Three different types of carbon nanotubes being considered for bio-recognition experiments were studied using resonance Raman spectroscopy. Raman spectroscopy, taken using several laser excitation energies, has been shown to provide an effective characterization tool for these carbon nanotubes. The technique yields structural information that both complements and corroborates structural information obtained using electron microscopy techniques, such as TEM, SEM, and AFM.

Scanning transmission electron microscopy (STEM) coupled with energy dispersive x-ray analysis (EDX) and electron energy-loss spectroscopy (EELS) has been used to characterize the elemental composition and oxidation conditions of various soot samples. The STEM employed in this investigation was the Vacuum Generators HB603, with a microanalytical resolution approaching 1 rnm, that allowed the analysis of individual soot particles and aggregates. The aim of this research is quantification of the EDX spectra which is possible after background and absorption corrections. This information can then be used for comparative studies of different fuels and combustion processes. EELS has been employed to determine the amount of graphitic carbon in a soot particulate, and the detection of trace elements of low atomic number. It has been shown in soot that for Carbon the energy-loss of the p shell electrons increases with the amount of oxidation at high temperatures. Analysis and characterization of gas turbine soot, collected from an engine exhaust duct of a 737-300 aircraft showed an abundance of different elements. Some of these elements originated from the fuel and combustion processes, while other elements were components of the engine itself that combined with the soot particulates during the combustion process. The study showed that soot impurities were found in all discrete sections of aggregates, and that only one or two small soot particulates were necessary to obtain a chemical fingerprint. Other investigations include; coal soot, diesel soot at different engine operating conditions and soot produced from wood burning. The richness of the spectra obtained and the ability to quantify results represents an opportunity to accomplish source identification in a novel, powerful way.

High resolution transmission electron microscopy (HRTEM) was used to characterize nanostructures in soots produced in flames of benzene, acetylene, or ethylene premixed with oxygen and an inert diluent gas. The nanostructures ranged from ∼2 nm to ∼30 nm in size with a hollow core measuring about ∼ 1 nm to ∼10 nm in diameter and containing 5 to 20 shells. The shapes of the nanostructures included spherical, spheroidal, tubular, and trigonous.

The objective of the work reported here is to reduce the thermal conductivity of thermoelectric materials in order to improve their figureof- merit and conversion efficiency. Theory predicts that the addition of ultra-fine, inert, phonon-scattering centers to thermoelectric materials will reduce their thermal conductivity [1]. To investigate this prediction, ultra-fine particulates (20Å to 120Å) of silicon nitride have been added to boron doped, p-type, 80/20 SiGe. All of the SiGe samples produced from ultra-fine powder have lower thermal conductivities, than that for standard SiGe, but high temperature heat treatment increases the thermal conductivity back to the value for standard SiGe. However, the SiGe samples with silicon nitride, inert, phonon-scattering centers, retained the lower thermal conductivity after several heat treatments. A reduction of approximately 25% in thermal conductivity has been achieved in these samples.

Individual particles of argon-atomized Fe-30Ni powder are electrodynamically levitated and remelted by a CO2 laser pulse. The thermal history of each droplet during remelting and solidification is monitored by single-color radiation pyrometry at each of three wavelengths (850, 750, and 550 nm). Experiments are done in an atmosphere of either air or nitrogen. The average supercooling of six experiments performed in nitrogen is 298 K with a standard deviation of 14 K. This value is of the same order as several others reported in the literature using bulk levitation and emulsification techniques. The average supercooling of seven experiments performed in air is 163 K with a standard deviation of 20 K. The difference suggests that oxides are forming in the air-remelting experiments and catalyzing nucleation at relatively low supercoolings. The average cooling rate of the liquid droplets prior to solidification in nitrogen is 1.5 × 105 K/s. This measured cooling rate is somewhat higher than that predicted by Newtonian heat flow modeling, and the difference is attributed to radiative losses not considered in the Newtonian model. The measured cooling rate is used to estimate the total heat transfer coefficient characterizing cooling of a small metal droplet in a quiescent gas atmosphere. A lower bound of 1.5 × 106 K/s on the droplet heating rate during recalescence and a minimum average liquid/solid interfacial velocity during recalescence of 0.1 m/s are estimated.