John B. VanderSande

The structure of electroless NiP films as a function of composition

Examines the evolution of the microstructure of Ni-P deposits with varying P content. Explains that electroless Ni-P was deposited on Cu-coated glass slides in a commercial nickel sulfate-sodium hypophosphite both held at 363K. Deposits of differing composition were prepared by varying the pH of the bath from 2.5 to 6.5 in increments of 1.0. Uses energy dispersive x-ray analyses from the electron microprobe and from the scanning transmission electron microscope (STEM) to semi-quantitatively determine the P content of the deposits as a function of pH. Finds that an amorphous-to-crystalline transformation occurs in the vicinity of 9.5 at .%P, the material being amorphous for P contents larger than 9.5 atomic percent, corresponding to a bath pH of less than or equal to4.5. Suggests that phosphorous segregation during deposition plays a role in the observed grain size variation, and a qualitative model for this is presented.

Fullerenic nanostructures in flames

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 {approximately}2 nm to {approximately}30 nm in size with a hollow core measuring about {approximately}1 nm to {approximately}10 nm in diameter and containing 5 to 20 shells. The shapes of the nanostructures included spherical, spheroidal, tubular, and trigonous. {copyright} {ital 1996 Materials Research Society.}

Microstructural changes in coal during low temperature ashing

Abstract Samples of two US coals were oxidized for 72 hours in a low temperature asher. Scanning transmission electron microscopy and automated electron microprobe analysis were employed to observe the mineralogical changes produced in the coal by the ashing process. It was found that the microstructure of the low temperature ash was strongly influenced by the mineral matter which was originally chemically-bound in the organic matrix of the starting coal. The partial oxidation of pyrite during the ashing was also observed. The results reveal some of the physical mechanisms involved in the low temperature ashing process.

Analysis of sub-micron mineral matter in coal via scanning transmission electron microscopy

The fine-scale mineral matter in three US coals has been analyzed via scanning transmission electron microscopy (STEM). The samples observed were a North Dakota lignite, a Kentucky bituminous, and a Pennsylvania anthracite. Specific mineral types, differing among the three coals examined, appear to predominate at this fine size scale (particles less than or equal to 200nm in diameter). Fe-rich and Ba-rich minerals in the lignite, a Ti-rich mineral in the bituminous, and Ca-rich and Ti-rich minerals in the anthracite were the predominant species found. The inherent mineral content in the observed organic background also differs from coal to coal. The distributions of mineral species in the size range less than or equal to 200nm reported herein do not reflect the distributions in the larger size ranges obtained by more macroscopic techniques.

Liquid supercoolings and droplet cooling rates of remelted argon-atomized Fe–30Ni powder particles

Individual particles of argon-atomized Fe-30Ni powder are electrodynamically levitated and remelted by a CO 2 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 × 10 5 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 × 10 6 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.

Raman Analysis of Carbon Nanotube Bundles for Bio-electronic Applications

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.

Transition Element Modifications of Al-Li

The development of aluminum-lithium metallurgy has led to alloys with unsurpassed combinations of density, specific strength, and specific modulus. This paper describes recent advances in the modification of aluminum-lithium binary alloys through additions of the Group IV-A transition metals (titanium, zirconium and hafnium). These elements lead to a duplex precipitation hardening behavior through the formation ofAlJLi and Al3(TM,Li) (TM = transition element) which act as strengthening precipitates. The influence of the duplex structure on deformation mechanisms and the improvement of mechanical properties in these systems is illustrated by using results for the Al-Li-Zr system.