8.1 General
Considering the depletion level of copper ores in the nature, the necessity of either recycling through extraction process or reusing the scraped copper at its leftover state is now an important issue. Since recycling is a difficult as well as costly affair, it is urgent to look for reusing options. As such, in an attempt to investigate the reuse potentials of waste/old scraped copper traditionally coming out from industries, buildings, ship breakings, etc., a physico-electro-mechanical characterization has been carried out under the influence of trace addition of SnPb-solder in it. To identify the changes in properties due to such inclusion of solder along with the effects of cold work and thermal ageing, three more sample materials were taken in addition to solder affected scraped copper. All sample materials have been homogenized for eight hours at a temperature of 500°C for the reduction of chemical segregation and then solution treated for two hours at a temperature of 700°C to improve their workability. Then required samples of different sizes and shapes were prepared in accordance with the experimental requirements. Once samples were ready, a series of tests were under taken to investigate a number of chosen physical parameters, namely, material micro-hardness, tensile behavior, wear behavior, corrosion behavior, conductivity, thermal stability, microstructural appearance, etc.
8.2 Summary of Major Findings
It is found that tiny amount of tin ( 1%) can contribute significantly to increase the micro-hardness of copper by an amount of 24%, while similar amount of lead decreases the corresponding micro-hardness by an amount of around 7%. The hardness of lead added copper alloys are found to supersede those of pure copper and tin added copper alloys at a particular level of cold-rolling condition (35% deformation).
The tensile tests of material-I (pure Cu), material-II (Cu-Sn alloy), material-III (Cu- Pb alloy) and material-IV (SnPb-solder affected Cu) exhibit that UTS and Yield strength
values have been increased for the inclusion of Sn and decreased for Pb in old Cu of its as cast condition. After cold-rolled work hardening, UTS and Yield strength have been improved for all sample materials, and it happens more significantly for material-III and -IV which contain about 1% Pb. Thermal ageing has shown initial rise of strength with the rise of temperature to the maximum strength level at the ageing temperature of approximately 150℃ and then falling trends at the elevated temperature. UTS and yield strength values have been found to be increased by the increase of strain rate for all four sample materials. The ultimate elongation values of all sample materials have been found to follow decreasing trends against cold work level. Thermal ageing has shown higher stable operating region of alloys than pure Cu. The increase of strain rate has lowered the ultimate elongation of all four sample materials. The micrographs of sample materials indicate the formation of CuxSny for material-II and -IV and solid solution of Pb in Cu for material-III and -IV. After work hardening their grains have been found deformed in the direction of rolling contributing to higher strength and hardness. No indication of grain refinement is also observed up to certain level of cold rolling, however, after reaching to about 75% cold work level, notice of grain refinement may be traced.
Elastic modulus values of Cu alloy samples have been found to be lower than that of pure Cu, i.e., modulus is affected by the change of composition. But, the cold work has not shown any effect on elastic modulus of sample materials. Thermal ageing has also no effect on the modulus values up to about 300℃, however, modulus values have been reduced at the ageing temperature of 350℃ and higher. The strain rate variations have not influenced elastic modulus of samples at lower cross head speed. Only at higher speed, little rise of modulus values have been observed.
Presence of little amount of Sn has increased the hardness and improved the wear resistance of Cu to a significant level, while similar amount of Pb in Cu has reduced the hardness but increased the wear resistance. ‘The bigger the hardness value the better the wear resistance’ has been matched partly with the results of pure Cu, high Cu-Sn alloy and high Cu-Sn-Pb alloy. But Cu-Pb alloy has shown considerable high wear resistance even with lower hardness values than of pure Cu. COF values of all four sample materials have shown non-linearly gradual increasing trends at the initial stage and after certain sliding distance finally reached to some steady state level. The highest COF has been found to be for high Cu-Pb alloy amongst four sample materials over the entire sliding
distance, whereas the lowest COF has been found for high Cu-Sn alloy. The target material, i.e., SnPb-solder affected Cu remains in between them with the maximum COF value of 0.533.
The corrosion immunity of work hardened copper materials are affected marginally in pH varied environments. However, pH1 solution has been found to be the highest corrosive environment and the next is the pH13 solution for all four copper based sample materials. Overall leaching losses have been found to be increased for addition of Sn and/or Pb in Cu for each pH value. The highest loss is found to be of Cu-Pb alloy amongst four sample materials. Cu-Pb alloy is followed by SnPb-solder affected copper, then Cu- Sn alloy and the lowest loss is of pure copper. It indicates that alloying of copper with tin or lead has reduced its corrosion resistance especially in acidic environment.
Electrical conductivity of Cu falls drastically with the addition of only about 1%
Sn or 1% Pb alloy. The conductivity of the solder affected copper alloys can be increased to some extent through cold-rolling up to ~35% deformation level which is also identified to be the optimum value for recovering a portion of the loss of conductivity due to inclusion of solder elements in Cu. A post hardening thermal treatment shows that the alloys can offer a higher stable range of hardness against ageing temperature than that of pure Cu, while the electrical conductivity of the alloys is increased to a little extent by the treatment with higher ageing period.
DSC results indicate that the first endothermic peak of Cu is shifted to higher temperature due to alloying through the inclusion of SnPb-solder in it. DSC curves also reveal that the second endothermic peaks of all four copper based sample materials are shifted toward lower temperature as a consequence of cold-rolled work hardening and thereby the corresponding recrystallization temperatures of the samples have been decreased by about 20oC. The OEM micrographs, SEM images and corresponding EDX spectra are found to conform to the observed changes in micro-hardness and electrical conductivity of the solder affected copper alloys due to formation of intermetallic compounds.
8.3 Possible Industrial Applications
With the present findings, it is expected that SnPb-solder affected old Cu can now be free from unknown fears which were making the end users skeptical to accept the direct use of old copper. Therefore, there will be number of industrial applications of scraped copper in manufacturing new mechanical engineering products, like, marine propellers, bush/liner of shaft bearings, valves, stern glands, bulkhead glands, fittings of fire-main lines, fire hydrants, etc. under controlled condition of properties through work hardening and thermal ageing.
8.4 Recommendations
The present research leads to underline following recommendations:
a. The characterization of few more properties of SnPb-solder affected old Cu, such as, optical behavior, magnetic behavior, etc. may be undertaken, which will eventually enhance its behavioral spectrum further and thus the reuse potential of scraped Cu will be well established with customized option for pure mechanical as well as electro-mechanical applications.
b. There may be a memorandum of understanding between academician conducting the research and concerned industries so that the reuse practice of scraped copper can be made acceptable to the end users and promoted further.
References
1. Davis J.R. (Eds). (2001). Copper and Copper Alloys. ASM Specialty Handbook Series, ASM International, Materials Park, Ohio 44073-0002, USA, 2001.
2. Collini L. (Ed). (2012). Copper Alloys – Early Applications and Current Performance – Enhancing Processes, InTech Janeza Trdine 9, 51000 Rijeka, Croatia, USA.
3. Srinivasan, S., Ranganathan, S. & Giumlia-Mair, A. (2015). Metals and Civilizations, National Institute of Advanced Studies, India.
4. Phillips, P. (2019). Electrical Principles, Edition 4, Cengage Learning Australia.
5. U.S. Geological Survey, Mineral Commodity Summaries, January 2020.
6. Villena, M. & Greve F. On resource depletion and productivity: The case of the Chilean copper industry. Resources Policy, 2018. doi:10.1016/
j.resourpol.2018.10.001
7. Cui, J. & Forssberg, E. (2003). Mechanical recycling of waste electric and electronic equipment: a review. Journal of Hazardous Materials, 99(3) 243–263.
doi:10.1016/s0304-3894(03)00061-x
8. Fogarasi, S., Imre-Lucaci, F., Imre-Lucaci, A. & Ilea, P. (2014). Copper recovery and gold enrichment from waste printed circuit boards by mediated electrochemical oxidation. Journal of Hazardous Materials, 273 215-221.
doi:10.1016/j.jhazmat.2014.03.043
9. Samuelsson, C. & Björkman, B. (2014). Copper Recycling. Handbook of Recycling, 85–94. doi:10.1016/b978-0-12-396459-5.00007-6
10. Rahman, M.M., Ahmed S.R. & Kaiser M.S. (2021). On the Investigation of Reuse Potential of SnPb-Solder Affected Copper Subjected to Work-Hardening and
Thermal Ageing, Materials Characterization, 172.
doi.org/10.1016/j.matchar.2021.110878
11. Rahman, M.M., Ahmed, S.R. & Kaiser, M.S. (2020). Behavior of work hardened SnPb-solder affected copper on corrosion resistance in pH varied environments.
European Journal of Materials Science and Engineering, 5(4). doi 10.36868/ejmse.2020.05.04.199.
12. Kasper, A.C., Berselli, G.B.T., Freitas, B.D., Tenório, J.A.S., Bernardes, A.M. &
Veit, H.M. (2011). Printed wiring boards for mobile phones: Characterization and recycling of copper. Waste Management, 31(12) 2536–
2545. doi:10.1016/j.wasman.2011.08.013
13. Ri, Kh., Komkov, V.G. & Ri, E.Kh. (2014). Effect of Alloying Elements on the Physico-mechanical Properties of Copper and Tin Bronze, Russian Metallurgy (Metally), 2014 (9) 750–755. doi: 10.1134/ S0036029514090158
14. Prakash, K.H. & Sritharan, T. (2004). Tensile fracture of tin-lead solder joints in copper, Elsevier, Materials Science and Engineering A, 379, 277–285.
15. Mitchell, T.E. & Thornton, P.R. (1963). The work-hardening characteristics of Cu and α-brass single crystals between 4•2 and 500°K, Philosophical Magazine, Cavendish Laboratory, Cambridge, 8 (91) 1127-1159, Published online: 2006.
doi:10.1080/ 14786436308207340
16. Chandler, H.D. (2009). Work hardening characteristics of copper from constant strain rate and stress relaxation testing, Materials Science and Engineering: A, 506, Issues 1–2, 130-134. doi:10.1016/j.msea.2008.11.020
17. Ivanov, S., Markovich, D., Stuparevich, L. & Guskovich, D. (1996). Effect of degree of cold work and annealing temperature on the microstructure and properties of cold drawn copper wires and tubes. Bull. Mater. Sci. 19 (1), 131–138. doi.org/
10.1007/BF02744795
18. Nestorovic, S. (2004). Influence of deformation degree at cold-rolling on the anneal hardening effect in sintered copper-based alloys, Journal of Mining and Metallurgy, 40B (1), 101–109.
19. Rafiee, E., Farzam, M., Golozar, M.A. & Ashrafi, A. (2013). An Investigation on Dislocation Density in Cold-Rolled Copper Using Electrochemical Impedance Spectroscopy, ISRN Corrosion Volume 2013, Article ID 921825.
doi.org/10.1155/2013/921825
20. Cielinski, M., Morawiec, H., Woch, M., Przybyla, J. & Sokolowski, A. (1980).
Effect of deformation and annealing on elastic properties of copper wires, Metals Technology, 7:1, 420-423. DOI: 10.1179/030716980803286892
21. Han, S.Z., Lim, S.H., Kim, S., Lee, J., Goto, M., Kim, H.G., Han, B. & Kim, K.H. (2016). Increasing strength and conductivity of Cu alloy through abnormal plastic deformation of an intermetallic compound. Nature, Scientific Reports, 6:30907. DOI: 10.1038/srep30907
22. Cho, J.H., Rollett, A.D., Cho, J.S., Park, Y.J., Moon, J.T. & Oh, K.H. (2006).
Investigation of Recrystallization and Grain Growth of Copper and Gold Bonding Wires, Metallurgical and Materials Transactions A, Vol. 37a, 3085-3097.
23. Madeni, J.C. & Liu, S. (2011). Effect of Thermal Ageing on the Interfacial Reactions of Tin-Based Solder Alloys and Copper Substrates and Kinetics of Formation and Growth of Intermetallic Compounds, Soldag. insp. São Paulo, 16 (1), 086-095.
24. Rahman, M.M., Kaiser, M.S. & Ahmed, S.R. (2019). Effect of thermal ageing on the tensile properties of hot and cold rolled commercial high conductive metal and its alloy, AIP Conference Proceedings 2121, 140004. doi.org/10.1063/1.5115955 25. Chiou, B.S., Chang, J.H. & Duh, J.G. (1995). Metallurgical Reactions at the
Interface of Sn/Pb Solder and Electroless Copper-Plated A1N Substrate, IEEE
transactions on components, packageing, and manufacturing technology-Part b, 18(3) (1995), 537-542.
26. Koleňák, R., Provazník, M & Koleňáková, M. (2013). A comprehensive investigation of copper tube joints made by resistance soldering, Technical Gazette, 20(3), 391-395.
27. Lezhnev, S.N., Volokitina, I.E., Panin, E.A. & Volokitin, A.V. (2020). Evolution of the Microstructure and Mechanical Properties of Copper during the Rolling–
ECAP Process. Physics of Metals and Metallography, 121(7), 689–693.
doi:10.1134/ s0031918x20070054
28. Okayasu, M., Muranaga, T. & Endo, A. (2017). Analysis of microstructural effects on mechanical properties of copper alloys. Journal of Science: Advanced Materials and Devices, 2(1), 128–139. doi:10.1016/j.jsamd.2016.12.003
29. Sobczak, N., Kudyba, A., Nowak, R., Radziwill, W. & Pietrzak, K. (2007). Factors affecting wettability and bond strength of solder joint couples, Pure Appl. Chem., 79(10), 1755–1769.
30. Ogawa, M., Kato, M., Majima, M., Awazu, T. Yata, H. & Ooe, M. (2017). Copper Recycling Technique Using Electrochemical Processes. Sei Technical Review.
31. Schlesinger, M.E., King, M. J., Sole, K.C. & Davenport, W.G.I. (2011). Extractive Metallurgy of Copper, Elsevier, UK.
32. Yin, Z., Sun, F. & Guo, M. (2018). The fast formation of Cu-Sn intermetallic compound in Cu/Sn/Cu system by induction heating process. Materials Letters, 215, 207–210; doi:10.1016/j.matlet.2017.12.102
33. Saunders, N. & Miodownik, A.P. (1990). The Cu-Sn (Copper-Tin) system. Bulletin of Alloy Phase Diagrams, 11(3), 278–287. doi:10.1007/bf03029299
34. Bernal, J. (1928). The Complex Structure of the Copper–Tin Intermetallic Compounds. Nature 122, 54. https://doi.org/10.1038/122054a0
35. Gupta, S.P. & Rathor, D. (2002). Kinetics of growth of intermetallics in the Cu-Sn system. Zeitschrift Für Metallkunde, 93(6), 516–522. doi:10.3139/146.020516 36. Fürtauer, S., Li, D., Cupid, D. & Flandorfer, H. (2013). The Cu–Sn phase diagram,
Part I: New experimental results, Intermetallics, Volume 34, Pages 142-147, https://doi.org/10.1016/j.intermet.2012.10.004.
37. Chakrabarti, D.J. & Laughlin, D.E. (1984). The Cu−Pb (Copper-Lead) system.
Bulletin of Alloy Phase Diagrams, 5(5), (1984), 503–510.
doi:10.1007/bf02872905
38. Hoyt, J.J., Garvin, J.W., Webb, E.B. & Asta, M. (2003). An embedded atom method interatomic potential for the Cu-Pb system, Modelling and Simulation in Materials Science and Engineering, 11(3), 287-299. DOI: 10.1088/0965- 0393/11/3/302
39. Cui, H., Guo, J., Su, Y., Ding, H., Wu, S., Bi, W., Xu, D. & Fu, H. (2006).
Microstructure evolution of Cu-Pb monotectic alloys during directional solidification. Transactions of Nonferrous Metals Society of China, 16(4), (2006). 783–790; doi:10.1016/s1003-6326(06)60326-9
40. Chikova, O.A., Sakun, G.V. & Tsepelev, V.S. (2016). Formation of Cu–Pb alloys by means of liquid metal homogenization. Russian Journal of Non-Ferrous Metals, 57(6), 580-585. doi:10.3103/s1067821216060043
41. Korojy, B., Ekbom, L. & Fredriksson, H. (2009). Microsegregation and Solidification Shrinkage of Copper-Lead Base Alloys. Advances in Materials Science and Engineering, 627937. doi:10.1155/2009/627937
42. Thompson, J.G. (1934). Effect of cold-rolling on the indentation hardness of copper, Journal of Research of the Rational Bureau of Standards, Vol. 13, Nov.
1934.
43. Rahman, M.M., Ahmed, S.R. & Kaiser, M.S. (2020). Thermal ageing effect on electro-mechanical properties of work hardened high conductive copper based material, Sustainable Structures and Materials, An International Journal, 3(2), 14- 22. doi.org/10.26392/SSM.2020.03.02.014
44. Fujiwara, H., Nishimoto, T. Miyamoto, H. & Ameyama, K. (2013). Microstructure and Mechanical Properties of Cu-Sn Alloy with Harmonic Structure. Proceedings of the 8th Pacific Rim International Congress on Advanced Materials and Processing 2013, 2455–2460. doi:10.1007/978-3-319-48764-9_304
45. Malin, A.S. & Hatherly, M. (1979). Microstructure of cold-rolled copper, Metal Science, 13 (8), 463-472.
46. Khodaverdizadeh, H., Mahmoudi, A., Heidarzadeh, A., & Nazari, E. (2012). Effect of friction stir welding (FSW) parameters on strain hardening behavior of pure copper joints. Materials & Design, 35, 330–334. doi:10.1016/
j.matdes.2011.09.058
47. Barmouz, M., Asadi, P., Besharati Givi, M. K., & Taherishargh, M.
(2011). Investigation of mechanical properties of Cu/SiC composite fabricated by FSP: Effect of SiC particles’ size and volume fraction. Materials Science and Engineering: A, 528(3), 1740–1749. doi:10.1016/j.msea.2010.11.006
48. Djavanroodi, F., Daneshtalab, M., & Ebrahimi, M. (2012). A novel technique to increase strain distribution homogeneity for ECAPed materials. Materials Science and Engineering: A, 535, 115–121. doi:10.1016/j.msea.2011.12.050
49. Yang, B., Motz, C., Grosinger, W., Kammrath, W., & Dehm, G. (2008). Tensile behaviour of micro-sized copper wires studied using a novel fibre tensile module.
International Journal of Materials Research, 99(7), 716–
724. doi:10.3139/146.101690
50. Copper Development Association Inc., Data sheet in the website for mechanical properties of copper and its alloy. https://www.copper.org/
resources/properties/144_8/
51. Lloyd, D.J. & Kenny, D. (1978). The stress - strain behaviour of copper over a large strain range. Scripta Metallurgica, 12(10), 903–907. doi:10.1016/0036- 9748(78)90179-5
52. Alisha, S., Venkateswaran, T., Amruth, M., Chakravarthy, P., & Sivakumar, D.
(2015). Effect of Heat Treatment on the Mechanical Properties of Copper- Beryllium Alloy (C17200). Materials Science Forum, 830-831, 168- 171. doi:10.4028/ www.scientific.net/msf.830-831.168
53. Osorio-Galica, R., Gomez-Garcia, C, Alcantara, M.A. & Herrera-Vazquez, A.
(2012). Influence of heat treatment and composition variation on microstructure, hardness and wear resistance of C 18000 copper alloy. International Scholarly Research Notices, vol. 2012, Article ID 248989, 6. Doi.org/10.5402/2012/248989 54. Yew, C.H., & Richardson, H.A. (1969). The strain-rate effect and the incremental
plastic wave in copper. Experimental Mechanics, 9(8), 366–
373. doi:10.1007/bf02327714
55. Dao, M., Lu, L., Shen, Y.F. & Suresh, S. (2006). Strength, strain-rate sensitivity and ductility of copper with nanoscale twins. Acta Materialia 54, 5421–5432.
doi:10.1016/j.actamat.2006.06.062
56. Croteau, J.F., Peroni, M., Atieh, S., Jacques, N. & Cantergiani, E. (2021). Effect of Strain Rate on the Tensile Mechanical Properties of Electron Beam Welded OFE Copper and High-Purity Niobium for SRF Applications. J. dynamic behavior mater. (2021). doi.org/10.1007/s40870-021-00293-9
57. Naofal, J., Naeini, H.M., & Mazdak. S.(2019). Effects of Hardening Model and Variation of Elastic Modulus on Springback Prediction in Roll Forming. Metals, 9(9), 1005. doi:10.3390/met9091005
58. Manninen, T. (2011). Influence of cold-work on the elastic properties of austenitic stainless steels, Proceedings of the 7thEuropean Stainless Steel Conference ESSC 2011, Como, Italy, September 201110.
59. Landau P, Shneck RZ, Makov G, Venkert A. Microstructure evolution in deformed copper. Journal of Materials Science, 42(23) (2007), 9775–
9782. doi:10.1007/s10853-007-1999-6
60. Sun, S. & Li, T. (2020). Effect of cold rolling process on microstructure and properties of T1 Copper sheet, Journal of Physics: Conference Series 1605 012132, IOP Publishing. doi:10.1088/1742-6596/1605/1/012132
61. Benchabanea, G., Boumerzouga, Z., Thibonb, I. & Gloriantb, T. (2008).
Recrystallization of pure copper investigated by calorimetry and microhardness,
Materials Characterization, 59(10), 1425-1428.
doi.org/10.1016/j.matchar.2008.01.002
62. Liu, Y.C. & Hibbard, W.R. (1953). Recrystallization of a Cold-Rolled Copper Single Crystal. JOM, 5(5), 672–679. doi:10.1007/bf03397536
63. Mirza, M., Barton, D., Church, P. & Sturges. J. (1997). Ductile Fracture of Pure Copper: An Experimental and Numerical Study. Journal de Physique IV Colloque, 07 (C3), pp.C3-891-C3-896. doi.org/10.1051/jp4:19973150
64. Molian, P.A., Buchanan, V.E., Sudarshan, T.S. & Akers, A. (1991). Sliding wear characteristics of non-equilibrium Cu-Pb alloys. Wear 146(2): 257–267.
doi:10.1016/0043-1648(91) 90067-5
65. Pathak, J.P. & Tiwari, S.N. (1992). On the mechanical and wear properties of copper-lead bearing alloys. Wear 155(1): 37–47. doi:10.1016/0043- 1648(92)90107-j
66. Ji, X., Chen, Y., Quan, Y. & Shen, Z. (2016). Tribological Performance of CuPb Alloy under Seawater Lubrication. Tribology Transactions 59(3): 502–506.
doi:10.1080/10402004 .2015.1088992
67. Ayyapan, M., Uttamchand, N.K. & Rajan, R.A.A. (2016). Mechanical and wear properties of copper-lead alloy prepared by powder metallurgy processing technique, Journal of Chemical Technology and Metallurgy 51(6): 726-734.
68. Zeren, A., Feyzullahoglu, E. & Zeren, M. (2007). A study on tribological behavior of tin-based bearing material in dry sliding. Materials & Design 28(1): 318–
323. doi:10.1016/j.matdes .2005.05.016
69. Kumar, P.S., Manisekar, K., Subramanian, E. & Narayanasamy, R. (2013). Dry Sliding Friction and Wear Characteristics of Cu-Sn Alloy Containing Molybdenum
Disulfide. Tribology Transactions 56(5): 857–
866. doi:10.1080/10402004.2013.806685
70. Archard, J.F. (1953). Contact and Rubbing of Flat Surfaces, Applied Phy. 24(8):
981–988. doi:10.1063/1.1721448
71. Archard, J.F. & Hirst, W. (1956). The Wear of Metals under Unlubricated Conditions, Proc. Royal Society A 236 (1206): 397–410.
doi:10.1098/rspa.1956.0144
72. Kato, K. (2000). Wear in relation to friction – a review. Wear 242(2): 151–157.
doi.org/ 10.1016/S0043-1648(00)00382-3
73. Kapoor, A. & Franklin, F.J. (2000). Tribological layers and the wear of ductile materials. Wear 245(1-2): 204–215. doi:10.1016/s0043-1648(00)00480-4
74. Jain, A., Singh, A. & Singh, A.P. (2018). Effect of tribological parameters on sliding wear and friction coefficient which relates to preload loss in tapered roller bearing. Industrial Lubrication and Tribology 71(1): 61-73. doi:10.1108/ilt-01- 2017-0019
75. Buckley, D.H. (1972). Influence of alloying elements on friction and wear of copper. NASA Report TN D-6912, Washington D. C. 20546.
76. Zhao, W., Zhang, G. & Dong, G. (2021). Friction and wear behavior of different seal materials under water-lubricated conditions. Friction 9, 697–709.
https://doi.org/ 10.1007/s40544-020-0364-5
77. Shangguan, B., Zhang, Y.Z., Xing, J.D., Sun, L.M., & Chen, Y. (2010). Study of the Friction and Wear of Electrified Copper against Copper Alloy under Dry or Moist Conditions. Tribology Transac., 53(6), 927- 932. doi:10.1080/10402004.2010.510621
78. Graedel, T.E., Nassau, K. & Franey, J.P. (1987). Copper patinas formed in the atmosphere—I. Introduction, Corrosion Science, 27(7), 639–
657. doi:10.1016/0010-938x(87)90047-3
79. Leygraf, C., Chang, T., Herting, G. & Wallinder, I.O. (2019). The Origin and Evolution of Copper Patina Colour, Corrosion Science, 157, 337-346. doi:10.1016/
j.corsci.2019.05.025
80. Cramer, S.D. & Covino, B.S. Corrosion: Materials. ASM Handbook, Volume 13B, ASM International. Materials Park, Ohio 44073-0002 USA, 2005, p125.
81. Hultquist, G., Chuah, G.K. & Tan, K.L. (1989). Comments on hydrogen evolution from the corrosion of pure copper, Corrosion Science, 29(11-12), 1371-1377.
doi:10.1016/ 0010-938x(89)90125-x
82. Szakálos, P., Hultquist, G. & Wikmark, G. (2007). Corrosion of Copper by Water, Electrochemical and Solid-State Letters, 10(11), C63-C67. doi: 10.1149/
1.2772085
83. Hultquist, G., Szakálos, P., Graham, M.J., Belonoshko, A.B., Sproule, G.I., Gråsjö, L. & Rosengren, A. (2009). Water Corrodes Copper, Springer, Catalysis Letters, 132(3-4), 311–316. doi:10.1007/s10562-009-0113-x
84. Hultquist, G., Graham, M.J., Szakalos, P., Sproule, G.I., Rosengren, A. & Gråsjö, L. (2011). Hydrogen gas production during corrosion of copper by water. Corrosion Science, 53(1), 2011, pp 310–319. doi:10.1016/j.corsci.2010.09.037
85. Hultquist, G. (2015). Why copper may be able to corrode in pure water, Corrosion Science, 93, 2015, 327–329. doi:10.1016/j.corsci.2015.01.002
86. Simpson, J.P. & Schenk, R. (1987). Hydrogen evolution from corrosion of pure copper, Corrosion Science, 27(12), 1365–1370. doi:10.1016/0010-938x(87)90131- 4
87. Hedin, A., Johansson, A.J., Lilja, C., Boman, M., Berastegui, P., Berger, R. &
Ottosson, M. (2018). Corrosion of copper in pure O 2 -free water? Corrosion Science, 137, 1–12. doi:10.1016/j.corsci.2018.02.008
88. Li, H., Shi, A., Li, M. & Zhang, X. (2013). Effect of pH, Temperature, Dissolved Oxygen, and Flow Rate of Overlying Water on Heavy Metals Release from Storm Sewer Sediments, Hindawi Publishing Corporation, Journal of Chemistry, Article ID 434012. doi.org/10.1155/2013/434012