3,230 research outputs found
Transmission electron microscopy and energy dispersive X-ray spectroscopy on the worn surface of nano-structured TiAlN/VN multilayer coating
Nano-structured TiAIN/VN multilayer hard coatings grown by cathodic arc metal ion etching and unbalanced magnetron sputtering deposition have repeatedly shown low coefficients of friction and wear. In this paper, we employed the combined methods of cross-sectional ion beam milling sample preparation, conventional transmission electron microscopy, energy dispersive X-ray spectroscopy and quantitative spectrum analysis to give a comprehensive characterization of wear induced tribofilm, worn TiAIN/VN surface as well as wear debris. The major wear mechanism operating in the TiAIN/VN coating is the tribo-oxidation wear. A 20-50 nm thick tribofilm was observed on the TiAIN/VN worn surface, having inhomogeneous density, amorphous structure and multicomponent V-Al-Ti-O composition. Therefore the real sliding contact during the ball-on-disk test was a three-body sliding system including the tribofilm, in which the self-sintering and shearing deformation of the multicomponent oxide film played a significant role in determining the low friction coefficient. Owing to the low friction and high hardness, the TiAIN/VN worn surface retained good structural integrity without any crack, delamination or detectable deformation, resulting in minimized mechanical wear. (c) 2005 Elsevier B.V. All rights reserved
X-ray microanalysis in STEM of short-term physico-chemical reactions at bioactive glass particles / biological fluids interface. Determination of O/Si atomic ratios
Short-term physico-chemical reactions at the interface between bioactive
glass particles and biological fluids are studied and we focus our attention on
the measurements of O/Si atomic ratio. The studied bioactive glass is in the
SiO2-Na2O-CaO-P2O5-K2O-Al2O3-MgO system. The elemental analysis is performed at
the submicrometer scale by STEM associated with EDXS and EELS. We previously
developed an EDXS quantification method based on the ratio method and taking
into account local absorption corrections. In this way, we use EELS data to
determine, by an iterative process, the local mass thickness which is an
essential parameter to correct absorption in EDXS spectra. After different
delays of immersion of bioactive glass particles in a simulated biological
solution, results show the formation of different surface layers at the
bioactive glass periphery. Before one day of immersion, we observe the presence
of an already shown (Si,O,Al) rich layer at the periphery. In this paper, we
demonstrate that a thin electron dense (Si,O) layer is formed on top of the
(Si,O,Al) layer. In this (Si,O) layer, depleted in aluminium, we point out an
increase of oxygen weight concentration which can be interpreted by the
presence of Si(OH)4 groups, that permit the formation of a (Ca,P) layer.
Aluminium plays a role in the glass solubility and may inhibit apatite
nucleation. After the beginning of the (Ca,P) layer formation, the size of the
electron dense (Si,O) layer decreases and tends to disappear. After two days of
immersion, the (Ca,P) layer grows in thickness and leads to apatite
precipitatio
Absence of room temperature ferromagnetism in bulk Mn-doped ZnO
Structural and magnetic properties have been studied for polycrystalline
Zn_1-xMn_xO (x=0.02, 0.03, 0.05). Low-temperature (~500 oC) synthesis leaves
unreacted starting ZnO and manganese oxides. Contrary to a recent report, no
bulk ferromagnetism was observed for single-phase materials synthesized in air
at temperatures above 900 oC. Single-phase samples show paramagnetic
Curie-Weiss behavior.Comment: Accepted for publication in J. Appl. Phys., RevTeX, 3 pages, 4
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Thermoelectric properties of lead chalcogenide core-shell nanostructures
We present the full thermoelectric characterization of nanostructured bulk
PbTe and PbTe-PbSe samples fabricated from colloidal core-shell nanoparticles
followed by spark plasma sintering. An unusually large thermopower is found in
both materials, and the possibility of energy filtering as opposed to grain
boundary scattering as an explanation is discussed. A decreased Debye
temperature and an increased molar specific heat are in accordance with recent
predictions for nanostructured materials. On the basis of these results we
propose suitable core-shell material combinations for future thermoelectric
materials of large electric conductivities in combination with an increased
thermopower by energy filtering.Comment: 12 pages, 8 figure
Effect of oxidizing concentration on the corrosion resistance of the cerium conversion coating on galvanized steel
Ce-based conversion films have been assessed as alternatives for replacement of Cr6+-based films,which have been forbidden for their toxicity and carcinogenic properties. However, corrosion protection associated with chromate films is difficult to achieve by other surface treatments. Experimental results have revealed that to obtain the highly satisfactory results provided by chromate-based conversion coatings, it is necessary to improve the anticorrosive properties of the new chromium-free coatings. The present work deals with the effect of the oxidant concentration in the cerium-based conversion baths on the corrosion resistance of the films deposited on galvanized steel. Electrogalvanized steel sheets were exposed to cerium chloride-based baths with different concentrations of oxidant for a minute. The surface of the treated samples was analyzed by XPS and SEM-EDXS, while its corrosion resistance was investigated using electrochemical tests (EIS) conducted in a 0.05 M NaCl solution and the impedance spectra evolution analyzed as a function of the exposure time. The results showed a direct relationship between oxidant concentration and corrosion resistance. When the oxidant concentration rose from2mL.L-1 to 12mL.L-1, the corrosion resistance increased about 5 times, and this was attributed to the decrease in the Ce3+/Ce4+ relationship of the conversion film.Fil: Culcasi, José Daniel. Universidad Nacional de La Plata; ArgentinaFil: Elsner, Cecilia Ines. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - La Plata. Centro de Investigaciones Ópticas. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones CientÃficas. Centro de Investigaciones Ópticas. Universidad Nacional de La Plata. Centro de Investigaciones Ópticas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Di Sarli, Alejandro Ramón. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - La Plata. Centro de Investigaciones Ópticas. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones CientÃficas. Centro de Investigaciones Ópticas. Universidad Nacional de La Plata. Centro de Investigaciones Ópticas; ArgentinaFil: Palomino, Luis. Universidade de Sao Paulo; BrasilFil: Tomachuk, Celia Regina. Instituto de Investigaciones Energéticas y Nucleares. San Pablo; BrasilFil: Costa, Ilda. Instituto de Investigaciones Energéticas y Nucleares. San Pablo; Brasi
Effect of Metallic Waste Addition on the Physical and Mechanical Properties of Cement-Based Mortars
© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).This paper investigates the influence of the type and amount of recycled metallic waste on the physical and mechanical properties of cement-based mortars. The physical and mechanical properties of cement mortars, containing four different amounts of metallic waste (ranged 4 to 16% by cement weight), were evaluated by measuring the bulk density, total porosity, flexural and compressive resistance, and dynamic elastic modulus by ultrasonic tests. All the properties were measured on test specimens under two curing ages: 7 and 28 days. Additionally, the morphological properties and elemental composition of the cement and metallic waste were evaluated by using Scanning Electron Microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), and X-ray fluorescence (XRF). Main results showed that the addition of metallic waste reduced the bulk density and increased the porosity of the cement-based mortars. Furthermore, it was observed that flexural and compressive strength proportionally increased with the metallic waste addition. Likewise, it was proven that elastic modulus, obtained by compressive and ultrasonic tests, increases with the metallic waste amount. Finally, based on a probability analysis, it was confirmed that the addition of metallic waste did not present a significant effect on the mechanical performance of the cement-based mortars.Peer reviewedFinal Published versio
Microstructure and corrosion evolution of additively manufactured aluminium alloy AA7075 as a function of ageing
Additively manufactured high strength aluminium alloy AA7075 was prepared
using selective laser melting. High strength aluminium alloys prepared by
selective laser melting have not been widely studied to date. The evolution of
microstructure and hardness, with the attendant corrosion, were investigated.
Additively manufactured AA7075 was investigated both in the as-produced
condition and as a function of artificial ageing. The microstructure of
specimens prepared was studied using electron microscopy. Production of AA7075
by selective laser melting generated a unique microstructure, which was altered
by solutionising and further altered by artificial ageing - resulting in
microstructures distinctive to that of wrought AA7075-T6. The electrochemical
response of additively manufactured AA7075 was dependent on processing history,
and unique to wrought AA7075-T6, whereby dissolution rates were generally lower
for additively manufactured AA7075. Furthermore, immersion exposure testing
followed by microscopy, indicated different corrosion morphology for additively
manufactured AA7075, whereby resultant pit size was notably smaller, in
contrast to wrought AA7075-T6.Comment: 37 pages, includes 4 Tables and 11 Figure
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