Corrosion inhibition of mild steelby P,P0-Bis (triphenylphosphonio) methylbenzophenone dibromide in HCl solution

Ayssar Nahle, Maysoon Al-Khayat, Ideisan Abu-Abdoun and Ibrahim Abdel-Rahman

Department of Chemistry, College of Sciences, University of Sharjah, Sharjah, United Arab Emirates

AbstractPurpose – The purpose of this paper is to study electrochemically and by weight loss experiments the effect of P,P0-Bis (triphenylphosphonio) methylbenzophenone dibromide (TPPMB) on the corrosion inhibition of mild steel in 1.0M 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 1.0M HCl and in 1.0M HCl containingvarious concentrations (2 £ 1028M and 2 £ 1025M) of the laboratory synthesized TPPMB at temperatures ranging from 303 to 343 K.Findings – TPPMB was found to be a highly efficient inhibitor for mild steel in 1.0M HCl solution, reaching about 98% at the concentration of2 £ 1025M at 303 K, a concentration and temperature considered to be very moderate. The percentage of inhibition in the presence of this inhibitorwas decreased with temperature which indicates that physical adsorption was the predominant inhibition mechanism because the quantity of adsorbedinhibitor decreases with increasing temperature.Practical implications – This inhibitor could have application in industries, where hydrochloric acid solutions at elevated temperatures are used toremove scale and 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 phosphonium salt corrosion inhibitors which are highly efficient and can beemployed in the area of corrosion prevention and control.

Keywords Steel, Corrosion inhibitors, P, P0-Bis (triphenylphosphonio) methyl benzophenone dibromide, Temkin adsorption isotherm

Paper type Research paper

Introduction

Metallic corrosion is a serious problem in many industries,

installations and civil services such as water and sewage

supplies. In searching for an economic method to prevent or

minimize corrosion, inhibitors frequently are suggested and

employed, especially in applications such as cooling systems.

Corrosion increases running costs and reduces plant efficiency,

availability and product quality.Organic compounds containing polar groups by which a

molecule can become strongly or specifically adsorbed on

the metal surface constitute most organic inhibitors

(Damaskin et al., 1968; Okamato et al., 1962). These

inhibitors, which include the organic N, P, S, and OH groups,

are known to be similar to catalytic poisons, as they decrease the

reaction rate at the metal/solution interface without, in general,

being involved in the reaction considered. It is generally

accepted that most organic inhibitors act via adsorption at the

metal/solution interface. The mechanism by which an inhibitor

decreases the corrosion current is achieved by interfering with

some of the steps for the electrochemical process.The corrosion inhibition of carbon steel in aggressive acidic

solutions has been widely investigated. In many industries,

hydrochloric acid solutions are used to remove scale and salts

from steel surfaces, cleaning tanks and pipelines. This treatment

may be prerequisite for coating by electroplating, galvanizing or

painting techniques. The acid must be treated to prevent an

extensive dissolution of the underlying metal. The treatment

involves addition of some organic inhibitors to the acid solution

that are adsorbed at the metal/solution interface by displacing

water molecules on the surface and forming a compact barrier

film.While extensive literature exists on corrosion inhibition in

acid media, detailed knowledge of the mode of action of

inhibitors is still lacking.Many authors have used various nitrogen-containing

compounds in their corrosion inhibition investigations. These

compounds have included quaternary ammonium salts

(Beloglazov et al., 1991; Fokin et al., 1983; Nahle, 1997,

1998, 2002; Nahle and Walsh, 1995; Savithri and Mayanna,

1996; Vasudevant et al., 1995), polyamino-benzoquinone

polymers (Muralidharan et al., 1995), benzimidazole and

imidazole derivatives (Benali et al., 2007; El Ashry et al., 2008;

Khaled, 2003; Popova, 2007; Popova et al., 2004, 2007;

Sastri et al., 2008; Scendo and Hepel, 2008; Vishwanatham and

Kumar, 2005; Zhang et al., 2004, 2008), bipyrazole

(Tebbji et al., 2011), stilbazole (Nahle et al., 2007),

substituted aniline-N-salicylidenes (Talati et al., 2005),

amides (Tuken et al., 2002), heterocyclic compounds

(Fattah et al., 1991; Granese et al., 1992), and cationic

surfactants (Al Lohedan et al., 1996; Qiu et al., 2005).

Other authors worked on phosphorous-containing and sulfur-

containing inhibitors (Ateya et al., 1984a, b; Fouda et al., 1986;

The current issue and full text archive of this journal is available at

www.emeraldinsight.com/0003-5599.htm

Anti-Corrosion Methods and Materials

60/1 (2013) 20–27

q Emerald Group Publishing Limited [ISSN 0003-5599]

[DOI 10.1108/00035591311287410]

The authors would like to thank the College of Graduate Studies andResearch at the University of Sharjah for financially supporting thisresearch project, as well as our research group entitled “CorrosionPrevention & Control”.

20

Nahle, 2001; Nahle et al., 2005, 2007, 2008; Raicheva et al.,1993; Sanad et al., 1995). Other studies involved the effect ofaddition of some ions on the inhibition efficiency of someorganic compounds. These ions included chromium(Zucchi et al., 1992), iodide (Huang et al., 1993; Popova et al.,2003a, b), and chloride (Yamaguchi and Nishihara, 1994). Thestructural effect of organic compounds as corrosion inhibitorsalso has been studied (Fouda et al., 2005; Kobayashi et al., 1993;Popova et al., 2003a, b, 2007; Skryler et al., 1991). In all thesestudies, the nitrogen atom(s) in the compounds were shown tobe able to absorb very well on the metal surface and formprotective layer, which in turn increased the corrosioninhibition with the increase in the concentration of theinhibitor, in some cases reaching 99 percent inhibition(Nahle, 1997).

No studies have been reported on P,P0-Bis(triphenylphosphonio) methyl benzophenone dibromide, interms of studying both the electrochemical and the temperatureeffects on the corrosion inhibition of carbon steel in 1.0M HClsolution. Plain carbon steel was chosen for the study becausehigh temperature aggressive acids are used widely in industriesin connection with the use of mild and low alloy steels.

Experimental details

Synthesis of P,P0-Bis (triphenylphosphonio) methyl

benzophenone dibromide

P,P0-Bis (triphenylphosphonio) methyl benzophenonedibromide (TPPMB) (Scheme 1) was prepared according tothe procedure described by Neckers and Abu-Abdoun(1984).

Instrumentation

The experimental set-up consisted of a 250-mL round bottomglass flask fitted with a reflux condenser and a long glass rodon which the specimen was hooked and in turn immersed in athermally controlled water bath.

Sample preparation

Rectangular specimens (1 cm £ 2.3 cm £ 0.3 cm) were cutfrom large sheet of 3 mm thick plain carbon steel (IS 226containing 0.18% C, 0.6% Mn, and 0.35% Si) supplied by“Reliable Steel Traders”, Sharjah, UAE, and were used forthe weight loss measurements. A 2-mm diameter hole wasdrilled close to the upper edge of the specimen and served tobe hooked with a glass rod for immersion purposes. Prior toeach experiment, the specimens were polished with 600 gradeemery paper, rinsed with distilled water, degreased withacetone, dried, and finally weighed precisely on an accurateanalytical balance.

Measuring procedure

The flask was filled with 100 mL of 1M HCl solution with andwithout TPPMB of various concentrations, and then placed in awater bath. As soon as the required working temperature wasreached, the sample coupon was immersed in the solution, and

left there for exactly 6 h, after which it was removed, rinsed with

distilled deionized water, degreased with acetone, dried, and

finally weighed precisely on an accurate analytical balance. This

procedure was repeated with all the samples with a variety of

inhibitor concentrations ranging from 2 £ 1028M up to

2 £ 1025M; and at temperatures ranging from 303 to 343 K.

Results

Weight loss corrosion tests were carried out on the steel samples

in 1M HCl in the absence and presence of TPPMB over a period

of 6 h. Table I represents the corrosion rates (mg.cm22.h21),

and the percentage efficiencies (%) for the studied inhibitor

with concentrations varying from 2 £ 1028M to 2 £ 1025M at

303, 313, 323, 333, and 343 K, respectively. The percentage

efficiency was calculated according to the following expression:

% Inhibition ¼ WUninh: 2WInh:

WUninh:£ 100 ð1Þ

where:WUninh. ¼ corrosion rate without inhibitor.Winh. ¼ corrosion rate with inhibitor.

Figures 1 and 2 show the plots of the corrosion rate of

(TPPMB) as a function of concentration at temperatures of

303, 313, 323, 333, and 343 K. At 303 K (Figure 1) the

corrosion rate dropped from 0.961 mg.cm22.h21 (1M HCl in

the absence of the inhibitor) to 0.427 mg.cm22.h21 when

2 £ 1028M of TPPMB was present in the 1M HCl. The

corrosion rate continued to decrease slightly to reach

0.281 mg.cm2 2.h2 1 (70.8 percent inhibition) at a

concentration of 2 £ 1027M, followed by a steep decrease to

reach 0.038 mg.cm22.h21 when the inhibitor concentration

was 2 £ 102 6M; and finally, at higher concentration

(2 £ 1025M) the corrosion rate as initially decreased slightly

to reach 0.018 mg.cm22.h21 (98.1 percent inhibition). At

313 K (Figure 1), the curve had a similar shape to that obtained

at 303 K. At concentrations greater than 2 £ 1027M, the

corrosion rate decreased steeply and reached about

0.058 mg.cm22.h21 (95.8 percent) at 2 £ 1025M.At 323 K (Figure 1), the concentration of the inhibitor

between 2 £ 1028 and 2 £ 1027M had very slight effect on the

corrosion rate, whereas at higher concentrations, the corrosion

rate dropped from 2.579 mg.cm22.h21 (at 2 £ 1027M) down

to 0.382 and 0.305 mg.cm2 2.h2 1 at 2 £ 102 6M and

2 £ 1025M, respectively.In Figure 2, the corrosion rates at 333 and 343 K are shown

as a function of the concentration of TPPMB. It can be

observed that the presence of the TPPMB inhibitor at these

high temperatures acted as a corrosion inhibitor, reaching a

percent inhibition of 91.1 and 86.0 percent when 2 £ 1025M

inhibitor was employed at 333 K and 343 K, respectively.Figure 3 shows the plots of the percent inhibition versus the

concentration of the inhibitor at temperatures of 303, 313,

323, 333, and 343 K, respectively. This figure shows that the

percent inhibition was significantly affected by the increase of

temperature (303-343 K) over all concentrations of inhibitor

(2 £ 102 8-2 £ 102 5M) and the presence of increased

concentrations of the inhibitor greatly increased the percent

inhibition at all temperatures.The data obtained from the weight loss measurements were

plotted in accordance to the Arrhenius equation:

Scheme 1 Structure of P,P0-Bis (triphenylphosphonio) methylbenzophenone dibromide

2Br–CH2P+ Ph3Ph3 P+ CH2

O

C

Corrosion inhibition of mild steel by TPPMB in HCl solution

Ayssar Nahle et al.

Anti-Corrosion Methods and Materials

Volume 60 · Number 1 · 2013 · 20–27

21

ln rate ¼ 2Ea

RTþ const: ð2Þ

where:

Ea ¼ activation energy (kcal.mol21).R ¼ gas constant (kcal.mol21).T ¼ absolute temperature (K).const. ¼ constant.

Figure 4 shows the Arrhenius plot of the corrosion of

carbon steel in 1M HCl solution (Ln corrosion rate as a

function of 1/T) with and without the presence of TPPMB

at concentrations ranging from 2 £ 102 8M to

2 £ 102 8M. From this Figure, the slope (2Ea/R) of

each individual line was determined and used to calculate the

activation energy according to equation (2), and taking

R ¼ 1.987 £ 1023 kcal.mol21 (Table II). The increase ofconcentration of TPPMB (from 2 £ 1028M to 2 £ 1028M),increased the activation energies for the corrosion of thesteel in 1M HCl (initially 18.27 kcal.mol21) (Table II).The increase in the activation energies for corrosion isattributed to a decrease in the adsorption of the inhibitoron the metal surface as the temperature increased.Subsequently, an increase in the corrosion rate will result dueto the greater exposed area of the metal surface to the acid.

Table III shows the surface coverage of variousconcentrations of TPPMB (from 2 £ 1028M to 2 £ 1025M)on steel surface as a function of temperature. These values wereextracted from the corresponding percent efficiency valuesreported earlier in Table I. The plot of surface coverage, u,against the natural logarithm of the concentration, ln C, for steel

Figure 1 Effect of concentration of P,P0-Bis (triphenylphosphonio)methyl benzophenone dibromide on the corrosion rate (mg.cm22.h21)of steel in 1M HCl at various temperatures

0

0.5

1

1.5

2

2.5

3

3.5

1.0E-08 1.0E-07 1.0E-06 1.0E-05 1.0E-04

Concentration, M

Cor

rosi

on R

ate,

mg.

cm–2

.h–1

Concentration(M)

Corrosion Rate(mg.cm–2.h–1) at Various Temperatures

303 313 323 333 343

2E–08 0.427 0.749 3.064

0.0000002 0.218 0.612 2.579

0.000002 0.038 0.088 0.382

0.00002 0.018 0.058 0.305

Notes: ♦ 303 K; 313 K; 323 K

Figure 2 Effect of concentration of P,P0-Bis (triphenylphosphonio)methyl benzophenone dibromide on the corrosion rate (mg.cm22.h21)of steel in 1M HCl at various temperatures

0

5

10

15

20

25

1.0E-08 1.0E-07 1.0E-06 1.0E-05 1.0E-04

Concentration, M

Cor

rosi

on R

ate,

mg.

cm–2

.h–1

Concentration(M)

Corrosion Rate(mg.cm–2.h–1) at Various Temperatures

303 313 323 333 3432E–08 9.448 23.584

0.0000002 7.501 20.367

0.000002 1.259 4.306

0.00002 1.09 3.677

Notes: + 333 K; 343 K

Table I Effect of concentration of P,P0-Bis (triphenylphosphonio) methyl benzophenone dibromide on the corrosion rate (mg.cm22.h21) andpercentage efficiency of mild steel in 1M HCl at various temperatures

Temperature/K

303 313 323 333 343

Concentration of inhibitor Corr. rate % efficieny Corr. rate % efficieny Corr. rate % efficieny Corr. rate % efficieny Corr. rate % efficieny

1M HCl 0.961 – 1.394 – 4.671 – 12.225 – 26.280 –

1M HCl 12 3 1028M 0.427 55.6 0.749 46.3 3.064 34.4 9.448 22.7 23.584 10.3

1M HCl 1 2 3 1027M 0.281 70.8 0.612 56.1 2.579 44.8 7.501 38.6 20.367 22.5

1M HCl 12 3 1026M 0.038 96.0 0.088 93.7 0.382 91.8 1.259 89.7 4.306 83.6

1M HCl 12 3 1025M 0.018 98.1 0.058 95.8 0.305 93.5 1.093 91.1 3.677 86.0

Corrosion inhibition of mild steel by TPPMB in HCl solution

Ayssar Nahle et al.

Anti-Corrosion Methods and Materials

Volume 60 · Number 1 · 2013 · 20–27

22

in the presence of the various inhibitor concentrations is shown

in Figure 4. After examining the data and adjusting them to

different theoretical adsorption isotherms, it was concluded

that all inhibitors were adsorbed on the steel surface according

to the Temkin Isotherm (Table IV):

22au ¼ lnK C ð3Þ

where:

a ¼ molecular interaction constant.u ¼ degree of coverage.K ¼ equilibrium constant for the adsorption reaction.C ¼ concentration of the inhibitor.

The equilibrium constant for the adsorption reaction, K, is

related to the standard free energy of adsorption via the

following equation given by Damaskin et al.:

K ¼ 1

55:5exp 2

DG

RT

� �ð4Þ

where:

K ¼ equilibrium constant for the adsorption reaction.55.5 ¼ concentration of water (mol.L21).DG ¼ standard free energy (kcal.mol21).

R ¼ gas constant (kcal.mol21).T ¼ absolute temperature (K).

According to equation (3), the straight lines shown in Figure 4

will have the following slopes and intercepts:

Slope ¼ 21

2að5Þ

Intercept ¼ 21

2alnK ð6Þ

Figure 3 Effect of concentration of P,P0-Bis (triphenylphosphonio)methyl benzophenone dibromide on the percent inhibition of steel in1M HCl at various temperatures

0

10

20

30

40

50

60

70

80

90

100

1.0E-08 1.0E-07 1.0E-06 1.0E-05 1.0E-04

Inhibitor Concentration, M

% In

hibi

tion

Concentration(M)

Inhibition% at Various Temperatures

303 K 313 K 323 K 333 K 343 K

2E–08 55.6 46.3 34.4 22.7 10.3

0.0000002 70.8 56.1 44.8 38.6 22.5

0.000002 96 93.7 91.8 89.7 83.6

0.00002 98.1 95.8 93.5 91.1 86

Notes: ♦ 303 K; 313 K; 323 K + 333 K; 343 K

Figure 4 Effect of temperature on the corrosion rate of steel in 1M HClsolution with and without the presence of various concentrations ofP,P0-Bis (triphenylphosphonio) methyl benzophenone dibromide

–5

–4

–3

–2

–1

0

1

2

3

4

2.9 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

(1/T)x103K–1

1M HCl

1M HCl

+ 2x10–8

M

1M HCl

+ 2x10–7

M

1M HCl

+ 2x10–6

M

1M HCl

+ 2x10–5

M

3.3 –0.03978 –0.85097 –1.2694 –3.27017 –4.01738

3.19 0.332177 –0.28902 –0.49102 –2.43042 –2.8473

3.1 1.541373 1.11972 0.9474 –0.96233 –1.18744

3 2.503483 2.2458 2.01504 0.23032 0.08893

2.92 3.268808 3.16057 3.01392 1.46001 1.3021

Notes: ♦ 1 M HCI K; 1 × 10–7M; 1 × 10–6M; + 1 × 10–5M; 1 × 10–4M; • 1 × 10–3M

Table II The activation energy (Ea) for the corrosion of mild steel in 1MHCl with and without P,P0-Bis (triphenylphosphonio) methylbenzophenone dibromide inhibitor at various concentrations

Activation energy, Ea (kcal.mol21)

System 2 3 1025M 2 3 1026M 2 3 1027M 2 3 1028M

1M HCl 18.27 18.27 18.27 18.27

1M HCl 1

inhibitor 28.32 25.23 23.07 21.97

Corrosion inhibition of mild steel by TPPMB in HCl solution

Ayssar Nahle et al.

Anti-Corrosion Methods and Materials

Volume 60 · Number 1 · 2013 · 20–27

23

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

Intercept ¼ Slope:ðln KÞ ð7Þ

from which the equilibrium constant for the adsorptionreaction, K, can be calculated:

K ¼ eðIntercept=SlopeÞ ð8Þ

The standard free energy of adsorption of the inhibitor, DG0,can be calculated from the results in Figure 5 used tocalculate the equilibrium constant, K, and equation (4) atvarious temperatures (303-343 K).

The enthalpy of adsorption, DH0, for the inhibitor can becalculated from the following equation:

DH0 ¼ Ea 2 RT ð9Þ

The entropy, DS0, can be calculated at various temperaturesfor the inhibitor using the following equation:

DG0 ¼ DH0 2 TDS0 ð10Þ

Discussion

The results summarized in Table II, show that the activationenergy (Ea) for the corrosion of steel in the presence of theinhibitor were higher compared to the activation energy in theabsence of inhibitor at all concentrations ranging from2 £ 102 5M to 2 £ 102 8M (from about 28 vs to22 kcal.mol21). This can be attributed to the fact that highervalues of Ea in the presence of inhibitor compared to its absenceare generally 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 (Popova et al.,2003a, b).

Tables V-VII show the thermodynamic data obtained in thepresence of the inhibitor at 2 £ 1025M. These thermodynamicquantities represent the algebraic sum of the values foradsorption and desorption. The negative value of DG0

indicates the spontaneous adsorption of inhibitor on the

surface of the mild steel. The standard free energy, DG0,

varies from 218.29 kcal.mol21.K21 at 303 K to 215.21

kcal.mol21.K21 at 343 K. The adsorption process is believed

Figure 5 Effect of concentration of P,P0-Bis (triphenylphosphonio)methyl benzophenone dibromide on the surface coverage of steel in 1MHCl at various temperatures

0

0.2

0.4

0.6

0.8

1

–18 –16 –14 –12 –10 –8

Ln Concentration, M

Sur

face

Cov

erag

e

303 313 323 333 343

–10.82 0.981 0.956 0.935 0.911 0.86

–13.12 0.96 0.937 0.918 0.897 0.836

–15.42 0.708 0.561 0.448 0.386 0.225

–17.71 0.556 0.463 0.344 0.227 0.103

Notes: ♦ 303 K; 313 K; 323 K + 333 K; 343 K

Table III Effect of concentration of P,P0-Bis (triphenylphosphonio) methyl benzophenone dibromide on surface coverage for mild steel in 1M HCl atvarious temperatures

Temperature/K

303 313 323 333 343

Concentration of inhibitor Surface coverage u Surface coverage u Surface coverage u Surface coverage u Surface coverage u

1M HCl 12 3 1028M 0.556 0.463 0.344 0.227 0.103

1M HCl 12 3 1027M 0.708 0.561 0.448 0.386 0.225

1M HCl 12 3 1026M 0.960 0.937 0.918 0.897 0.836

1M HCl 12 3 1025M 0.981 0.958 0.935 0.911 0.860

Table IV The data obtained from the weight loss measurements for Arrhenius equation: (1/T) against Ln corrosion rate

Ln corrosion rate (mg.cm22.h21)

(1/T) 3 103 K21 1M HCl 1M HCl 12 3 1028M 1M HCl 12 3 1027M 1M HCl 12 3 1026M 1M HCl 12 3 1025M

3.30 20.03978 20.85097 21.26940 23.27017 24.01738

3.19 0.332177 20.28902 20.49102 22.43042 22.84731

3.10 1.541373 1.11972 0.94740 20.96233 21.18744

3.00 2.503483 2.24580 2.01504 0.23032 0.08893

2.92 3.268808 3.16057 3.01392 1.46001 1.30210

Corrosion inhibition of mild steel by TPPMB in HCl solution

Ayssar Nahle et al.

Anti-Corrosion Methods and Materials

Volume 60 · Number 1 · 2013 · 20–27

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to be exothermic and associated with a decrease in entropy (DS)

of solute, while the opposite is true for the solvent. The

gain in entropy that accompanies the substitutional

adsorption process is attributable to the increase in the solvent

entropy. This agrees with the general suggestion that the values of

DG0 increase with the increase of inhibition efficiency

(Fouda et al., 1986, 2005) as adsorption of organic compound

is accompanied by desorption of water molecules from the

surface.The high inhibition efficiency may be attributed to the

preferred flat orientation of this compound on the

metal surface. An interaction occurs between the delocalized

p-electrons of the two rings, the diphenyl ketone and the lone

pair of electrons on P and O atoms with the positively charged

metal surface.

Conclusion

P,P0-Bis (triphenylphosphonio) methyl benzophenone

dibromide (TPPMB) was found to be a highly efficient

inhibitor for plain carbon steel in 1.0M HCl solution,

reaching about 98 percent at 2.0 £ 1025M and 303 K,

a concentration considered to be very low.P,P0-Bis (triphenylphosphonio) methyl benzophenone

dibromide (TPPMB) may function as a potential corrosion

inhibitor because it contains phosphorus and oxygen. It was

apparent from the molecular structure that this compound

would be adsorbed onto the metal surface through the lone

pair of electron of phosphorus and oxygen and p-electrons of

the diphenyl ketone.The percentage of inhibition in the presence of this

inhibitor was decreased with temperature, which indicated

that physical adsorption was the predominant inhibition

mechanism because the quantity of adsorbed inhibitor

decreased with increasing temperature.

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Table VI The free energy of adsorption (DGads) for mild steel in 1M HClin the presence of P,P0-Bis (triphenylphosphonio) methyl benzophenonedibromide at various temperatures (303-343 K)

DG, kcal.mol21

303 K 313 K 323 K 333 K 343 K

218.29 217.01 216.07 215.68 215.21

Table VII The change in entropy (DS) for mild steel in 1M HCl in thepresence of P,P0-Bis (triphenylphosphonio) methyl benzophenonedibromide at various temperatures (303-343 K)

DS, kcal. K21.mol21

303 K 313 K 323 K 333 K 343 K

0.152 0.143 0.135 0.130 0.125

Table V The enthalpy of adsorption (DH) for mild steel in 1M HCl in thepresence of 2 £ 1025M P,P0-Bis (triphenylphosphonio) methylbenzophenone dibromide at various temperatures (303-343 K)

DH, kcal.mol21

303 K 313 K 323 K 333 K 343 K

27.72 27.70 27.68 27.66 27.64

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Further reading

Frank, W.C., Kim, Y.C. and Heck, R.F. (1978),

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heterocyclic dibromides”, J. Org. Chem., Vol. 43 No. 15,

pp. 2947-9.Kumar, U., Kato, T. and Frechet, J.M.J. (1992), “Use of

intermolecular hydrogen bonding for the induction of

liquid crystallinity in the side-chain of polysiloxanes”,

J. Amer. Soc., Vol. 114, p. 6630.Nahle, A. (2005), “Inhibition of corrosion of iron

in HCl solution by semicarbazides and

thiosemicarbazides”, Bulletin of Electrochemistry, Vol. 21

No. 6, pp. 275-81.

Corresponding author

Ayssar Nahle can be contacted at: anahle@sharjah.ac.ae

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Corrosion inhibition of mild steel by TPPMB in HCl solution

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