A high yield of levulinic acid was produced by directly converting cellulose over a ZrO 2 catalyst by a one-pot catalytic aqueous phase partial oxidation (APPO) process. Compared to conventional acid hydrolysis, APPO is a highly selective and environmentally benign process with merits of easy recovery and re-use of heterogeneous catalysts.Conversion of cellulosic biomass is of vital importance in the biofuel/ biochemical industry. 1 Recently, several groups have reported that combining hydrolysis and hydrogenolysis of cellulose over noble metal 2 or metal carbide 3 catalysts produced sugar alcohols or polyols such as sorbitol, mannitol, or ethylene glycol, which are precursors in the production of fuels, polymers, and pharmaceuticals. However, these processes suffer from the high costs associated with mineral acids, cellulase enzymes, noble metals, external hydrogen, etc.
Corrosion behavior of Inconel 625 and 718 in subcritical, supercritical and ultrasupercritical water was studied as a function of temperature and time. The change in the chemistry of the as-received surface film on Inconel 625 and 718 after exposure to subcritical water at 325°C and supercritical water at 425°C and 527.5°C for 2 hours was studied. After exposure to 325°C subcritical water, the CrO4 2based film formed; however minor quantities of NiFexCr2-xO4 spinel compounds were observed. The oxide film formed on both alloys when exposed to supercritical water at 425°C consisted of NiFexCr2-xO4 spinel. The surface films on both alloys were identified as NiFe2O4 when exposed to supercritical water at 527.5°C. To characterize the fully developed oxide layer, studies were conducted at test solution temperatures of 527.5 and 600°C. Samples were exposed to these temperatures for 24, 96, and 200 hours. Surface chemistry was analyzed using Xray diffraction, as well as Raman and X-ray photoelectron spectroscopies. Inconel 718 exhibited greater mass gain than Inconel 625 for all temperatures and exposure times. The differences in corrosion behavior of the two alloys are attributed to the lower content of chromium and increased iron content of Inconel 718 as compared to Inconel 625.
Mg-Y-Nd alloy (WE43C or Elektron 43) is a heat treatable magnesium wrought alloy that can be used up to 250°C for aerospace application. This alloy has excellent mechanical properties (UTS: up to 345 MPa at room temperature) and improved corrosion resistance. Electrochemical passivation studies were conducted on this alloy under different heat treatment conditions in 0.1 M NaOH solution with the addition of chloride from 0 to 1000 ppm. The passive potential range typically extended to more than 1.5 VAg/AgCl. The transpassive potential was not dependent on the heat treatment condition of the alloy when the chloride concentration increased up to 500 ppm. However, pitting protection potential varied with the heat treatment condition when the chloride addition was 500 ppm or more. The specimen surface was analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy to understand the passivation behavior of this alloy. The passivated surface of the WE43C specimens indicated that the surface layer consisted of MgO, Mg(OH)2, and rare earth oxide phases, and the heat treatment conditions did not significantly affect the composition of the surface film.
The corrosion behavior of Inconel 625 in molten LiCl solutions maintained at 650°C and containing various quantities of Li 2 O and metallic Li was studied for possible application in the electroreduction of used oxide-based nuclear fuel. This study focusses on the morphological and elemental changes on the surface of the samples with an emphasis on cross-sectional analyses conducted using focused ion beam microscopy. In the absence of metallic Li, a stable oxide film is formed that limits the corrosion of the base material to 0.07mm/year. However, in the presence of metallic Li, the formation of this film is impeded, resulting in dealloying of the base material and the formation of a highly porous microstructure composed primarily of Ni.
Electrochemical corrosion testing was used to evaluate the corrosion resistance of four different nickel-based alloys, namely UNS N06230, UNS N06025, UNS N06617, and UNS N06625, in a molten nitrate salt that is used as a heat transfer media and thermal energy storage material in solar-thermal power plants. The tests were conducted at 500 °C to simulate near-maximum service temperature in the 3:2 by weight sodium nitrate: potassium nitrate mixture. All tested samples had corrosion current densities on the order of 10−4 A cm−2 with corrosion potentials varying from −227 mV to −66.2 mV vs Pt. The tested samples exhibited low corrosion current density in the range of 0.225 mA cm−2 to 0.431 mA cm−2. The morphology of the samples surfaces was studied using scanning electron microscopy which showed the formation of a surface film on all samples. Cross-sectional analysis was performed using focused ion beam scanning electron microscopy. The surface chemistry was ascertained using energy dispersive spectroscopy, X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Raman spectra paired with XPS suggested the formation of various nickel-chromium-iron spinels on UNS N06625. These results show that UNS N06625 has the potential to be a material for use in solar-thermal plants.
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