LCCA 1:1(2019)1- 4

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The Libyan Conference on Chemistry

and Its Applications (LCCA 2019)

(7 – 9 September, 2019)

Inhibition Mechanism of adsorption and thermodynamic of 304 stainless Steel Using

Isobutyl methyl ketone semicarbazonein Acid Medium

2Jazea B. Ramadan ,2a, N.Mohamed, Rahum1Imperiyka, M. Hammad

1Faculty of arts and science Alkufra, University of Benghazi 2Chemistry Department, Faculty of Science, University of Benghazi

A B S T R A C T A R T I C L E I N F O

The inhibition efficiency of corrosion on 304 stainless steel using isobutyl methyl ketone semicarbazones as inhibitor has been studied using weight loss, and scanning electron microscopy. The inhibition efficiency, corrosion rate, the nature of anchoring sites and the adsorption characteristics have been determined from the results. The inhibition efficiency increases with increasing the inhibitors concentration.In general IE% increases with increasing the temperature.It was found that the synthesized compound behaved as good inhibitor with high inhibition efficiency, which is 88.08%. The adsorption of the inhibitor on the stainless steel surface obey Langmuir adsorption isotherm.Scanning electron spectroscopy is used to examine the surface morphology of stainless steel samples both in the presence and absence of inhibitors at optimum conditions. Scanning electron microscope reveals the formation of a smooth, dense protective layer in the presence of inhibition.

Article history: Received 15July 2019 Revised 15Augst2019 Accepted 20Augst 2019 Available online 15 April 2020

Keywords:

Acid solutions” stainless

steel”Inhibitor” isobutyl methyl

ketone semicarbazones” weight loss

measurement”scanning electron

Spectroscopy.

Corresponding Author:

Imperiyka.msh@uob.edu.ly;

impeeriyka@gmail.com

Introduction

Nowadays, most metals corrode in

contact with water and also moisture in

the air, acids, bases, salts, aggressive

metal polishes and other corrosive solids

and liquid chemicals. stainless steel is of

high industrial value. Metals, when

subjected to surface treatment such as

painting, enameling etc. should have

clean surface, free from rust or oxide

scales.For removing these rusts and

scales, metals are immersed in acid

solutions known as acid pickling bath

[1,2].Generally hydrochloric acid is used

in pickling bath. Therefore, occurrence

of corrosion phenomenon is unavoidable.

Utilization of inhibitors to control

corrosion is indispensable. Corrosion

inhibitors not only work to prevent metal

dissolution but also reduce acid

consumption. A thorough survey of

literature reveals that large number of

inorganic and organic compounds have

been synthesized and employed as

corrosion inhibitors [2-4]. The survey

suggests that stainless steel corrosion is

effectively controlled by the use of

organic substances containing nitrogen,

oxygen or sulphur in the conjugated

system [4-6]. In the pursuit of a suitable

inhibitor for the corrosion of stainless

steel it was proposed to use isobutyl

methyl ketone semicarbazonefor the

present..work.

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2.1 Materials

Hydrochloric acid used as corrosion solution.

isobutyl methyl ketone, sodium acetate,

semicarbazide and ethanol were used to prepare

the organic compounds as inhibitorisobutyl

methyl ketonesemicarbazone.

2.2 samples preparation

Steel Sample Preparation

The steel sample used in this study was made

from a 304 stainless steel, the 304 stainless steel

obtain from Batron company in Benghazi –

Libya, the chemical composition of the 304

stainless steel is shown in Table (1). Rectangular

specimens (3cm x 2cm x 0.1cm) of 304 stainless

steel were used for the determination of the

weight loss of 304 stainless steel in the tested

solution, and cylindrical specimens form

electrode of (0.384 cm2) cross-sectional area

used for testing morphology of the 304 stainless

steel.

Table (1) the chemical composition of 304

stainless steel.

2.3 Corrosion Monitoring Techniques

Used

3.2.1 Weight loss method

In this method, the loss of metal due to

corrosion is measured by exposing the metal

specimen of known area to the environment for

a period of time and the difference in weight

before and after exposure is calculated.

Experimental procedure

The initial weight of the polished plate was

taken. The solutions were taken in a 100 ml

beaker and the specimens were suspended in

duplicate into the solution using glass hooks.

After a period of time hour, the specimens were

removed, washed with water, dried and weighed

to an accuracy of four decimals.The experiment

was repeated for various inhibitor concentrations

in 11% HCI. The procedure was repeated for

various concentrations of the inhibitor

prepared.The corrosion rate in g .cm-1.day-is

calculated as follows,

C.R = 𝑚1−𝑚2

𝐴.𝑡 … … … (1)

Where m1and m2 are the masses of the specimen

before and after corrosion, A is the total area of

the specimen and t is the corrosion

time.Evaluation of Inhibitor efficiency has been

determined by using the following

relationship[7].

IE %= 𝐶.𝑅0−𝐶.𝑅

𝐶.𝑅0× 100 … … … (2)

Where C.R and C.R are the corrosion rates of

304 stainless steel in absence and presence of

certain concentration of inhibitors, respectively.

Evalution of surface cover by using following

equation

θ = 𝐼𝐸

100 … … … (3)

Result and Discussion

Weight loos measurement The tested isobutyl methyl ketone

semicarbazonesinhibited the corrosion of steel

even at low concentration of the acid at room

temperature. Corrosion rate is deceased with

arising of concentration of inhibitor as shown in

Table (2).

Table (2) Corrosion rate of various conce. of

inhibitor for the corrosion of stainless steel in 11

% HCl solution.

Influence of Temperature

The.It is evident from Table 3that inhibition

efficiency was found to increase with increasing

inhibitor concentration. The increase in

inhibition efficiency with temperature indicates

the fact that the inhibitor film formed on the

metal surface is higher protective in nature at

higher temperature.The maximum efficiency of

about 80.88% was obtained at concentrations of

0.04 M of inhibitor (Tables 3).

Elements C Si Mn Cr Ni S Fe

Chemical

composition

(%)

0.08 1 2.0 18 10 0.03 Bal

Conc. 25°C 35 °C 45 °C

0 0.065592 0.01790 0.03443

0.005 0.061192 0.015050 0.01981

0.01 0.047053 0.078592 0.01280

0.02 0.033479 0.068296 0.01048

0.04 0.026555 0.05800 0.00926

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Table (3) Inhibition efficiencies, degree of

coverage of various concentrations of inhibitor

for the corrosion of stainless steel in 11 % HCl

solution.

Adsorption isothermal

The Langmuir isotherm was applied to

investigate the adsorption mechanism by the

following expression:

𝐶𝑖𝑛ℎ

𝜃=

1

𝐾+ 𝐶𝑖𝑛ℎ … … … (4)

Where Cinh the inhibitor concentration and K the

equilibrium constant of the adsorption process

[6]. K, is related to the standard free energy of

adsorption, ΔGoads., with the following equation:

𝐾 = (1 55.5)exp (⁄ −∆𝐺𝑎𝑑𝑠

°

𝑅𝑇) … … … (5)

Where R= ideal gas constant = 8.314 J/mol.K,

the value of 55.5 is the concentration of water in

the solution in moles and T is temperature in K

[6,7].The plot of Cinh./θ vs. Cinh. of inhibitor at

25ºC, 35ºC and 45ºC. s.and ΔGoads. can be

calculated according to the above Eq.(5).

Based on the calculated values of adsorption

free energy (G°ads) which indicates that

adsorption of inhibitoronto the 304 stainless

steel is a spontaneous process.The calculated

ΔGoads. Values is between -18 to -24 kJ/mol

suggesting that the adsorption mechanism of the

organic inhibitors on of 304 stainless steel in

studied acid media was typical of chemisorption.

) for ads⁰free energies of adsorption (∆G :4Table

the corrosion of stainless steel.

Thermodynamic Considerations

The effect of temperature on the corrosion of

stainless steel in the absence and presence of the

organic inhibitors was studied using the

Arrhenius equation;Singh in (2009) calculated

the activation energy by using Eq. (6).

log(C. R) = −Ea

2.303RT+ A … …. (6)

A is Arrhenius or pre-exponential factor, Ea is

the activation energy, R is the gas

constant[8].The plot of logC.R versus 1/T

inhibitor these plots gave straight lines andEa is

calculated from the slop of straight lines.The

values of Ea is given in Table 5. The values of

Ea in the inhibited acid solution are appreciably

greater than those obtained in the uninhibited

acid solution. This suggests that the presence of

reactive centers on the inhibitors, block the

active sites of corrosion resulting in an

increasing in activation energy [2, 9-11].

Table 5.Activation energy of for the corrosion

of stainless steel.

Scanning electron microscopy

Surface of polished stainlees steel

specimens immersed in 1M HCl in the

presence and absence of inhibitor was

showed in Fig (1,2). When a blank

determination was conducted, the metal’s

surface was corroded with etched grain

boundaries and other corrosion products

were also noticed as seen in the Fig.(1). The

micrograph reveals that the surface is

strongly damaged in the absence of

inhibitor (active corrosion). But in the

presence of inhibitors, the micrograph

reveals that there is decrease in the

corrosion sites and pits over the surface of

the stainless steel (Fig.2). This is due to the

formation of adsorption layer of inhibitor on

the metal surface.

25°C 35 °C 45 °C

Conc. IE 𝛉 IE 𝛉 IE 𝛉

0.005 19.10 0.019 40.784 0.407 54.53 0.545

0.01 28.26 0.282 56.052 0.560 73.06 0.730

0.02 48.95 0.4895 61.8357 0.618 77.325 0.7732

0.04 59.51 0.5951

\

67.5905 0.675 80.087 0.8008

T(⁰C ) 25 35 45

ads⁰G∆ -18.81 -23.85 -24.90

Conc. 0 0.005 0.01 0.02 0.04

Ea 68.91 39.56 41.61 48.85 51.96

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Fig. 1 scanning electron micrograph of stainless

steel sample immersion in 11% HCl.

Fig. 2 Scanning electron micrograph of

stainless-steel immersion in in 11% HCl in

presence of 0.04M of inhibitor.

Conclusion

The corrosion inhibition of stainless

steel in HCl in the presence of isobutyl

methyl ketone semicarbazones was

studied using weight loss and scanning

electron microscopy. The study revealed

that the corrosion rate increases with

temperature, time. Addition of inhibitor

to the corrodent solution lowered the

corrosion rate of 304 stainless steel.

Inhibition efficiency of inhibitor was

found to increase with concentration and

increased with temperature. Adsorption

of inhibitor molecule on steel surface

was found to obey the Langmuir

adsorption isotherm. The phenomenon

of chemisorption is proposed from the

obtained thermodynamic parameters.

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