Vertically aligned carbon nanotube based electrodes: Fabrication, characterisation and prospects

We present a methodology to fabricate carbon nanotube based electrodes using plasma enhanced chemical vapour deposition. The metal catalyst nanoparticles used to promote nanotube growth are removed using a water plasma treatment in combination with an acid attack. The final integrated microelectrode-based devices present excellent electrocatalytic properties that make them suitable for electrochemical applications. The presented methodology enables the construction of highly regular and dense vertically aligned carbon nanotube (VACNT) forests that can be confined within the patterned bounds of a desired surface. These VACNT electrodes display very low capacitive currents and are amenable to further chemical modifications.     

Boron carbide-copper infiltrated cermets

Porous boron carbide preforms, prepared with and without excess carbon, were infiltrated with a Cu-Si alloy. Contrary to unalloyed copper, the Cu-Si alloy wets and infiltrates the porous preforms. A thermodynamic analysis of the B-C-Cu-Si system indicated that a Si content of the alloy above 15 at% leads to the formation of SiC. At higher Si content, the composition of boron carbide in contact with the melt also changes towards higher boron content. Metallographic examination validated these conclusions. The SiC compound forms preferentially around the free carbon particles in preforms containing excess carbon, and also in the vicinity of carbide that did not contain any excess carbon. Eventually, SiC, a product of the reaction between the carbide and the melt, forms a continuous barrier that impedes completion of the reaction and accounts for the limited increase of hardness as a result of lengthy heat treatments.     

Structure,Composition, Mechanical,and Tribological Properties of BCN Films Deposited by Plasma Enhanced Chemical Vapor Deposition

In this work thin BCN films were deposited by plasma enhanced chemical vapor deposition (PECVD) using chloridic precursors. Through adjusting the BCl₃ content in the inlet gas mixture the chemical composition of the deposited films was changed from carbon rich to boron rich. Based on optical emission spectroscopy (OES) measurements, a correlation between film composition and precursor species concentration in the plasma was established. The films were amorphous as detected by grazing incidence X-ray diffraction (GIXRD). The hardness and the elastic modulus have maximal values of 25.5±1.2 and 191±6 GPa, respectively, for the films with a boron concentration of 45.2 at.%. GIXRD data suggest that a depletion in boron content may initiate the formation of graphitic domains in the amorphous matrix. The observed degradation of the mechanical properties is associated with the graphitization. The tribological behavior was studied with a tribometer operated in pin-on-plate configuration at the temperatures 25 and 400°C. The wear mechanisms were discussed with respect to the formation of a boric acid surface layer which was detected by reflection electron energy loss spectroscopy (REELS) analysis.     

A STUDY OF FRACTURE OF UNIDIRECTIONAL CF/SiC SINGLE EDGE-NOTCHED BEAM UNDER THREE-POINT BENDING- MACRO/MICRO-NUMERICAL MONTE CARLO SIMULATION

In this paper, the fracture process of a unidirectional CF/SiC single edge-notched beam (SENB) under three-point bending (TPB) is studied by means of macro/micro-statistical Monte Carlo simulation. The simulatedP-Δ curves are in agreement with the experimental results before the peaks of curves, and the simulated microevolution patterns are in agreement with the patterns of the crack surfaces, which have verified this method. It is preliminarily demonstrated that the second turning point in the compliance changing rate curve corresponds to the fracture initiation for experiments on SENB under TPB of unidirectional CF/SiC composites.