan), 209–17.
Thompson F C and Chatterjee A K 1952–4, ‘The Age-Embrittlement of Silver Coins’, Studies in Conservation 1(3), 115–26.
Turgoose S 1982, ‘Post-excavation changes in iron antiquities’, Studies in Conservation 27(2), 97–101.
Tylecote R F and Black J W 1980, ‘The effect of hydrogen reduction on the properties of ferrous materials’, Studies in Conservation 25(2), 87–96.
Vepřek S 1993, ‘A new method for the restoration of archaeological metallic artefacts by means of low pressure plasma treatment: the development and the present status’, in S Aoki (ed), Current Problems in the Conservation of Metal Antiquities (Tokyo), 71–87.
Vepřek S, Patscheider J and Elmer J 1985, ‘Restoration and Conservation of Ancient Artifacts: A New Area of Application of Plasma Chemistry’, Plasma Chemistry and Plasma Processing 5(2), 203–09.
Voute A 1997, ‘The Plasma Equipment at the Swiss National Museum – Observations and improvements’, in N Oswald (ed), Conservation of Metal Objects in Low-Pressure Hydrogen Plasma (Proceedings of the International Symposium held at the Swiss National Museum, Zurich) = Zeitschrift für Schweizerische Archäologie und Kunstgeschichte 54(1), 41–44.
Wanhill R J H, Steljaart J P H M, Leenheer R and Koens J F W 1998, ‘Damage assessment and preservation of an Egyptian silver vase’, Archaeometry 40(1), 123–37.
Wanhill R J H 2003, ‘Brittle archaeological silver: a fracture mechanisms and mechanics assessment’, Archaeometry 45(4), 625–36.
Wayman M L and Bringas J E 1995, The Metals Black Book 1: Ferrous Metals (Edmonton, Canada).
Werner A E 1967, ‘Two Problems in the Conservation of Antiquities: Corroded Lead and Brittle Silver’, in W J Young (ed), Application of Science in Examination of Works of Art (Boston), 96–104.
Williams A 2003, The Knight and the Blast Furnace (Leiden).
How to Cite
Craddock, P., & Lang, J. (2021). The effects of plasma treatment on the microstructure of metals. Historical Metallurgy, 39(2), 106-119. https://www.hmsjournal.org/index.php/home/article/view/238
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How to Cite
Craddock, P., & Lang, J. (2021). The effects of plasma treatment on the microstructure of metals. Historical Metallurgy, 39(2), 106-119. https://www.hmsjournal.org/index.php/home/article/view/238