Peter Angelini

Formation studies and controlled production of carbon nanohorns using continuous in situ characterization techniques

The formation of carbon nanohorns by laser ablation was investigated using a scanning differential mobility analyzer combined with an ultrafine condensation particle counter. The measurement technique provided time-resolved size distributions for the carbon nanoparticles every minute during the course of the production run. The instrument performance was reasonably stable most of the time; however, during laser ablation, shockwave oscillations leading to significant transient flow and pressure variations were shown to disrupt the DMAs ability to measure accurate distributions. On the basis of the general trend observed in the data taken during the laser-ablation experiments, we found that the geometric mean diameter of the produced population shifted to larger particle sizes with increases in pulse width. For a given laser peak power and repetition rate, carbon nanoparticles of mobility diameter close to 100 nm were produced in a large abundance using longer laser pulse lengths (e.g., 10 ms) as compared to the shorter pulse lengths (e.g., 1 ms). A quantitative assessment of the particle size dispersion (using statistics like the geometric standard deviation) in relation to the laser pulse width could not be done with certainty as the shockwave disturbances produced by the laser-ablation process caused significant disruption to SMPS measurements. When laser ablation was not in operation, it was found that carbon nanoparticles with mobility diameters centred at about 20 nm could be produced by thermally desorbing the previously deposited carbon nanoparticles from the reactor wall at temperatures greater than 1300 K.

Theoretical and experimental analysis of the toughening behavior of whisker reinforcement in ceramic matrix composites

A brief summary of recent analytical solutions which accurately describe the experimentally observed toughening behavior in a variety of whisker reinforced ceramics is presented. These results are found to provide important insights into the whisker, matrix, and interface properties required to obtain further increases in toughness by whisker reinforcement of ceramics.

Processing and Microstructural Characterization of TiB 2 Liquid Phase Sintered with Ni and Ni 3 Al

An Analytical Electron Microscopy investigation of TiB/sub 2/ hot-pressed and pressureless sintered with Ni revealed the presence of Ni/sub 3/B and tau intergranular phase, respectively. Convergent Beam Electron Diffraction (CBED) was used to crystal structure determination and compositions were determined by quantitative x-ray Energy Dispersive Spectroscopy (EDS) and Electron Energy Loss Spectroscopy (EELS). The phase analyses were compared with phase diagram data. An evaluation was also made of TiB/sub 2/ hot pressed with Ni/sub 3/Al. Quantitative EDS and EELS microanalysis indicated a Ni, Al type boride tau (Cr/sub 23/C/sub 6/ type) intergranular phase. 8 references, 4 figures.

Comparison of performance of an analytical electron microscope at 300 and 100 kV

Preliminary results on the performance of an analytical electron microscope (AEM) operating at 300 kV have been obtained and compared with the performance at 100 kV. Some features of the anticipated improvements for transmission electron microscopy (TEM) imaging, convergent beam electron diffraction (CBED), energy dispersive X-ray spectroscopy (EDS), and electron energy loss spectroscopy (EELS) have been studied from the aspect of materials science applications. The electron microscope used was a Philips EM430T operated with a LaB/sub 6/ cathode and equipped with EDAX 9100/90 EDS and Gatan 607 EELS systems. 12 references, 9 figures.