AISI 304 Stainless Steel is widely used in different industrial fields because of its mechanical and corrosion properties.
However, its tendency to corrosion in presence of halide ions limits the applications. One strategy to improve the corrosion
resistance is the use of coatings barriers containing corrosion inhibitors in their formulation. The lanthanides present attractive
green and corrosion properties for the substitution of chromates, which are the most common substances used as corrosion protection.
However, these compounds are highly toxic, and an intense effort is being undertaken to replace them. Cerium is a good alternative
because of its relatively low cost and abundance. It fulfils the basics requirements for being considered an alternative inhibitor:
the ions form insoluble hydroxides and they present low toxicity. Inorganic and hybrid sol-gel coatings have been developed
to increase the corrosion resistance of metals and they provide an excellent vehicle for the incorporation of secondary phases
including particles and metal ions as cerium ions.
The aim of this work was to study the influence of the incorporation of cerium ions in hybrid silica sol-gel coatings deposited
on AISI 304 stainless steel as substrate as a potential replacement of chromate treatments. This system should combine the
barrier protection effect of silica coating with the corrosion inhibitor effect of the cerium ions inside the coatings. After
7 days of immersion in NaCl, coated substrates showed lower current densities than the bare steel, although the coatings produced
from Ce (III) salts experience a slight weakening in time and those obtained from Ce (IV) chemicals evidence an enhance in
the coating performance, probably due to the plugging of corrosion products in the defective areas of the film. 相似文献
Functional coatings incorporating different types of particles developed by the sol–gel method have been proposed in the last few years for diverse applications. This work focuses on the preparation of homogeneous coatings prepared from stable suspensions with 10 wt% of glass and glass ceramic particles in a hybrid organic–inorganic solution as dispersing media. For this purpose, the pH was shifted up to 6–7 by adding tetrapropylammonium hydroxide (TPAH) which behaves as a cationic surfactant being probably adsorbed on the particles surface, while the sol maintains stable. Rheological measurements were performed to study the stability of the suspensions prepared at different conditions such as the kind and concentration of dispersant and the pH conditions. After sintering at 450∘C/30 min, coatings around 2 μ m in thickness were obtained. 相似文献
Due to its mechanical properties and ease of use, vinyl ester resin is enjoying increasing consideration. This resin normally is produced by reaction between epoxy resin and unsaturated carboxylic acid. In the present study, bis-phenol A based epoxy resin and methacrylic acid was used to produce vinyl ester resin. The reaction was conducted under both stoichiometric and non-stoichiometric conditions in the presence of triphenylphosphine as catalyst. The stoichiometric and non-stoichiometric experiments were conducted at 95, 100, 105 and 110℃and at 90 and 95℃, respectively. The first order rate equation and mechanism based rate equation were examined. Parameters are evaluated by least square method. A comparison of mechanism based rate equation and experimental data show an excellent agreement. Finally, Arrhenius equation and activation energy were presented. 相似文献
UV curable epoxy acrylates were reinforced with two different organically modified montmorillonites (MMTs) and an unmodified MMT. Conversion and rate of polymerization was monitored by real time infrared spectroscopy (RTIR) and photo-DSC. Microstructures were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and optical clarity. Optical clarity of the films containing clay was quite good as only a slight decrease was observed. Physical properties of the reinforced films were examined by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), hardness and tensile testing. Enhancements in glass transition temperature (Tg), thermal stability and mechanical properties were observed. The films reinforced with the unmodified MMT exhibit the most significant enhancements in properties. 相似文献
A new technique has been developed to prepare a highly filled epoxy-montmorillonite (MMT) nanocomposite using an organically modified MMT. Composites with clay content up to 70 wt.% exhibit unusual transparency, which is related to the spatial distribution of the mineral nanodomains. Dispersion of the layered silicate within the crosslinked epoxy matrix was verified using X-ray diffraction pattern, revealing layer spacings of 30 and 70 Å. Examination of these materials by scanning electron microscopy and transmission electron microscopy showed that intercalates have wholly layered morphology at all scales, oriented parallel to the surface of the specimen and have good wetting to the silicate surface by the epoxy matrix. Silicate lamellae intercalated with epoxy resin assembled into a cluster of about 50-120 nm thickness. These clusters assembled into superclusters with an average thickness of 300 nm. Studies by the Vickers hardness test of an epoxy-MMT nanocomposite containing 60 wt.% MMT indicated that the diamond pyramid hardness was 10-29 kg/mm2. 相似文献
Epoxy-timber composites have received increasing attention during the last decades because there are many advantages related to their uses as construction materials in applications such as timber bridges. However, the durability of epoxy-timber composites under outdoor conditions has become a concern for many epoxy resins. This study evaluated the chemical, thermal, and mechanical properties of two cured epoxies, the product of the diglycidyl ether of bisphenol A with 2,4-trimethyl-1,6-hexanediamine (DGEBA-TMDA) and the analogous resin prepared with the hydrogenated diglycidyl ether of bisphenol A (HDGEBA-TMDA), each mixed with 2?wt. % calcium sulfate (CS). We hypothesized that the use of CS, as an inorganic UV absorber, could decrease undesirable effects arising from exposure to UV light, moisture, and extreme temperatures.
An accelerated aging chamber simulated natural weathering for 1, 2, 3, 4, and 6?months. Chemical changes in cured epoxy systems over time in the presence and absence of CS fillers were determined using Fourier transform infrared spectroscopy (FT-IR). Thermal degradation profiles before and after exposure to accelerated weathering were followed by thermogravimetric analysis (TGA). The glass transition temperatures (Tg) before and after accelerated weathering were measured, and the effect of accelerated weathering on the surface morphology of the epoxy systems was investigated by scanning electron microscopy (SEM). In the presence of CS, after 6?months accelerated weathering the tensile strength of DGEBA-TMDA reduced by 23.8?±?2.4%, compared to 46.5?±?5.5% in its absence, while the corresponding values for HDGEBA-TMDA were 21.4?±?2.1% and 28.7?±?1.8%. 相似文献