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Effective strategy for improving infrared emissivity of Zn-Ni porous coating
Applied Surface Science 485 (2019) 92–100
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Effective strategy for improving infrared emissivity of Zn-Ni porous coating a
Jiacheng Guo , Xingwu Guo Wenjiang Dinga,b
a,b,⁎
a
a
a,b
, Jiyong Zeng , Lewen Nie , Jie Dong
a,b
, Liming Peng
,
T
a
National Engineering Research Center of Light Alloy Net Forming and Key State Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China Shanghai Innovation Institute for Materials, Shanghai 200444, China
b
ARTICLE INFO
ABSTRACT
Keywords: DHBT Porous Zn-Ni coating Infrared emissivity H2 bubbles Ceramic micro-particles
The purpose of this study is to prepare porous Zn-Ni coating with high infrared emissivity at a lower current density (1 A/cm2) by using dynamic hydrogen bubble template (DHBT) method. Three types of ceramic microparticles (Al2O3, SiO2 and TiO2) are introduced into the electrolyte to investigate their effects on the surface morphology and infrared emissivity of Zn-Ni coating. The results show that uniform porous coatings can be obtained when these micro-particles are added into the electrolyte. The suspended micro-particles in electrolyte can prevent the H2 bubbles from rising up and escaping from the cathode, which is beneficial to the formation of porous structure, especially the insulating micro-particles, Al2O3 and SiO2. The uniform porous structure containing ceramic micro-particles is beneficial to improve infrared emissivity. In addition, the infrared emissivity of porous composite coating is also significantly dependents on the type of ceramic particles inside pores. Among the three types of micro-particles, TiO2 micro-particles have the greatest effect on the improvement of infrared emissivity which is increased from 0.83 to 0.91 when TiO2 micro-particles are deposited into the Zn-Ni coating.
1. Introduction Dynamic hydrogen bubble template (DHBT) method is the most convenient method for the preparation of the metal or alloy coatings with macro-pores from aqueous solution. The coatings obtained by this method possess high specific surface area and are of vital importance in a diverse range of applications, such as catalysis, energy and hydrophobicity [1–8]. However, the surface dependent thermal performance is often neglected and less attention is paid on the infrared emissivity of the porous metal or alloy coatings. The emissivity is the ratio of energy radiated by the material to the energy radiated by a blackbody at the same temperature, which represents the key parameter to measuring the thermal radiation properties of materials [9–13]. The coatings with high infrared emissivity have attracted a lot attention in the fields of spacecraft applications, radiative cooling applications and electrical insulation [14–18]. It is known that most high infrared emissivity materials are insulators while the conductive materials like metals exhibit low infrared emissivity and high reflectivity [19,20]. However, the emissive properties of a surface coating can be altered profoundly when the geometric scale (s) of the radiators approximately equals the wavelength (λ) of the measured radiation (namely s ≈ λ) [21–27]. As a
result, the porous metal or alloy coating prepared by DHBT method will increase their infrared emissivity when the diameter of macro-pores equals the wavelength (λ) of infrared ray band region. In our previous works, a porous structure Zn-Ni coating with high infrared emissivity was prepared through the method of dynamic hydrogen bubble template (DHBT) at 3 A/cm2 [28], and the influence of sodium dodecyl sulfate (SDS) on the porous structure and infrared emissivity of porous Ni coating was investigated [29]. In this way, the porous coating with both high infrared emissivity and electrical conductivity can be obtained on electronic device shell used in space in order to lower their temperature and protect them from electromagnetic interference simultaneously. However, the applied deposition current density (3 A/ cm2) for the preparation of porous coating is too large to prepare big parts. For example, if a product part with a surface area of 100 cm2 is required to prepare, the current will be up to 300 A. The general power devices are not able to support large product. This limits the large-scale application of the porous coatings. The infrared emissivity is closely related to the distribution of pores on the surface, which depends upon the bubble behavior during electrodeposition process [1–3]. In order to obtain appropriate porous structure and high infrared emissivity at a lower current density, it is important to design and control hydrogen
⁎ Corresponding author at: National Engineering Research Center of Light Alloy Net Forming and Key State Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China. E-mail address: [email protected] (X. Guo).
https://doi.org/10.1016/j.apsusc.2019.04.191 Received 29 December 2018; Received in revised form 14 March 2019; Accepted 21 April 2019 Available online 22 April 2019 0169-4332/ © 2019 Elsevier B.V. All rights reserved.
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particle size distribution has been measured by Laser Particle Size Analyzer, and the average particle sizes of Al2O3, SiO2 and TiO2 are about 2.12 μm, 3.07 μm and 3.57 μm, respectively. These three particles possess high infrared emissivity in the mid-infrared region. The Al2O3 micro-particles were purchased from Lab Testing Technology (Shanghai) Co. Ltd., the SiO2 and TiO2 micro-particles were purchased from Aladdin Reagent Co. Ltd., and other analytical chemicals were purchased from Sinopharm Chemical Reagents Co. Ltd. without further purification. A copper (99.9%) sheet with an active area of 3.14 cm2 was chosen as a substrate material. Before electrodeposition, Cu substrate was wet ground with SiC papers down to 2000 grit, and was rinsed by dilute nitric acid, de-ionized water and alcohol sequentially. A Pt mesh with an area of 3 × 3 cm2 was used as an anode. The current density of electrodeposition was fixed at 1 A/cm2 to prepare a porous coating. Bath Composition and deposition parameters have been listed in Table 1. In the present work, the effects of deposition time, concentration and types of ceramic micro-particles on the formation of hydrogen bubbles, surface morphology and microstructure of Zn-Ni coating, finally the infrared emissivity have been studied when the current density of electrodeposition is fixed at 1 A/cm2. The surface morphology of the porous coating was characterized by field emission scanning electron microscope (FE-SEM, SIRION 200, FEI, America), coupled with energy-dispersive X-ray spectrometry (EDX, INCA, Oxford, U.K.). The phase structures were determined by X-ray diffraction (XRD, D/MAX 2000 V, Rigaku, Japan) with a Cu-Kα target. 2θ/θ scanning mode was executed in the range of 2θ = 20–80°at a scanning speed of 4°/min. The pore diameter in the coating was calculated by Ipwin32 Software, which is used to process, enhance and analyze images. The total hemisphere emissivity of the infrared spectrum with the wavelength in the range of 3 μm~30 μm was evaluated by TEMP 2000A (AZ Technology, Inc. 7047 Old Madison Pike, Suite 300 Huntsville, AL 35806) at room temperature.
Table 1 The bath composition and deposition parameters of porous Zn-Ni coatings. Composition Base solution
Additives
NiCl2·6H2O NH4Cl ZnCl2 NH4SCN SDS Al2O3 SiO2 TiO2
Concentration
Deposition current density (A/cm2)
Deposition time (s)
0.2 M 4M 0.2 M 0.2 M 0.1 mM 0–30 g/L 0–30 g/L 0–30 g/L
1
120, 180, 240, 300
bubble behavior during electrodeposition process. A number of directing agents including Halides [3,30–32], surfactants [33,34] and other additives [31,35,36] have been reported to adjust the nanostructured and macro-porous morphology of electrodeposits by DHBT method. However, less attention was paid to the effect of ceramic micro-particles on the porous structure. As Subramaniam et al. reported, the bubbles in the electrolyte can be protected by a closepacked shell of micro-particles — armored bubbles, which will influence the bubble behavior significantly during electrodeposition process [37]. 2. Experimental The porous Zn-Ni coating was electrodeposited in an electrolyte consisting of 0.2 M NiCl2·6H2O, 0.2 M ZnCl2, 4 M NH4Cl, 0.2 M NH4SCN and 0.1 mM sodium dodecyl sulfate (SDS), and herein defined as “base solution”. Three different types of ceramic micro-particles (Al2O3, SiO2 and TiO2) with diameter of 2–3.6 μm were introduced into the base solution as a source of additives to form different electrolytes. The
(a)
(b)
100 m
100 m
(d)
(c)
100 m
100 m
Fig. 1. The images of porous Zn-Ni coating from base solution (a) without any ceramic particles and with (b) 20 g/L Al2O3, (c) 20 g/L SiO2, (d) 20 g/L TiO2 at 1 A/ cm2 at 120 s. 93
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Al
(a)
Zn A site
A site
5 m
O
Ni
S
Si
(b)
Zn B site
B site
5 m O
Ni
S
Ti
(c)
Zn C site
C site
5 m
Ni
S
O
Fig. 2. The images and corresponding mapping spectrum of porous Zn-Ni coating from base solution with (a) 20 g/L Al2O3, (b) 20 g/L SiO2 and (c) 20 g/L TiO2 at 1 A/cm2 at 120 s.
(a)
(b)
Fig. 3. The schematic diagram of action mechanism of ceramic micro-particles on the inhibition of hydrogen bubbles coalescence.
94
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(a1-5g/L)
(b1-5g/L)
(c1-5g/L)
100 m
(a2-10g/L)
(b2-10g/L)
(c2-10g/L)
100 m
100 m
(b3-20g/L)
(a3-20g/L)
100 m
(c3-20g/L)
100 m
100 m
(a4-30g/L)
100 m
100 m
(b4-30g/L)
100 m (c4-30g/L)
100 m
100 m
100 m
Fig. 4. The images of Zn-Ni coatings electrodeposited from base solution containing 0.2 M NiCl2·6H2O, 0.2 M NH4SCN, 4 M NH4Cl, 0.2 M ZnCl2 and 0.1 mM SDS at 1 A/cm2 and 120 s with different concentration of ceramic micro-particles. a-Al2O3, b-SiO2, c-TiO2.
3. Results and discussions
particles were incorporated into the coating (see Fig. 2). The content of Al, Si and Ti element in the composite coating are ~4.4 at.%, ~4.2 at.% and ~6.1 at.%, respectively. These ceramic micro-particles were not only distributed on the bottom of pores but also distributed in the continuous matrix of coating as well. The ceramic particles in the bath have a very significant effect on bubble behavior and are beneficial to the formation of porous structure during electrodeposition process at a lower current density. The schematic diagram of the formation of porous Zn-Ni coating from the base solution with and without ceramic micro-particles is shown in Fig. 3. In the bath without any ceramic micro-particles, the bubbles will escape from the cathode easily, which results in the failure of the formation of porous structure at a lower current density and in shorter deposition time. However, in the bath with ceramic micro-particles, the suspended ceramic micro-particles in the electrolyte will adhere to the evolving H2 bubbles, and form armored bubbles and hinder the coalescence of the H2 bubbles. In addition, the ceramic particles can also prevent the bubbles escaping from the cathode. In other words, the retardant H2 bubbles on the cathode can act as dynamic template for Zn-Ni deposition, which is beneficial to the formation of the circular porous structure during the electrodeposition process.
3.1. Surface morphology of Zn-Ni coating 3.1.1. Effect of ceramic micro-particle types The images of Zn-Ni composite coating obtained from base solution without and with different types of ceramic micro-particles (Al2O3, SiO2 and TiO2) in the deposition time of 120 s are shown in Fig. 1. It can be seen that the Zn-Ni coating obtained without any ceramic micro-particles shows a rough surface topography, and only a few pores on the surface are observed. With adding ceramic micro-particles, the circular porous structure with an average pore diameter of ~20 μm has been formed. All these insulating ceramic particles can promote the formation of circular porous structure, especially the insulating ceramic particles Al2O3 and SiO2. However, TiO2 particles shows a weaker effect on the formation of circular porous structure. This may be due to the TiO2 micro-particles possessing certain electrical conductivity and are adhered to the H2 bubbles, make the H2 bubbles become armored bubbles. The TiO2 micro-particles and small armored H2 bubbles can easily co-deposited together with Zn2+ and Ni2+ ions to form the irregular circular porous structure. In addition, the analysis results of mapping spectrum show that these three types of ceramic micro95
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(a-120s)
(b-180s)
(c-240s)
(d-300s)
Fig. 5. The images of Zn-Ni coatings electrodeposited from base solution without any ceramic micro-particles at 1 A/cm2 at different deposition time.
(a2-240s)
(a1-180s)
(a3-300s)
100 m
100 m (b2-240s)
(b1-180s)
(b3-300s)
100 m
100 m (c1-180s)
100 m
(c2-240s)
100 m (c3-300s)
100 m
100 m
100 m
Fig. 6. The images of Zn-Ni coatings electrodeposited from base solution containing 0.2 M NiCl2·6H2O, 0.2 M NH4SCN, 4 M NH4Cl, 0.2 M ZnCl2 and 0.1 mM SDS with different types of ceramic micro-particles at 1 A/cm2 and different deposition time. a-20 g/L Al2O3, b-20 g/L SiO2, c-20 g/L TiO2.
3.1.2. Effect of concentration Fig. 4 shows the images of Zn-Ni coatings electrodeposited from base solution with a different concentration of ceramic micro-particles at 1 A/cm2 current density and at 120 s deposition time. With adding ceramic micro-particles and increasing their concentration, more pores are formed on the surface, but the porous structure of Zn-Ni coating
with circular pores has not been constructed yet until the concentration reaches to a certain concentration. It is observed that Zn-Ni coating presents a circular porous structure when the concentration reaches to 20 g/L. Further increasing the concentration of ceramic micro-particles to 30 g/L, Zn-Ni coating still presents a circular porous structure, but with shallow pore depth and irregular pores on the surface. In addition 96
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Average diameter of pore ( m)
90
pores. This is because the initial small bubbles evolved from the bottom began to coalesce and merge into big ones as they gradually rose up. The coalesced bubbles are growing beyond its limiting diameter and could not maintain stability and are vulnerable to break off. The effect of bubble template is gradually diminished in this stage and the Zn-Ni deposit mainly grow on the top of the pore wall rather than on the side of the pore wall. In other words, the growth direction of Zn-Ni coating was still perpendicular to the substrate. Compared with the coating prepared from base solution without any ceramic micro-particles, the porous structure of Zn-Ni coating electrodeposited from bath with ceramic micro-particles can be constructed in 120 s (see Fig. 1). However, as the deposition time increases, the circular porous structure gradually disappears (see Fig. 6). It is worth noting that the porous structure disappears for the Zn-Ni-Al2O3 and ZnNi-SiO2 composite coating, when the deposition time is increased to 300 s. However, for the Zn-Ni-TiO2 coating, the porous structure has been disappeared when the deposition time is merely increased to 180 s. This may be attributed to the TiO2 micro-particles possessing certain electrical conductivity and are distributed on the bottom of pores and the continuous matrix of the coating. TiO2 micro-particles can inhibit the formation of circular hydrogen bubbles and new Zn-Ni deposit can also grow on these TiO2 micro-particles and gradually fill the pores, resulting in the failure of circular porous structure. It is also found that the addition of Al2O3 and SiO2 micro-particles not only promotes the formation of circular porous structure but also reduces the pore size in the initial and second stage of the growth process of porous Zn-Ni coating. The dependence of average pore size from the bath with and without Al2O3 and SiO2 micro-particles on deposition time is shown in Fig. 7. It can be seen that both the addition of Al2O3 and SiO2 micro-particles not only reduces the pore diameter but also improves the uniformity of the diameter in the same deposition time. This is because the ceramic micro-particles in the bath would adhere to the H2 bubbles formed armored bubbles (see Fig. 3), which can hinder the coalescence and improve the size uniformity of the H2 bubbles during electrodeposition process.
Base solution Base solution with Al2O3
80
Base solution with SiO2
70 60 50 40 30 20 10 120
150
180 210 240 Deposition time (s)
270
300
Fig. 7. The addition of Al2O3 and SiO2 micro-particles reduce the pore diameter and improve the diameter uniformity.
to facilitating the formation of circular porous structure and shallow pore depth, the addition of ceramic micro-particles also consolidates the pore walls of Zn-Ni deposit and promotes the formation of continuous matrix. As mentioned above, The suspended ceramic microparticles in the bath can prevent the bubbles from rising up and escaping from the cathode. This effect would become more apparent as the concentration of ceramic micro-particles is increased. 3.1.3. Effect of deposition time The images of porous Zn-Ni coatings electrodeposited from base solution without ceramic micro-particles at different deposition times are shown in Fig. 5. It can be seen that the deposition time also has a significant effect on the formation of porous structure. The Zn-Ni coating does not possess a complete circular porous structure until the deposition time is increases to 180 s. The growth process of porous ZnNi coating can be divided into three stages, that is, the initial stage, the second stage and the third stage. In the initial stage (0–180 s), the circular porous structure has not been constructed yet, only several shallow circular pores being observed on the surface, and the coating thickness is thin and the coating adhesion is poor in this stage. The reason is that only a small quantity of hydrogen bubbles was generated and distributed on the cathode. In the second stage (180 s–240 s), the circular porous structure of Zn-Ni coating has been constructed and the coating thickness and adhesion are gradually increased. With the prolonged deposition time of Zn-Ni coating，more hydrogen bubbles were generated from the cathode and acted as the dynamic templates for Zn-Ni deposition. As a result, the circular porous structure can be constructed. In the third stage (240 s–300 s), the circular pores in the Zn-Ni coating begin to diminish and gradually become bigger non-circular
(a)
Cu substrate
(c)
Cu substrate
3.2. Cross-section morphology of Zn-Ni coating The cross-section morphologies of porous Zn-Ni coating obtained from the base solution in the same time of 120 s without any ceramic micro-particles, with 20 g/L Al2O3, with 20 g/L SiO2 and with 20 g/L TiO2 are shown in Fig. 8. It can be seen that all the cross-sections of porous Zn-Ni coating have similar “V” and “U” shaped voids. However, the Zn-Ni coating without any ceramic particles appears some isolated Zn-Ni deposit trees on the substrate. This may be attributed to the Zn-Ni deposit nucleate and grow on the surface of bubbles, and these bubbles leave the substrate freely before the Zn-Ni deposit became sufficiently dense. When the ceramic particles (Al2O3, SiO2 and TiO2) were added into the bath, the suspended ceramic micro-particles in the electrolyte
Zn-Ni coating
(b)
100 m
Cu substrate
(d)
Zn-Ni-SiO2 coating
100 m
Cu substrate
Zn-Ni-Al2O3 coating
100 m Zn-Ni-TiO2 coating
100 m
Fig. 8. The cross-section morphologies of porous Zn-Ni coating obtained from the base solution in the same time of 120 s. (a) Without any ceramic micro-particles. (b) With 20 g/L Al2O3, (c) with 20 g/L SiO2, (d) with 20 g/L TiO2. 97
Ni2Zn11 (444)
ZnO (311)
ZnO (220)
TiO2 (220)
Ni2Zn11 (422) TiO2 (211)
Ni2Zn11 (330) Ni2Zn11 (420)
NiO (200)
TiO2 (101) NiO (111)
TiO2 (110)
20
30
40
50
60
Al2O3 (208)
Al2O3 (300)
Al2O3 (116)
Al2O3
Al2O3 (110)
SiO2
Al2O3 (024)
TiO2 Al2O3 (104)
Intensity
Without any micro-particles
NiO (222)
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70
80
2 Theta (degree) Fig. 9. XRD patterns of porous Zn-Ni coatings electrodeposited from bath without and with different types of ceramic micro-particles at 1 A/cm2 and at 120 s. 0.92
Al2O3
0.91 0.90
Infrared emissivity
(b) 0.90
SiO2 TiO2
Infrared emissivity
(a)
0.89 0.88 0.87 0.86 0.85
0.88 0.86 0.84 0.82
base solution without micro-particles base solution with Al2O3 micro-particles
0.80
base solution with SiO2 micro-particles
0.84 0.83 0.82
0.78
0 5 10 15 20 25 30 Concentration of ceramic micro-particles (g/L)
base solution with TiO2 micro-particles
120
150
180 210 240 Deposition time (s)
270
300
Fig. 10. (a) The dependence of infrared emissivity of porous Zn-Ni coatings on the concentration of ceramic micro-particles in the solution. (b) The dependence of infrared emissivity of porous coatings obtained from base solution with and without ceramic micro-particles on the deposition time ranging from 120 s to 300 s.
structure but also be incorporated into the porous Zn-Ni coating. The phase compositions of these composite coatings were investigated by XRD method, and the XRD patterns of porous Zn-Ni coatings obtained from the bath with and without ceramic micro-particles are shown in Fig. 9. It is shown that the ceramic micro-particles uniformly distributed on the continuous matrix and the bottom of pores. All the coatings exhibit the similar diffraction peaks of Zn-Ni coating except some additional characteristic diffraction peaks of incorporated ceramic micro-particles. The four peaks appearing at 43.30, 44.60, 50.40 and 74.10 belong to Ni2Zn11 compound. The peaks appearing at 37.40, 41.70 and 77.60 belong to NiO, and the peaks appearing at 57.50 and 67.80 belong to ZnO. For the Zn-Ni-Al2O3 composite coating, the diffraction peaks appearing at 35.30, 37.40, 52.00, 57.50, 67.80 and 77.50 belong to Al2O3 micro-particles which partly are overlapping with other diffraction peaks. For the Zn-Ni-TiO2 composite coating, the diffraction peaks appearing at 27.50, 36.20, 52.00 and 54.40 belong to rutile TiO2 micro-particles. However, for the Zn-Ni-SiO2 composite coating, there is no additional diffraction peaks belong to SiO2 micro-particles. This may be due to the incorporated SiO2 micro-particles which are present in an amorphous state.
Fig. 11. Schematic diagram of the porous Zn-Ni composite coating with ceramic micro-particle inside.
hindered the rise of the H2 bubbles and increased the standing time of hydrogen bubbles on the cathode. The Zn-Ni deposit can form on the surface of bubbles directly and become dense before the bubbles left the cathode. The “V” shaped void in the coating can be attributed to the smaller pores formed in the former period and the coalesced bigger pores formed in the later period.
3.4. Infrared emissivity
3.3. XRD analysis on Zn-Ni coatings
3.4.1. Effect of concentration and deposition time The variation of surface morphology of the porous Zn-Ni coating has
The ceramic micro-particles not only can change the surface 98
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a significant effect on its thermal emission performance. The dependence of infrared emissivity of Zn-Ni coating on the concentration of ceramic micro-particles in the bath is shown in Fig. 10a. It can be seen that the addition of ceramic micro-particles in the bath has a significant effect on the improvement of infrared emissivity. The coating shows the highest infrared emissivity when the circular porous structure is constructed completely. The infrared emissivity of Zn-Ni coating increases with increasing the concentration of ceramic micro-particles in the bath, which can be attributed to the formation of a circular porous structure. However, when the concentration of ceramic micro-particles is increased from 20 g/L to 30 g/L, the infrared emissivity is unchanged or even decreases. This is because of the depth of circular pores become shallow. The multi-reflection and absorption of infrared radiation existing in the pores are reduced. According to Kirchhoff's law, an increase of absorption of infrared radiation equals to an increase of emittance [9–12]. As a result, the infrared emissivity of Zn-Ni coating decreases. The dependence of the deposition time on the infrared emissivity of Zn-Ni coating with and without ceramic micro-particles is shown in Fig. 10b. It can be seen that the deposition time has a significant effect on the infrared emissivity of Zn-Ni coating. This is because that the surface morphology changes as the deposition time increases. The Zn-Ni coating possesses the highest infrared emissivity when the circular porous structure is formed.
effect on the improvement of infrared emissivity. In addition, the surface infrared emissivity of porous Zn-Ni composite coating is obviously dependent upon the type of ceramic micro-particles inside the pores. Among the three types of micro-particles (Al2O3, SiO2 and TiO2), the TiO2 micro-particles have the greatest influence on the improvement of infrared emissivity, which increased the value of emissivity from 0.83 to 0.91 by depositing them into the Zn-Ni coating. Acknowledgments The authors gratefully acknowledge the National Natural Science Foundation of China (grant no. 51371116), the Joint Research Center of SJTU-SAST for Advanced Aerospace Technology (grant no.USCAST2013-23) and the 111 Project (Grant No. B16032) for financial support. The helpful assistance to film analysis from the Instrumental Analysis Center of Shanghai Jiao Tong University (SJTU) is sincerely acknowledged. References [1] B.J. Plowman, L.A. Jones, S.K. Bhargave, Building with bubbles: the formation of high surface area hyneycomb-like films via hydrogen bubble templated electrodeposition, Chem. Commun. 51 (2015) 4331–4364. [2] H. Zhang, Y. Ye, R. Shen, C. Ru, H. Yan, Effect of bubble behavior on the morphology of foamed porous copper prepared via electrodeposition, J. Electrochem. Soc. 160 (2013) D441–D445. [3] W.L. Tsai, P.C. Hsu, Y. Hwu, C.H. Chen, L.W. Chang, J.H. Je, H.M. Lin, A. Groso, G. Margaritondo, Electrochemistry: building on bubbles in metal electrodeposition, Nature 417 (2002) 139-139. [4] C.A. Marozzi, A.C. Chialvo, Development of electrode morphologies of interest in electrocatalysis. Part 1: electrodeposited porous nickel electrodes, Electrochim. Acta 45 (2000) 2111–2120. [5] C.A. Marozzi, A.C. Chialvo, Development of electrode morphologies of interest in electrocatalysis part 2: hydrogen evolution reaction on macroporous nickel electrodes, Electrochim. Acta 46 (2001) 861–866. [6] P.C. Hsu, S.K. Seol, T.N. Lo, C.J. Liu, C.L. Wang, C.S. Lin, Y. Hwu, C.H. Chen, L.W. Chang, J.H. Je, G. Margaritondo, Hydrogen bubbles and the growth morphology of ramified zinc by electrodeposition, J. Electrochem. Soc. 155 (2008) D400–D407. [7] N. D, N.G. Branković, V.M. Maksimović, Morphology and internal structure of copper deposits electrodeposited by the pulsating current regime in the hydrogen co-deposition range, J. Solid State Electrochem. 16 (2012) 321–328. [8] J. Niu, X. Liu, K. Xia, L. Xu, Y. Xu, X. Fang, W. Lu, Effect of electrodeposition parameters on the morphology of three-dimensional porous copper foams, Int. J. Electrochem. Sci. 10 (2015) 7331–7340. [9] P.M. Robitaille, A critical analysis of universality and Kirchhoff's law: a return to Stewart's law of thermal emission, Prog. Phys. 3 (2008) 30–35. [10] P.M. Robitaille, Blackbody radiation and the carbon particle, Prog. Phys. 3 (2008) 36–55. [11] P.M. Robitaille, Kirchhoff's law of thermal emission: 150 years, Prog. Phys. 4 (2009) 3–13. [12] P.M. Robitaille, On the equation which governs cavity radiation, Prog. Phys. 10 (2014) 126–127. [13] S. Maruyama, T. Kashiwa, H. Yugami, M. Esashi, Thermal radiation from two-dimensionally confined modes in microcavities, Appl. Phys. Lett. 79 (2001) 1393–1395. [14] S. Wijewardane, D.Y. Goswam, A review on surface control of thermal radiation by paints and coatings for new energy applications, Renew. Sust. Energ. Rev. 16 (2012) 1863–1873. [15] J.P. Huang, Y.B. Li, G.P. Song, X.J. Zhang, Y. Sun, X.D. He, S.Y. Du, Highly enhanced infrared spectral emissivity of porous CeO2 coating, Mater. Lett. 85 (2012) 57–60. [16] F.Y. Wang, L.F. Cheng, Q. Zhang, L.T. Zhang, Effect of surface morphology and densification on the infrared emissivity of C/SiC composites, Appl. Surf. Sci. 313 (2014) 670–676. [17] F.Y. Wang, L.F. Cheng, Y. N. X, J. J and L. T. Zhang, Effects of SiC shape and oxidation on the infrared emissivity properties of ZrB2–SiC ceramics, J. Alloys Compd. 625 (2015) 1–7. [18] S. Somasundaram, A.M. Pillai, A. Rajendra, A.K. Sharma, High emittance black nickel coating on copper substrate for space applications, J. Alloys Compd. 643 (2015) 263–269. [19] M.M.S.A. Bosta, K.J. Ma, Influence of electrolyte temperature on properties and infrared emissivity of MAO ceramic coating on 6061 aluminum alloy, Infrared Phys. Technol. 67 (2014) 63–72. [20] D.B. Mahadik, S. Gujjar, G.M. Gouda, H.C. Barshilia, Double layer SiO2/Al2O3 high emissivity coatings on stainless steel substrates using simple spray deposition system, Appl. Surf. Sci. 299 (2014) 6–11. [21] P.J. Hesketh, J.N. Zemel, B. Gebhart, Organ pipe radiant modes of periodic micromachined silicon surfaces, Nature 324 (1986) 549–551. [22] P.J. Hesketh, J.N. Zemel, B. Gebhart, Polarized spectral emittance from periodic
3.4.2. Effect of ceramic micro-particle type In addition to the deposition time and the concentration of ceramic micro-particles, the type of ceramic micro-particles also has a significant effect on the infrared emissivity of porous Zn-Ni composite coating. As shown in Fig. 10b, the Zn-Ni-TiO2 composite coating possesses the highest infrared emissivity of 0.91, while the other two Zn-Ni composite coatings (Zn-Ni-Al2O3 and Zn-Ni-SiO2) possess the highest infrared emissivity of 0.88. It is indicated that the infrared emissivity of Zn-Ni-TiO2 composite coating shows a higher value than that of other composite coatings. The difference of the infrared emissivity between pure Zn-Ni coating and Zn-Ni composite coating can be explained by the incorporation of particle type. Kirchhoff and Planck observed that the blackbody radiation spectrum could be obtained by inserting even very small particle of carbon within a perfectly reflecting cavity. It is clear that, given thermal equilibrium, all of the radiation which comes to fill the cavity is being produced by the carbon particle [10–12]. For the porous structure composite coating, the ceramic micro-particles are involved inside the pores. The schematic diagram of porous Zn-Ni composite coating with ceramic micro-particles inside the pores has been shown in Fig. 11. The effective emissivity of the porous coating comes from not only the pore walls of the Zn-Ni deposit but also from the ceramic micro-particles with higher infrared emissivity inside the pores. Although the Zn-Ni-TiO2 composite coating has a low degree of formation of circular porous structure, it possesses the highest emissivity of 0.91 because of the TiO2 particles with enhanced absorptivity at 3–30 μm than that of Al2O3 and SiO2 particles. 4. Conclusion Porous Zn-Ni composite coatings with high infrared emissivity were electrodeposited at a lower current density 1 A/cm2. Both the addition of ceramic micro-particles in the bath and deposition time have an obvious effect on the formation of porous structure of Zn-Ni coating. The addition of ceramic micro-particles in the bath can prevent H2 bubbles escaping from the cathode, and prolonged deposition time can increase the evolving hydrogen bubbles and Zn-Ni deposit. These effects on the bubble behavior during the electrodeposition process are beneficial to the formation of porous structure. However, the ceramic particles need to reach a certain concentration (about 20 g/L) and the deposition time must be within a certain range, otherwise, the uniform circular porous Zn-Ni coating cannot be obtained. The uniform circular porous structure containing ceramic micro-particles has a significant 99
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[23] [24] [25] [26] [27] [28] [29] [30]
micromachined surface. I. Doped silicon: the normal direction, Phys. Rev. B 37 (1988) 10795–10802. P.J. Hesketh, J.N. Zemel, B. Gebhart, Polarized spectral emittance from periodic micromachined surface. II. Doped silicon: angular variation, Phys. Rev. B 37 (1988) 10803–10813. H. Yugam, H. Sai, K. Hane, Y. Akiyama, Y. Kanamori, Spectral control of thermal emission by periodic microstructured surfaces in the near-infrared region, J. Opt. Soc. Am. A 18 (2001) 1471–1476. H. Sai, H. Yugam, Y. Akiyama, Y, Kanamori and K. Hane, Solar selective absorbers based on two-dimension W surface gratings with submicron periods for high-temperature photothermal conversion, Sol. Energy Mater. Sol. Cells 79 (2003) 35–49. I. Celanovic, D. Perreault, J. Kassakian, Resonant-cavity enhanced thermal emission, Phys. Rev. B 72 (2005) 075127–1~6. J.L. Gall, M. Olivier, J.J. Greffer, Experimental and theoretical study of reflection and coherent thermal emission by a SiC grating supporting a surface-phonon polaritons, Phys. Rev. B 55 (1997) 10105–10114. J.C. Guo, X.W. Guo, X.W. Xu, Z.C. Zhang, J. Dong, L.M. Peng, W.J. Ding, A Zn-Ni coating with both high electrical conductivity and infrared emissivity prepared by hydrogen evolution method, Appl. Surf. Sci. 402 (2017) 92–98. J.C. Guo, X.W. Guo, J.Y. Zeng, L. Nie, J. Dong, L.M. Peng, W.J. Ding, Influence of sodium dodecyl sulphate on the surface morphology and infrared emissivity of porous Ni film, Infrared Phys. Technol. 93 (2018) 162–170. H.C. Shin, M. Liu, Copper foam structure with highly porous nanostructured walls,
Chem. Mater. 16 (2004) 5460–5464. [31] J.H. Kim, R.H. Kim, H.S. Kwon, Preparation of copper foam with 3-dimensionaally interconnected spherical pore network by electrodeposition, Electrochem. Commun. 10 (2008) 1148–1151. [32] X.T. Yu, M.Y. Wang, Z. Wang, X.Z. Gong, Z.C. Guo, The structure evolution mechanism of electrodeposited porous Ni films on NH4Cl concentration, Appl. Surf. Sci. 360 (2016) 502–509. [33] N. Wang, W.C. Hu, Y.H. Lu, Y.F. Deng, X.B. Wan, Y.W. Zhang, Role of surfactants in construction of porous copper film by electrodeposition approach, Trans. IMF 89 (2011) 261–267. [34] X. Guo, X. Li, Y. Zheng, C. Lai, W. Li, B. Luo, D.X. Zhang, Effects of surfactants on high regularity of 3d porous nickel for Zn2+ adsorption application, J. Nanomater. 3 (2014) 1–9. [35] K. Tan, M.B. Tian, Q. Cai, Effect of bromide ions and polyethylene glycol on morphological control of electrodeposited copper foam, Thin Solid Films 518 (2010) 5159–5163. [36] D.H. Nam, R.H. Kim, D.W. Han, J.H. Kim, H.S. Kwon, Effects of (NH4)2SO4 and BTA on the nanostructure of copper foam prepared by electrodeposition, Electrochim. Acta 56 (2011) 9397–9405. [37] A.B. Subramaniam, C. Mejean, M. Abkarian, H.A. Stone, Microstructure, morphology, and lifetime of armored bubbles exposed to surfactants, Langmuir 22 (2006) 5986–5990.
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Full length article
Effective strategy for improving infrared emissivity of Zn-Ni porous coating a
Jiacheng Guo , Xingwu Guo Wenjiang Dinga,b
a,b,⁎
a
a
a,b
, Jiyong Zeng , Lewen Nie , Jie Dong
a,b
, Liming Peng
,
T
a
National Engineering Research Center of Light Alloy Net Forming and Key State Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China Shanghai Innovation Institute for Materials, Shanghai 200444, China
b
ARTICLE INFO
ABSTRACT
Keywords: DHBT Porous Zn-Ni coating Infrared emissivity H2 bubbles Ceramic micro-particles
The purpose of this study is to prepare porous Zn-Ni coating with high infrared emissivity at a lower current density (1 A/cm2) by using dynamic hydrogen bubble template (DHBT) method. Three types of ceramic microparticles (Al2O3, SiO2 and TiO2) are introduced into the electrolyte to investigate their effects on the surface morphology and infrared emissivity of Zn-Ni coating. The results show that uniform porous coatings can be obtained when these micro-particles are added into the electrolyte. The suspended micro-particles in electrolyte can prevent the H2 bubbles from rising up and escaping from the cathode, which is beneficial to the formation of porous structure, especially the insulating micro-particles, Al2O3 and SiO2. The uniform porous structure containing ceramic micro-particles is beneficial to improve infrared emissivity. In addition, the infrared emissivity of porous composite coating is also significantly dependents on the type of ceramic particles inside pores. Among the three types of micro-particles, TiO2 micro-particles have the greatest effect on the improvement of infrared emissivity which is increased from 0.83 to 0.91 when TiO2 micro-particles are deposited into the Zn-Ni coating.
1. Introduction Dynamic hydrogen bubble template (DHBT) method is the most convenient method for the preparation of the metal or alloy coatings with macro-pores from aqueous solution. The coatings obtained by this method possess high specific surface area and are of vital importance in a diverse range of applications, such as catalysis, energy and hydrophobicity [1–8]. However, the surface dependent thermal performance is often neglected and less attention is paid on the infrared emissivity of the porous metal or alloy coatings. The emissivity is the ratio of energy radiated by the material to the energy radiated by a blackbody at the same temperature, which represents the key parameter to measuring the thermal radiation properties of materials [9–13]. The coatings with high infrared emissivity have attracted a lot attention in the fields of spacecraft applications, radiative cooling applications and electrical insulation [14–18]. It is known that most high infrared emissivity materials are insulators while the conductive materials like metals exhibit low infrared emissivity and high reflectivity [19,20]. However, the emissive properties of a surface coating can be altered profoundly when the geometric scale (s) of the radiators approximately equals the wavelength (λ) of the measured radiation (namely s ≈ λ) [21–27]. As a
result, the porous metal or alloy coating prepared by DHBT method will increase their infrared emissivity when the diameter of macro-pores equals the wavelength (λ) of infrared ray band region. In our previous works, a porous structure Zn-Ni coating with high infrared emissivity was prepared through the method of dynamic hydrogen bubble template (DHBT) at 3 A/cm2 [28], and the influence of sodium dodecyl sulfate (SDS) on the porous structure and infrared emissivity of porous Ni coating was investigated [29]. In this way, the porous coating with both high infrared emissivity and electrical conductivity can be obtained on electronic device shell used in space in order to lower their temperature and protect them from electromagnetic interference simultaneously. However, the applied deposition current density (3 A/ cm2) for the preparation of porous coating is too large to prepare big parts. For example, if a product part with a surface area of 100 cm2 is required to prepare, the current will be up to 300 A. The general power devices are not able to support large product. This limits the large-scale application of the porous coatings. The infrared emissivity is closely related to the distribution of pores on the surface, which depends upon the bubble behavior during electrodeposition process [1–3]. In order to obtain appropriate porous structure and high infrared emissivity at a lower current density, it is important to design and control hydrogen
⁎ Corresponding author at: National Engineering Research Center of Light Alloy Net Forming and Key State Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China. E-mail address: [email protected] (X. Guo).
https://doi.org/10.1016/j.apsusc.2019.04.191 Received 29 December 2018; Received in revised form 14 March 2019; Accepted 21 April 2019 Available online 22 April 2019 0169-4332/ © 2019 Elsevier B.V. All rights reserved.
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particle size distribution has been measured by Laser Particle Size Analyzer, and the average particle sizes of Al2O3, SiO2 and TiO2 are about 2.12 μm, 3.07 μm and 3.57 μm, respectively. These three particles possess high infrared emissivity in the mid-infrared region. The Al2O3 micro-particles were purchased from Lab Testing Technology (Shanghai) Co. Ltd., the SiO2 and TiO2 micro-particles were purchased from Aladdin Reagent Co. Ltd., and other analytical chemicals were purchased from Sinopharm Chemical Reagents Co. Ltd. without further purification. A copper (99.9%) sheet with an active area of 3.14 cm2 was chosen as a substrate material. Before electrodeposition, Cu substrate was wet ground with SiC papers down to 2000 grit, and was rinsed by dilute nitric acid, de-ionized water and alcohol sequentially. A Pt mesh with an area of 3 × 3 cm2 was used as an anode. The current density of electrodeposition was fixed at 1 A/cm2 to prepare a porous coating. Bath Composition and deposition parameters have been listed in Table 1. In the present work, the effects of deposition time, concentration and types of ceramic micro-particles on the formation of hydrogen bubbles, surface morphology and microstructure of Zn-Ni coating, finally the infrared emissivity have been studied when the current density of electrodeposition is fixed at 1 A/cm2. The surface morphology of the porous coating was characterized by field emission scanning electron microscope (FE-SEM, SIRION 200, FEI, America), coupled with energy-dispersive X-ray spectrometry (EDX, INCA, Oxford, U.K.). The phase structures were determined by X-ray diffraction (XRD, D/MAX 2000 V, Rigaku, Japan) with a Cu-Kα target. 2θ/θ scanning mode was executed in the range of 2θ = 20–80°at a scanning speed of 4°/min. The pore diameter in the coating was calculated by Ipwin32 Software, which is used to process, enhance and analyze images. The total hemisphere emissivity of the infrared spectrum with the wavelength in the range of 3 μm~30 μm was evaluated by TEMP 2000A (AZ Technology, Inc. 7047 Old Madison Pike, Suite 300 Huntsville, AL 35806) at room temperature.
Table 1 The bath composition and deposition parameters of porous Zn-Ni coatings. Composition Base solution
Additives
NiCl2·6H2O NH4Cl ZnCl2 NH4SCN SDS Al2O3 SiO2 TiO2
Concentration
Deposition current density (A/cm2)
Deposition time (s)
0.2 M 4M 0.2 M 0.2 M 0.1 mM 0–30 g/L 0–30 g/L 0–30 g/L
1
120, 180, 240, 300
bubble behavior during electrodeposition process. A number of directing agents including Halides [3,30–32], surfactants [33,34] and other additives [31,35,36] have been reported to adjust the nanostructured and macro-porous morphology of electrodeposits by DHBT method. However, less attention was paid to the effect of ceramic micro-particles on the porous structure. As Subramaniam et al. reported, the bubbles in the electrolyte can be protected by a closepacked shell of micro-particles — armored bubbles, which will influence the bubble behavior significantly during electrodeposition process [37]. 2. Experimental The porous Zn-Ni coating was electrodeposited in an electrolyte consisting of 0.2 M NiCl2·6H2O, 0.2 M ZnCl2, 4 M NH4Cl, 0.2 M NH4SCN and 0.1 mM sodium dodecyl sulfate (SDS), and herein defined as “base solution”. Three different types of ceramic micro-particles (Al2O3, SiO2 and TiO2) with diameter of 2–3.6 μm were introduced into the base solution as a source of additives to form different electrolytes. The
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Fig. 1. The images of porous Zn-Ni coating from base solution (a) without any ceramic particles and with (b) 20 g/L Al2O3, (c) 20 g/L SiO2, (d) 20 g/L TiO2 at 1 A/ cm2 at 120 s. 93
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Fig. 2. The images and corresponding mapping spectrum of porous Zn-Ni coating from base solution with (a) 20 g/L Al2O3, (b) 20 g/L SiO2 and (c) 20 g/L TiO2 at 1 A/cm2 at 120 s.
(a)
(b)
Fig. 3. The schematic diagram of action mechanism of ceramic micro-particles on the inhibition of hydrogen bubbles coalescence.
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(a1-5g/L)
(b1-5g/L)
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(a4-30g/L)
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Fig. 4. The images of Zn-Ni coatings electrodeposited from base solution containing 0.2 M NiCl2·6H2O, 0.2 M NH4SCN, 4 M NH4Cl, 0.2 M ZnCl2 and 0.1 mM SDS at 1 A/cm2 and 120 s with different concentration of ceramic micro-particles. a-Al2O3, b-SiO2, c-TiO2.
3. Results and discussions
particles were incorporated into the coating (see Fig. 2). The content of Al, Si and Ti element in the composite coating are ~4.4 at.%, ~4.2 at.% and ~6.1 at.%, respectively. These ceramic micro-particles were not only distributed on the bottom of pores but also distributed in the continuous matrix of coating as well. The ceramic particles in the bath have a very significant effect on bubble behavior and are beneficial to the formation of porous structure during electrodeposition process at a lower current density. The schematic diagram of the formation of porous Zn-Ni coating from the base solution with and without ceramic micro-particles is shown in Fig. 3. In the bath without any ceramic micro-particles, the bubbles will escape from the cathode easily, which results in the failure of the formation of porous structure at a lower current density and in shorter deposition time. However, in the bath with ceramic micro-particles, the suspended ceramic micro-particles in the electrolyte will adhere to the evolving H2 bubbles, and form armored bubbles and hinder the coalescence of the H2 bubbles. In addition, the ceramic particles can also prevent the bubbles escaping from the cathode. In other words, the retardant H2 bubbles on the cathode can act as dynamic template for Zn-Ni deposition, which is beneficial to the formation of the circular porous structure during the electrodeposition process.
3.1. Surface morphology of Zn-Ni coating 3.1.1. Effect of ceramic micro-particle types The images of Zn-Ni composite coating obtained from base solution without and with different types of ceramic micro-particles (Al2O3, SiO2 and TiO2) in the deposition time of 120 s are shown in Fig. 1. It can be seen that the Zn-Ni coating obtained without any ceramic micro-particles shows a rough surface topography, and only a few pores on the surface are observed. With adding ceramic micro-particles, the circular porous structure with an average pore diameter of ~20 μm has been formed. All these insulating ceramic particles can promote the formation of circular porous structure, especially the insulating ceramic particles Al2O3 and SiO2. However, TiO2 particles shows a weaker effect on the formation of circular porous structure. This may be due to the TiO2 micro-particles possessing certain electrical conductivity and are adhered to the H2 bubbles, make the H2 bubbles become armored bubbles. The TiO2 micro-particles and small armored H2 bubbles can easily co-deposited together with Zn2+ and Ni2+ ions to form the irregular circular porous structure. In addition, the analysis results of mapping spectrum show that these three types of ceramic micro95
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(a-120s)
(b-180s)
(c-240s)
(d-300s)
Fig. 5. The images of Zn-Ni coatings electrodeposited from base solution without any ceramic micro-particles at 1 A/cm2 at different deposition time.
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Fig. 6. The images of Zn-Ni coatings electrodeposited from base solution containing 0.2 M NiCl2·6H2O, 0.2 M NH4SCN, 4 M NH4Cl, 0.2 M ZnCl2 and 0.1 mM SDS with different types of ceramic micro-particles at 1 A/cm2 and different deposition time. a-20 g/L Al2O3, b-20 g/L SiO2, c-20 g/L TiO2.
3.1.2. Effect of concentration Fig. 4 shows the images of Zn-Ni coatings electrodeposited from base solution with a different concentration of ceramic micro-particles at 1 A/cm2 current density and at 120 s deposition time. With adding ceramic micro-particles and increasing their concentration, more pores are formed on the surface, but the porous structure of Zn-Ni coating
with circular pores has not been constructed yet until the concentration reaches to a certain concentration. It is observed that Zn-Ni coating presents a circular porous structure when the concentration reaches to 20 g/L. Further increasing the concentration of ceramic micro-particles to 30 g/L, Zn-Ni coating still presents a circular porous structure, but with shallow pore depth and irregular pores on the surface. In addition 96
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Average diameter of pore ( m)
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pores. This is because the initial small bubbles evolved from the bottom began to coalesce and merge into big ones as they gradually rose up. The coalesced bubbles are growing beyond its limiting diameter and could not maintain stability and are vulnerable to break off. The effect of bubble template is gradually diminished in this stage and the Zn-Ni deposit mainly grow on the top of the pore wall rather than on the side of the pore wall. In other words, the growth direction of Zn-Ni coating was still perpendicular to the substrate. Compared with the coating prepared from base solution without any ceramic micro-particles, the porous structure of Zn-Ni coating electrodeposited from bath with ceramic micro-particles can be constructed in 120 s (see Fig. 1). However, as the deposition time increases, the circular porous structure gradually disappears (see Fig. 6). It is worth noting that the porous structure disappears for the Zn-Ni-Al2O3 and ZnNi-SiO2 composite coating, when the deposition time is increased to 300 s. However, for the Zn-Ni-TiO2 coating, the porous structure has been disappeared when the deposition time is merely increased to 180 s. This may be attributed to the TiO2 micro-particles possessing certain electrical conductivity and are distributed on the bottom of pores and the continuous matrix of the coating. TiO2 micro-particles can inhibit the formation of circular hydrogen bubbles and new Zn-Ni deposit can also grow on these TiO2 micro-particles and gradually fill the pores, resulting in the failure of circular porous structure. It is also found that the addition of Al2O3 and SiO2 micro-particles not only promotes the formation of circular porous structure but also reduces the pore size in the initial and second stage of the growth process of porous Zn-Ni coating. The dependence of average pore size from the bath with and without Al2O3 and SiO2 micro-particles on deposition time is shown in Fig. 7. It can be seen that both the addition of Al2O3 and SiO2 micro-particles not only reduces the pore diameter but also improves the uniformity of the diameter in the same deposition time. This is because the ceramic micro-particles in the bath would adhere to the H2 bubbles formed armored bubbles (see Fig. 3), which can hinder the coalescence and improve the size uniformity of the H2 bubbles during electrodeposition process.
Base solution Base solution with Al2O3
80
Base solution with SiO2
70 60 50 40 30 20 10 120
150
180 210 240 Deposition time (s)
270
300
Fig. 7. The addition of Al2O3 and SiO2 micro-particles reduce the pore diameter and improve the diameter uniformity.
to facilitating the formation of circular porous structure and shallow pore depth, the addition of ceramic micro-particles also consolidates the pore walls of Zn-Ni deposit and promotes the formation of continuous matrix. As mentioned above, The suspended ceramic microparticles in the bath can prevent the bubbles from rising up and escaping from the cathode. This effect would become more apparent as the concentration of ceramic micro-particles is increased. 3.1.3. Effect of deposition time The images of porous Zn-Ni coatings electrodeposited from base solution without ceramic micro-particles at different deposition times are shown in Fig. 5. It can be seen that the deposition time also has a significant effect on the formation of porous structure. The Zn-Ni coating does not possess a complete circular porous structure until the deposition time is increases to 180 s. The growth process of porous ZnNi coating can be divided into three stages, that is, the initial stage, the second stage and the third stage. In the initial stage (0–180 s), the circular porous structure has not been constructed yet, only several shallow circular pores being observed on the surface, and the coating thickness is thin and the coating adhesion is poor in this stage. The reason is that only a small quantity of hydrogen bubbles was generated and distributed on the cathode. In the second stage (180 s–240 s), the circular porous structure of Zn-Ni coating has been constructed and the coating thickness and adhesion are gradually increased. With the prolonged deposition time of Zn-Ni coating，more hydrogen bubbles were generated from the cathode and acted as the dynamic templates for Zn-Ni deposition. As a result, the circular porous structure can be constructed. In the third stage (240 s–300 s), the circular pores in the Zn-Ni coating begin to diminish and gradually become bigger non-circular
(a)
Cu substrate
(c)
Cu substrate
3.2. Cross-section morphology of Zn-Ni coating The cross-section morphologies of porous Zn-Ni coating obtained from the base solution in the same time of 120 s without any ceramic micro-particles, with 20 g/L Al2O3, with 20 g/L SiO2 and with 20 g/L TiO2 are shown in Fig. 8. It can be seen that all the cross-sections of porous Zn-Ni coating have similar “V” and “U” shaped voids. However, the Zn-Ni coating without any ceramic particles appears some isolated Zn-Ni deposit trees on the substrate. This may be attributed to the Zn-Ni deposit nucleate and grow on the surface of bubbles, and these bubbles leave the substrate freely before the Zn-Ni deposit became sufficiently dense. When the ceramic particles (Al2O3, SiO2 and TiO2) were added into the bath, the suspended ceramic micro-particles in the electrolyte
Zn-Ni coating
(b)
100 m
Cu substrate
(d)
Zn-Ni-SiO2 coating
100 m
Cu substrate
Zn-Ni-Al2O3 coating
100 m Zn-Ni-TiO2 coating
100 m
Fig. 8. The cross-section morphologies of porous Zn-Ni coating obtained from the base solution in the same time of 120 s. (a) Without any ceramic micro-particles. (b) With 20 g/L Al2O3, (c) with 20 g/L SiO2, (d) with 20 g/L TiO2. 97
Ni2Zn11 (444)
ZnO (311)
ZnO (220)
TiO2 (220)
Ni2Zn11 (422) TiO2 (211)
Ni2Zn11 (330) Ni2Zn11 (420)
NiO (200)
TiO2 (101) NiO (111)
TiO2 (110)
20
30
40
50
60
Al2O3 (208)
Al2O3 (300)
Al2O3 (116)
Al2O3
Al2O3 (110)
SiO2
Al2O3 (024)
TiO2 Al2O3 (104)
Intensity
Without any micro-particles
NiO (222)
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70
80
2 Theta (degree) Fig. 9. XRD patterns of porous Zn-Ni coatings electrodeposited from bath without and with different types of ceramic micro-particles at 1 A/cm2 and at 120 s. 0.92
Al2O3
0.91 0.90
Infrared emissivity
(b) 0.90
SiO2 TiO2
Infrared emissivity
(a)
0.89 0.88 0.87 0.86 0.85
0.88 0.86 0.84 0.82
base solution without micro-particles base solution with Al2O3 micro-particles
0.80
base solution with SiO2 micro-particles
0.84 0.83 0.82
0.78
0 5 10 15 20 25 30 Concentration of ceramic micro-particles (g/L)
base solution with TiO2 micro-particles
120
150
180 210 240 Deposition time (s)
270
300
Fig. 10. (a) The dependence of infrared emissivity of porous Zn-Ni coatings on the concentration of ceramic micro-particles in the solution. (b) The dependence of infrared emissivity of porous coatings obtained from base solution with and without ceramic micro-particles on the deposition time ranging from 120 s to 300 s.
structure but also be incorporated into the porous Zn-Ni coating. The phase compositions of these composite coatings were investigated by XRD method, and the XRD patterns of porous Zn-Ni coatings obtained from the bath with and without ceramic micro-particles are shown in Fig. 9. It is shown that the ceramic micro-particles uniformly distributed on the continuous matrix and the bottom of pores. All the coatings exhibit the similar diffraction peaks of Zn-Ni coating except some additional characteristic diffraction peaks of incorporated ceramic micro-particles. The four peaks appearing at 43.30, 44.60, 50.40 and 74.10 belong to Ni2Zn11 compound. The peaks appearing at 37.40, 41.70 and 77.60 belong to NiO, and the peaks appearing at 57.50 and 67.80 belong to ZnO. For the Zn-Ni-Al2O3 composite coating, the diffraction peaks appearing at 35.30, 37.40, 52.00, 57.50, 67.80 and 77.50 belong to Al2O3 micro-particles which partly are overlapping with other diffraction peaks. For the Zn-Ni-TiO2 composite coating, the diffraction peaks appearing at 27.50, 36.20, 52.00 and 54.40 belong to rutile TiO2 micro-particles. However, for the Zn-Ni-SiO2 composite coating, there is no additional diffraction peaks belong to SiO2 micro-particles. This may be due to the incorporated SiO2 micro-particles which are present in an amorphous state.
Fig. 11. Schematic diagram of the porous Zn-Ni composite coating with ceramic micro-particle inside.
hindered the rise of the H2 bubbles and increased the standing time of hydrogen bubbles on the cathode. The Zn-Ni deposit can form on the surface of bubbles directly and become dense before the bubbles left the cathode. The “V” shaped void in the coating can be attributed to the smaller pores formed in the former period and the coalesced bigger pores formed in the later period.
3.4. Infrared emissivity
3.3. XRD analysis on Zn-Ni coatings
3.4.1. Effect of concentration and deposition time The variation of surface morphology of the porous Zn-Ni coating has
The ceramic micro-particles not only can change the surface 98
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a significant effect on its thermal emission performance. The dependence of infrared emissivity of Zn-Ni coating on the concentration of ceramic micro-particles in the bath is shown in Fig. 10a. It can be seen that the addition of ceramic micro-particles in the bath has a significant effect on the improvement of infrared emissivity. The coating shows the highest infrared emissivity when the circular porous structure is constructed completely. The infrared emissivity of Zn-Ni coating increases with increasing the concentration of ceramic micro-particles in the bath, which can be attributed to the formation of a circular porous structure. However, when the concentration of ceramic micro-particles is increased from 20 g/L to 30 g/L, the infrared emissivity is unchanged or even decreases. This is because of the depth of circular pores become shallow. The multi-reflection and absorption of infrared radiation existing in the pores are reduced. According to Kirchhoff's law, an increase of absorption of infrared radiation equals to an increase of emittance [9–12]. As a result, the infrared emissivity of Zn-Ni coating decreases. The dependence of the deposition time on the infrared emissivity of Zn-Ni coating with and without ceramic micro-particles is shown in Fig. 10b. It can be seen that the deposition time has a significant effect on the infrared emissivity of Zn-Ni coating. This is because that the surface morphology changes as the deposition time increases. The Zn-Ni coating possesses the highest infrared emissivity when the circular porous structure is formed.
effect on the improvement of infrared emissivity. In addition, the surface infrared emissivity of porous Zn-Ni composite coating is obviously dependent upon the type of ceramic micro-particles inside the pores. Among the three types of micro-particles (Al2O3, SiO2 and TiO2), the TiO2 micro-particles have the greatest influence on the improvement of infrared emissivity, which increased the value of emissivity from 0.83 to 0.91 by depositing them into the Zn-Ni coating. Acknowledgments The authors gratefully acknowledge the National Natural Science Foundation of China (grant no. 51371116), the Joint Research Center of SJTU-SAST for Advanced Aerospace Technology (grant no.USCAST2013-23) and the 111 Project (Grant No. B16032) for financial support. The helpful assistance to film analysis from the Instrumental Analysis Center of Shanghai Jiao Tong University (SJTU) is sincerely acknowledged. References [1] B.J. Plowman, L.A. Jones, S.K. Bhargave, Building with bubbles: the formation of high surface area hyneycomb-like films via hydrogen bubble templated electrodeposition, Chem. Commun. 51 (2015) 4331–4364. [2] H. Zhang, Y. Ye, R. Shen, C. Ru, H. Yan, Effect of bubble behavior on the morphology of foamed porous copper prepared via electrodeposition, J. Electrochem. Soc. 160 (2013) D441–D445. [3] W.L. Tsai, P.C. Hsu, Y. Hwu, C.H. Chen, L.W. Chang, J.H. Je, H.M. Lin, A. Groso, G. Margaritondo, Electrochemistry: building on bubbles in metal electrodeposition, Nature 417 (2002) 139-139. [4] C.A. Marozzi, A.C. Chialvo, Development of electrode morphologies of interest in electrocatalysis. Part 1: electrodeposited porous nickel electrodes, Electrochim. Acta 45 (2000) 2111–2120. [5] C.A. Marozzi, A.C. Chialvo, Development of electrode morphologies of interest in electrocatalysis part 2: hydrogen evolution reaction on macroporous nickel electrodes, Electrochim. Acta 46 (2001) 861–866. [6] P.C. Hsu, S.K. Seol, T.N. Lo, C.J. Liu, C.L. Wang, C.S. Lin, Y. Hwu, C.H. Chen, L.W. Chang, J.H. Je, G. Margaritondo, Hydrogen bubbles and the growth morphology of ramified zinc by electrodeposition, J. Electrochem. Soc. 155 (2008) D400–D407. [7] N. D, N.G. Branković, V.M. Maksimović, Morphology and internal structure of copper deposits electrodeposited by the pulsating current regime in the hydrogen co-deposition range, J. Solid State Electrochem. 16 (2012) 321–328. [8] J. Niu, X. Liu, K. Xia, L. Xu, Y. Xu, X. Fang, W. Lu, Effect of electrodeposition parameters on the morphology of three-dimensional porous copper foams, Int. J. Electrochem. Sci. 10 (2015) 7331–7340. [9] P.M. Robitaille, A critical analysis of universality and Kirchhoff's law: a return to Stewart's law of thermal emission, Prog. Phys. 3 (2008) 30–35. [10] P.M. Robitaille, Blackbody radiation and the carbon particle, Prog. Phys. 3 (2008) 36–55. [11] P.M. Robitaille, Kirchhoff's law of thermal emission: 150 years, Prog. Phys. 4 (2009) 3–13. [12] P.M. Robitaille, On the equation which governs cavity radiation, Prog. Phys. 10 (2014) 126–127. [13] S. Maruyama, T. Kashiwa, H. Yugami, M. Esashi, Thermal radiation from two-dimensionally confined modes in microcavities, Appl. Phys. Lett. 79 (2001) 1393–1395. [14] S. Wijewardane, D.Y. Goswam, A review on surface control of thermal radiation by paints and coatings for new energy applications, Renew. Sust. Energ. Rev. 16 (2012) 1863–1873. [15] J.P. Huang, Y.B. Li, G.P. Song, X.J. Zhang, Y. Sun, X.D. He, S.Y. Du, Highly enhanced infrared spectral emissivity of porous CeO2 coating, Mater. Lett. 85 (2012) 57–60. [16] F.Y. Wang, L.F. Cheng, Q. Zhang, L.T. Zhang, Effect of surface morphology and densification on the infrared emissivity of C/SiC composites, Appl. Surf. Sci. 313 (2014) 670–676. [17] F.Y. Wang, L.F. Cheng, Y. N. X, J. J and L. T. Zhang, Effects of SiC shape and oxidation on the infrared emissivity properties of ZrB2–SiC ceramics, J. Alloys Compd. 625 (2015) 1–7. [18] S. Somasundaram, A.M. Pillai, A. Rajendra, A.K. Sharma, High emittance black nickel coating on copper substrate for space applications, J. Alloys Compd. 643 (2015) 263–269. [19] M.M.S.A. Bosta, K.J. Ma, Influence of electrolyte temperature on properties and infrared emissivity of MAO ceramic coating on 6061 aluminum alloy, Infrared Phys. Technol. 67 (2014) 63–72. [20] D.B. Mahadik, S. Gujjar, G.M. Gouda, H.C. Barshilia, Double layer SiO2/Al2O3 high emissivity coatings on stainless steel substrates using simple spray deposition system, Appl. Surf. Sci. 299 (2014) 6–11. [21] P.J. Hesketh, J.N. Zemel, B. Gebhart, Organ pipe radiant modes of periodic micromachined silicon surfaces, Nature 324 (1986) 549–551. [22] P.J. Hesketh, J.N. Zemel, B. Gebhart, Polarized spectral emittance from periodic
3.4.2. Effect of ceramic micro-particle type In addition to the deposition time and the concentration of ceramic micro-particles, the type of ceramic micro-particles also has a significant effect on the infrared emissivity of porous Zn-Ni composite coating. As shown in Fig. 10b, the Zn-Ni-TiO2 composite coating possesses the highest infrared emissivity of 0.91, while the other two Zn-Ni composite coatings (Zn-Ni-Al2O3 and Zn-Ni-SiO2) possess the highest infrared emissivity of 0.88. It is indicated that the infrared emissivity of Zn-Ni-TiO2 composite coating shows a higher value than that of other composite coatings. The difference of the infrared emissivity between pure Zn-Ni coating and Zn-Ni composite coating can be explained by the incorporation of particle type. Kirchhoff and Planck observed that the blackbody radiation spectrum could be obtained by inserting even very small particle of carbon within a perfectly reflecting cavity. It is clear that, given thermal equilibrium, all of the radiation which comes to fill the cavity is being produced by the carbon particle [10–12]. For the porous structure composite coating, the ceramic micro-particles are involved inside the pores. The schematic diagram of porous Zn-Ni composite coating with ceramic micro-particles inside the pores has been shown in Fig. 11. The effective emissivity of the porous coating comes from not only the pore walls of the Zn-Ni deposit but also from the ceramic micro-particles with higher infrared emissivity inside the pores. Although the Zn-Ni-TiO2 composite coating has a low degree of formation of circular porous structure, it possesses the highest emissivity of 0.91 because of the TiO2 particles with enhanced absorptivity at 3–30 μm than that of Al2O3 and SiO2 particles. 4. Conclusion Porous Zn-Ni composite coatings with high infrared emissivity were electrodeposited at a lower current density 1 A/cm2. Both the addition of ceramic micro-particles in the bath and deposition time have an obvious effect on the formation of porous structure of Zn-Ni coating. The addition of ceramic micro-particles in the bath can prevent H2 bubbles escaping from the cathode, and prolonged deposition time can increase the evolving hydrogen bubbles and Zn-Ni deposit. These effects on the bubble behavior during the electrodeposition process are beneficial to the formation of porous structure. However, the ceramic particles need to reach a certain concentration (about 20 g/L) and the deposition time must be within a certain range, otherwise, the uniform circular porous Zn-Ni coating cannot be obtained. The uniform circular porous structure containing ceramic micro-particles has a significant 99
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[23] [24] [25] [26] [27] [28] [29] [30]
micromachined surface. I. Doped silicon: the normal direction, Phys. Rev. B 37 (1988) 10795–10802. P.J. Hesketh, J.N. Zemel, B. Gebhart, Polarized spectral emittance from periodic micromachined surface. II. Doped silicon: angular variation, Phys. Rev. B 37 (1988) 10803–10813. H. Yugam, H. Sai, K. Hane, Y. Akiyama, Y. Kanamori, Spectral control of thermal emission by periodic microstructured surfaces in the near-infrared region, J. Opt. Soc. Am. A 18 (2001) 1471–1476. H. Sai, H. Yugam, Y. Akiyama, Y, Kanamori and K. Hane, Solar selective absorbers based on two-dimension W surface gratings with submicron periods for high-temperature photothermal conversion, Sol. Energy Mater. Sol. Cells 79 (2003) 35–49. I. Celanovic, D. Perreault, J. Kassakian, Resonant-cavity enhanced thermal emission, Phys. Rev. B 72 (2005) 075127–1~6. J.L. Gall, M. Olivier, J.J. Greffer, Experimental and theoretical study of reflection and coherent thermal emission by a SiC grating supporting a surface-phonon polaritons, Phys. Rev. B 55 (1997) 10105–10114. J.C. Guo, X.W. Guo, X.W. Xu, Z.C. Zhang, J. Dong, L.M. Peng, W.J. Ding, A Zn-Ni coating with both high electrical conductivity and infrared emissivity prepared by hydrogen evolution method, Appl. Surf. Sci. 402 (2017) 92–98. J.C. Guo, X.W. Guo, J.Y. Zeng, L. Nie, J. Dong, L.M. Peng, W.J. Ding, Influence of sodium dodecyl sulphate on the surface morphology and infrared emissivity of porous Ni film, Infrared Phys. Technol. 93 (2018) 162–170. H.C. Shin, M. Liu, Copper foam structure with highly porous nanostructured walls,
Chem. Mater. 16 (2004) 5460–5464. [31] J.H. Kim, R.H. Kim, H.S. Kwon, Preparation of copper foam with 3-dimensionaally interconnected spherical pore network by electrodeposition, Electrochem. Commun. 10 (2008) 1148–1151. [32] X.T. Yu, M.Y. Wang, Z. Wang, X.Z. Gong, Z.C. Guo, The structure evolution mechanism of electrodeposited porous Ni films on NH4Cl concentration, Appl. Surf. Sci. 360 (2016) 502–509. [33] N. Wang, W.C. Hu, Y.H. Lu, Y.F. Deng, X.B. Wan, Y.W. Zhang, Role of surfactants in construction of porous copper film by electrodeposition approach, Trans. IMF 89 (2011) 261–267. [34] X. Guo, X. Li, Y. Zheng, C. Lai, W. Li, B. Luo, D.X. Zhang, Effects of surfactants on high regularity of 3d porous nickel for Zn2+ adsorption application, J. Nanomater. 3 (2014) 1–9. [35] K. Tan, M.B. Tian, Q. Cai, Effect of bromide ions and polyethylene glycol on morphological control of electrodeposited copper foam, Thin Solid Films 518 (2010) 5159–5163. [36] D.H. Nam, R.H. Kim, D.W. Han, J.H. Kim, H.S. Kwon, Effects of (NH4)2SO4 and BTA on the nanostructure of copper foam prepared by electrodeposition, Electrochim. Acta 56 (2011) 9397–9405. [37] A.B. Subramaniam, C. Mejean, M. Abkarian, H.A. Stone, Microstructure, morphology, and lifetime of armored bubbles exposed to surfactants, Langmuir 22 (2006) 5986–5990.
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