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Journal of Alloys and Compounds 509 (2011) 1836–1840 Contents lists available at ScienceDirect Journal of Alloys and Compounds journa l homepage: www.e lsev ier .com Effect o ac compo Arman Z School of Meta n, Teh a r t i c l Article history: Received 26 A Received in re Accepted 10 O Available onlin Keywords: Electroless Ni- Nano-compos Carbon nano-t Corrosion es in and oless ) spe prop icros e mea ds. R oless corpo d mic 1. Introduction The abil deposited c [1]. Success ite coatings size [2,3] t objectives o the wear re machineryp forcement have the hi considered along a chir cal and ther ratio (ratio can be used posite reinf [6–8]. Som exhibited h comparison Ni-P-SiC an ∗ Correspon E-mail add (S.-R. Allahkar self-lubrication and unique topological structure of CNTs, the fric- tioncoefficientof thecomposite coatingsdecreasedwith increasing 0925-8388/$ – doi:10.1016/j. ity to co-deposit particulate matter within electroless oatings has led to generation of composite coatings ful co-deposition and properties of electroless compos- are dependent on various factors including particles heir concentration in the bath [4], etc. The primary f composite electroless coatings have been to improve sistance and/or corrosion resistance and/or lubricity of arts. Amongdifferent particles that canbeused as rein- phase in electroless Ni-P coatings, carbon nano-tubes ghest potential [5]. Carbon nano-tubes (CNTs) can be as cylinders formed upon rolling up a graphene sheet al vector. They posses exceptional mechanical, electri- mal properties, togetherwith a high geometrical aspect between length and diameter). This suggests that they for different types of applications ranging from com- orcement materials to nanoelectronics and sensing too e studies showed that a Ni-P-CNT composite coating igher wear resistance and lower friction coefficient in with traditional electroless composite coatings such as d Ni-P-graphite [9–13]. Wang et al. [10] showed, due to ding author. Tel.: +98 61114108; fax: +98 61114108. resses: arman.zare@gmail.com (A. Zarebidaki), akaram@ut.ac.ir am). the volume fraction of CNTs up to 11.2%Vol., but wear resistance decreased with further increasing the volume fraction. This behav- iorwas attributed to the conglomeration of CNTs in thematrixwith further increasing the volume fraction. Yang et al. [14] showed that electroless Ni-P-CNT composite coatings provide higher corrosion resistance than Ni-P coating. Some studies showed that the incorporation of carbon nano-tubes into the electrodeposited nickel coating significantly increased the corrosion resistance. The improvement in corrosion resistance is due to the CNTs acting as physical barriers to the corrosion process by filling in crevices, gaps and micro-holes on the surface of the nickel coating [15]. In the case of co-deposition of CNTs and met- als, uniform dispersion of CNTs in the bath and good suspension is the key factor for getting coatings with homogeneous CNT distri- bution. This is challenging because CNTs have a natural tendency for agglomeration. Ultrasonication andmagnetic stirring have been used to keep the CNTs in suspension. Ball milling of CNTs has been used to decrease their aspect ratio to help them being dispersed in the bath [16]. Acid cleaning and adding surfactants have also improved suspension of CNTs [16,17]. Studies showed that the dis- persion of CNTs in order to fill out the micro-holes and defects of Ni-P coatings can specially influence the corrosion resistance of Ni-P-CNT coatings [18]. There are little studies on dispersion of carbon nano-tubes in electroless bath and their effect on embed- ding of nano-tubes in electroless coatings. Furthermore only a few see front matter © 2010 Elsevier B.V. All rights reserved. jallcom.2010.10.057 f surfactant on the fabrication and char site coatings arebidaki, Saeed-Reza Allahkaram ∗ llurgy and Materials Engineering, University College of Engineering, University of Tehra e i n f o ugust 2010 vised form 4 October 2010 ctober 2010 e 21 October 2010 P ite coating ubes a b s t r a c t In order to disperse carbon nano-tub cyl sulfate (SDS) as anionic surfactant surfactant) were added to the electr by using ultra violet visible (UV–vis optimum surfactant-to-CNTs ratio of analyzed using a scanning electron m the applied composite coatings wer impedance spectroscopy (EIS) metho disperse CNTs throughout the electr resistance studies showed that the in coatings due to the filling of pores an corrosion attack. / locate / ja l l com terization of Ni-P-CNT ran 11155-4563, Iran electroless Ni-P coatings different surfactants (sodium dode- Hexadecyl Trimethylammonium Bromide (HTAB) as cationic bath and their respective dispersing power was monitored ctroscopy method. Then Ni-P-CNT coating deposited, using er surfactant. The morphologies of composite coatings were cope (SEM). Moreover, hardness and corrosion resistance of sured via microhardness, polarization and electrochemical esults showed that an optimum ratio of SDS can uniformly Ni-P coating, which yields the highest hardness. Corrosion ration of CNTs can increase the corrosion resistance of Ni-P ro-holes, while decreasing the metallic area that is prone to © 2010 Elsevier B.V. All rights reserved. A. Zarebidaki, S.-R. Allahkaram / Journal of Alloys and Compounds 509 (2011) 1836–1840 1837 nd (b researchers tance of Ni- nano-tubes have been tant ratio h Then the c oped under and electro a comparat tubes (MWN dodecyl sul surfactants mum dispe this area of to-surfactan in nano-tub sion of CNT corrosion a coatings wi 2. Experimen Pristine CV 40–60nm, len Co., Ltd., China and HTAB (pu improve thedi for8hwithap of 500 rpm. Ba Scanning Elect be seen ball m dispersion of C To investig dispersions of the concentrat tively. These s MWNTs. UV–v spectrometer baseline corre out any MWN MWNTs in ele mum concent were deposite composition s The proce already descri Table 1 Chemical com Fe Base ercia sphit posite a thi ml ele , the p c stirr ite coa ated b c stirr s adde th con layer. e cond morp d usin S-416 the co at a ment corros d via copy vanost mple coun ic po mVs re un r (FRA alvan 0.01– 98. Th , synt ults dle c Fig. 1. FESEM images of (a) as-received CNTs a have concerned themselves with the corrosion resis- P-CNT coatings. In this study the dispersion of carbon in electroless bath via UV–vis spectroscopy method investigated. An optimum condition of CNT to surfac- as been determined for two surfactants, HTAB and SDS. orrosion resistance of the composite coatings devel- the optimum condition was studied via polarization chemical impedance spectroscopy. This study reports ive analysis on dispersion of multiwalled carbon nano- Ts)withdifferent surfactants suchasHTABandsodium fate (SDS). The significance of using a particular ratio of and MWCNTs has been established for obtaining opti- rsion which may be cited as a relatively new finding in research. From the present study, the optimum CNT- t ratio turns out to be the most important parameter e dispersion. The effects of surfactants on the disper- s in electroless solution and the coating together with nd mechanical properties of the Ni-P-CNTs composite ll also be investigated. tal D-grown multi walled carbon nano-tubes (purity≥98%, diameter gth range 5–15�m) were purchased from Shenzhen Nanotech Port (trade name of the product is L-MWNTs-4060). The surfactants, SDS rchased from Merck Chemical Co.) were used as-received. In order to spersionofCNTs inelectrolessbath, as-receivedCNTswereballmilled lanetaryballmillmachine inanelectroless solutionat a rotating speed ll to powder ratiowas kept at 50:1. Fig. 1 shows FESEM (Field Emission ronMicroscopy) images of as-received and ball milled CNTs. As it can illed CNTs are shorter and more straight and therefore improves the NTs in the electroless bath. ate the effect of surfactant on dispersion of CNTs in electroless bath, MWNTs were prepared at concentration of 0, 5, 25, 50mg/l, keeping ion of SDS surfactant and HTAB constant at 2 g/l and 75mg/l, respec- amples were ultrasonicated for 2h in order to get surfactant coated .A comm hypopho Com ing with the 200 92±2◦C magneti compos and agit magneti bath wa CNTs. Ba ing inter the sam The examine Hitachi ness of indenter measure The evaluate Spectros stat/Gal of the sa platinum tiodynam rate of 1 tests we Analyze tiostat/G range of model 3 analyses 3. Res Bun is absorption spectrawere recordedwith UNICAM8700 series UV/vis operating between 200 and 1100nm. In the first set of experiments, ctionwas carried out using pure solutions contained surfactantswith- Ts, and at experimentally achieved optimum ratios of surfactant to ctroless bath. Ni-P-CNT composite coatings were deposited at opti- rations of two surfactants. Ni-P and Ni-P-CNT composite coatings d on API-5L X65 steel substrates (30mm×25mm×15mm) with the howed in Table 1. dure for preparing the substrate (30mm×25×15mm) has been bed [19]. The specimens were vertically positioned in a 250ml bath position of API-5L X65 steel was used as substrate. Mn Si Cu Mo C Cr 1.42 0.199 0.144 0.132 0.061 0.012 [20,21], on Hence, disp UV–vis abs is possible CNTs indiv correspond dispersion UV–vis spe depict the U SDS and HT It can be increases u tionof exfo CNT to SDS absorption ) ball milled CNTs. l electroless nickel bath (SLOTONIP 70 A from Schlotter) with sodium e as reducing agent was used to obtain the coatings. coating was performed after deposition of an interlayer of Ni-P coat- ckness of 9±2�m on the substrate by immersing the specimen in ctroless nickel bath. During the deposition, temperature was fixed at H of the bath was set at 4.6±0.1 and the bath was agitated using a er at a speed of 300 rpm during coating process. To obtain Ni-P-CNT tings, optimum ratio of surfactant to CNT was added to 50ml bath y an ultrasonic bath (at 50KHz frequency and 340W power) using ing for 1h. After deposition of Ni-P interlayer, the CNTs contained d to the main bath and coating continued for 2h in the presence of dition for deposition of composite coating was the same as deposit- For comparison purposes, pure Ni-P coating was also prepared under itions. hologies of the applied Ni-P and Ni-P-CNT composite coatings were g CamScanMV2300Oxford Scanning ElectronMicroscope (SEM) and 0 Field Emission Scanning Electron Microscope (FESEM). The hard- atings was measured using an (AMSLER D-6700) Vickers diamond load of 150g for a loading time of 20 s. The average of five repeated s has been reported. ion resistance of the coatings in 3.5wt.% sodiumchloride solutionwas both potentiodynamic polarization and Electrochemical Impedance (EIS). The corrosion tests were conducted using an EG&G Potentio- at Model 273A. A standard three-electrode configuration consisting as the working electrode, an Ag/AgCl as a reference electrode and a ter electrode was used to evaluate the polarization behaviors. Poten- larization test was carried out by sweeping the potential at a scan −1 in the range of ±400V vs. Open Circuit Potential (OCP). The EIS dertaken using a Solartron Model SI 1255 HF Frequency Response ) coupled to a Princeton Applied Research (PAR) Model 273A Poten- ostat. The EIS measurements were obtained at (OCP) in a frequency 100kHz with an applied AC signal of 5mV (rms) using EIS software e equivalent circuit simulation program (ZView2) was used for data hesis of the equivalent circuit and fitting of the experimental data. and discussion arbon nano-tubes are not active in the UV–vis region ly individual carbon nano-tubes absorb in this region. ersion of carbon nano-tubes can be characterized using orption spectroscopy. It has been suggested that it to establish a relationship between the amounts of idually dispersed in solution and the intensity of the ing absorption spectrum [20,22]. To characterize the of MWNTs in electroless solution containing surfactant, ctroscopy and absorbance values are used. Figs. 2 and 3 V–vis spectra of MWNTswith varying concentration of AB surfactants in electroless bath, respectively. seen that the absorbance increases as SDS to CNT ratio p to optimum ratio, so a gradual increase in concentra- liatednano-tubes in solution takeplace. At the optimum surfactant ratio (2 g SDS to 25mg CNT ratio), maximum is achieved. Above this ratio, absorption decreases and 1838 A. Zarebidaki, S.-R. Allahkaram / Journal of Alloys and Compounds 509 (2011) 1836–1840 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 300 400 500 600 700 800 900 Wavelenght, nm A b so rb an ce NiP-2 g/l SDS-5mg/l CNT NiP-2 g/l SDS-25mg/l CNT NiP-2 g/l SDS-50mg/l CNT NiP,NiP-2g/l SDS Fig. 2. UV–vis spectra of electroless bath containing CNTs and different amount of SDS surfactant. 0 0.2 0.4 0.6 0.8 1 1.2 1.4 300 A b so rb an ce NiP-75 ppm HTAB-5mg/l CNT NiP-75 ppm HTAB-25mg/l CNT Fig. 3. UV–vis HTAB surfacta this can be tants. At hig solution. In tions of sur each other. dispersion o there is an sion deterio HTAB to sur HTAB: 5mg Fig. 3 sh ratio increa atednano-t place at 75m Table 2 Microhardness of deposited coatings. Coating (surfactant-to-CNTs ratio) Microhardness (Hv150) Ni-P 607 ± 3 Ni-P-75ppm HTAB-5mg/l CNTs 706 ± 20 Ni-P-2 g/l SDS-25mg/l CNTs 806 ± 15 shows that the absorbance of UV waves in solution containing SDS is higher than those of the others, so the number of the dispersed MWNTs in the bath containing SDS is more than that of the bath containing HTAB surfactant. The experimental investigation shows that the dispersing power of SDS surfactant is higher than HTAB. In order to disperse nano-tubes, surfactant molecules oriented them- selves in such a fashion that hydrophobic tail groups face toward the nano-tube surface while hydrophilic head groups face toward the aqueous phase [17]. In the case of SDS, surface of nano-tubes were covered more by surfactant molecules due to higher concen- tration of the surfactant compared to HTAB surfactant, so more repulsive force is created between individual CNTs particles. SEM images of the surfacemorphologies of Ni-P-CNT coatings deposited mum at th . In o enou Ts in an b seen n to b ve ta persi le 2 coati ion. T theni 400 500 600 700 800 900 Wavelenght. nm NiP-75 ppm HTAB-75mg/l CNT NiP, NiP-75 ppm HTAB spectra of electroless bath containing CNTs and different amount of nt. at opti dent th matrix homog the CN tubes c can be be see CNT ha for dis Tab posite condit streng attributed to the theory of micelle formation in surfac- h concentrations, surfactantmolecules formmicelles in other words at high concentration of surfactants, por- factants extend into the liquid phase and interact with This interaction causes flocculation and decreases the f nano-tubes at high surfactant concentration [17]. So optimum ratio that the quality of nano-tubes disper- rates above this ratio. The optimum ratio for SDS and factant is found to be 2g/l SDS: 25mg/l CNT and 75mg/l /l CNT respectively. ows that the absorbance increases as HTAB to CNT ses up to optimum ratio, so the concentration of exfoli- ubes in solution increases too. Optimal absorption takes g/l HTAB to 25mg/l CNT ratio. Comparing Figs. 2 and 3 in hardness larger micr microhardn mum cond and less agg Fig. 5 sh and Ni-P-CN dition of SD current den rosion pote found to be ues forNi-P respectively ite coating Fig. 4. FESEM images of the surface morphology of (a) Ni-P-2 g/l SDS-25mg/l ratio of CNT-to-surfactants are shown in Fig. 4. It is evi- e co-deposited CNTs are distributed evenly in the Ni-P rder to obtain the composite coatings containing the s distribution of CNTs it is important to well disperse the electroless bath, thoroughly. In Fig. 4b carbon nano- e seen to be agglomerated, while some carbon bundles in the nodules boundaries, whereas in Fig. 4a CNTs can e more dispersed and no bundles or agglomeration of ken place. So SDS seems to bemore effective surfactant ng CNTs through electroless coatings than HTAB. shows the microhardness of Ni-P and Ni-P-CNT com- ngs deposited under optimum CNT-to-surfactant ratio he incorporation of CNTs in Ni-P coating has dispersive ng effects [23] and results more than 30% increscent . It is seen that the Ni-P-CNT composite coatings have ohardness than that of Ni-P coating and the maximum ess is achieved on the coating deposited under opti- ition of CNTs-to-surfactant ratio due to more uniform lomeration of incorporated particles. ows the potentiodynamic polarization curves for Ni-P T composite coatings deposited under optimum con- S-to-CNT ratio. The values of corrosion potential and sity were estimated using Tafel slope method. The cor- ntial and corrosion current density of the Ni-P were −330mV and 41.6×10−5 A/cm2, respectively. The val- -CNTcoatingwere found tobe−295mVand28.0A/cm2, . It can be seen that the corrosion potential of compos- is more positive than Ni-P coating and the corrosion CNT and (b) Ni-P-75ppm HTAB-5mg/l CNT. A. Zarebidaki, S.-R. Allahkaram / Journal of Alloys and Compounds 509 (2011) 1836–1840 1839 -600 -500 -400 -300 -200 -100 0 100 200 300 1E-06 1E-05 0.0001 0.001 0.01 0.1 1 10 100 I (A/sqcm) E ( V v s. A g /A g cl ) NiP-CNT NiP Fig. 5. Potentiodynamic polarization curves of Ni-P and Ni-P-CNT coatings in 3.5% NaCl solution. current density of Ni-P is higher than the composite coating. Cor- rosion resistance of Ni-P coating depends on many factors such as phosphorous content [24], and nature of corrosion solution [25]. Incorporation of particles in Ni-P has different effect on the cor- rosion resistance [26]. Xue et al. showed that the incorporation of proper amount of nano-SiC particles can improve the corro- sion resistance of the coating due to the increment of passive film nucleation sites. However in Fig. 5a typical passivation behavior could not be observed. Better corrosion resistance of Ni-P-CNT coating compared to Ni-P coating can be attributed to the less effective metallic area prone to corrosion due to the presence of CNTs. Another reason for this improvement can be correlated to the filling of crevice, gaps andmicro-holes of Ni-P coatings by CNTs [27–29,15]. Beside these facts, higher corrosion resistance of Ni- Fig. 6. Electro Ni-P and Ni-P- Table 3 Electrochemical parameters from EIS data of Ni-P and Ni-P-CNT electroless coatings in 3.5% NaCl. Type of coating Rs (� cm2) Rct (� cm2) CPE Ni-P Ni-P-CNTs P-CNT coat CNTs [30]. N ings obtain seen that b semi-circle tions have o diagrams sh stant. Form double laye The high the Ni-P-CN of this coat to the poros as compare of present s 4. Conclus From th troscopy is CNTs in ele to deposit a SDS to CNT According t CNTs throu sion resista can be attri sive media nces Balar 03) 80 Balar . Shre lireza 04) 17 i, S. Q Colem F. Lia, . Kova amkin . Che –222 .Wang ar 254 . Chen (2006 Refere [1] J.N. (20 [2] J.N. [3] N.K [4] S. A (20 [5] T. L [6] J.N. [7] X.- [8] A.A Kly [9] W.X 215 [10] L.Y We [11] X.H 39 chemical impedance diagrams (a) nyquist and (b) bode diagrams of CNT coatings in 3.5% NaCl solution. [12] W.X. Che Surf. Coa [13] Z.H. Li, X. [14] Z. Yang, H 1001–10 [15] X.H. Chen 191 (200 [16] S.R. Baksh [17] R. Rastog Colloid In [18] Z. Yang, 1001–10 [19] T. Rabiza [20] J. Yu, N. G [21] J.S. Laure Phys. Rev CPE-T (f cm−2) CPE-P 8.83 13,934 2.2585×10−5 0.9553 9.18 24,772 7.8299×10−6 0.8994 ing can be attributed to the low chemical reactivity of yquist and bode diagrams of Ni-P and Ni-P-CNT coat- ed in 3.5wt.% NaCl solution are shown in Fig. 6. It is oth coatings have similar EIS diagrams with only one in the nyquist diagrams so the same fundamental reac- ccurred but over a different effective area [31,32]. Bode ow the same results and they involve a single time con- ore clear comparison the charge transfer resistance and r capacitance are compiled in Table 3. er value of charge transfer resistance (Rct) obtained for T coating implies a better corrosion prot