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Now showing 1 - 4 of 4
  • Publication
    Effect on wear resistance of nanoparticles addition to a powder polyester coating through ball milling
    (Springer, 2018-05) Fernández Álvarez, María; Velasco López, Francisco Javier; Bautista Arija, María Asunción
    The wear properties of a textured polyester powder coating with pyrogenic silica nanoparticles addition were evaluated. Raw powders of a commercial, textured polyester organic coating were mixed with low amounts of SiO2 nanoparticles (0.5&-3 wt%) using ball milling, a simple and economical method. Nanoparticles were mixed into the powder of thermoset organic coating for 10 min in a two-body planetary ball mill. Particle size distribution of the powder was measured to evaluate the milling effect. The coatings were applied and cured in an industrial installation on aluminum substrates. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images of the coatings were taken to analyze the homogeneity of the organic coating. Roughness, gloss and color were measured in order to evaluate their appearance. The effect of nanoparticles on abrasive and erosion wear performances was measured. Pin-on-disk wear tests were carried out. Erosion measurements were performed with free fall of sand on the samples, a test based on ASTM D968 standard. The results showed that the milling process provides a good distribution of nanoparticles as no agglomerates were found. The addition of 0.5 wt% silica nanoparticles allows for improvement of the wear resistance of the coatings.
  • Publication
    Atmospheric pressure plasma hydrophilic modification of a silicone surface
    (Taylor & Francis, 2011-04) Encinas García, Noemí; Dillingham, R. G.; Oakley, B. R.; Abenojar Buendía, Juana; Martínez Casanova, Miguel Ángel; Pantoja Ruiz, Mariola
    The aim of this study was the creation of a silicone hydrophilic surface prior to bonding. Modifications in wettability and adhesion properties of silicone were performed with an atmospheric plasma torch (APPT). Surface energy variations of the substrate, both pristine and APPT-treated, were evaluated through contact angle measurements, studying the hydrophobic recovery of the samples up to 24 hours of aging. Compositional and topographical changes induced by APPT and aging were studied by attenuated total multiple reflection mode infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), mechanical profilometry, scanning electron microscopy (SEM), and atomic force microscopy (AFM), respectively. Adhesion pull-off tests were performed on silicone-aluminium stud joints using three commercial adhesives, which were Sikaflex®-252, polyurethane-based, Loctite®-330, urethane methacrylate ester-based acrylic, and Terostat®-922, modified silicone. Although experimental data of all the bonding specimens led to an undesired adhesive failure, it was found that APPT-treated samples gave higher adhesive strength than the pristine ones, which was explained by the higher surface energy, thus more wettable material, after APPT. This effect remained stable for just 1 h, when the substrate began its hydrophobic recovery, reaching the original surface energy values after 24 h of aging.
  • Publication
    Effect of EtOH/H₂O ratio and pH on bis-sulfur silane solutions for electrogalvanized steel joints based on anaerobic adhesives
    (Taylor & Francis, 2011-08-30) Pantoja Ruiz, Mariola; Martínez Casanova, Miguel Ángel; Abenojar Buendía, Juana; Encinas García, Noemí; Ballesteros, Y.
    A minimum hydrolysis time is required to get an adequate crosslinking between a silane film and a metallic substrate and that depends on the contents of silane, ethanol, and water in the silane solution. The objectives for this work are: 1) to study the effect of different ratios of ethanol/water on the hydrolysis time for a 1% bis-sulfur silane solution at pH 6, by attenuated total reflectance infrared spectroscopy. The different solutions studied correspond to different ratios of silane/ethanol/water by volume. The study was done following appearance of the siloxane and silanol groups and the disappearance of the ethoxysilane groups. 2) Also studied was the adhesion and corrosion behaviour of bis-sulfur silane (bis[3-(bis[3-(triethoxysilyl)propyl]disulfide, DS) in solutions of ethanol/water at pH 4 and 6 and γ-methacryloxypropyltrimethoxysilane (MPS) coatings obtained by a two-step process on galvanized steel samples. This coated surface was analysed by reflection absorption infrared spectroscopy (FTIR-RA), scanning electron miscroscopy (SEM), and polarization curves. Results obtained at pH 6 were compared with the ones for pH 4. Single lap shear tests were used to contrast the behaviour of anaerobic adhesives on electrogalvanized steel silanized samples. It was observed that higher hydrolysis time was necessary to get good adhesion behaviour if the solution was prepared at pH 4, while at pH 6 the best behaviour was observed for short hydrolysis times.
  • Publication
    Approaches to poly(tetrafluoroethylene) adhesive bonding
    (Taylor & Francis, 2011-08-30) Encinas García, Noemí; Pantoja Ruiz, Mariola; Martínez Casanova, Miguel Ángel; Torres Remiro, M.
    In this work, we present an approach to achieve improved adhesive bonding with a poly(tetrafluoroethylene) (PTFE) substrate. Surfaces were modified by abrasion, atmospheric air plasma torch (APPT) treatment, and by immersion in basic (NaOH) and strongly acidic/oxidizing (HNO3/KMnO4) solutions. The wetting properties of the polymer were studied in terms of surface energy, and adhesion tests were carried out using polyurethane, acrylic, and epoxy adhesives. The surface characterisation included surface energy calculation through contact angle measurements, infrared spectroscopy (FTIR-ATR), scanning electron microscopy (SEM), and X-ray electron diffraction (EDX). Adhesion was evaluated by pull-off tests following the UNE EN-24624 standard. Experiments revealed that both oxidation and plasma treatment enhanced surface energy, defluorination, and the creation of a rougher PTFE surface, resulting in adhesion. Simple oxidation and its combination with plasma treatments yielded the higher tensile strength results, with epoxy as the most suitable adhesive among those studied. Samples presented adhesive or mixed type failure modes.