Mohamed Atik

Investigation of new ion-conducting ORMOLYTES : structure and properties

Two families of hybrid organic-inorganic composites exhibiting Li+ ionic conduction (ORMOLYTES) have been prepared by the sol-gel process. The first family, prepared from a mixture of 3-isocyanatopropyltriethoxysilane, O,O′ Bis (2-aminopropyl)-polyethyleneglycol (or O,O′ Bis (2-aminopropyl)-polypropyleneglycol) and lithium salt, presents chemical bonds between the organic and the inorganic phase and an ionic conductivity σ higher than 10-4 S m-1 at room temperature. Their properties have been related to their structure using liquid state NMR measurements of 7Li between -100°C and +100°C and the DMTA technique. In the second family, prepared by ultrasonic method from a mixture of tetraethoxysilane (TEOS), polyethyleneglycol (PEG) and lithium salt, the organic and inorganic phases are not chemically bonded. Ionic conductivity σ has been studied as a function of the polymer chain length and concentration. Values of σ up to 10-2 S m-1 at room temperature have been obtained (with a silica-PEG300 system, PEG/TEOS = 40% in weight). Again, structure was investigated by liquid state 7Li NMR measurements.

Sol-gel thin films for corrosion protection

The preparation of sol-gel coatings with specific chemical functions offers potential advantages over traditional methods as it offers tailoring of their structure, texture and thickness and allows the fabrication of large coatings. The chemical protection of 316L stainless steel has been verified for ZrO2, TiO2SiO2 and Al2O3SiO2 coatings. The anticorrosion behavior of the films have been characterized in acidic and basic media by weight and loss, electrochemical techniques, XRD and FTIR and SEM spectroscopic techniques. Analysis of the data indicates that the films act as geometric blocking layers against exposure to the corrosive media and increase drastically the lifetime of the substrate (for instance up to 10 for stainless steel).

Sol-gel ZrO2 coatings for chemical protection of stainless steel

ZrO2 coatings deposited on 316 L stainless steel sheets were synthesized by sol-gel method using Zr(OC3H7)4 as precursor and isopropanol, glacial acetic acid, and water as solvents for application with ultrasounds. Different solutions for dip-coating were prepared with compositions varying between 0.025 and 0.9 mol/dm3 of ZrO2. X-ray diffraction shows that the films densified at 800°C are crystalline with a tetragonal structure. The thickness of the coatings varied from 0.35–0.75 μm. The influence of the ZrO2 coatings on the corrosion behavior of stainless steel substrates in aqueous NaCl was studied through potentiodynamic polarization curves at 1 mV/s. The values of the electrochemical parameters allow for an explanation of the role of the films in the increased resistance of steel against corrosion in moderately aggressive environments.

Protection of 316L stainless steel against corrosion by SiO2 coatings

Oxide films prepared by sol-gel methods and presenting high resistance to heat, corrosion, friction and wear, as well as excellent mechanical properties, have recently been developed and put into practical use as structuraI materials [1-5]. The process of preparation offers potential advantages for modifying the properties of surfaces by low-temperature treatment without altering the original properties of strength and toughness of the substrates. A number of reports on sol-gel coatings concerning the prevention of chemical corrosion and oxidation have been published [6-10]. All of these films increase the protection of metal substrates from air corrosion (tested up to 800 °C) and acid attack (tested up to 80 °C). The most promising corrosion prevention for stainless steel has been studied by our group using sol-gel films of ZrO2, SiO2, SiO2-TiO2 and SiO 2A1203 prepared by dip-coating using sonocatalysed sols [11-14]. The. properties of these coatings have been studied by electrochemical techniques in NaC1 and H2SO 4 solutions. Although preliminary measurements have shown that SiO2 films are not the best protective coatings [13], they provide a very adequate model system to correlate corrosion protection with the physical structure of the sol-gel films. In this work, amorphous coatings of SiO 2 were deposited on 316L stainless steel by the dip-coating technique using a sol preparation involving sonocatalysis. The films were prepared through hydrolysis polymerization of metal alkoxide solutions and conversion to an oxide layer by heating at relatively low temperatures. The effect of the time of heat treatment of the SiO2 films on the corrosion resistance of stainless steel was studied in 15% H2SO 4 through potentiodynamic polarization curves at 25 °C. The substrate used in the experiments was 316L stainless steel (SS 316L, Caseurop, France) with chemical composition (wt %): 67.25 Fe, 18.55 Cr, 11.16 Ni, 2.01 Mo, 0.026 Cu, 1.71 Mn and 0.028 C. The specimens were machined into dimensions of 30 mm × 15 mm x I mm, degreased ultrasonically in acetone, cleansed by distilled water then dried in air. For silica films, tetraethylorthosilicate Si(OC2H5) 4 (TEOS) was used as the source of silica, absolute ethanol (C2HsOH) as solvent and glacial acetic acid CH3COOH as catalyst. The silica sonosol was prepared by dissolving Si(OCzHs) 4 in absolute ethanol to which a small amount of acetic acid CH3COOH was added. The volume ratios of Si(OC2Hs)4/C2HsOH and Si(OC2Hs)4/CH3COOH were, respectively, 1 and 5. The mixture was submitted to intense ultrasonic irradiation (20 kHz) produced by a transducer (Heat Systems Ultrasonics W385). After 25 min the resulting sol was homogenized and remained stable for about five weeks at room temperature when kept in a closed vessel. Coating films were formed on the substrates by dipping into the clear sonosol and withdrawing at a speed of 10 cmmin -1. The resulting gel films were dried at 60 °C for 15 min and densified in a furnace with air atmosphere by increasing the temperature at a rate of 5 °C min -1 up to 450 °C when an isothermal holding of 1 h was applied in order to remove the organic residues. The temperature was then increased again at the same rate up to either 600 or 800 °C and maintained at that value for variable lengths of time to complete the densification and obtain adherent coatings. The average thickness of the heat-treated films at 800 °C was around 0.4/zm. X-ray diffraction (XRD) analysis of the substrate and coatings was done with a Philips diffractometer using CuKo, The diffractogram of SS 316L shows the existence of a crystalline phase which corresponds to the cubic phase of the alloy containing Cr, Fe and Ni [4]. When the steel was heated at 800 °C for 2 h in air, additional XRD peaks appear corresponding to a mixture of cubic and hexagonal CrzO 3 [4]. In contrast, samples coated with SiO2 analysed after oxidation tests in air at 800 °C for 2 h showed only the peaks of the original substrate, indicating that the silica coating remains amorphous and inhibits any oxidation of the base material. A Bomem Fourier transformation infrared (F-FIR) spectrometer was used to obtain high resolution spectra of the coatings in the 400-4000 cm -1 range; the measurements were carried out at room temperature by reflection at an incident angle of 30 ° . The spectrum of a coating deposited on SS 316L and

Electrochromism in materials prepared by the sol-gel process

Electrochromism is defined as the persistent but reversible optical change (usually transmission) produced electrochemically. The preparation by the sol-gel process of thin films made of amorphous or crystalline nanoparticles of WO3, V2O5, Nb2O5, TiO2, CeO2, Fe2O3 and mixed compounds such as WO3-TiO2, CeO2-TiO2, CeO2-SnO2, have opened remarkable new opportunities for obtaining electrochromic layers exhibiting large optical transmission variation in the UV, visible or infrared range and acceptable kinetics under H+ or Li+ insertion. In this paper we give an overview of what has been recently achieved in this field, with emphasis for cathodic electrochromic coatings of Nb2O5 and TiO2 composition. Finally we stress the future developments in this fast growing field.

Sol-gel TiO2-SiO2 films as protective coatings against corrosion of 316L stainless steel in H2SO4 solutions

Sol-gel TiO2-SiO2 films were deposited on 316L stainless steel by dip coating process from a sono-catalysed sol of composition 30TiO2-70SiO2 prepared from a mixture of Ti(OC2H5)4 and Si(OC2H5)4, absolute ethanol C2H5OH and glacial acetic acid CH3COOH as precursors and solvents. The films, densified at 800° C in air for 2 h, are composed of small orthorhombic titania (anatase) crystallites embedded in a SiO2 amorphous matrix as identified by X-ray diffraction. The temperature dependence of the film morphology was observed using scanning electron microscopy (SEM) and the content was determined by FTIR reflection spectroscopy. The corrosion behaviour of 316L stainless steel samples coated with densified 30TiO2-70SiO2 films was studied in 15% H2SO4 by potentiodynamic polarization curves at 25, 40 and 50°C. The measured corrosion rates show a considerable decrease for the protected steel samples in comparison to the bare substrate. The effect of time of heat treatment of the films on the corrosion parameters is also reported.

Ormocer (ZrO2-PMMA) Films for Stainless Steel Corrosion Protection

The chemical protection of 316 L stainless steel coated with ORMOCER coatings of polymethylmethacrylate (PMMA) and ZrO2 has been verified. The coatings were dip-coated on the substrates from sols prepared by mixing zirconium propoxide (ZrOC3H7)4, isopropanol (C3H7OH), glacial acetic acid (CH3COOH), polymethylmethacrylate and water under application of ultrasounds. The films were heat treated between 40 and 300°C in air up to 20 h. Their morphology was studied by electron scanning microscopy (SEM). Their anticorrosion behavior was analysed in 0.5M-H2SO4 solutions through potentiodynamic polarization curves at room temperature.The influence of the sol preparation, coating composition as well as of the duration and temperature of heat treatments on the corrosion parameters is reported. The films act as geometric blocking layers against the corrosive media and increase the lifetime of the substrate up to a factor 30.

Sol-gel coatings for chemical protection of stainless steel

Sol-gel thin coatings of ZrO2, SiO2, 70SiO2-30TiO2 and 88SiO2-12Al2O3 compositions (mole %) have been prepared from sonocatalyzed sols and deposited by dip-coating technique on 316L stainless steel foils. The influence of the coatings on the chemical corrosion of the substrate has been measured through potentiodynamic polarization curves in aqueous 15% H2SO4 solution between 25 and 50°C. The values of the corrosion potential, polarization resistance and corrosion rate have been determined. Analysis of the data combined with scanning electron microscopy studies indicate that the films act as a geometric blocking against exposure to the corrosive media and increase the lifetime of the substrate up to a factor 8.5.

Zirconia sol-gel coatings deposited on 304 and 316L stainless steel for chemical protection in acid media

Corrosion resistance is one property that many industries require for materials that are used in their equipment and components. Some researches have reported on corrosion behaviour in aqueous acid or basic solutions of steels, metals and alloys protected by sol-gel coatings [1-4]. Sol-gel films of zirconia, silica and mixed oxides of SiO2-TiO2 and SiO2A1203 prepared by dip-coating using sonocatalysed sols have been shown as promising coatings to prevent against corrosion of stainless steel [5-10]. All these inorganic films improve the chemical and physical properties and increase the protection of metal substrates from air corrosion, basic and acid attack. The alm of this work is the preparation of ZrO2 films coated on 304 and 316L austenitic stainless steel (SS) substrates, materials widely used for marine and chemical industry environments, and deposited by a dip-coating technique using a sol preparation involving sonocatalysis. The sols were obtained by hydrolysis and polymerization of Zr alkoxide, Zr(OC3H7)4, dissolved in alcohol, C3H7OH, acetic acid, CH3COOH, and water solutions. This technique leads to the development of homogeneous sols for gel coatings without cracks. The corrosion characteristics of the samples were evaluated through potentiodynamic polarization curves measured in 15% H2804 solutions at room temperature. Zirconium propoxide, Zr(OC;H7)4, was used as the source of zirconia. The sol was prepared by diluting the alkoxide in isopropanol, C3H7OH, to which was added glacial acetic acid, CH3COOH, as catalyst and distilled water. The concentration of the starting alkoxide solution was 0.5 moll 1 and the volume ratios of H20:C3HTOH and H20:CH3COOH were 1 and 2, respectively. The solution was homogenized with ultrasound irradiation produced by a transducer immersed in the mixture (Heat Systems Ultrasonics W 385 Sonicator, 20 kHz). After hydrolysis the resulting sols were clear, transparent and stable for five weeks at room temperature. The substrates used in the experiments were 304 and 316L austenitic stainless steels, their chemical compositions (wt%) are shown in Table I. These materials were chosen, taking into account the heat treatment necessary for densification of the coatings, because the materials have low carbon contents and are less susceptible to sensitization that promotes enhanced corrosion. Chemical analyses of the samples show that 304 SS has less amounts of Mo (0 wt%). The specimens were machined into the dimensions of 30 x 20 x 0.4 mm, degreased ultrasonically in acetone and rinsed with distilled water. They were dipped into the solution and withdrawn at a speed of 10cmmin -1. The gel coated SS were dried in ambient atmosphere for 15 min at 60 °C and then densified in a furnace in air atmosphere, increasing the temperature at a rate of 5 °Cmin -1 with two isothermal holdings, first at 450 °C for 1 h and then at 800 °C for 2 h in air to obtain adherent and dense coatings. Their thicknesses measured by ellipsometry, varied between 0.35 to 0.8 ~m, depending on the sol concentration. The average thickness of the heat-treated film at 800 °C was around 0.5 #m. X-ray diffraction patterns of the coatings were recorded with a Philips diffractometer with a Cu K« irradiation (wavelength, 2 = 0.154 18 nm). A Bomen Fourier transform infrared (FTIR) analyser was used to obtain high resolution optical reflection spectra of the coatings in the range 400-4000cm -1 a t an incident angle of 30 °. For the corrosion, the potentiodynamic polarization curves for each of the test specimens were carried out in deareated 15% H2SO4 at 25 °C using a computerized PAR model 273 potentiostat/galvanostat; the geometric areas of the specimens under evaluation were similar. A saturated calomel electrode (SCE) was used as reference and a Pt foil served as the auxiliary electrode. The working electrodes were 304 or 316L SS plates, either bare or coated, immersed 1 cm into the solution. The potentiodynamic measurements were initiated at -1 .0 V versus the SCE and scanned continuously in the anodic direction at a rate of 1 mVs -1. The data were analysed with PAR model 352 Corrosion Measurements software.

Preparation, characterization and properties of new ion-conducting ORMOLYTES

Two families of hybrid organic-inorganic composites exhibiting ionic conduction properties, so called ORMOLYTES (organically modified electrolytes), have been prepared by the sol-gel process. The first family has been prepared for a mixture of 3-isocyanatopropyltriethoxysilane (IsoTrEOS), O,O{prime} Bis (2-aminopropyl)polyethyleneglycol and lithium salt. These materials present chemical bonds between the organic (polymer) and the inorganic (silica) phases. The second family has been prepared by an ultrasonic method from a mixture of tetraethoxysilane (TEOS), polyethyleneglycol and lithium salt. The organic and inorganic phases are not chemically bonded. The Li{sup +} ionic conductivity has been studied by AC impedance spectroscopy up to 100 C. Values of {sigma} up to 10{sup {minus}4} Scm{sup {minus}1} have been found at room temperature. The conduction properties have been related to the materials structure using linewidth and relaxation times NMR measurements of {sup 7}Li between {minus}100 C and 90 C. A systematic study has been done changing the lithium concentration, the polymer chain length and the polymer to silica weight ratio. The structures and the ionic conduction properties of both families are compared with emphasis on the nature of the bonds between the organic and inorganic components.