Sandra H. Messaddeq

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.

Above bandgap induced photoexpansion and photobleaching in Ga-Ge-S based glasses

Abstract Photoexpansion and photobleaching effects have been examined in glass compositions Ga10Ge25S65 and Ga5Ge25As5S65. Such compositions are promising for optical storage and planar waveguide applications. To evaluate the photoinduced effect, samples were exposed to 351 nm light, varying power density (3–10 W / cm 2 ) and exposure time (0–120 min). The exposed areas have been analyzed using atomic force microscopy (AFM) and an expansion of 800 nm is observed for composition Ga10Ge25S65 exposed during 120 min and 5 W / cm 2 power density. The optical absorption edge measured by a spectrophotometer indicates a blue shift (80 nm) after illumination in the composition Ga10Ge25S65. The morphology was examined using a scanning electron microscopy (SEM). The chemical compositions measured using a energy dispersive analyzer (EDX) indicate an increase of the number of sulfur atoms in the irradiated area.

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.

Local order around of germanium atoms in Ga10Ge25S65 glass by EXAFS

Abstract Irreversible photoexpansion effect has been observed in amorphous Ga 10 Ge 25 S 65 glasses when its surface was exposed to light with energy greater than the band gap, 3.52 eV. A volume change of about 5% was reached in bulk samples by controlling illumination time and the laser power density. To understand the atomic scale processes of the photoexpansion effect, extended X-ray absorption fine structure (EXAFS) spectroscopy has been used as a local probe of the germanium environment in the glass samples before and after illumination. Modifications are observed in the average coordination shell around Ge atoms in the illuminated sample compared to the non-illuminated one. For the non-illuminated sample, the Ge coordination shell is described by a distorted tetrahedron of sulfur atoms at around 2.20 A. After illumination, the EXAFS signal can be explained by introducing an additional contribution to this average environment. Based on an analysis of the EXAFS data we proposed a two-shell model of 0.5 oxygen atoms at 2.01 A and 3.6 sulfur atoms at a 2.20 A. The existence of Ge–O bonds in the glass after illumination was confirmed by infrared measurements.

Formation of cross-superposed LIPSSs on bulk chalcogenide glasses using fs-laser

Abstract This paper reports the formation of laser-induced periodic surface structures (LIPSS) observed on the ablated surface of bulk As2S3 chalcogenide glasses produced after irradiation by a focused beam of femtosecond Ti:sapphire (fs)-laser (1 kHz, 100 fs, 800 nm). By controlling the irradiation condition of fs-laser, high spatial frequency LIPSS (HSFL) ripples parallel to polarisation of the incident light are formed. Nanovoids with an average diameter of ~300 nm and depth of 200 nm also appear between the ripples. Furthermore, we show a transition from the HSFL features toward the formation of low-spatial-frequency LIPSS (LSFL) with an intermediated complex structure of ripples, which are oriented simultaneously parallel and perpendicular to the polarisation of the incident light that we call cross-superposed LIPSSs.