Dynamic oxidation mechanism of carbon fiber reinforced SiC matrix composite in high-enthalpy and high-speed plasmas

This work employed an inductively coupled plasma wind tunnel to study the dynamic oxidation mechanisms of carbon fiber reinforced SiC matrix composite (Cf/SiC) in high-enthalpy and high-speed plasmas. The results highlighted a transition of passive/active oxidations of SiC at 800–1600 °C and 1–5 kPa. Specially, the active oxidation led to the corrosion of the SiC coating and interruption of the SiO2 growth. The transition borders of active/passive oxidations were thus defined with respect to oxidation temperature and partial pressure of atomic O in the high-enthalpy and high-speed plasmas. In the transition and passive domains, the SiC dissipation was negligible. By multiple dynamic oxidations of Cf/SiC in the domains, the SiO2 thickness was not monotonously increased due to the competing mechanisms of passive oxidation of SiC and dissipation of SiO2. In addition, the mechanical properties of the SiC coating/matrix and the Cf/SiC were maintained after long-term dynamic oxidations, which suggested an excellent thermal stability of Cf/SiC serving in thermal protection systems (TPSs) of reusable hypersonic vehicles.

Observations of gas-phase products from the nitrate radical-initiated oxidation of four monoterpenes

Chemical ionization mass spectrometry with nitrate reagent ion (NO3− CIMS) was used to investigate the products of nitrate radical (NO3) initiated oxidation of four monoterpenes in laboratory chamber experiments. α-Pinene, β-pinene, Δ-3-carene, and α-thujene were studied. The major gas-phase species produced in each system were distinctly different, showing the effect of monoterpene structure on the oxidation mechanism and further elucidated the contributions of these species to particle formation and growth. By comparing groupings of products based on ratios of elements in the general formula CwHxNyOz, the relative importance of specific mechanistic pathways (fragmentation, termination, radical rearrangement) can be assessed for each system. Additionally, the measured time series of the highly oxidized reaction products provide insights into the ratio of relative production and loss rates of the high molecular weight products of the Δ-3-carene system. Measured effective O : C ratio of reaction products were anti-correlated to new particle formation intensity and number concentration for each system; however, monomer : dimer ratio of products was positively correlated. Gas phase yields of oxidation products measured by NO3− CIMS correlated with particle number concentrations for each monoterpene system, with the exception of α-thujene, which produced a considerable amount of low volatility products but no particles. Species-resolved wall loss was measured with NO3− CIMS and found to be highly variable among oxidized reaction products in our stainless steel chamber.

The Oxidation Mechanism of Aniline by Ozone Water and Ozone Micro-nano Bubble Water and Its Influencing Factors

Aniline is a kind of refractory contaminant that is difficult to be degraded by microorganisms. Ozone is a green and efficient reagent to oxidize aniline, while the ozone oxidation efficiency is restricted by the low ozone mass transfer rate. Micro-nano bubble ozonation has been developed as a new method to significantly improve the ozone utilization rate, while the characteristics of ozone micro-nano bubble when compared with dissolved ozone is not clear. The paper carried out batch experiments to research the oxidation effect of aniline by ozone water (OW) and ozone micro-nano bubble water (OMNBW), and found that the degradation rate of aniline by OMNBW was 2.8~5.9% higher than that by OW. The increase of pH had a negative effect on the degradation of aniline by OW and OMNBW. SO42-, Cl-, HCO­3- and Mg2+ could inhibit the degradation efficiency by 0.04%, 0.99%, 0.44% and 10.4% for OW, while the ratios were 1.1%, 6.4%, 4.1% and 1.5% for OMNBW. The addition of humic acid and fulvic acid could decrease the oxidation rate of aniline by 35% and 49% for OW, while the ratios were 41% and 62% for OMNBW. Through quenching experiment, it was found that the direct oxidation by ozone molecules and the indirect oxidation by superoxide radicals were main pathways for aniline oxidation by OW and OMNBW. This work provided a practical guide for the application of OMNBW in wastewater and groundwater treatment process.

Activating the lattice oxygen oxidation mechanism in amorphous molybdenum cobalt oxide nanosheets for water oxidation

The cost-effective deployment of several key energy technologies, such as water electrolysis, CO2 electroreduction and metal-air batteries, relies on the design and engineering of cost-effective catalysts able to accelerate the...

Density Functional Theory (DFT) Investigation of The Oxidative Degradation of NaAsO2 Via Hydroxyl Radical

Arsenic is an environmentally ubiquitous health hazard due to its toxicity combined with its natural abundance and heavy industrial applications. Due to its role in cardiovascular disease, neurotoxicity, and various cancers, it is important to understand environmental fate of arsenic-containing compounds to take steps towards remediation. Sodium arsenite (NaAsO2) is one such compound that has been used worldwide as an herbicide, rodenticide, and insecticide. It is also toxic by ingestion, inhalation, and skin absorption. In aqueous environments arsenite (As(III))-containing compounds can be oxidized to the less-toxic arsenate (As(V)) form. We have investigated the oxidation of sodium arsenite in water solution at the density functional theory level using the Minnesota 06 hybrid (M06-2X) functional and Pople basis sets (6-31G(d,p) and 6-311G(d,p)) with polarizable continuum model (PCM) solvation approach. Our computational results indicate that the oxidation mechanism of NaAsO2 by hydroxyl radical proceeds via sequential addition reactions where sodium arsenite (III) converts to sodium arsenate (V) via an arsenic (IV) intermediate.