Electrochemical synthesis of novel polyaniline-montmorillonite nanocomposites and corrosion protection of steel [Elektronische Ressource] / vorgelegt von Hung Van Hoang

Hvh

Informations

• Publié par: technische_universitat_chemnitz
• Publié le: 01 janvier 2007
• Nombre de lectures: 36
• Langue: Deutsch
• Poids de l'ouvrage: 1 Mo

Extrait





Electrochemical Synthesis of Novel Polyaniline- Montmorillonite Nanocomposites and Corrosion Protection of Steel      von der Fakultät für Naturwissenschaften der Technischen Universität Chemnitz genehmigte Dissertation zur Erlangung des akademischen Grades

 doctor rerum naturalium (Dr. rer. nat)   vorgelegt von MSc. Hung Van Hoang geboren am 08.12.1973 in Hanoi, Vietnam eingereicht am 02 Sep 2006 

  Gutachter: Prof. Dr. Rudolf Holze  Prof. Dr. Stefan Spange  Dr.habil. Karin Potje-Kamloth     Tag der Verteidigung: 08 Januar 2007    

Bibliographische Beschreibung und Referat 

Bibliographische Beschreibung und Referat  Hung Van Hoang Elektrochemische Synthese neuartiger Polyanilin-Montmorillonite nanocomposite und Korrosionsschutz von Stahl   Diese Dissertation beschreibt eine neue elektrochemische Synthese neuartiger Compositmaterialien basierend auf dem Tonmineral Montmorillonite (MMT) und intrinsisch leitfähigem Polyanilin (PANI). Die Elektropolymerisation von Aniliniumionen, welche in die Tonmineralschichten eingebaut sind, wurde bei einem konstanten Potenzial durchgeführt. Das resultierende organisch-anorganische Hybridmaterial PANI-MMT wurde mit verschiedenen physikochemischen Methoden charakterisiert. Die Ergebnisse der Elementaranalyse zeigen, dass nur 10 % des Nanocompositmaterials aus leitfähigem PANI bestehen. Die Vergrößerung des Zwischenschichtabstandes von MMT, die bei Röntgendiffraktometrieuntersuchungen beobachtet wurde, lässt auf die Bildung von PANI innerhalb der Tonmineral-Taktoide schließen. IR-spektroskopische Untersuchungen deuten auf das Vorhandensein von Wechselwirkungen physikochemischer Art, wahrscheinlich Wasserstoffbindungen zwischen dem Tonmineral und Polyanilin, hin. Untersuchungen mit zyklischer Voltammetrie zeigten, dass die Anwesenheit von elektroinaktivem Tonmineral die elektrochemische Aktivität von PANI nicht beeinflusst. Das elektrochrome Verhalten von PANI-MMT Nanocompositen wurde mit UV-Vis-Spektroskopie untersucht, wobei sich herausstellte, dass das elektrochrome Verhalten vom PANI im Compositmaterial erhalten bleibt.  Eines der technologischen Hauptanwendungsgebiete von leitfähigen Polymeren, insbesondere von PANI, ist der Korrosionsschutz von aktiven Metallen. PANI-MMT Nanocomposite die mit der angegebenen Methode (elektrochemisch) synthetisiert wurden und chemisch synthetisiertes in organischen Medien lösliches PANI wurden zum Korrosionsschutz von C45 Stahl eingesetzt. Die Korrosionsuntersuchungen wurden mit Hilfe von elektrochemischen Impedanzmessungen (EIM) und anodischen Polarisationsuntersuchungen durchgeführt. Der von PANI-MMT und von in organischen Medien löslichem PANI gebotene Korrosionsschutz ist wahrscheinlich auf die Zunahme des Ladungsdurchtritts widerstandes der beschichteten Stahloberfläche zurückzuführen. Die anodische Verschiebung des Korrosionspotenzials, eine Verringerung der Korrosions- geschwindigkeit und eine deutliche Zunahme des Polarisationswiderstandes sind eindeutige Hinweise für das Antikorrosionsvermögen von PANI-MMT und auch von in organischen Medien löslichem PANI, welche auf der zu schützenden Stahloberfläche abgeschieden wurden. 



1

Abstract 

Abstract  Hung Van Hoang Electrochemical Synthesis of Novel Polyaniline−Montmorillonite nanocomposites and Corrosion Protection of Steel  Chemnitz University of Technology, Faculty of Natural Science  This dissertation describes a new electrochemical synthesis of novel composite materials based on montmorillonite (MMT) clay and intrinsically conducting polyaniline (PANI). PANI was successfully incorporated into MMT galleries to form PANI−MMT nanocomposites. Electropolymerization of anilinium ions which are intercalated inside the clay layers have been carried out at a constant applied potential. The synthetic conditions have been optimized taking into account the effect of concentration of aniline, magnetic stirring and potential cycling. The resulting organic-inorganic hybrid material, PANI- MMT has been characterized by various physicochemical techniques. Results of elemental analysis show that nanocomposite contains only 10 % of conducting PANI. Formation of PANI inside the clay tactoid has been confirmed by the expansion of inter layer distance of MMT as revealed by X-ray diffraction studies. Relatively lower interlayer expansion for PANI-MMT than that of anilinium-MMT indicates the higher stereoregularity in PANI- MMT which has strong influence on electrical properties of nanocomposites. Infrared spectroscopy studies reveal the presence of physicochemical interaction, probably hydrogen bonding, between clay and polyaniline. Cyclic voltammetry studies indicate that presence of electroinactive clay does not influence the electrochemical activity of PANI. Electrochromic behaviour of PANI-MMT nanocomposites have been studied usingin situ  UV-Vis spectroscopy which reveals that electrochromism of PANI in the composite material has been retained.  One of the main technological applications of conducting polymers, particularly PANI, is in the area of corrosion protection of active metals. PANI-MMT nanocomposites synthesized using the present method and a chemically synthesized PANI which is soluble in organic solvents have been used to protect C45 steel surface against corrosion. Corrosion studies have been performed using electrochemical impedance measurements



2

Abstract  (EIM) and anodic polarization studies. Electrochemical impedance data has been analyzed using a suitable equivalent circuit. Corrosion protection of steel offered by both PANI- MMT and organically soluble PANI is evident form the increase in the value of charge transfer resistance of the coated steel surfaces. Time dependent EIM measurements reveal that charge transfer resistance gradually decreases with time, however, the values are much higher than that of uncoated surfaces. Two capacitive loops, one at higher and another at lower frequencies, observed in the Nyquist plots have been assigned to the electrical properties of coating material (in the present case, PANI-MMT or soluble PANI) and electrochemical process at the interface, respectively. An anodic shift in the corrosion potential, a decrease in the corrosion rate and a significant increase in the polarization resistance indicate a significant anti-corrosion performance of both PANI-MMT nanocomposite and organically soluble PANI deposited on the protected steel surface.     



3

Zeitraum, Ort der Durchführung



Die vorliegende Arbeit wurde in der Zeit von November 2002 bis Januar 2005 unter

Leitung von Prof. Dr. Rudolf Holze

Universität Chemnitz durchgeführt.









am

Lehrstuhl

4

für

Elektrochemie

der Technischen



Dedication

Tomyteachers

Tomyparents

Tomysistersandbrothers

TowhomIlove

5

  Hung Van Hoang     

Dedication 



Table of contents

Table of contents 

BIBLIOGRAPHISCHE BESCHREIBUNG UND REFERAT ............................................... 1

ABSTRACT ................................................................................................................................. 2

DEDICATION ............................................................................................................................. 5

ACKNOWLEDGEMENT .......................................................................................................... 9

LIST OF ABBREVIATIONS ................................................................................................... 10

1. INTRODUCTION.................................................................................................................12

1.1 Intrinsically conducting polymer.......................................................................................13 1.1.1 Polyaniline ...................................................................................................................... 13 1.1.2SynthesisofPANI..........................................................................................................14 1.1.3 Conductivity of PANI..................................................................................................... 15

1.2 Montmorillonite (Clay minerals) ....................................................................................... 16

1.3 Organic-inorganic hybrid materials .................................................................................. 17 1.3.1 Polyaniline-montmorillonite (PANI-MMT)................................................................. 17 1.3.2 Characterization of PANI-MMT .................................................................................... 18 1.3.2.1 Cyclic voltammetry ................................................................................................. 18 1.3.2.2 X- ..................................................................................................... 20ray diffraction 1.3.2.3 FT-IR spectroscopy ................................................................................................ 21 1.3.2.4 UV-Vis spectroscopy.............................................................................................. 21 1.3.2.5.In situconductivity measurements ......................................................................... 22

1.4 Corrosion .............................................................................................................................. 23 1.4.1CorrosionprotectionofPANI.......................................................................................23 1.4.2 Techniques used in corrosion studies ............................................................................. 24 1.4.2.1 Electrochemical impedance measurements (EIM) .................................................. 24 1.4.2.2 Polarization measurements ...................................................................................... 29



6

Table of contents  1.5 Soluble PANI........................................................................................................................ 32 

1.6 Synthesis of PANI-MMT..................................................................................................... 33

1.7 Aim and scope ...................................................................................................................... 34

2. EXPERIMENTAL................................................................................................................. 36

2.1 Chemicals and materials ..................................................................................................... 36

2.2 Preparation of anilinium montmorillonite ........................................................................ 36

2.3 Synthesis of PANI- 37MMT nanocomposites ....................................................................... 2.3.1 Electrochemical synthesis of PANI-MMT nanocomposites ......................................... 37 2.3.2 Chemical synthesis of PANI- 37MMT nanocomposites....................................................

2.4 Synthesis of soluble PANI ................................................................................................... 38

2.5 Characterization of PANI-MMT nanocomposites .......................................................... 38 2.5.1 X-ray diffraction ............................................................................................................ 38 2.4.2 FT-................................................................pscertsoocyp....................RI................3...8 2.5.3Cyclicvoltammetry........................................................................................................39 2.5.4In situUV- 39Vis spectroscopy ......................................................................................... 2.5.5In situconductivity measurements ................................................................................. 40

2.6 Corrosion studies ................................................................................................................. 40 2.6.1 Impedance and polarization measurements .................................................................... 41 2.6.2 Polarization measurements ............................................................................................. 41

3. RESULTS AND DISCUSSION ............................................................................................ 43

3.1 Synthesis of PANI-MMT ................................................................................................... 43

3.2 Elemental analysis ............................................................................................................... 45

3.3 X-ray diffraction ................................................................................................................. 46

3.4 FT-IR analysis..................................................................................................................... 48



7

Table of contents  3.5 Cyclic voltammetry.............................................................................................................. 50 

3.6In situUV-Vis spectroscopy............................................................................................... 52

3.7In situ 54conductivity measurements.....................................................................................

3.9 Corrosion studies ................................................................................................................. 55 3.9.1 The anti-corrosion properties of PANI-MMT ................................................................ 56 3.9.1.1 Electrochemical impedance measurements ............................................................. 56 3.9.1.2 Polarization measurements ...................................................................................... 60 3.9.2 The anti-corrosion properties of soluble PANI .............................................................. 62 3.9.2.1 Electrochemical impedance measurements ............................................................. 62 3.9.1.2 Polarization measurements ...................................................................................... 66

4. SUMMARY ............................................................................................................................ 69

5. REFERENCES......................................................................................................................71

        



8

Acknowledgement 

Acknowledgement 

  I would like to take this opportunity to express my deep gratitude to people who have helped me in my research over the past 4 years. First of all, I would like to send special thanks to my supervisor Prof. Dr. Rudolf Holze for giving me a chance to study in Germany and invaluable guidance throughout this course. I would also like to thank Prof. Dr. Stefan Spange and Dr. Ing. habil. Karin Potje Kamloth for being as examiners and evaluating my thesis.  The financial support from The Ministry of Education of Vietnam is gratefully acknowledged.  I also wish to thank to Subbu, Susanne, Anwar and all other members, former and present, at department of electrochemistry−institute of chemistry−TU Chemnitz for their friendship, help and care during these years.  To my teachers in Vietnam Prof.Dr. Tran Thanh Hue, Prof.Dr. Nguyen Duc Chuy, Dr.Tran Hiep Hai, Dr. Nguyen Thi Thu, to my friends Nguyen Ngoc Ha, Nguyen Tien Dung, Tran Thi Hoa, Tong Duy Hien and to my students Duong, Huyen, Long, Ngan, Hoang. Thank you very much for your encouragement, love and care.  I am very grateful to Mr. M. Kehr in physics department for his help to record X-ray diffraction. Finally, the most grateful words are expressed to my parents, my sisters and brothers for their moral support and love that they have given me.



9

 



A AC AE A w b a b c C C C DL CE CEC C R CV d DBSA DC EB EC E corr E eq EIM EM EQ ES E SCE η  η a η c FT-IR i 0 i a

List of abbreviations

List of abbreviations 

Surface area Alternative current Auxiliary electrode Molecular weight Anodic slope Cathodic slope Coating capacitance Double layer capacitance Counter electrode Cation exchange capacity Corrosion rate Cyclic voltammogram Density of metals or alloys Dedocylbenzene sulfonic acid Direct current Emeraldine salt form of polyaniline Equivalent circuit Corrosion potentials Equilibrium potential Electrochemical impedance measurements Emeraldine form of polyaniline Equivalent weight Emeraldine base form of polyaniline Potential versus saturated calomel electrode Overpotential Anodic overpotential Cathodic potential Fourier transform infrared spectroscopy Exchange current density Anodic current density

10