CENIMAT/I3N (FCT-UNL) Dep. Ciências dos Materiais. FCT-UNL. Instituto Tecnológico e Nuclear Sacavém. Portugal

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1 INFLUENCE OF MINOR ELEMENTS IN ANCIENT CHINESE BRASS COINS MICROSTRUCTURES M.J. Furtado 1.2. R.J.C. Silva 1. M.F. Araújo 2. F.M. Braz Fernandes 1 1 CENIMAT/I3N (FCT-UNL) Dep. Ciências dos Materiais. FCT-UNL Monte de Caparica 2 Instituto Tecnológico e Nuclear Sacavém Portugal TOFA Porto September16th. 2010

OBJECTIVES Co-relate compositions & microstructures in 30 Chinese brass coins Assess the effects of minor elements in the brass microstructure Provenance - Produced

2 OBJECTIVES Co-relate compositions & microstructures in 30 Chinese brass coins Assess the effects of minor elements in the brass microstructure Provenance - Produced in China. bought at Macau (1990 s. for Macau Museum in Lisbon) Studied periods - Ming Dynasty (14 th to 17 th century) - Qing Dynasty [Ching] (17 th to 20 th century) 2

3 METHODOLOGY Polishing of a small rim area: 1 cm - micro-xrf. - OM. - SEM-EDS - micro-xrd 3

washing and drying 2 Metal pouring 4 Stringing 1 2 3(a) 3(b) 4 From http://www.history.

4 PRODUCTION TECNIQUES: As-cast (sand moulds) 1 Mother-coin and sprue system imprint on two shell sand moulds 3 Cold finishing: (a) filing. (b) polishing. washing and drying 2 Metal pouring 4 Stringing 1 2 3(a) 3(b) 4 From [Zuroku Nihon no kahei. vol.3. Tokyo: Touyou Keizai Shinpousha. 1974] 4

5 ELEMENTAL COMPOSITION (micro-xrf) Main elements Cu Zn (25<wt.%<52) Secondary elements Pb (up to 14 wt.%) Sn (up to 4 wt.%) Sb (up to 4 wt.%) Fe (up to 2 wt.%) As (up to 2 wt.%) Wt. % Cu Zn Pb Sn Sb Fe As Ni [0.42]

6 CASTING STRUCTURES: As-cast (dentritic) Coin ~ monophasic α-cu Etched. FeCl 3 α phase cored dendritic structure 68%Cu 30%Zn 6

7 MICRO-XRF: LEADED BRASSES Cu Zn Pb Sn Sb Fe As Ni [0.42]

8 LEADED BRASSES Microstructural effects of Pb Coin %Pb ~10%Pb Liquid 955 ºC 36.1 Eutectic globule (~99.9% Pb) α+l 2 OM-BF analysed brass coins Pb globules in beta matrix Alpha + gamma Cu α+(pb) 326 ºC Eutectic 99.9 % Pb Pb [Cu-Pb. adapted from AMS. 1973] Pb globules SEM -BSE 8

9 Microstructural effects of Zn Coin 2766 Coin 2773 Coin 2775 Coin µm α α+β β Cored α structure β+γ β γ L Lα L L β β β Redeposited βcu grains Coin 2710 α β α γ β βα γ Cu + Zn = 100% Cu Zn γ?! With 29% Zn 9

OTHER SYSTEMS CONSIDERED Microstructural effects of Sn Coin 2710. α+γ structure (Pb) γ Cu + Zn+ Sn = 100% Cu Sn Zn Sn 2710 64.1 33.1 2.

10 OTHER SYSTEMS CONSIDERED Microstructural effects of Sn Coin α+γ structure (Pb) γ Cu + Zn+ Sn = 100% Cu Sn Zn Sn α Cu Zn 2710 α Pb γ [Cu-Sn-Zn isothermal section at 450ºC. adapted from Vilarinho et al ] β α + γ [Hudson, 1915] SEM-EDS α SEM-EDS γ Micro-XRD analysis of coin

4 2785 Cu Zn [Cu-Sn-Zn isothermal section at

11 OTHER SYSTEMS CONSIDERED Microstructural effects of Sb Coin α+γ structure α γ Cu + Zn+ Sb = 100% Cu Sn Sb Zn Sb Cu Zn [Cu-Sn-Zn isothermal section at 450ºC. adapted from Vilarinho et al ] SEM-EDS γ Sn Sb [isothermal section of Cu-Sb-Sn. adapted from AMS. 1973] 11

12 MICRO-XRF: TIN BRASSES (Sn and/or Sb) Cu Zn Pb Sn Sb Fe As Ni [0.42]

13 OTHER SYSTEMS CONSIDERED Microstructural effects of Sn + Sb α α+β β β+γ α+γ α+β+γ Ming coins Qing coins + Sb + Sb + Sb + Sb + Sb [Cu-Sn-Zn isothermal section at 450ºC. adapted from Vilarinho et al ] Observed brasses phases 13

14 α-fe dendrites MICRO-XRF Micro-XRF Cu Zn Pb Sn Sb Fe As Ni [0.42]

15 OTHER SYSTEMS CONSIDERED Microstructural effects of Fe Coin α+γ structure α-fe Binary Cu-Fe ºC Cu + Fe = 100% Cu Fe L corrosion Fe rich primary phase L+ γ-fe %Fe γ-fe + α-fe (Cu) L γ-fe γ-fe α-fe Fe 800 α-fe 700 Fe Cu Cu (wt.%) [Cu-Fe. adapted from AMS. 1973] 15

OTHER SYSTEMS CONSIDERED Microstructural effects of Fe and As Coin 2785.

FeCl 3 Cu + Fe +As = 100% Cu Fe As 2785 93.1 4.1 2.

16 OTHER SYSTEMS CONSIDERED Microstructural effects of Fe and As Coin α+γ structure Ternary As-Cu-Fe α-fe Etched. FeCl 3 Cu + Fe +As = 100% Cu Fe As As rich phase [As-Cu-Fe isothermal section at 25ºC. adapted from Raghavan. 1992] The 3 coins with α-fe dendrites 16

17 Final considerations Chinese brass coins: Element association & use of binary/ternary systems allow microstrutural interpretation: Pb: immiscibility explains Pb dispersion and globule formation Sn-Sb: promote the formation of β and γ for lower Zn contents Fe-As: promote the formation primary ferrite and iron arsenide Even small elemental amounts (over 0.5%) affect phase constitution Microstructural characterization can help predict conservational issues in brass cultural heritage 17

18 Acknowledgements Macau Scientific and Cultural Centre Ministério da Ciência. Tecnologia e Ensino Superior 18

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