Tel : (90-312) Tele-Fax : (90-312) , korozyon@korozyondernegi.org.tr

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1 MİLLİ GELİRDEN ÖNEMLİ BİR KAYBIMIZ! KOROZYON DERGİSİ Derginin amacı, korozyonu önlemenin bilimsel ve teknolojik altyapısına ilişkin gelişmelerin izlendiği ve bunların özümlenmesi ve uygulamaya aktarılması imkân ve mekanizmalarının tartışılarak değerlendirildiği bir forum olarak etkili olabilmektir. Korozyon Dergisi nde konu ile ilgili olmak üzere Türkçe ve İngilizce de özgün makaleler, çeviri yazıları, öncelikle uygulama alanına hitap eden araştırma sonuçları, uygulama alanında edinilen bilgi ve deneyimlerin konu alındığı yazılar, tarama ve tanıma yazıları, konferans raporları ve kitap eleştirileri yayınlanır. Korozyon Dergisi ne gönderilecek yazılar 14 daktilo sayfasını geçmeyecek şekilde aşağıdaki düzende hazırlanmalıdır: (1) Makale başlığı (Türkçe ve İngilizce), (2) Yazar(lar)ın ad(lar)ı, (3) Yazar(lar)ın 50 kelimeyi geçmeyen kısa özgeçmiş(ler)i, (4) 100 kelimeyi geçmeyen Türkçe ve İngilizce özetler, (5) Makale, (6) Kaynakça. Yazarların makale yazım kuralları olarak Korozyon Dergisi nde daha önce yayınlanmış yazıları örnek almaları önerilir. JOURNAL OF CORROSION The objective of the journal is to provide an effective forum for the investigation of developments related to the scientifi c and technological infrastructure of corrosion prevention, as also for the discussion and evalution of adaption and application possibilities and procedures for these developments. The journal publishes original articles, translations, research results, especially related to practical applications, papers treating information from case-studies, survey and review articles, conference reports and book reviews in English and Turkish on the subject or corrosion. Contributions to the journal should not excead 14 typed pages in length and be prepared in the manner given below: (1) Title of article (Turkish and English) (2) Name(s) of author(s) (3) Biographical data of author(s) not exceed 50 words (4) Turkish and English summaries not to exceed 100 words each (5) Text of the article and (6) References. Authors may consult articles published in back issues of the journal for guidance in the preparation of their manuscripts. SAHİBİ / OWNER KOROZYON DERNEĞİ THE CORROSION ASSOCIATION YAYIN YÖNETMENİ PUBLISHING DIRECTOR Mustafa Doruk Orta Doğu Teknik Üniversitesi, Ankara YAYIN KURULU PUBLISHING BOARD Mustafa Doruk Orta Doğu Teknik Üniversitesi, Ankara Saadet Üneri Ankara Üniversitesi, Ankara Ali Fuat Çakır İstanbul Teknik Üniversitesi, İstanbul Semra Bilgiç Ankara Üniversitesi, Ankara Necil Kurtkaya Elek. Y. Muh. Oktay Akat AKAT Mühendislik A.Ş. Ankara YAYIN DANIŞMA KURULU PUBLISHING ADVISORY BOARD Hayri Yalçın Gazi Üniversitesi, Ankara Mehmet Erbil Çukurova Üniversitesi, Adana Ahmet Çakır Dokuz Eylül Üniversitesi, İzmir Mustafa Ürgen İstanbul Teknik Üniversitesi, İstanbul Melike Kabasakaloğlu Gazi Üniversitesi, Ankara Gözen Bereket Osmangazi Üniversitesi, Eskişehir Timur Koç Gazi Üniversitesi, Ankara Kadri Aydınol Orta Doğu Teknik Üniversitesi, Ankara Fatma Erdem Türkiye Şeker Fab. A.Ş., Ankara Vedat Yalçın Noksel Çelik Boru Sanayi A.Ş. Yves M. Günaltun Petroleum Institute of Abu Dhabi Abu Dhabi Kemal Nişancıoğlu Norwegian Institute of Technology NTH-Trondheim, Norway M.Tettamanti De Nora S.p.A., Milano, İtaly H.M. Shalaby Kuwait Institute for Scientific Research, Kuwait KOROZYON DERGİSİ yılda iki defa olmak üzere Korozyon Derneği tarafından yayınlanır ve ücretsiz olarak dağıtılır. Yazışma adresi : Korozyon Derneği, Orta Doğu Teknik Üniversitesi, Metalurji ve Malzeme Mühendisliği Bölümü, ANKARA JOURNAL OF CORROSION is published two times a year by the Corrosion Association in Turkey, Department of Metalurgical and Materials Engineering, Middle East Technical University, ANKARA/TURKEY Tel : (90-312) Tele-Fax : (90-312) , korozyon@korozyondernegi.org.tr Dizgi ve Baskı : Poyraz Ofset - İvedik O.S.B. 2. Matbaacılar Sitesi (578.) Sk. No. 9 ANKARA Tel : (312) Fax : (312)

2 KOROZYON DERNEĞİNDEN HABERLER Derneğimizin üyesi olduğu Avrupa Korozyon Federasyonu (EFS) nin 2013 Eylül ayında Portekiz in Estroil kentinde yapılan toplantısında yönetim ve danışma kurullarına çalışma dönemi için yeni üyeler atandı. Derneğimiz kurucu üyelerinden Prof.Dr.A.Fuat Çakır EFS Yöneticiler Kuruluna (BoA) en yüksek oyu alarak ikinci defa, derneğimiz üyesi ve Çukurova Üniversitesi öğretim üyesi Prof. Dr. Tunç Tüken ise EFC Bilim ve Teknoloji Danışma Komitesi (STAC) ne seçildiler. Prof. Çakır ve Prof. Tüken i kutlar, üstlendikleri bu önemli görevde başarılı olmalarını dileriz. Bilindiği gibi, Avrupa Korozyon Federasyonu çatısı altında çeşitli ilgi alanlarında etkinlik gösteren 21 çalışma grubu bulunmaktadır. Çalışma gruplarının görevi, korozyon ve önlenmesi konularında bilimsel ve teknolojik gelişmeleri izlemek, yayın, araştırma ve diğer etkinlikler için öneri ve girişimlerde bulunmak olarak özetlenebilir. Federasyon son dönemde aldığı bir kararla, grup çalışmalarına katılımın daha geniş bir tabana yayılması ve böylece üye kuruluşların bilgi paylaşım sürecine etkili olarak katılmalarını sağlamak yönünde yararlı bir adım attı. Bu çerçevede Derneğimiz 17 araştırma grubuna katılmak üzere üyelerimizden isimler önerdi (EFC araştırma gruplarına önerilen üyelerimizin tam listesi derneğimiz web sayfasında görülebilir). Önerilen üyelerin olanaklar ölçüsünde grup toplantılarına katılmaları, ve bilgi alış verişi için tüm iletişim kanallarından yararlanmaları beklenmektedir. Bilindiği gibi, Derneğimiz her iki yılda bir uluslar arası düzeyde korozyon sempozyumu düzenlemektedir. Bunlardan XIII. Uluslar arası Korozyon Sempozyumu Ekim 2014 tarihinde Elaziğ da yapılacaktır Derneğimiz onur üyesi Prof.Dr.Saadet Üneri nin adı ile sunulacak bu etkinliğin organizasyonunu Fırat Üniversitesi üstenecektir. Sanayide görevli ve korozyon sorunu ile er geç tanışmaya aday mühendis ve teknik elemanlar için eğitim kursları düzenlemek Derneğimizin başlıca amaçlarındandır. Bu çerçevede Aralık 2012 tarihlerinde gerçekleştirilen eğitim seminerine MAN Türkiye AŞ. den 36 kişi katıldı. Korozyonun temel ilkeleri, korozyonun türleri, korozyonu önlemede temel yaklaşımlar ve atmosferik korozyon konularının işlendiği seminerin sonunda uygulanan sınavda ba- NEWS FROM THE CORROSION ASSOCIATION At the meeting held in September, 2013 at Estroil/Portugal the European Federation of Corrosion (EFC) re-elected the members for its administrative and advisory bodies for the term Prof.Dr.A.Fuat Çakır, one of the founding members of our association has been elected to the Board of Administrators (BoA) for the second time having highest number of votes. Also one of our members, Prof.Dr.Tunç Tüken from Çukurova University has been elected to the Science and Technology Advisory Committee (STAC). We wood like to congratulate Prof. Çakır and Prof. Tüken and wish much success them during performing this important mission. As known, there are 21 working parties operated by European Federation of Corrosion that work in different areas. Missions of these working groups could be summarized as to monitor recent scientifi c and technological developments regarding corrosion and its prevention, provide feedbacks and suggestions to publications, research and other type of activities.. Recently the federation took the necessary steps to encourage participation of scientists from different background to working groups to enhance exchange of information and knowledge in more convenient ways with member societies. In line of this initiative, our association elected and proposed several of our members to participate 17 working group in the federation. (You can fi nd full list of proposed members from our association website). It is expected from our proposed members to use all means to attend respective working party meetings and exploit all communication channels for information exchange as much as they can. As known, our association has been organizing international corrosion symposium, once two years. The next one, 13rd International Corrosion Simposium will be held on October 2014 in Elazig for the name of our honorary member Prof.Dr.Saadet Uneri. The Fırat University will support the activity as the host organization. Our association organizes courses and training about corrosion and its impacts for industrial professionals and engineers regularly who will face such problems early or late in future. In line of this effort, our association organized a seminar at MAN Türkiye A.Ş. during December people attended to this seminar in which specifi c topics such as basic principles of corrosion, types of corrosion, basic measures to prevent corrosion and atmosp-

3 şarılı olanlara katılım belgesi verildi. Uygulama alanında karşılaşılan korozyon sorunlarını tanımlamak ve giderilmeleri için çözüm önermek derneğimizin bugüne değin başarı ile sürdürdüğü etkinlik alanlarındandır. Uluslar arası bir şirketin istemi üzerine derneğimiz tarafından görevlendirilen bir ekip Libya nın Sitre kenti yakınında, sahilde stoklanmış çelik saçların uğradığı korozyonu değerlendirerek kapsamlı bir rapor hazırlamıştır. Aşağıdaki resimler görevli ekibimizce yerinde yapılan araştırmadan kareler sunmaktadır. Gerek eğitim, gerekse uygulama alanı için dilimizde yazılmış eserlerin önemi ve gerekliliği yadsınamaz. Derneğimiz korozyon konusunda dilimizde mevcut yayınların çoğaltılması ve çeşitlendirilmesi için atılımlarını ara vermeden sürdürmeye özen göstermiştir. Korozyon Derneği yayını olarak yaşama geçirilen Prof.Dr.Saadet Üneri nin Korozyon ve Önlenmesi, ve Prof.Dr.Mehmet Erbil in Korozyon: İlkeler ve Önlemler adlı eserlerini, Prof.Dr.Mustafa Doruk un yazdığı ve yakın gelecekte edinilebilecek Metalik Malzemeler ve Korozyon adlı kitap izleyecektir. Derneğimiz için önemli saydığımız yayınlardan biri de Korozyon Dergisi dir. Derginin düzenli yayınını sağlamak için, mevcut kısıtların giderilmesi yönündeki çabalarımızı artırmamız gerekmektedir. İcten esenlik ve başarı dileklerimizle, heric corrosion were covered. At the end of seminar an evaluation test was performed to certify successful participants. Another principal mission of our association is to analyze corrosion failures in practice and propose solutions to these problems. By a request of an international company, an inspection team formed within our association for the assessment of corrosion of the tank steel plates stored in a coastal area due the atmospheric conditions and other effects near Sirte, Libya The photos below show the on-site investigation by scientists assigned by the association for this particular task. Publications written in our language are important sources for education as well as for the assessment and solution of corrosion problems. Our association continues its effort to increase and diversify such sources with due diligence. Corrosion and Its Prevention by Prof. Dr. Saadet Üneri and Corrosion: Principals and Prevention by Prof. Dr. Mehmet Erbil, will follow a new book entitled Metallic Materials and Corrosion by Prof. Dr. Mustafa Doruk which will be available in near future. Another signifi cant publication of our association is the Corrosion Journal. Obviously, we have to intensify our efforts to overcome limitations in order to provide its regular publication. With sincere wishes of success,

4 INHIBITION BEHAVIOR OF BENZONITRILES ON MILD STEEL IN HCl SOLUTION G. SIĞIRCIK T. TÜKEN M. ERBIL ABSTRACT The aim of this study is to investigate the inhibition effi ciency of benzonitriles with functional amine groups in different positions, for mild steel corrosion in 0.5 M HCl solution. For this purpose, electrochemical impedance spectroscopy (EIS) and potentiodynamic measurements were realized. The obtained experimental results were evaluated by the basis of polarization curves, polarization resistance and capacitance values. The surface analysis was also carried out by scanning electron microscopy technique. The results show that all these inhibitors have a good inhibition effect on mild steel in 0.5 M HCl solution. Also, the position of amine group affects the inhibitor effi ciency. BENZONİTRİLLERİN HCl ÇÖ- ZELTİSİNE BIRAKILMIŞ KARBON ÇELİĞİ ÜZERİNDEKİ İNHİBİTÖR ETKİNLİĞİ Bu çalışmada, 0,5M HCl çözeltisi içinde yumuşak çeliğin korozyonu üzerine, molekülünün farklı konumlarında amin fonksiyonel grubu bulunan benzonitrillerin inhibitor etkinliği araştırılmıştır. Bu amaçla, elektrokimyasal empedans spektroskopisi (EES) ve potansiyodinamik ölçümler ve taramalı elektron mikroskobu tekniği ile yüzey analizleri yapılmıştır. Elde edilen veriler, polarizasyon eğrileri, polarizasyon direnci ve çift tabaka kapasitesi bazında değerlendirilmiştir. Sonuçlar, çalışılan inhibitörlerin 0,5 M HCl çözeltisinde yumuşak çelik üzerinde iyi bir inhibisyon gösterdiğini ve inhibitörlerin etkinliğinde amin gruplarının molekül yapısındaki konumlarının da önemli olduğunu göstermiştir. 1. INTRODUCTION It is well known that mild steel is widely used material in a variety of industrial applications. The use of inhibitor in order to protect metal from corrosion is still in the foreground of many researchers. The effect of inhibitor depends on the molecular structure, size and the number of electron richfunctional groups. Furthermore, the surface state and surface potential of used metal can play important role for the inhibition effi ciency. Mostly used acid corrosion inhibitors are functionalized organic compounds. Benzonitrile compounds could be good inhibitor due to their molecular structure. Also, the number and position of functional groups should be considered in aspect of their activating effect on the aromatic ring. This issue should be taken into account for discussion of benzonitrile compounds as corrosion inhibitors. 2. EXPERIMENTAL Mild steel samples (MS) were cylindrical rods measuring 0.8 cm in the radius (0.502cm 2 exposure surface area). The working surface area was polished mechanically withsic paper to a 1200 grit fi nish, then degreased with 1:1 ethanol/water mixture and washed with distilled water, fi nally dried at room temperature. The corrosive test solution (0.5 M HCl) was prepared by dilution of analytical grade 37% HCl with distilled water. The concentration range of employed inhibitors 2-aminobenzonitrile (2-AB), 3-aminobenzonitrile (3-AB) was to M in 0.5 M HCl. The electrochemical cell consisted of a three electrode set up where the auxiliary electrode was a platinum sheet (2 cm 2 surface area) and Ag/AgCl (3M KCl)electrode was used as the reference. All the potentials given in this paper are referred to this electrode. The EIS measurements were obtained at instantaneous open circuit potential, in a frequency range of 1 mhz-100 khz, peak to peak perturbation voltage was 14 mv. The polarization curves were recorded with a scan rate of 2 mv/s, where the initial potential was the corrosion potential value reached after 1 h of exposure time. The surface morphology of the mild steel samples after 6 days immersion in HCl solution with and without inhibitor was investigated by SEM. 4

5 3. RESULT AND DISCUSSION 3.1. Electrochemical Impedance Spectroscopy (EIS) The corrosion behavior of mild steel in 0.5 M HCl solution with and without inhibitors was investigated by EIS at 25 o C.In Fig. 1 and 2 the EIS results were given for two different inhibitors. As can be seen from these fi gures, the plots of mild steel yield a slightly depressed semicircle. The real impedance at lower and higher frequencies at Nyquist plot is handled as polarization resistance. Electrochemical equivalent circuit used for modeling mild steel/solution interface is given in Fig. 3. CPE is the constant phase element, Rs and Rp are solution resistance and polarization resistance, respectively Z'' Z phase angle Z' Frequency (Hz) Figure 1. The EIS result of mild steel in 0.5 M HCl solutions (-) and containing ( ), ( ), ( ), M( )2-AB. (solid lines show fi tted results) Şekil ( ), ( ), ( ), M( ) 2-AB içeren 0,5 M HCl (-) çözeltisine bırakılan karbon çeliğiyle elde edilen EES sonuçları (koyu çizgiler fi tted sonuçları göstermektedir) Z'' Z phase angle Z' Frequency (Hz) Figure 2. The EIS result of mild steel in 0.5 M HCl solutions (-) and containing ( ), ( ), ( ), M ( )3-AB. (solid lines show fi tted results) Şekil ( ), ( ), ( ), M( ) 3-AB içeren 0,5 M HCl (-) çözeltisine bırakılan karbon çeliğiyle elde edilen EES sonuçları (koyu çizgiler fi tted sonuçları göster-mektedir). 5

6 Rs CPE Rp Figure 3. The equivalent circuit used to identify and fi t the EIS results. Şekil 3. EES sonuçlarını belirleme ve fi t etmede kullanılan eşdeğer devre. The double layer capacitance value (C dl ) calculated by using the following equation: 1 C dl = 2πƒmax R p Z ( Z - R s ) wheref max is the frequencyat which the imaginary component ()of the Nyquist plot is maximum, is the reel impedance at the same point. The surface coverage factor was calculated by using the following equation: C 0 and C are the double layer capacitances of dl dl the surfaces obtained in the solutions without and with inhibitor, respectively. The inhibition effi ciency was calculated from the surface coverage factor (IE% a ). The inhibition effi ciency was also calculated from the polarization resistance (IE% b ) by using the following equation: where and are the polarization resistancesobtained in the solutions without and with inhibitor, respectively. The EIS results were listed in Table 1. Table 1. EIS results. Çizelge 1. EES sonuçları Inhibitor C (M) Rp (Ω) Cdl(μF) n IE% a IE% b Blank AB AB

7 As it is seen from Table 1 with the addition of inhibitors the polarization resistances of mild steel have increased. The values which are related to open surface area have decreased. 3.2 Potentiodynamic polarization measurements The potentiodynamic polarization curves of mild steel in 0.5 M HClsolution without inhibitor and different range of inhibitor concentration were shown in Fig. 4 and 5. As it can be seen from fi gures, both anodic and cathodic current values decreased with addition of inhibitors. 3.3 Adsorption isotherm and thermodynamic parameters The inhibition effi ciency of inhibitors is related their adsorption ability on the metal surface. An inhibitor reduces the corrosion rate by covering active centers on the metal surface. So, it is important to determine surface coverage factor, θ. The lineer relationships of C/θ versus C (in Fig. 6) suggest that the adsorption of 2-AB, 3-AB on the mild steel obeys the Langmuir adsorption isoterm. This isotherm means that the adsorption of the molecule on metal surface is monolayer. Langmuir isoterm can be expresses by the following equation: where C inh is inhibitor concentration and K ads is the adsorption equilibrium constant. (a) C (10-3 ) C (10-3 ) Figure 4. The potentiodynamic polarization curves of mild steel in 0.5 M HCl( ) and containing ( ), ( ), ( ), M ( )2-AB. Şekil ( ), ( ), ( ), M ( )2-AB.içeren 0.5 M HCl( ) çözeltisine bırakılan karbon çeliğinin potansiyodinamik eğrileri. (b) C (10-3 ) C (10-3 ) C (10-3 ) Figure 5. The potentiodynamic polarization curves of mild steel in 0.5 M HCl( ) and containing ( ), ( ), ( ), M ( )3-AB. Şekil ( ), ( ), ( ), M ( )3-AB içeren 0.5 M HCl( ) çözeltisine bırakılan karbon çeliğinin potansiyodinamik eğrileri. Figure 6. Langmuir adsorption plots for mild steel in 0.5 M HCl containing different concentrations of 2-AB (a), 3-AB (b). Şekil 6. Çeşitli miktarlarda 2-AB (a), 3-AB (b) içeren 0,5 M HCl çözeltilerine bırakılan karbon çeliği için Langmuir yüzerme eğrileri, The free energy of adsorption) of the inhibitors on mild steel surface can be determined using the following equation: The calculated and results were listed in Table 2. The values of there calculated as and ) 7

8 kj/mol for 2-AB and 3-AB, respectively. The negative value of free energy of adsorption indicates spontaneous adsorption of inhibitor molecules on mild steel surface. These values show that the adsorption is mostly physical adsorption. Table 2. The andvalues of 2-AB and 3-AB on mild steel in 0.5 M HCl. Çizelge 2. 2-AB and 3-AB içeren 0.5 M HCl çözeltisine bırakılan karbon çeliği için ve değerleri. (kj/mol) 2-AB 0,240 x AB 1,067 x Scanning electron microscopy studies The SEM images of mild steel in the absence and presence of M 2-AB and 3-AB after 6 days immersion time are given in Fig. 7. The surface of mild steel was strongly damaged in the absence of inhibitor due to metal dissolution in corrosive solution. However, the SEM images of mild steel in the presence of inhibitors are very different (Fig. 7b and c). As long as the inhibitor molecules covered the surface, the corrosion rate reduced signifi cantly. Thus, there was less much damage on the mild steel surface. a b c Figure 7. The SEM images of mild steel in the absence (a) and presence of M 2-AB (b) and 3-AB (c) after 6 days immersion time. Şekil M 2-AB (b) ve 3-AB (c) içeren çözeltilere bırakılmş karbon çeliğinden elde edilen SEM görüntüleri. 4. CONCLUSION (1) Both 2-AB and 3-AB have good corrosion inhibition effi ciency for mild steel in 0.5 M HCl solution. (2) The potentiodynamic polarization results show that these compounds which inhibit both anodic metal dissolution and also cathodic hydrogenevolution reaction have mixed type inhibitor properties. (3) The adsorption isotherm of 2-AB and 3-AB molecules on the mild steel in 0.5 M HCl solution obey Langmuir adsorption isotherm with high correlation coeffi cient. (4) SEM images show that these inhibitor molecules form a good protective fi lm on the metal surface. REFERENCES 1. I. Ahamad, R. Prasad, M.A. Quraishi, Corrosion Science 52 (2010) R. Solmaz, G. Kardaş, M. Çulha, B. Yazıcı, M. Erbil,ElectrochimicaActa 53 (2008) R. Agrawal, T.K.G. Namboodhiri, Journal of Applied Electrochemistry 27 (1997) S. Ghareba, S. Omanovic,ElectrochimicaActa 56 (2011) K.F. Khaled,ElectrochimicaActa 48 (2003) R.A. Prabhu,T.V. Venkatesha, A.V. Shanbhag, G.M. Kulkarni, R.G. Kalkhambkar,Corrosion Science 50 (2008) AUTHORS Gökmen SIĞIRCIK, Tunç TÜKEN, Mehmet ERBIL Cukurova University, Science & Arts Faculty, Chem. Dept., 01330, Adana, Turkey Yazarlarla iletişim için: gsigircik@cu.edu.tr, ttuken@cu.edu.tr, merbil@cu.edu.tr 8

9 SYNERGISM CAUSED BY A BLEND OF NITRITE BASED INHIBITORS AND VACCINIUM MYRTILLUS (BLUEBERRY) PLANT EXTRACT ON BOILER STEEL IN DE-AERATED WEAK ACID A. TURHAN B. KARAHAN A. ALBAYRAK H. EKINCI A. ÇAKIR SUMMARY This article presents results of an interdisciplinary project focusing on the development of a hybrid type of inhibitors composed of inorganic and plant based natural substances. Hence use was made of total plant extract Vaccinium myrtillus (VM) mixed with nitrite based inorganic inhibitors with additional chemicals, commercially named as Technophos (TP), at different ratios in fully de-aerated M blank solution. The effects of the presence of TP ( ppm), VM ( ppm ) and their synergistic mixture (TP+VM) on EN boiler steel in fully de-aerated solution sequentially at temperatures of on the ability to act as corrosion inhibitors were investigated by Tafel extrapolation, Potentiodynamic anodic polarization and optical microscopy methods. The aim of this work was to study the inhibiting effi ciency of Vaccinium myrtillus in presence and absence of TP in mildly acidic solution. Corrosion effi ciency (IE%) of inhibitors was estimated by Tafel extrapolation technique. Results indicated an increase in IE% upon the addition of TP in blank solution at varying concentration between ppm with increasing temperature beyond 25. Results obtained for VM extract also revealed some protection at concentrations and temperatures used in blank solution. However no systematic approach could be made regarding IE% with increasing concentration and temperatures. Highest IE% of 82% was recorded at 40 for 100 ppm VM. Additions of (TP+VM) resulted in a 100 fold decrease in corrosion current density (i corr ) at all temperature except 25 when compared with no inhibitor. A corresponding increases in inhibition effi ciency as high as 94-99% was recorded at different mixtures of (TP+VM) concentrations. Potentiodynamic anodic polarization in de-aerated blank solution was performed at all temperatures studied. Effectiveness of inhibitors either single or mixed state was evaluated for polarization curve of 40 o C, since it was most explicitly displayed among others with regard to active-passive transition region, critical current density (i crit ), passive current (i p ) and passivation potential (E pp ). Addition of inhibitors increased i p while decreasing i crit. The highest decrease in i crit was found with a blend of (TP+VM). A competitive adsorption between inhibitor molecules on an active surface involving formation of a chelating complex was proposed to explain these changes. Thermodynamic, kinetic and adsorption characteristics of TP and VM were determined. Adsorption of (TP+VM) on EN boiler steel surface was found to obey Langmuir adsorption isotherm at temperatures40 studied. NİTRİT ESASLI İNHİBİTÖR VE MERSİN YAPRAĞI (BLUEBERRY- VM) ÖZÜTÜ KARIŞIMININ HAVASIZ ZAYIF ASİTLERDEKİ KAZAN ÇELİKLERİ ÜZERİNDE SİNERCİK ETKİSİ Bu makalede inorganik ve bitki esaslı doğal madde karışımından meydana gelen hibrit türü korozyon önleyicilerin geliştirilmesi üzerine yürütülen disiplinler arası bir projenin sonuçları verilmiştir. Çalışma içinde başka kimyasallar da bulunan esaslı, ticari adı Technophos (TP) olan inorganik inhibitörü ve mersin yaprağı özütünün farklı oranlardaki karışımının havası tamamen giderilmiş M çözeltisi içindeki korozyon önleyici özellikleri üzerine yürütülmüştür. TP ( ppm), VM ( ppm ) ve sinercik karışımların (TP+VM) lerdeki havasız çözeltilerde EN kazan sacı üzerindeki korozyon koruyucu olarak etkileri Tafel ekstrapolasyonu, potansiyodinamik anodik polarizasyon ve optik mikroskop metotları ile araştırılmıştır. Çalışmanı amacı VM nin TP içeren ve içermeyen hafi f asidik çözeltilerdeki koruyucu etkinliğini araştırmaktır. İnhibitörlerin koruyucu etkinliği (%IE) Tafel eksrapolasyon tekniği ile hesaplanmıştır. Sonuçlar 25 o C üzeri sıcaklıklarda referans çözeltiye yapılan ppm arasındaki TP ilavelerinde %IE nin arttığını göstermiştir. VM ekstresi ile elde edilen sonuçlar referans çözeltide kullanılan bazı konsantrasyon ve sıcaklıklarda korumanın olduğunu göstermiştir. Ancak konsantrasyon ve sıcaklık artışlarında %IE ile ilgili sistemli bir yaklaşım yapmak mümkün değildir. En yüksek %IE (%82), koruyucu etkinliği 40 o C ve 100 ppm VM de kaydedilmiştir. 25 o C hariç tüm sıcaklıklarda yapılan (TP+VM) ilaveleri, inhibitörsüzlerle karşılaştırıldığında, korozyon akım yoğunluğunda (i kor ) 100 kat azalma yaratmıştır. Farklı (TP+VM) konsantrasyonlarında %94-99 gibi yüksek koruma etkinliği kaydedilmiştir. Çalışılan tüm sıcaklıklardaki havasız referans çözeltilerde i potansiyodinamik anodik polarizasyon çalışmaları yürütülmüştür. İnhibitörlerin tekil veya karışık haldeki koruyucu etkinliği, aktif-pasif geçiş bölgesi, kritik akım yoğunluğu (i kr ), pasif akım (i p ) ve pasif potansiyel (E pp ) değerleri bakımında en belirgin ve açık olduğundan, 40 o C deki polarizasyon eğrileri ile değerlendirilmiştir. İnhibitörlerin katkısı i kr değerini azaltırken i p değerini artırmıştır. i kr değerindeki en yüksek artış (TP+VM) karışımında gözlenmiştir. Bu değişiklikleri açıklamak için inhibitör molekülleri arasında şelat (chelating) oluşumuna yol açan soğrulma yarışı önerilmiştir. TP ve VM nin termodinamik, kinetik ve soğrulma özellikleri belirlenmiştir. (TP+VM) nin EN kazan çelik yüzeyindeki soğrulmasının 40 o C sıcaklıklarda Langmuir soğrulma teorisine uyduğu bulunmuştur. 9

10 1. INTRODUCTION Use of inhibitors is a signifi cant means to prevent corrosion of structural materials occurring under aqueous conditions. In cases where other preventive measures such as design, materials selection, coatings etc., are likely to fail to protect metals and alloys from corrosion, altering the environment in such cases by the use of corrosion inhibitors becomes the only possible means of corrosion prevention. Due to some restriction imposed on structural materials owing to their inherent and unavoidable properties usage of inhibitors becomes indispensable. Application of inhibitors ranges from chemical to production and manufacturing industries, including utilities such as gas distribution, drinking water and sewage systems etc. Cost of corrosion prevention is negligible small when compared to the amounts spend to invest on industrial installations. Therefore every penny of the investment spend on corrosion prevention is well worth for considering. However the extent of investments, expected to be made in USA alone in 2012, amounts to one trillion dollars, which underlines the importance of corrosion prevention alone. The number of published articles in corrosion literature also indicates the ever growing interest in corrosion inhibitors. Types of inhibitors and mechanism of inhibition are well documented in detail in corrosion literature where their classifi cation and vivid account of mode of protections are featured 1-5. The most prominent aspect of corrosion prevention by inhibitors depends solely on the interaction between molecules of inhibitors and the surface of metallic materials resulting either in a two dimensional adsorption (chemisorption or physisorption) layer or a three dimensional oxide layers which are closely related to the chemical and molecular structures of inhibitor ions. Chemisorption types of inhibitors, mostly organic compounds, contain heteroatoms like N, S, P and O atoms, capable of forming coordinate covalent bond with metals due to their free electron pairs. Chemisorption takes place when the free electrons of these atoms are donated to the metal cations on the surface and forms a strong coordination bond resulting in high effi cacy of inhibition. Easy donation of electrons by these heteroatoms induces high rate of inhibition. The increasing order of inhibition effi cacy have been reported to follow the sequence O < N < S < P 1, 3, 6. This is the reverse order of electronegativity of these atoms. Accordingly S atoms are less electronegative than N atoms which means to say that S atoms are less effective in drawing electrons to themselves, therefore are better electron donor resulting in improved inhibition. Therefore heteroatoms form active centres of the organic inhibitors for the process of adsorption on the metal surface. The strength of chemisorptions bond depends on the electron density on the donor atom of the functional group as well as polarizability of the group. It is stated that replacement of H atom in the aromatic rings by some functional groups such as -NH 2, -NO 2 and COOH improves inhibition owing to the high electron density of the heteroatoms of the functional group 7. According to H. Wang as cited in reference [8] the compounds containing both nitrogen and sulphur found in some synthetic organic compounds such as mercapto-triazol were reported to provide excellent inhibition, compared with compounds containing only nitrogen or sulphur atoms. There has been a number of works where the presence of functional groups, such as HC=N, N=N, -CHO, R-OH, C=C, etc., in the inhibitor molecule, the aromaticity, molecular and chemical structures and electron density at the donor atoms were reported to infl uence the adsorption of the inhibitor molecule over corroding metal surface promoting effective inhibition 6, Upon the attachment of the organic inhibitors, the electron density in the metal at the point of attachment changes which in return results in the deceleration of anodic and cathodic reactions. Thus electrons produced at the anode are consumed at the cathode side. As far as structural characteristics are concerned, the inhibition effi ciency of straight chain amines was claimed to increase with the increasing number of carbon atoms in the chain up to Increasing length of carbon chain beyond 10 was told to be indifferent in terms of inhibitor effi ciency, due to the decreasing solubility of the organic inhibitors. A vast number of works devoted in corrosion prevention of metallic materials has been published ever since the considerable efforts has been deployed to develop chromate-free inhibitors for the last couple of decades. In vast majority of the inhibitors literature it has been almost unanimously agreed that the inhibition mechanisms are largely associated with the ability of adsorption of inhibitor s molecules on the protected metal surface which in return grossly depends on the molecular structure of the inhibiting components. It has also been agreed that although considerable attention was devoted to developing chromate-free inhibitors either inorganic or organic, fi nding a suitable replacement was not fully achieved 16. However efforts were made to develop more effective and effi cient inhibitors by combining organic and inorganic components to provide environmentally friendly, multi-functional corrosion 10

11 inhibitors High-throughput screening (HTS) methods introduced by S.R. Taylor et al. 19 to test combination of inhibitors (synergistic effect) have revealed that the synergistic combinations of nonchromate inhibitors have exhibited better corrosion inhibition properties exceeding those of chromate. The synergistic inhibition effects between plant extracts and inorganic inhibitors, though very rare in inhibitor s literature, was reported to improve corrosion of EN boiler steel in de-aerated 10-4 M solution 18. Synergistic effects produced by combination of the rare earth and organic inhibitor components were also reported recently to mitigate stress corrosion cracking (SCC) of high strength steels and fi liform corrosion 19. The results of screening methods, as reported in a review paper by G. Gece 20, have indicated many structural similarities of drugs and corrosion inhibitors, such as carbocyclic and heterocyclic systems existing ubiquitously in both structures. It was also indicated that drugs as classifi ed in this work contain heteroatoms containing lone pair of electrons as well as aromatic rings with delocalised Π-electron systems acting as active adsorption centres. Corrosion, as an undesirable phenomenon, can simply be defi ned as a degradation of metallic materials causing to lose their integrity by the anodic metal dissolution reaction with the surrounding environmental conditions. Oxidation of metal atoms occurs in almost every type of corrosion and results in formation of metallic ions which either dissolve in aqueous environment or form corrosion compounds. Formation of corrosion compounds might take place both in aqueous solution or on metallic surfaces with or without any capacity to protect the surface from further corrosion. Preventing metal atoms from getting oxidised in some ways would bring about the protection of metallic materials to some extent. As one of the most signifi cant corrosion preventive measures, the use of inhibitors are highly regarded among others due to the applicability in situ conditions without any interruption of the ongoing processes. Inhibitors, when used in small amounts in aqueous environment, reduce the rate of corrosion and/or oxidation of materials exposed to that environment. This is to say that the inhibitors act as an anticorrosive or antioxidant agents by forming a protective fi lms of some forms on the metal surface. In this regards corrosion scientists have long been after fi nding suitable chemicals with a high antioxidant activity reconciled by their eco-friendly attributes. This is just the case where plant extracts with naturally occurring constituents raised scientist s interest not just in domains such as medicine, nutrition, fl avouring, beverages, dyeing, repellents, fragrances and cosmetics as stated in 22 but also in corrosion prevention 3, 21, 23, 24. Therefore intensive efforts motivated by the desire to replace toxic inhibitors used for corrosion prevention has been going on for the last couple of decades. Studies on plant extracts as antioxidant agent has started as early as, if not earlier than, works on anticorrosive activity of natural plant extracts. The use of vegetal tannins, for example, was reportedly disclosed since Total equivalent antioxidant capacity (TEAC) of plant extracts are generally related to their phenolic contents whose determination were reported to depend on the methods of extraction and chemicals used thereby 26. Antioxidant capacity of some medicinal plants was ascribed to the contribution made by phenolic and fl avonoid compounds and strong correlation as high as was determined between antioxidant activity and the contents of fl avonoid and phenolic compounds 22. However total phenolic contents were reported not to have necessarily incorporated in all the antioxidants found in plant extracts 27, 28. Accordingly it was stated that same aqueous extracts with a higher phenolic content than some others may have lower antioxidant activity. In view of these fi ndings antioxidant (components inhibiting oxidation) activity of plant extracts may not always be associated with their phenolic contents. A number of factors were found to infl uence the concentration of the active constituent s particularly phenolic compounds present in the plant extracts. Time and period of collection, geographical origin and climatic conditions, method of extraction, type of the solvents used for extraction, part of the plants such as leaves, bark, fl owers, fruits used for extraction are a few of the noticeable factors to mention here 29, 30. According to Marcus et al. cited in 29 the infl uence of these factors could be such dominant that even lead to the absence of active constituents in the same plant collected from different regions. A positive correlation between the polyphenolic contents and solvent s dielectric constant (R=0.728, P<0.05) was reported to exist indicating how signifi cant infl uence could the dielectric constant of the solvent chosen for extraction play on the total phenolic contents and subsequently on the antioxidant activity of the plant extract 29. Plants belong to the world s most precious legacy and mankind enjoys much goodness provided by the plant world. Now they are exploited for their extracts for a variety of reasons, corrosion prevention being just one of them. Therefore the extracts rich in polyphenolic compounds have now been studied for their activity to prevent or mitigate corrosion of metals. However there are a number 11

12 of factors that infl uence the concentration of the constituents, phenolic compounds in particular. Extracts when used as prospect echo-friendly inhibitor; question is generally raised as to how the main constituents of plant extracts can be associated with their chemical and structural properties. However there are limited amount of inhibitor literature where structural and chemical properties of the components existing as the main ingredients in natural extracts were investigated 16, 21. A number of structurally-related compounds some with others without similar substructures attached were tested for their capacity to inhibit corrosion of high strength aluminium alloys, namely AA2024 and AA Among the functional groups tested, SH (thiol) group, besides the orthoand para- positions to a carboxylate on a monoaromatic ring and substitution of N for C in certain position of aromatic ring were found to display a high inhibitive activity, while hydroxyl group with slight and carboxylate little or no capacity to inhibit on their own. SH (thiol) group was found to be the most effective to inhibit aluminium alloys, unless the inhibiting capacity of an aromatic component is disrupted by substituting for N in the ring. An argument was put forth saying that this interruption would be caused by the remaining N on the ring withdrawing electrons from the thiol group and reducing its activity. Some phenolic compounds such as (1) o-aminophenol, (2) catechol, (3) salicaldehyde and (4) salicylic acid was investigated for their inhibition effi ciency tested on carbon steel in HCl acid with and without some potassium salts 21. This is one of the few works where inhibition effi ciency of the inhibitors was investigated in association with chemical structure of inhibiting molecules. Thermodynamic parameters of adsorption process such as, and were determined to assess the inhibition effi ciency. All parameters found indicated a spontaneous physisorption with decreasing inhibition effi ciency in the order: 1>2>3>4. The negative values of and indicated exothermic nature of the adsorption process. Kinetic parameters for the adsorption process also indicated same inhibition mechanism for the inhibitors since E a increases in with the presence of inhibitors. In this work fi nding were based on the adsorption capacity of the inhibitors explained in terms of electronegativity and electron donating capacity of the inhibitors molecules. According to the functional groups accommodated in inhibitor molecules, the inhibition effi ciency of the inhibitors as determined by weight loos and electrochemical technique were shown to decrease in the following order: -NH 2 > -OH > -CHO > -COOH. It is obvious from the fi ndings that, compounds 1 and 2 containing electron donating groups (-NH 2, -OH) with lone pairs on the atoms next to the π-system activate the aromatic ring through a resonance donating effect. Thus, electron density on the ring is increased and the compound becomes more nucleophilic leading to an increase in the inhibition effi ciency. Compounds 3 and 4 however, as they contain electron withdrawing groups (-CHO, -COOH) with electronegative atoms next to the π-system, deactivate the aromatic ring through a resonance withdrawing effect. These electron withdrawing groups by removing electron density from the π-system make the compounds less nucleophilic therefore they have lower inhibition effi ciency compared to compounds 1 and 2. Among these substituents, NH 2 is the most electron donating and COOH is the most electron withdrawing one which correlates well with the order of the inhibition effi ciency. A special effort has been put forth to explain inhibiting mechanisms in association with the chemical and molecular structure of some plant extracts, hypericum perforatum, vaccinium myrtyllus (blueberry) in particular. Computer modelling techniques are powerful tools for studying the mechanism of corrosion and foretelling molecular structures that are better as corrosion inhibitors. Researchers have begun to use theoretical data in their studies to support their experimental results as well as to fi nd a solution by consuming lesser chemicals. The geometry of the inhibitor in its ground state and energy of its molecular orbital (HOMO-LUMO) calculated using computational methodologies were shown to be well correlated with inhibitor s activity. According to the frontier molecular orbital theory, high E HOMO values indicate that the molecule has a tendency to donate electrons to acceptor molecules with unoccupied molecular orbital whereas low E LUMO values mean that the molecule has a tendency to accept electrons. K.F. Khaled studied the inhibition performance of triazole derivatives (triazole, aminotriazole and benzotriazole) on mild steel in 1M HCl both experimentally and computationally 31. They found out that aminotriazole was the best inhibitor among these three. According to the quantum chemical parameters for triazole derivatives, max. charge on N-atoms was calculated to be highest for aminotriazole which enhanced the stronger adsorption possibility of it on iron surface. Actually, it is well known that, the more negative the atomic charges of the adsorbed centre, the more easily the atom donates its electrons to the unoccupied orbital of the metal. Also, highest E HOMO value of aminotriazole enhanced the assumption that it would 12

13 adsorb better on iron surface. The negative sign of E HOMO is generalized as an indicator that adsorption is physisorption. In addition to this, adsorption power in other words inhibitor effi ciency was correlated with dipole moments such that as dipole moment decreases, inhibitor effi ciency increases. According to the experimental results, inhibition effi ciency of the aminotriazole was the best with 90.2% at a concentration of 10-2 M and ΔG ads value is KJ/mol indicating that adsorption mechanism was typical of physisorption. In another study, the interaction between L-tryptophan molecule and iron surface was investigated using computational modelling. L-tryptophan molecular structure was optimized and probable negative and positive charge centres were found within the molecule. It was stated that negative charge centres can offer electrons to the iron atoms to form coordinate bond and positive charge centres can accept electrons from iron atoms to form back-bonding. This dual interaction was assumed to be the reason of the excellent corrosion inhibition. 1.1 Nomenclatures related to the contents of plant extracts Aromaticity: An aromatic compound contains; i) delocalized conjugated π-system, ii) coplanar structure with contributing atoms arranged in one or more ring and iii) 4n + 2 number of π electrons (Hückel s Rule). The positions of the 6 p-orbitals of benzene is shown on the left fi gure. Since they are out of the plane, these orbitals can interact with each other and become delocalized. Phenolics: Phenol is an organic compound with the chemical formula C 6 H 5 OH. The molecule consists of a phenyl group (-C 6 H 5 ) bonded to a hydroxyl group (-OH). There is an interaction between the delocalised electrons in the benzene ring and one of the lone pairs on the oxygen atom. The donation of the oxygen s lone pair into the ring system increases the electron density around the ring. That makes the ring much more reactive than it is in benzene itself. It also helps to make the -OH group s hydrogen a lot more acidic than it is in alcohols. Heterocyclic Aromatic Compounds: In heterocyclic compounds an element other than carbon is present in the ring. Heterocyclic compounds containing nitrogen, oxygen, or sulfer are by far the most common and they are quite commonly encountered in nature. Pyridine, pyrrole, furan and thiophene are examples of heterocyclic aromatic compounds. Steric effects: The infl uence of the spatial confi guration of reacting substances upon the rate, nature, and extent of reaction. Steric effects arise from the fact that each atom within a molecule occupies a certain amount of space. If atoms are brought too close together, there is an associated cost in energy due to overlapping electron clouds and this may affect the molecule s preferred shape (conformation) and reactivity. Flavonoids: Flavonoids are polyphenolic compounds found in plants and are categorized according to their chemical structures into fl avonols, fl avones, fl avanones, isofl avones, catechins, anthocyanidins and chalcones. The fl avonoids have drawn attention because of their potential benefi cial effects on human health. They have been reported to have antiviral, anti-allergic, antiplatelet, anti-infl ammatory, antitumor and antioxidant activities. 2. EXPERIMENTAL 2.1 Inorganic inhibitor The inorganic nitrite based inhibitor, commercially named as Technophos (TP), was provided by Günsu A.S, manufacturers of household and industrial cleaning products and water treatment chemicals, in Antalya-Turkey. Inhibition effi ciency of TP was studied earlier by this group and its inhibition characteristics with and without Hypericum Perforatum (HP) has been reported [18]. Inhibiting attributes of TP in combination of blueberry was studied and reported in this work. 13

14 2.2 Preparation of plant extracts and Determination of their total phenolic and flavonoid contents Vaccinium myrtillus (blueberry) plant powder (15 g) provided by a regional company in Izmir was extracted with ethanol in a Soxhlet extractor for 16 h. The extraction solvent was evaporated in an oven at o C to dryness. Crude extract was evaluated for their total phenolic and fl avonoid contents as well as for DPPH radical scavenging activity as described in 18. Four different plants selected from the Turkish species was considered as a candidate of prospect inhibitors, but only blueberry extract was studied and reported for their inhibitive attributes in this work. Some characteristic of the selected plant extracts are given in Table 1. Main ingredients of the plant extracts studied in this work and some other are given in Table 2. Structure of some main ingredients of the studied plant extracts are shown in Table 3. Table 1. Antioxidant activity of plant extracts in association with total fl avonoid and phenolic contents selected for corrosion studies. Çizelge 1. Korozyon çalışmaları için seçilen bitki özütlerinin toplam fl ovanoid ve fenolik içerikleri ile ilgili antioksidan aktiviteleri Plant Extract Extraction Yield % Total fl avonoid contents (QEmg /100mg) Total phenolic contents (GAE mg/100mg) Radical scavenging activity, DPPH % Rosmarinus Offi cinalis Olea europea Vaccinium Myrtillus Hypericum Perforatum Table 2. Main ingredients of plant extracts studied. Çizelge 2. Çalışılan bitki özütlerinin ana içerikleri Extracts 1. ST. John s wort (Hypericum perforatum) 2. Blueberry (Vaccinium myrtyllus) 3. Mimosa (Acacai Mearnsii) 4. Quebracho Red Wood (Schinopsis Lorentzii) Main ingredients 1.a. Protohypericin 1 1.b.Protopsedohypericin 1.c. Hypericin 1 1.d. Pseudohypericin 1 1.e. Quercetin 1 1.f. Quercitrin 1 1.g.Isoquercitrin 1 1.h. Hyperoside 1 1.i Rutin 1 1.j. Hypuercitrinerforin 1.k. 8-Biapigenin 1 1.l Tannic acid 1 2.a Gallic acid 2 2.b Cafeic acid 2 2.c Coumaric acid 2 2.d Ferulic acid 2 2.e Catechin 2 2.f Epicatechin 2 2.g Quercetin 2 2.h Kaempferol 2 2.i Delphinidin 2 2.j Cyanidin 2 2.k Petunidin 2 2.l Peonidin 2 2.m Malvidin 2 3.a C-glycosylfl avones 3 3.b Isoorintin 3 3.c Rhamnosylorientin 3 3.d Hydroxymaysin 3 3.e Cassiaoccidentalin 3 3.f Quercitrin 4 3.g Myricitrin 4 3.h Catechin 4 3.i Gallocatechin 4 3.j Mearnsitrin 4 3.k Quercetin 4 3.l Myricetin 4 4.a Catechin 5 4.b Epicatechin 5 4.c Gallocatechin 5 4.d Epigallocatechin 5 4.e Fisetinidol 5 4.f Gallic acid 5 4.g Chlorogenic acid 5 1. S.H. Hansen, A. G. Jensen, C. Cornett, I. Bjornsdottir, S. Taylor, B. Wright, I.D. Wilson, High-performance liguid chromatography online coupled to highfi eld NMR and Mass spectrometry for structure elucidation of constituents of Hypericum Perforatum,Anal. Chem., 71, (1999), K. Riihinen, L. Jaakola, S. Karenlampi, A. Hohtola, Organ-specifi c distribution of phenolic compounds in bilberry (Vaccinium myrtillus) and northblue blueberry (Vaccinium corymbosum x V. angustifolium), Food Chemistry, 110, (2008) L.M. de M. Camargo, J. Fe re zou, L. W. Tinoco, C. R. Kaiser, S. S. Costa, Flavonoids from Mimosa xanthocentra (Leguminosae: Mimosoideae) and molecular modeling studies for isovitexin-200-o-a-l-rhamnopyranoside rotamers, Phytochemistry Letters, (2012). 4. A.M. MacKenzie, The fl avonoids of the leaves of Acacia mearnsii Phytochemistry, Volume 8, Issue 9, September 1969, Pages ]. 5. P.B. Venter, M. Sisa, M. J. van der Merwe, S. L. Bonnet, J. H. van der Westhuizen, Analysis of commercial proanthocyanidins. Part 1: The chemical composition of quebracho (Schinopsis lorentzii and Schinopsis balansae) heartwood extract Original Research Article Phytochemistry, 73, 2012,

15 Table 3. Chemical structures of the main ingedients fort he studied plant extracts. Çizelge 3. Çalışılan bitki özütlerinde bulunan ana içeriklerin kimyasal yapıları. Some compounds present in the mentioned plant extracts Structure Phenolic Compounds Cafeic Acid (R 1 =OH, R 2 =H) p-coumaric Asit (R 1 =H, R 2 =H) Ferulik asit (R 1 =OCH 3, R 2 =H) Gallic Acid (R 1 =OH, R 2 =OH) Chlorogenic acid (ester formed between caffeic acid and L-quinic acid) Kaempferol (fl avonol) (R 1 =R 2 =H) Quercetin (fl avonol) (R 1 =OH, R 2 =H) Quercitrin (fl avonol-glycoside) (R 1 =OH, R 2 =H, R 3 =Rha) Rutin (fl avonol-glycoside) (R 1 =OH, R 2 =H, R 3 =Rutinose) Flavonol backbone Flavonoids Hyperoside (fl avonol-glycoside) (R 1 =OH, R 2 =H, R 3 =Gal) Catechin (fl avan-3-ol) Catechin Cyanidin (R 1 =OH, R 2 =H) Delphinidin (R 1 =R 2 =OH) Peonidin (R 1 =OCH 3, R 2 =H) Petunidin (R 1 =OH, R 2 =OCH 3 ) Malvidin (R 1 =R 2 =OCH 3 ) Anthocyanidin backbone Anthraquinones Hypericin Hypericin 2.3 Characterization of plant extracts using FTIR analysis The infrared spectra of the plant extracts were recorded with a Perkin Elmer Spectrum BX instrument equipped with ATR apparatus in the spectra range between 4000 and 650 cm-1 with a resolution of 4 cm-1 and 25 scans per sample. FTIR analysis of hypericum perforatum, vaccinium myrtyllus (blueberry) are given in Fig.1 15

16 0,35 0, Vaccinium Myrtillus, VM Absorbance 0,25 0,20 0,15 0,10 0,05 0,00 0,125 0,100 0,075 0,050 0,025 0,000 Hypericum Perforatum,HP Figure 1. FT-IR absorbance spectra of VM and HP extracts. Şekil 1. VM ve HP özütlerinin FT-IR abzorbans spektrumları Wavenumber (cm -1 ) Table 4. FT-IR absorbance spectra of VM and HP extracts and their identifi cations Çizelge 4. VM ve HP özütlerinin FT-IR abzorbans spektrumları ve tanımlayıcı özellikleri. Wavenumber (cm -1 ) Vaccinium Myrtillus,VM (Bluberry) Wavenumber (cm -1 ) Hypericum Perforatum, HP (St. John s wort) O-H stretching (Phenolic) O-H stretching (Phenolic) 2937 C-H stretching (Aromatic) 2937 C-H stretching (Aromatic) 2832 C-H stretching (OCH 3 ) 2855 C-H stretching (cyclic) 1705 (C=O)OH stretching 1714 (C=O)OR stretching 1646 C=O stretching (Ketone) 1648 C=O stretching (Ketone) 1597 C=C stretching(aromatic) 1597 C=C stretching(aromatic) 1457 C=C stretching(aromatic) 1435 C=C stretching(aromatic) 1341 C-O stretching (Phenolic) 1369 C-O stretching (Phenolic) C-H in plane bending (Aromatic) C-H in plane bending (Aromatic) or or C-O stretching (Phenolic) C-O stretching (Phenolic) 1000 C-O stretching (Phenolic) 1050 C-O stretching (Phenolic) O-H bending (Phenolic) or CH out of plane bending (Aromatic) O-H bending (Phenolic) or CH out of plane bending (Aromatic) Both Bluberry and St Johns wort plant extracts show similar characteristic absorption peaks as shown in Table 4. However, the intensity of absorption due to C=C (1597 cm -1 ) in the aromatic rings is much lower in VM compare to HP (Fig. 1).From this result better inhibition effi ciency is expected from HP as it has more π-electrons. 16

17 2.4 Electrolyte and Specimen preparation The corrosion tests were performed in a mixture of 10-4 M H 2 SO 4 (Merc k) and 0.25 M K 2 SO 4 soluti on (Sigma Aldrich) named as a blank solution with ph=4.62. However addition of TP has increased ph value of blank solution from 4.62 to 9-11 depending on the amount of addition. Preparation of the electrolytes, the test specimens and test setup were carried out as described previously 18. The chemical composition (wt%) of working electrode used for the experiments was C:0.1, Si:0.22, Mn:0,44, P:0.012, S:0.012 and Fe: balance. 2.5 Potentiodynamic polarization studies Electrochemical experiments were carried out in the conventional three-electrode cell with a graphite counter electrode (CE) and a saturated calomel electrode (SCE) coupled to a fi ne lugging capillary as the reference electrode (RE). To minimize ohmic contribution in the cell circuit, the lugging capillary was kept close to working electrode (WE). All polarization experiments were performed using Gamry reference 3000 potentiostat/galvanostat corrosion measurement system according to ASTM G59 norm 32 and G102 norm 33. Before potentiodynamic polarization tests the electrode was immersed in the test solution under open circuit condition and open circuit potential (OCP) was measured for 55 min. until a steady state was attained. Potentiodynamic polarization curves in uninhibited and inhibited solution were carried out in test solution at 25, 40, 60 and 80 ±1 C and Arrhenius plots were obtained by measuring corrosion current density at these temperature. The potential was increased at a rate of 0.17mV/s (0.6 V/h) for Tafel extrapolation measurement curves and changed within a potential range of ± 30 mv around OCP. Corrosion potential (E corr ) and corrosion current density (i corr ) were measured within a selected range of ±15 mv on Tafel curve. Potentiodynamic Anodic Polarization curve measurement was obtained at a scan rate of 1 mv/s starting from cathodic potential (E corr -100 mv) going to anodic direction 1500 mv. The aim of potentiodynamic anodic polarization was to enable inhibitors molecule interacts directly on the bare surface for comparison purposes. In order to check the reproducibility and consistency of the results, each experiment was repeated at least two or more times and the average of repetitions were recorded correspondingly. Inhibition effi ciencies, %IE, and polarization resistance, R p were calculated using the equations (1) and (2): - (1) (2) where and are corrosion current densities in absence and presence of inhibitor, and are anodic and cathodic Tafel constants respectively. 3. RESULT AND DISCUSSION 3.1 Tafel extrapolation measurements Kinetic of corrosion reactions occurring on mild steel surfaces in solution at various concentrations of TP and VM were studied through polarization measurements Effect of TP concentration and temperature on inhibition efficiency Corrosion inhibition of TP was evaluated at various temperatures and concentrations by Tafel extrapolation technique insolution. The electrochemical parameters and the corresponding inhibition effi ciency obtained from Tafel polarization measurements are given in Table 5. Electrochemical parameters shown in Table 5 indicate an increase in inhibition effi ciency as a functi on of temperature as compared to blank solution. This increase remained rather low at 25 o C and varied between 11-40%. At higher temperatures there was a remarkable increase varying between 80-95% at different concentrations. Change in inhibition effi ciency with increasing temperature is given in Fig.2. The highest inhibition effi ciency of 40% at 25 o C was obtained at 800 ppm TP, while at higher temperatures 200 ppm seems to suffi ce to obtain a high IE% around 95%. The signifi cant increase in IE% of TP with temperature beyond 25 o C indicates that the deployment of TP in blank solution at temperatures 40 o C is benefi cial to decrease the rate of corrosion reaction. IE% ppm 400 ppm ppm 800 ppm 1000 ppm T, o C Figure 2. Inhibition effi ciency of TP as a function of temperatures at different concentrations in blank solution. Şekil 2 Ana çözeltideki farklı konsantrasyonlarda sıcaklığın fonksiyonu olarak TP nin koruyucu etkinliği. 17

18 Table 5. Kinetic parameters derived from Tafel polarization plots and inhibition effi ciencies of mild steel in solution c ontaining ppm TP at different temperature.. Çizelge 5. Tafel polarizasyonu kinetik parametreleri ve farklı sıcaklıklardaki ana çözelti içinde ppm arasındaki konsantrasyonlarda TP nin imalat çeliği üzerindeki koruyucu etkin T ( o C) Concentration of TP, ppm β a β c E corr OCP (mv/dec) (mv/dec) (mv) (mv) i corr x10-4 R p IE% (ma/ cm 2 ) (Ω cm 2 ) Blank Blank Blank Blank Corrosion of metals in near neutral and alkaline solution oxygen reduction reaction can occur as shown in equation (3). 4O 2 +2H 2 O+4e - 4OH - (3) Nitrite as an oxidizing inhibitor has no direct effect on anodic oxidation of iron; rather it involves primarily in the cathodic reactions as shown in equations (3.1) which increase the ph of solution near electrode surface and accelerates anodic metal dissolution accordingly 34 NO H+ +6e - NH + +2H O (3.1) 4 2 The consumption of protons in equation (3.1) increases ph and promotes the formation of oxide fi lm on the surface according to reaction (3.2) 35, (3.2) At the defected sites of a passive fi lm where anodic metal dissolution takes place, hydrolysis of is expected to produce ferrous hydroxide according to the following reaction (4) (4) Acidity caused by the reaction (4) in the anodic sites is counterbalanced by the presence of ions in the solution and ph is shifted to 9. Nitrite ions was reported to perform better in solution with ph 18

19 higher than 6. Ferrous hydroxide thus produced by the reaction (4) was reported to have converted to a more protective iron oxide according to the following reaction (5): (5) Passivation and then adsorption of NO - in the 2 metal oxide layer was presumed as a mechanism of corrosion prevention which was facilitated by B 4 O -2. The oxidizing power of 7 NO- in forming a passive ferric oxide layer was further proved by the XPS 2 data from NO - induced fi lm and reported to have 2 composed largely of γ-fe 2 O As regard to the formation of a passive oxide layer, seemingly acts as an anodic-active inhibitor that prevents local corrosion at defected sites of the fi lm. The increasing effi ciency of with increasing temperature 40 O C, as shown in Fig. 2, complies with the assumption that increase in anodic dissolution process with increasing temperature accelerate the rate of fi lm formation according to the reaction (5). This process of fi lm formation by nitrite ions in slightly alkaline solution may not ignore the adsorption of ions on the metal as postulated by Kuznetsov Effect of VM con centration and temperature on inhibition efficiency As regards to the corrosion inhibition of most organic component there is general agreement on the mechanism of inhibitory action controlled by adsorption mechanism. Some of the concepts largely gained acceptance as regards to adsorption mechanism. The electrochemical test measurements indicated that the extract inhibit the corrosion processes by blocking the available cathodic and anodic sites of the metal surface through adsorption of the extract chemical constituents on the metal/solution interface 39. According to D. Schweinsgberg et al., as reported in 39, this phenomenon could take place via (i) electrostatic attraction between the positively charged protonated nitrogen atom and negatively charged mild steel surface (cathodic sites) (ii) dipole-type interaction between unshared electron pairs of oxygen atom or p electrons-interaction with the vacant, low energy d-orbitals of Fe surface atoms (anodic sites) and (iii) a combination of all of the above (mixed type). According to Martinez and Hucovic, as cited in 40, corrosion inhibition by organic components is brought about by two means: (i) the available reaction area is decreased by absorption causing so-called geometric blocking effect; and (ii) the activation energy on anodic and/or cathodic reaction during the course of corrosion inhibition process is modifi ed by the adsorption. In cases where geometric blocking effect is stronger than energy effect, no shift in the corrosion potential should be observed. The polarization parameters obtained with addition of varying VM concentrations are given in Table 6. VM addition caused signifi cant decrease in IE%, when 100 ppm VM was added in blank solution at 25 o C. There is hardly any change in between blank solution and VM at three concentrations (20, 60, 100 ppm) tested at all temperatures as seen in Table 6. Since the displacement in E corr <<85 mv VM can be regarded as mixed type of inhibitors as reported in 41. However addition of TP at all temperatures tested shifted E corr in anodic direction more than 100 mv signifying the anodic character of TP (See Table 5). Table 6 also indicates some small changes with no noticeable trend in β a and β c upon addition of VM into the blank solution which was in line with small changes in E corr indicating VM as a mixed type of inhibitors, similar to some studies on plant extracts 42, 43. A dark blue fi lm was produced during the electrochemical polarization studies in solution of VM extract alone at all temperatures and concentrations tested. According to Brouillard and Favre as reported in 44 similar fi lm formation in solutions containing natural polyphenolic compounds with a catechol group in their B-ring was reported to form a complex with di- and thrivalent ions. A noticeable increase up to 3 to 4 folds in β a and β c was recorded upon the addition of 100 ppm VM into blank solution at 25 which resulted in an increase in corrosion current density almost 40 folds. This increase was accompanied by the peeling off the dark blue deposits (a complex fi lm) formed on the surface during the time interval of the Tafel polarization. VM addition at concentration greater than 60 ppm was assumed to form a loosely bond complex fi lm on the surface with a high internal stresses causing the complex to peel off. Formation of this dark blue complex fi lm taking place indiscriminately all over the surface, at anodic and cathodic sites, could also account for the mixed type of character of VM. Solution temperatures at 40 and 60 seemed to cause a stress relaxation of the fi lm and increased the adherence to the surface providing better protection as indicated in increased IE%. These results seemed to be in conformity with some other studies of plant extract where increase in temperature was reported to have caused an increase in IE% 45, 46. However this argument didn t seem to apply for 80 where all concentration of VM provided smaller IE% than obtained for other temperatures. In line with these β a and β c increased at 80 at all VM concentrations tested with respect 19

20 Table 6. Kinetic parameters derived from Tafel extrapolation plots, inhibition effi ciencies and synergistic parameters of mild steel in blank solution in the absence and presence of TP, VM and mixture of TP and VM at different ratio of concentrations. Çizelge 6. TP ve VM içermeyen, her birini tek olarak ve farklı konsantrasyon oranlarındaki karışımlarını içeren dört farklı sıcaklıktaki ana çözeltide imalat çeliğinin Tafel polarizasyonu kinetik parametreleri, özütlerin koruyucu etkinlikleri ve sinercik parametreleri T( o C) TP, VM, β a β c E corr i corr x10-4 Rp %IE S θ ppm ppm (mv/ dec) (mv/dec) (mv) (ma/ cm 2 ) (Ω cm 2 ) Blank Blank Blank Blank Blank Blank Blank Blank