Corrosion-protective performance of nano polyaniline/ferrite dispersed alkyd coatings.Introduction Nanostructured materials have been establishing themselves as the modern generation of high-performance materials in many areas, ranging from automotive engineering to bioengineering, owing to a vast array of unique properties. (1,2) The tiny size of the nanoparticles produces an extraordinarily high surface energy, an increased number of surface atoms that exhibit enhanced compactness, and physico-mechanical and physico-chemical resistance performance compared to common microparticles. Advancements in modern engineering and technology have hastened the development of high-performance, corrosion-resistant coatings that have a broad spectrum of effectiveness under a wider range of hostile environments. (3) There has been a lot of interest in the possibility of using conducting polymers--such as polypyrrole, polyaniline, and their derivatives--in the corrosion protection of iron and aluminum-based materials. (4) The interest in these polymers stems from the fact that they can exist in different oxidation states and can be easily converted from one state to another. The polyaniline (PANI) based paint formulation consists of predispersed and highly concentrated PANI (3-5wt%) in different binder matrices such as alkyd al·kyd n. A widely used durable synthetic resin derived from glycerol and phthalic anhydride. Also called alkyd resin. [alky(l) + (aci)d.] Noun 1. , polyurethane, epoxy. (5) These formulations however do not fulfill all chemical, physical and technical requirements, of corrosion protective coatings. (6) It has been reported that the PANI primer itself does not work properly under all widely varying practical applications. (7-9) The technique proposed by the NASA/Los Alamos group (6) is not practical for the general coatings industry because it fails in terms of adhesion and reproducibility, and lacks superior performance compared with high-performance coating systems. The Monsanto variation (7) also has yet to show practical applicability and good performance of its intrinsically conducting polymer (ICP (1) (Internet Cache Protocol) A protocol used by one proxy server to query another for a cached Web page without having to go to the Internet to retrieve it. See CARP and proxy server. )-based paint formulations to an acceptable standard. The design and production of PANI-based coating systems with commercial viability requires paint formulations with a minimum possible agglomeration ag·glom·er·a·tion n. 1. The act or process of gathering into a mass. 2. A confused or jumbled mass: of ICP, well-dispersed nanoparticles (70-100 nm) of uniform size, superior adhesion, and prolonged protective performance under different corrosive conditions. A critical obstacle in assembling and maintaining a nanoscale material is usually its tendency to agglomerate agglomerate Large, coarse, angular rock fragments associated with lava flow that are ejected during explosive volcanic eruptions. Although they may appear to resemble sedimentary conglomerates, agglomerates are igneous rocks that consist almost wholly of angular or rounded , which is a deterrent to its applications. (10) Furthermore, several processing techniques require consolidation and sintering sintering, process of forming objects from a metal powder by heating the powder at a temperature below its melting point. In the production of small metal objects it is often not practical to cast them. of nanomaterials into solid blocks, coatings, or thin films that often leads to unavoidable formation of agglomerations and larger grains that effectively disrupt the properties of the materials. The utilization of PANI/ferrite nanocomposites may serve as a suitable alternative to the problem of dispersion and agglomerate formation because the coating is expected to provide a binder matrix for the particles to prevent grain growth and agglomeration--thereby yielding uniform overall size distribution. The small and uniform particle size of the nanocomposite is expected to drastically enhance the corrosion-protective performance even at a lower concentration (0.5-1.5 wt%) of intrinsically conducting polymer (ICP). Literature surveys reveal that no work has been reported on the corrosion-protective performance of PANI/ferrite/alkyd-based nanocomposite coatings. In our study, the corrosion-protective performance of PANI/ferrite nanocomposite-based alkyd coatings was investigated on mild steel (MS) with very low PANI/ferrite content (0.5-1.5 wt%) in alkyd. The obtained results were compared with pristine PANI/alkyd coatings with a similar loading of the conducting polymer as that of the nanocomposite. Materials Materials including soya alkyd (Shankar Dyes, India), xylene xylene (zī`lēn) or dimethylbenzene (dī'mĕthəlbĕn`zēn), C6H4(CH3)2 (Merck, India), sodium dodecylsulfate (SDS 1. (company) SDS - Scientific Data Systems. 2. (tool) SDS - Schema Definition Set. ) (Merck, India), ammonium per sulfate sulfate, chemical compound containing the sulfate (SO4) radical. Sulfates are salts or esters of sulfuric acid, H2SO4, formed by replacing one or both of the hydrogens with a metal (e.g., sodium) or a radical (e.g., ammonium or ethyl). (APS) (Merck, India), and ferric chloride (Merck, India) were used as received. Aniline aniline (ăn`əlĭn), C6H5NH2, colorless, oily, basic liquid organic compound; chemically, a primary aromatic amine whose molecule is formed by replacing one hydrogen atom of a benzene molecule with an amino monomer monomer (mŏn`əmər): see polymer. monomer Molecule of any of a class of mostly organic compounds that can react with other molecules of the same or other compounds to form very large molecules (polymers). (Sigma, Aldrich) was double-distilled prior to use. Synthesis of PANI/ferrite nanocomposites and PANI/ferrite-alkyd coatings The synthesis of ferrofluid A ferrofluid (from the Latin , meaning iron) is a liquid which becomes strongly polarised in the presence of a magnetic field. Ferrofluids are composed of nanoscale ferromagnetic particles suspended in a carrier fluid, usually an organic solvent or water. used for the preparation of PANI/ferrite nanocomposite was reported in our earlier studies. (11) A fixed volume of ferrofluid was added dropwise to a 250 mL round bottom flask containing hydrochloric acid hydrochloric acid: see hydrogen chloride. hydrochloric acid or muriatic acid Solution in water of hydrogen chloride (HCl), a gaseous inorganic compound. (HC1) (8 mL, 1 N) and double-distilled aniline (5 mL) with slow and continuous stirring maintained at a constant temperature and pH of 1. After an induction period induction period n. The interval between an initial injection of an antigen and the appearance of demonstrable antibodies in the blood. of 30 min, the color of the solution changed from red to green, which confirmed the polymerization polymerization Any process in which monomers combine chemically to produce a polymer. The monomer molecules—which in the polymer usually number from at least 100 to many thousands—may or may not all be the same. of aniline in conducting form. Polymerization was further continued for 12 h at 20[degrees]C. The green precipitate of obtained [Fe.sub.3][O.sub.4]/PANI composite was filtered, washed several times with distilled water and then methanol, and then dried in a vacuum for 72 h at 60[degrees]C. Synthesis of PANI/alkyd and PANI/ferrite-alkyd coatings The polyaniline used for the preparation of PANI/alkyd coatings was synthesized by emulsion polymerization using SDS, as reported by others. (12) The PANI alkyd coatings were prepared by dispersing 0.5, 1.0, and 1.5 wt% PANI in 10 wt% solution of alkyd in xylene. Likewise, the PANI/ferrite/alkyd was prepared by mixing the appropriate amount of PANI/ferrite with 10 wt% alkyd solution in xylene to obtain different loadings of the nanocomposite, varying from 0.5 to 1.5 wt%. Characterization PANI/ferrite/alkyd coatings were applied by brush (15 wt% of the blend solution in xylene) on all sides of steel strips (70 x 30 x 1 mm) for determination of specular spec·u·lar adj. Of, resembling, or produced by a mirror or speculum. spec  u·lar·ly adv.Adj. 1. gloss at 60[degrees] by gloss meter (model RSPT-20; Veeco, Santa Barbara, CA), scratch hardness (BS 3900), bending test (ASTM-D3281), and impact resistance (IS:101 par 5/sec-31988). The thickness of the coated samples was measured by elcometer (Model 345; Elcometer Instruments, Manchester, England). Scanning electron micrographs of the uncorroded coated (as well as corroded cor·rode v. cor·rod·ed, cor·rod·ing, cor·rodes v.tr. 1. To destroy a metal or alloy gradually, especially by oxidation or chemical action: acid corroding metal. coated) specimens were taken on a JEOL JEOL Japan Electron Optics Laboratory JSM JSM Journal of Sexual Medicine JSM Just Shoot Me (sitcom) JSM Journal of Sport Management JSM Journal of Software Maintenance JSM Jabber Session Manager JSM John Sidney McCain JSM JEOL Scanning Microscope 840 scanning electron microscope scan·ning electron microscope n. Abbr. SEM An electron microscope that forms a three-dimensional image on a cathode-ray tube by moving a beam of focused electrons across an object and reading both the electrons scattered by the object and . Corrosion tests were performed in water, acid (5 wt% HCl), alkali (5 wt% NaOH), and NaCl (3.5 wt%) by placing the steel strips in 3-inch diameter porcelain dishes and dipping the coated samples in the test media until the coatings showed deterioration and development of cracks. The protective behavior of the coatings against the dissolution of MS was evaluated by calculating the corrosion rate (Vc) for each one of the samples. (13) This calculation was performed using the expression: [V.sub.c] = [DELTA]g/[A x t x d] where [DELTA]g is the weight loss in grams for each sample, A is the exposed area of the sample in [cm.sup.2], t is the time of exposition in years, and d is the density of the metallic species in g/[cm.sup.3]. The weight loss was measured after carefully washing the samples with distilled water to remove the deposited corrosion product, and dried in a vacuum at 60[degrees]C to remove moisture from the samples. Results and discussion Spectral analysis of PANI/ferrite The UV-vis spectra of PANI/ferrite nanocomposite (see Fig. 1) shows maximum absorption at 350 nm, as well as 600 nm. The former is assigned to [PI]-[PI]* transitions, while the later peak can be correlated to the polaronic transitions. The presence of a polaronic transition peak confirms the emeraldine-doped state of [Cl.sup.-] doped PANI in a [Fe.sub.3][O.sub.4]/PANI nanocomposite. (11) [FIGURE 1 OMITTED] Physico-mechanical properties The physico-mechanical characteristics of PANI/alkyd and PANI/ferrite-alkyd coatings are depicted in Table 1. The scratch hardness value of pristine alkyd was found to be only 0.2 kg, while that of 0.5 PANI/alkyd was found to be 3.0 kg. The scratch hardness values were found to increase from 3.0 to 4.0 kg as the loading of PANI increased. This was attributed to the enhanced adhesion between the PANI/alkyd coatings with MS substrate when the loading of the conducting polymer was increased. In the case of aniline, the amino group and the aromatic ring aromatic ring, n closed ring structure formed by six carbon atoms, with a single hydrogen atom attached to each one. Also called a phenyl ring or a benzene ring. are in the same plane, and this coplanar co·pla·nar adj. Lying or occurring in the same plane. Used of points, lines, or figures. co  pla·nar orientation with
respect to the metallic surface confers to PANI a greater capacity to
form more homogeneous films, which, in turn, translates into a better
adhesion to the metal substrate. Furthermore, the presence of a lone
pair of electrons on polyaniline enhances the electrostatic interaction
between coatings and the metal substrate, resulting in superior scratch
hardness.
The scratch hardness values of PANI/ferrite/alkyd were found to be higher than the PANI/alkyd coatings (see Table 1, Fig. 2). A maximum scratch hardness of 5 kg was obtained at 1.5 PANI/ferrite loading in alkyd, while the scratch hardness value was found to be 4 kg at similar loadings of PANI. The difference between the scratch hardness values at similar loadings can be correlated to the variation in the morphology of the PANI/alkyd and PANI/ferrite/alkyd coatings (see Fig. 3a, b). The presence of ferrite fer·rite n. 1. Any of a group of nonmetallic, ceramiclike, usually ferromagnetic compounds of ferric oxide with other oxides, especially such a compound characterized by extremely high electrical resistivity and used in computer memory in PANI/ferrite nanocomposite promotes adhesion as well as toughness of the coatings due to higher electrostatic interaction of ferrite with the metal substrate. Moreover, the PANI/ferrite contains uniformly dispersed (maximum 70-100 nm particle size) nanoparticles of PANI/ferrite in alkyd, leading to the formation of an agglomerate-free morphology of the nanocomposites that ensures better adhesion, with more compact structure in comparison to PANI/alkyd. Likewise, the impact resistance was found to increase from 70 kg/[cm.sup.2] in case of pure alkyd to 84 kg/[cm.sup.2] in PANI/alkyd. The impact resistance of PANI/ferrite/alkyd was also found to be higher than the PANI/alkyd coatings. All the coatings passed the conical mandrel mandrel /man·drel/ (man´dril) the shaft on which a dental tool is held in the dental handpiece, for rotation by the dental engine. man·drel or man·dril n. 1. bend test. The gloss values were found to decrease with the loading of ferrite in PNI/alkyd due to the increase in the opacity Refers to being "opaque," which means to prevent light from shining through. For example, in an image editing program, the opacity level for some function might range from completely transparent (0) to completely opaque (100). of the coatings. It can be concluded that the physico-mechanical properties of the PANI/alkyd coatings were found to be significantly enhanced with the loading of the PANI/ferrite nanocomposite in alkyd. Analysis of corrosion rate The pristine alkyd coatings dissolved completely within 2 h when placed in different corrosive media, revealing a rapid corrosion rate of the organic coatings. The corrosion rates of PANI/alkyd and PANI/ferrite/alkyd were monitored for a period of 960 h, and the coatings revealed no visual deterioration or dissolution during this period. It was noted that the sample of the MS had a higher Vc, which decreased notably for the coated specimens. The corrosion rate of PANI/alkyd was found to be lower than bare MS (see Fig. 4a-c). Phenomena like fissures, pulverization pulverization in dentistry, high-speed burs may be used to remove root fragments that cannot be extracted or are ankylosed. , and discoloration dis·col·or·a·tion n. 1. a. The act of discoloring. b. The condition of being discolored. 2. A discolored spot, smudge, or area; a stain. Noun 1. usually observed for alkyd coatings are clearly not observed in the presence of PANI, indicating the improved degradation resistance of the coating. This has been reported by others. (5) [FIGURE 2 OMITTED] In the case of PANI/alkyd, a compact iron/dopant complex layer formation at the metal-coating interface acts as a passive protective layer--as long as the PANI has redox redox (rē`dŏks): see oxidation and reduction. capability to undergo a continuous charge transfer reaction at the metal-coating interface in which PANI is reduced from emeraldine salt form (ES) to an emeraldine base (EB) (Scheme 1). (14) Upon accumulation of excessive corrosive ions, coating alkalization alkalization the act of making alkaline. takes place, followed by a breakdown of the passive layer. This type of corrosion protection usually depends on the strength of the passive oxide film that forms while the protective behavior depends on the size and charge of the dopant--i.e., as the size of the dopant dopant Any impurity added to a semiconductor to modify its electrical conductivity. The most common semiconductors, silicon and germanium, form crystalline lattices in which each atom shares electrons with four neighbours (see bonding). increases, the strength of the iron/dopant complex film increases, which improves the protective efficiency. (13-15) This explains why the corrosion rate was found to vary insignificantly when the wt% loading of PANI in alkyd was increased. However, the corrosion rate of PANI/ferrite/alkyd was found to decrease appreciably with the increase in the PANI/ferrite loading in alkyd (see Fig. 4a-c). In the case of PANI/ferrite/alkyd, the inhibition effect of the nanocomposite coatings can be attributed to the presence of ferrite particles. The presence of excessive ferrite particles maintains PANI in its doped state (i.e., prevents the reduction of PANI from ES to EB) using faradic fa·rad·ic also far·a·da·ic adj. Of, relating to, or using an intermittent asymmetrical alternating electric current produced by an induction coil. [After Michael Faraday.] charge, and prevents metal dissolution. (16) Moreover, the small pore size and uniform dispersion of the PANI/ferrite nanocomposite in alkyd (Scheme 1) helps in the formation of a well-adhered, dense, and continuous network-like structure that impedes the penetration of the corrosive ions through to the metal substrate, and inhibits the MS from the attack of the corrosive species. (17) Therefore, the PANI/ferrite/alkyd coatings act as excellent inhibitors to protect metals from corrosion. [ILLUSTRATION OMITTED] Morphology The SEM micrograph micrograph /mi·cro·graph/ (-graf) 1. an instrument used to record very minute movements by making a greatly magnified photograph of the minute motions of a diaphragm. 2. of 1.5 PANI/ferrite/alkyd-coated MS specimen (Fig. 3a) reveals the formation of a closely packed, continuous, dense uniform layer of PANI/ferrite/alkyd coating. Despite being a composite coating in nature, it was observed that neither a dispersion nor a two-phase system was visible, indicating intimate, homogeneous mixing of the PANI/ferrite in alkyd. The SEM micrograph of a 1.5 PANI/alkyd coated MS specimen (see Fig. 3b) shows an uneven surface morphology with aggregation of PANI particles exhibited as white phase. Even after 960 h exposure in 5% HCl (see Fig. 3c), the coating exhibited a slight deposition of salt but remains completely intact. The dense and continuous structure is consistent with the ability of the coatings to protect the metal substrate from corrosion as evidenced from the significantly low corrosion rate of these coatings. In the case of 1.5 PANI/alkyd coatings (Fig. 3d), formation of cracks and deep fissures was noticed, along with the deposition of the corrosion product. [FIGURE 3 OMITTED] [FIGURE 4 OMITTED] Conclusion A novel PANI/ferrite/alkyd coating material coating material, n a biologically acceptable, usually porous nonmetal applied over the surface of a metallic implant with the expectation that tissue ingrowth will occur in the pores. Often a carbon polymer or ceramic substance. based on a nanotechnological approach that was able to effectively protect steel from corrosion in acid, alkaline, and saline media was developed during this process. PANI/ferrite/alkyd coatings were found to act as inhibitors, maintaining high resistance to corrosive ions due to the presence of a dense, nonporous, continuous network-like structure. This uniformly dispersed nanocomposite coating provides space for a variety of modifications to its physical structure, making it more malleable and adaptable for many application processes, including spraying, dipping, or spin coating. Acknowledgment This work was funded by C.S.I.R, New Delhi, India, through grant No. 01/(1953)/04/EMR-II. References 1. Nalwa, HS. Handbook of Nanostructured Materials and Nanotechnology, Vol. 1 Academic Press, San Diego (2000) 2. Guilemany, JM, Dosta, S, Nin, J, Miguel, JR, "Study of the Properties of WC-Co Nanostructured Coatings Sprayed by Highvelocity Oxy Fuel." J. Thermal Spray Technol., 14 405-413 (2005) 3. Voevodin, N, Balbyshev, VN, Khobaib, M, Donley, MS, "Nanostructured Coatings Approach for Corrosion Protection." Prog. Org. Coat., 47 416-423 (2003) 4. Rout, TK, Jha, G, Singh, AK, Bandyopadhyay, N, Mohanty, ON, "Development of Conducting Polyaniline Coating: A Novel Approach to Superior Corrosion Resistance." Surf. Coat. Technol., 157 16-24 (2003) 5. Laco, JII JII Journey Into Imagination (Disney ride) JII Joint Integration Interface JII Jupiter II (ship on "Lost In Space" TV series) , Villota, FC, Metres, FL, "Corrosion Protection of Carbon Steel with Thermoplastic A polymer material that turns to liquid when heated and becomes solid when cooled. There are more than 40 types of thermoplastics, including acrylic, polypropylene, polycarbonate and polyethylene. Coatings and Alkyd Resins Containing Polyaniline as Conductive Polymer." Prog. Org. Coat., 52 151-160 (2005) 6. Thompson, KG, Bryan, CJ, Benicewicz, BC, Wroblewski, DA, Los Alamos National Laboratory Los Alamos National Laboratory (LANL) (previously known at various times as Site Y, Los Alamos Laboratory, and Los Alamos Scientific Laboratory) is a United States Department of Energy (DOE) national laboratory, managed and operated by Los Alamos National Report LA-UR-92-360D 7. http://www.ormecon.de/research 8. Wroblewski, DA, Bencewicz, BC, Thompson, KG, Bryan, CJ, "Corrosion Resistant Coatings from Conducting Polymers." Polymers." Prepr., 35 (1) 265-270 (1994) 9. Racicot, R, Brown, T, Yang, SC, "Corrosion Protection of Aluminum Alloys by Double-strand Polyaniline." Synth. Met., 85 1263-1264 (1997) 10. Heilman, A, Polymer Films with Embedded Metal Nanoparticles. Springer, New York New York, state, United States New York, Middle Atlantic state of the United States. It is bordered by Vermont, Massachusetts, Connecticut, and the Atlantic Ocean (E), New Jersey and Pennsylvania (S), Lakes Erie and Ontario and the Canadian province of (2003) 11. Alam, J, Riaz, U, Ahmad, S, "Effect of Ferro fluid Concentration on Electrical and Magnetic Properties of [Fe.sub.3][O.sub.4]/PANI Nanocomposites." J. Mag. Mater., 314 (2) 93-99 (2007) 12. Oh, SG, Im, SS, "Electroconductive Polymer Nanoparticles Preparation and Characterization of PANI and PEDOT Nanoparticles." Curr. Appl. Phys., 2 (4) 273-277 (2002) 13. Rosa, VA, Hugo, RB, Eduardo, A, "Synthesis and Characterization of Polyaniline and Poly(o-methoxy aniline). Behavior against Carbon Steel Corrosion." J. Chil. Chem. Soc. 48 (1), Conception Mar. (2003) 14. Jose, E, Pereira, S, Susana, I, Cordoba cor·do·ba n. See Table at currency. [American Spanish córdoba, after Francisco Fernández de Córdoba (1475?-1526?), Spanish explorer.] Noun 1. , T, Roberto, MT, "Polyaniline Acrylic Coatings for Corrosion Inhibition: The Role Played by Counter-ions." Corros. Sci., 47 (3) 811-822 (2005) 15. Trivedi, DC, "Influence of the Anion anion (ăn`ī'ən), atom or group of atoms carrying a negative charge. The charge results because there are more electrons than protons in the anion. on Polyaniline." J. Solid State Electrochem., 2 85-87 (1998) 16. Garcia, B, Lamzoudi, A, Piller, F, Le, NHT NHT National Housing Trust NHT Now Hear This (speaker manufacturer; Benicia, California) NHT National Heritage Trust (Australia) NHT Naphtha Hydrotreater NHT Now Here This , Deslouis, C, "Oxide/polypyrrole Composite Films for Corrosion Protection of Iron." J. Electrochem. Soc., 149 (12) 52-60 (2002) 17. Zarras, P, Anderson, N, Webber, C, Irvin, DJ, Irvin, JA, Guenthner, A, Stenger Smith, JD, "Progress in Using Conductive Polymers as Corrosion-inhibiting Coatings." Rad. Phy. Chem., 68 387-394 (2003) [c] FSCT FSCT Federation of Societies for Coating Technology FSCT Fire Support Control Terminal and OCCA OCCA Oklahoma Court of Criminal Appeals OCCA Oil & Colour Chemists' Association OCCA Oregon Community College Association OCCA Orthodox Catholic Church of America OCCA Organized Crime Control Act OCCA Open Cooperative Computing Architecture 2007 J. Alam, U. Riaz, S. M. Ashraf, S. Ahmad ([mailing address]) Materials Research Laboratory, Department of Chemistry, Jamia Millia Islamia Jamia Millia Islamia (Urdu: جامعہ ملیہ اسلامیہ, Hindi: जामिया मिलिया , New Delhi 110025, India e-mail: sharifahmad_jmi@yahoo.co.in
Table 1: Physico-mechanical characteristics of PANI/ferrite/alkyd
coatings
Drying time (h) Impact Scratch
Dry to Dry to resistance hardness
Resin touch hard (kg/[cm.sup.2]) (kg)
Alkyd 0.5 96 70 0.2
0.5 PANI/Alkyd 0.25 72 70 3
1.0 PANI/Alkyd 0.15 48 84 3.5
1.5 PANI/Alkyd 0.15 48 84 4
0.5-PANI/FERRITE-ALKYD 0.25 48 100 3.5
1.0-PANI/FERRITE/ALKYD 0.20 24 100 4.2
1.5-PANI/FERRITE-ALKYD 0.10 24 100 5
Flexibility
(1/8" inch
Conical Gloss (at
Resin Mandrel) 45[degrees]) Conductivity (S/cm)
Alkyd FAIL 85 -
0.5 PANI/Alkyd PASS 83 1.7 x [10.sup.-4]
1.0 PANI/Alkyd PASS 82 2.3 x [10.sup.-3]
1.5 PANI/Alkyd PASS 75 2.4 x [10.sup.-3]
0.5-PANI/FERRITE-ALKYD PASS 50 2.7 x [10.sup.-3]
1.0-PANI/FERRITE/ALKYD PASS 30 3.1 x [10.sup.-3]
1.5-PANI/FERRITE-ALKYD PASS 30 3.1 x [10.sup.-3]
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