- Email: [email protected]
Electroless silver plating on modified fly ash particle surface
Applied Surface Science 513 (2020) 145857
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Full Length Article
Electroless silver plating on modified fly ash particle surface ⁎
T
Ranfang Zuo , Jingyun Chen, Zhihua Han, Yang Dong, Jinder Jow National Institute of Clean-and-Low-Carbon Energy, Future Science City, Changping District, Beijing 102211, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Modified electroless plating Silver film Fly ash Properties
Ag-plated fly ash (FA) powders were prepared through modified electroless plating, which could be utilized for manufacturing conductive polymers for Electromagnetic interference (EMI) shielding applications. In order to improve the FA surface activity, alkali cleaning and coupling modification were employed. Extensive characterizations of Ag-plated FA particles were carried out by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) techniques. The mechanism of electroless Ag plating was mainly studied by using XPS. The XPS results showed that the diammonia functional group from the coupling agent adsorbed silver ions to form the N-Ag coordination bond and produce pure Ag film. In addition, electrical conductivity and electromagnetic properties were studied by Four-probe resistance tester and vector network analyzer, respectively. The results indicated that uniform and compact Ag films were formed on FA particle surface strongly after alkali cleaning and coupling modification. The electrical conductivity of the as-prepared 0.6-FA-S-Ag particles with a coated thickness of 200 nm was about 8.2 × 10−5 Ω·cm. The electromagnetic parameters and calculated reflection loss indicate that Ag-plated FA powders have no magnetic conductivity and the main contribution of electromagnetic loss comes from dielectric loss.
1. Introduction Silver powder is widely used in the field of electromagnetic interference (EMI), based on its high conductivity, high-thermal conductivity. However, the application of silver powder is limited, due to its high price, high density and easy sedimentation [1,2]. Therefore, it is of great economic value to develop a kind of conductive particle material with low density, low price and high conductivity. In order to overcome this problem, silver as the shell, core-shell structures have been suggested. The core is light in weight and the shell is conductive. FA, a by-product in power generation plants, has the advantages of low density, low price, high temperature resistance and good chemical stability, which can be used as substrate of conductive composites [3–5]. Also, FA with high sphericity in a different and desired size range can be obtained by our classification technology. Generally, the metallic layer on the surface of inorganic powders can be obtained through electroless plating or magnetron sputtering deposition techniques [6]. Magnetron sputtering is a rapid and low-temperature coating method used to prepare the coating layers with good uniformity, strong adhesion and good compactness [7–9]. But magnetron sputtering is more suitable for bulk matrix materials than for inorganic powders, such as FA powders [7]. Electroless plating is one of the simplest methods for
⁎
generating metallic films on the surface of inorganic powders. It is important to activate FA particle surface to coat the uniform metallic films, because of its no electrical and magnetic conductivity. The effect of the adhesion between the metallic coating film and substrate on the coating properties has been reported [10]. In order to achieve strong metallic films, it is necessary to improve the bonding strength between the metallic film and substrate. Traditional electroless plating has used roughening, sensitization, activation steps to modify substrate surface [11]. However, sensitizer is toxic and activator is expensive, which will be a major problem in commercialization. In this study, a modified electroless plating process was achieved by depositing silver films on FA particles to fabricate the core-shell structure particles. We employed a low-cost two step pretreatment procedure, including alkali cleaning and silane modification. The morphologies, electrical conductivity, adhesive strength, film thickness, electromagnetic properties and the electroless plating mechanism of the as-prepared samples were characterized comprehensively. In addition, the formation mechanism of the resulting conductive coating on pretreated FA powders was also discussed.
Corresponding author. E-mail address: [email protected] (R. Zuo).
https://doi.org/10.1016/j.apsusc.2020.145857 Received 5 December 2019; Received in revised form 19 February 2020; Accepted 21 February 2020 Available online 25 February 2020 0169-4332/ © 2020 Elsevier B.V. All rights reserved.
Applied Surface Science 513 (2020) 145857
R. Zuo, et al.
2. Experimental
FA (chemical composition: 41.94% SiO2, 28.63% Al2O3, 8.86% CaO, 5.75% Fe2O3, 1.19% K2O, 1.32% TiO2, 0.85% Na2O, 0.57% MgO; particle size: D50 = 13.8 μm, density: 2.3 g/cm3) was obtained from the Sanhe power plant. The silane coupling agent (NH2(CH2)2NH (CH2)3Si(OCH3)3)was supplied by Qufu chemical co. LTD; Sodium hydroxide (NaOH, AR) and ammonium hydroxide (NH3·H2O, AR) were purchased from Sinopharm group chemical reagent co. LTD; Formaldehyde (HCHO, AR) and silver nitrate (AgNO3, AR) were purchased from Tianjin Damao chemical reagent company and Tianjin Jinbo Lan fine chemical co. LTD respectively.
chemistry of FA particles during the electroless Ag plating process was studied with the help of Escalab250Xi X-ray photoelectron spectrometer (XPS). Small amount of particles were removed after each step involved in the electroless plating process for X-ray photoelectron spectroscopy (XPS) analysis to understand the mechanism of electroless Ag plating of FA particles. The adhesive strength between the Ag film and FA was evaluated by ultrasonication and energy dispersive spectroscopy (EDS) mapping was used to evaluate its surface uniformity. The Ag film thickness was measured by embedding cutting technology. The electrical conductivity was measured by Four-probe resistance tester (SB100A/20A). The electromagnetic parameters were measured in the frequency range of 0–16 GHz by vector network analyzer E5071c. X-ray fluorescence spectrometer (XRF) was used to evaluate the silver content of the metallic coating.
2.2. Modified electroless plating process
4. Results and discussion
1. Pre-treatment: Fly ash (FA) needs to be modified by alkali cleaning and silane coupling agent modification. The specific method as follows:
4.1. Morphologies of Ag-plated FA powders and their electrical conductivity
2.1. Materials and chemicals
In this study, we employed formaldehyde as reducing agent and AgNO3 as an Ag precursor. In order to control the self-decomposition of AgNO3, ammonium hydroxide was used as the complexing agent and complexed with AgNO3 to form the silver ammonia solution. Fig. 1 shows SEM images of Ag-platted FA composites prepared via a chemical reduction of the Ag precursor in the presence of formaldehyde. It can be clearly observed that much free Ag particles are produced and agglomerated during electroless silver plating on untreated FA particle surfaces, as shown in Fig. 1(a). The as-received FA-Ag powders have poor uniformity, compactness and part of FA-Ag powders are not plated with Ag, exposed seriously. After alkali cleaning, free Ag particles decrease obviously and all particles are observed to be platted compactly, which could be attributed to the wettability of FA improved by alkali cleaning, as shown in Fig. 1(b) and Fig. 1(c). It also shows poor coating efficiency and Ag agglomerates on the 0.6-FA-Ag and 1.2-FA-Ag surface, resulting in poor economic benefit. Fig. 1(d) and Fig. 1(e) illustrate the morphologies of 0.6-FA-S-Ag and 1.2-FA-S-Ag, which were prepared after alkali cleaning and coupling treatment. It clearly indicates that all pretreated FA particles are plated with Ag, without free Ag produced, and the good quality Ag films are obtained. These Ag films have good uniformity, compactness and smooth morphology, which could be attributed to the fact that double amino groups (eNH2, eNHe) absorb silver ammonia complex ions and form N-Ag coordination bond after the formaldehyde reduction, so that silver particles are preferentially deposited on the amino-silane treated FA surface and closely bounded to FA [12]. FA-S-Ag powders were obtained only with coupling treatment and the morphology is shown in Fig. 1(f). It can be seen that FA-S-Ag composite have a thin silver coating, and a large area of FA surface is exposed, which may be caused by the uneven distribution of coupling agent on FA surface after silane coupling agent modification. The results indicate that the alkali cleaning and coupling treatment are both important to electroless plating on FA. The electrical resistivity and Ag content of Ag plated FA powders were measured by Four-probe resistance tester and XRF respectively, as listed in Table 2. The Ag content of FA-Ag is up to 63.21%, corresponding to the electrical resistivity of 2.06 × 10−4 Ω·cm. Ag contents of 0.6-FA-Ag and 1.2-FA-Ag are relatively low, with 34.65%, 55.60% respectively, and their electrical resistivity are 1.25 × 10−3 Ω·cm, 1.83 × 10−4 Ω·cm respectively. The Ag contents of 0.6-FA-S-Ag and 1.2-FA-S-Ag are 46.61%, 54.18% respectively, less than that of FA-Ag, while their relative electrical resistivity are reduced by an order of magnitude, only 8.2 × 10−5 Ω·cm and 5.37 × 10−5 Ω·cm, respectively. The results indicate that the electrical resistivity is not only related to the silver content, but also related to the distribution of silver. However, the Ag content of FA-S-Ag is only 32.11%, nearly half of FA-Ag and its electrical resistivity is higher than FA-Ag by an order of magnitude (4.11 × 10−3 Ω·cm). According to our market research,
Alkali cleaning: Fly ash (FA) was dispersed in the NaOH solution with concentration of 0.6 mol/L and 1.2 mol/L, respectively for stirring at room temperature and then 0.6-FA and 1.2-FA were obtained by centrifuging and drying. Silane modification: 0.6-FA, 1.2-FA and FA were dispersed in the coupling agent solution for stirring respectively and then 0.6-FA-S, 1.2FA-S and FA-S were obtained by centrifuging and drying. 2. Electroless plating: silver plating FA powders were prepared by modified electroless plating and the composition of the basic baths and its operating conditions were given in Table 1. For the electroless silver deposition, AgNO3 and HCHO were used as the source of Ag and reducing agent, respectively·NH3·H2O was used as complexing agent to inhibit the self-decomposition of AgNO3. The electroless silver plating process was conducted as follows: (1) NH3·H2O was dispersed in deionized water (NH3·H2O: H2O = 1: 10) to obtain the NH3·H2O solution. (2) Solution A: AgNO3 was dispersed in deionized water and then dropped NH3·H2O solution with agitation to have pH of 10–11. (3) Solution B: Added untreated and pretreated FA particles into solution A and stirred for 15–20 min to obtain a good mixture of solution A and FA. (4) Solution C: HCHO was dispersed in ethanol (HCHO: ethanol = 1: 45). (5) Solution B and solution C were mixed together and stirring for 30 min at room temperature, then silver plating FA were obtained by washing and drying. 3. Characterization FEI Nova Nano scanning electron microscope (SEM) 450 was used to analyze the surface morphology, the film uniformity and compactness of FA and silver plating FA powders. The variation in the surface Table 1 Compositions and operating conditions for preparing silver plating FA powders. Compositions
Content
AgNO3 NH3·H2O HCHO FA
10–20 g/L 15–40 ml/L 10–30 ml/L 5–15 g/L
Conditions
Scope
pH Temperature
10–11 18–25 °C
2
Applied Surface Science 513 (2020) 145857
R. Zuo, et al.
Fig. 1. SEM images of Ag-plated FA composites: (a) FA-Ag, (b) 0.6-FA-Ag, (c) 1.2-FA-Ag, (d) 0.6-FA-S-Ag, (e) 1.2-FA-S-Ag, (f) FA-S-Ag.
indentation /scratch etc., used to test the adhesive strength between substrates and films generally [13–16]. The Ag-plated FA powder prepared in this study is mainly used as filler for rubber, resin and other electromagnetic shielding materials (EMI). The process mainly involves mechanical force mixing. Therefore, it is most suitable to use ultrasonic oscillation method to test the adhesive strength the Ag film on the FA particle surface. In Fig. 2, it shows the morphologies and EDS mapping of FA-Ag and 0.6-FA-S-Ag powders after sonicating 60 min at room temperature. It can be clearly seen that there are still a lot of free Ag existing, as shown in Fig. 2(a). Fig. 2(b) is the morphology of FA-Ag at high magnification and it is smooth, uniform and compact. Also, EDS
different applications require different conductive properties of conductive fillers. The conductive filler with low electrical resistivity (≥1.0 × 10−3 Ω·cm) can be used in the civil applications, but not in the military applications. Ag-plated FA powders with a wide range of conductivity can be used as conductive fillers in the fields of rubber, coating, fabric for both civil and military applications.
4.2. Adhesive strength between Ag and FA There are about five methods, including ultrasonic oscillation, cold and hot cycle, friction marks, PP composite powder fracture, Table 2 Electrical resistivity of Ag-plated FA composite. Samples
FA-Ag
0.6-FA-Ag
1.2-FA-Ag
0.6-FA-S-Ag
1.2-FA-S-Ag
FA-S-Ag
Ag (%) Electrical resistivity (Ω·cm)
63.21 2.06 × 10−4
34.65 1.25 × 10−3
55.60 1.83 × 10−4
46.61 8.2 × 10−5
54.18 5.37 × 10−5
32.11 4.11 × 10−3
3
Applied Surface Science 513 (2020) 145857
R. Zuo, et al.
Fig. 2. SEM images and EDS mapping of Ag-plated FA particles after sonicating 60 min at room temperature: (a), (b), (C): FA-Ag, (d), (e), (f): 0.6-FA-S-Ag.
4.4. Electromagnetic parameters of Ag-plated FA powders
analyses indicate that it is 100% Ag totally, which can be attributed to its falling off from FA-Ag after sonicating. Fig. 2(c) shows the EDS mapping of FA-Ag at high magnification and it can be seen clearly that the detached Ag remains intact. Fig. 2(d) shows the morphology of 0.6-FA-S-Ag particle and it can be observed clearly that all FA particles are still plated with Ag, without falling off of Ag after sonicating 60 min at room temperature. The morphology and EDS mapping of 0.6-FA-S-Ag particles are shown in Fig. 2(e) and Fig. 2(f) at high magnification, respectively. After the ultrasonic oscillation, Ag film on the FA particle surface is still uniform, compact and smooth, and there is no obvious change as compared with 0.6-FA-S-Ag particles before sonicating (Fig. 1(d)). As shown in Fig. 2(f), no detached Ag can be observed, which indicates that Ag film is strongly coated on the fly ash (FA) particle surface.
The electromagnetic parameters of the functional composites are analyzed in the frequency range of 0–16 GHz by vector network analyzer E5071c. The samples were prepared by mixing each sample with paraffin wax at 30% weight fraction. Fig. 4(a) and (b) show the real permittivity (ε′) and the imaginary permittivity (ε″) of the samples containing Ag-plated FA powders and the commercial conductive powders. As shown in Fig. 4, sample #1 and sample #2 are 0.6-FA-S-Ag powders prepared with different concentrations of AgNO3, so that their Ag contents are 46.6% and 31%, respectively. Sample #3 is the sample containing the conductive powders purchased from market. The real parts ε′ of three samples, are almost constant at around 5.2, 4.2 and 3.5, respectively, whereas the imaginary parts ε″ of three samples are almost the same, around 0.1. Meanwhile, Fig. 4(c) and (d) show the real permeability (μ′) and imaginary permeability (μ″) of the samples containing the Ag-plated FA powders. Similar to the real part of the complex permittivity, the real part and imaginary part of the complex permeability also remain constant with the value of 1 and 0 at tested frequencies for these three samples, respectively, which means that the three samples have no magnetic conductivity. Therefore, the main contribution of electromagnetic loss comes from dielectric loss. For further investigation of microwave absorption, the reflection loss of Ag-plated FA powder is calculated. The reflection loss curves are shown in Fig. 5. The reflection loss of a microwave absorbing layer is given as follows [17]:
4.3. Thickness of Ag film The diamond knife cutting technology was used to measure the thickness of Ag film plated on the FA particle surface. Our lab-made 0.6FA-S-Ag powders and conductive powders purchased from market were embedded into resin and then cut under microscope by the same diamond knife. Fig. 3 shows the morphologies of 0.6-FA-S-Ag and commercial products after cutting. It can be seen clearly that it consists of Si, Al, Ca and Ag, which comes from FA except Ag, as shown in Fig. 3(a). Fig. 3(b) shows that the Ag film with red dots and the thickness of the Ag film is uniform, about 200 nm, as shown in Fig. 3 (c) and Fig. 3(d). The Ag film is firmly coated on the FA particle surface without any cracks after cutting, which further indicates that the adhesive strength between the Ag film and modified FA particle surface is strong enough, consistent with the result of sonicating, as shown in Fig. 2. Fig. 3(e), (f), (g), (h) show the morphologies of products purchased from market. The thickness of the Ag film is uneven, about 170 nm. However, cracks are observed and may beproduced during cutting, as shown in Fig. 3(g) and Fig. 3(h), which means that the adhesive strength is poor.
R = 20 lg |Γ| = 20 lg
Z in = Z 0
Zin − Z0 Zin + Zn
μr j2π fd tan h ⎡ εr μ r ⎤ εr ⎦ ⎣ c
(1)
(2)
where Zin is the normalized input impedance; Z0 is the impedance under vacuum (its value is 1); c is the velocity of electromagnetic waves in free space; f is the microwave frequency; and d is the thickness of the absorbing layer. Therefore, microwave propagation in electromagnetic media is largely determined by the complex relative permeability and permittivity of the absorbing materials. All calculated values were 4
Applied Surface Science 513 (2020) 145857
R. Zuo, et al.
Fig. 3. The thickness of Ag film: (a), (b), (C), (d): 0.6-FA-S-Ag, (e), (f), (g), (h): commercial products.
4.5. The mechanism of electroless Ag plating FA
predicted based on a constant thickness of d, in the range of 0.5–3.0 mm. It is obvious that the microwave absorbing properties of microspheres increase substantially with the increase of thickness (d). As reported in the literature, the effective reflectivity of Rf should less than −10 dB. However, the reflectivity of all three samples is from −4 dB to −2.5 dB, not less than −10 dB, which further illustrates that the three samples are nonmagnetic materials.
XPS was used for the surface quantitative analyses of FA before and after aminosilane modification. The result (Fig. 6a) showed that the untreated FA contained trace amount of N element, with an N/Si atomic ratio of 0.016. For aminosilane modified fly ash (referred to as FA-S), characteristic peak of N element was detected on the surface of fly ash,
Fig. 4. Permittivity and permeability curves of Ag-plated FA composite: (a) Real permittivity, (b) Imaginary permittivity, (c) Real permeability, (d) Imaginary permeability. 5
Applied Surface Science 513 (2020) 145857
R. Zuo, et al.
The XPS fitting results of 0.6-FA-S sample showed that there were two chemical states of N1s spectra, as shown in Fig. 6b: 399.1 eV (eNH2) and −401.2 eV (eNHe), which corresponded to two amino groups of amino silane. The 0.6-FA-S sample was then plated with Ag, and Fig. 6c showed that the silver film was all metallic silver. There was an obvious satellite peak near 372 eV, which was attributed to metallic silver. XPS is a surface analysis instrument with a detection depth of less than 10 nm, so Ag-plated FA conditions were changed to reduce the thickness of silver plating layer so that a bond between N and Ag can be easily detected by XPS. Reducing the concentration of AgNO3 solution and the reaction time of silver plating were used to reduce the thickness of silver coating. Two samples of silver plating for 2 min and 5 min were taken for the XPS tests. The XPS N1s fitting spectra (Fig. 6d, e) showed that the N1s peak position shifted to 401.6 eV and 399.6 eV, respectively, which were relatively higher than that of silane modified FA. While the Ag3d5 peaks of 2 min and 5 min silver plating samples were 368.05 eV and 368.10 eV, respectively, as shown in Fig. 6f. Compared with the elemental silver 368.2 eV, the Ag3d5 peak shifted to a lower binding energy, illustrating that the coordination bonding of NAg did occur[10,18], which could be considered as the main reason for the strong adhesive strength between the silver plating layer and the fly ash particle surface. The coordination bond increased the bonding strength between the silver-plated layer and the FA surface, and the newly formed silver particles were preferably adsorbed and aggregated by the silver on the surface of the FA substrate through the metal interaction, thus forming a uniform and compact silver film. 5. Conclusion The alkali cleaning and aminosilane pretreatment process is very critical for electroless Ag plating on the FA particle surface. The mechanism of electroless Ag plating FA is studied by XPS, which involves modification and electroless plating. XPS results indicate that aminosilane coupling agent is successfully bonded to the surface of FA particles after alkali cleaning and provides the diammonia functional group used to adsorb silver ions and form the N-Ag coordination bond. After Ag plating, the characteristic peaks of N1s and Ag3d shift accordingly, indicating the formation of N-Ag coordination bond. Also, the peaks of diammonia (eNH2, eNHe) are shifted to higher binding energy after peak-differentiating and imitating of N1s, which further indicates that diammonia functional group can adsorb silver ions. After sonicating and cutting, no observation of detached Ag or cracks indicates that the adhesive strength between Ag film and modified FA particle surface is strong enough, much better than that of products purchased from market. The as-prepared Ag plating FA powder (0.6-FAS-Ag) has good electrical conductivity, with electrical resistivity of 8.2 × 10−5 Ω·cm and a thickness of 200 nm. The electromagnetic parameters and calculated reflection loss also indicate that Ag-plated FA powders have no magnetic conductivity and the main contribution of electromagnetic loss comes from dielectric loss. Fig. 5. Calculated reflection loss curves of Ag-plated FA composite: (a) #1, (b) #2, (c) #3.
CRediT authorship contribution statement and the N/Si atomic ratio increased to 0.086, about 4.5 times higher than that of pure FA, indicating that the FA surface was successfully coated with aminosilane. When FA was treated with two different concentrations of the NaOH solution and silane coupling agent, the N/ Si atomic ratio was increased from 0.112 (0.6-FA-S) to 0.159 (1.2-FA-S) with the concentration of NaOH solution increased from 0.6 mol/L to 1.2 mol/L respectively, which indicated that more aminosilane was coated on the FA surface with increasing of alkali concentration. The results showed that FA surface was more easily coated after alkaline washing and aminosilane treatment. Meanwhile, with the increase of the aminosilane concentration, the surface uniformity of coated FA increased, so the surface uniformity of silver plating film was improved.
Ranfang Zuo: Conceptualization, Methodology, Formal analysis, Investigation, Resources, Writing - original draft, Writing - review & editing. Jingyun Chen: Formal analysis, Resources. Zhihua Han: Formal analysis, Resources. Yang Dong: Supervision, Data curation. Jinder Jow: Supervision, Project administration, Funding acquisition.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. 6
Applied Surface Science 513 (2020) 145857
R. Zuo, et al.
Fig. 6. High-resolution XPS spectra: (a) N1s for FA, FA-S, 0.6-FA-S, 1.2-FA-S, (b) N1s for 0.6-FA-S, (c) Ag3d for 0.6-FA-S-Ag, (d) N1s for 0.6-FA-S, 0.6-FA-S-2 min-Ag, 0.6-FA-S-5 min-Ag, (e) N1s for 0.6-FA-S-2 min-Ag, (f) Ag3d for 0.6-FA-S-Ag, 0.6-FA-S-2 min-Ag, 0.6-FA-S-5 min-Ag.
References
Acknowledgements The authors gratefully acknowledge financial support from National Institute of Clean-and-Low-Carbon Energy.
[1] W. Kim, S. Kim, Preparation of Ag-coated hollow microspheres via electroless plating for application in lightweight microwave absorbers, Appl. Surf. Sci. 329 (2015) 219–222. [2] X.G. Cao, H.Y. Zhang, Investigation into conductivity of silver-coated cenosphere composites prepared by a modified electroless process, Appl. Surf. Sci. 264 (2013) 756–760.
7
Applied Surface Science 513 (2020) 145857
R. Zuo, et al.
[11] J. Pang, Q. Li, B. Wang, D. Tao, X. Xu, W. Wang, J. Zhai, Preparation and characterization of electroless Ni-Fe-P alloy films on fly ash cenospheres, Powder Technol. 226 (2012) 246–252. [12] M.R.T. Doidjo, L. Belec, E. Aragon, Y. Joliff, L. Lanarde, M. Meyer, M. Bonnaudet, F.X. Perrin, Influence of silane-based treatment on adherence and wet durability of fusion bonded epoxy/steel joints, Prog. Org. Coat. 76 (2013) 1765–1772. [13] W. Hou, G. Pan, H. Guan, N. Chen, Electroless silver plating on surface of carbon fiber, Mater. Prot. 40 (2007) 45–47. [14] G. Zhu, J. Zhang, H. Zhang, A study of electroless silver plating with Pd-free activation on cenosphere, Electroplat. Pollut. Control 32 (2012) 32–35. [15] S. Hu, C. Zhang, M. Zhao, H. Chen, Electroless silver plating activated with thermoalkaline solution on fly ash cenosphere surface, Mater. Sci. and Eng. Powder Metall. 15 (2010) 79–83. [16] X. Zhu, Y. Mi, N. Hu, J. He, Discussion on the evaluation method of membrane base bond strength, China Surf. Eng. 4 (2002) 28–31. [17] X. Li, Y. Duan, Y. Zhao, L. Zhun, Effects of heat treatment on magnetic properties of Co−Fe-plated hollow ceramic microspheres, Prog. Nat. Sci. Mater. 21 (2011) 392–400. [18] J. Ou, B. Wu, M. Xue, F. Wang, Silver ions anchored to fabric via coordination: Evaluation on washing durability and antibacterial activity, Mater. Lett. 237 (2019) 134–136.
[3] Q. Li, J. Pang, B. Wang, D. Tao, X. Xu, L. Sun, J. Zhai, Preparation, characterization and microwave absorption properties of barium-ferrite-coated fly-ash cenospheres, Adv. Powder Technol. 24 (2013) 288–294. [4] Z. Aixiang, X. Weihao, X. Jian, Electroless Ni-P coating of cenospheres using silver nitrate activator, Surf. Coat. Tech. 197 (2005) 142–147. [5] S. Shukla, S. Seal, J. Akesson, R. Oder, R. Carter, Z. Rahman, Study of mechanism of electroless copper coating of fly-ash cenosphere particles, Appl. Surf. Sci. 181 (2001) 35–50. [6] Y. Hu, H. Zhang, F. Li, X. Cheng, T. Chen, Investigation into electrical conductivity and electromagnetic interference shielding effectiveness of silicone rubber filled with Ag-coated cenosphere particles, Polym. Test. 29 (2010) 609–612. [7] X. Yu, Z. Shen, Z. Xu, Preparation and characterization of Ag-coated cenospheres by magnetron sputtering method, Nucl. Instrum. Meth. B 265 (2007) 637–640. [8] X. Yu, Z. Xu, Z. Shen, Metal copper films deposited on cenosphere particles by magnetron sputtering method, J. Phys. D: Appl. Phys. 40 (2007) 2894–2898. [9] X. Yu, Z. Shen, The electromagnetic shielding of Ni films deposited on cenosphere particles by magnetron sputtering method, J. Magn. Magn. Mater. 321 (2009) 2890–2895. [10] W. Li, Y. Chen, S. Wu, J. Zhang, H. Wang, D. Zeng, C. Xie, Preparing high-adhesion silver coating on APTMS modified polyethylene with excellent anti-bacterial performance, Appl. Surf. Sci. 436 (2018) 117–124.
8
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
Full Length Article
Electroless silver plating on modified fly ash particle surface ⁎
T
Ranfang Zuo , Jingyun Chen, Zhihua Han, Yang Dong, Jinder Jow National Institute of Clean-and-Low-Carbon Energy, Future Science City, Changping District, Beijing 102211, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Modified electroless plating Silver film Fly ash Properties
Ag-plated fly ash (FA) powders were prepared through modified electroless plating, which could be utilized for manufacturing conductive polymers for Electromagnetic interference (EMI) shielding applications. In order to improve the FA surface activity, alkali cleaning and coupling modification were employed. Extensive characterizations of Ag-plated FA particles were carried out by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) techniques. The mechanism of electroless Ag plating was mainly studied by using XPS. The XPS results showed that the diammonia functional group from the coupling agent adsorbed silver ions to form the N-Ag coordination bond and produce pure Ag film. In addition, electrical conductivity and electromagnetic properties were studied by Four-probe resistance tester and vector network analyzer, respectively. The results indicated that uniform and compact Ag films were formed on FA particle surface strongly after alkali cleaning and coupling modification. The electrical conductivity of the as-prepared 0.6-FA-S-Ag particles with a coated thickness of 200 nm was about 8.2 × 10−5 Ω·cm. The electromagnetic parameters and calculated reflection loss indicate that Ag-plated FA powders have no magnetic conductivity and the main contribution of electromagnetic loss comes from dielectric loss.
1. Introduction Silver powder is widely used in the field of electromagnetic interference (EMI), based on its high conductivity, high-thermal conductivity. However, the application of silver powder is limited, due to its high price, high density and easy sedimentation [1,2]. Therefore, it is of great economic value to develop a kind of conductive particle material with low density, low price and high conductivity. In order to overcome this problem, silver as the shell, core-shell structures have been suggested. The core is light in weight and the shell is conductive. FA, a by-product in power generation plants, has the advantages of low density, low price, high temperature resistance and good chemical stability, which can be used as substrate of conductive composites [3–5]. Also, FA with high sphericity in a different and desired size range can be obtained by our classification technology. Generally, the metallic layer on the surface of inorganic powders can be obtained through electroless plating or magnetron sputtering deposition techniques [6]. Magnetron sputtering is a rapid and low-temperature coating method used to prepare the coating layers with good uniformity, strong adhesion and good compactness [7–9]. But magnetron sputtering is more suitable for bulk matrix materials than for inorganic powders, such as FA powders [7]. Electroless plating is one of the simplest methods for
⁎
generating metallic films on the surface of inorganic powders. It is important to activate FA particle surface to coat the uniform metallic films, because of its no electrical and magnetic conductivity. The effect of the adhesion between the metallic coating film and substrate on the coating properties has been reported [10]. In order to achieve strong metallic films, it is necessary to improve the bonding strength between the metallic film and substrate. Traditional electroless plating has used roughening, sensitization, activation steps to modify substrate surface [11]. However, sensitizer is toxic and activator is expensive, which will be a major problem in commercialization. In this study, a modified electroless plating process was achieved by depositing silver films on FA particles to fabricate the core-shell structure particles. We employed a low-cost two step pretreatment procedure, including alkali cleaning and silane modification. The morphologies, electrical conductivity, adhesive strength, film thickness, electromagnetic properties and the electroless plating mechanism of the as-prepared samples were characterized comprehensively. In addition, the formation mechanism of the resulting conductive coating on pretreated FA powders was also discussed.
Corresponding author. E-mail address: [email protected] (R. Zuo).
https://doi.org/10.1016/j.apsusc.2020.145857 Received 5 December 2019; Received in revised form 19 February 2020; Accepted 21 February 2020 Available online 25 February 2020 0169-4332/ © 2020 Elsevier B.V. All rights reserved.
Applied Surface Science 513 (2020) 145857
R. Zuo, et al.
2. Experimental
FA (chemical composition: 41.94% SiO2, 28.63% Al2O3, 8.86% CaO, 5.75% Fe2O3, 1.19% K2O, 1.32% TiO2, 0.85% Na2O, 0.57% MgO; particle size: D50 = 13.8 μm, density: 2.3 g/cm3) was obtained from the Sanhe power plant. The silane coupling agent (NH2(CH2)2NH (CH2)3Si(OCH3)3)was supplied by Qufu chemical co. LTD; Sodium hydroxide (NaOH, AR) and ammonium hydroxide (NH3·H2O, AR) were purchased from Sinopharm group chemical reagent co. LTD; Formaldehyde (HCHO, AR) and silver nitrate (AgNO3, AR) were purchased from Tianjin Damao chemical reagent company and Tianjin Jinbo Lan fine chemical co. LTD respectively.
chemistry of FA particles during the electroless Ag plating process was studied with the help of Escalab250Xi X-ray photoelectron spectrometer (XPS). Small amount of particles were removed after each step involved in the electroless plating process for X-ray photoelectron spectroscopy (XPS) analysis to understand the mechanism of electroless Ag plating of FA particles. The adhesive strength between the Ag film and FA was evaluated by ultrasonication and energy dispersive spectroscopy (EDS) mapping was used to evaluate its surface uniformity. The Ag film thickness was measured by embedding cutting technology. The electrical conductivity was measured by Four-probe resistance tester (SB100A/20A). The electromagnetic parameters were measured in the frequency range of 0–16 GHz by vector network analyzer E5071c. X-ray fluorescence spectrometer (XRF) was used to evaluate the silver content of the metallic coating.
2.2. Modified electroless plating process
4. Results and discussion
1. Pre-treatment: Fly ash (FA) needs to be modified by alkali cleaning and silane coupling agent modification. The specific method as follows:
4.1. Morphologies of Ag-plated FA powders and their electrical conductivity
2.1. Materials and chemicals
In this study, we employed formaldehyde as reducing agent and AgNO3 as an Ag precursor. In order to control the self-decomposition of AgNO3, ammonium hydroxide was used as the complexing agent and complexed with AgNO3 to form the silver ammonia solution. Fig. 1 shows SEM images of Ag-platted FA composites prepared via a chemical reduction of the Ag precursor in the presence of formaldehyde. It can be clearly observed that much free Ag particles are produced and agglomerated during electroless silver plating on untreated FA particle surfaces, as shown in Fig. 1(a). The as-received FA-Ag powders have poor uniformity, compactness and part of FA-Ag powders are not plated with Ag, exposed seriously. After alkali cleaning, free Ag particles decrease obviously and all particles are observed to be platted compactly, which could be attributed to the wettability of FA improved by alkali cleaning, as shown in Fig. 1(b) and Fig. 1(c). It also shows poor coating efficiency and Ag agglomerates on the 0.6-FA-Ag and 1.2-FA-Ag surface, resulting in poor economic benefit. Fig. 1(d) and Fig. 1(e) illustrate the morphologies of 0.6-FA-S-Ag and 1.2-FA-S-Ag, which were prepared after alkali cleaning and coupling treatment. It clearly indicates that all pretreated FA particles are plated with Ag, without free Ag produced, and the good quality Ag films are obtained. These Ag films have good uniformity, compactness and smooth morphology, which could be attributed to the fact that double amino groups (eNH2, eNHe) absorb silver ammonia complex ions and form N-Ag coordination bond after the formaldehyde reduction, so that silver particles are preferentially deposited on the amino-silane treated FA surface and closely bounded to FA [12]. FA-S-Ag powders were obtained only with coupling treatment and the morphology is shown in Fig. 1(f). It can be seen that FA-S-Ag composite have a thin silver coating, and a large area of FA surface is exposed, which may be caused by the uneven distribution of coupling agent on FA surface after silane coupling agent modification. The results indicate that the alkali cleaning and coupling treatment are both important to electroless plating on FA. The electrical resistivity and Ag content of Ag plated FA powders were measured by Four-probe resistance tester and XRF respectively, as listed in Table 2. The Ag content of FA-Ag is up to 63.21%, corresponding to the electrical resistivity of 2.06 × 10−4 Ω·cm. Ag contents of 0.6-FA-Ag and 1.2-FA-Ag are relatively low, with 34.65%, 55.60% respectively, and their electrical resistivity are 1.25 × 10−3 Ω·cm, 1.83 × 10−4 Ω·cm respectively. The Ag contents of 0.6-FA-S-Ag and 1.2-FA-S-Ag are 46.61%, 54.18% respectively, less than that of FA-Ag, while their relative electrical resistivity are reduced by an order of magnitude, only 8.2 × 10−5 Ω·cm and 5.37 × 10−5 Ω·cm, respectively. The results indicate that the electrical resistivity is not only related to the silver content, but also related to the distribution of silver. However, the Ag content of FA-S-Ag is only 32.11%, nearly half of FA-Ag and its electrical resistivity is higher than FA-Ag by an order of magnitude (4.11 × 10−3 Ω·cm). According to our market research,
Alkali cleaning: Fly ash (FA) was dispersed in the NaOH solution with concentration of 0.6 mol/L and 1.2 mol/L, respectively for stirring at room temperature and then 0.6-FA and 1.2-FA were obtained by centrifuging and drying. Silane modification: 0.6-FA, 1.2-FA and FA were dispersed in the coupling agent solution for stirring respectively and then 0.6-FA-S, 1.2FA-S and FA-S were obtained by centrifuging and drying. 2. Electroless plating: silver plating FA powders were prepared by modified electroless plating and the composition of the basic baths and its operating conditions were given in Table 1. For the electroless silver deposition, AgNO3 and HCHO were used as the source of Ag and reducing agent, respectively·NH3·H2O was used as complexing agent to inhibit the self-decomposition of AgNO3. The electroless silver plating process was conducted as follows: (1) NH3·H2O was dispersed in deionized water (NH3·H2O: H2O = 1: 10) to obtain the NH3·H2O solution. (2) Solution A: AgNO3 was dispersed in deionized water and then dropped NH3·H2O solution with agitation to have pH of 10–11. (3) Solution B: Added untreated and pretreated FA particles into solution A and stirred for 15–20 min to obtain a good mixture of solution A and FA. (4) Solution C: HCHO was dispersed in ethanol (HCHO: ethanol = 1: 45). (5) Solution B and solution C were mixed together and stirring for 30 min at room temperature, then silver plating FA were obtained by washing and drying. 3. Characterization FEI Nova Nano scanning electron microscope (SEM) 450 was used to analyze the surface morphology, the film uniformity and compactness of FA and silver plating FA powders. The variation in the surface Table 1 Compositions and operating conditions for preparing silver plating FA powders. Compositions
Content
AgNO3 NH3·H2O HCHO FA
10–20 g/L 15–40 ml/L 10–30 ml/L 5–15 g/L
Conditions
Scope
pH Temperature
10–11 18–25 °C
2
Applied Surface Science 513 (2020) 145857
R. Zuo, et al.
Fig. 1. SEM images of Ag-plated FA composites: (a) FA-Ag, (b) 0.6-FA-Ag, (c) 1.2-FA-Ag, (d) 0.6-FA-S-Ag, (e) 1.2-FA-S-Ag, (f) FA-S-Ag.
indentation /scratch etc., used to test the adhesive strength between substrates and films generally [13–16]. The Ag-plated FA powder prepared in this study is mainly used as filler for rubber, resin and other electromagnetic shielding materials (EMI). The process mainly involves mechanical force mixing. Therefore, it is most suitable to use ultrasonic oscillation method to test the adhesive strength the Ag film on the FA particle surface. In Fig. 2, it shows the morphologies and EDS mapping of FA-Ag and 0.6-FA-S-Ag powders after sonicating 60 min at room temperature. It can be clearly seen that there are still a lot of free Ag existing, as shown in Fig. 2(a). Fig. 2(b) is the morphology of FA-Ag at high magnification and it is smooth, uniform and compact. Also, EDS
different applications require different conductive properties of conductive fillers. The conductive filler with low electrical resistivity (≥1.0 × 10−3 Ω·cm) can be used in the civil applications, but not in the military applications. Ag-plated FA powders with a wide range of conductivity can be used as conductive fillers in the fields of rubber, coating, fabric for both civil and military applications.
4.2. Adhesive strength between Ag and FA There are about five methods, including ultrasonic oscillation, cold and hot cycle, friction marks, PP composite powder fracture, Table 2 Electrical resistivity of Ag-plated FA composite. Samples
FA-Ag
0.6-FA-Ag
1.2-FA-Ag
0.6-FA-S-Ag
1.2-FA-S-Ag
FA-S-Ag
Ag (%) Electrical resistivity (Ω·cm)
63.21 2.06 × 10−4
34.65 1.25 × 10−3
55.60 1.83 × 10−4
46.61 8.2 × 10−5
54.18 5.37 × 10−5
32.11 4.11 × 10−3
3
Applied Surface Science 513 (2020) 145857
R. Zuo, et al.
Fig. 2. SEM images and EDS mapping of Ag-plated FA particles after sonicating 60 min at room temperature: (a), (b), (C): FA-Ag, (d), (e), (f): 0.6-FA-S-Ag.
4.4. Electromagnetic parameters of Ag-plated FA powders
analyses indicate that it is 100% Ag totally, which can be attributed to its falling off from FA-Ag after sonicating. Fig. 2(c) shows the EDS mapping of FA-Ag at high magnification and it can be seen clearly that the detached Ag remains intact. Fig. 2(d) shows the morphology of 0.6-FA-S-Ag particle and it can be observed clearly that all FA particles are still plated with Ag, without falling off of Ag after sonicating 60 min at room temperature. The morphology and EDS mapping of 0.6-FA-S-Ag particles are shown in Fig. 2(e) and Fig. 2(f) at high magnification, respectively. After the ultrasonic oscillation, Ag film on the FA particle surface is still uniform, compact and smooth, and there is no obvious change as compared with 0.6-FA-S-Ag particles before sonicating (Fig. 1(d)). As shown in Fig. 2(f), no detached Ag can be observed, which indicates that Ag film is strongly coated on the fly ash (FA) particle surface.
The electromagnetic parameters of the functional composites are analyzed in the frequency range of 0–16 GHz by vector network analyzer E5071c. The samples were prepared by mixing each sample with paraffin wax at 30% weight fraction. Fig. 4(a) and (b) show the real permittivity (ε′) and the imaginary permittivity (ε″) of the samples containing Ag-plated FA powders and the commercial conductive powders. As shown in Fig. 4, sample #1 and sample #2 are 0.6-FA-S-Ag powders prepared with different concentrations of AgNO3, so that their Ag contents are 46.6% and 31%, respectively. Sample #3 is the sample containing the conductive powders purchased from market. The real parts ε′ of three samples, are almost constant at around 5.2, 4.2 and 3.5, respectively, whereas the imaginary parts ε″ of three samples are almost the same, around 0.1. Meanwhile, Fig. 4(c) and (d) show the real permeability (μ′) and imaginary permeability (μ″) of the samples containing the Ag-plated FA powders. Similar to the real part of the complex permittivity, the real part and imaginary part of the complex permeability also remain constant with the value of 1 and 0 at tested frequencies for these three samples, respectively, which means that the three samples have no magnetic conductivity. Therefore, the main contribution of electromagnetic loss comes from dielectric loss. For further investigation of microwave absorption, the reflection loss of Ag-plated FA powder is calculated. The reflection loss curves are shown in Fig. 5. The reflection loss of a microwave absorbing layer is given as follows [17]:
4.3. Thickness of Ag film The diamond knife cutting technology was used to measure the thickness of Ag film plated on the FA particle surface. Our lab-made 0.6FA-S-Ag powders and conductive powders purchased from market were embedded into resin and then cut under microscope by the same diamond knife. Fig. 3 shows the morphologies of 0.6-FA-S-Ag and commercial products after cutting. It can be seen clearly that it consists of Si, Al, Ca and Ag, which comes from FA except Ag, as shown in Fig. 3(a). Fig. 3(b) shows that the Ag film with red dots and the thickness of the Ag film is uniform, about 200 nm, as shown in Fig. 3 (c) and Fig. 3(d). The Ag film is firmly coated on the FA particle surface without any cracks after cutting, which further indicates that the adhesive strength between the Ag film and modified FA particle surface is strong enough, consistent with the result of sonicating, as shown in Fig. 2. Fig. 3(e), (f), (g), (h) show the morphologies of products purchased from market. The thickness of the Ag film is uneven, about 170 nm. However, cracks are observed and may beproduced during cutting, as shown in Fig. 3(g) and Fig. 3(h), which means that the adhesive strength is poor.
R = 20 lg |Γ| = 20 lg
Z in = Z 0
Zin − Z0 Zin + Zn
μr j2π fd tan h ⎡ εr μ r ⎤ εr ⎦ ⎣ c
(1)
(2)
where Zin is the normalized input impedance; Z0 is the impedance under vacuum (its value is 1); c is the velocity of electromagnetic waves in free space; f is the microwave frequency; and d is the thickness of the absorbing layer. Therefore, microwave propagation in electromagnetic media is largely determined by the complex relative permeability and permittivity of the absorbing materials. All calculated values were 4
Applied Surface Science 513 (2020) 145857
R. Zuo, et al.
Fig. 3. The thickness of Ag film: (a), (b), (C), (d): 0.6-FA-S-Ag, (e), (f), (g), (h): commercial products.
4.5. The mechanism of electroless Ag plating FA
predicted based on a constant thickness of d, in the range of 0.5–3.0 mm. It is obvious that the microwave absorbing properties of microspheres increase substantially with the increase of thickness (d). As reported in the literature, the effective reflectivity of Rf should less than −10 dB. However, the reflectivity of all three samples is from −4 dB to −2.5 dB, not less than −10 dB, which further illustrates that the three samples are nonmagnetic materials.
XPS was used for the surface quantitative analyses of FA before and after aminosilane modification. The result (Fig. 6a) showed that the untreated FA contained trace amount of N element, with an N/Si atomic ratio of 0.016. For aminosilane modified fly ash (referred to as FA-S), characteristic peak of N element was detected on the surface of fly ash,
Fig. 4. Permittivity and permeability curves of Ag-plated FA composite: (a) Real permittivity, (b) Imaginary permittivity, (c) Real permeability, (d) Imaginary permeability. 5
Applied Surface Science 513 (2020) 145857
R. Zuo, et al.
The XPS fitting results of 0.6-FA-S sample showed that there were two chemical states of N1s spectra, as shown in Fig. 6b: 399.1 eV (eNH2) and −401.2 eV (eNHe), which corresponded to two amino groups of amino silane. The 0.6-FA-S sample was then plated with Ag, and Fig. 6c showed that the silver film was all metallic silver. There was an obvious satellite peak near 372 eV, which was attributed to metallic silver. XPS is a surface analysis instrument with a detection depth of less than 10 nm, so Ag-plated FA conditions were changed to reduce the thickness of silver plating layer so that a bond between N and Ag can be easily detected by XPS. Reducing the concentration of AgNO3 solution and the reaction time of silver plating were used to reduce the thickness of silver coating. Two samples of silver plating for 2 min and 5 min were taken for the XPS tests. The XPS N1s fitting spectra (Fig. 6d, e) showed that the N1s peak position shifted to 401.6 eV and 399.6 eV, respectively, which were relatively higher than that of silane modified FA. While the Ag3d5 peaks of 2 min and 5 min silver plating samples were 368.05 eV and 368.10 eV, respectively, as shown in Fig. 6f. Compared with the elemental silver 368.2 eV, the Ag3d5 peak shifted to a lower binding energy, illustrating that the coordination bonding of NAg did occur[10,18], which could be considered as the main reason for the strong adhesive strength between the silver plating layer and the fly ash particle surface. The coordination bond increased the bonding strength between the silver-plated layer and the FA surface, and the newly formed silver particles were preferably adsorbed and aggregated by the silver on the surface of the FA substrate through the metal interaction, thus forming a uniform and compact silver film. 5. Conclusion The alkali cleaning and aminosilane pretreatment process is very critical for electroless Ag plating on the FA particle surface. The mechanism of electroless Ag plating FA is studied by XPS, which involves modification and electroless plating. XPS results indicate that aminosilane coupling agent is successfully bonded to the surface of FA particles after alkali cleaning and provides the diammonia functional group used to adsorb silver ions and form the N-Ag coordination bond. After Ag plating, the characteristic peaks of N1s and Ag3d shift accordingly, indicating the formation of N-Ag coordination bond. Also, the peaks of diammonia (eNH2, eNHe) are shifted to higher binding energy after peak-differentiating and imitating of N1s, which further indicates that diammonia functional group can adsorb silver ions. After sonicating and cutting, no observation of detached Ag or cracks indicates that the adhesive strength between Ag film and modified FA particle surface is strong enough, much better than that of products purchased from market. The as-prepared Ag plating FA powder (0.6-FAS-Ag) has good electrical conductivity, with electrical resistivity of 8.2 × 10−5 Ω·cm and a thickness of 200 nm. The electromagnetic parameters and calculated reflection loss also indicate that Ag-plated FA powders have no magnetic conductivity and the main contribution of electromagnetic loss comes from dielectric loss. Fig. 5. Calculated reflection loss curves of Ag-plated FA composite: (a) #1, (b) #2, (c) #3.
CRediT authorship contribution statement and the N/Si atomic ratio increased to 0.086, about 4.5 times higher than that of pure FA, indicating that the FA surface was successfully coated with aminosilane. When FA was treated with two different concentrations of the NaOH solution and silane coupling agent, the N/ Si atomic ratio was increased from 0.112 (0.6-FA-S) to 0.159 (1.2-FA-S) with the concentration of NaOH solution increased from 0.6 mol/L to 1.2 mol/L respectively, which indicated that more aminosilane was coated on the FA surface with increasing of alkali concentration. The results showed that FA surface was more easily coated after alkaline washing and aminosilane treatment. Meanwhile, with the increase of the aminosilane concentration, the surface uniformity of coated FA increased, so the surface uniformity of silver plating film was improved.
Ranfang Zuo: Conceptualization, Methodology, Formal analysis, Investigation, Resources, Writing - original draft, Writing - review & editing. Jingyun Chen: Formal analysis, Resources. Zhihua Han: Formal analysis, Resources. Yang Dong: Supervision, Data curation. Jinder Jow: Supervision, Project administration, Funding acquisition.
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. 6
Applied Surface Science 513 (2020) 145857
R. Zuo, et al.
Fig. 6. High-resolution XPS spectra: (a) N1s for FA, FA-S, 0.6-FA-S, 1.2-FA-S, (b) N1s for 0.6-FA-S, (c) Ag3d for 0.6-FA-S-Ag, (d) N1s for 0.6-FA-S, 0.6-FA-S-2 min-Ag, 0.6-FA-S-5 min-Ag, (e) N1s for 0.6-FA-S-2 min-Ag, (f) Ag3d for 0.6-FA-S-Ag, 0.6-FA-S-2 min-Ag, 0.6-FA-S-5 min-Ag.
References
Acknowledgements The authors gratefully acknowledge financial support from National Institute of Clean-and-Low-Carbon Energy.
[1] W. Kim, S. Kim, Preparation of Ag-coated hollow microspheres via electroless plating for application in lightweight microwave absorbers, Appl. Surf. Sci. 329 (2015) 219–222. [2] X.G. Cao, H.Y. Zhang, Investigation into conductivity of silver-coated cenosphere composites prepared by a modified electroless process, Appl. Surf. Sci. 264 (2013) 756–760.
7
Applied Surface Science 513 (2020) 145857
R. Zuo, et al.
[11] J. Pang, Q. Li, B. Wang, D. Tao, X. Xu, W. Wang, J. Zhai, Preparation and characterization of electroless Ni-Fe-P alloy films on fly ash cenospheres, Powder Technol. 226 (2012) 246–252. [12] M.R.T. Doidjo, L. Belec, E. Aragon, Y. Joliff, L. Lanarde, M. Meyer, M. Bonnaudet, F.X. Perrin, Influence of silane-based treatment on adherence and wet durability of fusion bonded epoxy/steel joints, Prog. Org. Coat. 76 (2013) 1765–1772. [13] W. Hou, G. Pan, H. Guan, N. Chen, Electroless silver plating on surface of carbon fiber, Mater. Prot. 40 (2007) 45–47. [14] G. Zhu, J. Zhang, H. Zhang, A study of electroless silver plating with Pd-free activation on cenosphere, Electroplat. Pollut. Control 32 (2012) 32–35. [15] S. Hu, C. Zhang, M. Zhao, H. Chen, Electroless silver plating activated with thermoalkaline solution on fly ash cenosphere surface, Mater. Sci. and Eng. Powder Metall. 15 (2010) 79–83. [16] X. Zhu, Y. Mi, N. Hu, J. He, Discussion on the evaluation method of membrane base bond strength, China Surf. Eng. 4 (2002) 28–31. [17] X. Li, Y. Duan, Y. Zhao, L. Zhun, Effects of heat treatment on magnetic properties of Co−Fe-plated hollow ceramic microspheres, Prog. Nat. Sci. Mater. 21 (2011) 392–400. [18] J. Ou, B. Wu, M. Xue, F. Wang, Silver ions anchored to fabric via coordination: Evaluation on washing durability and antibacterial activity, Mater. Lett. 237 (2019) 134–136.
[3] Q. Li, J. Pang, B. Wang, D. Tao, X. Xu, L. Sun, J. Zhai, Preparation, characterization and microwave absorption properties of barium-ferrite-coated fly-ash cenospheres, Adv. Powder Technol. 24 (2013) 288–294. [4] Z. Aixiang, X. Weihao, X. Jian, Electroless Ni-P coating of cenospheres using silver nitrate activator, Surf. Coat. Tech. 197 (2005) 142–147. [5] S. Shukla, S. Seal, J. Akesson, R. Oder, R. Carter, Z. Rahman, Study of mechanism of electroless copper coating of fly-ash cenosphere particles, Appl. Surf. Sci. 181 (2001) 35–50. [6] Y. Hu, H. Zhang, F. Li, X. Cheng, T. Chen, Investigation into electrical conductivity and electromagnetic interference shielding effectiveness of silicone rubber filled with Ag-coated cenosphere particles, Polym. Test. 29 (2010) 609–612. [7] X. Yu, Z. Shen, Z. Xu, Preparation and characterization of Ag-coated cenospheres by magnetron sputtering method, Nucl. Instrum. Meth. B 265 (2007) 637–640. [8] X. Yu, Z. Xu, Z. Shen, Metal copper films deposited on cenosphere particles by magnetron sputtering method, J. Phys. D: Appl. Phys. 40 (2007) 2894–2898. [9] X. Yu, Z. Shen, The electromagnetic shielding of Ni films deposited on cenosphere particles by magnetron sputtering method, J. Magn. Magn. Mater. 321 (2009) 2890–2895. [10] W. Li, Y. Chen, S. Wu, J. Zhang, H. Wang, D. Zeng, C. Xie, Preparing high-adhesion silver coating on APTMS modified polyethylene with excellent anti-bacterial performance, Appl. Surf. Sci. 436 (2018) 117–124.
8