Exploration of Dextran for Application as Corrosion Inhibitor for Steel

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Exploration of Dextran for Application as Corrosion Inhibitor for Steel in Strong Acid Environment: Effect of Molecular Weight, Modification, and Temperature on Efficiency Moses M Solomon, Saviour A. Umoren, Ime B. Obot, Ahmad A. Sorour, and Husnu Gerengi ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b09487 • Publication Date (Web): 30 Jul 2018 Downloaded from http://pubs.acs.org on August 1, 2018

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ACS Applied Materials & Interfaces

Exploration of Dextran for Application as Corrosion Inhibitor for Steel in Strong Acid Environment: Effect of Molecular Weight, Modification, and Temperature on Efficiency Moses M. Solomona*, Saviour A. Umorena, Ime B. Obota, Ahmad A. Soroura, and Husnu Gerengib a

Centre of Research Excellence in Corrosion, Research Institute, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia b

Corrosion Research Laboratory, Department of Mechanical Engineering, Faculty of Engineering, Duzce University, 81620, Duzce, Turkey * [email protected] (M. M. Solomon) Abstract The possibility of utilizing dextran as a green corrosion inhibitor for steel in strong acid environment was explore using weight loss, electrochemical (electrochemical impedance spectroscopy (EIS), electrochemical frequency modulation (EFM), potentiodynamic polarization (PDP), and linear polarization (LPR)) supported with surface analysis via scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) techniques. The effect of molecular weight, temperature, and modification on the inhibition efficiency of dextran was also studied. Results from all the applied techniques reveal that dextran exhibit moderate anticorrosion property towards St37-2 steel dissolution in 15% H2SO4 solution. Dextran with molecular weight of 100,000 – 200,000 g/mol (Dex 1) exhibited the highest inhibition efficiency of 51.38% at 25 oC. Based on PDP results, dextran behaved as a mixed type corrosion inhibitor. Inhibition efficiency of dextran varies inversely with molecular weight but directly with temperature. Two modification approaches, namely incorporation of silver nanoparticles (AgNPs) into dextran matrices and combination with 1 mM KI were adopted to enhance the inhibition efficiency of dextran and the approaches proved effective. The protective capability of Dex 1 has been upgraded from 51.38% to 86.82% by infusion of AgNPs and to 94.21% by combination with KI at 25 oC. Results from the study on the effect of temperature reveals that Dex 1 + KI mixture could synergistically offer 99.8% protection to St37-2 steel in 15% H2SO4 environment at 60 oC. Surface analysis results confirm the presence of additives molecules on the studied metal surface. XPS results disclose that AgNPs are in oxide form while iodide ions are in the form of triiodide and pentaiodide ions on the metal surface. Modified dextran is a promising candidate for application as corrosion inhibitor in acid induced corrosive environment. Keywords:

Metals

corrosion;

Inhibition;

Dextran;

Molecular

Temperature.

1 ACS Paragon Plus Environment

weight;

Modification;

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1. Introduction Steel has a long standing history of application as structural, civil, and industrial engineering material because of its guaranteed strength 1. Sulphuric acid is the workhorse chemical of the industrial world and is produced in larger volume than other acids. It is also cheaper when compared with other industrial acids like the hydrochloric acid. Acid solution gets in contact with metal during industrial processes like acid cleaning, pickling, acidizing, etc. and corrosion is facilitated by the process 2. Normally, acid solutions used for such industrial practices are fortified with corrosion inhibitors so as to guard against metals deterioration. The recent past has been characterized with research activities focused mainly on green chemicals. In the area of corrosion inhibition, substances of natural origin – plant extract 3-5 and natural polymers

6-9

have been the target. Properties such as abundance in nature, renewability,

biodegradability, biocompatibility, ecological friendliness, as well as their low prices are the attractive features

10

. In addition, polymers have multiple functionalities which should induce

participation of many sites during adsorption process. However, research findings have shown that some natural polymers are not very effective metals corrosion inhibitors

8, 11, 12

. Insolubility

and instability at elevated temperatures have been identified as the possible cause of their poor performance

13

. The current research focus is on the enhancement of the desire corrosion

inhibition property in the so-called green substances to be in the same level with the ‘labeled’ toxic chemicals which they are expected to replace in the nearest future or perform better than them. To this end, natural polymers have been subjected to several modifications using techniques like functionalization

14

, copolymerization

15

, grafting

16

, blending with other

substances for synergistic effect 13, and compositing 6, 7. Dextran is a polysaccharide consisting of chains of varying lengths of α-D-pyran. The linear chain contains α-1,6 glycosidic linkages between glucose molecules and the branches start from α-1,3 linkages (Fig. 1(a)). This unique branching distinguishes it from a dextrin (a straight chain glucose polymer linked by α-1,4 or α-1,6 linkages). Dextran contains multiple oxygen heteroatom (Fig. 1(b)) thus fulfilling one of the essential requirements for a metal corrosion inhibitor. It has log Po/w value of – 7.6 and LD50 of 10700 mg/kg 17 hence could be classified as green. A green chemical is expected to have log Po/w value of less than 3 and LD50/LC50 that


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falls within category 4 (LD50/LC50 = ≥ 2000) or 5 (LD50/LC50 = ≥ 5000)

18-20

. Dextran is

available in multiple molecular weights; high branching level in dextran can lower its solubility in aqueous solution and medical field

21

24

. Dextrans have gained application in the food industry

22

, oil drilling

23

,

. It has been reported as inhibitor for the corrosion of 6061Al—15%(v)

SiC(P) composite in 0.25 M HCl medium 25. In this investigation, we explore the potentials of various molecular weight dextran as corrosion inhibitor for steel in strong acid medium using weight loss, electrochemical (EIS, EFM, & PDP), and surface screening (SEM, EDAX, AFM, & XPS) techniques. The influence of modification (two approaches, compositing and combination with iodide ions for synergistic effect are considered) and temperature (25 – 60 oC) on the inhibition efficiency of dextran is also studied. To the best of our knowledge, there has been no report on dextran as corrosion inhibitor for steel in 15% H2SO4 solution.

2. Experimental Section 2.1

Sample preparation and Chemicals Used

A St37-2 metal sheet procured from Erdemir Steel Co., Turkey was used for this investigation. The chemical composition of the metal in wt.% is as follows: C = 0.17, Mn = 1.40, P = 0.05, Si = 0.30, S = 0.05, and Fe = 98.03 7. The metal sheet was mechanically cut into coupons of 3 cm ×3 cm (sectional area = 9 cm2) for weight loss experiments and round disc specimens of 0.79 cm2 as the surface area for electrochemical experiments. Prior to each experiment, the samples were mechanically abraded with emery paper of #240, #320, #400, #600, and #800 grits. The abraded specimens were washed under water and cleaned with acetone to do away with the dust generated from the abrasion. They were thereafter dried in warm air. The chemicals used in this study include dextran of different molecular weight (100,000 – 200,000 g/mol, 200,000 – 300,000 g/mol, and 3,000,000 – 7,000,000 g/mol), sulphuric acid, silver nitrate, and potassium iodide. The dextran with molecular weight of 100,000 – 200,000 g/mol is designated herein as Dex 1 while Dex 2 and Dex 3 are used for dextran with molecular weight of 200,000 – 300,000 g/mol, and 3,000,000 – 7,000,000 g/mol respectively. Dextran was purchased from Polysciences Inc., USA while the other chemicals were products of Sigma



Aldrich, USA. All the chemicals were used as procured without further purification and distilled water was used in all preparations.

2.2

Solutions

The corrodent was 15% H2SO4 solution prepared by diluting a concentrated H2SO4 acid. The concentration of KI used in this study was 1 mM while 1000 mg/L was used for dextran and composite. 1000 mg/L was chosen after preliminary results showed that this concentration is the optimum concentration for dextran in 15% H2SO4 solution.

2.3

Synthesis of Silver Nanoparticles (AgNPs)/Dextran Nanocomposite

The AgNPs/dextran nanocomposite was synthesized in-situ following the procedure outlined in our previous reports

6, 7

. Summarily, 1000 mg/L dextran solution was prepared using 15%

H2SO4 solution and the solution used to prepare 1 mM AgNO3. 5 mL of natural honey was added to 100 mL of the dextran + AgNO3 solution and left to stand at room temperature for 4 days.

2.4

Confirmation of AgNPs/Dextran Nanocomposite Formation

The elemental composition of AgNPs/dextran nanocomposite was determined using an energy dispersive X-ray spectroscopy (EDAX) coupled to the Scanning Electron Microscope (SEM) JEOL JSM-6610 LV. Sample for this analysis was prepared by depositing colloidal solution of AgNPs/dextran nanocomposite on aluminum sample holder and allowing it to dry at room temperature. The morphology of AgNPs in dextran matrix was observed in a transmission electron microscopy (TEM), JEM-2100F model operated at accelerating voltage of 200 kV. A JASCO770- UV−Vis spectrophotometer (200 to 800 nm) operated at a resolution of 1 nm with a scan rate of 100 nm/min at room temperature was used for UV-vis studies.

2.5

Weight Loss (WL) Experiments

Four (4) 150 mL capacity glass bottles labeled as blank, Dex 1, Dex 1 + KI, and composite were filled with 100 mL of the respective solutions. Two pre-weighed cleaned coupons were freely suspended with the aid of a thread in each of the bottles. They were kept in digital thermostatic water bath maintained at desired temperatures (25 – 60 oC) for 6 h. The specimens 4 ACS Paragon Plus Environment

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were removed from the test solutions, washed thoroughly in running water and distilled water, cleaned with acetone, and dried with warm air. The dried coupons were reweighed and the mean value calculated. The mean weight loss (g) was used to calculate the corrosion rate (ν ) in g cm-2 h-1 according to the following Equation 12:

ν=

∆W At

(1)

where ∆W is the mean weight loss value, A the sectional area of the specimen (9 cm2), and t is the immersion duration (6 h). The inhibition efficiency (ηWL) of the additives in percentage was computed using Equation 2:

η WL = W 0

−W

W0

× 100

(2)

where W 0 and W are the mean weight losses of the samples in the uninhibited and inhibited systems respectively.

2.6

Electrochemical Experiments

A Gamry Potentiostat/Galvanostat/ZRA Reference 600 instrument was used for all electrochemical measurements namely open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), electrochemical frequency modulation (EFM), linear polarization (LPR), and potentiodynamic polarization (PDP). Measurements were done in the afore listed order. The electrochemical set-up consisted of St37-2 steel sample as the working electrode, silver/silver chloride (Ag/AgCl) as reference electrode, and a graphite rod as the counter electrode. The OCP measurement was for 3600 s which was found sufficient for steady-state condition to be achieved (Fig. 2). EIS tests were conducted over the frequency range of 104 to 10 mHz, with acquirement of 10 points per decade and a signal amplitude of 10 mV at corrosion potential (Ecorr). EFM experiments were performed utilizing potential perturbation signal with amplitudes of 10 mV. Measurements were done using two frequencies, 2 and 5 Hz. The base frequency was 1 Hz with 32 cycles so that the sinusoidal waveform repeats after 1 s. LPR tests were carried out from −15 mV to +15 mV versus EOCP at the scan rate of 0.125 mV s−1. PDP tests were carried out at the potential of ± 250 mV from OCP at a scan rate of 0.5 mVs−1. All measurements were repeated at least three times and good reproducibility of the results was observed. Echem analyst software was used to analyze the experimental data. 5 ACS Paragon Plus Environment


2.7

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Surface Analysis

The morphologies of the surfaces of St37-2 samples exposed to 15% H2SO4 solutions without and with additives for 24 h and the elemental composition of the films on the surfaces were determined using the same SEM and EDAX instruments listed in sub-section 2.4. The roughness characteristics of the exposed surfaces were ascertained using 5420 atomic force microscope (N9498S, Agilent Technologies, UK) operated in the contact mode under ambient conditions. Unlike the samples for SEM, EDAX, and XPS analysis, the samples for AFM analysis after retrieving from test solutions were gently washed in running water and acetone, dried in warm air before submitting for the analysis. X-ray photoelectron spectroscopy (XPS) analysis was carried out using a ESCALAB 250Xi XPS spectrometer with a monochromatic Al Kα X-ray source. The XPS data were obtained from the sample surface directly without Ar ion sputtering and were analyzed using Avantage v 5,51,0,5371 software.

3. Results and Discussion 3.1

Corrosion Inhibition by Dextran

Electrochemical techniques namely EIS, EFM, LPR, and PDP were used to study the effect of addition of dextran on the dissolution behavior of St37-2 steel in 15% H2SO4 solution. Fig. 3 presents the EIS graphs obtained from the study in (a) Nyquist and (b) Bode modulus and Phase angle formats. At high frequencies, the Nyquist diagrams are characterized with a single and imperfect capacitive loop which is a common feature of a charge transfer controlled corrosion process

26, 27

. The imperfectness is caused by the presence of micro roughness and

other heterogeneities on the working electrode surface which could arise from corrosive attack on exposure to the acid solution

26, 28

. If metals corrosion resistance is a direct function of

29

capacitive loop radius , then the presence of dextran in the acid solution boosted the corrosion resistance of St37-2 since the capacitive loops recorded in the presence of dextran are larger than that in the absence. Furthermore, a second unresolved semicircle can be identified at the medium frequencies in the Nyquist diagrams recorded in the presence of dextran. This can be associated with the double layer structure of adsorbed dextran films on the metal surface

30-32

. By

comparing the capacitive loop in Dex 1, Dex 2, and Dex 3 representative plots, it is seen that molecular weight has great impact on the corrosion inhibition effectiveness of dextran. For 6 ACS Paragon Plus Environment

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instance, the size of the capacitive loop is in this order Dex 1 > Dex 2 > Dex 3; meaning that the low molecular weight dextran exhibited the highest corrosion inhibition effect. The effect can also be observed in the Bode modulus and Phase angle diagrams. The Bode modulus is shifted towards noble direction while Phase angle is displayed towards more negative angle in the aforementioned order at low frequencies (Fig. 3(b)). Worthy of note is the fact that the Nyquist, Bode modulus, and Phase angle plots of Dex 1, Dex 2, and Dex 3 are identical inferring that molecular weight has no influence on the corrosion inhibition mechanism of the polymer. Accordingly, the equivalent circuit in Fig. 4(a) was used for the analysis of the electrochemical impedance representing the blank while the equivalent circuit in Fig. 4(b) was used for the dextran inhibited electrochemical impedances. In the equivalent circuit, Rs stands for solution resistance, Rct represents charge transfer resistance, CPEdl and CPEf connote constant phase element of the inner and outer film layer respectively, while Rf describes the resistance of the outer layer of the adsorbed film. As it is known, CPE is recommended for good quality fit of an imperfect capacitive loop

33

. Actually, good fitting was obtained with the selected equivalent

circuits as could be seen in Fig. S1 of the supporting information and the quite small chi square values (Table 1) support this claim. The derived values for the relevant parameters are given in Table 1. The inhibition efficiency (ηEIS, %) was calculated making use of the Rct values according to the following Equation:

ηEIS (%) =

Rct ( inhibited ) − Rct (uninhibited ) × 100 Rct ( inhibited )

(1)

In Table 1, it is seen that Rs increased in the presence of dextran. The Rs value of the uninhibited acid solution is 0.667 Ω cm-2 but becomes 0.730 Ω cm-2, 0.676 Ω cm-2, and 0.789 Ω cm-2 in the presence of Dex 1, Dex 2, and Dex 3 respectively. The influence of molecular weight on the corrosion inhibition property of dextran becomes so clear in Table 1. The presence of 1000 mg/L Dex 1 in the acid solution raised the charge transfer resistance of St37-2 steel from 104.2 Ω cm-2 to 214.300 Ω cm-2 protecting the metal surface by 51.377%. The inhibiting ability of dextran declined as the molecular weight increases such that Dex 2 and Dex 3 increased the metal charge transfer resistance to 179.400 Ω cm-2 and 165.200 Ω cm-2 respectively with 41.918% and 36.925% being the inhibition efficiency. This finding is contrary to the reports of Umoren and Gasem

34

, Abdallah et al.

35

, and Finsgar et al.

36

that the inhibition efficiency of

polyvinyl alcohol, polyethylene glycol, and polyethyleneimine increased with increasing 7 ACS Paragon Plus Environment


molecular weight but agreed with the submissions of Wang et al.

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37

on carboxymethyl starch.

Obviously, high molecular weight organic inhibitor should possess higher inhibiting property than low molecular weight counterpart since it should cover greater surface area. However, solubility is very essential for effective corrosion inhibition. An inhibitor that is completely soluble in its area of application would be effective than the one that is partially soluble

13

. As

mentioned in the introductory section, the solubility of dextran in aqueous solution decreases with increase in branching level and molecular weight

21

and this might be the reason for the

observed decrease in inhibition efficiency with increasing molecular weight. Fig. 5 shows the intermodulation spectra recorded for St37-2 steel in 15% H2SO4 solution in the absence and presence of dextran at 25 oC. The EFM technique is attractive because of its high sensitivity occasioned by the tracking of corrosion parameters at harmonic and intermodulation of input frequencies and the fact that it has inbuilt validation apparatus – the causality factors 38, 39. In Fig. 5, the harmonic and intermodulation bands can easily be separated from the peaks arising from the background noise as they are more intense 39. The harmonic and intermodulation peaks were therefore selected for the computation of corrosion kinetic parameters namely corrosion density (icorr), anodic and cathodic slopes (βa, βc), and causality factors 2 and 3 (CF-2, CF-3) using relevant equations as given in Obot and Onyeachu 38. The inhibition efficiency (ηEFM, %) was calculated following Equation 2:

ηEFM (%) =

i corr (uninhibited ) − i corr ( inhibited ) × 100 i corr (uninhibited )

(2)

All the parameters derived from the EFM experiments are presented in Table 2. As could be seen in the table, the values of CF-2 and CF-3 are within the theoretical range of 0-2 and 0-3 38, 39 thus validate the EFM results. The icorr value is reduced in the presence of dextran pointing to the inhibiting effect of dextran in the studied environment. Dex 1 is found to still exhibit the highest inhibition efficiency (43.347%) from this technique agreeing with the EIS results. It is observed from the results in the table that the presence of dextran in the acid corrodent has slight influence on both βa and βc, i.e the values of βa and βc for dextran inhibited systems are slightly higher than those of the blank. This suggests that dextran behaved in the studied environment as a mixed type corrosion inhibitor retarding both the anodic and cathodic corrosion reactions 6. To verify the mixed type behavior suggested by the EFM results, PDP experiments were performed. Fig. 6 shows the potentiodynamic polarization curves obtained for St37-2 steel in 8 ACS Paragon Plus Environment

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15% H2SO4 solution devoid of and containing Dex 1, Dex 2, and Dex 3 respectively at 25 oC and the polarization parameters derived by the extrapolation of the linear portions of the anodic and cathodic sections of the curves are listed in Table 3. It is obvious from the figure and table that dextran exhibited mixed type tendency. There is no noticeable displacement of the corrosion potential (Ecorr) and both the anodic and cathodic current densities are affected on addition of dextran into the corrosive system. The icorr, ηPDP, and ηLPR values follow the trend noted in Table 2. Also, the polarization resistance (Rp) is in good agreement with the Rct value in Table 1. Based on the results from all the electrochemical techniques (Tables 1 – 3), it is concluded that dextran moderately inhibits St37-2 corrosion in 15% H2SO4 solution and that inhibition ability is in the order Dex 1 > Dex 2 > Dex 3.

3.2

Effect of Silver Nanoparticles Incorporation on Dextran Performance

Modification of dextran for better inhibition performance was necessary after the realization from the electrochemical studies (Tables 1-3) that the polymer has moderate corrosion inhibiting ability for St37-2 steel in the studied acid medium. We modified Dex 1 by incorporating silver nanoparticles (AgNPs) into the polymer matrix. Dex 1 was selected because it was the most promising and the choice of compositing as a modification approach was motivated by our previous successes in enhancing the corrosion protective power of natural polymers through this approach

6, 7, 40

. Fig. 7 presents the EDAX spectrum, TEM picture, and

UV-vis spectrum of Dex 1/AgNPs nanocomposite. The characteristic AgNPs peak is eminent in Fig. 7(a) at 3 keV and this signal is often associated with Surface Plasmon Resonance effect 40-42. The component elements of dextran (i.e C and O) can as well be seen in the figure. With these evidences, it could be said that Dex 1/AgNPs nanocomposite was successfully synthesized. The TEM picture in Fig. 7(b) and the sharp UV-vis peak in Fig. 7(c) reveal that, in the polymer matrix, the nanoparticles were well dispersed without agglomeration and are spherical in shape. The effect of incorporation of AgNPs into dextran matrix on the inhibition efficiency was examined using EIS, EFM, PDP, and LPR techniques. Fig. 8 depicts the (a) Nyquist graphs and (b) polarization curves derived from the EIS and PDP experiments respectively. The intermodulation spectra for the same system are given as supporting information in Fig. S2. The parameters associated with Fig. 7(a), Fig. 7(b), and Fig. S2 are respectively displayed in Tables 1, 2, and 3. There is noticeable increment in the diameter of the semicircle gotten for Dex 9 ACS Paragon Plus Environment


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1/AgNPs composite relative to the one for Dex 1 (Fig. 7(a)). The quantitative results in Table 1 reveal that this increment is by 68.992% in terms of inhibition efficiency; that is, inhibition efficiency of Dex 1 is upgraded from 51.377% to 86.823% upon incorporation of AgNPs. The difference is almost same as the inhibition efficiency of Dex 3. From Table 2, the presence of AgNPs in Dex 1 matrix further reduced the corrosion current density from 118.200 µA cm−2 to 30.970 µA cm−2 while the polarization resistance in Table 3 is increased from 97.610 Ω cm2 to 927.010 Ω cm2; as effect, the inhibition efficiency is stepped up from 43.347% to 85.153% and 47.037% to 89.470% respectively. The effect of AgNPs incorporation is also very obvious in Fig. 7(b). Both the anodic and cathodic current densities are appreciably reduced and 88.401% inhibition efficiency is achieved as against 47.893% for Dex 1 (Table 3). AgNPs, because of their active properties have the tendency to interact chemically with St37-2 steel surface. Such interaction will replenish the metal surface which had been established in other reports

43, 44

to

acquire net positive charge in a strong acid environment like the one considered in this investigation. Zhang et al.

45

explained that when such interaction occur, extra electrons on the

metal surface are transferred from the d-orbital to the anti pi orbital of the inhibitor molecules and the retro-donation favors adsorption of inhibitor molecules.

3.3

Effect of Iodide Ions Addition on Dextran Performance

It has been established that iodide ions are predispose to adsorption on metals surfaces than other halide ions halide ions

46-48

46-48

. This is because iodide ion has a higher ionic radius than the other

. This make iodide ions to exhibit higher hydrophobicity and lower

electronegativity than the other halides

46-48

. For this reason, iodide ions are often selected in

expense of other halide ions in the formulation of metals corrosion inhibitors

46-49

. Fig. 9 shows

comparative electrochemical impedance spectra for dextran and dextran + KI combination. In the Nyquist representation (Fig. 9(a)), the semicircles at the high frequency regions in the dextran + KI graphs are remarkably larger compared to those of dextran meaning the charge transfer process was suppressed in dextran + KI systems than in dextran systems. Again, the additional capacitive loop at the medium frequency regions is more pronounced in the dextran + KI graphs than in dextran diagrams suggesting a thicker adsorption layer of dextran + KI than dextran alone on the substrate surface. In Fig. 9(b) the positive influence of iodide ions addition is also seen in the impedance and Phase angle displacements. The two time constants of the Nyquist plots (Fig. 10 ACS Paragon Plus Environment

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9(a)) can be clearly differentiated in the Bode representation (Fig. 9(b)). The electrochemical parameters deduced from the analysis of these graphs are also listed in Table 1. Inspection of the results in the table reveals remarkable enhancement of the corrosion inhibition ability of dextran by iodide ions. For instance, the Rct of the metal is further raised from 214.300 Ω cm2, 179.400 Ω cm2, and 165.200 Ω cm2 which was achieved with Dex 1, 2, & 3 respectively to 1800.000 Ω cm2, 1590.000 Ω cm2, and 1503.000 Ω cm2. Consequently, the η of Dex 1, 2, & 3 increased from 51.377%, 41.918%, and 36.925% to 94.211%, 93.447%, and 93.067% respectively. This significant improvement could be due to a synergy in the adsorption of dextran and iodide ions. This can be ascertained by calculating the synergism parameter (Sθ). Normally, Sθ > 1 is indicative of synergistic effect while Sθ < 1 is reflective of antagonistic effect 46. For the studied systems, Sθ was calculated using the formula 50:

Sθ =

1 − (θ 1 + θ 2 − θ 1θ 2 ) 1 − θ 11+ 2

(3)

where θ1 is degree of surface coverage of dextran, θ2 is the degree of surface coverage of iodide 1 ions and θ 1+ 2 is the degree of surface coverage of dextran + KI combination. Meanwhile, θ was

computed using the following formula 47:

θ=

η

(4)

100

The calculated Sθ value for Dex 1+ KI, Dex 2 + KI and Dex 3+ KI is 1.35, 1.46, and 1.50 respectively. The implication of this is that, dextran and iodide ions cooperatively adsorbed on St37-2 steel surface in 15% H2SO4 solution leading to the observed enhancement in inhibition efficiency. Iodide ions first chemisorbed on the metal surface and protonated forms of dextran adsorbed thereafter through columbic attraction. The stabilization of the adsorbed films gave rise to larger surface coverage and better corrosion inhibition

46, 51

. However, Dex 1+ KI still

demonstrates greater corrosion inhibition performance. Worthy of mentioning in Table 1 is the fact that ndl and nf values are either unity or near unity in all cases. This is indicative of capacitive interfaces 40, 52. The influence of iodide ions addition on the corrosion inhibition efficiency of dextran was also studied using EFM. The intermodulation spectra recorded for St37-2 steel in 15% H2SO4 solution containing dextran + iodide ion combination at 25 oC are depicted as Fig. S3 in the supporting information and the parameters derived from the analysis of the graphs are 11 ACS Paragon Plus Environment


displayed in Table 2. It is observed from the table that upon addition of iodide ions to dextran, icorr significantly diminished and the inhibition efficiency improved. The icorr value decrease from 118.200 µA cm−2, 152.2 00µA cm−2 and 127.800 µA cm−2 to 17.640 µA cm−2, 17.890 µA cm−2, and 19.400 µA cm−2 while η increased from 43.347%, 27.037%, and 38.734% to 91.544%, 91.424%, and 90.700% upon addition of iodide ions to Dex 1, 2, & 3 respectively. This results are adjudged valid as the CF-2 and CF-3 values acquired for the studied systems are within the acceptable limit. Results from this technique are in good agreement with those from EIS and further show that addition of iodide ions to dextran is a good option towards enhancing the polymer inhibition efficiency in strong acid environment. Fig. 10 presents various potentiodynamic polarization curves for St37-2 steel in 15% H2SO4 solution in an attempt to point out the ability of iodide ions to boost the corrosion retardation property of dextran. The associated polarization parameters alongside the parameters derived from LPR experiments are also listed in Table 3. As could be seen in Fig. 10, dextran + KI combination acted as mixed type corrosion inhibitor and greatly displaces both the anodic and cathodic current densities towards lower values compared to dextran alone. The remarkable reduction in the icorr, increase in Rp values, and the upgrading of the η in Table 3 again reflect the effectiveness of dextran + KI combination as inhibitor for St37-2 steel in the studied environment. The maximum inhibition efficiency of 94.797% and 95.441% was achieved with Dex 1 + KI from PDP and LPR techniques. It should be noted that the η obtained from all the applied methods for dextran + KI combination exceeds 90% (Tables 1 – 3) portraying this modification approach as effective and benefitting.

3.4

Effect of Temperature on Inhibition Efficiency/Kinetic Studies

Weight loss method was used to study the effect of temperature on the dissolution and corrosion retardation of St37-2 steel in 15% H2SO4 solution without and with dextran, dextran/AgNPs nanocomposite, and dextran + KI respectively at 25 – 60 oC. From the experiments, the weight loss (WL, g), corrosion rate (ν, g/cm2 h), θ, and η were calculated and listed in Table 4. By examining the values in the table, it is seen that all the parameters vary directly with temperature. However, at specific temperature, the WL and ν for the inhibited systems are smaller than those of the uninhibited. The decrease in these parameters (WL and ν)


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is in the order: Dex 1 + KI < Dex 1/AgNPs nanocomposite < Dex 1. Dex 1 + KI is found to be very effective for the corrosion mitigation of St37-2 in the studied acid solution particularly at higher temperatures. For instance, the presence of this mixture in the corrosive acid solution protected the metal surface by 98.715%, 99.153%, 99.253%, and 99.400% at 25 oC, 40 oC, 50 C, and 60 oC respectively. In fact, the θ values at elevated temperatures are near unity

o

suggesting that the entire substrate surface was almost completely covered by the inhibitor film. Going by the variation of η with temperature (Table 4), chemisorption was the prevalence mechanism of adsorption of the additives onto the steel surface

40, 53

. This could be possible

through the transfer or sharing of electron pairs on the oxygen heteroatoms in dextran molecules with the empty d-orbital of iron 53. To examine the contribution of temperature on the dissolution behavior of St37-2 steel in the considered systems, the corrosion kinetic parameters, namely activation energy (Ea), enthalpy of activation (∆Ha), and entropy of activation (∆Sa) were calculated from the well-known Arrhenius and Transition State equations which usually have the form: logν = log A − log

Ea 2.303RT

(5)

  R   ∆S a    ∆H a =  log    − + T   Nh   2.303 R    2.303 RT

ν

(6)

where ν is the corrosion rate, R the molar gas constant, T the absolute temperature, N is the Avogadro’s number, and h is the Planck’s constant. The plots of log v versus 1/T and log v/T against 1/T are given in Fig. S4 in the supporting information. From the slopes and intercepts of the graphs, the values of Ea, ∆Ha, ∆Sa were computed accordingly and are listed in Table 5. Compared with those of the blank, the values of Ea and ∆Ha are smaller and this behavior is usually linked to chemisorption

40, 54, 55

. The Ea values are however positive and infer that the

process of adsorption of the additives onto the metal surface was endothermic 46. As required by the thermodynamic equation, Ea - ∆Ha = RT, the Ea values are bigger than ∆Ha values. The ∆Sa values for the inhibited systems are larger compared to that of the uninhibited and this is due to increase in solvent entropy 26.

3.5

Surface Observation Studies 3.5.1

SEM and EDAX 13 ACS Paragon Plus Environment


Fig. 11 shows the SEM pictures and EDAX spectra of St37-2 steel surface after exposure to 15% H2SO4 solution (a, b) without and with (c, d) 1000 mg/L Dex 1, (e, f) 1000 mg/L Dex 1/AgNPs nanocomposite, (g, h) 1000 mg/L Dex 1 + 1 mM KI combination for 24 h at 25 oC. The exposure of the steel sample to the corrosive medium rendered the surface severely damaged. Greater portion of the metal sample dissolved in the acid solution and the products that emanated from the corrosion process can be clearly seen deposited in the surface shown in Fig. 11(a). The EDAX spectrum in Fig. 11(b) discloses that the products are mainly oxides as evidenced in the high wt.% of O in the inserted table. The wt.% of S is also high in the surface supporting the most acceptable corrosion mechanism of steel in H2SO4 environment, i.e the metal surface is hydrated with sulphate ions

40, 56

. In the acid solution containing dextran (Fig.

11(c)), the deposits seen on the surface are quite different from the one in Fig. 11(a). The deposits appear flake-like. This suggest that the polymer molecules adsorbed on the substrate surface and the adsorbed films may have retarded further corrosion on the metal surface. This claim is also backed up with the decrease in wt.% of S in Fig. 11(d). Nevertheless, the deposited films appear porous (Fig. 11(c)) and this could be the reason dextran poorly inhibited the corrosion of St37-2 steel in the studied environment (Tables 1-4). Despite the adsorption, corrosive ions may have still ingress into the specimen surface. Although some pores could still be seen in the surface in Fig. 11(e), it is more compact than the one in Fig. 11(c). The EDAX spectrum in Fig. 11(f) confirmed the presence of AgNPs in the surface (Ag peak appears at 3 keV). The AgNPs particles may have improved the barrier property of the polymer on the surface such that ingression of corrosive ions was limited. Authors have reported such possibility with nanoparticles

57, 58

. Unarguably, the dextran + KI mixture offered satisfactory protection to

St37-2 steel in H2SO4 medium. Clearly, the film on the surface in Fig.11(g) is compact and uniformly covered the surface. In the corresponding EDAX spectrum (Fig. 11(h)), there is substantial reduction in the wt.% of S. The SEM results are in excellent agreement with the experimental results (Tables 1-4).

3.5.2

AFM

One of the attractive features of AFM is its ability to provide information on surface roughness. Surface roughness defined as the measure of the texture of a surface can be used to


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determine the extent of metal deterioration 40. The International Organization of Standardization (ISO) have outlined various parameters which can be used to characterize a surface. Some of the basic parameters listed in the ISO 1487 include Ra, Rp, Rv, Rz, Rc, Rt, and Rq average value of profile deviation from the mean line

59, 60

59,60

. Ra is the

. Rp is the maximum peak height, Rv

the maximum valley depth, and Rz is the average peak to valley height

59, 60

. Rc describes the

average peak to valley height with no limit to the amount of bands and valleys

59, 60

. Rt and Rq

are used to describe the largest peak to valley height and the root-mean-square deviation of a profile respectively 59, 60. Fig. 12 presents the representative pictures of St37-2 steel specimens in 2-dimension and 3-dimension after immersion in (a) free 15% H2SO4 solution and in the acid solution containing (b) 1000 mg/L Dex 1, (c) 1000 mg/L Dex 1/AgNPs nanocomposite, and (d) Dex 1+ KI mixture for 24 h at 25 oC. Judging from the values of the roughness parameters in the table inserted in Fig. 12(a) and the AFM pictures, it could be said that there was serious corrosive attack on the metal surface. The surface is so rough that 26.210 µm was recorded as the largest peak to valley height (Rt). The presence of the additives in the acid solution drastically reduced the samples surface roughness such that the Rp, Rv, Rz, and Rt values became one digit (Fig. 12(b-d)). The effectiveness of dextran + KI combination is also seen with the AFM results. For instance, the values of all the roughness parameters (Fig. 12(d)) are less than one.

4. Mechanism of Corrosion Inhibition To gain insight into the chemical nature of St37-2 steel/sulphate containing solution interface and to demonstrate the adsorption and adsorption mechanism of dextran, dextran/AgNPs nanocomposite, and dextran + KI mixture on the steel surface, XPS experiments were undertaken. Since our interest was on the products deposited on the samples surfaces, the experiments were performed on the samples without leaching after retrieval from the test solutions. Fig. 13 presents the high resolution Fe 2p, S 2p, O 1s, and C 1s spectra for St37-2 steel surface immersed in 15% H2SO4 solution for 24 h at 25 oC. The Fe 2p structure is a complex one with series of energy bands. The complexity is due to the existence of spin-orbital doublets of Fe0, Fe2+, Fe3+, and satellites of Fe3+ species

61

. Specifically, energy bands are identified at

704.48 eV, 709.88 eV, 714.08 eV, 723.88 eV, 730.29 eV, and 735.98 eV. The band at 704.48 eV and 709.88 eV are assigned to Fe0 and FeO respectively 62. The medium band at 714.08 eV is a signal emanating from a mixture of Fe2+ and Fe3+ in species such as FeO, Fe(OH)2, Fe(OH)3, 15 ACS Paragon Plus Environment


FeOOH, Fe2O3, and Fe3O4

61, 63

. The prominent peak in 723.88 eV is associated with FeSO4

Page 16 of 49

64

and the medium bands at 730.29 eV and 735.98 eV could be linked to ferrhydrates 64, 65. In the S 2p, O 1s, and C 1s spectra of Fig. 13, single and intense bands are seen at 168.68 eV, 532.14 eV, and 284.76 eV respectively and correspond to SO 24 − oxides

16

, and C

64, 67

66

, hydrated oxides and/or hydrous ferric

. The results reveal that St37-2 steel corroded in the acid solution and the

products of the corrosion process are mixture of oxides, hydroxides, carbonates, and sulphates. The presence of SO 24 − is a proof that the steel surface was hydrated with sulphate ions in the studied systems. Fig. 14 shows the high resolution Fe 2p, S 2p, O 1s, and C 1s spectra for St37-2 steel surface immersed in 15% H2SO4 solution containing 1000 mg/L Dex 1 for 24 h at 25 oC. By comparing the spectra in Fig. 14 with those of Fig. 13, some differences can be spotted. For instance, in the Fe 2p spectrum in Fig. 14, the Fe0 band is found at 707.05 eV as against 704.48 eV in Fig. 13. The FeO, Fe2O3/FeOOH, and FeSO4 bands appear at 710.79 eV, 714.85 eV, and 724.52 eV respectively in Fig. 14. Similarly, the SO 24 − , hydrated oxides and/or hydrous ferric oxides, and the C bands at 168.68 eV, 532.14 eV, and 284.76 eV in the S 2p, O 1s, and C 1s spectra in Fig. 13 are rather found at 168.91 eV, 532.26 eV, and 284.63 eV in Fig. 14. In the C 1s spectrum in Fig. 14, additional band which is absent in the C 1s spectrum of Fig. 13 is seen at 286.90 eV and this band correspond to the C–O group 68 of the dextran molecule. The afore noted changes in the energy bands may have been caused by the adsorption of dextran molecules on the metal surface. The appearance of C–O band provides evidence that dextran molecules were adsorbed. In H2SO4 solution, the hydroxyl functional groups in dextran molecules (Fig. 1) would be protonated and the charged dextran species would be dragged onto the SO 24 − hydrated steel surface through columbic attraction. The surface recharging ability of SO 24 − would have a serious influence on the adsorption and corrosion inhibition of dextran. Our experimental results (Table 1-4) suggest that 2− SO 4 did not appreciably suppress the opposing force from charged steel surface to have allowed

sufficient amount of protonated dextran to be adsorbed on the surface and offer satisfactory protection. On the steel surface, deprotonation can occur such that O lone sp2 electron pairs are send into the empty 3d orbitals of Fe

16

, i.e chemical adsorption takes place as predicted by the

variation of inhibition efficiency with temperature in Table 4. This mechanism is illustrated in Fig. 15 (a). 16 ACS Paragon Plus Environment

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The high resolution Fe 2p, S 2p, O 1s, C 1s, and Ag 3d spectra recorded on St37-2 steel surface that was immersed in 15% H2SO4 solution containing 1000 mg/L Dex 1/AgNPs naocomposite for 24 h at 25 oC are depicted in Fig. 16. In the Fe 2p, S 2p, O 1s, and C 1s spectra of Fig. 16, the changes in the binding energy noted for the major constituents in Fig. 14 are also obvious. The C–O band can as well be identified in the C 1s spectrum of Fig. 16 at 286.11 eV. On this surface, additional element was found, for instance Ag which serves as a proof that AgNPs interacted with the steel surface. In the Ag 3d spectrum, two prominent splitting are seen at 368. 21 eV and 374.22 eV and are assigned to Ag 3d5/2 and Ag 3d3/2 64 respectively. According to Ferraria et al. 69, the Ag 3d5/2 is a characteristic peak of Ag+ in AgO. As earlier explained, the dextran/AgNPs composite molecules are electrostatically drawn onto the steel surface. On the steel surface, AgNPs due to its active properties interact chemically with the surface (Fig. 15(b)). Nevertheless, the presence of oxides of Ag on the surface (note that the oxidation of AgNPs is after adsorption and not in its native form

64, 70

) could also bring about the possibility of

passivation. Fig. 17 shows the high-resolution Fe 2p, S 2p, O 1s, C 1s, and I 3d spectra for film formed on St37-2 steel substrate in 15% H2SO4 solution containing 1000 mg/L Dex 1 + 1 mM KI after 24 h of immersion. Beside Fe, S, and O which were identified in the other surfaces (Fig.12 – 15), iodine was found on the surface whose spectra are shown in Fig. 16. In the I 3d spectrum, two split peaks at 619.53 eV and 630.98 eV are observed and are associated with I 3d3/2 and I 3d5/2 71, 72

respectively. This splitting is quite different from the splitting of pure iodine molecules (I2)

that was reported by Some et al. 71 but similar to the spectra obtained by Kalita et al. 72. In Some

et al. report, the iodine spectrum exhibited a single peak at 619.9 eV. According to Kalita et al., the band at 619.53 eV is due to triiodide while the band at 630.98 eV is consistent with pentaiodide. In the acid solution, dissolved oxygen oxidized iodide ions to triiodide and pentaiodide ions. In the system, there is competitive adsorption between these ions and sulphate ions but because triiodide and pentaiodide ions are smaller than sulphate ions, they are preferred. The chemisorption of these ions on the metal surface satisfactorily replenished the steel surface such that sufficient amount of the charged polymer species are adsorbed on top of the triiodide and pentaiodide ions layers (Fig. 15(c)). The cooperative co-adsorption as earlier established by the value of the synergism parameter (Sθ) led to the formation of thicker protective layer and



larger surface coverage that posed stiff resistance to charge transfer process as evident in the larger capacitive loops in Fig. 9(a) and the improved inhibition efficiency in Table 3.

5. Summary/Conclusion Dextran is a natural polymer, a polysaccharide with α-D-pyran as its monomeric unit. Metals corrosion is a serious challenge that has drained the world economy and has kept many lives in perpetual pains. The interest of the present day is to use green substances (substances without negative influence on human lives and the natural environment) as metals corrosion inhibitors. Dextran is one of such substances hence we explore the possibility of using it for the corrosion prevention of steel in strong acid environment. Weight loss, electrochemical, and surface analysis methods have been used for this investigation. The influence of molecular weight, temperature, and modification on the inhibition efficiency of dextran has been equally examined. Dextran is found to behaved as a mixed type corrosion inhibitor and moderately inhibits the corrosion of St37-2 steel in 15% H2SO4 solution. Inhibition efficiency of dextran decreases with increase in molecular weight but increases with rise in temperature. Dextran with molecular weight of 100,000 – 200,000 g/mol exhibited the highest inhibition efficiency of 51.38% at ordinary temperature from electrochemical impedance spectroscopy measurements. Two modification approaches, namely compositing with silver nanoparticles and combination with 1 mM KI were adopted to boost the inhibition efficiency of dextran in the studied environment. The two approaches proved effective as the inhibition efficiency of dextran was raised from 51.38% to 86.82% and 94.21% by compositing and combination with KI respectively at 25 oC. Results from the study on the effect of temperature reveals that inhibition efficiency as high as 99.8% could be achieved with dextran + KI combination at 60 oC. Surface analysis results confirm that inhibition by the additives is by adsorption of the additives molecules onto the metal surface. XPS results disclose that AgNPs are in oxide form on the metal surface while iodide ions are in the form of triiodide and pentaiodide ions. Based on the results obtained in this investigation, it is concluded that modified dextran is effective corrosion inhibitor for steel in strong acid environment.

Acknowledgements


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Moses M. Solomon is thankful to the King Fahd University of Petroleum and Minerals for the offer of a postdoctoral research fellowship at the Center of Research Excellence in Corrosion. The authors are grateful to Mr. Muhammad Al-Saeed for assisting in the XPS experiments.

Declaration of Conflict of Interest The authors declare no competing interest.

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(51) Bouklah, M.; Hammouti, B.; Aouniti, A.; Benkaddour, M.; Bouyanzer, A. Synergistic Effect of Iodide Ions on the Corrosion Inhibition of Steel in 0.5 M H2SO4 by New Chalcone Derivatives. Appl. Surf. Sci. 2006, 252, 6241 (52) Zheng, X.; Zhang, S.; Li, W.; Gong, M.; Yin, L. Experimental and Theoretical Studies of Two Imidazolium-Based Ionic Liquids as Inhibitors for Mild Steel in Sulfuric Acid Solution. Corros. Sci. 2015, 95, 168−179. (53) Gowraraju, N. D.; Jagadeesan, S.; Ayyasamy, K.; Olasunkanmi, L. O.; Ebenso, E. E.; Subramanian, C. Adsorption Characteristics of Iota-carrageenan and Inulin Biopolymers as Potential Corrosion Inhibitors at Mild Steel/Sulphuric Acid Interface. J. Mol. Liq. 2007, 232, 9–19 (54) Oguzie, E. E.; Unaegbu, C.; Ogukwe, C. N.; Okolue, B. N.; Onuchukwu, A. I. Inhibition of Mild Steel Corrosion in Sulphuric Acid using Indigo Dye and Synergistic Halide Additives. Mater. Chem. Phys. 2004, 84, 363−368. (55) Solomon, M. M.; Umoren, S. A.; Abai, E. J. Preparation and Evaluation of the Surface Protective Performance of Poly (Methacrylic Acid)/Silver Nanoparticles Composites (PMAA/Agnps) on Mild Steel in Acidic Environment. J. Mol. Liq. 2015, 212, 340−351. (56) Abd El-Maksoud, S. A. The Effect of Organic Compounds on the Electrochemical Behaviour of Steel in Acidic Media—A Review. Int. J. Electrochem. Sci. 2008, 3, 528–555 (57) Tallman, D. E.; Levine, K. L.; Siripirom, C.; Gelling, V. G.; Bierwagen, G. P.; Croll, S. G. Nanocomposite of Polypyrrole and Alumina Nanoparticles as a Coating Filler for the Corrosion Protection of Aluminium Alloy 2024-T3. Appl. Surf. Sci. 2008, 254, 54525459. (58) Sharifi, G. S.; Attar, M. M.; Ramezanzadeh, B. Studying the Influence of Nano-Al2O3 Particles on the Corrosion Performance and Hydrolytic Degradation Resistance of an Epoxy/polyamide Coating on AA-1050. Prog. Org. Coat. 2014, 77, 1391-1399. (59) Mitutoyo Corporation. Surface Finish Analysis 2014, pp. 1 – 58 (https://www.mitutoyo.com/wp-content/uploads/2012/.../1984_Surf_Roughness_PG.pd). (60) EN ISO 4287:1998. Geometrical Product Specifications (GPS) – Surface Texture: Profile Methods – Terms, Definitions, and Surface Parameters. (61) de Oliveira, L. A.; Correa, O. V.; dos Santos, D. J.; Zúñiga Páez, A. A.; Lopes de Oliveira, A. C.; Antunes, R. A. Effect of Silicate-based Films on the Corrosion Behavior of the API 5L X80 Pipeline Steel. Corros. Sci. 2018, 139, 21 – 34.


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(62) Casaletto, M. P.; Figà, V.; Privitera, A.; Bruno, M.; Napolitano, A.; Piacente, S. Inhibition of Cor-Ten Steel Corrosion by “Green” Extracts of Brassica campestris. Corros. Sci. 2018, 136, 91–105 (63) Usman, B. J.; Umoren, S. A.; Gasem, Z. M. Inhibition of API 5L X60 Steel Corrosion in CO2-saturated 3.5% NaCl Solution by Tannic Acid and Synergistic Effect of KI Additive. J. Mol. Liq. 2017, 237, 146–156 (64) Solomon, M. M.; Gerengi, H.; Umoren, S. A.; Essien, N. B.; Essien, U. B.; Kaya, E. Gum Arabic-silver Nanoparticles Composite as a Green Anticorrosive Formulation for Steel Corrosion in Strong Acid Media. Carbohyd. Polym. 2018, 181, 43–55 (65) Descostes, M.; Mercier, F.; Thromat, N.; Beaucaire, C.; Gautier-Soyer, M. Use of XPS in the Determination of Chemical Environment and Oxidation State of Iron and Sulfur Samples: Constitution of a Data Basis in Binding Energies for Fe and S Reference Compounds and Applications to the Evidence of Surface Species of an Oxidized Pyrite in a Carbonate Medium. Appl. Surf. Sci. 2000, 165, 288–302 (66) Zhang, Z.; Tian, N.; Zhang, W.; Huang, X.; Ruan, L.; Wu, L. Inhibition of Carbon Steel Corrosion in Phase-change-materials Solution by Methionine and Proline. Corros. Sci. 2016, 675 – 689. (67) Nam, N. D.; Somers, A.; Mathesh, M.; Seter, M.; Hinton, B.; Forsyth, M.; Tan, M.Y.J. The Behaviour of Praseodymium 4-hydroxycinnamate as an Inhibitor for Carbon Dioxide Corrosion and Oxygen Corrosion of Steel in NaCl Solutions. Corros. Sci. 2014, 80,128– 138. (68) Azzaoui K.; Mejdoubi, E.; Jodeh, S.; Lamhamdi, A.; Rodriguez-Castellón, E.; Algarra, M.; Zarrouk, A.; Errich, A.; Salghi, R.; Lgaz, H. Eco Friendly Green Inhibitor Gum Arabic (GA) for the Corrosion Control of Mild Steel in Hydrochloric Acid Medium. Corros. Sci. 2017, 129, 70–81 (69) Ferraria, A. M.; Carapeto, A. P.; Botelho do Rego, A. M. X-ray Photoelectron Spectroscopy: Silver Salts Revisited. Vacuum 2012, 86, 1988 – 1991 (70) Wang, C.; Zanna, S.; Frateur, I.; Despax, B.; Raynaud, P.; Mercier-Bonin; M.; Marcus, P. BSA Adsorption on a Plasma-deposited Silver Nanocomposite Film Controls Silver Release: A QCM and XPS-based Modelling. Surf. Coat. Technol. 2016, 307, 1–8. (71) Some, S.; Sohn, J. S.; Kim, J.; Lee, S. H.; Lee, S. C.; Lee, J.; Shackery, I.; Kim, S. K.; Kim, S. H.; Choi, N.; Cho, I. J.; Jung, H. I.; Kang, S.; Jun, S. C. Graphene-Iodine Nanocomposites: Highly Potent Bacterial Inhibitors that are Bio-compatible with Human Cells. Sci. Reports 2016, 6, 20015 (72) Kalita, G.; Wakita, K.; Takahashi, M.; Umeno, M. Iodine Doping in Solid Precursorbased CVD Growth Graphene Film. J. Mater. Chem. 2011, 21, 15209-15213 25 ACS Paragon Plus Environment



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1 2 3 4 5 6 7 Table 1: Electrochemical impedance parameters for St37-2 steel in 15% H2SO4 solution in the absence and presence of additives at 25 8 °C 9 10 System CPEdl Rs Rct CPEf Rf ࢞૛ (×10-4) 11 (Ω cm2) (Ω cm2) (Ω cm2) 12 Y0dl ndl Y0f nf 13 −1 2 −2 -3 −1 2 −2 -3 (Ω s cm ) ×10 (Ω s cm ) ×10 14 0. 236 0.906 17.800 0.667 ± 0.006 104.200 ±0.005 15 Blank 16 Dex 1 0. 183 0.921 241.400 1.000 2.290 0.730 ± 0.007 214.300 ±0.002 3.341±0.001 17 Dex 2 0. 188 0.921 117.100 1.000 4.185±0.017 12.600 0.676 ± 0.006 179.400 ±0.001 18 Dex 3 0. 362 0.878 0.180 0.933 1.597±0.002 2.440 0.789 ± 0.002 165.200 ±0.010 19 Composite 0. 449 0.773 0. 080 0.958 5.310 0.850 ± 0.015 790.800 ±0.018 20.780±0.001 20 0. 595 0.835 0.080 0.911 3.004±0.011 4.610 21 1 mM KI 0.701 ± 0.008 631.700 ±0.011 22 Dex 1 + KI 0. 096 0. 832 0.717 ± 0.012 1800.000±0.030 0.100 1.000 452.300±0.001 26.500 23 Dex 2 + KI 0.303 0.851 0.080 0.907 10.000 0.698 ± 0.012 1590.000±0.011 6.192±0.003 24 0.363 0.850 0.080 0.906 5.089±0.002 7.960 0.760 ±0.006 1503.000±0.020 25 Dex 3 + KI 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 27 44 ACS Paragon Plus Environment 45 46 47

ηEIS (%)

51.377 41.918 36.925 86.823 83.505 94.211 93.447 93.067

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

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Table 2: Electrochemical frequency modulation (EFM) parameters for St37-2 steel in 15% H2SO4 solutions in the absence and presence of different additives at 25 °C System Blank Dex 1 Dex 2 Dex 3 Composite Dex 1 + KI Dex 2 + KI Dex 3 + KI

icorr (µA cm−2) 208.600± 0.018 118.200± 0.004 152.200± 0.025 127.800± 0.011 30.970± 0.002 17.640± 0.017 17.890± 0.003 19.400± 0.015

βa (mV dec−1) 84.810 83.550 93.150 83.010 94.350 92.060 89.170 100.800

βc (mV dec−1) 93.490 98.590 109.000 98.620 106.500 108.300 103.300 124.600


CF–2

CF–3

2.100 1.875 1.888 1.917 1.807 1.810 1.774 2.002

3.077 3.259 2.964 3.336 3.584 2.230 3.353 3.427

ηEFM (%) 43.347 27.037 38.734 85.153 91.544 91.424 90.700

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Table 3: Corrosion parameters for St37-2 steel in 15% H2SO4 solutions in the absence and presence of different additives at 25 °C from potentiodynamic polarization (PDP) and linear polarization (LPR) methods System

Blank Dex 1 Dex 2 Dex 3 Composite Dex 1 + KI Dex 2 + KI Dex 3 + KI

PDP ̶ Ecorr (mV vs. Ag/AgCl) 442.000 443.000 448.000 447.000 434.000 441.000 443.000 433.000

icorr (µA cm−2) 394.000± 0.102 205.300± 0.052 257.800± 0.033 263.500± 0.009 45.700± 0.043 20.500± 0.008 28.900± 0.065 30.300± 0.021

LPR βa (mV dec−1) 36.100 40.100 41.100 43.200 39.400 89.100 84.500 84.700

βc (mV dec−1) 67.500 68.400 71.400 72.900 91.500 84.900 80.800 81.000


ηPDP (%) 47.893 34.569 33.122 88.401 94.797 92.665 92.310

Rp (Ω cm2) 97.610± 0.002 184.300± 0.030 174.920± 0.052 167.300± 0.003 927.010± 0.012 2141.020± 0.002 2017.100± 0.011 2007.210± 0.031

ηLPR (%) 47.037 44.197 41.656 89.470 95.441 95.161 95.137

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12System 13 14 15 16 17 18 Blank 19 20 Dex 1 21 22 Composi 23 24 te 25Dex 1 + 26 KI 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

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Table 4: Calculated values of weight loss (WL), corrosion rate (ν), surface coverage (θ), and inhibition efficiency (η) from weight loss measurements at various temperatures 25oC WL (g)

0.389 ±0.038 0.217 ±0.003 0.105 ±0.012 0.005 ±0.000

40oC

ν (g/cm 2 h) ×10-3 7.194

θ

ηWL (%)

-

-

4.011

0.442

1.950

0.730

0.083

0.987

WL (g)

ν (g/cm2 h) ×10-3 28.407

1.534 ±0.005 44.216 0.785 14.543 ±0.035 73.007 0.374 6.933 ±0.015 98.715 0.013 0.248 ±0.000

50oC θ

ηWL (%)

WL (g)

-

-

0.488

48.827

0.756

75.619

0.992

99.153

2.814 ±0.009 1.345 ±0.011 0.673 ±0.045 0.021 ±0.000


60oC

ν (g/cm2 h) ×10-3 52.111

θ

ηWL (%)

-

-

24.907

0.522

12.461

0.761

0.381

0.993

WL (g)

5.004 ±0.006 52.203 2.667 ±0.026 76.084 1.039 ±0.018 99.254 0.030 ±0.002

ν (g/cm2 h) ×10-3 92.665

θ

ηWL (%)

-

-

49.380

0.467

46.703

19.233

0.792

79.237

1.370

0.991

99.400

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Table 5: Calculated values of activation for St37-2 steel in 15% H2SO4 solutions in the absence and presence of different additives. System Blank Dex 1 Composite Dex 1 + KI

Ea (kJ mol-1) 60.239 58.448 54.442 67.432

∆Ha (kJ mol-1) 57.625 55.834 51.828 64.309

-∆Sa (J mol-1 K-1) 103.092 122.201 106.817 197.584



Page 32 of 49

(b)

(a)

Figure 1: (a) The chemical structure of dextran and (b) Ball-and-stick model of dextran molecule (the heteroatom which could serve as the possible site for adsorption is painted red)

ACS Paragon Plus Environment

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(a)

(b)

Figure 2: OCP variations with time of St37-2 steel in 15% H2SO4 solution without and (a) with different molecular weight dextran and (b) various additives at 25 oC



(b)

Fig. 3: Electrochemical impedance spectra for St37-2 steel in 15% H2SO4 solution in the absence and presence of 1000 mg/L of different molecular weight dextran in (a) Nyquist and (b) Bode modulus and Phase angle representations at 25oC


Page 34 of 49

Page 35 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(a)

(b)

Figure 4: Equivalent circuit diagrams used to fit impedance data in the (a) blank and (b) presence of additives



(a)

(c)

Figure 5: Intermodulation spectra recorded for St37-2 steel in (a) 15% H2SO4 solution without inhibitor and with (b) 1000 mg/L Dex 1, (c) 1000 mg/L Dex 2, and (d) 1000 mg/L Dex 3 at 25oC.


Page 36 of 49

(b)

(d)

Page 37 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6: Potentiodynamic polarization curves for St37-2 steel in 15% H2SO4 without and with 1000 mg/L of different molecular weight dextran 25 oC



Spectrum 1

(a) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Ag Ag

Ag

CO

Al

Ag

0 1 2 3 Full Scale 29765 cts Cursor: 3.893 (501 cts)

4

5

6

7

8

9

10 keV

(b)

(c)

Figure 7: (a) EDAX spectrum and (b) TEM image and (c) UV-vis spectra of Dex 1/AgNPs nanocomposite obtained by treating 5 mL honey with 1000 mg/L Dex 1 + 1 mM aqueous AgNO3 solution


Page 38 of 49

Page 39 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(b)

Figure 8: (a) Electrochemical impedance and (b) potentiodynamic polarization diagrams of St37-2 steel in 15% H2SO4 in the absence and presence of 1000 mg/L Dex 1 and 1000 mg/L Dex 1/AgNPs nanocomposite respectively at 25 oC



(b)

Fig. 9: Electrochemical impedance spectra of St37-2 steel in 15% H2SO4 solution in the absence and presence of different additives in (a) Nyquist and (b) Bode modulus and Phase angle representations at 25oC


Page 40 of 49

Page 41 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fig. 10: Potentiodynamic polarization curves for St37-2 steel in 15% H2SO4 solution in the absence and presence of different additives at 25oC



(a) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 42 of 49

(b)

(c)

(e)

(g)

(d)

(f)

(h)

Fig. 11: SEM images and EDAX spectra for St37-2 steel after immersion in 15%H2SO4 solution (a, b) without ACS1, Paragon Environment and (c, d) containing 1000 mg/L of Dex (e, f) Plus containing 1000 mg/L Dex 1/AgNPs nanocomposite, (g, h) o containing Dex 1 + 1 mM KI for 24 h at 25 C

Page 43 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(a)

(b)

(c)

(d)

Fig. 12: AFM images in 2D and 3D formats for St37-2 steel after immersion in 15%H2SO4 solution (a) without inhibitor and (b) containing 1000 mg/L of Dex 1, (c) containing 1000 mg/L Dex 1/ AgNPs nanocomposite, and (d) containing Dex 1 + 1 mM KI for 24 h at 25oC


735.98

730.98

723.88 727.28

719.98

709.88

Page 44 of 49

168.68

702.18 704.48

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

714.08


532.14

284.76

Fig. 13: High-resolution Fe2p, S2p, O1s, and C1s spectra for corrosion products formed on St372 steel substrate in 15% H2SO4 solution after 24 h of immersion.


Page 45 of 49

168.91 728.88

719.96

724.52

710.79 714.85

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


707.05

532.26

284.63

286.90

Fig. 14: High-resolution Fe2p, S2p, O1s, and C1s spectra for film formed on St37-2 steel substrate in 15% H2SO4 solution containing 1000 mg/L Dex 1 after 24 h of immersion.



(c)

(b)

(a)

+ + + +

+ ++

+

+ +

+ +

+

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 46 of 49

St37-2 steel Fig. 15: An illustration of the corrosion inhibition of St37-2 corrosion in 15% H2SO4 solution by (A) dextran, (B) dextran/AgNPs nanocomposite, and (C) dextran + KI combination. implies chemisorption while depicts physisorption.


Page 47 of 49


711.11 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

169.33

724.13 715.12

726.83

710.76

703.19

532.49

284.11

D 286.11

368.21 374.22

Fig.16: High-resolution Fe2p, S2p, O1s, C1s, and Ag3d spectra for film formed on St37-2 steel substrate in 15% ACS Paragon Plus Environment H2SO4 solution containing 1000 mg/L Dex 1/AgNPs composite after 24 h of immersion.

710.48 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


724.08

532.33

724.08

Page 48 of 49

284.84

619.53 630.98

Fig. 17: High-resolution Fe2p, S2p, O1s, C1s, and I3d spectra for film formed on St37-2 steel substrate in 15% H2SO4 solution containing 1000 mg/L Dex 1 + 1 mM KI after 24 h of immersion. ACS Paragon Plus Environment

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TOC


Exploration of Dextran for Application as Corrosion Inhibitor for Steel

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