A heterogeneous reaction mechanism based on elementary reaction steps is proposed for the prediction of pyrolytic carbon deposition in chemical vapor infiltration, involving 72 surface species and 277 surface elementary reactions. A “prototype” gas-phase reaction is chosen to match with the corresponding surface reaction, and correction methods for kinetic data are also proposed for three kinds of surface reactions (i.e., surface/gas reactions, unimolecular surface reactions, surface/surface reactions) in the present work. Simulation results of deposition kinetics and gas-phase compositions of propane pyrolysis are validated by previously published experimental results of Marquaire’s group, with a surface to volume ratio from 5 to 175 cm–1 and temperature from 1173 to 1323 K. The reaction pathways of the heterogeneous surface reactions and homogeneous gas-phase reactions are studied on the basis of the reaction flow rate analysis. An acceptable agreement indicates that the present heterogeneous reaction mechanism is reasonable, and acetylene, ethylene, and benzene are recognized as the main precursors of the pyrolytic carbon deposition at the present processing conditions.

•NGHMs were constructed using PSMs as template and melamine as nitrogen source.•NGHMs exhibited high catalytic activity towards ORR.•NGHMs displayed a comparable ORR limiting current density to JM 40 wt% Pt/C.•ORR on NGHMs electrode was dominated by 4e− pathway in a wide potential range.Nitrogen-doped graphene hollow microspheres (NGHMs) were constructed, using polystyrene microspheres (PSMs) as the sacrificial template. Negatively charged graphene oxide nanosheets (GONs) were assembled onto sulfonated PSMs with the aid of poly(ethyleneimine) through electrostatic interaction. NGHMs were obtained by pyrolysis the mixture of melamine and GON-wrapped PSMs under a nitrogen atmosphere. During the pyrolysis, the removal of PSMs and reduction of GONs and incorporation of heteroatoms were realized simultaneously. The nitrogen atomic percentage in NGHMs reached 7.13%, and sulfur content was also detected. The prepared NGHMs exhibited high catalytic activity toward oxygen reduction reaction (ORR) in alkaline solution with a comparable limiting current density to JM 40 wt% Pt/C. The ORR on NGHMs electrode was dominated by the four-electron pathway in a wide potential range with long-term stability and high fuel selectivity. The enhanced electrocatalytic performance of NGHMs could be ascribed not only to the high nitrogen content, but also to the hollow sphere architecture. Moreover, the nitrogen precursor, melamine, increased the percentage of graphitic-N and prevented hollow spheres from aggregation, which also helped to improve the catalytic activity of NGHMs.

We studied using dynamic Monte Carlo (DMC) models the size-selective kinetic characteristics of CO monolayer oxidation (CO stripping) on multiscale nanostructured Pt/GC model electrodes comprising nanodisks with diameters of 120 nm and nanoparticles with diameters of 6 nm. We used the DMC models to simulate preadsorbed CO (COad) oxidation peaks and voltammetry responses for the two types of nanostructures and compared them to experiments. Our DMC simulations showed that the different CO stripping voltammetry peaks for the nanodisks and the nanoparticles observed in experiments result from different surface motilities of the COad molecules on the catalyst surfaces and from different initial COad configurations.

This paper proposes a method to model hydrocarbon reforming by coupling detailed chemical kinetics with complex computational fluid dynamics. The entire chemistry of catalyzed reactions was confined within the geometrically simple channels and modeled using the low-dimensional plug model, into which the interactive thermal control of the multi-channel reforming reactor has been implemented with a tail-gas combustor around the external surface of these catalytic channels. The geometrically complex flow in the tail gas combustor was simulated using FLUENT without involving any chemical reactions. The influences of the conditions at the reactor inlet such as the inlet gas velocity, the inlet gas composition and the variety of hydrocarbons of each channel on gas conversions were investigated numerically. The impact of the tail gas combustor setup on the efficiency of the reforming reactor was also analyzed. Methane catalytic partial oxidation (CPOx) and propane steam reforming (SR) were used to illustrate the approach reported in the present work.

C/C–SiC composites were prepared by molten infiltration of silicon powders, using porous C/C composites as frameworks. The porosities of the C/C–SiC composites were about 0.89–2.8 vol%, which is denser than traditional C/C composites. The ablation properties were tested using an oxyacetylene torch. Three annular regions were present on the ablation surface. With increasing pyrocarbon fraction, a white ceramic oxide layer formed from the boundary to the center of the surface. The ablation experimental results also showed that the linear and mass ablation rates of the composites decreased with increasing carbon fraction. Linear SiO2 whiskers of diameter 800 nm and length approximately 3 μm were formed near the boundaries of the ablation surfaces of the C/C–SiC composites produced with low-porosity C/C frameworks. The ablation mechanism of the C/C–SiC composites is discussed, based on a heterogeneous ablation reaction model and a supersaturation assumption.

The viscoelastic characterization and thermal stability property of some multifunctional epoxy/anhydride systems cured at different schedules were investigated by dynamic mechanical thermal analysis (DMTA) in single cantilever mode at fixed frequency, and by non-isothermal thermogravimetric (TG) analysis, respectively. According to the DMTA results, three obviously different glass transition temperatures (Tg), were observed, among which TGDDM/MHHPA system exhibits the largest Tg. While from the TG curves, the results of the mass loss and thermal stability showed that, after cured for a prolonged duration, the TGDDM/MHHPA system possessed the most excellent performance in heat resistance.

A reliable and optimized process to grow carbon nanotubes (CNTs) in templated pores of polymer derived ceramic (PDC) matrix was developed. It is realized through the pyrolysis of a preceramic polymer, i.e., poly (methyl-phenyl-silsesquioxane) (denoted as PMPS), in argon atmosphere at 1000 °C together with nickel-catalyst-coated poly-methyl-methacrylate (PMMA) microbeads (denoted as PMMA-Ni). PMPS served as both a precursor for the ceramic matrix and a carbon source for the CNT growth. PMMA microbeads were used as sacrificial pore formers and coated with nickel via an electroless plating method, which provides an improved control of particle size of the catalyst and its distribution in the material. The influence of PMMA-Ni loading on the in situ growth of CNTs and the properties of CNTs/SiOC nanocomposites were studied through thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and density/porosity measurements. Under optimized conditions, uniform distribution of in situ grown CNTs was observed within the templated pores of the SiOC matrix. The optimized process leads to reproducible high yield of CNTs in the pores. The development of such novel CNT/cellular ceramic nanocomposite materials is of significant interest for a variety of sensor applications.