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Lead patination in the atmosphere of Athens, Greece
Nuclear Instruments and Methods in Physics Research B 269 (2011) 3074–3076
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Lead patination in the atmosphere of Athens, Greece A. Godelitsas a,⇑, N. Stamatelos-Samios a, M. Kokkoris b, E. Chatzitheodoridis c a
University of Athens, 15784 Zographou, Athens, Greece School of Applied Mathematics & Physics, National Technical University of Athens, Greece c School of Mining & Metallurgical Engineering, National Technical University of Athens, Greece b
a r t i c l e
i n f o
Article history: Available online 22 April 2011 Keywords: Lead Atmosphere Corrosion Patination Nuclear reaction analysis Raman spectroscopy
a b s t r a c t Pure metallic Pb foils were exposed to the atmosphere of Athens for different periods of time (up to 150 non-rainy days) in the summer of 2005. The interacted Pb surfaces were probed using the 12C(d,p)13C reaction (Ed: 1100 keV) at the Tandem accelerator of the NCSR ‘‘DEMOKRITOS’’. Laser-lRaman and SEM–EDS were also complementary applied. Using the above methodology we recorded surface carbon profiles and concentrations as a function of the exposure time, corresponding to the evolution of the carbonate layer formed onto Pb foils due to the interaction with atmospheric H2O and CO2. The C-containing surface layer was found to be stabilized after 120 days. Further investigation by means of laser-lRaman and SEM–EDS indicated that the patina initially consists of Pb-hydroxycarbonates (hydrocerussite) overgrowing Pb-oxides, whereas Pb-sulfates (anglesite) and possibly basic Pb-sulfates are formed at the end of the patination process. The crystal growth of Pb-sulfates, or most likely the transformation of hydroxycarbonates to sulfates, is attributed to the pollution of Athens atmosphere by SO2. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
The phenomenon of metallic lead corrosion under atmospheric conditions (also mentioned as atmospheric ‘‘patination’’— o9 qumxrg in Greek—of Pb) was initially described by Graedel [1] who reported the surface formation of Pb-sulfates (anglesite) and Pb-carbonates (cerussite). In more detailed studies Black et al. [2] and Black and Allen [3,4] referred to the formation of Pb-oxides followed by prompt overgrowth of Pb-hydroxycarbonates or basic Pb carbonates (hydrocerussite) and, finally, of Pb-sulfates due to SO2 pollution in urban environment. The coverage of metallic Pb by rather stable carbonate and/or sulfate layers (the so-called ‘‘patina’’) is also of great interest for the archaeology and the conservation science [5–7]. The present work demonstrates the first experimental results concerning the study of atmospheric lead patination in the Athens (Greece) area hosting significant monuments of the human civilization and populated, nowadays, by ca. 4 million people (alpha-world city). In order to investigate the carbonate layers initially formed on the Pb surface, the 12C(d,p)13C nuclear reaction [8] was applied also for the first time in the literature for such purpose.
The surfaces of pure metallic lead foil samples exposed to the atmosphere of Athens, Greece for different periods of time (up to 150 non-rainy days, from May 2005 to October 2005) were investigated using the 12C(d,p0)13C nuclear reaction (Ed = 1100 keV, detector angle: 165°, as shown in. Fig. 1) at the 5.5 MV HVEE Tandem van de Graaff accelerator of the Nuclear Physics Institute of National Centre of Scientific Research (NCSR) ‘‘DEMOKRITOS’’ (Athens, Greece). Surface-deposited SiC was used as reference material whereas the spectra were simulated using the differential cross section data from [8] and the SIMNRA 6.04 software package [9]. Laser-lRaman spectra were obtained using a Renishaw Ramascope RM 1000 instrument with a HeNe laser (633 nm). Pure Pbcarbonate, -hydroxycarbonate and -sulfate minerals (cerussite, hydrocerussite and anglesite) were used as reference materials. The SEM–EDS investigations were carried out using a JEOL JSM5600 system. For comparison reasons, a relevant laser-lRaman and SEM–EDS study was also performed using Pb foil samples exposed for 5 months in the atmosphere of Ioannina city located in N.W. Greece. 3. Results and discussion
⇑ Corresponding author. Tel.: +30 2107274689. E-mail address: [email protected] (A. Godelitsas). 0168-583X/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2011.04.062
The NRA investigation, using the 12C(d,p0)13C reaction, showed the existence of stable C-containing layers (including also O) on the metallic Pb surfaces exposed to the atmosphere of Athens (Fig. 2). The increase of surface carbon concentration, derived from
3075
A. Godelitsas et al. / Nuclear Instruments and Methods in Physics Research B 269 (2011) 3074–3076
SURFACE CARBON
Fig. 1. Schematic presentation of the spectroscopic measurements.
CARBON (atoms/cm2)
2.0E+18 1.5E+18 1.0E+18 5.0E+17 0.0E+00 0
Energy [keV] 150
2750
2800
2850
2900
2950
3000
140 130
12C(d,p
3050
3100
3150
Θ=165o
o)
120 110 100
AKA 15
EXPOS
30
URE T IM
PAN
45
E (day
120
s)
150
Fig. 3. Surface carbon concentrations, based on NRA spectra, as a function of exposure time, for metallic Pb samples exposed in the center of Athens (Academy of Athens, Akadimia/AKA) and in Athens University campus (Panepistimio/PAN) at the foot of Hymettos mountain (all experimental spectra taken at Ed, lab = 1100 keV, h = 165°).
Counts
90 80 70 60 50 40 30 20 10 0 450 455 460 465 470 475 480 485 490 495 500 505 510 515 520
Channel Fig. 2. Representative NRA spectrum from the surface of metallic Pb exposed in the atmosphere of the center of Athens (Academy of Athens, Akadimia/AKA) for 1 month (Ed, lab = 1100 keV, detector angle h = 165°).
the carbon surface profiles, as a function of the exposure time, revealed the evolution of the entire carbonate layer (Fig. 3). Thus, it can be demonstrated that this layer was stabilized after 120 days. The subsequent SEM–EDS investigation of the Pb foil samples indicated that, after the above period of time, the corroded surface was extensively covered by Pb- and occasionally S-containing platy microcrystals and aggregates (Fig. 4). The laser-lRaman spectra indicated that, during the first stages of the interaction of metallic Pb with Athens atmosphere, the patina (see also upper left image of Fig. 4) consists of Pb-oxides and Pbhydroxycarbonates. The oxides, corresponding most probably to massicot-type compounds (a-PbO), give a peak at about 287 cm1 whereas the hydroxycarbonates can be attributed to hydrocerussite (Pb3(CO3)2(OH)2) giving a characteristic peak at 1050 cm1 [3]. It should be noted that Pb-carbonates, represented by cerussite (PbCO3), exhibit a strong Raman peak at 1054 cm1, and thus such compounds are not formed on the surface of Pb. It
Fig. 4. SEM images from the patina formed on the surface of metallic Pb exposed in the atmosphere of Athens (Academy of Athens, center) in a period from 1 week up to 5 months.
3076
A. Godelitsas et al. / Nuclear Instruments and Methods in Physics Research B 269 (2011) 3074–3076
Wavelength (nm) 10000
15000
25000
45000
1.1
Intensity
0.7
0.3
0 1000
600
200 -1
Wavenumbers (cm ) Fig. 5. Successive laser-lRaman spectra from the patina formed on the surface of metallic Pb exposed in the atmosphere of Athens (University campus area) in a period from 1 week up to 5 months.
Wavelength (nm) 10000
1.1
15000
25000 45000
Intensity
0.9
0.7
0.5
(PbSO4) giving a Raman peak at 977 cm1 (Fig. 5). Except Pb-sulfates, basic Pb-sulfates may also be present into the patina, taking into account a small Raman peak at 965 cm1. Obviously, the growth of Pb-sulfates reflects intense reaction with SO2 which is a major pollutant of Athens atmosphere [10]. During the experiment (May 2005 to October 2005) the concentration of SO2 in Athens atmosphere was rather elevated (average ca. 40,000 lg/m2) with a maximum of 85,400 lg/m2 on 6th of July 2005 (Zerefos 2005, personal communication). The overall atmospheric Pb patination process, i.e., Pb ? PbO ? Pb3(CO3)2(OH)2 ? PbSO4, described in the present work for Athens megacity, is analogous to that reported by Black and Allen [3] for major UK cities (Bristol and Birmingham). However, it should be emphasized that, all previous studies had not included ‘‘kinetic’’ results associated to the evolution of the carbonate (in fact hydroxycarbonate) layer acting as proper substrate for the reaction with SO2 molecules and the subsequent growth of Pb-sulfates. On the other hand, it is stated that gaseous pollutants, and particularly SO2, can dramatically influence the metal corrosion and the chemical composition of the patina covering the interacted surfaces. Besides it is clear that this phenomenon, causing formation of Pb secondary phases with different physicochemical properties and solubilities, also affects the dispersion of the hazardous heavy metal. A similar experiment performed in the atmosphere of Ioannina city (N.W. Greece), having no severe SO2 pollution, revealed only Pb-hydroxycarbonates and not any Pb-sulfates after 5 months exposure (Fig. 6). Since anglesite is significantly more soluble than hydrocerussite (logK ANGLESITE ¼ 7:9 and logK HYDROCERUSSITE ¼ 43:7 respectively) sp sp can be concluded that Pb patina in Athens, due to atmospheric pollution, is much more susceptible to further dissolution processes which can lead to extra migration of Pb, from the initial metal to the urban environment. Acknowledgements
0.3
0.1 1800
1400
1000
600
200
Many thanks are due to Dr. S. Harissopulos and Dr. A. Lagoyannis (NCSR ‘‘DEMOKRITOS’’) for their collaboration during the measurements as well as to Prof. Zerefos (Univ. Athens) for the information about the SO2 concentration in Athens atmosphere during the experiment.
-1
Wavenumbers (cm ) Fig. 6. SEM image and successive laser-lRaman spectra from the patina formed on the surface of metallic Pb exposed in the atmosphere of Ioannina city (N.W. Greece) for 5 months.
is evident that primary reaction with atmospheric O2 leads to oxidation and formation of oxides which are the basis for the development of hydroxycarbonates due to reaction with CO2 and moisture (H2O) present in the apparently dry summer atmosphere. The Ccontaining surface layers detected by NRA are due to the above mentioned Pb-hydroxycarbonate phase. The prolonged interaction leads to partial transformation of hydrocerussite to anglesite
References [1] [2] [3] [4] [5] [6] [7]
T.E. Graedel, J. Electrochem. Soc. 141 (4) (1994) 922. L. Black, G.C. Allen, P.C. Frost, Appl. Spectrosc. 49 (9) (1995) 1299. L. Black, G.C. Allen, Br. Corros. J. 34 (3) (1999) 192. L. Black, G.C. Allen, Br. Corros. J. 35 (1) (2000) 39. J. Tétreault, J. Sirois, E. Stamatopoulou, Stud. Conserv. 43 (1998) 17. H. Kawinski, H. Kutzke, Restauro 3 (2000) 193–199. M. García-Heras, M.A. Villegas, J.M.A. Caen, C. Domingo, J.V. García-Ramos, Microchem. J. 83 (2006) 81. [8] E. Kashy, R.R. Perry, J.R. Risser, Phys. Rev. 117 (5) (1960) 1289. [9] M. Mayer, Computer code SIMNRA, Version 6.04, Max-Planck-Institut für plasmphysik, Garching, February 2008. [10] D.P. Lalas, V.R. Veirs, G. Karras, G. Kallos, Atmos. Environ. 16 (1982) 531.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Lead patination in the atmosphere of Athens, Greece A. Godelitsas a,⇑, N. Stamatelos-Samios a, M. Kokkoris b, E. Chatzitheodoridis c a
University of Athens, 15784 Zographou, Athens, Greece School of Applied Mathematics & Physics, National Technical University of Athens, Greece c School of Mining & Metallurgical Engineering, National Technical University of Athens, Greece b
a r t i c l e
i n f o
Article history: Available online 22 April 2011 Keywords: Lead Atmosphere Corrosion Patination Nuclear reaction analysis Raman spectroscopy
a b s t r a c t Pure metallic Pb foils were exposed to the atmosphere of Athens for different periods of time (up to 150 non-rainy days) in the summer of 2005. The interacted Pb surfaces were probed using the 12C(d,p)13C reaction (Ed: 1100 keV) at the Tandem accelerator of the NCSR ‘‘DEMOKRITOS’’. Laser-lRaman and SEM–EDS were also complementary applied. Using the above methodology we recorded surface carbon profiles and concentrations as a function of the exposure time, corresponding to the evolution of the carbonate layer formed onto Pb foils due to the interaction with atmospheric H2O and CO2. The C-containing surface layer was found to be stabilized after 120 days. Further investigation by means of laser-lRaman and SEM–EDS indicated that the patina initially consists of Pb-hydroxycarbonates (hydrocerussite) overgrowing Pb-oxides, whereas Pb-sulfates (anglesite) and possibly basic Pb-sulfates are formed at the end of the patination process. The crystal growth of Pb-sulfates, or most likely the transformation of hydroxycarbonates to sulfates, is attributed to the pollution of Athens atmosphere by SO2. Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
The phenomenon of metallic lead corrosion under atmospheric conditions (also mentioned as atmospheric ‘‘patination’’— o9 qumxrg in Greek—of Pb) was initially described by Graedel [1] who reported the surface formation of Pb-sulfates (anglesite) and Pb-carbonates (cerussite). In more detailed studies Black et al. [2] and Black and Allen [3,4] referred to the formation of Pb-oxides followed by prompt overgrowth of Pb-hydroxycarbonates or basic Pb carbonates (hydrocerussite) and, finally, of Pb-sulfates due to SO2 pollution in urban environment. The coverage of metallic Pb by rather stable carbonate and/or sulfate layers (the so-called ‘‘patina’’) is also of great interest for the archaeology and the conservation science [5–7]. The present work demonstrates the first experimental results concerning the study of atmospheric lead patination in the Athens (Greece) area hosting significant monuments of the human civilization and populated, nowadays, by ca. 4 million people (alpha-world city). In order to investigate the carbonate layers initially formed on the Pb surface, the 12C(d,p)13C nuclear reaction [8] was applied also for the first time in the literature for such purpose.
The surfaces of pure metallic lead foil samples exposed to the atmosphere of Athens, Greece for different periods of time (up to 150 non-rainy days, from May 2005 to October 2005) were investigated using the 12C(d,p0)13C nuclear reaction (Ed = 1100 keV, detector angle: 165°, as shown in. Fig. 1) at the 5.5 MV HVEE Tandem van de Graaff accelerator of the Nuclear Physics Institute of National Centre of Scientific Research (NCSR) ‘‘DEMOKRITOS’’ (Athens, Greece). Surface-deposited SiC was used as reference material whereas the spectra were simulated using the differential cross section data from [8] and the SIMNRA 6.04 software package [9]. Laser-lRaman spectra were obtained using a Renishaw Ramascope RM 1000 instrument with a HeNe laser (633 nm). Pure Pbcarbonate, -hydroxycarbonate and -sulfate minerals (cerussite, hydrocerussite and anglesite) were used as reference materials. The SEM–EDS investigations were carried out using a JEOL JSM5600 system. For comparison reasons, a relevant laser-lRaman and SEM–EDS study was also performed using Pb foil samples exposed for 5 months in the atmosphere of Ioannina city located in N.W. Greece. 3. Results and discussion
⇑ Corresponding author. Tel.: +30 2107274689. E-mail address: [email protected] (A. Godelitsas). 0168-583X/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2011.04.062
The NRA investigation, using the 12C(d,p0)13C reaction, showed the existence of stable C-containing layers (including also O) on the metallic Pb surfaces exposed to the atmosphere of Athens (Fig. 2). The increase of surface carbon concentration, derived from
3075
A. Godelitsas et al. / Nuclear Instruments and Methods in Physics Research B 269 (2011) 3074–3076
SURFACE CARBON
Fig. 1. Schematic presentation of the spectroscopic measurements.
CARBON (atoms/cm2)
2.0E+18 1.5E+18 1.0E+18 5.0E+17 0.0E+00 0
Energy [keV] 150
2750
2800
2850
2900
2950
3000
140 130
12C(d,p
3050
3100
3150
Θ=165o
o)
120 110 100
AKA 15
EXPOS
30
URE T IM
PAN
45
E (day
120
s)
150
Fig. 3. Surface carbon concentrations, based on NRA spectra, as a function of exposure time, for metallic Pb samples exposed in the center of Athens (Academy of Athens, Akadimia/AKA) and in Athens University campus (Panepistimio/PAN) at the foot of Hymettos mountain (all experimental spectra taken at Ed, lab = 1100 keV, h = 165°).
Counts
90 80 70 60 50 40 30 20 10 0 450 455 460 465 470 475 480 485 490 495 500 505 510 515 520
Channel Fig. 2. Representative NRA spectrum from the surface of metallic Pb exposed in the atmosphere of the center of Athens (Academy of Athens, Akadimia/AKA) for 1 month (Ed, lab = 1100 keV, detector angle h = 165°).
the carbon surface profiles, as a function of the exposure time, revealed the evolution of the entire carbonate layer (Fig. 3). Thus, it can be demonstrated that this layer was stabilized after 120 days. The subsequent SEM–EDS investigation of the Pb foil samples indicated that, after the above period of time, the corroded surface was extensively covered by Pb- and occasionally S-containing platy microcrystals and aggregates (Fig. 4). The laser-lRaman spectra indicated that, during the first stages of the interaction of metallic Pb with Athens atmosphere, the patina (see also upper left image of Fig. 4) consists of Pb-oxides and Pbhydroxycarbonates. The oxides, corresponding most probably to massicot-type compounds (a-PbO), give a peak at about 287 cm1 whereas the hydroxycarbonates can be attributed to hydrocerussite (Pb3(CO3)2(OH)2) giving a characteristic peak at 1050 cm1 [3]. It should be noted that Pb-carbonates, represented by cerussite (PbCO3), exhibit a strong Raman peak at 1054 cm1, and thus such compounds are not formed on the surface of Pb. It
Fig. 4. SEM images from the patina formed on the surface of metallic Pb exposed in the atmosphere of Athens (Academy of Athens, center) in a period from 1 week up to 5 months.
3076
A. Godelitsas et al. / Nuclear Instruments and Methods in Physics Research B 269 (2011) 3074–3076
Wavelength (nm) 10000
15000
25000
45000
1.1
Intensity
0.7
0.3
0 1000
600
200 -1
Wavenumbers (cm ) Fig. 5. Successive laser-lRaman spectra from the patina formed on the surface of metallic Pb exposed in the atmosphere of Athens (University campus area) in a period from 1 week up to 5 months.
Wavelength (nm) 10000
1.1
15000
25000 45000
Intensity
0.9
0.7
0.5
(PbSO4) giving a Raman peak at 977 cm1 (Fig. 5). Except Pb-sulfates, basic Pb-sulfates may also be present into the patina, taking into account a small Raman peak at 965 cm1. Obviously, the growth of Pb-sulfates reflects intense reaction with SO2 which is a major pollutant of Athens atmosphere [10]. During the experiment (May 2005 to October 2005) the concentration of SO2 in Athens atmosphere was rather elevated (average ca. 40,000 lg/m2) with a maximum of 85,400 lg/m2 on 6th of July 2005 (Zerefos 2005, personal communication). The overall atmospheric Pb patination process, i.e., Pb ? PbO ? Pb3(CO3)2(OH)2 ? PbSO4, described in the present work for Athens megacity, is analogous to that reported by Black and Allen [3] for major UK cities (Bristol and Birmingham). However, it should be emphasized that, all previous studies had not included ‘‘kinetic’’ results associated to the evolution of the carbonate (in fact hydroxycarbonate) layer acting as proper substrate for the reaction with SO2 molecules and the subsequent growth of Pb-sulfates. On the other hand, it is stated that gaseous pollutants, and particularly SO2, can dramatically influence the metal corrosion and the chemical composition of the patina covering the interacted surfaces. Besides it is clear that this phenomenon, causing formation of Pb secondary phases with different physicochemical properties and solubilities, also affects the dispersion of the hazardous heavy metal. A similar experiment performed in the atmosphere of Ioannina city (N.W. Greece), having no severe SO2 pollution, revealed only Pb-hydroxycarbonates and not any Pb-sulfates after 5 months exposure (Fig. 6). Since anglesite is significantly more soluble than hydrocerussite (logK ANGLESITE ¼ 7:9 and logK HYDROCERUSSITE ¼ 43:7 respectively) sp sp can be concluded that Pb patina in Athens, due to atmospheric pollution, is much more susceptible to further dissolution processes which can lead to extra migration of Pb, from the initial metal to the urban environment. Acknowledgements
0.3
0.1 1800
1400
1000
600
200
Many thanks are due to Dr. S. Harissopulos and Dr. A. Lagoyannis (NCSR ‘‘DEMOKRITOS’’) for their collaboration during the measurements as well as to Prof. Zerefos (Univ. Athens) for the information about the SO2 concentration in Athens atmosphere during the experiment.
-1
Wavenumbers (cm ) Fig. 6. SEM image and successive laser-lRaman spectra from the patina formed on the surface of metallic Pb exposed in the atmosphere of Ioannina city (N.W. Greece) for 5 months.
is evident that primary reaction with atmospheric O2 leads to oxidation and formation of oxides which are the basis for the development of hydroxycarbonates due to reaction with CO2 and moisture (H2O) present in the apparently dry summer atmosphere. The Ccontaining surface layers detected by NRA are due to the above mentioned Pb-hydroxycarbonate phase. The prolonged interaction leads to partial transformation of hydrocerussite to anglesite
References [1] [2] [3] [4] [5] [6] [7]
T.E. Graedel, J. Electrochem. Soc. 141 (4) (1994) 922. L. Black, G.C. Allen, P.C. Frost, Appl. Spectrosc. 49 (9) (1995) 1299. L. Black, G.C. Allen, Br. Corros. J. 34 (3) (1999) 192. L. Black, G.C. Allen, Br. Corros. J. 35 (1) (2000) 39. J. Tétreault, J. Sirois, E. Stamatopoulou, Stud. Conserv. 43 (1998) 17. H. Kawinski, H. Kutzke, Restauro 3 (2000) 193–199. M. García-Heras, M.A. Villegas, J.M.A. Caen, C. Domingo, J.V. García-Ramos, Microchem. J. 83 (2006) 81. [8] E. Kashy, R.R. Perry, J.R. Risser, Phys. Rev. 117 (5) (1960) 1289. [9] M. Mayer, Computer code SIMNRA, Version 6.04, Max-Planck-Institut für plasmphysik, Garching, February 2008. [10] D.P. Lalas, V.R. Veirs, G. Karras, G. Kallos, Atmos. Environ. 16 (1982) 531.