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•WC particles were prepared by high energy milling.•Mesoporous BaFe12O19 particles were synthesized by chemical co-precipitation.•The addition of just 5% of WC to the BaFe12O19 ...increased the surface area by 13%.•The average particle size decreased by 18% by the incorporation of 5% of WC.•BaFe12O19-WC mixture improves ferrite properties for catalysis applications.
Among the magnetic catalysts, barium hexaferrite (BaFe12O19) stands out, mainly due to its capacity to absorb light in the whole visible light range, its magnetic properties, and chemical stability. In this work, the synthesis of mesoporous barium hexaferrite was performed by the chemical co-precipitation method. Then BaFe12O19 particles were subsequently mixed with 1%, 3%, and 5% of tungsten carbide (WC) particles in order to enhance its properties for visible light catalysis. WC powders were prepared by high energy ball milling (HEBM), and its crystallite size was estimated over time from X-ray Diffraction (XRD) measurements. The particle size of the milled WC powders was analyzed using a Laser diffraction analyzer. Besides, Ultraviolet–visible (UV–VIS) spectroscopy was performed to study the light absorption properties of the mixture. In addition, the specific surface area of the samples was measured with a Brunauer-Emmett-Teller Surface Analyzer. Finally, the size and morphology of BaFe12O19-WC mixtures were studied by Scanning Electron Microscopy (SEM). In accordance with the specific surface area measurements, a considerable area increasing up to 13% was observed for the BaFe12O19-WC (5%) sample in comparison to the pure BaFe12O19. On the other hand, the addition of the WC particles slightly increased the bandgap energy by 1.6% in comparison to the pure BaFe12O19. The results indicate that by the incorporation of WC additive, by this simple and inexpensive method, the surface area of the BaFe12O19 can be modified to enhance its properties for its use in visible light catalysis applications.
The microstructural and chemical evolution after different processing steps of Ta-containing NiCoCrAlY bond coats (BC) sprayed by high velocity oxy-fuel on Ni-base superalloy (SA) substrates, ...top-coated with 7YSZ and furnace cycled at 1100 °C focusing along the BC/SA interfaces is presented. Three superalloys were selected considering their Ta content relative to that within the BC: a) no Ta in the superalloy composition (IN100) and either b) similar or c) higher Ta content with respect to the BC (M247LC SX and CMSX-4, respectively). The processing conditions were as-sprayed, as-annealed, after EB-PVD deposition of a 7YSZ top coat, and after furnace cyclic tests (1100 °C/120 h). The evolution of chemical composition after the different process steps are presented that include a normalization criteria to a Ni-Al-Cr system, elemental profiles as well as Weibull distribution plots of minor containing elements such as Ti, Ta, Mo, or W at the BC/SA interface. The effect of Ta was activated in some coated substrates by the presence of Ti and C in the superalloy consisting of inward Ta-diffusion, trapping of outward diffusing Ti and the subsequent formation of (Ta, Ti)-rich carbides in the BC avoiding possible segregation effects as titanium oxide in the oxide scale.
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•NiCoCrAlYTa coatings were deposited by HVOF on IN100, M247LC SX, and CMSX-4.•Elemental diffusion along BC/SA was investigated after different processing stages.•Coating microstructure under cyclic tests is affected by SA composition.•A gradient of carbides composition is observed due to Ti from the SA trapped by Ta.•Composition of (Ta, Ti)-carbides within the BC on IN100 and M247LC SX are reported.
(Na0.5Bi0.5)TiO3 (NBT) ceramics are candidates to be used as coarse coatings in several applications including environmental remediation, alternative energies, electromechanical devices, etc. In this ...work, visible-light photoactive thermally sprayed coatings deposited from spray-dried NBT microspheres are reported. NBT powder was synthesized and processed by mixed oxides solid state reaction and milling. The spray drying process and sintering treatments to produce NBT microspheres were optimized to obtain a size distribution suitable to be used as a feedstock for flame spray deposition. The effect of spray drying and sintering parameters on the characteristics of NBT microspheres are presented and discussed. NBT microspheres with size distribution described by D10 = 25 μm and D90 = 83 μm were prepared in a design of experiments using a two-fluid nozzle spray dryer equipment varying nozzle size, atomizing pressure, feeding rate of the spray drying equipment, and the solid content (vol%) of the slurry formulation. NBT spray-dried agglomerates showed predominantly dense spheres with D50 sizes in the range of 17–55 μm. NBT Perovskite was confirmed by XRD in the synthesized powders and sintered microspheres. NBT powder was fed into a flame spray gun and a thick coating of approx. 100 μm was deposited. Rapid solidification and high temperature of the flame spray process allowed to couple a heterojunction composed by NBT with small amounts of TiO2 in both, anatase and rutile phases. The heterojunction showed a direct band gap of 1.93 eV, which makes the NBT + flame spray process an excellent combination to couple visible light photoactive NBT + TiO2 heterojunctions.
•Spray-drying parameters for NBT microspheres preparation for spray deposition are reported.•Suitable particle size distribution is reached combining low atomizing pressure and high solid loading and feeding rate.•Bandgap of NBT microspheres decreased from 3.2 to 3.0 eV by increasing sintering temperature and time.•Visible-light photoactive properties of flame-sprayed NBT coatings are reported.•A Rutile/NBT/Anatase multi-heterojunction was obtained by flame-sprayed coating deposition from pure NBT microspheres.
The effect of pre-oxidation treatments at various oxygen partial pressures (pO2) on the microstructure of ReneN5/(Ni,Pt)Al/7YSZ thermal barrier coatings systems and the number of furnace cycles at ...1100 °C up to top coat spallation is here presented. (Ni,Pt) Al bond coats deposited on ReneN5 superalloy were pre-oxidized under different pO2 before top coat deposition. After pre-oxidation, a 7YSZ ceramic top coat was deposited on the samples using the electron beam physical vapor deposition. The pre-oxidized specimens in the range of 1 × 10−19 ≤ pO2 ≥ 1 × 10−1 atm showed a higher number of furnace cycles compared to those either pre-oxidized at pO2 = 2.1 × 10−1 atm and without pre-oxidation. The thermally grown oxide (TGO) scale after top coat deposition of pre-oxidized samples in the range of 1 × 10−19 ≤ pO2 ≥ 1 × 10−1 atm showed the lowest thickness and thus slow growth kinetics. Moreover, a microstructural analysis by scanning electron microscopy revealed the formation of a mixed zone within the TGO of non-pre-oxidized samples, whereas for all pre-oxidized conditions a dense continuous Al2O3 scale was observed. Upon furnace cyclic exposure, phase transformations from B2 to L10 and L12 were identified by electron backscattering diffraction in all bond coats, which are most likely a feature associated with high heating/cooling rates under furnace cyclic tests.
•Furnace cyclic testing data of pre-oxidized ReneN5/(Ni,Pt)Al/7YSZ TBC's are reported.•Pre-oxidation at low PO2 of ReneN5/(Ni,Pt)Al/7YSZ leads to high number of thermal cycles.•Pre-oxidation of ReneN5/(Ni,Pt)Al/7YSZ prevents a mixed zone formation within the Al2O3 scale.•Rapid cooling in furnace cyclic test caused B2 to L10 and L12 phase transformations in/(Ni,Pt)Al.
The effect of isothermal pre-oxidation treatments on the β-(Ni,Pt)Al + IDZ + René N5 system degradation is reported here. The pre-oxidation treatments were carried out from 900 °C (mostly θ-Al2O3 ...growing conditions) to 1200 °C (mainly α-Al2O3 growing conditions) for 5 h, under an Ar-stream with pO2 = 1 × 10−5 atm. The correlation between the structural, microstructural, and chemical properties of the β-(Ni,Pt)Al BC show that pre-oxidation parameters have an important effect on the multi-elemental counter diffusion phenomena along the BC. Heat treatments performed above 1100 °C resulted in loss of stability of the BC, partially disordering of the β phase promoting the β → β + L10 and β → β + L12 transformations. A significant BC + IDZ thickness increase of 55% at 1200 °C was observed with respect to the as-received specimen resulting in a severe BC degradation. Multi-elemental inward diffusion is the main mechanism responsible for BC degradation at high temperatures.
•BC microstructural degradation is highly dependent on the pre-oxidation temperature.•An unbalanced diffusivity due to TGO formation promotes an excessively TGO/BC-interfacial voids and a BC Pt-enrichment.•The two-sublattice model adequately describes the elemental distribution within the β phase.•A partially disordering and phase transformations β → β + L10 and β → β + L12 take place for pre-oxidation above 1100 °C.
Corrosion behavior of 304 stainless steel exposed to a NaCl (3.5 wt %) solution saturated with CO
2
has been analyzed using electrochemical techniques including, potentiodynamic polarization, ...polarization resistance, and electrochemical impedance measurements. The stainless steel samples were evaluated having different surface and pre-oxidation treatments. The oxide scales formed on 304 stainless steel oxidized in different
p
O
2
at 1100°C have also been studied and compared. Different morphologies and chemical composition of the oxide scales were observed after oxidation at low and high oxygen partial pressures. Oxide layers with high chromium content were formed on the ground sample pre-oxidized in Ar while iron-rich oxides were mainly formed under air atmosphere. The electrochemical corrosion results indicate that non-oxidized 304 SS exhibits the best corrosion performance followed by the ground sample heat-treated in argon. For the oxidized stainless steels, the differences in the electrochemical responses are associated to the morphological characteristics and composition of the oxide layer. Homogeneous and dense Cr-rich oxide scale provides protection to 304 SS during exposure to CO
2
-saturated solutions while the formation of Fe-oxides with porous morphology increases the corrosion rate of 304 stainless steel.
Measurement of mechanical properties in cermets is complex since they are formed by several phases. How to quantitatively determine the relationship between the performance and the complex ...microstructure of this particular group of materials, especially when analyzing the effect of the reinforcement phase, is still one of the top challenging problems yet to be solved. Hardness and elastic modulus of bimodal WC–Co HVOF thermal spray coatings doped with vanadium carbide (VC) additions were studied by performing a statistical analysis of nanoindentation results. A mathematical deconvolution procedure and a Weibull distribution analysis of hardness and elastic modulus results are proposed to identify the individual contribution of each phase to the mechanical properties of different WC–12Co coatings. Both analysis methods allowed to detect a reinforcing effect of vanadium on the hardness and elastic modulus of bimodal VC-doped coatings. The combination of VC additions and a bimodal WC particle size distribution in the WC–Co coatings proved successful in increasing their mechanical properties, as the coatings processed in this work showed better mechanical properties than that reported in the literature for coatings having exclusively a bimodal WC particle size distribution or those only doped with VC additions.
•Bimodal VC-doped coatings showed better mechanical properties than commercial systems.•Nanoindentation helped studying H and E of phases present in HVOF WC–VC–Co coatings.•Deconvolution of indentation data was used to study H and E of phases in the coatings.
In this work, thin films deposited by pulsed DC magnetron sputtering of Ti–Al/Ti–Al–N
n
and Ti–Cr/Ti–Cr–N
n
multilayers of nanometric periods were analyzed by AFM in contact mode to measure values of ...lateral and normal forces. From these measurements, the coefficient of friction (COF) of these materials in contact with the AFM tip was calculated. Measurements were made with three types of silicon tips, diamond-coated, Pt–Cr-coated, and bare silicon. Significant differences between the tip materials in contact with the samples, which affected the COF, were observed. The effect of the environmental layer of water covering the surface sample and the tip appears as the most important factor affecting the tribology behavior of the tip-sample contact. For diamond-coated and bare silicon tips there is an additional adherence force increasing the normal load. But for tips platinum–chromium-coated there is a repulsive force due to this water layer, which behaves as a lubricant layer before a threshold load.
Structural evolution during the synthesis of B2–NiAl intermetallic compound by mechanical alloying of equiatomic elemental mixtures was studied by Rietveld analysis, DSC and HTXRD. The lattice ...parameter, crystallite size, microstrain, amount of phase and ordering of the B2 phase were monitored as a function of milling time. Formation of the B2–NiAl phase shows a sigmoidal behavior, which suggests that Johnson–Mehl–Avrami nucleation and interface-controlled growth are the responsible mechanisms in the transformation. Almost complete transformation (~ 97 mol%) was obtained after 25 h of milling. A specific phase transformation sequence during milling was not absolutely determined, however, the sequence Ni + Al → NiAl
3
→ Ni
2
Al
3
→ B2–NiAl was identified by HTXRD. This sequence was confirmed by DSC. The transformation temperature of the B2–NiAl phase and the presence of additional intermetallic compounds show a direct dependence on the Ni–Al layer spacing. Using a production-scale Simoloyer horizontal Attritor Mill, the presence of Ni
2
Al
3
phase was observed prior to the full synthesis of B2-NiAl.
The latest Difficult Airway Society (DAS) guidelines recommend that all anaesthesiologists should to be trained in the performing of a surgical cricothyrotomy (CtQ). The aim of this study was to ...analyse the learning results of a CtQ workshop by assessing the success rate and time to perform CtQ on a porcine tracheal model.
A workshop was designed in which each student completed a questionnaire with demographic data and theoretical knowledge about surgical approaches of airway. During the following hour, a review was presented theoretical aspects of CtQ. The model was shown and a CtQ was performed using a classical technique. Afterwards, in groups of 3-4 students with an instructor, each one of the students performed 6 CtQ. A record was made on whether the ventilation was correct, the time to perform CtQ, and the ease of performing the CtQ by the students and instructors. Finally, students completed a questionnaire on the theoretical aspects. Students and instructors performed a workshop debriefing. A statistical analysis was performed, considering a P-value <0.05 as statistically significant.
A total of 8 workshop sessions were held with a total of 91 students. At first attempt, 86% of students performed a CtQ with successful ventilation, and 92% at the sixth attempt (P<.0001). Time taken was 163 107-211 seconds at first attempt, and 70 55-85 seconds at the sixth (P<.0001). At the end of workshop, students had improved their theoretical knowledge (P<.0001) and perception of the ease of the technique.
Workshop performance improved theoretical knowledge and competence in surgical cricothyrotomy.
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