Volume 16 Preprint 63


Corrosion resistance and hardness characteristics of electrodeposited ternary Ni-Cu-Co black alloy coatings

S. Karthikeyan,P.A.Jeeva,S.Narayanan

Keywords: Ni-Cu-Co coatings, corrosion resistance, impedance, salt spray

Abstract:
An attempt has been made to develop a novel ternary Ni-Cu-Co black coatings with improved corrosion resistance and micro hardness values. XRD and XPS studies have proved that the enhancement of corrosion resistance and hardness by coating after annealing at 300oC could be due to the formation of Ni3Cu5, CuO and NiO and confirmed from the appearance of core peaks at Co 2p3/2, Cu 3p, Cu 3p3/2, Ni 2p3/2 and Ni 2p with binding energies of 785 eV, 45 eV, 933 eV, 853 eV and 839 eV respectively. The formation of uniform layer of Ni-Cu-Co coatings is evident from SEM images. The coatings offered the corrosion resistance of 40 times of uncoated mild steel surface in 3.5% NaCl. The reduction of Ecorr, Icorr, Cdl and enhancement of Rt value from polarization and impedance measurement indicated the corrosion resistance ability of Ni-Cu-Co black coatings.

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` ISSN 1466-8858 Volume 16, Preprint 63 submitted 14 October 2013 Corrosion resistance and hardness characteristics of electrodeposited ternary black Ni-Cu-Co alloy coatings S. Karthikeyan1*, P.A. Jeeva2, S. Narayanan2 1* Surface Engineering Research lab, Centre for Nanobiotechnology, VIT University, Vellore632 014, India. 2 School of Mechanical &Building Sciences, VIT University, Vellore-632 014, India. Abstract An attempt has been made to develop a novel ternary Ni-Cu-Co coatings with improved corrosion resistance and micro hardness values. XRD and XPS studies have proved that the enhancement of corrosion resistance and hardness by coating after annealing at 300oC could be due to the formation of Ni3Cu5, CuO and NiO and confirmed from the appearance of core peaks at Co 2p3/2, Cu 3p, Cu 3p3/2, Ni 2p3/2 and Ni 2p with binding energies of 785 eV, 45 eV, 933 eV, 853 eV and 839 eV respectively. The formation of uniform layer of Ni-Cu-Co coatings is evident from SEM images. The coatings offered the corrosion resistance of 40 times of uncoated mild steel surface in 3.5% NaCl. The reduction of Ecorr, Icorr, Cdl and enhancement of Rt value from polarization and impedance measurement indicated the corrosion resistance ability of Ni-Cu-Co black coatings. Keywords Ni-Cu-Co coatings, corrosion resistance, impedance, salt spray © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of1 Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ` ISSN 1466-8858 Volume 16, Preprint 63 submitted 14 October 2013 Introduction In the field of surface treatments, black coatings are extensively used for decorative or solar absorbing functions. The films deposited should have high optical properties (absorption of solar radiations). Black coatings used for both decorative and solar absorbing functions are mostly prepared by liquid phase deposition or vapour phase deposition. Black nickel and black chromium are the most significant electrodeposited materials, whereas the films elaborated by vapour phase deposition comprise generally titanium alloys and carbon based materials. The studies on black coatings based in electrodeposition of nickel alloys in recent years are gaining much value as they discover a great range of applications in different fields like solar absorbance and gas turbines. Electrodeposited black nickel bath was prepared from sulphate, chloride and combination of both chemicals by Dennis et.al.[1] and Ibrahim [2]. Mehra and Sharma [3] are of view that black nickel coatings for solar applications could be obtained by chemical conversion of zinc-coated aluminium. Monteiro et.al.[4] have reported that the black colour of the nickel and zinc electro coatings are due to the formation of zinc sulfide and nickel sulfide particles in the film. But, they found that these coatings did not show consistent resistant to corrosion above 75oC. Koltun [5] et.al., Peterson [6] et.al. and Bonora and his co-workers[7] have investigated that corrosion resistance of coatings using polarization techniques. These coatings showed better optical properties as compared with earlier reports. Electroless black nickel coating was first developed by Guofeng Cui et.al.[8] to improve the © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of2 Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ` ISSN 1466-8858 Volume 16, Preprint 63 submitted 14 October 2013 mechanical properties and corrosion resistance and they claimed that improvement in mechanical properties are due to the surface texture modification in coatings. However, the uses of black Ni-Cu-Co ternary alloys on improvement of mechanical properties on metallic objects have not been exposed. This lead to an identification of appropriate black coatings to be used for enhancing the mechanical properties in order to enable to extend life time of machineries. The performance of coatings is to be evaluated by weight gain studies, micro hardness evaluation, corrosion resistant measurement by electrochemical methods. The surface morphology of the coatings is the predominant properties of the coating which will be assessed by XRD, SEM and XPS. Salt spray analysis to be carried out to follow up the corrosion and get an idea about the performance of Ni-Cu-Co black coatings in automobile parts. Experimental Procedure The optimized bath used in the present study had the following composistions. NiSO4.6H2O = 40 g/l CuSO4.6H2O = 8 g/l CoSO4.5H2O = 15 g/l Ammonium thiocyanate = 25 g/l Boric acid = 30 g/l EDTA = 3 g/l © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of3 Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ` ISSN 1466-8858 Volume 16, Preprint 63 submitted 14 October 2013 pH = 4.7 Current density = 400 mA/cm2 Plating time = 180 seconds Evaluation of black coatings through different techniques Weight-gain method Mild steel specimens of 99.52% purity of size 20 x 50 x 2 mm3 were used in the plating bath. They were polished with fine grit paper and degreased using tri choloro ethylene to remove oil and greases. Mild steel panels were pretreated in acid bath followed by alkali bath and washed with tap water. They were rinsed in double distilled water and dried. The initial weight of panel was recorded using digital weighing balance machine. The same operating conditions were used for coating on radiator drain plug, lock nut and vehicle brake tube made of mild steel. Then, both metallic components and mild steel test specimens were introduced into the plating solution under optimized conditions of the bath. The rate of deposition was calculated using the following formula: Where, W – Weight of the deposit (g) D – density of the deposit (g/cm3) T – plating duration (h) © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of4 Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ` ISSN 1466-8858 Volume 16, Preprint 63 submitted 14 October 2013 A – Surface area of the specimen (cm2) Micro hardness measurements Micro hardness measurements for all the as plated specimens (20 x 50 x 2 mm3) and also for the annealed samples at 300oC were made by Vicker’s harness tester as per ASTM E-384 with a load of 100 g. A diamond shaped indentation was made on each sample at 8 different places and the average value of hardness was measured from the diagonal of indendation on Vicker’s scale using the formula. V.H.N = (1854 x load) / d2 where d = diagonal of the indentor Corrosion resistance measurements The electrochemical polarization measurement and impedance studies were made with the black coated steel surface of 10 mm2 area (working electrode), 40 mm of platinum electrode (counter electrode) and saturated calomel as reference electrode in three electrode cell assembly. Potentiodynamic polarization method A constant quantity of 200 ml of 3.5% NaCl solution was taken in a 250 ml beaker. The working electrode, reference electrode and the counter electrode were assembled in position and the connections were made. Initially, the potential is noted which is recorded as OCP. From OCP, polarization studies were performed using Sinsil Model 604E Electrochemical Analyzer imported from USA. The readings © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of5 Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ` ISSN 1466-8858 Volume 16, Preprint 63 submitted 14 October 2013 were obtained by ranging the potential values from OCP ± 1000 mV with scan rate 10 mV per second for both as plated and annealed black coated steel surfaces. The corrosion kinetic parameters such as Ecorr, Icorr, anodic and cathodic Tafel slopes (ba and bc) were measured. The reduction in potential values of Tafel slopes gave an idea that whether the black coatings have reduced the oxidation of metal from surface or involved in reducing cholorine gas evolution. Impedance measurement The SINSIL Model 604E electrochemical analyzer was used for this measurement in the frequency range of 100 kHz to 0.01 Hz under potentiostatic conditions using 3.5% NaCl as corrosive medium. The impedance measurements were carried out both as plated and annealed black coated steel surface at room temperature. The electrical equivalent circuit for the corroding system is given below: RS - Solution resistance Rt - Charge transfer resistance W - Warburg impedance Cdl - Double layer capacitance © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of6 Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ` ISSN 1466-8858 Volume 16, Preprint 63 submitted 14 October 2013 The cell impedance consists of real part (Z’) Vs imaginary part (Z’’). A plot of real part (Z’) Vs imaginary part (Z’’) gives a semicircle which cuts the real axis at higher and at low frequency Z corresponds to (RS + Rt). The difference between the two values gives Rt. The double layer capacitance can be determined from the frequency at which Z’’ is maximum from the relation Surface morphological studies of black Ni-Cu-Co coatings X-ray diffraction studies The X-ray diffraction patterns for the black electrodeposited mild steel specimens were made using X’ pert pro XRD,(make- Panalytical, USA) both as plated as well as annealed conditions. These measurements help to explain the intermetallic phases formed in the coatings. The X-ray diffraction patterns were obtained with Cu Kα radiation in the above instrument with the step of 0.02o. XRD patters were recorded for different depth profiles employing grazing incidents X-ray technique. Scanning electron microscopic studies (SEM) The morphology of the black electrodeposits were examined under high magnification to assess the grain size, deposit nature, heterogeneities and pores present in the deposits using a scanning electron microscope. The scanning electron microscope, which makes use of reflected primary electrons and secondary electrons, enable one to obtain information from regions that cannot be examined by others. © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of7 Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ` ISSN 1466-8858 Volume 16, Preprint 63 submitted 14 October 2013 The deposited specimens of various black coatings were cut into 10 x 10 mm2 size and mounted suitably and examined under the microscope. The SEM photographs were taken by using S-3000 model with an acceleration voltage range of 20,000 V and with the magnification range of 1000. Surface Characterization (XPS or ESCA analysis) The surface characterization measurements were carried out on black coated samples under annealed conditions having surface area of 10 x 10 mm2 using X-ray photoelectron spectra also known as Electron Spectroscopy for Chemical Analysis (ESCA) in a physical electronics PHI 5600 ESCA system with Al Kα monochromatic source was used to obtain oxidation states of species along with chemical composition of surfaces. The binding energy values were calculated with a precision of ±0.2 eV. For these measurements, the samples were mounted in to an ultra high vacuum chamber at 10-9 Torr housing the analyzer. Prior to mounting, the black coated samples were placed in the preparation chamber for 6 hours in order to remove any volatile species exist on the surface. Salt spray analysis for corrosion resistance of black Ni-Cu-Co coated samples The salt spray rest of the black coated steel panels were conducted in SF 850 salt spray cabinet as per ASTM B-117 in 3.5% NaCl to understand the corrosion resistance of the coatings in aggressive environment i.e. sea water medium. The corrosion degree of the samples was evaluated by average weight loss which was visibly noted by the appearance of formation of red rust spots on the coated samples used under annealed conditions. This test has established that the © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of8 Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ` ISSN 1466-8858 Volume 16, Preprint 63 submitted 14 October 2013 corrosion resistance of the coatings is higher in sea water medium as a validated result for potentiodynamic polarization and A/C impedance test. The surface morphological studies were performed using X-ray diffraction technique and scanning electron microscopic images. In order to understand the existence of metallic atoms in black coatings, X-ray photo electron spectra have been carried out for all coatings. Results and Discussions Weight gain studies The results of black coatings obtained in the present study by weight gain method and eddy current tests are presented in Table 1. It has been observed that the addition of copper into nickel-cobalt system improves the black colour in the coating. If the copper concentration exceeds 8 grams per liter the coating failed to show intense black colour which is the required colour for the present investigations. However, the addition of cobalt did not show any significant changes in black colour. The optimum loading of copper and cobalt were found as 8 gram per liter and 15 gram per liter. The rate of deposition for Ni-Cu-Co black coatings was observed as 31µm at the plating timing of 180 seconds. Hence, the above formulations can be used for industrial applications as high speed plating baths. © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal of9 Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ` ISSN 1466-8858 Volume 16, Preprint 63 submitted 14 October 2013 Micro hardness measurements The hardness of the electrodeposited Ni-Cu-Co coatings measured by Vicker’s hardness tester is given in Table 2. The higher hardness of black coatings can be ascribed to the formation of inter metallic phases of Ni-Cu, Cu-Co in the coatings. After annealing, the coatings hardness was found to increase due to the precipitation hardening mechanism formed by Ni6Cu6 phases. The results were in good conformity as reported by Kotnarowska [9]. Corrosion resistance studies Potentiodynamic polarization studies The corrosion resistance studies of black Ni-Cu-Co black coatings have been carried out potentio dynamically by shifting the potentials from ± 1000 mV from OCP vs Hg/Hg2Cl2/KCl(Satd.) which starts from -1474 mv to +526 mV at the scan rate of 10 mV/sec using platinum wire as a counter electrode. The Ecorr value for mild steel is -894 mV which is shifted to positive direction for the black Ni-Cu-Co coatings both in the as plated as well as annealed conditions at 300oC. Ecorr values for nickel based black coatings were found as -788 mV for NiCu-Co in the as plated condition [10-11]. This is further shifted to more positive direction(-435 mV for black Ni-Cu-Co coatings) due to the formation of intermetallic phase precipitations resulted from annealing the coatings at 300oC. The results are presented in table 3. © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal 10 of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ` ISSN 1466-8858 Volume 16, Preprint 63 submitted 14 October 2013 It is concluded that after annealing, the coatings exhibited better corrosion resistance than as plated condition. These results are in good agreement with XRD and SEM studies. Also the corrosion currents(Icorr), anodic(ba) and cathodic(bc) tafel slopes for coatings both in the as plated and annealed conditions have been reduced to greater extent in comparison with mild steel immersed in 3.5% NaCl confirming that the black coatings offered excellent corrosion resistance. Electrochemical Impedance Spectroscopy (EIS) studies The measured impedance spectra of the mild steel substrate and black coatings in 3.5% NaCl solution are shown in the table 4. It is evident from table 4 that the Rt values increased at the expense of Cdl values for the black coatings. In the case of Ni-Cu-Co black coatings, Rt and Cdl values were obtained as 1900 Ohm.cm2 and 3.26 µF.cm-2. The enhanced values of Rt for black coatings were noticed as 2810 Ohm.cm2 in annealed conditions. However, the double layer capacitance values have been brought down to 2.47 µF.cm-2 indicating that these black coatings could offer higher corrosion resistance in annealed conditions than the as plated steel panels and mild steel [12]. Surface morphology of the Ni-Cu-Co coatings X-ray diffraction analysis The results of XRD analysis of Ni-Cu-Co black coatings are shown in Figure 1. The crystalline peaks are resulted from the nickel and alloys. A broad dominant peak appearing around d value of 1.98 indicated the existence of nickel in the black © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal 11 of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ` ISSN 1466-8858 Volume 16, Preprint 63 submitted 14 October 2013 coatings. The feeble peaks at d values of 2.3 and 1.41 corresponded to the presence of copper and cobalt metals in the black coatings which accounts for the highest hardness of black coatings than mild steel substrate [13]. A thin peak at d value 7.66 corresponds to the formation of Nickel oxide in the black coatings. This result is in good agreement with results of XPS analysis. The appearance of peaks at d values of 4.75 and 3.45 confirmed the presence of cobalt in the coatings. The formation of peaks at d values of 1.67 and 1.58 indicated [Figure 2] the formation of intermetallic phase viz., Ni3Cu5 which is a soft matrix due to the presence of copper (soft metal). Scanning Electron Microscopic studies Figure 3 shows the morphologies of Ni-Cu-Co black coatings obtained from nickel electroplating bath. It can be found that the morphology changes remarkably. For the black coatings, the best evenness and compactness can be observed and needle holes hardly appear on its surface, as evidenced from SEM images[Figure 3(a) & (b)]. The appearance of corn like structure in figure 3(b) indicated the presence of cobalt which has diffused to surface after annealing at 300oC. After annealing, the surface morphologies become more even in compared with SEM images of as plated Ni-CuCo black coatings. In the as plated conditions, it was noticed that crowding of particles with coalescence [Figure 3(a)]. XPS analysis of black coatings The annealed ternary Ni-Cu-Co black coatings were subjected to XPS analysis in order to determine the oxidation state of particular elements in the deposits. In © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal 12 of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ` ISSN 1466-8858 Volume 16, Preprint 63 submitted 14 October 2013 figure 4, the core peak of cobalt appeared as Co2p3/2 at binding energy 785 eV along with appearance of Cu3p peak at binding energy of 45 eV confirming that copper and cobalt are existing as their oxides with oxidation state of +2 [14-15]. This is further confirmed by the formation of O1s peak with binding energy value 531 eV. The traces of C1s, S1s and N1s at binding energy values 213 eV, 162 eV and 127 eV have shown the utility of ammonium thiocynate which acted as a complexing agent for nickel ions to prevent powdery deposits. The appearance of core peaks i.e. doublet peaks for nickel as Ni 2p3/2 and Ni 2p along with a singlet strong peak of Cu 2p3/2 and O KLL at their corresponding binding energy values of 853 eV, 839 eV, 933 eV and 1008 eV establishing that at inner layers nickel is existing as NiO with oxidation state of +2. Similar is the trend with copper which existed as CuO with oxidation state Cu(II). Analysis of Salt spray test The results of salt spray test are shown in table 5. For steel samples, it is noticed that 30% red rust formed on uncoated sample at 30 minutes stay in salt spray chamber. 2% rust area formation on black coatings after 1200 hours stay in salt spray chamber. Therefore, it can be concluded that corrosion resistance of black NiCu-Co coatings in salt spray is 40 times higher than uncoated mild steel. References [1]. J.K. Dennis, T.E. Such. Nickel and Chromium plating. Butterworth & Co, Londres 1972. [2]. Magdy A.M. Ibrahim, J. Appl. Electrochemistry, 36 (2006) 295. [3]. N.C. Mehra, S. K. Sharma, J. Mater. Sci. Lett. vol 8, n° 6 (1989) 707. [4]. F.J. Monteiro, F. Oliviera, R. Reis, O. Paiva, Plat. Surf. Fin. (1992) 46. [5]. M. Koltun, G. Gukhman, A. Gavrilina, Sol. Energy Mater. Sol. Cells 33 (1994) 41. © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal 13 of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ` ISSN 1466-8858 Volume 16, Preprint 63 submitted 14 October 2013 [6]. R.E. Peterson, J.W.Ramsey, J. Vaccum Sci. Technol. 12 (1975) 174. [7]. P.L. Bonora, A. Krolikowska, Journal of Corrosion Science and Engineering, 15, pp. 1-12, 2012. [8]. Guofeng Cui, Ning Li, Jian Zheng, Qinglong Wu, Surf. Coat. Technol. 200 (2006) 6808. [9]. D. Kotnarowska, Journal of Corrosion Science and Engineering, 6, 2003. [10]. M.G. Pujar, U.K. Mudali, Journal of Corrosion Science and Engineering, 15, pp. 1-15, 2012. [11]. S.Karthikeyan, P.A.Jeeva, V.Raj , Devanthranath Ramkumar, N.Arivazhagan, S.Narayanan, Journal of Corrosion Science and Engineering, 16, 2013. [12]. Y. Raja Sekhar, S. Angel Jeba, J. Premjit Daniel, Journal of Corrosion Science and Engineering, 15, pp. 1-20, 2012. [13]. S.N. Basu, V.K. Sarin, Journal of Corrosion Science and Engineering, 6, 2003. [14]. G.D. Wilcox, Journal of Corrosion Science and Engineering, 6, 2003. [15]. L.U. Ogbuji, Journal of Corrosion Science and Engineering, 6, 2003. © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal 14 of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ` ISSN 1466-8858 Volume 16, Preprint 63 submitted 14 October 2013 Table 1 The results of weight gain studies and eddy current test obtained for Ni-Cu-Co black coatings Thickness (µm) S.No. Ni-Cu-Co Deposition Weight Eddy Colour of timings (sec.) gain current coatings method test 31 31 coating 1 Optimized 180 bath Intensive black Table 2 Micro hardness values for black Ni-Cu-Co coatings Hardness (V.H.N) S.No Load:100g Coatings As plated 1. Ni-Cu-Co 295 Annealed at 300oC 410 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal 15 of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ` ISSN 1466-8858 Volume 16, Preprint 63 submitted 14 October 2013 Table 3 Potentiodynamic polarization studies of black Ni-Cu-Co coatings Nature deposit of Ecorr (mV vs SCE) Tafel slopes ba (mV.dec-1) Icorr bc (mV.dec-1) (µA. cm-2) Mild steel -894 235 212 617 Ni-Cu-Co -788 201 192 540 -435 165 157 472 (As plated) Ni-Cu-Co (Annealed) Table 4 Impedance values of Ni-Cu-Co black coatings Rt Cdl (Ohm.cm2) (µF. cm-2) Mild steel 1710 4.56 Ni-Cu-Co 1900 3.26 2810 2.47 Nature deposit of (As plated) Ni-Cu-Co (Annealed) © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal 16 of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ` ISSN 1466-8858 Volume 16, Preprint 63 submitted 14 October 2013 Table 5 Results of salt spray analysis as per ASTM B-117 Time Uncoated Black Ni-Cu-Co (hr) Steel 0 White Black 0.5 30% red rust area Black 1 100% red rust area Black 36 100% red rust area Black 120 100% red rust area Black 240 100% red rust area Black 480 100% red rust area Black 960 100% red rust area Black 1100 100% red rust area Black 1200 100% red rust area 2% red rust area coatings(Annealed) © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal 17 of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ` ISSN 1466-8858 Volume 16, Preprint 63 submitted 14 October 2013 Legends for figure 1. XRD results for Ni-Cu-Co black coatings (As plated) 2. XRD results for Ni-Cu-Co black coatings (Annealed) 3(a). SEM image for Ni-Cu-Co black coatings(As plated) 3(b). SEM image for Ni-Cu-Co black coatings (Annealed) 4. XPS analysis of Ni-Cu-Co black coatings Figure 1 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal 18 of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ` ISSN 1466-8858 Volume 16, Preprint 63 submitted 14 October 2013 Fig gure 2 Figurre 3(a) Figure 3(b)) F © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal 19 of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work. ` ISSN 1466-8858 Volume 16, Preprint 63 submitted 14 October 2013 Figure 5 © 2013 University of Manchester and the authors. This is a preprint of a paper that has been submitted for publication in the Journal 20 of Corrosion Science and Engineering. It will be reviewed and, subject to the reviewers’ comments, be published online at http://www.jcse.org in due course. Until such time as it has been fully published it should not normally be referenced in published work.