Study on oxidation behavior during process of recycling carbon fibers from CFRP by pyrolysis

The study utilized a pyrolysis method to recycle carbon fibers from carbon fiber reinforced polymer (CFRP), followed by oxidation to remove pyrolysis carbon. The obtained recycled carbon fibers had good mechanical properties, and the tensile strength could reach 96.2% of the virgin carbon fibers under the optimal process conditions. The recycled carbon fibers displayed similar chemical structure and graphitization degree as the virgin carbon fibers, and showed better wettability with epoxy resin. In addition, density functional theory (DFT) calculations were also employed to analyze the mechanism of pyrolysis carbon oxidation removal. The results showed that the adsorption energy of oxygen on pyrolytic carbon and the reaction activation energy were lower than those of carbon fibers, indicating that pyrolytic carbon was more easily oxidized than carbon fibers. This allowed pyrolytic carbon to be removed by oxidation at relatively low temperatures and preserved the integrity of carbon fibers, thus ensuring that the carbon fibers also maintained excellent mechanical properties after recycling. This study helps to reveal the oxidation mechanism of resin pyrolysis carbon, providing technical support for efficient and clean recycling of carbon fibers.

Effect of lubricating base oil on the oxidation behavior of diesel exhaust soot

In this study, the oxidation behaviors of soot particles from diesel engine when using neat diesel fuel (DF) and lubricating base oil-blended fuel (BBF) were investigated. The changes in the average particle size and nanostructure parameters during soot oxidation process were analyzed. Exhaust particulate matter (PM) samples were collected from a four-stroke, four-cylinder and turbo0charged diesel engine operated under 1200 rpm and 200 Nm. DF and BBF Soot samples with different oxidation weight losses of 20 %, 40 %, and 60 % were obtained by thermogravimetric isothermal oxidation experiments at 600 °C, and the particle size and nanostructure parameters (fringe length, L_a; fringe tortuosity, T_f) were characterized using high-resolution transmission electron microscopy (HRTEM). Results show that the DF soot particles exhibited an oxidation mode that was initially dominated by surface oxidation and gradually deviated to internal oxidation. Combustion of the base oil increased the soot internal oxidation tendency. HRTEM results showed that as the soot oxidation progressed, the primary particles showed a shell-core, onion-like and hollow structure gradually. The L_a of the primary particles gradually increased, and the T_f gradually decreased, indicating that the soot layer crystallites were rearranged during the oxidation process, which resulted in a disordered nanostructure that transitioned to a more graphitized nanostructure.

Effect of Co on the microstructure and oxidation behavior of CoxCrCuFeMnNi high entropy alloy powders

The microstructure, phase, alloying behavior, and oxidation behavior of the Co_xCrCuFeMnNi (x = 0, 0.5, 1.0, 1.5, 2.0, named as Co₀, Co_0.5, Co_1.0, Co_1.5, and Co_0.5, respectively) high entropy alloy powders (HEAPs) prepared by mechanical alloying were studied. The results indicated that the HEAPs began to be alloyed after ball milling for 5 h, and the particle size is about 40∼60 μm. After 50 h of milling, the Co₀ and Co_0.5 HEAPs are composed of metastable FCC and minor BCC solid solution phases, while the other HEAPs consist of single metastable FCC solid solution phase. After vacuum annealing or atmospheric oxidation at 700 °C, the metastable FCC and BCC phases decompose into FCC1 and FCC2 and ρ phases, respectively. The oxidation mass gain of Co_xCrCuFeMnNi HEAPs shows a parabolic upward trend. With the increase of Co content, the oxidation rate constant decreases, indicating that the oxidation resistance of the HEAPs decreases with the increase of Co content.

Experimental characterization of enhanced SNCR process with carbonaceous gas additives

Carbonaceous gases such as CO and alkanes are commonly used as additives to enhance the selective non-catalytic reduction (SNCR) performance due to their high reducibility. This study compared the effect of CO and CH₄ on NO reduction in a tubular reactor with simulated flue gas. The enhancement of C₃H₈ on SNCR process was tested at extremely low temperature, i.e. 650 °C. Experimental results suggested that reactions between NH₃ and SO₂ were favored at low temperatures and the competition for NH₃ between SO₂ and NO was influenced by gas additives. A maximum downward shift of 25 °C and 100 °C in temperature window for 50% NO reduction efficiency was obtained with the addition of CO and CH₄, respectively. Considerable CO emission was observed with addition of CH₄. The addition of CH₄ contributed to the formation of a self-accelerating reaction route within NO/O₂/NH₃ SNCR reaction system. NO₂ produced from NO accelerates the oxidation of CH₄ to CO, while the oxidation of CH₄ returns to enhance the NO reduction globally. Optimal NO reduction of 44% was achieved with addition of C₃H₈ at 650 °C. Substantial portion of C₃H₈ was partially oxidized to CO and the remaining was converted into C₂H₄ and C₃H₆ during the SNCR process. Oxidative dehydrogenation of C₃H₈ was involved. High reactivity of C₃H₆ and C₂H₄ favored the further oxidation and cracking to produce CO. These differences in oxidation behavior significantly influence the promotion capacities of CO, CH₄ and C₃H₈ for NO reduction.

Oxidation Resistance of Materials Based on Ti3AlC2 Nanolaminate at 600 °C in Air

The oxidation behavior of Ti3AlC2-based materials had been investigated at 600 °C in static air for 1000 h. It was shown that the intense increase of weight gain per unit surface area for sintered material with porosity of 22 % attributed to oxidation of the outer surface of the specimen and surfaces of pores in the bulk material. The oxidation kinetics of the hot-pressed Ti3AlC2-based material with 1 % porosity remarkably increased for the first 15 h and then slowly decreased. The weight gain per unit surface area for this material was 1.0 mg/cm(2) after exposition for 1000 h. The intense initial oxidation of Ti3AlC2-based materials can be eliminated by pre-oxidation treatment at 1200 °C in air for 2 h. As a result, the weight gain per unit surface area for the pre-oxidized material did not exceed 0.11 mg/cm(2) after 1000 h of exposition at 600 °C in air. It was demonstrated that the oxidation resistance of Ti3AlC2-based materials can be significantly improved by niobium addition.