1,720,994 research outputs found
SYNTHESIS AND CHARACTERIZATION OF ELECTROLESS Ni-P ALLOYS FOR ANTI-WEAR AND ANTI-FOULING COATINGS
No full textIntroduction: Fouling is a typical problem in compressors used for processing
of hydrocarbon gasses and it is caused by solids adsorption onto the internal
surfaces of the machinery. This phenomenon can influence the performance of the facility and, in some
cases, it causes the stop or the failure of the system. Surface coating can be a
suitable solution to this kind of problem.
Anti-fouling and anti-wear coatings can be obtained by electroless-nickel
plating technique. It allows for depositing very uniform and dense Ni-P alloy
coatings on irregular shaped surface and on different kind of substrate.
Materials and methods: Ni-P amorphous alloy was deposited on a steel
substrate. The electroless plating bath is an acid solution and consists of
a nickel source, a reducing agent (P compounds), stabilizing agents and a
buffer. The temperature and the pH were continuously monitored during
the deposition and kept constant. Plating parameters were optimized and
several coatings were deposited. Nano-particles were added in order to improve
the performance of the coating, in particular particles of polytetrafluoroethylene
(PTFE) were chosen to improve anti-fouling behavior while
nano-zirconia particles were added to improve wear resistance. In order
to prevent agglomeration of nano-ZrO2, nano-particles were previously
surface modified with methacrylic acid. Ni-P coatings were characterized
through SEM imaging and EDS analysis. Coating thickness and roughness
were measured. Top view and cross section Vickers hardness was evaluated.
The morphology of the samples was compared through a surface
profilometry analysis. The wettability was evaluated considering the drop
contact angle for different fluids.
Results: All deposited coatings (Ni-P, Ni-P with ZrO2, Ni-P with PTFE, Ni-P
with ZrO2 and PTFE) are dense layers with a very good adhesion with the
substrate. As expected the morphology of the coating follows the morphology
of the substrate. SEM micrographies show an optimal dispersion and
distribution of nano-particles. Nano-zirconia addiction allows for obtaining
small values of roughness and high values of Vickers hardness. Nano-ZrO2
and PTFE particles cause a reduction of drop contact angle for different
fluid. In particular PTFE results to be more beneficial for a decrease of the
wettability.
Discussion: Electroless Nickel Plating technique was well optimized resulting
in dense coatings and good rate of deposition. The results show improvements
of the desired coating properties in particular when PTFE and ZrO2
are both added
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Diffusion aluminide coatings for hot corrosion and oxidation protection of nickel-based superalloys. Effect of fluoride-based activator salts
Full text linkThe influence of two different fluoride-based activator salts (NH4F and AlF3) was studied for diffusion aluminide coatings obtained via pack cementation on a Ni-based superalloy (René
108DS). The resistance to oxidation and hot corrosion was assessed as a function of the concentration of activator salts used during the synthesis process by means of pack cementation. Two different concentrations were selected for activator salts (respecting the equimolarity of fluoride in the synthesis) and the obtained diffusion coatings were compared in terms of morphology, thickness and composition, as well as in terms of microstructural evolution after high temperature exposure. Isothermal oxidation tests were conducted at 1050 C in air for 100 h in a tubular furnace. The oxidation kinetics were evaluated by measuring the weight variation with exposure time. The microstructural evolution induced by the high temperature exposure was investigated by SEM microscopy, EDS
analysis and X-ray diffraction. Results showed that the coatings obtained with AlF3 activator salt are thicker than those obtained using NH4F as a consequence of different growth mechanism during
pack-cementation. Despite this evidence, it was found that the NH4F coatings show a better oxidation resistance, both in terms of total mass gain and of quality of the microstructure of the thermally grown oxide. On the other hand, coatings produced with high concentration of AlF3 exhibited a better resistance in hot corrosion conditions, showing negligible mass variations after 200 h of high
temperature exposure to aggressive NaCl and Na2SO4 salts
Microstructural, mechanical and corrosion characterization of electroless Ni-P composite coatings modified with ZrO2 reinforcing nanoparticles
Full text linkThis study aims to develop medium P (MP, 6 wt%) and high P (HP, 11 wt%) Ni-P-ZrO2 nanocomposites on F22 steel substrate using an original lead-free and surfactant-free solution and to quantitatively relate nanocomposite characteristics to microhardness improvement and corrosion resistance. Incorporation, dispersion and distribu-tion of the nanosized reinforcing phase were evaluated quantitatively by coupling Scanning Electron Microscope (SEM) imaging acquisition with original procedure for image processing and analysis. X-ray Diffraction (XRD) analysis revealed that nanoparticles introduction does not alter microstructure, which remains amorphous for HP and nanocrystalline for MP. Significant differences in particles distribution are found between MP and HP nanocomposites, which are induced by the difference in plating rate of the two formulations. Faster growth of MP (approximate to 35 mu m/h) associates with greater enveloping capability, with higher incorporation and agglomeration phe-nomena that result in non-uniform microhardness across the thickness. Conversely, the slower growth of HP nanocomposites coatings (approximate to 20 mu m/h) relates to lower but uniform incorporation and good dispersion of the reinforcing nanoparticles. Effective dispersion strengthening was observed for nanoparticles concentration up to 13.5 g/l. Microhardness increase by >25 % was achieved for both MP and HP coatings. The combined effect of nanoparticles incorporation level and their agglomeration was systematically studied and a mathematical model was implemented. It was demonstrated that strengthening effectiveness depends on both the amount of embedded nanoparticles and the mean size of agglomerates, following a bi-liner relation that reliably predicts experimental microhardness. Potentiodynamic corrosion test revealed that introduction of ZrO2 nanoparticles enhance corrosion resistance of both MP and HP coatings. The presented hardening strategy for Ni-P coatings can be an efficient solution for midstream and downstream applications in the oil & gas industry, in order to increase service-life of components in contact with both wearing and corrosive media
Variations on the Author
Full text link“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
Ni-fluoropolymers composite coatings obtained via electroless plating for anti-icing application
Full text linkElectroless pure nickel plating was used as a manufacturing technique to produce Ni-fluoropolymers composite
coatings on Ti6Al4V substrates. To evaluate the influence of the surface roughness on the water drop contact
angle, four different coating architectures (Ni, Ni+FEP, Ni polished and Ni+FEP polished) have been proposed
and implemented. Firstly, as a coating reference, a single layer of pure Ni coating was deposited (thickness
around 10 μm); then, Ni+FEP single layer was deposited with the help of a surfactant added to the nanoparticles
solution to avoid the agglomeration of the filler. Water drop contact angles as a function of time were studied for
the different samples and it turns out that the presence of the fluoropolymer fillers inside the matrix deeply modify
the wettability of the Ni matrix surface. These results show how coatings obtained by this synthesis technique
can be used as possible candidates for passive anti-icing system
High temperature mechanical characterization of innovative ceramic materials for thermal barrier coatings
No full textThis study investigates the thermo-mechanical properties of three different solutions for top coat of plasma-sprayed thermal barrier coatings, in order to comprehend their behavior over a wide range of temperatures. The studied materials are a conventional PSZ, a nanostructured PSZ and a lanthanum zirconate-based material. While the nanostructured PSZ shows a different sintering behaviour, keeping its original porosity at high temperatures [1], lanthanum zirconate does not suffer from the allotropic transformations experienced by the PSZ. On the other hand, previous analyses show that lanthanum zirconate-based materials appear to be less tough than the conventional PSZ, while the nanostructured one is slightly tougher. [2, 3]
Four-points bend tests were carried out at different temperatures in order to evaluate and compare their Young modulus, modulus of rupture and deformation at break, while dilatometric analysis provided information about their CTE over a wide range of temperatures. In order to better understand the effects of the sintering process, some lanthanum zirconate samples were previously heat treated
Carbon-phenolic ablative materials for re-entry space vehicles: manufacturing, properties and plasma wind tunnel test
No full textThermal Protection Systems (TPS) are designed to protect re-entry space vehicles from the severe heating encountered during hypersonic flight through a planet’s or the earth’s atmosphere. A carbon-phenolic ablative TPS was developed, manufactured and tested with the aim of fulfilling the thermal and mechanical requirements corresponding to the actual loads experienced by a vehicle during a moon-earth re-entry. Experimental activities were carried out on two different composite systems (a resole resin coupled with a graphitic felt and a graphitic foam), and were aimed to the optimization of the manufacturing procedure and to the characterization of the mechanical behaviour and of the insulation performance of the fabricated composites.
On the basis of the preliminary results, the selected ablators were tested in a Plasma Wind Tunnel (Scirocco, CIRA, Italy)
PRODUCTION AND CHARACTERIZATION OF CARBON-PHENOLIC ABLATIVE MATERIALS MODIFIED WITH NANO-FILLERS
No full textConcept: Ablative materials represent the traditional approach to protect
space vehicles from the severe heating during hypersonic flight through a
planet’s or the Earth’s atmosphere. The Materials and Surface Engineering
Lab (LIMS) of Sapienza-University of Rome has developed carbon-phenolic
ablative materials with several densities and compositions. This work presents
a new methodology for their manufacture adding functionalized nanofillers.
In particular acetic, decanoic and methacrylic acid were chosen as
functionalizing group of nano-zirconia. Mechanical (bending and compression
tests) and thermal characterization (TGA/DSC) are carried out in order to
understand the effect of nano-fillers on the material properties.
Motivations and objectives: Ablative materials consist of a rigid felt impregnated
with phenolic resin. During the process the resin is diluted and nanoparticles
are added to this solution. Nano-filler are introduced in order to
improve mechanical and thermo-physical properties of virgin and charred
material, but their efficiency is strictly connected to the homogenous dispersion
of the particles. An acid surface modification were conducted to avoid
the agglomeration of particles according to Chiang et al. The efficiency of the
method was proved by FE-SEM photographs, mechanical and thermal tests
will enlighten the properties improvement.
Results and discussion: The FE-SEM photograph (Fig. 1) of a cured carbonphenolic
ablative material shows that addition of nano-fillers does not decrease
the goodness of the distribution of the resin in the sample without
density variation. Figure 2 shows that the surface modification and the impregnation
procedure does not change the dimension of the nanoparticles
(as shown in the inset). Although the particles are well dispersed in the resin.
Bending and compression tests will provide a comparison between samples
manufactured with and without nano-zirconia
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