Corrosion Inhibition of Medium Carbon Steel in the Acidic Medium Using Alcoholic and Aqueous Extract of Kujarat Tea Plant

: This study deals with the corrosion inhibition of metal corrosion process of medium carbon steel using 1M HCl for kinetic studies and rate reaction determination. The weight loss method is applied to pieces of Medium carbon steel divided to Cubans with dimensions (0.4*2*2.4) cm , and use Tafel Extrapolation Method, the samples were polished using carbide silicon paper with dimensions of (180,200,400,600,800,1000). The samples were immersed in the alcoholic medium ethanol at a temperature 293K for 3hr. Natural inhibitor Kujarat Tea ( Hibiscus sabdarriffa L.) is used which is extracted in aqueous and alcoholic medium, different concentrations (1000،2000, 3000) ppm have been used ; The best concentration found through the results is a concentration found that is 1000 and 2000 ppm, the results indicate that the highest degree of inhibition for aqueous extract is 93.3% with the concentration of 2000 ppm and 90.5% with 1000 ppm at293K. While the alcoholic inhibitor shows the highest efficiency 92.4% with a concentration of 2000 ppm and 88.6% with a concentration of 1000 ppm respectively. The structure of the inhibitor was investigated using infrared spectroscopy (FTIR), and the surface morphology of the tested samples was investigated using a scanning electron microscope (SEM).


Introduction:
Corrosion is defined as damage of metals or alloys due to their chemical or electrochemical reaction with the surrounding environment for metal. Metals and alloys gradually change into compounds such as oxides, hydroxides, carbonates, and sulphides 1 . Corrosion is the atmospheric oxidation/degradation of metals. It is an electrochemical process by which metallic surfaces react with their environment causing the metal to lose its material properties due to surface deterioration 2 , as defined by scientists in the year (1830 A.D) , a complex phenomenon that has been studied physically, chemically, electrochemically, kinetically or thermodynamically. The studies prove that it is entirely dependent on mechanical properties of metal 2 . In general, the driving force for the completion of the corrosion reaction is the change in the free energy of the material as a result of their transformation into compounds with a generally lower free energy than their constituent metals 1 , therefore they are automatically formed if exposed to the appropriate environment. The compounds are more stable than the metal which is naturally composed of them 3 . The process of corrosion of the metal leads to ions generation with some electrons that are consumed by a secondary reaction. When the metal is placed in pure water, some ions will be transferred directly to the solution 4 . Fe +2 + 2e -………… 3 The potential difference depends on the type of metal and the composition of the solution 5,6 . The inhibitors affect the electrochemical reaction kinetics in the corrosion process and fixed on the inhibitors on the metal surface, thus the process ease the electrical double layer changes if the same active inhibitors used in the industry are organic compounds, containing oxygen, nitrogen, and sulfur atoms which can lead to adsorption of compounds on the surface of the metal 6 . Also, biodegradable green inhibitors that do not contain heavy metals or other toxic compounds are used. Corrosion inhibitors generally control corrosion through the mechanism inhibitors, which are applied to the surface of the metal, which on adsorption on the metal surface 7 . Adsorption depends on the charged nature of the metal surface, electronic properties and, properties of solvents, the temperature and the electrochemical potential 8,9 . There are many applications to corrosion inhibition, such as oil and gas ducts corrosion inhibition 10 , corrosion inhibitor tested on mild steel supported by electrochemical 11 , evaluation of electrocoagulation in the treatment of olive debittering wastewater (ODW), and many other applications.
The aim of this study is to use the Kujarat Tea leaves as an environmental corrosion inhibitor to control the corrosion process in the acidic medium, and to find the difference in the corrosion rate in the static phase at over time and in a range of different temperatures. 293-313 K

Samples preparation
The samples were divided into small Cubans with dimensions 2 cm length and 2.4 cm width and 0.4 cm thickness 12 . The medium carbon steel metal sample was obtained.

Chemical analysis
The medium carbon steel samples and the Kujarat Tea plant (aqueous and alcoholic) were analyzed spectroscopically Tables 1, 2, shows that the extract of the kujurat plant contains the elements shown below Table 2, using the atomic absorption spectrophotometer device CS.

Preparation of Kujarat Tea extracts (inhibitor) 13 :
The plant extract was prepared using tap water to wash the plant and freeing it from the dust suspended in its limit to (40-60%) and then using polar solvents (aqueous and ethanol) as follows: 11 .
The organic extract was prepared as follows: 50gm of the Kujarat Tea plant powder in a conical flask 500ml was mixed with 250 ml of petroleum ether, the mixture was stirred for 72hr using a magnetic stirrer and then the solution was filtered off and dried in an oven at (293-313 ) for 2hr , the filtrate was keep it in a glass container in the refrigerator at a temperature of 277 .
The alcoholic extract of the Kujarat Tea plant was prepared by the following procedure. 50 gm with of the powder prepared in (3-1) was mixed with 250 ml of ethanol 99.9% and stirred for 72hr using the magnetic stirrer. The solution was then filtered off and the filtrate was evaporated under low pressure using a rotary evaporator at 313 K and the remaining extract 50% is reserved until use 11,12 .
The aqueous extract was prepared as mention in (3-2) by mixing 50gm with 250 ml of distilled water, and stirred for 72hr using the magnetic stirrer. The solution is then filtered off and the filtrate was evaporated under vacuum at 277 K and the remaining extract 50% 11,12 .

Electrochemical cell (Tafel Extrapolation Method)
The device used consists of a measuring cell and its electrodes, where the cell is made of a noncorrosive material such as glass, the capacity of the cell is one liter, and the cell includes three electrodes: the working electrode, which is the sample used, and the auxiliary electrode, which is of platinum, and the reference electrode use for find working electrode potnational is the saturated is placed in a salt bridge containing the same electrolyte solution used in the cell, and the electrical circuit is connected to conduct the test. The test was conducted in the absence and quality of the inhibitor. The tests were done with the best concentrations and at a different temperature. 12 The cell is filled with 1 M HCl and the auxiliary electrode and the reference electrode are placed in the cell solution, then the working electrode is prepared with an alcohol wash and then placed in the measuring cell (PRT) is ability equipped provides a constant current in the range (0-500 mA) by device voltmeter which is used to measure the potential difference between the working electrode and the reference electrode. A milliampere device was also used to measure the current passing between the working electrode and the reference, where the potential difference is changed at a rate of (10 mV / min) and the peak of the current corresponding to each value of the applied voltage and in the range (± 250 mV) is measured approximately at a voltage point open circuit. The total values of current density, i, were considered as the sum of two contributions, anodic and cathodic current ia and ic, respectively. For a potential field not too far from the open circuit, it may be considered that both processes follow Tafel's law 13 The equation below was used to calculate the inhibitory inhibitory efficiency.

Preparation of the corrosion solution:
By dilution method, 1M concentration of HCl was prepared 8 Measurement of the weight loss: All metal samples were placed in 100 ml of 1M HCl and then transferred to a water bath and subjected to the required temperature at the required concentration of the inhibitor 3hr. The samples were then cleaned and washed with deionized water and dried with tissue papers or smoothed papers which is type 180-1000 P and then washed with acetone and dried again. The weight loss was determined in the presence of the inhibitor at concentrations of 2000,1000 ppm at temperatures of 293,303, 313 K 14 .

Results and discussion:
Method of weight loss Corrosion rates (CR) were determined in the presence and absence of inhibitor using the following Equation 15 : Where ∆ is weight loss gm , A: is surface area of the sample m 2 , t: is time of sample exposure for the day. Corrosion rates were obtained in g / m 2 . day (g.m -2 d).
The inhibition efficiency was calculated using the equation: Where and are the corrosion rates in the absence of different concentrations of inhibitors, respectively. The inhibition efficiency IE% can be also calculated using the following equation in 5 Surface cover can be calculated by the following equation 16: = 100 ……………….. 8 Where: is surface coverage, (IE) is inhibition efficiency 17. Corrosion rate, inhibition efficiency, corrosion current efficiency, and surface coverage were assessed under different conditions. The results were collected in Tables 3 and 4 . It is clear that the rate of corrosion increases with increasing temperature and concentration of 1M HCl and decreases with increasing inhibitory concentrations, due to the occurrence of a reverse process due to the saturation of the metal surface with the inhibitor, which made the increase of the inhibitor leads to a decrease in the corrosion rate 18 . It was found that the best concentration of the plant extract is at 1000 and 2000, because the percentage of the inhibitory efficiency was the highest in it, and this shows that when the concentration is higher than these concentrations, there will be an inverse relationship with the inhibition efficiency (by increasing the concentration of the inhibitor, the inhibition efficiency of the extract decreases). Because to the occurrence of a reverse process due to the saturation of the metal surface with the inhibitor, which made the increase of the inhibitor leads to a decrease in the corrosion rate 19 .

Evaluation of corrosion rate
The weight-loss method was used to calculate the corrosion rates in non-inhibitory acid solutions at different temperatures (293, 303, 313 K). The average carbon steel corrosion rate in 1M HCl increased from 530 to (1440 g.m -2 d) with increasing temperature (293 -313) K. And the density of the Corrosion current of the medium carbon steel was increased from 450.5 -682.7 (μA.cm -2 ) with an increase in temperature 293 -313 K. Fig. 1, Shows the increase in the rate of corrosion with an increase of temperature, the relationship between temperature as variable and the rate of corrosion, and Fig. 2, shows the increase of the density of the corrosion current with increased temperature.

Figure 2. Effect of temperature on the corrosion current density of carbon medium in (1) M of HCl acid The Effect of acid in presence of inhibitor at different temperatures
From Figs 3 and 4 we found that the effect of temperature on corrosion rate which was expressed for the different inhibitor concentrations. The two forms show that the corrosion rate increases with the increase of temperature and increase inhibitor concentration. When using 1000 ppm of the inhibitor at temperatures (293-313K), the highest corrosion rate was 310 g.m -2 d at 313K when (1000, 2000 ppm) concentration of alcoholic Kujarat Tea extract was used, while the lowest corrosion rate was 50 g.m -2 d at 293 with the aqueous extract.
The concentration of 2000 ppm of the inhibit at different temperatures gave the highest corrosion rate 280 g.m -2 d at 313K when using extract of the alcoholic. The lowest value of the corrosion rate was 35 g.m -2 d at 293K with the aqueous extract in Figs. 5-12.  In Figs. 5-14 the IE was found to vary with acid temperature, acid concentration, of alcoholic extract and aqueous extract concentration and average molecular weight. Also it was found that the corrosion inhibition behavior of PEG is greater in hydrochloric acid. The adsorption of the inhibitor on the LCS surface is in agreement with Langmuir and Frumkin adsorption isotherms. The inhibition efficiencies are increased by increase of the inhibitor's concentration and average molecular weight decreases with an increase in the concentration and temperature of the acid 20 .

Scanning Electron Microscopy Study (SEM)
The microscopic examination of the surface of the eroded sample in the acid medium showed dark color indicating that corrosion products result from corrosion due to direct exposure to the acid medium. However, with the inhibitors, the damage is much smaller on the surface with clear color, and that because of formation protective layer on the steel surface which prevents the contact between the surface and medium 17

Studies of inhibitory structures and infrared radiation
FTIR study of inhibitor composition for metal surface protection shows that the plant extract was used and the FT-IR spectra were recorded to elucidate the potential interactions between the adsorbed inhibitor Kujarat Tea and the surface of carbon steel which are immersed in 1M HCl. FT-IR, the results in Table. 5, and Figs. 19, 20, show that the stretching frequencies of the inhibitor were shifted to lower values in comparison with the frequencies of the free extract and that may be a result of the reaction between the extract molecules and the surface of the metal 19 . These stretching frequencies are assigned to the presence of the alkaloids and flavone compounds which are responsible for such surface for the purpose of protecting the surface of the metal using plant extracts and finding the best plant that provides protection [21][22][23] . Fig. 21, show tifel curves and Fig. 22, show polarization curves, where b=bond, w=weak, s=strong.   where a straight line was obtained, the value of its slope is the value of the activation enthalpy ( −∆ * ) and the intercept is (ln / ℎ) + ∆ * . If it is shown by the drawing that the enthalpy value is a positive value for the inhibitors, which indicates that the adsorption of the inhibitor on the surface of the metal is endothermic due to the metal dissolution process, and the positive entropy values indicate an increase in randomness in the system. Figs. 23, 24.

Conclusions:
Kujarat Tea extract acts as a good inhibitor for the corrosion of Carbone carbon steel in 1 M HCl solution. The inhibition efficiency increases with increasing inhibitor concentration but decreases with an increasing in temperature. The results obtained from polarization measurements revealed that Kujarat Tea extract behaves as a mixed type of inhibitor. Kujarat Tea alcoholic extract is a beater from Kujarat Tea aqueous extract at a lower Ci=1000 Ci=2000 Ci=3000