Carbide

About: Carbide is a research topic. Over the lifetime, 36331 publications have been published within this topic receiving 503586 citations.

Magnetic Nanoparticles of Iron Carbide, Iron Oxide, Iron@Iron Oxide, and Metal Iron Synthesized by Laser Ablation in Organic Solvents

Abstract: Iron-based nanoparticles can have useful magnetic and catalytic properties. We investigated the synthesis of iron-based nanostructures by laser ablation of bulk iron with 1064 nm nanosecond pulses in the following organic solvents: tetrahydrofuran, acetonitrile, dimethylformamide, dimethylsulfoxide, toluene, and ethanol. Structural analysis carried out by transmission electron microscopy and X-ray diffraction revealed that the solvent has a dramatic influence on both the composition and the nanostructure of nanoparticles. Various magnetic nanoparticles like iron carbide (Fe3C), magnetic iron oxide (magnetite/maghemite), metal iron (α-Fe), and iron@iron oxide are obtained by varying the solvent and keeping unchanged all the other experimental conditions. These results are the consequences of the different reactivity of solvent molecules exposed to the plasma plume generated during the ablation process.

The Phase of Iron Catalyst Nanoparticles during Carbon Nanotube Growth

Abstract: We study the Fe-catalyzed chemical vapor deposition of carbon nanotubes by complementary in situ grazing-incidence X-ray diffraction, in situ X-ray reflectivity, and environmental transmission electron microscopy. We find that typical oxide supported Fe catalyst films form widely varying mixtures of bcc and fcc phased Fe nanoparticles upon reduction, which we ascribe to variations in minor commonly present carbon contamination levels. Depending on the as-formed phase composition, different growth modes occur upon hydrocarbon exposure: For γ-rich Fe nanoparticle distributions, metallic Fe is the active catalyst phase, implying that carbide formation is not a prerequisite for nanotube growth. For α-rich catalyst mixtures, Fe3C formation more readily occurs and constitutes part of the nanotube growth process. We propose that this behavior can be rationalized in terms of kinetically accessible pathways, which we discuss in the context of the bulk iron–carbon phase diagram with the inclusion of phase equilibri...

Pressureless Sintering of Zirconium Diboride: Particle Size and Additive Effects

Abstract: Zirconium diboride (ZrB 2 ) was densified by pressureless sintering using <4-wt% boron carbide and/or carbon as sintering aids. As-received ZrB 2 with an average particle size of ∼ 2 μm could be sintered to ∼ 100% density at 1900°C using a combination of boron carbide and carbon to react with and remove the surface oxide impurities. Even though particle size reduction increased the oxygen content of the powders from ∼ 0.9 wt% for the as-received powder to ∼ 2.0 wt%, the reduction in particle size enhanced the sinterability of the powder. Attrition-milled ZrB 2 with an average particle size of <0.5 μm was sintered to nearly full density at 1850°C using either boron carbide or a combination of boride carbide and carbon. Regardless of the starting particle size, densification of ZrB 2 was not possible without the removal of oxygen-based impurities on the particle surfaces by a chemical reaction.