UAE Rhazya Stricta Decne extractas a corrosion inhibitor for mild steel

in HCl solutionAyssar Nahlé, Ibrahim Almaidoor and Ibrahim Abdel-Rahman

Department of Chemistry, College of Sciences, University of Sharjah, Sharjah, UAE

AbstractPurpose – This study aims to study electrochemically and by weight-loss experiments the effect of UAE Rhazya Stricta Decne extract on thecorrosion inhibition of mild steel in 1.0 M HCl solution, which will serve researchers in the field of corrosion.Design/methodology/approach – Weight loss measurements were carried out on mild steel specimens in 1.0 M HCl and in 1.0 M HCl containingvarious concentrations (ranging from 2.0 to 0.002 g/L.) of the UAE Rhazya Stricta Decne extract at temperatures ranging from 303 to 343 K.Findings – The aqueous Rhazya Stricta Decne leaves extract was found to be a highly efficient inhibitor for mild steel in 1.0 M HCl solution, reachingabout 90 per cent at 2.0 g/L and 303 K, a concentration considered to be very moderate. Even with one-tenth of that concentration, 0.2 g/L, aninhibition of about 82 per cent was obtained at 303 K. The rate of corrosion of the mild steel in 1.0 M HCl is a function of the concentration ofthe Rhazya Stricta Decne extract. This rate increases as the concentration of the Rhazya Stricta Decne extract is increased. The percentage ofinhibition in the presence of this inhibitor was decreased with temperature which indicates that physical adsorption was the predominant inhibitionmechanism because the quantity of adsorbed inhibitor decreases with increasing temperature.Practical implications – This inhibitor could have application in industries, where HCl solutions at elevated temperatures are used to remove scaleand salts from steel surfaces, such as acid cleaning of tankage and pipeline, and may render dismantling unnecessary.Originality/value – This paper is intended to be added to the family of green corrosion inhibitors which are highly efficient and can be used in thearea of corrosion prevention and control.

Keywords Corrosion, Inhibitors, “Mild” steel, Rhazya Stricta Decne, Azadirachta indica, Inhibitor, Weight loss, Corrosion, Temkin adsorptionisotherm

Paper type Research paper

1. Introduction

In many industries, the corrosion of metals is a serious problem.To prevent or minimize corrosion, inhibitors often are used,especially in cooling water systems. Organic, inorganic or amixture of both inhibitors can inhibit corrosion by eitherchemisorption on the metal surface or by reacting with metal ionsand forming a barrier-type precipitate on its surface(Al-Sehaibani, 2000).

Natural products can be considered as a good source forinhibitors. The aqueous extracts from different parts of someplants such as henna, Lawsonia inermis (Al-Sehaibani, 2000);Rosmarinus officinalis L. (Kliski=c et al., 2000); Carica papaya(Okafor et al., 2007); Cordia latifolia and curcumin (Farooqiet al., 1999); date palm, Phoenix dactylifera, henna, Lawsoniainermis and corn, Zea mays (Rehan, 2003); and Nypa FruticansWurmb (Orubite et al., 2004) have been found to be goodcorrosion inhibitors for many metals and alloys. Recently, an

excellent review of “natural products as corrosion inhibitors formetals in corrosive media” has been published (Raja et al., 2008).

No studies have been reported on the aqueous extract ofRhazya Stricta Decne leaves as grown in UAE, the corrosioninhibitor used in our present work, in terms of studying theeffect of temperature on the corrosion inhibition of plaincarbon steel in 1.0 M HCl solution. Mild steel was chosen inthese studies because hot corrosive acids are used widely inindustries in connection to mild-and low-alloy steels.

The aim of the project was to study, using weight-lossmeasurements, the effect of temperature on the corrosioninhibition of steel in 1.0 M HCl solution by the aqueousextract of Rhazya Stricta Decne leaves and to calculate theassociated thermodynamic parameters. The output of thisstudy is intended to be a cheap and eco-friendly natural sourceof corrosion inhibitor that can be utilized for metals and alloys.

2. ExperimentalThe leaves of Rhazya Stricta Decne (harmal, edfir) were collectedfrom “Shawka” village, Emirate of Ras Al-Khaima, UAE, driedat room temperature and stored in the dark for later use.

The extraction procedure was carried out according to thework of Nahlé et al. (2010). In this work, 2.0 g of dry RhazyaStricta Decne (harmal, edfir) leaves were soaked in 60.0 mLdistilled water at room temperature (20°C) for seven hours andthen filtered. The filtrate was added to an aqueous HCl solutionto make a 1.0-L stock solution in 1.0 M HCl. From the stock

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solution, a series of diluted solutions in 1.0 M HCl were preparedwith concentrations ranging from 2.0 to 0.002 g/L.

2.1 Specimen preparationRectangular specimens (1 � 2.3 � 0.3 cm3) were cut from a3-mm thick mild steel sheet (IS 226 containing 0.18 per cent C,0.6 per cent Mn and 0.35 per cent Si) supplied by “Reliable SteelTraders”, Sharjah, UAE; and it was used for the weight-lossdeterminations. Close to the upper edge of the specimen, a2-mm diameter hole was drilled and served to be hooked with aglass rod for immersion purposes. The specimens were polishedwith 600-grade emery paper, rinsed with distilled water,degreased with acetone, dried and finally weighed precisely on anaccurate analytical balance prior to each experiment.

2.2 InstrumentationFor the weight-loss measurements (Nahlé, 2001, Nahlé et al.,2005, 2007, 2008, 2010, 2012a, 2012b, 2013), a 250-mLround bottom flask was fitted with a reflux condenser and longglass rod, which served to hook and immerse the specimen,the flask then was immersed in a thermally controlled waterbath.

2.3 Measuring procedureHundred-microliter of 1.0 M HCl solution, either with orwithout the presence of various concentrations of aqueousRhazya Stricta Decne extract, was transferred into the flask.The flask then was placed in the water bath. When therequired temperature was reached, the precisely weighed steelspecimen was immersed in the solution for exactly six hours.After that time, the sample was removed, rinsed with distilleddeionized water, degreased with acetone, dried and weighedprecisely on an accurate analytical balance. This procedurewas repeated for a variety of inhibitor concentrations rangingfrom 0.002 to 2.00 g/L and at temperatures ranging from 303to 333K.

3. ResultsWeight loss corrosion tests were carried out on the steelspecimens immersed in 1.0 M HCl in the absence or presenceof aqueous Rhazya Stricta Decne extract over six hours. Table Isummarizes the corrosion rate [mg · cm�2 · h�1] andinhibition efficiencies for the Rhazya Stricta Decne inhibitorwith concentrations varying from 0.002 to 2.00 g/L at 303,313, 323 and 333K. The percentage efficiency was calculatedaccording to the following equation (1):

% Inhibition �WUninh. � WInh.

WUninh.� 100 (1)

where:

WUninh. � Corrosion rate without inhibitor.WInh. � Corrosion rate with inhibitor.

The corrosion rate of the steel in 1.0 M HCl as a function ofvarious concentrations of aqueous extract of Rhazya StrictaDecne leaves at temperatures between 303 and 343 K areshown in Figure 1. It was evident that the corrosion ratedecreased more rapidly at lower concentrations of the RhazyaStricta Decne extract than was the case at higher concentrationsat all temperatures.

The plots of the percentage inhibition as a function of theconcentration of the aqueous extract of Rhazya Stricta Decneleaves at temperatures ranging from 303 to 333K are shown inFigure 2. Similar to the rate of corrosion shown in Figure 1,the inhibition efficiency was high at all temperatures reachinga maximum of approximately 90 per cent. A decrease ininhibition appeared at 333 and 343 K at high inhibitorconcentrations.

According to the Arrhenius equation (2), the values ofnatural logarithms of the rate of corrosion (ln rate of corrosion)and the values of the reciprocal of the temperature in K�1

(1/T) were calculated and are presented in Table II.

ln rate � �Ea

RT� const. (2)

where:

Ea � activation energy [kcal · mol�1].R � gas constant [kcal · mol�1].T � absolute temperature [K].const. � constant.

Figure 3 represents the Arrhenius plots of the corrosion of thesteel in 1.0 M HCl solution, (ln corrosion rate as a function of1/T) with or without the presence of the aqueous extract ofRhazya Stricta Decne leaves at concentrations ranging from 0.002to 2.0 g/L. From this figure, the slope (� Ea / R) of each line wasdetermined and used to calculate the activation energy accordingto equation (2), with R � 1.987 � 10�3 kcal · mol�1� It is clearlyevident that as the concentration of the extract increased, theactivation energy for the corrosion of steel in 1.0 M HCl alsoincreased (13.87 kcal · mol�1 in 1.0 M HCl without inhibitor to

Table I The effect of concentration of the aqueous extract of Rhazya Stricta Decne leaves on the corrosion rate (mg · cm�2 · h�1) and percentage efficiencyof mild steel in 1M HCl at various temperatures

Temperature/K303 313 323 333

Concentration of inhibitorCorrosion

ratePer cent

efficiencyCorrosion

ratePer cent

efficiencyCorrosion

rateper cent

efficiencyCorrosion

ratePer cent

efficiency

1 M HCl 0.421 – 0.799 – 1.56 – 3.29 –1 M HCl � 0.0020 g/L extract 0.384 8.79 0.746 6.63 1.50 3.85 3.22 2.131 M HCl � 0.0200 g/L extract 0.223 47.0 0.442 44.7 0.936 40.0 2.14 35.01 M HCl � 0.2000 g/L extract 0.0739 82.4 0.150 81.1 0.313 79.9 0.724 78.01 M HCl � 2.0000 g/L extract 0.0528 87.5 0.112 86.0 0.234 85.0 0.526 84.0

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15.30 kcal · mol�1 with an aqueous extract of Rhazya StrictaDecne leaves of 2.0 g/L in 1.0 M HCl) (Table III).

The values of the surface coverage of various concentrationsof the aqueous Rhazya Stricta Decne leaves extract (from 0.002to 2.0 g/L) on the steel surface at various temperatures arepresented in Table IV. These values were extracted from thecorresponding percentage efficiency values reported earlier in

Table I. The plot of the values of surface coverage, �, againstthe natural logarithm of the concentration of Rhazya StrictaDecne leaves aqueous extract; ln C, for carbon steel at variousinhibitor temperatures is shown in Figure 4. After examiningthese data and adjusting them to different theoreticaladsorption isotherms, it was concluded that the inhibitor wasadsorbed on the steel surface according to the Temkinadsorption isotherm:

–2a � � lnK C (3)

where:

a � molecular interaction constant.� � degree of coverage.K � equilibrium constant for the adsorption reaction.C � concentration of the inhibitor.

The equilibrium constant for the adsorption reaction, K, isrelated to the standard free energy of adsorption via equation(4) (Damaskin et al., 1968):

K �1

55.5exp ��

�GRT � (4)

where:

K � equilibrium constant for the adsorption reaction.55.5 � concentration of water [mol · L�1].�G � standard free energy [kcal · mol�1].R � gas constant [kcal · mol�1].T � absolute temperature [K].

According to equation (3), the straight lines shown in Figure4 will have the following slopes and intercepts:

Slope � �12a

(5)

Intercept � �12a

ln K (6)

Combining equations (5) and (6) leads to the followingrelationships:

Intercept � �Slope� �ln K� (7)

K � e � Intercept

Slope� (8)

Using equation (8), the equilibrium constant for theadsorption reaction, K, was calculated.

The free energy of adsorption of the inhibitor, �G, wascalculated using equation (4) at various temperatures(303-333K), as shown in Table V.

The enthalpy of adsorption, �H, for the inhibitor wascalculated from the following equation (9) and is shown inTable VI:

�H � Ea � RT (9)

The entropy, �S, was calculated at various temperatures forthe inhibitor using the following equation (10) and is shown inTable VII:

�G � �H � T�S (10)

Figure 1 Effect of concentration of the aqueous extract of RhazyaStricta Decne leaves on the corrosion rate (mg · cm�2 · h–1) of mildsteel in 1.0 M HCl at various temperatures

0

0.5

1

1.5

2

2.5

3

3.5

0.00

Notes: 303; 313; 323; 333 K

0.01 0.10 1.00 10.00

Concentration, g/L

Cor

rosi

on R

ate,

mg•

cm−2•h

−1

Figure 2 Effect of concentration of the aqueous extract of RhazyaStricta Decne leaves on the per cent inhibition of mild steel in 1.0 MHCl at various temperatures

0

10

20

30

40

50

60

70

80

90

100

0.00 0.01 0.10 1.00 10.00Inhibitor Concentration, g/L

% In

hibi

tion

Notes: 303; 313; 323; 333 K

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4. Discussion

The activation energy (Ea) (Table III) for the corrosion ofsteel in the presence of the aqueous extract of Rhazya StrictaDecne leaves at all concentrations (0.002-2.0 g/L) are higherthan the activation energy in the absence of the extract (15.30kcal · mol�1 with the extract of 2.0 g/L in 1.0 M HClcompared with 13.87 kcal · mol�1 in 1.0 M HCl withoutextract). This can be attributed to the fact that higher values ofEa in the presence of inhibitor compared to its absencegenerally are consistent with a physisorption, while unchangedor lower values of Ea in inhibited solution suggest chargesharing or transfer from the organic inhibitor to the metalsurface to form coordinate covalent bonds (chemisorption).

The increase in the activation energies for the corrosion wasattributed to a decrease in the adsorption of the inhibitor onthe metal surface as the temperature increased. Subsequently,an increase in the corrosion rate will result due to the greaterarea of the metal surface that is exposed to the acid.

The thermodynamic data obtained in the presence of theRhazya Stricta Decne extract at various temperatures weretabulated in Tables V-VII These thermodynamic quantitiesrepresent the algebraic sum of the values for adsorption anddesorption. The negative value of �G indicates spontaneousadsorption of inhibitor on the surface of the steel. The freeenergy, �G, decreased from �6.96 kcal · mol�1 at 303K toabout �7.11 kcal · mol�1 at 333K. The adsorption process isbelieved to be exothermic and associated with a decrease inentropy (�S) of solute (303-333K), while the opposite is true forthe solvent (Sanad et al., 1995). The gain in entropy, whichaccompanies the substitutional adsorption process, wasattributed to the increase in the solvent entropy (Table VII). Thisagrees with the general suggestion that the absolute values of freeenergy,|�G|, increase with increase in inhibition efficiency(Ateya et al., 1984a, 1984b; Talati et al., 2005), as the adsorptionof organic compound is accompanied by desorption of watermolecules from the surface.

Table II The data obtained from the weight loss measurements for Arrhenius equation: (I/T) against ln corrosion rate

Ln corrosion rate (mg · cm�2 · h�1)

(1/T) � 103 K�1 1 M HCl1 M HCl �

0.0020 g/L extract1 M HCl �

0.0200 g/L extract1 M HCl �

0.2000 g/L extract1 M HCl �

2.000 g/L extract

3.30 �0.865 �0.957 �1.502 �2.605 �2.9413.19 �0.224 �0.293 �0.816 �1.897 �2.1893.10 0.445 0.406 �0.0660 �1.161 �1.4523.00 1.191 1.169 0.7608 �0.323 �0.643

Figure 3 Effect of temperature on the corrosion rate of mild steel in1.0 M HCl solution with and without the presence of variousconcentrations of the aqueous extract of Rhazya Stricta Decne leaves

-3

-2

-1

0

1

2

2.9

Notes: 1.0 M HCl; 0.002; 0.020 g/L; 0.2 g/L; 2.00 g/L

3 3.1 3.2 3.3 3.4

1/T x 103, K−1

Ln C

orro

sion

Rat

e, m

g•cm

−2•h

−1

Table III The activation energy (Ea) for the corrosion of mild steel in 1MHCl with and without the aqueous extract of Rhazya Stricta Decne leavesat various concentrations

System

Activation energy, Ea (kcal · mol�1)2.0000

g/L0.2000

g/L0.0200

g/L0.0020

g/L

1M HCl 13.87 13.87 13.87 13.871M HCl � the aqueousextract of RhazyaStricta Decne leaves 15.30 15.19 15.09 14.18

Table IV The effect of concentration of the aqueous extract of Rhazya Stricta Decne leaves on surface coverage for mild steel in 1 M HCl at varioustemperatures

Temperature/K303 313 323 333

Concentration of inhibitor Surface coverage � Surface coverage � Surface coverage � Surface coverage �

1 M HCl � 0.0020 g/L extract 0.0879 0.0663 0.0385 0.02131 M HCl � 0.0200 g/L extract 0.470 0.447 0.400 0.3501 M HCl � 0.2000 g/L extract 0.824 0.811 0.799 0.7801 M HCl � 2.0000 g/L extract 0.875 0.860 0.850 0.840

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The high inhibition efficiency may be attributed to thepresence of tannins, triterpenes and many other organiccompounds that have been extracted by only soaking the dryRhazya Stricta Decne leaves in distilled water. This inhibitionalso may be due to synergistic interactions between theadsorbed compounds.

These results agree with the findings of Fouda et al. (1986),2005), who suggested that the inhibition efficiency of organiccompounds depends on many factors including their chargedensity, number of adsorption sites, heat of hydrogenation,mode of interaction with the metal surface and the formationof metallic complexes.

5. ConclusionsThe aqueous Rhazya Stricta Decne leaf extract was found to bea highly efficient inhibitor for carbon steel in 1.0 M HClsolution, reaching about 90 per cent at 2.0 g/L and 303K, aconcentration considered to be very moderate. Even withone-tenth of that concentration, 0.2 g/L, an inhibition ofabout 82 per cent was obtained at 303K.

The rate of corrosion of the steel in 1.0 M HCl was afunction of the concentration of the Rhazya Stricta Decneextract. This rate increased as the concentration of the RhazyaStricta Decne extract was increased.

The aqueous Rhazya Stricta Decne leaves extract is anexcellent, green, eco-friendly and very cheap corrosioninhibitor for carbon steel in 1.0 M HCl solution and is foundin great amounts in the UAE, so it can be used to replace toxicand high-cost chemicals.

References

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Ateya, B.C., El-Anadouli, B.E. and El-Nizamy, F.M.(1984b), “The adsorption of thiourea on mild steel”,Corrosion Science, Vol. 24 No. 6, pp. 509-515.

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Figure 4 Effect of concentration of the aqueous extract of RhazyaStricta Decne leaves on the surface coverage of mild steel in 1.0 M HClat various temperatures

0

0.2

0.4

0.6

0.8

1

-7 -6 -5 -4 -3 -2 -1 0 1Ln Concentration, g/L

Sur

face

Cov

erag

e

Notes: 303 K; 313 K; 323 K; 333 K

Table V The free energy of adsorption (�Gads) for mild steel in 1 M HClin the presence of the aqueous extract of Rhazya Stricta Decne leaves atvarious temperatures (303-333 K)

�G, kcal · mol�1

303 K 313 K 323 K 333 K�6.96 �7.06 �7.07 �7.11

Table VI The enthalpy of adsorption (�H) for mild steel in 1M HCl in thepresence of the aqueous extract of (2 g/L) Rhazya Stricta Decne leaves atvarious temperatures (303-333 K)

�H, kcal · mol�1

303 K 313 K 323 K 333 K14.70 14.68 14.66 14.64

Table VII The change in entropy (�S) for mild steel in 1 M HCl in thepresence of the aqueous extract of (2 g/L) Rhazya Stricta Decne at varioustemperatures (303-333 K)

�S, kcal · K�1 · mol�1

303 K 313 K 323 K 333 K0.0715 0.0695 0.0673 0.0653

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About the authors

Ayssar Nahlé holds a PhD degree in Electrochemistry fromthe University of Southampton, England, (1989). From 1989to 1990, Nahlé worked as an Assistant Research Scientist atthe “Wolfson Center for Electrochemical Science” in theUniversity of Southampton. From 1990 to 1998, he worked asan Assistant Professor of Analytical Chemistry at theAmerican University of Beirut, the Lebanon, where hisresearch interests expanded to include corrosion, metalfinishing, radioactive labeling and scanning probe microscopy.In 1998, he took up an Assistant Professorship position ofAnalytical Chemistry at the University of Sharjah, UAE,where he is currently an Associate Professor carrying out hisduties. In addition, he is the Coordinator of “CorrosionPrevention & Control Research Center” at the University ofSharjah. Ayssar Nahlé is the corresponding author and can becontacted at: anahle@sharjah.ac.ae

Ibrahim Almaidoor holds a BSc degree in Chemistry fromthe University of Sharjah, Sharjah, UAE (January, 2013).During his BSc studies in the Department of Chemistry at theUniversity of Sharjah, he was deeply involved in research inthe area of corrosion and protection of metals. In 2013,Almaidoor took up a position of Assistant expert in theGeneral Department of Forensic Science and Criminology atthe Dubai Police General Headquarter, Dubai, UAE, wherehe is currently holding a rank of “Second Lieutenant” andcarrying out his duties in the Laboratories.

Ibrahim Abdel-Rahman holds an MSc degree in PhysicalChemistry from Kuwait University, Kuwait, (1984). From1984 to 1990, he worked as an Assistant Researcher at theKuwait Institute for Scientific Research “KISR”, Kuwait.From 1991 to 1994, he worked as the Head of Quality Controlat The Arab Center for Pharmaceuticals and ChemicalsIndustries, Jordan. From 1994 to 2000, he was employed as alecturer at the Applied Science University, Jordan. From 2000till present, he is still working as a lecturer in the Departmentof Chemistry at the University of Sharjah, Sharjah, UAE. Hewas a member of “Corrosion Prevention & Control ResearchGroup” at the University of Sharjah from 2005 to 2010.

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Corrosion inhibition

Ayssar Nahlé, Ibrahim Almaidoor and Ibrahim Abdel-Rahman

Anti-Corrosion Methods and Materials

Volume 61 · Number 4 · 2014 · 261–266

266