Synthesis of carbon nanofiber films and nanofiber composite coatings by laser-assisted catalytic chemical vapor deposition

Uniform carbon nanofiber films and nanofiber composite coatings were synthesized from ethylene on nickel coated alumina substrates by laser-assisted catalytic chemical vapor deposition. Laser annealing of a 50 nm thick nickel film produced the catalytic nanoparticles. Thermal decomposition of ethylene over nickel nanoparticles was initiated and maintained by an argon ion laser operated at 488 nm. The films were examined by scanning electron microscopy and by transmission electron microscopy. Overall film uniformity and structure were assessed using micro-Raman spectroscopy. Film quality was related to the experimental parameters such as incident laser power density and irradiation time. For long irradiation times, carbon can be deposited by a thermal process rather than by a catalytic reaction directly over the nanofiber films to form carbon nanocomposite coatings. The process parameters leading to high quality nanofiber films free of amorphous carbon by-products as well as those leading to nanofiber composite coatings are presented.     

Syngas production from ethanol dry reforming using Cu-based perovskite catalysts promoted with rare earth metals

This paper reports about the production of syngas from dry reforming of ethanol (EDR) upon LaCuO₃ and CeCuO₃ catalysts that were prepared by using citrate sol-gel method. EDRs were run with fresh catalyst at each varied variable and 42 L/g_cat/h of feed in a tubular reactor under atmospheric pressure. At equal feed pressure of reactants, steady state CO₂ conversion increased exponentially from 700 to 800 °C while H₂ and CO yields were increasing differently in sigmoid trend rendering H₂/CO ratios to drop linearly from 1.7 to 1.0. However, these reaction results except the latter are otherwise when ethanol-CO₂ ratio was increased (reducing CO₂ pressure) at 750 °C. A minimum H₂/CO ratio was evidenced at the ethanol-CO₂ ratio of 1.48. LaCuO₃ catalyst was more superior in producing syngas owing to its relatively low reduction temperature, high surface area and crystallinity, many active sites, good surface morphology and many C–O, C–H and hydroxyl groups.     

Thermal conductivity of SiC microwires: Effect of temperature and structural domain size uncovered by 0 K limit phonon scattering

A comparative study of structure and thermal properties is reported for three 3C crystalline silicon carbide (SiC) microwires, including Sylramic, Hi-Nicalon S and a sample fabricated by laser chemical vapor deposition (LCVD). Structural characterization by Raman spectroscopy and x-ray diffraction (XRD) finds that the LCVD-based sample contains excessive silicon and smallest grains of SiC but detectable free carbon. Thermal characterization from room temperature down to 20 K uncovers the effect of nanosized grain on thermal properties. The thermal properties are correlated with the structure via structural thermal domain (STD) size, defined as the grain boundary-induced phonon mean free path at the 0 K limit. The STD size of the three samples is found as 9.35, 1.42 and 1.03?nm for the Sylramic, Hi-Nicalon S and LCVD SiC fibers, proportional to and nearly one order of magnification smaller than the corresponding crystalline size determined by XRD: 67–113, 14.6–18.4, and 5.85–7.84?nm.