КОЛЛОИДНАЯ ХИМИЯ И ЭЛЕКТРОХИМИЯ
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MODELING OF CORROSION INHIBITION OF COPPER-NICKEL ALLOY IN HYDROCHLORIC ACID BY BENZOTRIAZOLE
© 2011 Anees A. Khadom" and Aprael S. YaroA
aMechanical Engineering Department, College of Engineering, University of Daiyla, Baquba 32001, Iraq bChemical Engineering Department, College of Engineering, University of Baghdad, Aljadrea 71001, Baghdad, Iraq
E-mail: aneesdr@gmail.com Received October 14, 2010
Abstract — The corrosion inhibition of copper-nickel alloy by benzotriazole (BTA) in 1.5 M HCl has been investigated by weight loss and polarization techniques at different temperatures. Maximum value of inhibitor efficiency was 99.8% at 35°C and 0.1 M inhibitor concentration, while the lower value was 86.3% at 65°C and 0.02 M inhibitor concentration. The activation energy values were higher in presence of BTA which indicate that in presence of inhibitor, corrosion reaction requires more energy to occur. Two mathematical models were used to represent the weight loss corrosion rate data with high correlation coefficients. Electrochemical polarization measurements showed that BTA is a mixed type inhibitor.
Keywords: activation parameters, corrosion inhibition, copper—nickel alloy, benzotriazole.
INTRODUCTION
Copper and its alloys have an excellent thermal conductivity, good corrosion resistance and mechanical workability and are widely used in heating and cooling systems. It is well-known that corrosion products have a negative effect on heat transfer on the copper based heat exchanger, which can be reduced by periodic cleaning in hydrochloric acid pickling solutions. Corrosion inhibitors could effectively eliminates some of the undesirable reaction connected with destructive effects of hydrochloric acid pickling solutions on copper surface and prevents its dissolution [1]. Corrosion inhibitor is a chemical substance when it is added with little concentration to environment effectively checks, decreases or prevents the reaction of metal with environment [2]. It must be clearly understood that no universal corrosion inhibitor exists. Each inhibitor must be tailored to the specific corrosion problem that needs solution. While the use of inhibitors for some types of corrosion can be similar to other, this similarity must be treated as coincidence. Most inhibitors have been developed by empirical experimentation. Amines and triazoles derivatives have been reported to be very effective inhibitors for copper in acidic solutions [3, 4]. It has been reported by Loshkarav et al. [5] that benzotriazole (BTA) exists as protonated species
C6H 6N + in acidic solution, as the undissociated compound C6H5N3 in near neutral solutions, and as the
simple anion C 6H 4N- in alkaline solutions. The molecular structure of benzotriazole is
■N
N
N H
The present work is an attempt to study the corrosion inhibition of BTA for copper—nickel alloy in 1.5 M HCl at different temperatures. The combined effect of temperature and inhibitor concentration on corrosion rates were correlated by using mathematical models. Activation and electrochemical parameters were also obtained.
EXPERIMENTAL
The corrosion behavior of copper—nickel alloys, which used widely in many industrial equipments, was studied using weight loss and polarization techniques in absence and presence BTA in freely — aerated 1.5 M HCl solution at different temperature (35, 45, 55 and 65°C), and different inhibitor concentrations (0.02, 0.04, 0.08, 0.1 M). Ring shape specimen of Cu-Ni alloy with dimension (2.22 cm) outside diameter, (1.5 cm) width, and (0.13 cm) thickness. Specimens were washed by detergent and flushed by tap water followed by distilled water, degreased by analar benzene and acetone, then annealed in vacuums to 600°C for one hour and cooled under vacuum to room temperature. Before each run, specimens of Cu-Ni were abraded in sequence using emery paper of grade number 220,320, 400, and 600, then washed by running tap water followed by distilled water then dried by clean tissue, degreased with benzene, dried, degreased with acetone, dried, and finally left in desicater over silica gel.
Weighing the specimen was carried out using 4 decimals digital balance and its dimensions were measured with vernier. The metal samples for weight loss runs were completely immersed in 250 cm3 solution of corrodant contained in a conical flask. They were exposed for a period of three days at a desired tempera-
Table 1. Effect of temperature and inhibitor concentration on the corrosion of Cu—Ni alloy in 5% HCl acid solution
Run с, M T, °C W, gmd n, %
1 0 35 12.5
2 0 45 15.87
3 0 55 20.83
4 0 65 26.84
5 0.02 35 1.545 87.6
6 0.04 0.35 97.2
7 0.08 0.27 97.8
8 0.1 0.0193 99.8
9 0.02 45 2.088 87.8
10 0.04 0.695 95.6
11 0.08 0.422 97.3
12 0.1 0.105 99.3
13 0.02 55 2.543 86.8
14 0.04 1.131 94.5
15 0.08 0.668 96.8
16 0.1 0.277 98.7
17 0.02 65 3.666 86.3
18 0.04 1.985 92.6
19 0.08 0.887 96.7
20 0.1 0.406 98.5
mounted directly to the working electrode. Saturated calomel electrode (SCE) was used as reference electrode.
To ensure that KCl solution was saturated, a small amount of KCl (solid) was kept in the solution of SCE as long as the test. After preparation of the working electrode, the corrosion cell parts were joined to each other, and then connected to the power supply (type 6236B, Hewlett Packard, USA). The cathodic polarization was carried out beginning from low potential of (—450 mV) until reaching the corrosion potential. The potential was changed to (10—15 mV) for each step after a one-minute period, then, the current was recorded. Inverting the connection of the power supply after polarization readings had been over. The anodic polarization readings started at a potential resulting in zero current density and increased in a step of (10—15 mV) with the current recorded at each step and with one minute interval until a potential of about (—50 mV).
RESULTS AND DISCUSSION
The corrosion rates of Cu—Ni alloy in 1.5 M HCl acid solution as a function of temperature in absence and presence of different inhibitors concentrations are summarized in Table 1 through 20 runs using weight loss technique. The value of corrosion rate was calculated from the following equation:
ture, acid concentration, and inhibitor concentration. Weight losses were determined in absence and presence of inhibitors. The data are expressed as mass loss per unit time per unit area; in the present work the units of corrosion rate were g/(m2 day) (gmd). The chemical compositions of Cu—Ni alloy were (0.148% Sn, 0.2% Fe, 0.134% Zn, 0.015% Al, 0.0003% P, 0.5% Sb, 0.0583% Pb, 0.0202% Si, 0.017% S, 0.0056% As, 10% Ni, and the remainder is Cu).
For polarization measurements, tests were carried out using a standard cell of 2.5 liter. The cell was equipped with six necks, five of them were used. One for working electrode (Cu—Ni ring). One had a spherical joint for mounting the lugging capillary prob., one for thermometer, and two for the two counter gold electrodes. All potential values were measured in reference to saturated calomel electrode (SCE). The lugging capillary prob. was adjusted such that it was at a distance not more than (2 mm) from the working electrode. The working electrode was copper—nickel alloy ring; this ring was fixed on brass zone on the shaft. Gold electrodes were used as a counter electrode each has a dimension of 1.44 cm (diameter) x 3 cm (long), a wire was connected to gold sheet, then covered with arraldit and rolled on teflon shaft. The electrodes were
W = A m/st,
(1)
where A m is weight loss, g; s is area, m2, and t is time, days.
From the corrosion rate, the percentage inhibition efficiency was calculated using the following equation:
W - W n,% = ^-un—^ x 100, W
' ' 11Г1
(2)
where Wun and Wn are the corrosion rates in absence and presence of inhibitor respectively. It is clear that at certain experimental temperature, corrosion rate of copper—nickel alloy decreases with an increase in concentration of inhibitor. In absence and presence of a certain concentration of inhibitor, the corrosion rate of steel increases with rise in temperature, obeying the Arrhenius type reactions. It was reported that the rate for iron corroding in acid solutions is approximately doubled for every 10 K rise in temperature [6]. Values of inhibitor efficiency increase with increasing inhibitor concentration. Table 1 and Fig. 1 show the effect of temperature on inhibitor efficiency. Generally, inhibitor efficiency decreased slightly with increasing of temperature, which indicated the stability of adsorbed
n, %
98
94
90
86
0.02 M BTA
0.04
0.08
0.10
30
40
50
60
T, oC
Fig. 1. Effect of temperature on inhibitor efficiency.
log W [gmd] 2
-1
3.2 3.3
103/T, K-1
Fig. 2. Arrhenius plot of Cu-Ni alloy in 1.5 M HCl containing various concentration of BTA: (1) 0, (2) 0.02, (3) 0.04, (4) 0.08, (5) 0.1 M.
inhibitor molecules. Maximum value of inhibitor efficiency was 99.8% at 35°C and 0.1 M BTA.
Effect of temperature and activation parameters
The effect of temperature and activation parameters for some systems can be estimated either from an Arrhenius-type plot equation:
W = Aexp (-E/RT )
(3)
or from transition state theory [7]. The basic assumption about the system that is made in transition state theory is that molecular system that has crossed the transition state in the direction of products cannot turn around to form reactants. A transition state complex of relatively high energy is formed; the complex is then decays to products. The mathematical form of transition state theory may be written as;
W = (RT ) exp (—) exp Í-M!),
, exp I
Nh \ R
RT
(4)
where Wis corrosion reaction rate, A is modified frequency factor (pre-exponential factor), E is activation energy (J/mol), R is gas constant, T is absolute temperature (K), AH* is enthalpy of activation, AS* is entropy of activation, N is Avogadr
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