Effect of Halides Ions and Temperature on the Electrochemical Behavior and Corrosion of Carbon Steel in Organic Acid

Review Article

Austin J Chem Eng. 2014;1(2): 1010.

Effect of Halides Ions and Temperature on the Electrochemical Behavior and Corrosion of Carbon Steel in Organic Acid

Deyab MA*

Egyptian Petroleum Research Institute, Egypt

*Corresponding author: Deyab MA, Egyptian Petroleum Research Institute (EPRI), Nasr City, Cairo, Egypt

Received: May 22, 2014; Accepted: August 11, 2014; Published: August 14, 2014


Hydrogen evolution and cyclic voltammetry techniques were used to investigate the corrosion behavior of carbon steel in formic acid solution under different experimental conditions. Results obtained reveal that the carbon steel corrodes in formic acid solutions and the corrosion rate increases with the increase in acid concentration and temperature. Cyclic voltammograms of carbon steel in formic acid exhibit active/passive transition. The data reveal that increasing formic acid concentration and temperature increases the anodic peak current density (jPA) and shifts its peak potential towards more positive values. Activation parameters for the corrosion process were evaluated. Additions of Cl -, Br - and I- ions increase both the hydrogen evolution rate and the active dissolution rate of carbon steel and tend to breakdown the passive film and induce pitting attack. The aggressiveness of the halide ions towards the stability of the passive film decreases in the order Cl - > Br - > I -.

Keywords: Halides; Carbon steel; Organic acid; Corrosion


Most research on corrosion behavior of carbon steel has been done in mineral acids [1-4]. Despite the importance of organic acids in industry, few corrosion studies involving these acids have been made [5-7]. However, at high temperatures, these acids can dissociate, forming more aggressive ions that can cause faster corrosion than might otherwise be expected. Formic acid is the most corrosive of the common organic acids. However, no systematic study of the corrosion behavior of carbon steel in formic acid solution has been found in the literatures.

The corrosion of carbon in acid environment proceeds according to the overall reaction:

Fe + 2H+ → Fe2+ + H2 (1)

This reaction includes the anodic partial reaction (2) and the cathodic partial reaction (3):

Fe → Fe2+ + 2e- (2)

2H+ + 2e → H2 (3)

According to Faraday's low, there is a linear relationship between the metal dissolution rate at any potential (CRM), and the partial anodic current density for metal dissolution jPA [8].

CRM = jPA / n x F (4)

In this equation n is the number of electrons exchanged in the dissolution reaction, and F is the Faraday constant.

Additions of halide ions in the Fe/acid system causes destabilize the iron passive film [9]. They influence the chemical, ionic and electronic properties of the oxide. It has been proposed that halides ions interact with the oxide layer preferentially at local sites. This interaction results in the film breakdown and initiation of pitting corrosion [10].

The work described in this paper was undertaken to apply the hydrogen evolution and cyclic voltammetry measurements to study the corrosion behavior of carbon steel in formic acid solutions. It was also the purpose of the present work is to study the effect of some halides as aggressive anions on the pitting corrosion of carbon steel in formic acid solution.


Corrosion tests were performed on a carbon steel of the following percentage composition (in wt.%): 0.06 C; 0.06 Si; 0.7 Mn; 0.005 P; 0.001 S; 0.012 Ni; 0.015 Cr; 0.004 Mo; 0.002 V; 0.02 Cu and balance Fe. Prior to each experiment, the carbon steel electrodes were first briefly ground with different grades of emery paper (120, 400, 800, 1000 and 1200) and washed thoroughly with distilled water and degreased with acetone.

The apparatus and procedure followed for hydrogen evolution and cyclic voltammetry methods were similar to that earlier reported [11-12]. In hydrogen evolution method, 100 ml of the corrodent (formic acid) was introduced into the reaction vessel and carbon steel sheets of dimensions 2 cm x 3 cm were carefully dropped into the test solution of formic acid and the reaction vessel was quickly closed to avoid any escape of hydrogen gas. The volume of hydrogen gas evolved from the corrosion reaction was monitored by the depression (in cm3) in the paraffin oil level. This depression was monitored at fixed time intervals. From the volume of hydrogen gas evolved, the hydrogen evolution rate (which can be correlated to corrosion rate) was calculated using the following expression [11]:

CRH = (Vt-Vi)/(tt-ti) (5)

where Vt and Vi are the volumes of hydrogen evolved at time tt and ti, respectively.

In cyclic voltammetry method, the electrochemical set-up consisted of a classical three electrode arrangement in a transparent glass cell with a Pt counter electrode and a saturated calomel reference electrode. Cyclic voltammetry experiments were performed with cylindrical rods of carbon steel with an apparent surface area of 0.358 cm2. Cyclic voltammetry studies were carried out using a potentioscan type (potentioscan/Galvan stat EG&G model 273) connected with a personal computer. Cyclic voltammetry measurements were carried out by sweeping linearly the potential from the starting potential (-2.0 V vs. SCE) into the positive direction at a given scan rate till a required potential value and then reversed with the same scan rate till the starting potential to form one complete cycle.

Water used was triply distilled. All chemicals were used as received without further purification. Formic acid (Merck) of AR grade was used for preparing solutions. The temperature of the test electrolyte was controlled by immersing the cell in a water thermostat.

Results and Discussion

Hydrogen evolution measurements

Figure 1 shows the hydrogen evolution rate (i.e. corrosion rate) during the corrosion reaction of carbon steel electrode in formic acid measured as a function of acid concentration at 25°C. Inspection of the figure reveals that the hydrogen evolution rate increases with increase in formic acid concentration (from 0.2 to 1.0 M), indicating acceleration behavior for the carbon steel dissolution. The dissolution of carbon steel in formic acid solution may be considered in the following steps [13]: