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Linear carborane-carbosilane-phenylacetylene co-polymer has been synthesized as precursor for thermosets and ceramics for the protection of carbon fibers from oxidation in an oxidizing environment. The novel linear co-polymers can be processed conveniently and converted into thermoset or ceramics since they are either liquids or low melting solids at room temperature and are soluble in most organic solvents. Treatment of carbon fibers with poly(carborane-carbosilane-phenylacetylene) by precursor infiltration and pyrolysis (PIP) process can provide a protective barrier at elevated temperatures. Tensile strength measurement revealed that the coated carbon fiber maintained 81.39% of its original strength. It was found that the novel co-polymer is highly efficient in protecting the carbon fibers from oxidation breakdown when used as a matrix material (ceramic). Boron and C C group appear to be the key to the unique oxidative stability of the composite compositions. The derived ceramic coatings on carbon fibers were characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Anti-oxidation studies were performed by thermogravimetric analyses (TGA). The results showed that the oxidation resistance of carbon fibers has been promoted obviously by the ceramic coatings. [ABSTRACT FROM AUTHOR]

[Display omitted] • NH 4 +-N denitrogenation under near-neutral pH and aerobic conditions. • NH 4 +-N conversion rate of ∼0.35 mg N L–1 min–1 and N 2 selectivity of >97 %. • Efficient Cl− conversion into reactive chlorine species over BiOCl photocatalyst. • Cl−-mediated Mars-van Krevelen mechanism for reactive chlorine species production. Selective oxidation of ammonia nitrogen (NH 4 +-N) into N 2 is critical to remove the superfluous nitrogen in the hydrosphere and control the fixed nitrogen inventory for the global nitrogen cycle. Herein, on the basis of chlorine radical chemistry, we report the photocatalytic denitrogenation over BiOCl with high N 2 selectivity (>97 %). Efficient Cl– conversion into reactive chlorine species (RCS) is achieved, serving as the predominant reactive species for NH 4 +-N oxidation. According to the zero-order kinetics of Cl– for RCS generation, as well as the Cl– extraction/insertion over BiOCl, a Cl–-mediated Mars-van Krevelen mechanism is revealed, by which the catalytic performance shifts from the undesired deactivation (because of photocorrosion) towards the remarkably enhanced reactivity. This system exhibits great potential for the denitrogenation of saline wastewater, also provides an interesting strategy to activate inert chemical bond via the chlorine cycle. [ABSTRACT FROM AUTHOR]

In this review, the physical and chemical properties of the pyrrhotite group minerals are discussed, particularly their mineralogical behavior during mineral processing and phase transitions. Pyrrhotites are often associated with nickel ores and gold deposits. Consideration of the leaching processes of pyrrhotites focuses on the recovery of Ni and Au. The mechanisms of acid leaching are presented from physical, chemical, electrochemical, and crystallographic viewpoints. Other pyrrhotite processing techniques, including oxidation and flotation, are also included in this article. [ABSTRACT FROM AUTHOR]

Abstract: In this work, the effects of stoichiometry on phase evolution during the oxidation of mss (monosulfide solid solution) were investigated. A series of mss samples, ranging from Fe7.9S8 to Fe2.37Ni5.53S8 were synthesized from pure components. Samples with grain size 53–90μm were oxidized at 830 and 850K in air in a muffle furnace. The Rietveld quantitative phase analysis method was used to identify and quantify the phase information from powder X-ray diffraction (XRD) profiles. Hematite was observed and accounted for most of the oxidized iron. Nickel in mss was not oxidized to NiO under current isothermal conditions; instead, it was finally transformed to Ni17S18. Hematite, Fe2(SO4)3 and residual mss were identified in the final phases after 24h oxidation of the mss composition Fe7.9S8; hematite and Ni17S18 for compositions Fe6.15Ni1.54S8 and Fe2.37Ni5.53S8; hematite, Ni17S18 and pentlandite for Fe6.4Ni1.6S8. Given a constant iron to nickel atomic ratio of 4:1, the sample with lower metal concentration, Fe6.15Ni1.54S8, showed a faster oxidation rate than its metal richer counterpart, Fe6.4Ni1.6S8. The mean oxidation rates for these two samples are 1.85 × 10-4 and 1.22 × 10-4s-1 respectively for 1.5h heating at 830K. Vyazovkin''s theory of changing activation energy (Ea) with reaction extent (y) was employed in the current kinetic study. The activation energy was determined using a model-free method. The oxidation of Fe6.4Ni1.6S8 exhibited a higher Ea than Fe6.15Ni1.54S8 over the course of reaction. The activation energy increases with y from 67.1 to 103.3kJmol-1 for mss composition Fe6.15Ni1.54S8; 76.1 to 195.0kJmol-1 for Fe6.4Ni1.6S8. Bulk compositions Fe7.9S8, Fe2.37Ni5.53S8 were selected to give a constant metal to sulfur atomic ratio of 7.9:8. Oxidation of Fe2.37Ni5.53S8 achieved equilibrium within 1h, compared to 5h for Fe7.9S8. [Copyright &y& Elsevier]

In this work, a study of the solid-phase, colouring reaction was undertaken in pure calcite and natural marble. Inorganic iron redox couples (Fe2+/Fe3+) and their redox product hematite (Fe2O3) produce a natural red colour on the treated surface of the marble. Pure calcite was used to simulate the marble matrix under colouring treatment. This simulation quantified the kinetics of the colour enhancement process as well as minimised the complexity of analysis caused by trace impurities in natural marble. The practical importance of this work was verified by following the colour change in a natural marble sample annealed at 380 °C. The observed kinetics is modelled using the well-known Avrami equation. A change in reaction mechanism was observed at around 400–420 °C and it is proposed that an annealing temperature of 380 °C be adopted. This provides a good practical compromise between maximising rate and the constraint imposed by excessive acid-gas evolution at higher temperatures. The activation energy of the reaction was estimated to be 398 kJ mol-1. This is within the normal range expected for solid-phase, redox reactions. [Copyright &y& Elsevier]

Abstract: An oxidation protective Si–SiC coating with randomly oriented SiC nanowires was prepared on the SiC-coated carbon/carbon (C/C) composites by a two-step technique. First, a porous network of SiC nanowires was produced using chemical vapor deposition. This material was subjected to pack cementation to infiltrate the porous layer with a mixture of Si and SiC. The nanowires in the coating could efficiently suppress the cracking of the coating by various toughening mechanisms including nanowire pullout, nanowire bridging, microcrack deflection and good interaction between nanowire/matrix interface. The results of thermogravimetric analysis and thermal shock showed that the coating had excellent oxidation protection for C/C composites between room temperature and 1500°C. These results were confirmed by two additional oxidation experiments conducted at temperature of 900 and 1400°C, which demonstrated that the coating could efficiently protect C/C composites from oxidation at 900°C for more than 313h or at 1400°C for more than 112h. [Copyright &y& Elsevier]