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Chemical Engineering Communications
ISSN: 0098-6445 (Print) 1563-5201 (Online) Journal homepage: http://www.tandfonline.com/loi/gcec20
A. S. Fouda , H. A. Mostafa , G. Y. Elewady & M. A. El-Hashemy
To cite this article: A. S. Fouda , H. A. Mostafa , G. Y. Elewady & M. A. El-Hashemy (2008) LOW
TYPE 304 IN HCL SOLUTION, Chemical Engineering Communications, 195:8, 934-947, DOI:
To link to this article: http://dx.doi.org/10.1080/00986440801905148
Published online: 25 Apr 2008.
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Low Molecular Weight Straight-Chain Diamines as
Corrosion Inhibitors for SS Type 304 in HCl Solution
Chemistry Department, Faculty of Science, El-Mansoura University,
El-Mansoura, Egypt
The effect of some low molecular weight straight-chain diamines to inhibit the
corrosion of SS type 304 in 1M HCl solution is examined by weight loss and
galvanostatic polarization techniques. The inhibition efficiency increases with
increasing the number of carbon atoms in the chain up to 8 carbons, but at higher
than 8 carbon atoms (12 carbons) it decreases again. These diamine compounds
act as mixed-type inhibitors, but the cathode is more polarized than the anode when
an external current was applied. The corrosion rate in the presence of the investigated diamine compounds was found to increase with increasing the temperature
and decrease with increasing the concentration of these compounds. Activation parameters for the corrosion of SS in 1M HCl were calculated and showed that
corrosion was much reduced in the presence of inhibitors. The adsorption of these
compounds on SS from 1M HCl solution obeys the Langmuir adsorption isotherm.
The synergistic effect of KI on the inhibitive efficiency of the investigated diamine
compounds was also studied.
Keywords Corrosion inhibition; Diamine compounds; HCl; SS; Synergistic
Amines and their derivatives are well known corrosion inhibitors (Lykina et al.,
1990; Fouda et al., 2005; Podobaev et al., 1989; Fouda et al., 1990; Al-Suhybani,
1990; Levichev and Kardash, 1991). Low molecular weight amines can be used as
inhibitors in aqueous solutions, owing to their relatively high solubility in water.
In this study diamines with linear carbon chains containing between 2 and 12
carbons have been examined. This series of diamines is of interest due to the possibility of adsorption at the metal=solution interface in several different configurations. These include the vertical position, in which only one of the two end groups
is adsorbed with the hydrocarbon chain extending outward, and the flat position,
in which both end groups are adsorbed with the hydrocarbon network parallel to
the surface. In addition, if the molecule is long enough to be flexible, the hydrocarbon can be buckled between the two adsorbed end groups, as shown in Figure 1.
Address correspondence to A. S. Fouda, Chemistry Department, Faculty of Science,
El-Mansoura University, El-Mansoura-35516, Egypt. E-mail: asfouda@yahoo.com
Chem. Eng. Comm., 195:934–947, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 0098-6445 print/1563-5201 online
DOI: 10.1080/00986440801905148
Experimental Section
Materials and Chemicals
The composition of the stainless steel (SS) used in these experiments is 18% Cr, 8%
Ni, 0.08% C, and the remainder Fe.
A solution of 1M HCl was prepared from an analytical reagent grade 37% HCl
and bidistilled water and used as the corrosion medium. The selected diamine
compounds studied are presented below. All compounds investigated were obtained
from BDH.
1. Ethylenediamine.
H2N ðCH2Þ2 NH2
2. 1,3-Propanediamine.
H2N ðCH2Þ3 NH2
3. 1,4-Butanediamine.
H2N ðCH2Þ4 NH2
4. 1,8-Octanediamine.
H2N ðCH2Þ8 NH2
5. 1,12-Dodecanediamine.
H2N ðCH2Þ12 NH2
Weight Loss Measurements
The test pieces were used in the form of sheets of the dimensions 20 20 0.078mm.
Before being used, these were mechanically polished with emery papers (a coarse
paper was used initially and then progressively finer grades were employed), ultrasonically degreased in methanol, rinsed in bidistilled water, and finally dried between
two filter papers and weighed. This treatment was carried out immediately before
each measurement. Each experiment was carried out in 100mL of the aggressive
solution. Duplicate tests were conducted for each experiment.
Figure 1. Possible configurations for the a, x polymethylene diamines.
Diamines as Corrosion Inhibitors 935
Polarization Measurements
The SS electrodes were cut from SS sheets type 304 and 0.078mm in thickness. The
electrodes were of the dimensions 1 cm 1 cm and were welded from one side to a
copper wire used for electric connection. The samples were embedded in a glass tube
of just larger diameter than the samples. Epoxy resin was used to attach the sample
to the glass tube. The electrodes were treated as before. A saturated calomel
electrode and a platinum wire were used as reference and auxiliary electrodes,
respectively. Polarization studies were carried out using a potentiostat=galvanostat
(Amel model 549). All experiments were repeated using different specimens to
confirm the reproducibility of the results and are carried out at 30C
Results and Discussion
Weight Loss Measurements
Figure 2 shows the weight loss-time curves for SS type 304 in 1M HCl in the absence
and presence of different concentrations of 1,8-octanediamine at 30C. As shown
from this figure, the weight loss of SS samples is decreased by increasing the concentration of the inhibitor. The linear variation of weight loss with time in inhibited 1M
Figure 2. Weight loss-time curves for the corrosion of 304 SS in presence and absence of
different concentrations of 1,8-octanediamine at 30C.
936 A. S. Fouda et al.
HCl indicates the absence of insoluble surface films during corrosion. In the absence
of any surface films, the inhibitor is first adsorbed onto the metal surface and thereafter impedes corrosion either by merely blocking the reaction sites (anodic and
cathodic) or by altering the mechanism of the anodic and cathodic partial processes.
The protection efficiencies (%P) of diamine compounds were determined by
using the equation (Gomma and Wahdan, 1995):
%P ¼ ½ðWW0Þ=W  100 ð1Þ
where W and W0 are the weight losses of SS type 304 in the absence and presence of
diamine compounds, respectively.
The results of weight-loss measurements (%P) are shown in Table I. The %P
increases with increasing the inhibitor concentration. The %P of the compounds
studied is in the following order: 1,8-octanediamine > 1,12-dodecanediamine > 1,4butanediamine > 1,3-propanediamine > ethylenediamine.
Adsorption Isotherm
The mechanism of corrosion inhibition may be explained on the basis of adsorption
behavior (Al-Andis et al., 1995). The degrees of surface coverage (h) for different
inhibitor concentrations were evaluated from weight-loss data. Data were tested
graphically by fitting to various isotherms. Plots of h=1 h versus C (Figure 3)
for tested diamine compounds were linear, suggesting that the adsorption of these
compounds on SS surface follows the Langmuir adsorption isotherm, which obeys
the relation:
logðh=1 hÞ ¼ logKþ logC ð2Þ
where K is the equilibrium constant of the adsorption reaction, and C is the inhibitor
concentration in the bulk of the solution. The surface coverage, h was calculated
from the following equation:
h ¼ 1 ðW0=WÞ ð3Þ
All adsorption expressions include the equilibrium constant of the adsorption
process, K, which is related to the standard free energy of adsorption (DGads.) by
(Langmuir, 1947):
Table I. Values of protection efficiencies (%P) for different diamine compounds for
the corrosion of SS in 1M HCl at 30C; duration of experiment: 300min immersion
Protection efficiency (%P)
Concentration (M) 1 104 3 104 5 104 7 104 9 104 11 104
Ethylenediamine 33.76 37.34 39.30 41.51 43.36 46.68
1,3-Propanediamine 38.03 41.25 43.45 45.30 47.04 49.58
1,4-Butanediamine 40.97 43.92 46.00 47.97 49.53 51.97
1,8-Octanediamine 46.58 49.31 51.35 53.56 55.77 58.32
1,12-Dodecanediamine 43.73 46.42 49.43 51.58 53.35 55.09
Diamines as Corrosion Inhibitors 937
K ¼ 1=55:5 expDGads:=RT ð4Þ
where R is the universal gas constant and T is the absolute temperature.
The entropies of adsorption DSads were calculated from the relation between
DGads: and T (Rudresh and Mayanna, 1977):
DSads: ¼ ð@DGads:=@TÞP ð5Þ
which is illustrated in Figure 4. From the values of DGads: and DS

ads: the heats of
adsorption, DHads., were calculated. The thermodynamic parameters of the inhibitors investigated are listed in Table II. Inspection of the data of this table shows that
the negative sign of DGads: indicates that the adsorption of diamine compounds on
the SS surface is proceeding spontaneously.
Figure 3. Curve fitting of corrosion data for SS in 1M HCl in presence of different concentrations of diamine compounds to the Langmuir isotherm at 30C.
938 A. S. Fouda et al.
Figure 4. DGads: vs. temperature for 304 SS in 1M HCl in presence of aliphatic diamine
Table II. Thermodynamic parameters for the adsorption of investigated diamine
compounds in 1M HCl on SS surface
Thermodynamic parameters
DGads., kJ
DSads., J
DHads:, kJ
Ethylenediamine 24.84 24.76 32.39
1,3-Propanediamine 24.95 24.58 32.47
1,4-Butanediamine 25.19 24.45 32.64
1,8-Octanediamine 26.11 22.15 32.85
1,12-Dodecanediamine 25.71 23.23 32.81
Diamines as Corrosion Inhibitors 939
Effect of Temperature
The corrosion rates of SS type 304 in 1M HCl solution in the absence and presence
of the investigated inhibitors increase rapidly with increase in temperature. In order
to investigate this effect on the mechanism of corrosion, weight-loss measurements
were studied in the temperature range 30–70C in the absence and presence of
5 104M of different additives.
The apparent activation energy Ea, the enthalpy of activation DH
, and the
entropy of activation DS for the corrosion of SS type 304 sample in 1M HCl
solution in the absence and presence of different concentrations of investigated
diamine compounds were calculated from Arrhenius-type equation:
Rate ¼ AexpðEa=RTÞ ð6Þ
where rate is given by DW=time mg min1 and transition-state equation:
Rate ¼ RT=Nh expðDS=RÞ expðDH=RTÞ ð7Þ
where A is the frequency factor, h is Planck’s constant, N is Avogadro’s number, and
R is the universal gas constant. A plot of log rate versus 1=T and log (rate=T) versus
1=T gives straight lines with slope of Ea=2.303R and DH=2.303R, respectively.
The intercepts will be A and log R=NhþDS=2.303R for Arrhenius and transition
state equations, respectively.
Figures 5 and 6 represent plots of the log rate versus 1=T and log (rate=T) versus
1=T data. The calculated values of the apparent activation energy, Ea, activation
entropies, DS, and activation enthalpies, DH, are given in Table III.
The almost similar values of Ea suggest that the inhibitors are similar in the
mechanism of action and the order of efficiency may be related to the preexponential
factor A in Equation (6). This is further related to concentration, steric effects, and
metal surface characters.
The value of activation energy obtained in free acid solution (1MHCl) is equal to
31.23 kJmol1 (7.5 kcalmol1), but Vajpeyi et al. (1985) found it to equal
12.4 kcalmol1 for the corrosion of AISI SS in H2SO4 contaminated with HCl and
HNO3, and Abd El-Rehim et al. (1999) found it to be 36 kJmol
1(8.6 kcalmol1)
for the corrosion of mild steel in H2SO4 acid. From the above, one can conclude that
the activation energy depends on the type of the metal and electrolyte.
Synergistic Effect
Halide ions are found to enhance the inhibitive effect of several nitrogen-containing
organic compounds in acid solutions (Hackerman et al., 1966; Murakawa et al.,
1968; Rawat and Udayabhanu, 1987; Chatterjee et al., 1991). In the present study
the influence of iodide ions on the inhibitive performance of investigated diamine
compounds has been studied using the weight-loss technique.
Figure 7 shows the weight loss-time curves for SS in 1M HCl for various concentrations of KI and at specific concentrations of the 1,8-octanediamine at 30C.
The values of protection efficiency (%P) for specific concentrations of inhibitors
in the presence of various concentrations of KI are given in Table IV.
It is observed that %P of the inhibitors increases on addition of KI due to synergistic effects (Cahskan and Bilgic, 2000). The strong chemisorption of iodide ions
on the metal surface (Sanad et al., 1992) is responsible for the synergistic effect of
940 A. S. Fouda et al.
iodide ions in combination with cation of the inhibitor. The cation is then adsorbed
by coulombic attraction on the metal surface where iodide ions are already adsorbed
by chemisorption. Stabilization of adsorbed iodide ions with cations leads to greater
surface coverage and therefore greater inhibition.
The interaction of inhibitor molecules can be described by introducing, Sh, a
synergism parameter (Aramaki and Hackerman, 1969), which is defined as:
Sh ¼ 1 h1þ2=1 h01þ2 ð8Þ
where h1þ2 ¼ (h1þ h2)–(h1h2); h1 ¼ surface coverage by anion; h2 ¼ surface coverage
by cation; h01þ2 ¼ measured surface coverage by both the anion and cation.
The synergism parameters were calculated from the above equation. The plot of
the synergism parameter (Sh) against various concentrations of investigated diamine
compounds is given in Figure 8. As can be seen from this figure the values of (Sh) are
nearly equal to unity, which suggests that the enhanced protection efficiencies caused
by the addition of iodide ions to the investigated diamine compounds is due mainly
to the synergistic effect.
Figure 5. Log corrosion rate vs. 1=T for 304 SS in presence of 5 104M of aliphatic diamine
Diamines as Corrosion Inhibitors 941
Figure 6. Log corrosion rate=T vs. 1=T for 304 SS in presence of 5 104M of aliphatic
diamine compounds.
Table III. Activation parameters of the dissolution of SS in 1M HCl in the absence
and presence of 5 104M investigated diamine compounds
Activation parameters
Inhibitors Ea, kJmol
1 DH, kJmol1 DS, Jmol1K1
Free acid 31.23 28.55 202.91
Ethylenediamine 37.81 35.13 185.30
1,3-Propanediamine 38.15 35.48 184.75
1,4-Butanediamine 38.32 35.64 184.65
1,8-Octanediamine 38.75 36.08 184.11
1,12-Dodecanediamine 38.55 35.87 184.45
942 A. S. Fouda et al.
Table IV. Values of protection efficiencies (%P) for 5 104M different
investigated diamine compounds in presence and absence of different
concentrations of KI for the corrosion of SS in 1M HCl at 30C; duration of
experiment: 300min immersion
Protection efficiency (%P)
Concentration of KI, (M) 0.00 1 106 1 105 1 104
Ethylenediamine 39.30 41.70 59.23 71.77
1,3-Propanediamine 43.45 45.76 61.81 74.54
1,4-Butanediamine 46.00 47.60 64.02 76.57
1,8-Octanediamine 51.35 49.82 67.16 80.07
1,12-Dodecanediamine 49.43 48.34 66.24 78.41
Figure 7. Weight loss-time curves for the corrosion of 304 SS in 1M HCl containing
5 104M of 1,8-octanediamine with and without addition of various concentrations of KI
at 30C.
Diamines as Corrosion Inhibitors 943
Polarization Measurements
Galvanostatic polarization curves of SS type 304 in 1M HCl in the absence and
presence of different concentrations of 1,8-octanediamine at 30C are illustrated in
Figure 9. The numerical values of the variation of corrosion current density (icorr.),
corrosion potential (Ecorr.), Tafel slopes (ba and bc), degree of surface coverage (h),
and protection efficiency (%P) with the concentrations of 1,8-octanediamine
compound are given in Table V, and similar results were obtained for other tested
compounds (not shown). This indicates that:
Figure 8. Plot of synergism parameter (Sh) vs. concentration of aliphatic diamine compounds
at 30C.
944 A. S. Fouda et al.
1. The cathodic and anodic curves obtained exhibit Tafel-type behavior. Addition of
aliphatic diamine compounds increased both cathodic and anodic over-voltages
and caused mainly parallel displacement to the more negative and positive values,
2. The corrosion current density (icorr.) decreases with increasing the concentration
of investigated diamine compounds, which indicates that the presence of these
Figure 9. Polarization curves for the dissolution of 304 SS in 1M HCl in presence and absence
of different concentrations of 1,8-octanediamine at 30C.
Table V. Effect of concentration of 1,8-octanediamine on the free corrosion
potential (Ecorr.), corrosion current density (icorr.), Tafel slopes (ba and bc),
protection efficiency (%P), and degree of surface coverage (h) of SS in 1M HCl
at 30C
Concentration, M
mV icorr.,
mV dec1
mV dec1 h %P
0 396 264.55 132 121 — —
1 104 387 137.25 139 130 0.481 48.12
3 104 386 128.49 147 135 0.514 51.43
5 104 385 122.49 157 144 0.537 53.70
7 104 385 117.38 164 156 0.556 55.63
9 104 384 111.01 173 162 0.580 58.04
11 104 383 104.90 185 174 0.604 60.35
Diamines as Corrosion Inhibitors 945
compounds retards the dissolution of SS in 1M HCl solution and the degree of
inhibition depends on the concentration and type of the inhibitor present.
3. Tafel lines (ba and bc) of nearly equal slopes were obtained, as can be seen from
Table V. This indicates (Hackerman and McCafferty, 1974) that the adsorbed
molecules of diamine compounds do not affect the mechanism of the corrosion
4. The values of corrosion potential (Ecorr.) were shifted to less negative values in the
presence of inhibitors and by increasing their concentrations.
Chemical Structure and Corrosion Inhibition
Corrosion inhibition of SS type 304 in HCl solution by the investigated diamine
compounds as indicated from weight-loss and galvanostatic polarization was found
to depend on the concentration and nature of the inhibitor.
Increasing the chain length of the investigated aliphatic diamines from 2 to 8 carbons increases the molecular area of these compounds and then increases the surface
area of the stainless steel covered by these compounds at the same concentration
used. But for longer hydrocarbon chains (12 carbons), the corrosion inhibition
decreases due to a decrease in the solubility of the longer diamines (Hackerman
and McCafferty, 1974) and the deformation of the hydrophobic chain, which destabilizes the adsorbed layer, so that the protection efficiency of 1,12-dodecanediamine
is less than that of 1,8-diaminooctane.
The trend of the protection efficiency of the investigated diamine compounds is
as follows: 1,8-octanediamine > 1,12-dodecanediamine > 1,4-butanediamine > 1,3propanediamine > ethylenediamine. This is found to be in agreement with the
previously determined results by galvanostatic polarization and weight-loss
1. All the investigated diamine compounds are found to perform well as corrosion
inhibitors in 1M HCl solution for SS and the inhibition efficiency values follow
the order 1,8-octanediamine > 1,12-dodecanediamine > 1,4-butanediamine >
1,3-propanediamine > ethylenediamine. The %P were found to be depend on
the type and nature of the inhibitor.
2. The inhibition efficiencies increase with increasing inhibitor concentration and
with decreasing temperature.
3. Activation parameters (E, DH, DS) for the corrosion of SS in HCl were calculated and indicate that corrosion is much reduced in the presence of inhibitors.
4. Adsorption on SS in 1M HCl solution was found to obey the Langmuir adsorption isotherm.
5. Diamine compounds inhibit the corrosion of SS in HCl due to physical adsorption and affect both anodic and cathodic Tafel slopes and thus are mixed-type
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