Dorothy W. Coffey

Study of the physico-chemical properties of some packing materials II. General properties of the particles

Abstract Scanning electron microscopy reveals the shape and illustrates the particle size distribution of four different brands of spherical silica particles used in preparative chromatography (C18-bonded Kromasil, Vydac, YMC, and Zorbax). Pycnometry provides a direct estimate of the unaccessible volume fraction in a column. The retention volumes of benzene in dichloromethane and of uracil in methanol provide two independent estimates of the total column porosity which are in excellent agreement. Within 2 to 3%, the sum of these two fractional volumes is equal to unity, as expected, in spite of a possible disagreement between the two sets of measurements due to the fact that the C18 bonded chains are collapsed during the pycnometric measurements and are dissolved in the mobile phase during the chromatographic measurements. Finally, estimates of the volume fractions of the column occupied by the bonded layer and the silica skeleton for two of the packing materials suggest that the closed pore porosity is negligible (1 to 2% at most).

EFTEM and Spectrum Imaging of Mechanically Alloyed Oxide-Dispersion- Strengthened 12YWT and 14YWT Ferritic Steels

J. Bentley, D.T. Hoelzer, D.W. Coffey and K.A. YarboroughMetals & Ceramics Division, Oak Ridge National Laboratory, PO Box 2008, Oak Ridge, TN 37831Late last century, a cooperative effort by Kobe Steel, Nagoya University and Oak Ridge NationalLaboratory (ORNL) resulted in the production of a mechanically alloyed (MA), oxide-dispersion-strengthened (ODS) Fe-12%Cr-3%W-0.4%Ti-0.25%Y

Thermally-induced microstructural changes in a three-way automotive catalyst

The use of advanced electron microscopy techniques to characterize both the bulk and near-atomic level microstructural evolution of catalyst materials during different dynamometer/vehicle aging cycles is an integral part of understanding catalyst deactivation. The study described here was undertaken to evaluate thermally-induced microstructural changes which caused the progressive loss of catalyst performance in a three-way automotive catalyst. Several different catalyst processing variables, for example changing the washcoat ceria content, were also evaluated as a function of aging cycle and thermal history. A number of thermally-induced microstructural changes were identified using high resolution electron microscopy techniques that contributed to the deactivation of the catalyst, including sintering of all washcoat constituents, {gamma}-alumina transforming to {alpha}-, {beta}-, and {delta}-alumina, precious metal redistribution, and constituent encapsulation. The data accumulated in this study have been used to correlate microstructural evolution with thermal history and catalyst performance during various aging cycles and to subsequently evaluate different washcoat formulations for increased thermal stability.

Microstructure, Morphology, and Nanomechanical Properties Near Fine Holes Produced by Electro-Discharge Machining

Fine holes in metal alloys are employed for many important technological purposes, including cooling and the precise atomization of liquids. For example, they play an important role in the metering and delivery of fuel to the combustion chambers in energy-efficient, low-emission diesel engines. Electro-discharge machining (EDM) is one process employed to produce such holes. Since the hole shape and bore morphology can affect fluid flow, and holes also represent structural discontinuities in the tips of the spray nozzles, it is important to understand the microstructures adjacent to these holes, the features of the hole walls, and the nanomechanical properties of the material that was in some manner altered by the EDM hole-making process. Several techniques were used to characterize the structure and properties of spray-holes in a commercial injector nozzle. These include scanning electron microscopy, cross sectioning and metallographic etching, bore surface roughness measurements by optical interferometry, scanning electron microscopy, and transmission electron microscopy of recast EDM layers extracted with the help of a focused ion beam.

Novel Method for Precision Controlled Heating of TEM Thin Sections to Study Reaction Processes

Improving the efficiency of gas turbine engines necessitates the development of structural alloys that can operate at higher temperatures. The alloys must maintain structural integrity while possessing excellent high-temperature oxidation resistance. The formation of a stable oxide scale is needed to protect the material from aggressive oxidizing environments [1]. Previous research has shown that the addition of reactive elements (RE), such as Hf, Y, La, Ti, improves oxidation resistance of the materials by improving oxide-scale adhesion and decreasing the overall oxide growth rate [1-3]. Oxide-scale growth is retarded by the segregation of RE elements to oxide grain boundaries, which effectively block cation diffusion from the underlying base material. Often, the structure and chemistry of the oxide scale is characterized following exposure to high-temperature oxidation [3]. Direct heating of TEM thin-foil specimens in an oxidizing environment is a useful method to study oxide growth kinetics. The recent development of a heating capability based on MEMS-fabricated heater devices that are used for in situ microscopy studies offers the potential to study thin alloy specimens, with precision control of temperature at heating and cooling rates up to 10 6 °C/s [4]. With proper specimen preparation, devices such as Protochips Aduro TM E-chip heaters offer the capability to stop testing at any time to examine oxide scale chemistry and elemental segregation with electron energy-loss spectroscopy (EELS) or energy dispersive X-ray spectroscopy (EDS).

Radial Distribution Function Analyses of Amorphous Carbon Films Containing Silicon and Hydrogen by Energy-Filtered Diffraction and EXELFS

Short-range order in amorphous materials is most commonly characterized with the use of radial distribution functions (RDFs). Two analytical electron microscopy methods were used in this study to measure RDFs from amorphous carbon films containing different levels of silicon and hydrogen (Si-aC:H): energy-filtered convergent-beam electron diffraction (EFCBED) and extended electron energy-loss fine structure (EXELFS) analyses. The films were deposited in an industrial-scale system onto a thin adhesive titanium layer on silicon substrates by reactive sputtering of carbon with a feed gas of tetramethyl silane (TMS) and argon, to produce a series of films with different Si and H contents (Si/C = 0, 0.04, 0.10, and 0.18).

TEM Specimen Preparation of Thin Interfacial Coatings on Continuous Ceramic Fibers Using the Focused Ion Beam (FIB) Technique

Continuous ceramic fibers, such as Nicalon,TM Hi-Nicalon,TM or Nextel 720,TM typically have a fiber diameter ranging from 5-20 μm. The continuous fibers are bundled into fiber tows (100-300 fibers/tow) and the tows are woven into cloth for incorporation into a dense matrix, usually a compositionally-compatible ceramic. Continuous ceramic fibers impart strength and toughness to normally brittle ceramics such as SiC and Al2O3 and also help these composites retain their strength at high temperatures. Prior to incorporation into a ceramic matrix, continuous fibers (either as tows or woven into a cloth) are coated with a thin interfacial coating such as BN. Coatings can be applied to the fibers via many different processing methods, but thin BN coatings (< 0.5 μm) are normally applied using chemical vapor deposition (CVD). These interfacial coatings provide the necessary fiber/matrix interfacial debonding required for enhanced toughness and have the most critical role in determining the bulk mechanical properties of ceramic matrix composites (CMCs). Interfacial coatings are also required to protect the fiber surfaces during high-temperature matrix processing. Optimization of the coating structure and composition is necessary during the deposition process and ideally, the coating should be evaluated at this stage rather than following CMC processing.