From figure 2 above, it is shown that by increasing time of exposure, weight loss €w is increased accordingly because corrosion process is rate process and it is affected by time.Figure 3 below shows the behavior of aluminum with and without different concentrations of ketonaz. From this figure, it is clearly shown that ketonaz inhibited the corrosion process and this inhibition is proportional to the inhibitor quantity, the inhibition efficiency is shown in figure 4. Fig. 3: Weight loss vs. time with and without the presence of different amounts of ketonaz Fig.
4: Inhibition efficiency vs. time at differentamount of ketonaz In figure 4 above the inhibition got maximum after 10 minutes (ranged from about 75% at 2g/l of ketonaz to 100% at 4 and 6 g/l) of exposure and this figure gave no clear indication at what time the inhibition was started within this period of 10 minutes which represents too much time of exposure. In the coming paragraph by electrochemical means the statements of inhibitor actions will be presented from the beginning of immersion.
To detect the mode of Ketonaz action, both anode and cathode current-time were drawn as shown in figures 5-6 below (6 g/l of ketonaz was used because it gave the best inhibition action). It can be shown that ketonaz works as inhibitor only on the anode at -600 mV (corrosion potential E corr ) where the current before addition was approximately 0.4mA and after 5 minutes, -the dosing of the ketonaz to the acid solution- it was reduced to about -1mA , after that it reached a very low value of current ~ -0.92 mA, this reflects the potent role of the inhibitor in which it eliminates the anodic sites, reversing polarity to the cathode sites where it gives additional cathodic reaction stabilized at about -0.36 mA with the minimum current while by regarding the cathode current at -900 mV-figure 6- in which the dosage of ketonaz was started after an elapsed of 5 minutes where the current slightly fluctuated around -90 mA.Since the corrosion is free without any external driving force-imposed voltage-, therefore, inspection must be done at the corrosion potential which it had the value of -773 mV in this study and by doing so, figure 7 was obtained, at which the current was reduced to about 81 mA which refers to efficiency of about 50 %, i.e, after an elapsed of 900 sec of dosing. Fig. 5: Current evolution at -600mV-in the anodic region- with addition of 6 g ketonaz after about 300 sec of aluminum immersion in 18% HCl Fig. 6: Current-time evolution at -900 mV -in cathodic region- with addition of 6 g ketonaz after about 300 sec of aluminum immersion in 18% HCl Fig 7: Current behavior at Ecorr of -773 mV with addition of 6 g of ketonaz after 300 sec of aluminum immersion in 18% HCl solution When one considers the inhibition evolution with time as in figure 8 below it can be seen that after 1000 (700 sec after dosing) elapsed there will be about 52% inhibition. This period -1000 sec- of the appearance of appreciable inhibition efficiency of 52% represents a very long period to give reasonable protection. Fig 8: Evolution of inhibitor efficiency with time based on figure 7 it can be seen that the protection increased as the time went on especially after about 550 sec and this represents too much time for inhibition to give useful performance. Since the inhibitor action is Improved with the progressing of time, therefore, it is anticipated that the mode of action is through the dissolution of aluminum to give Al+3 that combined with HCl solution and dissolved ketonaz , then precipitation mechanism takes place when the concentration of the reaction products exceeds some limits. Fig 9: Current”time in the presence of 6g ketonaz added beforealuminum immersion at -773 mVBy focusing on figure 9 in which ketonaz was added before immersion of aluminum, it is concluded that there is approximately no current as soon as the piece is immersed meaning that the efficiency is 100% which resembles the results of the weight loss given in table 2. This current is changed to cathodic one in accordance with figure 5, assuring that ketonaz is instantaneously blocked the surface of aluminum by forming a film barrier which retards HCl attack without any time delay meaning that the mechanism of ketonaz action is by adsorption (see below) and not by solubility effect of the corrosion product. This gives the answer to the questioning about the efficiency curve of figure 4. Therefore ketonaz protects aluminum efficiently when it added at the start of operation (before aluminum immersion).3.1 Mechanism of Ketonaz Action Excellent corrosion inhibitor is not that one which gives electrons to the unfilled orbitals of the metal (HUMO energy) but also accepts free electrons from the metal (LUMO energy)  the aluminum has unfilled P orbital and when ketonaz comes in contact with the surface of aluminum, electrostatic interaction (physisorption) take place. This mechanism explained the high value of inhibition when ketonaz is added before immersion but when ketonaz is added after 300 seconds of immersion Al is reacted with HCl to liberate AlCl3 which could propagate on the surface of aluminum giving the a weak protection compared to the above state with the feasibility of physisorption interaction to a lesser degree.3.2 Adsorption isothermThe main step in the action of inhibitor in acid solution is the adsorption onto the surface of the metal . Adsorption depends on many factors; inhibitor concentration, pH, temperature, type of surfaces and type of anions [6,8]. It was found that the best applicable isotherm in this study is Langmuir isotherm (equation 2) in which a plot of C/ versus C gives a straight line of slope of about unity (C stands for inhibitor concentration and inhibitor coverage) [8,11,12]. Figure 10 below shows the Langmuir relation in which 20,40 and 50 minutes of exposure were selected in order to check the progressing of time effect on the isotherm; Cinh/ = 1/Kads + C inh (2) and Kads = 1/55.5 e (-”Gads/ RT) (3) a. at 20 minute b. at 40 minute c.after 50 minuteFig. 10: Langmuir adsorption isotherm for aluminum in 18%HCl solution in presence of 6 g/l of ketonaz, a. after 20 minute of exposure b. after 40 minute of exposure and c. after 50 minute of exposure.The energy values of adsorption were -5.28 kJ/mol -7.66 kJ/mol and -5.11 after 20, 40 and 50 minutes of exposure respectively. These values suggest physisorption of interaction of ketonaz with aluminum spontenously and the strength of interaction is increased with the time but beyond 40 minute the energy of adsorption decreases meaning that the inhibition is decreased, as can be assured by returning back to figure 4. 4. ConclusionsIn this study:1-From experimental work ketonaz works as inhibitor for the corrosion of aluminum in 18% HCl solution.2-As the concentration of inhibitor increases the inhibition efficiency increases.3-The adsorption process of ketonaz is spontaneous.4-Ketonaz adsorption on aluminum surface in 18% HCl solution obeys Langmuir adsorption isotherm.5-Ketonaz gives excellent protection. 5. References  Abd El Maksoad S.A., The effect of organic Compounds on the electrochemical behavior of steel in acidic media, A review, Int. J. Electrochem. Sci. 3)2008) 528-555.  Amitha Rani B. E., Basu, Bharathi Bai J., Green inhibitors for corrosion protection of metals and alloys: An Overview, International Journal of Corrosion., 2012, Article ID 380217(2011) 15 pages. Mohd Norzila, Ishak Anis Suhaina, Thermodynamic study of corrosion inhibitionof mild steel in corrosive medium by piper nigrum extract, Indian Journal of Science and Technology 8(2015) 2015.  Christian Vargel, Corrosion of Aluminum, Elsevier Ltd. 2004.  Elewady G.Y., El-Said I.A., Fouda S.A., Anion surfactants as corrosion inhibitors for aluminum dissolution in HCl solutions, Int. J. Electrochem. Sci. 3(2008) 177-190.  Rozenfeld L.L., Corrosion Inhibitors, Mc-Graw Hill, 1981. Devakai H. Preya, P. Gomathi, Corrosion studies using zeolite synthesized from fly ash, Indian Journal of Science and Technology 9 (216). Obot I.B., Obi-Egbedi N.O., Adsorption properties and inhibition of mild steel corrosion in sulphuric acid solution by ketoconazole: Experimental and theoretical investigation, Corrosion Science 52, (2010) 198-204.  Nestor Perez, Electrochemistry and Corrosion Science, Kluwer Academic Publisher, 2004.11-Ali I.A., Fouad N., Inhibition of aluminum corrosion in hydrochloric acid solution using black mulberry extract., J. Mater. Environ. Sci.3 (2012) 917-924.12-Bouklah M., Hammouti B., Thermodynamic characterization of steel corrosion for the corrosion inhibition of steel in Sulphuric Acid solution by Artemisia , Portugaliae Electrochemica Acta 24 (2006) 457-468.
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