Papers by Keyword: Oxidation

Abstract: High temperature oxidation of Al₈₆Ce₁₀Fe₄ amorphous alloy at 630°C in static air for 15, 60, 300, 600, 1,200, 3,000, 6,000 and 12,000 minutes was studied. The morphology, composition and microstructure of the oxide films were investigated using SEM, EDS and XRD. The hardness and corrosion resistance of the oxide films were determined by micro-indentation and polarization technique. The results indicate oxidation at 630 °C instigates nucleation, growth and coarsening of fcc-Al, Al₁₁Ce₃ and Al₁₃Fe₅ crystalline phases inside the Al₈₆Ce₁₀Fe₄ matrix, reducing the hardness of the alloy, and oxidation of the alloy surface, forming crystallized Al₂O₃ and AlFeO₃ chemical compounds. Active anodic dissolution behavior and diffusion-controlled cathodic polarization of the oxidized alloy were observed. The corrosion resistance of the oxide films rates in the level of 10^-7 ~10^-5 [A/cm²]. The results demonstrate Al₈₆Ce₁₀Fe₄ amorphous alloy, as a new-developed high temperature high strength glass, exhibits potential application for aerospace and national defense in terms of its high mechanical strength, high temperature endurance, and satisfactory oxidation and corrosion resistance.

Abstract: The contact between fuels and various metals used in vehicles make them susceptible to corrosion. Aluminum is a metal widely used in automotive components owing to its corrosion resistance as well as mechanical properties. The ABNT 14359 standard establishes a method for determining fuel corrosion; however, it is restricted to copper and fossil fuels. In this standard, corrosion is assessed qualitatively by visual comparison of patterns, which can lead to uncertain results. The methodology used in this study involves the immersion of metallic materials in fuels for a specific period of time for further analysis by scanning electron microscopy (SEM), and electrochemical analysis by electrochemical impedance spectroscopy (EIS) and anodic potentiodynamic polarization (APP). The results indicated that aluminum alloy AA 3003 is suitable for use in the production of vehicle components that will be in contact with biodiesel, diesel, ethanol, or gasoline, since no serious case of corrosion occurred.

Abstract: Iron aluminides have been considered as materials resistant against high temperature oxidation in air and sulphur-containing environments. Previous research of our team proved that the oxidation resistance in the air can be significantly improved by the addition of silicon. Fe-Al-Si alloys have also very good mechanical properties at high temperatures. However, the resistance in the environments simulating combustion gasses have not been studied yet. This work focuses on the oxidation resistance in carbon dioxide, which is the main component of the combustion gasses. It was found that the Fe-Al-Si, Fe-Al-Si-Ni and Fe-Al-Si-Ti alloys have lower oxidation resistance in carbon dioxide containing atmosphere than in the air due to carbon diffusion to the material and even to the formation of carbides below the oxide layer. It leads to the spallation of the oxide layer, especially in FeAl20Si20Ni20 alloy.

Abstract: The structure and properties of graphene oxide aerogels (GOA), prepared by a modified Hummer’s method followed by a freezing-drying process in addition to a pre-oxidized procedure, were studied through FTIR, Raman, SEM and XDR techniques. FTIR results indicated the existence of -C-O, -C-OH and -C=O function groups on the GOA surface. Therefore, the D band intensity of GOA sample exhibited remarkable increasing in the Raman spectra compared with of graphite; it may be due to change the order-structure of graphite to disorder-structure of GOA. The diffractive peak for the graphite at 2θ of 26.5° vanishes instead the one around 10.0° occurred in the XRD pattern for the GOA supported that the structure and d-spacing changed seriously from graphite to GOA. The SEM images revealed that the micro-structure of graphene layer of GOA was wrinkler and softer than that of graphite, however, the former involved fewer lamellar layer appearance with wrinkles on the edges of the graphene. All the characterized evaluation confirmed that the graphite powder has been transformed into a GOA structure through the modified Hummers’ method.

Abstract: This research investigates the application of three sulfonic resins (Amberlyst-15, Dowex-G26 and Dowex Monosphere-650C) as acid heterogeneous catalysts for oxidation reaction of furfural with hydrogen peroxide solution. The reaction was carried out in a batch reactor with varied reaction time (4-24 h) and temperature (70-90 °C). The sulfonic resins were characterized as to their structure and chemical composition by N₂ adsorption-desorption isotherm, Fourier transformed-infrared (FTIR) spectroscopy, acid-base titration, and scanning electron microscopy (SEM). The results showed that all three resins gave similar catalytic activities. The highest yield of succinic acid was 75.7 % in the presence of Dowex-G26 catalyst at 80 °C and 4 h.

Abstract: In this work, the potential of muon spin rotation (μSR) with low-energy muons (LE-μ) for the investigation of oxidation-induced defects at the SiO₂/4H-SiC interface is explored. By using implantation energies for the muons in the keV range and comparing the fractions of muonium in different regions, the depth distribution of defects in the first 200 nm of the target material can be resolved. Defect profiles of interfaces with either deposited or thermally grown SiO₂ layers on 4H-SiC are compared. The results show an increased number of defects in the case of a thermal oxide, both on the oxide and on the SiC side of the interface, with a spatial extension of a few tens of nm.

Abstract: 1.25 – 5wt%Pt/Al₂O₃, 1.25 – 5wt%Pd/Al₂O₃, 1wt%Pd/TiO₂, 1 – 5wt%Pd/TiO₂-NF, 1.25wt%Pt+1.25wt%Pd/Al₂O₃, 5wt%Pt/SiO₂, 5wt%Pt/C catalysts were synthesised and tested in the selective oxidation of 1,2-propanediol by molecular oxygen. It was found that all catalysts were active in alkaline water solutions; lactic acid was obtained as the main product of the reaction. The conversion of 1,2-propandiol and the yield of lactic acid depended on the content of active metal in the catalysts. The most active for the oxidation of 1,2-propandiol were palladium-containing catalysts supported on TiO₂ nanofibers (Pd/TiO₂-NF). The highest 1,2-propanediol conversion (100 %) and lactic acid yield (96 %) were obtained using the 5wt%Pd/TiO₂-NF catalyst at the following oxidation parameters: c₀(1,2-propanediol) = 0.3 mol/L, P(O₂) = 1 atm, n (1,2-propanediol)/n (Pd) = 500 mol/mol, t = 60 °C, c₀(NaOH) = 1.5 mol/L.

Abstract: This work demonstrates that 5wt% gold catalysts supported on Al₂O₃ and TiO₂ nanopowders as well as on TiO₂ nanofibers are active in the 1,2-propanediol (1,2-PDO) oxidation to lactic acid. The influence of catalysts different parameters and reaction conditions on 1,2-PDO conversion and oxidation process selectivity was studied. The best result was achieved using 5wt%Au/TiO₂ catalyst over the following oxidation parameters: c₀(1,2-PDO) = 0.3 mol/L, n (1,2-PDO)/n (Au) = 4000 mol/mol, p (O₂) = 6 bar, c₀(NaOH) = 2 mol/L, t = 60 °C: 1,2-propanediol conversion was 98 % and lactic acid selectivity 89 %.

Abstract: Activated carbon is one of the most widely used adsorbents, but it shows low removal efficiency for polar molecules such as ammonia or ions due to the low content of oxygen containing groups. To increase the amount of oxygen containg groups, activated carbon was modified by the oxidation of activated carbon using the HNO₃/H₃PO₄-NaNO₂. The results showed that the carboxyl content of the modified activated carbon (MAC) increased with an increase in reaction time and temperature. The condition at 50°C for 60 hours yielded the MAC with a carboxyl content 1.07 mmol/g. The oxygen content of MAC also increased, suggesting the formation of carboxyl or carbonyl groups in the products after the oxidation. Brunauer-Emmett-Teller (BET) analysis and scanning electron microscopy (SEM) images demonstrated an increase in porosity of the MAC. The maximum capacity of ammonia adsorption was 5.81 mg/g for MAC.

Abstract: This work investigated the influence of oxidation durations on the formation of oxide on the surface of wrought Co-28Cr-6Mo-1Si alloy. The iso-thermal oxidation was individually performed in air at 550°C for 4, 12 and 24 h. For comparison, the surface of the non-oxidized Co-28Cr-6Mo-1Si alloy was concurrently examined. The chemical compositions of the non-oxidized and oxidized alloys were principally analyzed via X-ray photoelectron spectroscopy (XPS). The XPS results revealed that the surface of the non-oxidized alloy enriched in Cr-oxide. After oxidation treatment, the Co-oxide, existing as Co²⁺ state was observed coexisting with two Cr-oxide states, Cr³⁺ and Cr⁴⁺. The low concentrations of Mo⁶⁺ were also observed on the oxidized alloy surface. With the increase in oxidation durations, the Co-oxide was suppressed by Cr-oxide. The XPS depth profile analysis indicated that the thickness of the oxide film increased with increasing the oxidation duration.