Oxidation behavior of Ti–46Al–8Nb alloy with boron and carbon addition under thermal cycling conditions

Oxidation behavior of Ti–46Al–8Nb (in at.%) alloy with boron and carbon addition under thermal cycling conditions was investigated. Oxidation of Ti–46Al–8Nb, Ti–46Al–8Nb–1B and Ti–46Al–8Nb–1B-0.25C (in at.%) alloys was carried out at 1073 K in laboratory air for 42 cycles (1 cycle, 24 h), 1008 h in total. The mass loss rates of Ti–46Al–8Nb and Ti–46Al–8Nb–1B measured during the oxidation were similar. The best oxidation resistance was found for Ti–46Al–8Nb–1B-0.25C alloy with the smallest mass change. XRD and SEM-EDS investigations showed that in all cases, the oxide scales compositions were substantially similar. The scale consisted of an outer layer built of Al₂O₃ with the presence of some amounts of TiO₂, an intermediate layer of the scale consisting of TiO₂, an inner layer composed of oxides and nitrides. Additionally, niobium rich particles at the scale/substrate interface were present. The oxidation mechanism of Ti–46Al–8Nb was studied via two-stage isothermal oxidation (24 h in ¹⁶O₂ followed by 24 h in ¹⁸O₂) at 1073 K combined with secondary neutral mass spectroscopy (SNMS). These results indicate that the oxidation mechanism depends on a mixed diffusion process, consisting of outward transport of cations and simultaneous oxygen inward transport.     

Management of thiosalts in mill effluents by chemical oxidation or buffering in the lime neutralization process

Laboratory studies were conducted to investigate the removal or management of thiosalts within the lime-neutralization process, to prevent or minimize the adverse effects of thiosalts that cause delayed acidity to downstream environment. The oxidizing reagent hydrogen peroxide (H₂O₂) and the pH stabilizing (buffering) reagents carbon dioxide (CO₂), sodium bicarbonate (NaHCO₃) and sodium carbonate (Na₂CO₃) were examined for removal and management of thiosalts, respectively. Chemical oxygen demand (COD) was determined to be a proxy for thiosalts and was employed for their rapid assessment. The Target Level of thiosalts harmless to aquatic life was found to be 30 mg/L or less. The optimized lime-neutralization process required a pH level of 9.5–10 and aeration. Over-liming to pH levels >11 did not provide excess alkalinity, hardness, or a decrease in thiosalt levels.Addition of H₂O₂ to either the acid or lime-neutralized water at a molar H₂O₂:S₂O₃ ratio of 1–1.5 removed thiosalts to safe levels. About 10–15 min. at room temperature was ample time low temperatures slowed down the process but the dosages were not affected. Removal of thiosalts from 170 to 30 mg/L caused a decrease in pH from 9.6 to 6.5. Among the buffering reagents studied, both NaHCO₃ and Na₂CO₃ provided adequate buffering and a stable pH of 7 to the lime-neutralized water; whereas CO₂ resulted in poor buffering and an unstable pH that remained below 6. In cold temperatures, NaHCO₃ and Na₂CO₃ also outperformed CO₂ with higher alkalinity and hardness. Na₂CO₃ addition to lime neutralized water at pH 9.5 was found to be the most cost-effective option. Other methods could have niche applications, depending on seasonal variations and temperature.     

Oxygen influenced intergranular crack propagation: analysing microstructure and chemistry in the crack tip region

Abstract

Ni-base superalloys have for decades been studied with regard to environmentally influenced intergranular crack propagation. For high temperature fatigue frequencies <0.1 Hz, it has been shown that an oxygen-rich environment promotes time-dependent crack growth while at >0.1 Hz and/or in inert environments (e.g. vacuum) crack growth is cycle dependent. Oxygen interaction at, or ahead of, the crack tip has been pointed out as the reason for the degraded mechanical properties. While many aspects of this type of crack growth have been previously investigated there is still no consensus about the detailed mechanisms, mainly due to the lack of in-detail investigations of the crack-tip region.

Here, crack tip regions in the Ni-base superalloy Alloy 718 were studied. Specimens were subjected to 90 s hold-times at 550°C and 650°C. Crack growth was arrested before final fracture, allowing cross-sectional analyses of the crack-tip region using scanning electron microscopy (SEM). Detailed studies of the crack-tip region were performed using transmission electron microscopy (TEM) and atom probe tomography (APT). For both APT and TEM samples, site-specific focussed ion beam (FIB) sample preparation was performed in a combined FIB-SEM system. The methodology of accessing and analysing the crack tip region is shown. Initial results on oxidation, oxygen penetration and plastic deformation are shown and discussed.     

Effect of Ni7+ Ion Irradiation on Structure and Ammonia Sensing Properties of Thermally Oxidized Zinc and Indium Films

ZnO and In2O3 films were prepared by thermal oxidation of vacuum deposited zinc and indium films, respectively onto the glass substrate at 30 C. The fabricated films have been irradiated with 100-MeV Ni7+ ions at different fluences ranging from 5×1011 to 5×1013 ions/cm2. The structural and gas sensing properties of pristine and irradiated films have been discussed. X-ray diffraction (XRD) pattern of pristine and irradiated films reveal that the films are polycrystalline in nature and crystallinity increases after irradiation. In this study, highly porous In2O3 nanorods evolved when being irradiated at a fluence of 5×1013 ions/cm2 while ZnO film shows decrease in number of nanowires. The ammonia sensing performance of the Ni7+ irradiated In2O3 films shows an improvement as compared to its pristine counterpart.     

Cytosine assisted aqueous synthesis of AgPt hollow alloyed nanostructures as highly active electrocatalyst for ethylene glycol oxidation and hydrogen evolution

Herein, a simple one-pot aqueous method was developed for synthesis of AgPt hollow alloyed nanostructures (AgPt HANS) with polyvinylpyrrolidone (PVP) and cytosine as the dispersing agent and eco-friendly growth-director, respectively. The synthesized architectures displayed the improved catalytic performance toward ethylene glycol oxidation reaction (EGOR) relative to commercial Pt black in alkaline media. Meanwhile, the catalyst exhibited the enhanced catalytic activity for hydrogen evolution reaction (HER) with the positive onset potential (E_onset, ?39 mV) and a small Tafel slope (40 mV dec^?1) relative to commercial Pt/C (20 wt%, ?31 mV, 33 mV dec^?1) in 0.5 M H₂SO₄, along with the more positive E_onset (?34 mV) and a smaller Tafel slope (59 mV dec^?1) in 0.5 M KOH compared with Pt/C (?35 mV, 85 mV dec^?1).     

Light-induced changes in bottled white wine and underlying photochemical mechanisms

Bottled white wine may be exposed to UV-visible light for considerable periods of time before it is consumed. Light exposure may induce an off-flavor known as “sunlight” flavor, bleach the color of the wine, and/or increase browning and deplete sulfur dioxide. The changes that occur in bottled white wine exposed to light depend on the wine composition, the irradiation conditions, and the light exposure time. The light-induced changes in the aroma, volatile composition, color, and concentrations of oxygen and sulfur dioxide in bottled white wine are reviewed. In addition, the photochemical reactions thought to have a role in these changes are described. These include the riboflavin-sensitized oxidation of methionine, resulting in the formation of methanethiol and dimethyl disulfide, and the photodegradation of iron(III) tartrate, which gives rise to glyoxylic acid, an aldehyde known to react with flavan-3-ols to form yellow xanthylium cation pigments.     

工作面采长对自燃危险性及经济效益的影响

本文阐述了工作面采长与采空区防灭火的关系,并以石港公司为例,通过计算明确了工作面采长的取值范围,并结合经济效益进行综合分析,最终确定石港公司工作面设计采长应为120m。充分论证了合理设计工作面采长可以有效防治自燃。     

Novel interactions of caffeic acid with different hemoglobins: Effects on discoloration and lipid oxidation in different washed muscles

Caffeic acid (CA) accelerated methemoglobin (Hb) formation at pH 5.8 and 25 °C. This was attributed to electron donation from CA to liganded O₂ in Hb. CA inhibited hemin dissociation from metHb. Pig Hb remained mostly as oxyHb and did not promote lipid oxidation in washed cod muscle (WCM) nor washed turkey muscle (WTM) during iced storage at pH 5.8. Conversely, perch Hb rapidly was converted to metHb and readily promoted lipid oxidation based on lipid peroxide and hexanal formation. CA strongly inhibited perch Hb-mediated lipid oxidation during storage. Once metHb formation occurred in WCM, CA appeared to maintain the heme protein as metHb during the remainder of iced storage. CA may have become bound to perch Hb based on filtration analysis. CA facilitated the transfer of perch Hb (but not pig Hb) from the aqueous phase to the insoluble components of WCM. Collectively, these results suggest that CA inhibited Hb-mediated lipid oxidation by various mechanisms not related to inhibition of metHb formation.