^lETNAM JOURNAL OF CHEMISTRY VOL. 50(1) 105-110 FEBRUARY 2012
INHIBITION OF THE CORROSION OF CARBON STEEL IN NEUTRAL SOLUTIONS BY WATER SOLUBLE POLYANILINE
Vu Dinh Huy, Nguyen Thi Minh Hoc
Vietnam National University of Ho Chi Minh City-Ho Chi Minh City University of Technology Received 30 September 2010
Abstract
The aim of this work is to study the inhibition effect of water-soluble polyaniline (sulphonate polyaniline) on the corrosion of carbon steel in neutral solutions. The effect on the inhibition efficiency of concentration, temperamre has been studied systematically by mass-loss method and by electrochemical measurements. All these methods confirmed that the inhibition efficiency of sulphonate polyaniline increases in increasing its concenUation, but decreases in increasing temperature. The studies of polentiodynamic polarization and electrochemical impedance spectroscopy reveal that sulphonate polyaniline acts as an anodic inhibitor
Keywords: Polyaniline, sulphonate polyaniline, corrosion inhibitor, water solution.
1. INTRODUCTION
Polyaniline (PANi) belongs to i class of conductive polymers that can be differentiated from one to another by its oxidation states and doping
levels.
Although it was discovered over 150 years ago, only recently polyaniline captured the attention of the scientific community because of the discovery of its high electrical conductivity.
H
Figure 1: Main polyaniline structures n-i-m = 1, x =
N=^
of polymerization Many previous •works showed the positive
anticorrosive behavior of PANi towards iron [1, 2], carbon steel [3-6], stainless steel [7], aluminum [8, 9], and copper [10],
But water indissoluble properties of polyaniline have significantly limited its applied range.
Therefore, the use of water-soluble polyaniline for protecting corrosion of metals was not widely studied.
In a previous paper [11], we presented a simple synthetic method to produce fiilly soluble polyaniline in water and do not cause environmental pollution. Sulphonate polyaniline (SPANi).
This paper deals with a sUidy of carbon steel corrosion inhibiting properties of SPANi in fresh water under static condition at temperatures from SOT to 140*^0.
Figure 2: Water-soluble sulphonate polyaniline structures (SPANi) 2. EXPERIMENTAL
2.1. Chemical composition of steel and water Specimens machined from the commercial steel
pipeline (PI 10 grade) have been used. The nominal composition of PI 10 carbon steel is listed in table 1.
The chemical composition of fresh water is given in table 2.
50(!).2012 VuDinhi Table I The element composhion {%) of the PI 10 carbon steel
1 k'liiL-nl 1 Conteiil,%
C 0.24
M i l 1.32
Si 0.16
P 0.22
S 0.013 Yield strength: Min 110000 psi; Max 140000 psi Tensile strength, Min 125000 psi Table 2: The chemical composition of water (density 0.998 g/cm' and pH 6 95 al 23 9"C)
Ion Content, mg/1
CI 145
iOi 22
HCO3"
70 C O f -
0 Ca'"
13
Mr*
11
Fe-" + Fe' 0.2
Na' + K ' 98
2.2. Mass-loss measurement method
The size of steel specimens was 50 mm =< 10 mm 3 mm. Preparing, cleaning and evaluating the mass-loss of the test specimens was done according to the ASTM standards G1 -90, 031 -72 and G111 -92 [12-14]. The specimens were immersed in aerated static fresh water solutions at temperatures of 30"C.
60"C, lOOX' and I40"C (±2''C). The time of exposure was 4 hours.
The SPANi was selected by mass at concentrations of 0,500, 1000, 1500 and 2000 ppm.
Corrosion inhibition efficiency (CIE) of SPANi was evaluated by measuring average steel corrosion rates in the lest solutions with (V) and without (V^) adding to SPANi.
Corrosion inhibition efficiency in terms of percent was defined as
CIE(%) .100.
(!)
The average steel corrosion rate in millimeters per year was calculated on the mass-loss data as
V{mm I year) =
K X Massloss {g) Density {g I cm ) x Area {cm') x Time {hours )
(2) where constant K = 8,76x10^
2.3. Optical microscopy observation
A PI 10 carbon steel ( 1 x 1 cm") substrate was mounted on a cold cured epoxy resin and abraded down to 1200-mesh silicon-carbide paper, and washed uilh methanol and then distilled water. The steel specimens were immersed in aerated static solutions containing different concentrations of SPANi at room leniperature. The immersion time was 4 hours. We examined the corrosion behavior of the steel specimens by using the optical microscopy (luodel Kyowa)
2.4. Electrochemical methods
A model of Solatron 1280Z was used for measurements of polentiodynamic polarization curves and electrochemical impedance spectroscopy in solutions at room temperature in accordance with ASTM standards: G5-94. G106-89, 0102-89 and G59-91 [15-18].
2.4.1- Testing of polentiodynamic polarization The exposure area of steel was 2 cm'. A platinum electrode was used as counter electrode, and a saturated calomel electrode (SCE) was used as a reference electrode.
The scan rate is 5 mV/sec from stable corrosion potential (Ej-^ir)- Current corrosion density (i^„n) was measured through both Tafel extrapolation and linear polarization methods near the corrosion potential.
2.4-2. Testing of electrochemical impedance spectroscopy
Testing of electrochemical impedance spectroscopy was performed in order to analyze charge transfer reaction of SPANi in the solutions.
Applied frequency was successively decreased from 1 MHz to 10000 Hz with each voltage amplitude is 0.2 mV to maintain linear between input and output signal,
3. RESULTS AND DISCUSSION 3.1 Mass-loss measurements
3.1.1. The dependence of steel corrosion rule on concentration of SPANi and temperuture in neutral water solutions
Results from mass-loss measurement tests in the 4 hours immersion time at temperatures of 30"C 6 0 T , 100°C and MOT (±2"C) are shown in figure 3.
VJC. Voi. 50(1). 2012 Inhibition of the corrosion of...
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| 0 2 .
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! = ^
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30 60 100 140 T e m p e r a t u r e ( ° C )
-4-Oppin SPANI - | - 5 0 0 p p m SPANI -4-tlOOppniSPANi -W-BOOppni SPANI -*-2000ppin SPANI
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^ ^ ^ v V -t-ioo-c
^ : | ^ * J ^ - x - 1 4 0 " C 500 1000 1500 2000 CoQceDtratioD of SPANi (ppm)
(a) (b) Figure 3: The corrosion rate of steel depends on temperature (a) and SPANi concentration (b) in
fresh water solutions 3.1.2. The dependence of steel corrosion inhibition efficiency on concentration of SPANi and temperature in neutral fresh water solutions
Data in figures 3 and 4 indicate that:
- The average corrosion rates of steel in fresh water solution without SPANi reached the maximum value is 1.1 mm/year at temperature of 100°C in range from 3O^C to MCC.
Adding SPANi inhibitor to fresh water solutions, the corrosion rate of steel was considerably decreased in increasing the concentration of SPANi from 500 ppm to 2000 ppm, but It was increased in increasing temperature: The corrosion rate of steel decreased from 2 to 17 times depending on the SPANi concentration and temperature of solution.
a 40
\ 20
I '^
30 60 100 140Tempeniture (°C)
500 1000 1500 2000 Concentration of SPANi (ppm)
(a) (b) Figure 4: The steel corrosion inhibition efficiency of SPANi depends on temperature (a) and
SPANi concentration (b) in water solutions - In consequence, the steel corrosion inhibition
efficiency of SPANi increased in increasing its concentration, but decreased in increasing temperature: With adding SPANi to 2000 ppm, the maximum steel corrosion inhibition efficiency of SPANi decreased from 94% to 83% in increasing temperature of solution from 30°C to 140°C (Fig. 4).
These remarks may be explained as below:
- As the temperature rises, the electrochemical corrosion reaction kinetics of steel will increase, but it reduces the concentration of dissolved oxygen As a result of the corrosion rate of steel reached maximum value at the temperature of lOO^C in solution without SPANi.
- SPANi inhibitor adsorbed on the surface of
steel and protected it by blocking effect. The SPANi adsorption increased in increasing its concentration.
On the contrary, SPANi desorption increased in increasing temperature. The competition between the adsorption and desorption conducted the steel corrosion inhibition efficiency of SPANi increased in increasing its concentration, but decreased in increasing temperature.
3.2. Optical microscopy observation
Our optical microscopic observations verify that the SPANi inhibitor induced the development of a protective film on the surface of steel The area of corroding steel surface was considerably reduced in
VJC, Vol 50(1), 2012
increasing eoncentration of SPANi (figure 5)
Vlt Dinh lluY el III
0 pp SP w
I ppm SI \N
A
""UOO ppm SP \ \
Figure 5: Images of the steel surface after 4 hours immersion in fresh water solutions with and without adding SPANi at room temperature (x|0 magnified)
3.3. Electrochemical measurements 3 3 1. Polentiodynamic polarization
Some of anodic and cathode polentiodynamic polarization curves of steel in aerated static fresh water solutions with and without adding SPANi at room temperature listed in figure 6 and table 1
Table 1: Polentiodynamic polarization parameters for the corrosion of steel in aerated static fresh water solutions containing different concentrations of SPANi SPANi concentration, ppm
0 500 1000 1500 2000
E.„, mV -533 -531 -500 -494 -464
b„mV 343 567 2.958x10' 5.534x10' 1.103x10'
be, mV -627 -255 -273 -157 -151
i„„xlO-', A/em' 1.851 1.227 0.894 0.368 0.364
CIE, % 33.71 51 70 80.12 8033 (Corrosion potential (E„n)- anode Tafel slope (b,), cathode Tafel slope (be), corrosion current density (i,^) and corrosion inhibition efficiency (CIE)).
VJC, Vol. 50(0.2012 Lnhibition of the corrosion of..
Figure 6: Polentiodynamic polarization curves of steel measured in solutions without SPANi (a) and added 2000 ppm SPANi (b)
3 3 2 Electrochemical impedance .spectroscopy AC impedance measurements acquired as Nyquist plots are presented in figures 7 and 8.
Polarization resistance and double layer capacitance values from AC impedance spectra (Nyquist plots) are given in table 2.
Consistent with testing the immersion, the data given in table I shows that SPANI increases the corrosion inhibition efficiency (CIE) of steel in increasing its concentration in the solutions.
SPANi shifts the corrosion potential (E^on) of steel in the positive direction, significantly increases anode (ba) Tafel slope and polarization resistance (Ri>). reduces double layer capacitance (C) and the corrosion current density (icorr) of steel Therefore, SPANi is considered as an anodic inhibitor, which strongly adsorbs on anodic sites of the surface of steel and inhibits the anodic dissolution of steel, protects it by blocking effect of a passive film and an active electronic barrier can afford coatings containing SPANi molecules.
fiODO I-
(b)
Figure 7: Nyquist plots of AC impedance data of steel in solutions without SPANi (a) and added 2000 ppm SPANi (b)
' , • • " '
/
!'.
3 Ml (2) (31
11X1 ppi
Z'l
SPANi i i S I ' \ N i 1 SPANi 1 SP \ N i
figure 8 Effect of SPAN! concentration on Nyquist impedance spectra of steel in solutions containing 500 ppm, 1000 ppm, 1500 ppm and 2000 ppm SPANi
109
I able 2. Polarization resistances (Rp), double layer capacitance values (C) from AC impede:
measurement to the steel corrosion in solutions containing different concentrations of SPA"
SPANi concentration, ppm 0 SOO 1000 1500 2000
E.„„, mV -536 -532 -492 -411 -404
CxlO', F/cm=
0.007161 274.77 9.6343 9.0967 0.1627
Rp, Ohm.cnr 4362 4552 9984 80459 93991 4. CONCLUSIONS
Reducing of corrosion rate of carbon steel in aerated neutral fresh water solutions mainly is caused by the adsorption of water-soluble polyaniline (sulphonate polyaniline - SPANi) on the surface of steel
The carbon steel corrosion inhibition efficiency of SPANi increases in increasing its concentration, but decreases in increasing temperature.
The studies of polentiodynamic polarization and electrochemical impedance spectroscopy reveal that SPANi acts as an anodic inhibitor, which strongly adsorbs on anodic sites of the surface of steel and inhibits the anodic dissolution of steel, protects it by blocking effect of a passive film.
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Corresponding author: Vu Dinh Huy
Vietnam National University of Ho Chi Minh City Ho Chi Minh City University of Technology 268 Ly Thuong Kiel, 10 district. Ho Chi Minh City Email: [email protected]