Identifying Fe3Mn3O8 Phase as the Superior Catalyst for Low-Temperature Catalytic Oxidation of Formaldehyde in Air

This work reports the efficient binary Fe-Mn metal oxide catalysts for low-temperature formaldehyde (HCHO) oxidation in air. The highest catalytic activity was obtained at the molar ratio of Fe/Mn =...

Effect of Al Addition on the Oxidation Resistance of HfC Thin Films

In this paper, we focus on the research of Al addition on Hf–Al–C film structure and oxidation resistance. It was found that obtained Hf–A–C films consist of a solid solution of Al in non-stoichiometric cubic HfC and have identical XRD patterns to bcc–HfC. Besides, the Al addition decreases the sample mass gain during oxidation in air at temperatures up to 800 °C. Mass gain for Hf–Al–C was 44.3 and 22.5% less, compared to pristine HfC, at 600 and 800 °C, respectively.

Kinetic and Metallography Study of the Oxidation at 1250 °C of {Co+Ni}-Based Superalloys Containing Ti to Form MC Carbides

Six conventionally cast chromium-rich titanium-containing alloys based on cobalt and nickel with various Co/Ni ratios were considered. They were tested in oxidation in air at 1250 °C for 70 h in a thermo-balance. The mass gain curves were exploited to specify different types of kinetic constants as well as several parameters characterizing the oxide spallation occurring during cooling. The obtained results show that, the higher the Ni content, the slower the mass gain and the better the quality of the protective external chromia scale. Secondly, no dependence of the oxide spallation characteristics on the Co content was clearly noted. Globally, the isothermal oxidation behavior becomes better when Ni is more and more present at the expense of Co. Titanium seems to be playing a particular role in the process of oxidation. It notably leads to the presence of an external thin TiO2 continuous scale beyond the chromia scale. The thermogravimetry records were numerically treated to determine the parabolic constant and the chromia volatilization constant. The values of these constants evidenced a double tendency: chromia growth acceleration and chromia volatilization slow-down. These trends are to be confirmed and further investigated.

Microstructural regulation, oxidation resistance, and mechanical properties of Cf/SiC/SiHfBOC composites prepared by chemical vapor infiltration with precursor infiltration pyrolysis

To further improve the oxidation resistance of polymer derived ceramic (PDC) composites in harsh environments, Cf/SiC/SiHfBOC composites were prepared by chemical vapor infiltration (CVI) and precursor impregnation pyrolysis (PIP) methods. The weight retention change, mechanical properties, and microstructure of Cf/SiC/SiHfBOC before and after oxidation in air were studied in details. Microscopic analyses showed that only the interface between the ceramics and fibers was oxidized to some extent, and hafnium had been enriched on the composite surface after oxidizing at different temperature. The main oxidation products of Cf/SiC/SiHfBOC composites were HfO2 and HfSiO4 after oxidation at 1500 °C for 60 min. Moreover, the weight retention ratio and compressive strength of the Cf/SiC/SiHfBOC composites are 83.97% and 23.88±3.11 MPa, respectively. It indicates that the Cf/SiC/SiHfBOC composites should be promising to be used for a short time in the oxidation environment at 1500 °C.

Preparation, Characterization, and Activity of Pd/PSS-Modified Membranes in the Low Temperature Dry Reforming of Methane with and without Addition of Extra Steam

The external surface of a commercial porous stainless steel (PSS) was modified by either oxidation in air at varying temperatures (600, 700, and 800 °C) or coating with different oxides (SiO2, Al2O3, and ZrO2). Among them, PSS-ZrO2 appears as the most suitable carrier for the synthesis of the Pd membrane. A composite Pd membrane supported on the PSS-ZrO2 substrate was prepared by the electroless plating deposition method. Supported Ru catalysts were first evaluated for the low-temperature methane dry reforming (DRM) reaction in a continuous flow reactor (CR). Ru/ZrO2-La2O3 catalyst was found to be active and stable, so it was used in a membrane reactor (MR), which enhances the methane conversions above the equilibrium values. The influence of adding H2O to the feed of DRM was investigated over a Ru/ZrO2-La2O3 catalyst in the MR. Activity results are compared with those measured in a CR. The addition of H2O into the feed favors other reactions such as Water-Gas Shift (RWGS) and Steam Reforming (SR), which occur together with DRM, resulting in a dramatic decrease of CO2 conversion and CO production, but a marked increase of H2 yield.

Effect of Toluene Addition in an Electric Arc on Morphology, Surface Modification, and Oxidation Behavior of Carbon Nanohorns and Their Sedimentation in Water

Carbon nanohorns (CNHs) are attractive for various applications, where a high specific surface area and long dispersion stability in water are important. In the present work, we study these parameters of CNHs prepared by arc evaporation of graphite depending on the conditions of the synthesis and subsequent oxidation in air. It is shown that the addition of toluene in the reactor during the arcing allows obtaining CNHs functionalized with −CHx groups. Heating of CNHs in air at 400 °C leads to substitution of −CHx groups for oxygen-containing groups. Moreover, the CNH endcaps are opened at 500 °C, and as a result, the specific surface area of CNHs increases 4 times. Aqueous suspensions with a concentration of oxidized CNHs of 100 µg/mL are stable for 8 months.

PRODUCTION OF CARBON NANOFIBERS BASED ON COAL TAR AND POLYACRYONITRILE BY ELECTROSPINNING METHOD

The article presents experiments on obtaining composite fibers based on Shubarkol coal tar (CT) and polycarlonitrile (PAN) by electrospinning in a laboratory setup. As a result of energy dispersive X-ray spectroscopy and SEM microscopy, the elemental composition (C-85.83%) and the diameter of the carbon fiber were determined, which ranged from 89.0 nm to 449.8 nm. The resulting CNF was subjected to oxidation in air at 300 °C, the holding time was 1 hour, after which the carbonization process was carried out at 800 °C, followed by cooling to room temperature. Raman spectra were recorded to study the degree of graphitization. The results of Raman scattering of light (RS) showed the degree of graphitization - 15.98%. Ratio I (D) / I (G) = 0.99, I (G) / I (D) = 1. The broad bands D (disordered part) and G (ordered graphite structure) suggest that CNFs contain partially graphitized carbon along with amorphous carbon. The ID / IG ratio represents the conversion of disordered carbon to graphite carbon during carbonization. The resistance of this material is 70-200 ohms. The results obtained confirm the semiconductor nature of the conductivity. On the basis of SEM drawings of CNFs from CT and PAN, it was found that the structure of CNFs after oxidation and carbonization retains the original fibrous structure. It was also found that the diameter of nanofibers decreases from 320.5 - 625.7 nm to 89-449.8 nm. Thus, the proposed method of obtaining CNF is built on the basis of the electrospinning method, which is the most promising method of industrial production.

STRUCTURE AND PROPERTIES OF FeCr, CrAl AND FeCrAl COATINGS DEPOSITED BY CATHODIC ARC EVAPORATION

Protective coatings with different compositions of Fe, Cr, and Al were deposited by cathodic arc evaporation method on fragments of Zr1Nb alloy fuel claddings. The influence of the composition and structural state of the developed coatings on their physical and mechanical properties (microhardness, resistance to corrosion and cavitation and abrasive wear) has been studied. It is shown that the optimal combination of mechanical properties and high resistance to oxidation from a series of studied coatings FeCr, FeCrAl, and CrAl have coatings of the FeCrAl system with a concentration of Cr ~ 22 at.% and Al ~ 14.3 at.%. It was found that protective coatings such as FeCr, FeCrAl, and CrAl with a thickness of ~ 12 μm significantly increase the resistance to oxidation and prevent the destruction of fuel claddings under oxidation in air at a temperature of 1150 °C for 1 h.

Anisotropic Growth and Magnetic Properties of α″-Fe16N2@C Nanocones

α″-Fe16N2 nanomaterials with a shape anisotropy for high coercivity performance are of interest in potential applications such as rare-earth-free permanent magnets, which are difficult to synthesize in situ anisotropic growth. Here, we develop a new and facile one-pot microemulsion method with Fe(CO)5 as the iron source and tetraethylenepentamine (TEPA) as the N/C source at low synthesis temperatures to fabricate carbon-coated tetragonal α″-Fe16N2 nanocones. Magnetocrystalline anisotropy energy is suggested as the driving force for the anisotropic growth of α″-Fe16N2@C nanocones because the easy magnetization direction of tetragonal α″-Fe16N2 nanocrystals is along the c axis. The α″-Fe16N2@C nanocones agglomerate to form a fan-like microstructure, in which the thin ends of nanocones direct to its center, due to the magnetostatic energy. The lengths of α″-Fe16N2@C nanocones are ~200 nm and the diameters vary from ~10 nm on one end to ~40 nm on the other end. Carbon shells with a thickness of 2–3 nm protect α″-Fe16N2 nanocones from oxidation in air atmosphere. The α″-Fe16N2@C nanocones synthesized at 433 K show a room-temperature saturation magnetization of 82.6 emu/g and a coercive force of 320 Oe.