benzotriazole: Solution phase and coating phase studies

Accepted Manuscript Synthesis and characterization of a new generation of inhibitive pigment based on zinc acetate/ benzotriazole: Solution phase and coating phase studies Assistant Professor B. Ramezanzadeh, E. Ghasemi, F. Askari, M. Mahdavian PII:

S0143-7208(15)00281-8

DOI:

10.1016/j.dyepig.2015.07.013

Reference:

DYPI 4853

To appear in:

Dyes and Pigments

Received Date: 6 May 2015 Revised Date:

14 June 2015

Accepted Date: 12 July 2015

Please cite this article as: Ramezanzadeh B, Ghasemi E, Askari F, Mahdavian M, Synthesis and characterization of a new generation of inhibitive pigment based on zinc acetate/ benzotriazole: Solution phase and coating phase studies, Dyes and Pigments (2015), doi: 10.1016/j.dyepig.2015.07.013. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT Synthesis and characterization of a new generation of inhibitive pigment based on zinc acetate/ benzotriazole: Solution phase and coating phase studies B.Ramezanzadeha1, E.Ghasemib, F.Askaria,b, M.Mahdaviana a

Department of Surface Coatings and Corrosion, Institute for Color Science and Technology, Tehran, Iran Inorganic Pigment and Glazes Department, Institute for Color Science and Technology, Tehran, Iran

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b

Abstract: An organic/inorganic hybrid corrosion inhibitive pigment based on zinc acetate/

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benzotriazole was synthesized. The chemical composition of the pigment was investigated by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. In addition,

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the morphology of the pigment was studied by scanning electron microscopy. The pigment solubility in 3.5 wt.% NaCl solution was characterized by UV-Visible, total carbon content and inductively coupled plasma-optical emission spectrometer analyses. The corrosion inhibition properties of the zinc acetate/benzotriazole was compared with conventional zinc

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phosphate pigment in 3.5 wt.% NaCl solution containing pigments extracts on mild steel samples by polarization test and electrochemical impedance spectroscopy. X-ray photoelectron spectroscopy and scanning electron microscopy characterizations were

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performed on the steel samples exposed to the extracts to investigate the surface chemistry and morphology of the pigment, respectively. Also, the effects of addition of zinc

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acetate/benzotriazole and zinc phosphate pigments on the corrosion protection performance of the epoxy coating were studied. Results obtained from X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analyses confirmed that a complex of Znbenzotriazole was successfully synthesized. The zinc acetate/benzotriazole pigment showed good solubility in NaCl solution and released inhibitive species including benzotriazole and Zn2+ cations. Zinc acetate/benzotriazole pigment showed good inhibitive properties and 1

Corresponding author: (B.Ramezanzadeh) Assistant Professor email: [email protected], [email protected] Tel: +989113441961

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ACCEPTED MANUSCRIPT reduced dissolution rate of steel through forming Fe-benzotriazole and Zn-benzotriazole complexes, and Zn(OH)2 on the cathodic sites. Also, zinc acetate/benzotriazole enhanced the corrosion protection performance of the epoxy coating and reduced cathodic delamination rate of the coating more than zinc phosphate pigment.

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Keywords: Hybrid zinc acetate/benzotriazole pigment; UV-Visible; Fourier transform infrared spectroscopy; X-ray photoelectron spectroscopy; Corrosion inhibition; Epoxy.

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1. Introduction

Organic coatings are used to protect metal substrates against corrosion through four

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mechanisms: barrier, inhibition, adhesion and sacrificial effects [1-4]. The corrosive agents coming from the outside can easily access the metal surface through diffusion from defects and microscopic porosities presented in the coating matrix. The gradually diffusion of water and ions results in the protective properties of the coating system declined. The coating

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degradation process results in the partially loss of barrier effect of the film in certain areas. As a result, the corrosive electrolyte arrives at coating/substrate interface. The electrochemical reactions at the coating/metal interface cause the increase of pH at cathodic

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sites resulting in the coating delamination [5-6]. One effective approach to enhance the

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corrosion protection properties of the organic coatings is formulating them with inhibitive pigments. The pigments with inhibitive properties can protect damaged areas where the barrier effect has broken down. These pigments can protect the damaged areas of the coatings by inhibitive effects through slowing down the corrosion reactions rates at the metal surface. The relative solubility of the pigment influences the inhibitive performance of the pigments where the precipitation mechanisms are developed. Among various types of the inhibitive pigments the zinc chromates are the most famous due to their effective inhibitive role. However, the use of this pigment has been restricted recently

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ACCEPTED MANUSCRIPT due to its toxic and carcinogenic nature causing a risk to human health [7-11]. The first generation of zinc phosphate and related substances are suggested as possible replacements for the chromates. However, the zinc phosphate pigments showed less inhibitive performance than zinc chromates due to their low solubility in aqueous corrosive electrolyte. Several

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physical and/or chemical modifications are performed on the zinc phosphate pigment to enhance its solubility as well as inhibitive action. These resulted in development of second and third generations of the zinc phosphates [12-20]. However, most of the zinc phosphate

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based pigments could not provide long term inhibitive role in the organic coatings.

One common approach to provide coatings with active protection behavior is direct loading

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of various corrosion inhibitors. Loading corrosion inhibitors into the organic coatings is one way to achieve active protection of the metal substrate. There are various methods for introducing corrosion inhibitors to the coating and the easiest of them is simple mixing with the coating formulation. However, direct incorporation of the inhibitors can raise many

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problems. Very low solubility of the inhibitor results in a lack of active agent at the substrate and the high solubility usually leads to rapid depletion of the coating at relatively short period. Incorporation of high loadings of inhibitors is needed for this case reaching long term

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protection performance [21]. However, this will disturb the coating curing behavior; and due

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to the osmotic pressure forces, water diffusion will lead to blistering and delamination of the coating. Most of the organic inhibitors have heteroatoms like N, O and S which can interact with functionalities of the organic coating weakening its barrier properties through reducing cross-linking density. In addition, the inhibitors interaction with coating matrix will result in complete deactivation of its inhibiting activity. Also, low cross-linking density may cause fast stripping of the polymer film from the substrate [22-23]. One approach to overcome these problems is capsulation of active inhibiting compounds into nano-, microscale containers (carriers). In this way the active corrosion inhibiting species can be encapsulated and stay in a

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ACCEPTED MANUSCRIPT “trapped state” as long as the coating is undamaged [24-29]. Another approach is producing hybrid complexes between the organic and inorganic inhibitors. Most of the organic inhibitors have N, O and S heteroatoms which have high affinity of producing chelates with transition metals i.e. Zn2+ and Fe2+ cations [30-31]. In this way, a hybrid pigment can be

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obtained which does not have the problems of direct incorporation of the inhibitors in the organic coatings. In our previous work [32] we characterized the active protection properties of the benzimidazole (BIA) and zinc cations (Zn2+) intercalated sodium montmorillonite clay

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particles in an epoxy ester coating. Results revealed that sodium montmorillonite clay particles could release benzimidazole (BIA) and zinc cations (Zn2+) on demand on the

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corrosion sites and promising self-healing and active protection properties were demonstrated. Most of the organic inhibitors i.e benzimidazole (BIA) and benzotriazole (BTA) are good corrosion inhibitors in acidic environments but they do not show proper inhibitive performance in neutralized pHs (6-7). However, a synergetic behavior can be seen

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when the mentioned inhibitors are used in combination with the metal cations [32-35]. We used this idea to produce a new generation of hybrid inhibitive pigment based on benzotriazole (BTA) and zinc cations. To the best of our knowledge synthesis of this pigment

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previous studies.

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with the aim of obtaining inhibitive corrosion properties has not been considered in the

This study aims at producing and characterization of a new inhibitive hybrid pigment based on zinc acetate-BTA (ZAB). X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM) techniques were utilized to evaluate the coating phase and morphology. The pigment solubility in the 3.5 wt.% NaCl solution was characterized by inductively coupled plasma-optical emission spectrometer (ICP-OES), total carbon (TOC) analyzer and UV-Visible analyses. In addition, the inhibition properties of ZAB was compared with a conventional zinc phosphate pigment

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ACCEPTED MANUSCRIPT both in the solution phase (in the 3.5 wt.% NaCl solution) and coating phase (epoxy coating) on the steel substrates by polarization and electrochemical impedance spectroscopy (EIS) techniques.

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2. Experimental 2.1. Materials

Zinc acetate (ZA, Zn(O₂CCH₃)₂.(H₂O)₂), potassium hydroxide and benzotriazole (BTA)

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were purchased from Merck Co. The commercial grade zinc phosphate pigment (ZP) was purchased from Nubiola Co. The steel panels used in this study have the following

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composition: (composition wt.%: Al: 0.04, S: 0.05, P: 0.05, Mn: 0.32, Si: 0.34, C: 0.19 and Fe: balance) and were supplied by Foolad Mobarakeh Co. (Iran). Araldite GZ7 7071X75 from Huntsman Co. was provided and used as epoxy coating. The solid content, epoxy value and density of the resin were 74–76%, 0.1492–0.1666 Eq/100 g, and 1.08 g cm−3,

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respectively. An amido polyamide, CRAYAMID 115, was purchased from Arkema Co. as the epoxy hardener. The solid content, density and viscosity at 40 °C of the hardener are

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50%, 0.97 g/cm3 and 50000 cps, respectively. 2.2. ZAB pigment synthesis procedure

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To synthesis ZAB hybrid pigment, firstly 0.06 mole of zinc acetate was dissolved in 100 ml deionized water. In addition, 0.015 mole BTA was added to 80 ml deionized water. Each of solutions was stirred for 1 h under magnetic stirrer to obtain a homogenous solution. In the next step, the aqueous solution containing zinc acetate was added to the solution containing BTA and stirred for 3 h. It was heated at 100 °C for 24 h. Finally, the products were obtained by recovering and filtering the residue, and then they were washed with distilled water to neutral pH (6-6.5) and dried at 100 °C for 3 h.

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ACCEPTED MANUSCRIPT 2.3. Pigments extract preparation ZAB and ZP extracts were prepared by stirring 1 g of the pigments in 1 liter of 3.5 wt.% NaCl solution for 24 h followed by filtration. The type and concentration of the species released from the pigments were characterized by inductively coupled plasma-optical

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emission spectrometer [Varian Vista Pro ICP-OES], ultraviolet–visible spectrum (Perkin– Elmer Lambda 25) and total organic carbon (TOC) content by TOC-L model instrument. 2.4. Epoxy composite coating formulation and application

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10 wt.% of ZAB and ZP pigments were separately introduced into the epoxy resin. Then, the

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mixtures were mixed by a pearl-mill mixer for 3 h in order to obtain an average particle size up to 10 µm. In the next step, the mixture was mixed with a stoichiometric amount of hardener (30:70 w/w). At the end, the coatings prepared were applied on the surface prepared samples. For this purpose, the mild steel panels were abraded by emery papers of 600 and 800 grades followed by solvent degreasing using Toluene. Then, they were washed with

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deionized water and dried by warm air pressure. All coatings were cured at 120 °C for 30

2.5. Techniques

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min. The dry film thickness was about 50±5 µm for all of the samples.

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2.5.1. ZAP pigment characterization The morphology of the ZAB was studied by a scanning electron microscope (SEM) model XL30, Philips. Fourier transform infrared (FT-IR) spectroscopy and X-ray photo electron spectroscopy (XPS) were used to analyze the ZAB pigment structure. The FT-IR spectra of the pigments were obtained in the transmission mode in the range of 4000-450 cm-1 using Perkin Elmer Spectrum using KBr pellet. The chemical bonds of pigments were investigated by a Specs EA 10 Plus XPS using Al Kα monochromated radiation as the exciting source at

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ACCEPTED MANUSCRIPT pressure of 10-9 mbar. The shift of binding energies (BE) was calibrated with respect to the reference peak of carbon at binding energy of 285 eV.

2.5.2. ZAB pigment inhibitive performance characterization

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The inhibition effect of the ZAB pigment was studied on the mild steel panels immersed in 3.5 wt.% NaCl solution containing the pigment extract. Mild steel panels were cut into the size of 30 mm×20 mm×1.5 mm, then the samples were abraded using SiC sand papers up to

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2400 grit finish. Finally, the samples were washed with deionized water and acetone, and then dried in air. The cleaned steel samples were immersed in 100 cc test solutions containing

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ZP and ZAB extracts. The electrochemical impedance spectroscopy (EIS) measurements were conducted in a three electrode cell (like the one used in the polarization test) at the frequency range and peak to zero amplitude of 10 kHz-100 mHz and ±10 mV, respectively. The impedance data analysis was done by NOVA 1.8 software. The working electrode area

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was 1 cm2 and the measurements were conducted at open circuit potential (OCP) after 4, 24 and 48 h. AUTOLAB G1 was employed to obtain polarization curves at the sweep rate of 1 mV/s from -100 mV to +100 mV of OCP. The test was performed at immersion time of 24 h on an area of 1

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cm2 of each sample that was exposed to the electrolyte while the rest of the sample surface was sealed with a hot melt 3:1 mixture of beeswax: colophony. Three parallel experiments were carried out

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for each sample and the middle one was selected among the three obtained values.

2.5.3. Epoxy/ZAB composite coating characterization

The effects of addition of ZAB and ZP pigments on the corrosion protection properties and cathodic delamination of the epoxy coating were studied. Salt spray test was performed on the samples containing 10 wt.% ZAB and ZP pigments on the steel substrates. The coatings with x-scribes were exposed to salt spray test according to ASTM B117 (NaCl 5 wt% solution) for 200 h. The cathodic delamination test was done using a circular cell of 9 cm2 7

ACCEPTED MANUSCRIPT full of 3.5 wt.% NaCl solution. A hole of 5 mm in diameter was made in the center of the coating samples. The test was carried out at a potential polarization of –1.34 V (compared with Ag/AgCl) during 100 h. After polarization, the cell was dismounted from the samples

3. Results and discussion 3.1. ZAB pigment characterization

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to investigate the repeatability of the measurements.

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and the average disbonded area was measured. The test was carried out on three replications

The SEM micrograph of the ZAB pigment is presented in Fig.1. It seems that ZAB particles

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are plate like with particle size less than 10 µm.

Fig.1

The chemical structure of the ZAB hybrid pigment was characterized by FT-IR, XPS and UV-Visible analyses. The BTA molecules can be deprotonated (Eq.1) in the presence of

(1)

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[36].

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transition metals i.g. Zn2+ cations and then form metal-nitrogen (dative bonding) interactions

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The organic/inorganic hybrid pigment obtained in this way denoted as ZAB. The FT-IR spectra of BTA, zinc acetate and ZAB molecules are depicted in Fig.2. The FT-IR spectrum of BTA shows -NH stretching at 3400 cm-1 ,–N=N- vibration at 1210 cm-1, –C-N bending at 2700-3100 cm-1 and =C-H bending vibrations in the aromatic ring of BTA at 750 cm-1. It is expected to see the disappearance of the –NH stretching and –N=N- vibrations at near 3400 and 1210 cm-1, respectively and a new peak generation at near 1170 cm-1 related to zincnitrogen in the FT-IR spectrum of ZAB [36-38]. A peak was appeared at near 1170 cm-1

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ACCEPTED MANUSCRIPT related to the bond formed between zinc from inorganic part to nitrogen from organic part (Zn-BTA). However, observation of –N=N- adsorption peak at 1210 cm-1 and broad peak of –NH stretching vibration at 3300 to 3700 cm-1 range in the FT-IR spectrum of ZAB confirms

Fig.2

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that some of BTA molecules are physically adsorbed on the ZAB structure.

XPS analysis was performed to better characterize the bond formed between zinc from inorganic part to the nitrogen from organic part (Zn-BTA). The survey spectrum of ZAB is

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presented in Fig.3. The spectrum demonstrated four peaks related to carbon, zinc, oxygen and nitrogen elements at binding energies of 285, 1023, 531 and 400 eV, respectively. To better

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investigation, high resolution XPS spectra for N 1s, Zn 2p3/2, and O 1s were displayed in Fig. 3. The results obtained from peak decovolotion are displayed in Table 1. It can be seen from Fig.3 and Table 1 that each of Zn 2p, O 1s and N 1s includes two regions. The deconvolution of N1s region resulted in understanding of –N=N and N-H at binding energy of 399.71 eV

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and N-Zn at 401.2 eV [39]. This confirms the FT-IR results that BTA molecules are presented in both forms of physically adsorbed and chelated with Zn. Also, the peak area for the N-Zn bond is much greater than –N=N and N-H bonds indicating that the BTA molecules

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are mostly chelated with Zn. Zn 2p deconvoluted into two peaks at 1021.76 and 1023.05 eV

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corresponding to Zn-O and Zn-N, respectively. The greater area of the Zn-N peak than Zn-O confirms that most of the Zn cations participated in Zn-BTA complex formation rather than zinc oxide and/or hydroxide formation. The O 1s was deconvoluted into two peaks at binding energies of 530.27 and 531.01 eV corresponding to O-H and O-Zn bonds. All of these observations reveal that Zn-BTA chelate was successfully produced through Zn2+ cations and BTA molecules chelation. Fig.3 Table 1

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ACCEPTED MANUSCRIPT 3.2. ZAB and ZP pigments solubility studies ZAB has slight solubility in the aqueous solution which is responsible for its inhibitive role. The ZAB pigment solubility in the 3.5 wt.% NaCl solution was studied by ICP-OES, TOC and UV-Visible analyses. ICP was performed to evaluate the Zn2+ cations concentration in

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the solution. Results showed that the ZAB could release Zn2+ with concentration of 111.3 ppm indicating good solubility of the pigment in 3.5 wt.% NaCl solution. The Zn2+ cations come from the decomposed Zn-BTA complex. Total carbon content (TOC) analysis was

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performed to reveal the amount of acetate concentration (A) in the solution.

The calculated acetate concentration based on TOC was 274 ppm. UV-Visible analysis was

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performed to reveal the presence of BTA molecules released from the decomposed ZAB pigment. The absorbance as a function of wavelength is depicted in Fig.4. An absorbance peak can be seen in the wavelength region of 230-300 nm which is related to the absorption of BTA molecules [40]. ZAB decomposition and physically adsorbed BTA molecules are

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responsible for the observed absorbance peak. All of these observations reveal that ZAB has good solubility in aqueous solution leading to the release of BTA and Zn2+ components. The solubility amounts for ZP were also studied by ICP analysis in 3.5% NaCl solution.

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According to the results, the ZP released 1.46 mg/l P and 7.89 mg/l Zn. Comparing the

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solubility parameters obtained from ZP with ZAB confirms that the later has higher solubility in 3.5 wt.% NaCl solution.

Fig.4

3.3. Corrosion inhibition properties of ZAB 3.3.1. Polarization test measurements Steel samples were dipped in the 3.5 wt.% NaCl solution containing ZAB and conventional ZP extracts for 24 h. It has been shown that the extract contains BTA and Zn2+ cations released from the ZAB pigment. The inhibition role of the pigment was studied by

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ACCEPTED MANUSCRIPT polarization test (Fig.5). Corrosion current density (icorr), anodic Tafel (ba) and cathodic Tafel (bc) were extracted from the polarization plots. The results are presented in Table 2. Table 2 Fig.5

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Inspection of Table 2 and Fig.5 shows that the corrosion potential shifted toward less negative values and the corrosion current density decreased in the extracts containing ZP and ZAB extracts. However, ZAB showed much more inhibitive action than ZP and decreased

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icorr significantly. These results indicate that ZAB extract acts as a good inhibitor for the corrosion of steel in neutral medium. This may be a consequence of deposition of a protective

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layer on the surface, blocking the active sites. It can be seen from Fig.6 that both anodic and cathodic branches shifted toward lower current densities in the presence of ZAB extract. These are indicative of cathodic and anodic reactions suppression through solubilized species adsorption on the active sites of the metal surface.

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It is clear from the results presented in Table 2 that the cathodic Tafel slope changed markedly in the extract of ZAB pigment while the anodic Tafel slope remained almost unchanged. In fact, in the presence of ZAB extract, the determining rate step of the cathodic

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reaction is changed; however, no significant effect on the anodic reaction (mild steel

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dissolution) mechanism was observed. Fig.5

3.3.2. EIS measurements

EIS is a rapid and convenient way to investigate film formation on the metal surface exposed to a corroding solution containing inhibitive species. Therefore, the steel panels were dipped in the extract of ZP and ZAB as well as in the blank solution for different immersion times. The Nyquist and Bode plots of the samples are presented in Figs.6 to 8. Fig.6

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ACCEPTED MANUSCRIPT Fig.7 Fig.8 The data of Figs.6 to 8 show only one relaxation time in the Bode phase of the samples immersed in the blank solution and ZP extract. This may imply that the electrochemical

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events on these samples are mainly under control of charge transfer process. In fact, the ZP could not form good protective film to block the active sites responsible for this phenomenon. However, two relaxation times were observed for the sample dipped in the solution

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containing ZAB extract. The one observed at higher frequencies is attributed to the charge transfer resistance (Rct) and the one at lower frequencies is related to the film formed on the

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steel surface. In fact, a protective film composed of the inhibitors released from the ZAB pigment formed on the steel surface. The impedance data were fitted by suitable equivalent circuits shown in Fig.9.

Fig.9

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where Rs, Rct, Rf, CPEdl, and CPEf are the solution resistance, charge transfer resistance, film resistance, constant phase element of double layer and constant phase element of the film,

from Eq.2 [41].

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C x =(Qx.Rx 1−n)1/n

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respectively. Double layer capacitance (Cdl) and film capacitance (Cc) values were obtained

where Cx, Qx, Rx and n show capacitance (double layer or film capacitance), admittance of CPE, charge transfer (Rct) or film resistance (Rf) and the empirical exponent of CPE, respectively. The chi-squared (χ2) was used to evaluate the precision of impedance data fitting. The χ2<0.008 was obtained for all data fitting indicating that the fitted data have good agreement with the experimental data.

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ACCEPTED MANUSCRIPT The data obtained from the fitting of Bode and Nyquist plots are presented in Table 3. In addition, impedance at low frequency limit (10 mHz) and phase angle at high frequency domain (10 kHz) of the samples were measured and compared in Fig.10.

Fig.10

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Table 3

Inspection of Table 3 and Fig.10 shows higher Rp (Rct+Rc) and impedance at 10 mHz (/Z/0.01 Hz),

and lower Ct (Cdl+Cf) values of the sample immersed in the solution containing ZAB

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extract than blank solution and the one with ZP extract. This would suggest the superior corrosion inhibition offered by ZAB compared to ZP. The Rp and |Z|0.01

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values of the

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samples exposed to the blank solution and those containing ZP and ZAB extracts decreased with time. As the immersion time elapsed an increase of Ct was observed for all of the samples. These indicate that the inhibition efficiency of the pigments decreased at long immersion times which can be attributed to the film deterioration. Phase angle (Ө) is another

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useful parameter to investigate the inhibitive species adsorption on the steel surface. It varies between 0 for an uncoated metal up to -90 phase degree for a system with intact coating [42]. Fig.10 shows higher phase angle of the samples exposed to the solution containing ZAB than

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other samples. This is an indication of capacitive behavior for this sample due to the

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formation of a barrier film on the steel surface confirming the previous results that ZAB could form protective layer on the steel surface.

3.4. Surface characterization 3.4.1. SEM analysis The electrochemical assessment showed film formation on the steel surface exposed to ZAB containing extract. The SEM micrographs were obtained from the surface of the steel samples exposed to the blank solution and solutions containing ZP and ZAB extracts (Fig.11).

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ACCEPTED MANUSCRIPT Scattered corrosion products were only observed on the surface of the samples exposed to the solutions without extract and with ZP extract. However, the surface of the sample exposed to the solution containing ZAB extract was covered by a porous film with the morphologies presented in Fig.11. This observation reveals that ZAB could show better film formation

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behavior than ZP during exposure to corrosive electrolyte. The mechanism of film formation in the presence of ZAB will be discussed later. The composition of the film precipitated was studied by XPS analysis.

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Fig.11 3.4.2. XPS analysis

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The nature of the film precipitated on the steel surface in the presence of ZAB was investigated by XPS analysis. The XPS overview spectra of the sample exposed to 3.5% NaCl solution containing ZAB extract for 24 h is depicted in Fig.12. Peaks representing species containing Zn, O, C, Fe and N and Fe were detected on the surface of this sample.

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The high resolution XPS spectra for each element are exhibited in Fig.12. Also, the deconvolution of multiple peaks in the O 1s, Zn 2p, Fe 2p and N 1s regions were performed.

Fig.12

Table 4

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The results obtained are listed in Table 4.

It can be seen in Fig.12 that O1s signal can be fitted into two Gaussian Lorentzian peaks at binding energies of 530.24 and 531 eV corresponding to the metal oxide bond (i.e. Zn-O and Fe-O) and hydroxide component (OH), respectively. The XPS spectra for Zn 2p displayed two peaks, centered at 1021.7 and 10.24 eV related to the ZnO/Zn(OH)2 and Zn-N, respectively. Fe 2p3/2 spectrum deconvoluted into three peaks at binding energies of 710.16, 711.59 and 712.88 eV corresponding to the Fe-O containing component (i.e. Fe2O3, Fe3O4 and Fe-OH) and one peak centered at binding energy of 715.4 eV related to the Fe-N

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ACCEPTED MANUSCRIPT containing phase. N 1s was fitted into two peaks centered at binding energies of 399.7 and 401.2 eV corresponding to the N=N and N-H, and N-Zn and N-Fe, respectively. These results confirm that the film precipitated on the steel surface contains BTA and Zn molecules [38]. Also, detection of Zn-N and Fe-N bonds on the surface indicates that BTA formed complexes

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with Zn2+ and Fe2+ cations (Zn-BTA and Fe-BTA). The higher ratio of N-Zn peak than N-H means that BTA molecules were mostly precipitated on the surface in the form of complexes

3.5. Corrosion inhibition mechanism of ZAB

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with Zn and Fe cations rather than physical adsorption.

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It has been found from the EIS and polarization test results that ZAB could significantly reduce the dissolution rate of steel substrate in 3.5 wt.% NaCl solution. The inhibition role of this pigment comes from the organic (Zn2+) and inorganic inhibitive (BTA) species released from the ZAB pigment when exposed to corrosive electrolyte. The ICP-OES, TOC and UV-

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Visible analyses confirmed the slight solubility of the pigment resulting in Zn2+ and BTA molecules release. The released compounds reach the active anodic and cathodic sites of the metal surface. Zn2+ cations behave as cathodic inhibitor and their adsorption on the cathodic

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sites led to the film formation according to Eqs.3 and 4 [32-33]. (Cathodic reaction)

(3)

Zn2+ + 2OH-→ Zn(OH)2

(Film precipitation on the cathodic sites)

(4)

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H2O + O2 +4e→ 4(OH-)

However, this is not the only reaction occurred on the steel surface in the presence of the released inhibitors. The BTA molecules may also form protective film on the steel surface through adsorption on the anodic and cathodic sites and/or forming complexes with metal cations i.e. Zn2+ and Fe2+. The acetate anion also could help the film formation properties of Zn2+ cations on the steel surface which is in accordance with previous reports [43]. The XPS results confirmed the presence of such complexes on the steel surface. It was found from the

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ACCEPTED MANUSCRIPT XPS results that the BTA molecules adsorption on the steel surface is not significant which may be attributed to the low affinity of this inhibitor to be adsorbed on the steel surface in neutral pHs. The BTA molecules adsorption on the steel surface can be intensified through Zn2+ cations and BTA molecules chelation resulting in insoluble film precipitation on the

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steel surface. The XPS results confirmed the Fe-N and Zn-N bonds formation on the steel surface which confirms the complex between the released metal cations and BTA molecules. Zn2+ cations tend to be adsorbed on the cathodic sites reducing the cathodic reaction rate

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which has been previously proved by polarization test results. Also, the Zn-BTA and Fe-BTA complexes can be formed on both anodic and cathodic sites leading to the shift of both anodic

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and cathodic branches toward lower current densities. It seems that the inhibitors tendency for film formation on the cathodic region is higher than anodic one and because of this the cathodic braches slope changed considerably indicating that the corrosion mechanism has been changed. A schematic illustration of the film formation in the presence of ZAB extract

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has been shown in Fig.13.

Fig.13

It has been shown that ZP has less inhibitive performance than ZAB which can be related to

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its low solubility in aqueous solution leading to an insignificant release of the corrosion inhibitors. Also, it has been shown previously that Zn2+ and BTA molecules can show

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synergetic effect resulting in significant film formation and reducing the corrosion rate of the substrate. The insoluble complexes that can be formed in the presence of the Zn2+ and BTA molecules can block the anodic and cathodic sites from the corrosion species attack. All of these observations declare that ZAB is an efficient inhibitive pigment with acceptable solubility in 3.5 wt.% NaCl solution.

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3.6. Epoxy/ZAB composite coating properties 3.6.1. Salt spray test The epoxy/polyamide coatings without and with 10 wt.% ZAB pigment were prepared and

visual performances of the samples are displayed in Fig.14 Fig.14

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applied on the steel substrates. Samples were then exposed to salt spray test for 200 h. The

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Fig.14 shows that rust and corrosion products were appeared near the scribes of the blank epoxy coating. It can be seen that addition of ZP to the coating caused decrease of the

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corrosion products accumulation near scribes but blisters were appeared at this area. This indicated that ZP could not improve the corrosion protection properties of the epoxy coating. However, the number of corrosion spots and blisters were significantly reduced in the presence of ZAB pigment. This is in accordance with previous results that ZAB could

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enhance the epoxy coating corrosion resistance. However, some small blisters can be seen near scribes and on the surface of the coating. This may be attributed to the effect of ZAB on decreasing the coating cross-linking density at some parts due to the presence of physically

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adsorbed BTA molecules on the pigment surface resulting in coating curing distortion. The

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cathodic reaction can occur in the scribe resulting in the increase of pH as a result of OH- ions creation. This causes the decrease of coating adhesion leading to the coating delamination and corrosion products development beneath the coating near scribes. The ZAB could release inhibitive spices i.e. Zn2+ and BTA which highly tend to produce Zn-BTA and Fe-BTA complexes on the corrosion sites of the metal surface. Also, the Zn2+ cations reaction with OH- produced Zn(OH)2 products at the cathodic sites resulting in the decrease of cathodic reaction rate. These all can result in the decrease in corrosion products creation rate and coating delamination.

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3.6.2. Cathodic delamination test The visual performances of the blank coating and coatings containing 10 wt.% ZAB and ZP after cathodic delamination test are depicted in Fig.15.

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Fig.15

From Fig.15 it can be seen that addition of ZAB and ZP pigments could reduce the delamination area compared to the blank coating. It is clear from the results that ZAB

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reduced the coating delamination greater than other samples. It is well known that the increase of pH inside artificial defect as a result of the following reactions, H2O+O2+4e→4

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(OH-) and 2H2O+2e→H2+2OH-, is responsible for the coating adhesion bonds damage leading to the coating delamination. The ZP and ZAB pigments improved the coating resistance against cathodic delamination through releasing inhibitive species i.e. Zn2+, PO43and BTA. The released inhibitive spices could react with hydroxyl ions and produce insoluble

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components on the cathodic sites leading to the decrease of the steel substrate cathodic activity. Compared to ZP, ZAB could produce denser and more protective film on the steel surface and therefore lower coating delamination was obtained. All of these observations

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reveal that ZAB is a good inhibitive pigment which could successfully enhance the corrosion

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protection properties of the epoxy coating on the steel substrate.

4. Conclusion •

Results showed that a hybrid inhibitive pigment based on zinc acetate and

benzothriazole (ZAB) was successfully synthesized. Results revealed that the Zn2+ cations could form a chelate with benzothriazole molecules through dative interaction. Electrochemical investigations revealed that ZAB inhibited the corrosion of steel sample much greater than conventional ZP pigment. This pigment significantly

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ACCEPTED MANUSCRIPT reduced the dissolution rate of the steel sample through precipitation of a protective film on the active anodic and cathodic sites. It mostly behaved as cathodic inhibitor and changed the cathodic reaction mechanism. •

Surface analyses revealed that the inhibitive species released by this pigment could

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form insoluble Zn(OH)2, Zn-BTA and Fe-BTA compounds on the steel surface. The film growth on the steel surface blocked the access of oxygen, Cl- and water to corrosion sites. A synergetic effect of Zn2+ cations and BTA was seen.

It was shown that addition of ZAB to the epoxy coating enhanced its corrosion

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•

protection properties and reduced the cathodic delamination rate. The ZAB could

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prevent the increase of pH at cathodic regions and decreased the coating delamination and blistering.

References

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[1] Kalendová A, Šňupárek J, Kalenda P. Nontoxic anticorrosion pigments of the spinel type compared with condensed phosphates. Dyes and Pigments 1996;30 (2):129-140. [2] Funke W. ACS Symposium Series, Colymeric Materials for Corrosion Control, American

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Chemical Society, Washington, DC (1986) p. 222

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[3] Jalili M, Rostami M, Ramezanzadeh B. An investigation of the electrochemical action of the epoxy zinc-rich coatings containing surface modified aluminum nanoparticle. Appl Surf Sci 2015;328 (15):95-108. [4] Ramezanzadeh B, Khazaei M, Rajabi A, Heidari G, Khazaei D. Corrosion Resistance and Cathodic Delamination of an Epoxy/Polyamide Coating on Milled Steel. Corrosion 2014;70 (1):56-65. [5] Liu X, Xiong J, Lv Y, Zuo Y. Study on corrosion electrochemical behavior of several different coating systems by EIS. Prog Org Coat 2009;64:497–503

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ACCEPTED MANUSCRIPT [6] Leidheiser Jr H. Whitney Award Lecture—1983: Towards a Better Understanding of Corrosion beneath Organic Coatings. Corrosion 1983;39 (5):189-201. [7] Sinko J. Challenges of chromate inhibitor pigments replacement in organic coatings. Prog Org Coat 2001;42 (3):267-282.

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[8] Buxbaum G, Pfaff G. Cadmium pigments, Industrial Inorganic Pigments. Wiley–VCH, 2005;121-123.

[9] Hernandez M, Genesca J. Effect of an inhibitive pigment zinc-aluminum-phosphate

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(ZAP) on the corrosion mechanisms of steel in waterborne coatings. Prog Org Coat 2006;56(2):199-206.

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[10] Galliano F, Landolt D. Evaluation of corrosion protection properties of additives for waterborne epoxy coatings on steel. Prog Org Coat 2002;44 (3):217-225. [11] Kalenda P. Properties of anticorrosion pigments depending on their chemical composition and PVC value. Pigm Resin Technol 2006;35 (4):188-199.

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[12] Naderi R, Attar M.M. Electrochemical study of protective behavior of organic coating pigmented with zinc aluminum polyphosphate as a modified zinc phosphate at different pigment volume concentrations. Prog Org Coat 2009;66 (3):314–320.

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[13] Mousavifard S.M, MalekMohammadi Nouri P, Attar M.M, Ramezanzadeh B. The

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effects of zinc aluminum phosphate (ZPA) and zinc aluminum polyphosphate (ZAPP) mixtures on corrosion inhibition performance of epoxy/polyamide coating. J Ind Eng Chem 2013;19 (3):1031-1039.

[14] Heydarpour MR, Zarrabi A, Attar MM, Ramezanzadeh B. Studying the corrosion protection properties of an epoxy coating containing different mixtures of strontium aluminum polyphosphate (SAPP) and zinc aluminum phosphate (ZPA) pigments. Prog Org Coat 2014;77 (1):160-167.

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ACCEPTED MANUSCRIPT [15] Naderi R, Attar MM. Electrochemical assessing corrosion inhibiting effects of zinc aluminum polyphosphate (ZAPP) as a modified zinc phosphate pigment. Electrochim Acta 2008;53 (18):5692–5696. [16] Naderi R, Attar MM. The inhibitive performance of polyphosphate-based anticorrosion

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pigments using electrochemical techniques. Dyes Pigments 2009; 80 (3):349–354.

[17] Bethencourt M, Botana FJ, Marcos M, Osuna RM, Sanchez JM. Inhibitor properties of “green” pigments for paints. Prog Org Coat 2003;46 (4):280–287.

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[18] Naderi R, Arman SY, Fouladvand Sh. Investigation on the inhibition synergism of new

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generations of phosphate-based anticorrosion pigments. Dyes and Pigments 2014;105:23-33 [19] Askari F, Ghasemi E, Ramezanzadeh B, Mahdavian M. Mechanistic approach for evaluation of the corrosion inhibition of potassium zinc phosphate pigment on the steel surface: Application of surface analysis and electrochemical techniques. Dyes and

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Pigments 2014;109:189-199.

[20] Askari F, Ghasemi E, Ramezanzadeh B, Mahdavian M. Effects of KOH:ZnCl2 mole ratio on the phase formation, morphological and inhibitive properties of potassium zinc

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phosphate (PZP) pigments. Journal of Alloys and Compounds 2015; 631:138-145. [21] Sinko J. Challenges of chromate inhibitor pigments replacement in organic coatings.

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Prog Org Coat 2001; 42: 267-282.

[22] Garcia-Heras M, Jimenez-Morales A, Casal B, Galvan JC, Radzki S, Villegas MA. Preparation and Electrochemical Study of Cerium-Silica Sol–Gel Thin Films. J. Alloys Compd 2004;380:219–224. [23] Sinko J. Challenges of Chromate Inhibitor Pigments Replacement in Organic Coatings. Prog. Org. Coat 2001;42:267–282.

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ACCEPTED MANUSCRIPT [24] Shchukin DG, Zheludkevich M, Yasakau K, Lamaka S, Ferreira MGS, M◌hwald H. ِ Layer-by-Layer Assembled Nanocontainers for Self-Healing Corrosion Protection. Adv Mater 2006;18:1672-1678. [25] Shchukin DG, Lamaka SV, Yasakau KA, Zheludkevich ML, M◌hwald H, Ferreira ِ

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MGS. Active anticorrosion coatings with halloysite nanocontainers. J Phys Chem C 2008;112 (4):958-964.

[26] Shchukin DG, Mohwald H. Self-repairing coatings containing active nanoreservoirs.

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Small 2007;3:926-943.

[27] Lamaka SV, Shchukin DG, Andreeva DV, Zheludkevich ML, M◌hwald H, Ferreira ِ

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MGS. Sol-Gel/Polyelectrolyte Active Corrosion Protection System. Adv Funct Mater 2008;18 (20):3137-3147.

[28] Snihirova D, Lamaka SV, Taryba M, Salak AM, Kallip S, Zheludkevich ML, Ferreira MGS, Montemor MF. Hydroxyapatite microparticles as feed-back active reservoirs of

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corrosion inhibitors. ACS Appl. Mater. Interfaces 2010;2 (11):3011-3022. [29] Zheludkevich ML, Serra R, Montemor MF, Yasakau KA, et al.. Nanostructured Sol–Gel Coatings Doped with Cerium Nitrate as Pre-treatments for AA2024-T3: Corrosion Protection

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Performance. Electrochim. Acta 2005;51:208–217

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[30] Poling GW. Reflection infrared studies of films formed by benzotriazole on Cu. Corros Sci 1970;10:370-395

[31] Mennucci MM, Rodrigues PRP, Costa I. Evaluation of benzotriazole as corrosion inhibitor for carbon steel in simulated pore solution. Cement and Concrete Composites 2009;31(6):418–424. [32] Ghazi A, Ghasemi E, Mahdavian M, Ramezanzadeh B, Rostami M. The application of benzimidazole and zinc cations intercalated sodium montmorillonite as smart ion exchange inhibiting pigments in the epoxy ester coating. Corros Sci 2015;94:207–217.

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ACCEPTED MANUSCRIPT [33] Mahdavian M, Attar MM. The effect of benzimidazole and zinc acetylacetonate mixture on cathodic disbonding of epoxy coated mild steel. Prog Org Coat 2009;66 (2):137-140. [34] Mahdavian M, Naderi R. Corrosion inhibition of mild steel in sodium chloride solution by some zinc complexes. Corros Sci 2011;53 (4):1194–1200.

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[35] Mahdavian M, Ashhari S. Mercapto functional azole compounds as organic corrosion inhibitors in a polyester-melamine coating. Prog Org Coat 2010;68 (4):259-264

[36] Riccardo O, Francesco T, Process for promoting adhesion between an inorganic

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substrate and an organic polymer, U.S. Patent No 6372027, Dec 7, 2000.

[37] Mennucci M, Banczek E, Rodrigues P, Costa I. Evaluation of benzotriazole as corrosion

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inhibitor for carbon steel in simulated pore solution. Cement Concrete Compos. 2009;31(6):418-24.

[38] Nilsson J-O, Törnkvist C, Liedberg B. Photoelectron and infrared reflection absorption spectroscopy of benzotriazole adsorbed on copper and cuprous oxide surfaces. Appl Surf Sci.

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1989;37(3):306-26.

[39] Alkharafi FM, El-Shamy AM and Ateya BG. Comparative Effects of Tolytriazole and Benzotriazole Against Sulfide Attack on Copper. Int J Electrochem Sci 2009;4:1351-1364.

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[40] Carlos Borin A, Serrano-Andrés L, Ludwig V, Canuto S. Theoretical absorption and

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emission spectra of 1H- and 2H-benzotriazole. Phys Chem Chem Phys 2003;5:5001-5009. [41] Hirschorna B, Orazema ME, Tribollet B, Vivier V, Frateurc I, Musianid M, Determination of effective capacitance and film thickness from constant-phase-element parameters. Electrochim Acta 2010;55:6218–6227. [42] Mahdavian M, Attar MM. Another approach in analysis of paint coatings with EIS measurement: Phase angle at high frequencies. Corros Sci 2006;48 (12):4152-4157. [43] Mahdavian M, Naderi R. Corrosion inhibition of mild steel in sodium chloride solution by some zinc complexes. Corros Sci 2011;53:1194–1200

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ACCEPTED MANUSCRIPT Figure captions: Fig.1. SEM micrographs of the ZAB powder. Fig.2. FTIR spectra of (a) BTA, (b) zinc acetate and (c) ZAB. Fig.3. XPS survey spectrum and deconvoluted spectra of the elements for ZAB powder.

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Fig.4. UV-Visible spectrum for the extract solution containing ZAB.

Fig.5. Polarization plots for the steel samples immersed in the 3.5 wt.% NaCl solution containing ZP and ZAB extract for 24 h.

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Fig.6. Nyquist and Bode plots of the steel panel immersed in the 3.5 wt.% NaCl solution containing ZAB extract for 4 h.

containing ZAB extract for 24 h.

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Fig.7. Nyquist and Bode plots of the steel panel immersed in the 3.5 wt.% NaCl solution

Fig.8. Nyquist and Bode plots of the steel panel immersed in the 3.5 wt.% NaCl solution containing ZAB extract for 48 h.

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Fig.9. Electrochemical equivalent circuits proposed to model impedance data; (a) steel sample immersed in the 3.5 wt% NaCl solution containing ZAB extract after 4 h immersion and (b) steel sample immersed in the blank solution and the one containing ZP extract.

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Fig.10. The values of (a) impedance at low frequency limit (10 mHz) and (b) phase angle at

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high frequency region (10 kHz) obtained from Bode plots data. Fig.11. SEM micrographs from the surface of the steel panels immersed in the blank solution and solutions containing ZP and ZAB extract for 4 h. Fig.12. XPS overview spectrum and deconvoluted spectra of the elements detected on the surface of steel panel immersed in the solution containing ZAB extract for 4 h Fig.13. Schematic illustration of the inhibitors adsorption on the steel surface in the presence of ZAB extract.

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ACCEPTED MANUSCRIPT Fig.14. Visual inspection from the surface of X-scribed epoxy coated samples without and with 5 wt. % ZP or ZAB pigments after 200 h salt spray test. Fig.15. Visual inspection from the surface of epoxy coated samples without and with 10

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wt.% ZP or ZAB pigments after 100 h cathodic delamination test.

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ACCEPTED MANUSCRIPT Table captions: Table 1. Characterization results of existence bonds of synthesized ZAB pigment for each element in their XPS convoluted spectra.

wt.% NaCl solution containing pigment extracts.

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Table 2. The results obtained from Polarization curves of steel samples after 24 h immersion in 3.5

Table 3. The electrochemical parameters extracted from impedance data of different sample; for ZP and blank sample Rp=Rct and for ZAB Rp=Rct+Rf.

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Table 4. Characterization results of existence bonds of synthesized PZP-BTA pigment for each element in their XPS convoluted spectra.

ACCEPTED MANUSCRIPT Table 1. Characterization results of existence bonds of synthesized ZAB pigment for each element in their XPS convoluted spectra.

Characterized bonds

Binding energy (eV)

% composition in each element

N-H, N=N

399.71

27.9

N-Zn

401.2

O-H

530.27

N 1s

Zn 2P3/2

Metal-O (example O-Zn) Zn-O (Oxygen owned to zinc hydroxide)

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72.1

48.7

51.3

1021.76

33.6

1023.05

66.4

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Zn-N

531.00

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O 1s

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Name of convoluted spectrum

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Table 2. The results obtained from Polarization curves of steel samples after 24 h immersion in 3.5 wt.% NaCl solution containing pigment extracts.

ZAB ZP No pigment

Ecorra (V) -0.624 -0.675 -0.692

icorr b (µA/cm2) 2.6 10.1 11.6

ba c (V/dec) 0.32 0.3 0.29

a

bc (V/dec) d 0.05 0.18 0.18

The standard deviation range for Ecorr values was between 0.3% and 1.2%. The standard deviation range for icorr values was between 1.5% and 7.3%. c The standard deviation range for ba values was between 2.0% and 4.2%. d The standard deviation range for bc values was between 0.5% and 3.0%.

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b

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Sample

ACCEPTED MANUSCRIPT Table 3. The electrochemical parameters extracted from impedance data of different sample; for ZP and blank sample Rp=Rct and for ZAB Rp=Rct+Rf

3.97 3.92 2.6 1.7 1.4 0.91 1.3 1.5 1.1

a

Cdl(nF/cm2) 0.0638 0.0722 0.0688 0.258 0.285 0.334 0.268 0.391 0.277

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ZAB (4h) ZAB (24h) ZAB (48h) ZP (4h) ZP (24h) ZP (48h) No pigment (4h) No pigment (24h) No pigment (48h)

CPE Y 0b nc (µsn.Ωcm-2) 8.8×10-5 0.81 9.7×10-5 0.79 1.0×10-4 0.78 0.82 3.0×10-4 -4 3.6×10 0.74 4.7×10-4 0.70 3.4×10-4 0.77 4.4×10-4 0.77 0.79 3.5×10-4

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Rpa (kohm)

The standard deviation range for Rp values was between 1.5% and 3.5%. The standard deviation range for Y0 values was between 0.6% and 3.6%. c The standard deviation range for n values was between 0.1% and 1.2%.

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ACCEPTED MANUSCRIPT Table 4. Characterization results of existence bonds of synthesized PZP-BTA pigment for each element in their XPS convoluted spectra. Name of convoluted spectrum

Characterized bonds

Binding energy (eV)

% composition in each element

N-H, N=N

399.71

27.3

N-Zn

401.2

72.7

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N 1s

Fe 2p3/2

O-H

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Zn-N

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Zn 2P3/2

Metal-O (example O-Zn and O-Fe) Zn-O (Oxygen owned to zinc hydroxide)

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O 1s

710.16 711.59 712.88 715.4

27 30 23 20

530.27

13.3

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Fe2O3 Fe3O4 Fe-OH Fe-N

531.00

86.7

1021.76

54.4

1023.05

45.6

ACCEPTED MANUSCRIPT Figure captions: Fig.1. SEM micrographs of the ZAB powder. Fig.2. FTIR spectra of (a) BTA, (b) zinc acetate and (c) ZAB. Fig.3. XPS survey spectrum and deconvoluted spectra of the elements for ZAB powder.

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Fig.4. UV-Visible spectrum for the extract solution containing ZAB.

Fig.5. Polarization plots for the steel samples immersed in the 3.5 wt.% NaCl solution containing ZP and ZAB extract for 24 h.

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Fig.6. Nyquist and Bode plots of the steel panel immersed in the 3.5 wt.% NaCl solution containing ZAB extract for 4 h.

containing ZAB extract for 24 h.

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Fig.7. Nyquist and Bode plots of the steel panel immersed in the 3.5 wt.% NaCl solution

Fig.8. Nyquist and Bode plots of the steel panel immersed in the 3.5 wt.% NaCl solution containing ZAB extract for 48 h.

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Fig.9. Electrochemical equivalent circuits proposed to model impedance data; (a) steel sample immersed in the 3.5 wt% NaCl solution containing ZAB extract after 4 h immersion and (b) steel sample immersed in the blank solution and the one containing ZP extract.

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Fig.10. The values of (a) impedance at low frequency limit (10 mHz) and (b) phase angle at

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high frequency region (10 kHz) obtained from Bode plots data. Fig.11. SEM micrographs from the surface of the steel panels immersed in the blank solution and solutions containing ZP and ZAB extract for 4 h. Fig.12. XPS overview spectrum and deconvoluted spectra of the elements detected on the surface of steel panel immersed in the solution containing ZAB extract for 4 h Fig.13. Schematic illustration of the inhibitors adsorption on the steel surface in the presence of ZAB extract.

ACCEPTED MANUSCRIPT Fig.14. Visual inspection from the surface of X-scribed epoxy coated samples without and with 5 wt. % ZP or ZAB pigments after 200 h salt spray test. Fig.15. Visual inspection from the surface of epoxy coated samples without and with 10

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wt.% ZP or ZAB pigments after 100 h cathodic delamination test.

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ZAB

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Fig.1. SEM micrographs of the ZAB powder.

ACCEPTED MANUSCRIPT 100

Transmittance (%)

95

ZA (Zinc acetate)

-N-H

-C-N

=C-H

85

80

-N=N

(a)

-CH

3950

3450

2950

2450

1950

Wavenumber (cm-1 )

-C-H (CH3) 80

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Transmittance (%)

90

70 60

OH (H2O)

50

Zn(O₂₂CCH₃₃)₂₂.(H₂₂O)₂₂

(b) 3450

2950

2450

950

450

1950

950

450

-C=O 1450

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3950

1450

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100

40

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90

Wavenumber (cm-1 )

98

-N-H

98

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93

-N=N

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Transmittance (%)

=C-H

93

88

-N-Zn -CH

88

(c)

83

3950

1210

3450

1190 2950

1170 2450

1950

Wavenumber (cm-1 )

Fig.2. FTIR spectra of (a) BTA, (b) zinc acetate and (c) ZAB.

1450

950

450

ACCEPTED MANUSCRIPT 5000 160

Zn 2p

O 1s

3000

C 1s

Zn (LMM)

O 1s

O (KLL)

N 1s

80

40

1000

0

0 0

200

400

600

800

1000

1200

526

Binding energy (eV)

160

528

530 532 Binding energy (eV)

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120

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Intensity/count

Intensity/count

4000

N 1s

Zn 2p3/2

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80

0 397

399

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40

401

Binding energy (eV)

403

Intensity/count

120

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Intensity/count

600

400

200

0 1015

1020 1025 Binding energy (eV)

Fig.3. XPS survey spectrum and deconvoluted spectra of the elements for ZAB powder.

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ACCEPTED MANUSCRIPT 3

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2.5

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1.5

1 0 200

0 200

250

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0.5

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Absorbanc Unit

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300

600

Wavelength (nm)

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Fig.4. UV-Visible spectrum for the extract solution containing ZAB.

350

700

800

ACCEPTED MANUSCRIPT 1

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0.1

0.001

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i (mA/cm2)

0.01

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0.0001

0.000001 -0.78

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0.00001

-0.73

-0.68

-0.63

ZAB ZBA ZP Blank

-0.58

-0.53

EAg/AgCl (V)

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Fig.5. Polarization plots for the steel samples immersed in the 3.5 wt.% NaCl solution containing ZP and ZAB extract for 24 h.

ACCEPTED MANUSCRIPT 4000

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2000

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1000

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1000

2000

Z'/ohm

4

3000

ZB A

80 ZP

Blank

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60

2

40

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log (Z/ohm cm2)

3

4000

cm2

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1

20

0

-1

-Phase angle (deg)

-Z"/ohm cm2

3000

0 0

1

2

3

4

log (f/Hz)

Fig.6. Nyquist and Bode plots of the steel panel immersed in the 3.5 wt.% NaCl solution containing ZAB extract for 4 h.

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Z'/ohm

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ZB A

ZP

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60

40

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log (Z/ohm cm2)

3

4000

cm2

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1

20

0

-1

-Phase angle (deg)

-Z"/ ohm cm2

3000

0 0

1

2

3

4

log (f/Hz)

Fig.7. Nyquist and Bode plots of the steel panel immersed in the 3.5 wt.% NaCl solution containing ZAB extract for 24 h.

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2500

1500

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1000

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500

0 0

500

1000

1500

4

ZB ZAB

ZP

2500

Blank

80

60

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3

log(Z/ohm cm2)

2000

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Z' / ohm

cm2

2

20

EP

1

40

AC C

0

-1

-Phase angle (deg)

-Z" / ohm cm2

2000

0 0

1

2

3

4

log (f/Hz)

Fig.8. Nyquist and Bode plots of the steel panel immersed in the 3.5 wt.% NaCl solution containing ZAB extract for 48 h.

70

(a)

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50

40

30

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-Phase angle (degree)

60

20

10

-1

0

11

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0 22

33

log (f/Hz)

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50 50

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0 0 -1 -1

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10 10

(b)

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40 40

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-Phase angle (degree)

60 60

44

0 0

1

2 1

3 2

4 3

4

log (f/Hz)

Fig.9. Electrochemical equivalent circuits proposed to model impedance data; (a) steel sample immersed in the 3.5 wt% NaCl solution containing ZAB extract after 4 h immersion and (b) steel sample immersed in the blank solution and the one containing ZP extract.

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3.7

4 hr

(a)

24 hr

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48 hr

3.3

3.1

2.9

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log (Z/ohm cm2)

3.5

2.5 Blank sample 25 4 hr

10

(b)

EP

15

48 hr

ZBA

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-Phase angle (deg)

20

ZP

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24 hr

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5

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Blank sample

ZP

ZBA

Fig.10. The values of (a) impedance at low frequency limit (10 mHz) and (b) phase angle at high frequency region (10 kHz) obtained from Bode plots data.

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Fig.11. SEM micrographs from the surface of the steel panels immersed in the blank solution and solutions containing ZP and ZAB extract for 4 h.

400

Fe 2p3/2

Zn 2p MANUSCRIPT ACCEPTED O (KLL)

O 1s

Intensity (Count)

300

Fe 2p3/2

200

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100

C 1s Zn (LMM) N 1s

0

800

600

O 1s

712

714

716

718

Binding energy (eV)

Zn 2p

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Intensity (Count)

600

400

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0 526

528

530

532

534

400 300 200 100

0 1016

536

1018

1020

1022

1024

1026

Binding energy (eV)

EP

Binding energy (eV) 160

AC C

N 1s

120

Intensity (Count)

Intensity (Count)

710

SC

708

80

40

0 394

396

398

400

402

404

406

Binding energy (eV)

Fig.12. XPS overview spectrum and deconvoluted spectra of the elements detected on the surface of steel panel immersed in the solution containing ZAB extract for 4 h

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ACCEPTED MANUSCRIPT BTA adsorption Zn-BTA chelate

Fe-BTA chelate 2+

Zn2++2OH-→Zn(OH)2

-

Fe :

:

O Anode&Cathode

Fe OO

Zn

Zn

Fe

Zn O Fe

O Fe

:

:

:

Anode& Cathode

SC

Fe

n

: n

Zn Zn (OH) 2 O Fe Cathode

TE D

M AN U

Fig.13. Schematic illustration of the inhibitors adsorption on the steel surface in the presence of ZAB extract.

EP

Cathode

:

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Zn (OH)2

:

:

Fe

RI PT

Zn +2OH →Zn(OH)2

ACCEPTED MANUSCRIPT ZP sample

Blank sample

RI PT

Blisters

SC

Corrosion products accumulation

AC C

EP

TE D

ZAB sample

M AN U

Corrosion products accumulation

Fig.14. Visual inspection from the surface of X-scribed epoxy coated samples without and with 5 wt. % ZP or ZAB pigments after 200 h salt spray test.

ACCEPTED MANUSCRIPT

Blank sample

AC C

EP

TE D

ZP sample

M AN U

SC

RI PT

ZAB sample

Fig.15. Visual inspection from the surface of epoxy coated samples without and with 10 wt.% ZP or ZAB pigments after 100 h cathodic delamination test.

ACCEPTED MANUSCRIPT

EP

TE D

M AN U

SC

RI PT

A hybrid inhibitive pigment based on zinc acetate/ benzotriazole was synthesized The chemical composition and morphology of the pigment was investigated Zinc acetate/benzotriazole pigment showed good inhibitive properties Zinc acetate/benzotriazole enhanced the corrosion resistance of the epoxy coating

AC C

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