SÃO PAULO STATE UNIVERSITY- UNESP INSTITUTE OF CHEMISTRY - ARARAQUARA, BRAZIL Highly corrosion resistant organic-inorganic hybrid coatings prepared using the sol-gel process P. Hammer*, F. C. dos Santos, S. V. Harb, C. V. Santilli *peter@iq.unesp.br
Corrosion prevention Introduction Surface protection: hexavalent chromium conversion Cr 6+ toxic! Anti corrosion coatings: o Organic paints o Ceramic films o Organic inorganic hybrid coatings
Introduction Organic-inorganic hybrids: Siloxane-PMMA Combined properties of polymeric e ceramic materials: - processability - mecanical - flexibility - thermal - transparency - chemical stability - hydrophobicity - adhesion Sol-Gel process: Inorganic Hybrid Organic Precursor solution Alkoxi-silane Methylmethacrylate Nanoparticles Powder Bulk material Fibers Coatings
Organic-inorganic hybrids: Siloxane-PMMA Introduction Classe II hybrids: Covalentes bonds between the organic and inorganic phase: Organic Inorganic Aplications: Optoelectronic devices Drug release systems Transparent insulating coatings Corrosion resistant coatings Dense barrier against corrosion
Objective Investigation the relation between the structural properties and corrosion protection efficiency of Syloxane-PMMA hybrid coatings deposited on carbon steel
Siloxane-PMMA hybrid preparation Experimental Precursor: Organic Inorganic MMA : MPTS : TEOS = 4 : 1 : 2 M4 Ethanol : H 2 O = 0.0 0.2 0.5 0.7 1.0 E00 E02 E05 E07 E1 + Methylmethacrylate Alkoxi-silane: Tetraethoxysilane Structrural analysis Corrosion tests + MPTS stirring heat HNO 3 + H 2 O (ph 1) + Eth Synthesis 3 dips Dip-coating 55 C / 24 h, 160 C / 3 h Curing
Siloxane-PMMA hybrid preparation Experimental Influence of Eth/H 2 O ratio on the Inorganic phase Solution Tetraethoxysilane Hydrolysis: Condensation:
Characterization methods Experimental Structural and morfogogical analysis Atomic Force Microscopy (AFM) Nuclear Magnetic Resonance (RMN) Thermogravimetric analysis (TG/DTG) X-ray Photoelectron Spectroscopy (XPS) Corrosion analysis Electrochemical Impendance Spectroscopy (EIS) Potentiodynamic Polarization Curves XPS
Structural analysis AFM: M4E02 coating Results RMS Roughness: < 0.4 nm Film thickness: 1.5-2.0 µm Adhesion to A1010: > 8 MPa pull-off force
Structural analysis Thermogravimetic Analysis: TG/DTG Results Random scission Scission Vinyliden end Silanol dehydration
Results Structural analysis Thermogravimetic Analysis: DTG Organic phase: Polimethyl methacrylate (PMMA) T 1 T 2 Scission of vinylidene end Random scission Silanol dehydration Improvement of the hybrids stability for higher Eth/H 2 O ratios
Structural analysis NMR 13 C 13 C NMR indicates a complete polymerization of the organic phase MMA Results PMMA c c b a b a
Structural analysis NMR 29 Si MPTS TEOS Results Highest policondensation degree of 83% for Eth/H 2 O = 0,5 C d = [(T 1 + 2T 2 + 3T 3 ) / 3 + (Q 1 + 2Q 2 + 3Q 3 + 4Q 4 ) / 4] x 100
Structural analysis XPS C 1s, O 1s Si 2p spectra: Results Composition: MMA:MPTS:TEOS = 4:1:2 C: 58.7 O: 34.8 Si: 6.5 at.% Bonding structure: Syloxane-PMMA MPTS MMA CH 3 CH 3 R C CH 2 C CH 2 n O C O C O O H 2 C H 3 C HC O CH 2 O Si O Si O O O SILOXANE (TEOS)
Structural analysis XPS: Si-O peaks Si 2p vs. O1s Results NMR C d vs. XPS Si 2p Correlation between NMR hybrid connectivity, C d, and XPS Si-O binding energies Most stoichiometric SiO 2 phase for Eth/H 2 O = 0,5
Results Corrosion analysis EIS results: 3.5% NaCl solution, 1d Corrosion resistance: > 1 GΩ Broad band 10-10 4 Hz, Φ H 90 M4E02 > M4E05 > M4E...>> Steel M4E02: C d = 82%, Si-O = 103.4 ev
Corrosion analysis EIS results vs. Immersion time: 3.5% NaCl > 6 months Results M4E02 with best long-term saline performance Excellent corrosion resistance after 196 days exposure Stability of all other samples > 40 d
Corrosion analysis Results EIS results: 0.05 mol L -1 NaCl + 0.05 mol L -1 H 2 SO 4 > 3 months M4E02 with best long-term acidic/saline performance Excellent corrosion resistance after 105 days exposure
Corrosion analysis Results EIS results: Equivalent circuit M4E05 Diffusion controlled process: one HF time constant - constant phase element, R ohm - Warburg element
Results Corrosion analysis Potentiodynamic Polarization Curves in 3% NaCl solution E05 sample with current density < 10-10 A cm -2 Current density 10 8 times lower than carbon steel No rupture at overpotential Efficient corrosion protection by cross-linked hybrid structure
Conclusions Results and discussion Sol-gel Siloxane-PMMA coatings are crack-free, smooth and have good adhesion and thermal stability 15 NMR results show highest degree of polycondensation (83%) for intermediate Eht/H 2 O ratios (M4E05) indicating the formation of a highly cross-linked hybrid network Clear correlation between the NMR network connectivity (C d ) and the XPS Si-O binding energies of the inorganic phase High corrosion resistance (> 1 GΩ) and long-term stability (>66 weeks) of the coatings can be explained by the formation of a dense, highly cross-linked hybrid network which hermetically seals the steel surface Siloxane-PMMA coatings: environmentally compliant substitutes of chromate-based corrosion inhibitors
Results and discussion 15 ACKNOWLEDGEMENTS
Film failure Results and discussion Microscopy and XPS: M4E05, immersion 50 d NaCl 15