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Optimization and structure-property correlation of black chrome solar selective coating on Copper and Nickel plated copper substrates
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 5 (2018) 23423–23427
www.materialstoday.com/proceedings
ICAER-2015
Optimization and structure-property correlation of black chrome solar selective coating on Copper and Nickel plated copper substrates Rajesh Kumara, Ajoy K. Sahaa, Belal Usmania and Ambesh Dixit a, * a
Department of Physics & Center for Solar Energy, Indian Institute of Technology Jodhpur, Rajasthan, India-342011
Abstract We used two electrode electrodeposition techniques to optimize the black chrome solar selective coatings on copper and nickel plated copper substrates. The process was optimized and optimal absorptivity ~ 0.92 and emissivity ~ 0.4 was achieved for black chrome coatings on bare copper substrates. The addition of nickel metal layer prior to black chrome on copper substrate resulted into lower emissivity ~ 0.14 and enhanced absorptivity ~0.92 or more. The electrochemical bath and process conditions were optimized for the best solar thermal response. Also, the effect of post deposition treatment of deposited samples, such as washing and drying are investigated to understand their impact on solar thermal performance in conjunction with their structure-property relations.
© 2018 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the Conference Committee Members of International Conference on Advances in Energy Research 2015 (ICAER-2015). Keywords: Solar selective coating; black chrome; electroplating; emittance; absorbance
1. Introduction Solar selective coatings (SSCs) with high spectral absorbance and low thermal emittance are required to harness solar energy for possible solar thermal applications. Black chrome (BC) has shown promise because of its low cost
* Corresponding author. Tel.: +91-2912449045 E-mail : [email protected] 2214-7853 © 2018 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the Conference Committee Members of International Conference on Advances in Energy Research 2015 (ICAER-2015).
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Kumar et al. / Materials Today: Proceedings 5 (2018) 23423–23427
and the relatively better optical response in the medium temperature range and is one of the oldest SSC material [1,2]. Numerous physical and chemical processes are being used to deposit black chrome, yet there are continuous efforts to design and develop a low cost deposition process for black chrome solar selective coatings. Electrochemical deposition is one such solution based low cost process, which can be scaled up for large area deposition easily [2,3]. This process has been explored widely for deposition of black chrome solar selective coatings, yet there is very little literature, which correlates structure-property-process conditions for optimal solar thermal response [4,5,6,7,8]. We have investigated the optimized electrodeposition conditions for optimal absorptivity and emissivity on copper, Cu, and nickel, Ni, plated copper substrates. The deposited BC/Cu and BC/Ni/Cu solar selective structures are investigated using X-ray diffraction (XRD), scanning electron microscopic (SEM) and energy dispersive X-ray (EDX) measurements. The optical properties were measured using UV-Vis and Fourier Transform Infrared (FTIR) spectrophotometric measurements. 2. Experimental details Copper substrates with 3 cm x 1 cm dimensions were used for deposition of black chrome solar selective coatings. These Cu substrates were subjected to grinding and polishing, followed by heating in trichloroethylene and acetone at 80 °C for 3-5 minutes for cleaning. The cleaned substrates were then coated electrochemically with nickel and black chrome baths for 30 and 60 seconds respectively. The electrochemical deposition experiments were optimized for surface currents (~ 0.17 A/cm2 for nickel and 0.7A/cm2 for black chrome thin films) and deposition times to ensure the homogeneous deposition with optimal solar thermal performance. BC/Cu and BC/Ni/Cu structures are intensively characterized to understand the development of black chrome phase and structural/microstructural properties. 3. Results and discussion
Fig. 1. XRD patters for Bare Cu, Ni/Cu and BC/Ni/Cu structures, respective planar orientations are marked for different observed metallic phases.
The representative XRD spectra for Ni/Cu and BC/Ni/Cu structures are shown in Fig. 1, together with Cu substrate. Cu substrate peaks are observed in both Ni/Cu and BC/Ni/Cu structures and for comparison, XRD pattern of Cu substrate is also plotted to distinguish the substrate from the fabricated thin film structures. The bare Cu
Kumar et al./ Materials Today: Proceedings 5 (2018) 23423–23427
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substrate exhibits (111) intense planar orientation with (200) and (220) planar orientations. The (111) and (200) Cu diffraction peaks are observed in all deposited SSC structures, whereas the intensity of (220) substrate peak decreased significantly in Ni/Cu and BC/Ni/Cu structures. Ni/Cu films clearly exhibit the onset of Ni diffraction peak with (111) and (200) planar orientations, Fig. 1 (middle panel), adopting from substrate planar orientation, as growth will favor along substrate orientation. BC/Ni/Cu structure XRD pattern, Fig. 1 (top panel), consists of (111) and (200) Cu substrate diffraction peaks and (111) and (200) Ni infrared reflector layer. The (111) and (200) Ni diffraction peaks overlap with (111) and (200) (Cr2Ni23)0.16 alloy phase, and thus difficult to distinguish the observed metallic phase in top black chrome layer. These measurements suggest the presence of large metallic content in the chromium oxide matrix, whose presence was not observed in XRD measurements. The absence of chromium oxide diffraction pattern may be due to its amorphous nature in the fabricated structure. This is possible because of the adopted synthesis process and conditions, especially room temperature electrochemical deposition, whereas crystallization of chromium oxide, usually takes place at relatively higher temperatures.
Fig. 2. SEM micrographs of (a) Bare Cu (b) Ni/Cu and (c) BC/Ni/Cu structures, with inset EDX spectrum and relative elemental atomic fractions.
The surface morphologies of the cleaned Cu substrates, Ni/Cu and BC/Ni/Cu fabricated structures were collected using scanning electron microscope and are summarized in Fig. 2. The grinding and polishing imprints on copper substrates, Fig. 2(a), are clearly visible, generated during cleaning process. These surface imprints are transferred into Ni films, as explained in Fig. 2(b), where Cu surface imprints can be seen clearly. The black chrome surface, coated on Ni plated Cu substrate, is shown in Fig. 2(c). The thickness of the top black chrome layer is ~ 1μm, which helped in minimizing the substrate surface imprints partially, important for reduction of emissivity for the fabricated structures. The atomic fraction of BC/Ni/Cu structure was estimated using EDX measurements and values are summarized in inset of Fig 2(c). These measurements suggest that films are rich in metal content. The deposited BC structures on Ni/Cu are homogeneous over the entire deposited surface. Optical reflectance measurements are carried out using UV-Vis and FTIR spectrophotometer measurements over the entire wavelength range 0.2 – 25 μm. The reflectance measurements, in 2.5 – 25 μm wavelength range, are plotted in Fig. 3 for Cu, Ni/Cu and BC/Ni/Cu structures and these data were used to calculate emissivity. The respective emissivity values are shown in Fig. 3. We found that Ni plated Cu substrates exhibit very low emissivity ~ 0.03, whereas black chrome structures on Ni plated Cu substrates show relatively low emissivity values ~ 0.14 with respect to that of pure Cu substrates ~ 0.4. The reduction in emissivity in BC/Ni/Cu structures with respect to BC/Cu structures is mainly due to the introduction of the Ni black infrared reflector, which helps in minimizing the interface defects and introducing the metallic content, especially metallic (Cr2Ni23)0.16 alloy content in black chrome thin films, as observed in XRD measurements. We observed that the surface of these black chrome samples, with optimized absorptivity ~ 0.92 and emissivity ~ 0.4 samples, are smutted with residues/leftovers and hampering the solar thermal performance. To rectify the surface residues, black chrome layers were synthesized with optimized current density for time and further subjected to
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washing immediately after electrochemical deposition of these black chrome layer. The washing was done in an ultrasonication bath for 30 seconds. These washed layers were dried and their optical response was collected using `reflectance measurements in the entire wavelength region to estimate their absorptivity and emissivity. These reflectance results for unwashed and washed BC/Ni/Cu structures are plotted in Fig. 4. A clear difference can be noticed for washed BC/Ni/Cu reflectance spectrum with respect to that of unwashed BC/Ni/Cu reflectance spectrum. These measurements are carried out on several unwashed and washed BC/Ni/Cu samples and results are nearly identical within experimental limits. The BC/Ni/Cu layers subjected to washing immediately after electrodeposition step, exhibit emissivity ≤ 0.14, as represented in Fig. 4 (top panel) as compared to unwashed film, where emissivity values are ~ 0.4. In addition the reflectance measurements in 0.3 – 0.9 m wavelength range, shown as an inset in Fig. 4 (bottom panel) is used to estimate the absorptivity in UV-Vis range and calculated values are ≥ 0.92 for washed samples. These observations suggest that washing, followed by drying, effect solar thermal properties drastically, especially emissivity.
Fig. 3. FTIR reflectance versus wavelength graphs for Cu, Ni/Cu and BC/Ni/Cu structures, deposited for different times.
1.0
0.8
(a)
=0.39 =0.14
0.4
JBC=0.7A/cm
2 2
JNi=0.17A/cm
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=0.14
(b)
12 11 10
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Fig. 4. FTIR reflectance versus wavelength for (a) unwashed and washed BC/Ni/Cu structures and for (b) optimized BC/Ni/Cu deposited structure.(Inset UV-Visreflectance, used for estimating absorptivity).
Kumar et al./ Materials Today: Proceedings 5 (2018) 23423–23427
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4. Conclusions We investigated the impact of pre and post synthesis process on solar thermal properties of electrochemically deposited black chrome SSCs on Cu and Ni plated Cu substrates. These results suggest the need of Ni metal reflector layer and its impact on solar thermal performance of black chrome solar selective structures. The synthesized BC/Ni/Cu structures exhibit absorptivity ~ 0.92 and emissivity ~ 0.14. These findings suggest that washing, followed by drying, is a crucial step to in developing black chrome solar selective coatings with enhanced solar thermal response. Acknowledgement The authors gratefully acknowledge the financial support from the Ministry of New and Renewable Energy(MNRE) through grant # 15/40/2010-11/ST. References [1] C.E. Kennedy, Review of Mid-to-High Temperature Solar Selective Absorber Materials, (2002) NREL/TP-520-31267 [2] F. Cao, Mc. Enaney, G. Chen, Z. Ren, Energ. Environ. Sci., 7 (2014) 1615. [3] M. Daryabegya, A.R. Mahmoodpoor. Isesaco Sci. Techonol. Vision 2 (2006) 35–39. [4] G. E. McDonald, Refinement in Black Chrome for use as a Solar Selective Coating. NASA TM X-3136,1974 [5] M. Aguilar, E. Barrera, M. Palomar-Pardave, L. Huerta, S. Muhl, J. Non-Crys. Sol. 329 (2003) 31–38. [6] M. Joly, Y. Antonetti, M. Python, M. Gonzalez, T. Gascou, J. Scartezzini, A. Schuler, Sol. Energ. 94 (2013) 233–239. [7] S. Khamlich, Physica B (2011),doi:10.1016/j.physb.2011.09.073 [8] K. D. Lee, J. Kor. Phys. Soc., 51(2007) 135–144.
ScienceDirect Materials Today: Proceedings 5 (2018) 23423–23427
www.materialstoday.com/proceedings
ICAER-2015
Optimization and structure-property correlation of black chrome solar selective coating on Copper and Nickel plated copper substrates Rajesh Kumara, Ajoy K. Sahaa, Belal Usmania and Ambesh Dixit a, * a
Department of Physics & Center for Solar Energy, Indian Institute of Technology Jodhpur, Rajasthan, India-342011
Abstract We used two electrode electrodeposition techniques to optimize the black chrome solar selective coatings on copper and nickel plated copper substrates. The process was optimized and optimal absorptivity ~ 0.92 and emissivity ~ 0.4 was achieved for black chrome coatings on bare copper substrates. The addition of nickel metal layer prior to black chrome on copper substrate resulted into lower emissivity ~ 0.14 and enhanced absorptivity ~0.92 or more. The electrochemical bath and process conditions were optimized for the best solar thermal response. Also, the effect of post deposition treatment of deposited samples, such as washing and drying are investigated to understand their impact on solar thermal performance in conjunction with their structure-property relations.
© 2018 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the Conference Committee Members of International Conference on Advances in Energy Research 2015 (ICAER-2015). Keywords: Solar selective coating; black chrome; electroplating; emittance; absorbance
1. Introduction Solar selective coatings (SSCs) with high spectral absorbance and low thermal emittance are required to harness solar energy for possible solar thermal applications. Black chrome (BC) has shown promise because of its low cost
* Corresponding author. Tel.: +91-2912449045 E-mail : [email protected] 2214-7853 © 2018 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the Conference Committee Members of International Conference on Advances in Energy Research 2015 (ICAER-2015).
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Kumar et al. / Materials Today: Proceedings 5 (2018) 23423–23427
and the relatively better optical response in the medium temperature range and is one of the oldest SSC material [1,2]. Numerous physical and chemical processes are being used to deposit black chrome, yet there are continuous efforts to design and develop a low cost deposition process for black chrome solar selective coatings. Electrochemical deposition is one such solution based low cost process, which can be scaled up for large area deposition easily [2,3]. This process has been explored widely for deposition of black chrome solar selective coatings, yet there is very little literature, which correlates structure-property-process conditions for optimal solar thermal response [4,5,6,7,8]. We have investigated the optimized electrodeposition conditions for optimal absorptivity and emissivity on copper, Cu, and nickel, Ni, plated copper substrates. The deposited BC/Cu and BC/Ni/Cu solar selective structures are investigated using X-ray diffraction (XRD), scanning electron microscopic (SEM) and energy dispersive X-ray (EDX) measurements. The optical properties were measured using UV-Vis and Fourier Transform Infrared (FTIR) spectrophotometric measurements. 2. Experimental details Copper substrates with 3 cm x 1 cm dimensions were used for deposition of black chrome solar selective coatings. These Cu substrates were subjected to grinding and polishing, followed by heating in trichloroethylene and acetone at 80 °C for 3-5 minutes for cleaning. The cleaned substrates were then coated electrochemically with nickel and black chrome baths for 30 and 60 seconds respectively. The electrochemical deposition experiments were optimized for surface currents (~ 0.17 A/cm2 for nickel and 0.7A/cm2 for black chrome thin films) and deposition times to ensure the homogeneous deposition with optimal solar thermal performance. BC/Cu and BC/Ni/Cu structures are intensively characterized to understand the development of black chrome phase and structural/microstructural properties. 3. Results and discussion
Fig. 1. XRD patters for Bare Cu, Ni/Cu and BC/Ni/Cu structures, respective planar orientations are marked for different observed metallic phases.
The representative XRD spectra for Ni/Cu and BC/Ni/Cu structures are shown in Fig. 1, together with Cu substrate. Cu substrate peaks are observed in both Ni/Cu and BC/Ni/Cu structures and for comparison, XRD pattern of Cu substrate is also plotted to distinguish the substrate from the fabricated thin film structures. The bare Cu
Kumar et al./ Materials Today: Proceedings 5 (2018) 23423–23427
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substrate exhibits (111) intense planar orientation with (200) and (220) planar orientations. The (111) and (200) Cu diffraction peaks are observed in all deposited SSC structures, whereas the intensity of (220) substrate peak decreased significantly in Ni/Cu and BC/Ni/Cu structures. Ni/Cu films clearly exhibit the onset of Ni diffraction peak with (111) and (200) planar orientations, Fig. 1 (middle panel), adopting from substrate planar orientation, as growth will favor along substrate orientation. BC/Ni/Cu structure XRD pattern, Fig. 1 (top panel), consists of (111) and (200) Cu substrate diffraction peaks and (111) and (200) Ni infrared reflector layer. The (111) and (200) Ni diffraction peaks overlap with (111) and (200) (Cr2Ni23)0.16 alloy phase, and thus difficult to distinguish the observed metallic phase in top black chrome layer. These measurements suggest the presence of large metallic content in the chromium oxide matrix, whose presence was not observed in XRD measurements. The absence of chromium oxide diffraction pattern may be due to its amorphous nature in the fabricated structure. This is possible because of the adopted synthesis process and conditions, especially room temperature electrochemical deposition, whereas crystallization of chromium oxide, usually takes place at relatively higher temperatures.
Fig. 2. SEM micrographs of (a) Bare Cu (b) Ni/Cu and (c) BC/Ni/Cu structures, with inset EDX spectrum and relative elemental atomic fractions.
The surface morphologies of the cleaned Cu substrates, Ni/Cu and BC/Ni/Cu fabricated structures were collected using scanning electron microscope and are summarized in Fig. 2. The grinding and polishing imprints on copper substrates, Fig. 2(a), are clearly visible, generated during cleaning process. These surface imprints are transferred into Ni films, as explained in Fig. 2(b), where Cu surface imprints can be seen clearly. The black chrome surface, coated on Ni plated Cu substrate, is shown in Fig. 2(c). The thickness of the top black chrome layer is ~ 1μm, which helped in minimizing the substrate surface imprints partially, important for reduction of emissivity for the fabricated structures. The atomic fraction of BC/Ni/Cu structure was estimated using EDX measurements and values are summarized in inset of Fig 2(c). These measurements suggest that films are rich in metal content. The deposited BC structures on Ni/Cu are homogeneous over the entire deposited surface. Optical reflectance measurements are carried out using UV-Vis and FTIR spectrophotometer measurements over the entire wavelength range 0.2 – 25 μm. The reflectance measurements, in 2.5 – 25 μm wavelength range, are plotted in Fig. 3 for Cu, Ni/Cu and BC/Ni/Cu structures and these data were used to calculate emissivity. The respective emissivity values are shown in Fig. 3. We found that Ni plated Cu substrates exhibit very low emissivity ~ 0.03, whereas black chrome structures on Ni plated Cu substrates show relatively low emissivity values ~ 0.14 with respect to that of pure Cu substrates ~ 0.4. The reduction in emissivity in BC/Ni/Cu structures with respect to BC/Cu structures is mainly due to the introduction of the Ni black infrared reflector, which helps in minimizing the interface defects and introducing the metallic content, especially metallic (Cr2Ni23)0.16 alloy content in black chrome thin films, as observed in XRD measurements. We observed that the surface of these black chrome samples, with optimized absorptivity ~ 0.92 and emissivity ~ 0.4 samples, are smutted with residues/leftovers and hampering the solar thermal performance. To rectify the surface residues, black chrome layers were synthesized with optimized current density for time and further subjected to
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Kumar et al. / Materials Today: Proceedings 5 (2018) 23423–23427
washing immediately after electrochemical deposition of these black chrome layer. The washing was done in an ultrasonication bath for 30 seconds. These washed layers were dried and their optical response was collected using `reflectance measurements in the entire wavelength region to estimate their absorptivity and emissivity. These reflectance results for unwashed and washed BC/Ni/Cu structures are plotted in Fig. 4. A clear difference can be noticed for washed BC/Ni/Cu reflectance spectrum with respect to that of unwashed BC/Ni/Cu reflectance spectrum. These measurements are carried out on several unwashed and washed BC/Ni/Cu samples and results are nearly identical within experimental limits. The BC/Ni/Cu layers subjected to washing immediately after electrodeposition step, exhibit emissivity ≤ 0.14, as represented in Fig. 4 (top panel) as compared to unwashed film, where emissivity values are ~ 0.4. In addition the reflectance measurements in 0.3 – 0.9 m wavelength range, shown as an inset in Fig. 4 (bottom panel) is used to estimate the absorptivity in UV-Vis range and calculated values are ≥ 0.92 for washed samples. These observations suggest that washing, followed by drying, effect solar thermal properties drastically, especially emissivity.
Fig. 3. FTIR reflectance versus wavelength graphs for Cu, Ni/Cu and BC/Ni/Cu structures, deposited for different times.
1.0
0.8
(a)
=0.39 =0.14
0.4
JBC=0.7A/cm
2 2
JNi=0.17A/cm
0.2
0.6
=0.14
(b)
12 11 10
Reflectance
0.6
BC/Ni/cu-60Sec
R eflectance
Reflectance
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BC/Cu/Ni unwashed BC/Cu/Ni washed
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Fig. 4. FTIR reflectance versus wavelength for (a) unwashed and washed BC/Ni/Cu structures and for (b) optimized BC/Ni/Cu deposited structure.(Inset UV-Visreflectance, used for estimating absorptivity).
Kumar et al./ Materials Today: Proceedings 5 (2018) 23423–23427
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4. Conclusions We investigated the impact of pre and post synthesis process on solar thermal properties of electrochemically deposited black chrome SSCs on Cu and Ni plated Cu substrates. These results suggest the need of Ni metal reflector layer and its impact on solar thermal performance of black chrome solar selective structures. The synthesized BC/Ni/Cu structures exhibit absorptivity ~ 0.92 and emissivity ~ 0.14. These findings suggest that washing, followed by drying, is a crucial step to in developing black chrome solar selective coatings with enhanced solar thermal response. Acknowledgement The authors gratefully acknowledge the financial support from the Ministry of New and Renewable Energy(MNRE) through grant # 15/40/2010-11/ST. References [1] C.E. Kennedy, Review of Mid-to-High Temperature Solar Selective Absorber Materials, (2002) NREL/TP-520-31267 [2] F. Cao, Mc. Enaney, G. Chen, Z. Ren, Energ. Environ. Sci., 7 (2014) 1615. [3] M. Daryabegya, A.R. Mahmoodpoor. Isesaco Sci. Techonol. Vision 2 (2006) 35–39. [4] G. E. McDonald, Refinement in Black Chrome for use as a Solar Selective Coating. NASA TM X-3136,1974 [5] M. Aguilar, E. Barrera, M. Palomar-Pardave, L. Huerta, S. Muhl, J. Non-Crys. Sol. 329 (2003) 31–38. [6] M. Joly, Y. Antonetti, M. Python, M. Gonzalez, T. Gascou, J. Scartezzini, A. Schuler, Sol. Energ. 94 (2013) 233–239. [7] S. Khamlich, Physica B (2011),doi:10.1016/j.physb.2011.09.073 [8] K. D. Lee, J. Kor. Phys. Soc., 51(2007) 135–144.