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TABLE OF CONTENTS 1. Introduction 2. Experimental 3. Results and discussion 4. Conclusion 5. References

1.Introduction Corrosion Definition and Importance of Corrosion Study: The word corrosion is as old as the earth, but it has been known by different names. Corrosion is known commonly as rust, an undesirable phenomena which destroys the luster and beauty of objects and shortens their life. Several definitions of corrosion have been given and some of them are reproduced below: Corrosion is the destructive attack of a metal by chemical or electrochemical reaction with the environment. Inhibition of Corrosion in Acid Media: Corrosion posses a very serious problem to industries and mankind, affecting both to the cost and productivity. Corrosion inhibitors are one of the most promising methods to combat corrosion. Inhibitors, the protection of metals or alloys against corrosion can be achieved either by special treatment of the medium to depress its aggressiveness or by introducing into it small amounts of special substances called corrosion inhibitors. Inhibitors are classified according to their action (as anodic, cathodic and mixed inhibitors) and according to their mechanism of action (as hydrogen evolution, scavengers, vapour-phase and adsorption inhibitors. Also, corrosion inhibitors, can be divided into three kinds: (i) inorganic inhibitors, (ii) organic inhibitors and (iii) mixed material inhibitors Hydrochloric acid is a very important industrial chemical, with numerous diverse uses throughout the chemical processing industry. It is a strong reducing acid and is employed as an intermediate reactant in the production of many everyday products. Hydrochloric acid is highly corrosive and attacks most common metals including iron, stainless steel and lead. Stainless steels and high performance alloys can only be used to handle very dilute and/or low temperature HCl)

The aim of this study was to investigate the inhibition effect of Sidr as a cheap, raw and non-toxic corrosion inhibitor on steel corrosion in hydrochloric acid. The electrochemicalmeasurements were used to evaluate the inhibition efficiencies. In addition, the effect of temperature on inhibition behavior of the inhibitor was also studied. Sidr is one of the important fruit crops in the dry parts is and rich in vitamin C. The dry fruit (i.e., per 100 g). a multipurpose tree species belonging to the botanical contains 314 calories, 9.3% H O, 4.8% protein, 0.9% fat. It is an important cultivated tree and 80.6% total carbohydrate, 4.4% ash, 140 mg Ca, 3 mg Fe one of the few truly native tree species of Arabia that is 0.04 mg thiamin, 0.13 mg riboflavin, 3.7 mg niacin and still growing along with many newly introduced exotic 30 mg ascorbic acid..It is consumed fresh, dried and plants, candied. Sidr has been used in folk medicine as demulcent, Mahran et al.The flower are important for used in folk medicine for treatment, it is therefore deemed the production of wild bee honey (Waggas and Al-Hasani,2009).

2.Experimental Materials preparation:. The steel electrode was bolished first with emery paper of type (231 QwetordrylmperialPapelAesco), the spectrum of starting paper more roughness to the more softer, then the sample wash with bidestilled water and acetone (AR)and then dried with stream of cold air. So, the clean weighed rod was immersed in the test solution inabsence and presnce of different amounts of the studied extract. In each new study the measurements of the sample area was checked. Solutions of Hydrochloric acid (2.5M HCl) were prepared using bi-distilled water as the corrosive medium. Hydrochloric acid was analytical grade quality (panreac) Preparation of the extract: The study can be divided in two parts: Part one : at constant temperature (30° C). Effect of concentration of Buckthorn extract on the corrosion of Two kined of measurements were used in this part, these are: 1- Chemical methods. 2- Electrochemical methods

Hydrogen Evolution Measurements: : From the volume of hydrogen gas evolved per minute, inhibition efficiency (Inh. HE % ), degree of surface coveage ( (and corrosion rate (R)were calculated using equations 1, 2 and 3, respectively : Where V 1 Ht is the volume of hydrogen gas at time t for inhibited solution and V 1 Ht is the volume of hydrogen gas evolved at time t for uninhibited solution 1 -The chemical methods: This method is done in two ways, hydrogen evolution method (HEM) and mass loss method (MLM).

Mass loss Measurements: From the weight loss results, the inhibition efficiency( Inh.%) of the inhibitor, degree of surface coverage and corrosion rates were calculated using equations 4,5 and 6, respectively: Inh. ML = (1-W 1 \W 2 )×100 (4 ) R`(g min -1 cm -2 ) = W\ A (6 ) Where W 1 and W 2 are the weight losses in peresence and in absence of the Buckthorn extract in HCl solutions, respectively,() is the degree of surface coverage of the inhibitor, A is the area of the steel electrode (in Cm 2 ), t is the time of immersion (in minutes) and W is the weight loss of steel after time( t ).

Electrochemical methods: Two types of electrochemical measurements has been applied which are electrochemical impedance spectroscopy (ElS) measurements,andpotentiodyanamic polarization (PDP), the measurements were obtained by using impedance spectrum analyzer of the kind ACM instrument. from electrochemical measurements (ElS and PDP), the inhibition efficiency is calculated from equations 7 and 8 as follows: %Inh.R ct = (1-R -1 ct \ R -1 cto ) X 100 (7) Inh. p = (1 - I corr \ I° corr. )×1 (8) % Part two : at different temperatures. The effect of temperature on corrosion and corrosion inhibition of steelin HCl solutions in presence of Buckthorn extract : The study of corrosion and corrosion inhibition of mild steel in 2.5M HCl in absence and presence of the studied extract (at 7ml.), using chemical measurements, by hydrogen evolution and mass-loss methods at 20,30,40,50 and 60 0 C, is carried out.

Part1 : Effect of concentration of Buckthorn (Sidr) extract on the corrosion of steel in 2.5M HCl at 30 o C: The chemical and electrochemical studies of mild steel in 2.5 M HCl solutions in the absence and presence of different concentrations of Buckthorn at 30 o C, were carried out. 3.Results and discussion 1- Chemical study Fig(1) :Volume of hydrogen\ time curves of steel corrosion in 2.5 M HCl in absence and presence of different concentrations of Buckthorn extract at 30° C

. As the figure reveals, the increase in the concentration of correlates with a decease in the slope of the curve i.e. increases the inhibition efficiency. This means that the presence of studied extract in the medium retards the corrosion of steel in 2.5 M of HCl ( in the range 3-6 ml. ), and the extent of inhibition of corrosion depends on the concentration of the Buckthorn extract in the acid. The rate, then increases with higher concentrations, i.e, decrease in the inhibition, this may be attributed to the formation of soluble compound Table (1) Percentage of inhibition at different concentrations of Buckthorn extract from hydrogen evolution (Inh. HE% ) and mass loss (Inh. ML% ) measurements Inh. HEM %Inh. ML %C Table (1) Percentage of inhibition at different concentrations of Buckthorn extract from hydrogen evolution (Inh. HE% ) and mass loss (Inh. ML% ) measurements.

In Fig(2), the inhibition efficiency Inh.% of the extract is described. An increase with increasing the extract concentration,then a decrease in the inhibition is found Fig (2):The relationship between Inh.% deduced from the two chemical methods and the concentration of the extract..

The adsorption isotherm obtained for the studied extract is plotted in Fig 3.Fig Langmuir adsorption isotherm can be expressed as: Fig (3): Langmuir isotherm adsorption model of the steel in 2.5 M HCl in presence of Buckthorn extract. Table (2): Regression coefficient,slope, adsorption constants (K ads ) and free enrgy of adsorption (  G° ads ) obtained from Langmiur isotherm for extract in 2.5M HCl at 30°C. Inh.ML%Inh.HEM% Regression coefficient Slope K (M −1 ) −ΔG (kJ mol −1 ) × ×10 -4

The study of corrosion and corrosion inhibition of mild steel in 2.5M HCl in absence and presence of (7ml) of the studied extract using chemical measurements were carried out by hydrogen evolution and mass-loss methods at 20,30,40,50 and 60 0 C. Fig(4): Volume of hydrogen/time curves of mild steel in 2.5 M HCl (free acid ) at different temperatures The effect of temperature on corrosion and corrosion inhibition on mild steel in 2.5M HCl by studied extract: Figures (6,7) show the effect of temperature on the volume of hydrogen evolved in 2.5M HClin absence and presence of studied exrtact respectivly.

Fig(5): Volume of hydrogen/time curves of mild steel in 2.5 M HCl in presence of (7Ml) of the extract at different temperatures It is clear that the corrosion rate of mild steel increases with rising temperature in both uninhibited and inhibited acid,i.e., the slope of the resulting straight lines mostly increases. The inhibition percentages were calculated from hydrogen evolution ( Inh. HEM %) and mass –loss ( Inh. MLM %) measurements using equations (1&2) The variation of the Inh. % with temperature for the studied extractin 2.5 HClare illustrated in Fig(6).

Fig(6): Variation of inhibition efficiency with temperature for the dissolution rate As it can be seen that the inhibition percentage almost decreases with the increase of temperature, this may be explained to be due to the physical adsorption of extract on mild steel. The results calculated from two methods chemical are in good agreements as indicated by table (3). Inh.% درجات مختلفة

2- Electrochemical study : Two types of electrochemical studies had been applied at the inhibition area,these are electrochemical impedance spectroscopy (ElS),and potentiodyanamic polarization (PDP). The corrosion behavior of mild steel in 2.5M HCl in absence and presence of different concentrations of studied Buckthorn extract was also investigated by the EIS method at 30° C. Figure (4) Nyquist plots for mild steel in 2.5 M of HCl acid in the absence and presence Figure (4) Nyquist plots for mild steel in 2.5 M of HCl acid in the absence and presence of presence of different concentrations of studied Buckthorn extract.

It can be seen that the increase of the concentration of the studied compounds produced a decrease on the corrosion current. In all studied cases the polarization curves show that the investigated extract affect both the anodic and cathodic over potentials and shift parallel to the position of the Tafel lines to both directions i.e.; the studied extract affect both the hydrogen evolution and the anodic dissolution of steel. The Buckthorn extract acting as a mixed type inhibitors. Figure (5) Figure (5) Polarization curves of mild steel in 2.5M HCl solution in absence and presence of the studied Buckthorn extract at 30 C.

Table (4): Electrochemical parameters and inhibition percentages from PDP for mild steel corrosion in 2.5M HCl solution in absence and presence of the studied Buckthorn extract at 30 C. Symbol C (Ml) -E corr (v) I corr. (mA.cm. -2 ) a β (mV.dec. -1 ) β c (mV.dec. -1 ) Inh.%Inh.% Free Acid (2.5 HCl) ______ (2.5 HCl) (2.5HCl) (2.5 HCl) (2.5 HCl) (2.5 HCl) (2.5 HCl)

4.Conclusion: The Following results can be drawn from this study: 1- Buckthorn is an effective inhibitor of corrosion of mild steel in 2.5 M of HCl soluions. 2-The inhibition efficiency of the extract is described. An increase with increasing the extract concentration,then a decrease in the inhibition is found 3- The inhibition efficiency increase is to form an insoluble complex adsorbed on mild steel surface, leading to more inhibition efficiency 4-The inhibition process occurs by the adsorption of the inhibitor molecules under study at the interface metal/solution as a result of the existence of electrostatic attraction. 5-The decrease in corrosion rate of mild steel under study by adding the studied inhibitors is due to the adsorption of the inhibitor molecules on the metal surface or due to the formation of a protective barrier layer which separate the surface of the mild steel sample and the center of corrosion.

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