1,720,979 research outputs found
Polypyrrole coatings on rheocast aluminum‐silicon alloy: A correlation between properties and electrodeposition conditions
No full textThe effect of the electrolyte composition and the deposition potential range on the physical properties and possible corrosion protection effect of polypyrrole coatings on rheocast aluminum–2.5 % silicon alloy is investigated. Solutions with different concentrations of sodium nitrate and an electron transfer mediator reagent were used for the electrodeposition. Polypyrrole coating is able to hinder the entrance of electrolyte. Upon the penetration of chloride ions, the coating can induce passivation of the alloy's surface by its reduction. The thickness of the coating and its ion‐barrier properties, controlled by the electrodeposition conditions, are shown as the important factors influencing the protection efficiency. However, localized drastic galvanic coupling at the polypyrrole/aluminum interface forms blisters, causes failure, and limits the possible protection
Deposition and Characterization of Cerium-Based Conversion Coating on HPDC Low Si Content Aluminum Alloy
Get PDFCerium-based conversion coatings were deposited on high pressure die cast (HPDC) Al-Si alloys using an immersion method. Hydrogen peroxide and sodium chloride were added to the conversion solution to accelerate the coating formation and to understand its formation mechanism. These studies showed that the deposition of cerium hydroxide/ oxide conversion layer starts from iron-rich intermetallic particles, which are located inside the eutectic region and then the coating growth continues to cover the entire alloy surface. This phenomenon passivates the active interfaces between iron-rich intermetallic particles and/ or the eutectic silicon phase and the aluminum matrix, which are prone to localized corrosion in chloride ions containing environments. Accordingly, values of the total impedance in EIS measurements significantly increased for the treated substrates. Morphologies of the conversion coatings and the oxidation state of cerium compounds were found to be dependent on the composition of the solution and the presence of chloride ions and/ or hydrogen peroxide. Aluminum alloy with higher silicon content showed a more active surface during immersion in the conversion solution. This makes it more difficult to be treated using aggressive conversion solutions.
New Pigments and Additives for Corrosion Protection by Organic Coatings
No full textThis eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contac
Advances in Organic Coatings 2018
Get PDFThe recent huge developments in nanotechnology and surface science are allowing the production of multifunctional coatings materials combining different properties: corrosion-protective actions, aesthetic functions, hydrophobic properties, self-healing abilities, etc. Moreover the increasing attention to environmental issues is driving the development of new systems, joining advanced performance with high sustainability, which can be better understood using new highly efficient experimental techniques. This frame is inducing us to consider the advances in organic coatings (the skin of materials) as one of the most interesting and promising innovation fields in material science and technology, with important consequences, not only considering fundamental aspects in science, but also for industrial applications, positively affecting everyday life. The aim of this Special Issue is to provide an update of the most advanced research in this area, showing the innovation trends and promoting further research for better properties of new coating materials
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Advances in Organic Coatings 2018
No full textThe recent huge developments in nanotechnology and surface science are allowing the production of multifunctional coatings materials combining different properties: corrosion-protective actions, aesthetic functions, hydrophobic properties, self-healing abilities, etc. Moreover the increasing attention to environmental issues is driving the development of new systems, joining advanced performance with high sustainability, which can be better understood using new highly efficient experimental techniques. This frame is inducing us to consider the advances in organic coatings (the skin of materials) as one of the most interesting and promising innovation fields in material science and technology, with important consequences, not only considering fundamental aspects in science, but also for industrial applications, positively affecting everyday life. The aim of this Special Issue is to provide an update of the most advanced research in this area, showing the innovation trends and promoting further research for better properties of new coating materials
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Environmentally friendly hybrid coatings for corrosion protection: silane based pre-treatments and nanostructured waterborne coatings
No full textThis thesis considers a nanotechnology approach based on the production of metals pre-treatments and organic coatings (a complete protection system at all) designed from the nanoscale. The final aim is to develop protection systems with improved corrosion protection properties and a low environmental impact. In particular, multifunctional silane hybrid molecules were used to design sol-gel pre-treatments for metals and to modify the inner structure of
UV curable waterborne organic coatings. In the first part of this thesis thin (hundreds of nanometers) sol-gel films consisting of an experimental mixture of hybrid silicon alkoxides molecules were applied onto aluminium and hot dip
galvanized (HDG) steel for the development of effective and environmentally friendly corrosion protection systems A chemical and electrochemical characterization of the sol-gel films highlighted their good corrosion protection properties both for aluminium and HDG steel. To test the effectiveness of the sol-gel coatings as coupling agent between metallic substrates and organic coatings (paints) both a powder coating paint and a cataphoretic coating paint
were applied on the silane pre-treated substrates. The electrochemical measurements and the accelerated tests carried out on these protection systems proved the capability of these sol-gel conversion coatings to improve the corrosion protection properties of the traditional protective cycles. The performance of the silane pre-treatments was also compared to commonly used surface conversion coatings for metals. The result of this comparison evidenced that the corrosion protection properties ensured by the sol-gel conversion treatment is comparable or higher than most of the commonly used pretreatments.
A study about the incorporation of inorganic nanoparticles into these sol-gel films gave evidences of an improved corrosion resistance due to the addition of certain amount of montmorillonite nanoparticles in the sol-gel matrix. The
same hybrid silicon alkoxide molecules used to perform the pre-treatments were used modify the inner structure of UV curable waterborne coatings in order to improve the corrosion protection properties maintaining the environmental compatibility of the protecting system. The design, application and characterisation of urethane, acrylic and epoxy waterborne UV curing coatings modified with the hybrid silicon molecules in order to obtain nanostructured waterborne films with improved corrosion resistance and thermomechanical properties were studied. The characterization proved the great potential of the silicon alkoxide molecules as a tool to modify the properties of the organic matrix of the paint: silicon alkoxides can promote the self assembly of inorganic nanoparticles into the matrix or can act as an effective coupling agent between inorganic nanoparticles and the polymeric matrix. Silicon alkoxide molecules were proved to be an efficient tool to design a protection system from the nanoscale leading to the prospective of an accurate control of the overall properties of the macroscopic systems
Micro- and Nanostructured Polymeric Materials for art protection and Restoration
No full textIn the restoration field the synthetic resins are commonly used and they are selected in order to replace natural products and possibly overcome their drawbacks. Nevertheless, these resins are not completely able to cover the specific mechanical properties required in each restoration work. The main aim of this research is the development of innovative micro/nanocomposite materials with enhanced features for artwork conservation operations. The introduction of appropriate amounts of micro- and nanofillers within commercially available art preserving polymers may allow the improvement of their mechanical deficiencies, without impairing their physical and chemical properties.
Cellulose microcrystals (CMC) and nanocrystals (CNC) were selected as natural reinforcing fillers for a commercial acrylic copolymer (Paraloid B72) widely applied as a consolidant of wooden objects and two molecular weights of a thermoplastic water soluble adhesive used in the restoration of oil paintings (Aquazol 200 and 500). In particular, melt-compounded Paraloid and Aquazol based microcomposites with various amounts (5÷30 wt%) of CMC and thin films of Aquazol 500 micro- and nanocomposites produced by the solution mixing method with a CMC and CNC content of 5-10-30 wt% were investigated. Several characterization techniques were used in order to assess the effect of micro- and nanocellulose on the physical and thermo-mechanical behavior of these three thermoplastic polymers.
In the first part of the work, the characterization of melt-compounded and compression molded microcomposites under dry and conditioned state (T= 23°C, RH= 55%) was performed. All dried and wet formulations showed a similar stabilizing effect of CMC flakes with an increase of elastic modulus and a decrease of thermal expansion coefficient and creep compliance, regardless of the moisture content. Interestingly, conditioned composites
exhibited the enhancement of the tensile properties at break, in contrast to
dried microcomposites that reported a drop in these properties. On the other hand, the highest amount of CMC led to a chromatic change of the three matrices towards yellow-brown tones.
In the second part of the work, the characterization of solution mixed micro and nanocomposites based on Aquazol 500 highlighted the systematic increment of the dimensional stability of the neat resin due to the presence of both CMC and CNC particles. Remarkably, CNC proved to be more effective than CMC in increasing of the stiffness and the elongation at break of Aquazol as the filler loading increased, without impairing the good optical properties of this material.
In the third part of the work, the application of melt-compounded Paraloid/CMC composites as consolidants for damaged wood was investigated. CMC introduction did not change the good viscosity of the neat matrix and especially its good water repellency. Wood samples treated with microfilled Paraloid exhibited an increment of the stiffness and the flexure strength under quasi-static and impact conditions and, additionally, a systematic enhancement of the radial and tangential surface hardness almost up to the intact wood values was observed.
In the last part of this thesis, the practical application of CMC and CNC Aquazol based adhesive films made by melt-compounding and solution mixing was investigated for the lining of oil paintings. Single-lap shear tests confirmed the stabilization action of both CMC and CNC particles on all experimental formulations with a progressive reduction of the compliance proportionally to the filler loading. Even in this case the increment of the Aquazol dimensional stability was mainly imparted by the presence of CNC. Only for solution mixed CMC composites a dramatic drop in the adhesive strength as the filler content increased was detected
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