Larry A. Chick

Glycine-nitrate combustion synthesis of oxide ceramic powders

Abstract A new combustion synthesis method, the glycine-nitrate process, has been used to prepare oxide ceramic powders, including substituted chromite and manganite powders of high quality. A precursor was prepared by combining glycine with metal nitrates in their appropriate stoichiometric ratios in an aqueous solution. The precursor was heated to evaporate excess water, yielding a viscous liquid. Further heating to about 180°C caused the precursor liquid to autoignite. Combustion was rapid and self-sustaining, with flame temperatures ranging from 1100 to 1450°C. The chromite product was compositionally homogeneous with a specific surface area of 32 m2/g, while the manganite product was composed of two distinct phases with a 23 m2/g surface area after calcination. When compared to similar compositions made using the amorphous citrate process, glycine-nitrate-produced powders had greater compositional uniformity, lower residual carbon levels and smaller particle sizes.

Synthesis, air sintering and properties of lanthanum and yttrium chromites and manganites

Abstract A new combustion process, the Glycine-Nitrate Process (GNP), is used for synthesizing ultra-fine, single- or multi-phase electrically conducting oxide powders. The resulting powders are crystalline, homogenous, softly agglomerated, and vary in size between 1 and 100 nm depending upon composition and synthesis parameters. The process is simple, rapid, low-cost and environmentally compatible. GNP synthesized yttrium and lanthanum chromite powders can be air-sintered to high density below 1550°C. The air-sintering mechanism are functions of alkaline-earth concentration, cation ratio, vapor loss and liquid-phase formation. Sintered densities increase with increasing alkaline-earth substitution and with increasing (La+Sr)/Cr and (Y+Ca)/Cr ratios. Large changes in air sinterability can occur with small changes in these cation ratios. Vaporization of Cr appears to be a major influence in La 1− x Sr x CrO 3 air-sintering. Liquid-phase sintering appears to be a major factor in the sintering of Y 1− x Ca x CrO 3 . The electrical conductivity and thermal expansion also increase with ncreasing alkaline-earth substitution for the lanthanum or yttrium chromites and manganites. In addition, the electrical, thermal and structural properties of these perovskite materials are also influenced by the synthesis and processing conditions as well as by thermal cycling and heat treatment in air.

Transitions to Ordered Phases in Systems Containing Rodlike Particles: I. A New Continuum Monte Carlo Approach

Abstract A new continuous-placement Monte Carlo (CMC) approach was developed that measures the entropy of rodlike particle configurations having pre-set global orientation distributions. Entropies are measured through a range of concentrations, independently of whether these configurations represent equilibrium conditions. Rod concentrations, orientation distribution shapes, and order parameters that are expected to be present at equilibrium can then be determined by comparing free energy curves. The method was applied to two-dimensional, monodisperse, athermal systems and the results demonstrated that choice of the shape of the global orientation distribution in the anisotropic phase can result in shifting from a first-order to a continuous isotropic-to-nematic phase transition.

Transitions to Ordered Phases in Systems Containing Rod-like Particles: III. Four Fundamental Reasons for the Predictive Deficiencies of Discrete Lattice Models

Abstract This paper identifies and discusses four fundamental causes for the discrepancy between the entropy predictions of our new continuous-placement Monte Carlo (CMC) approach and the discrete lattice model (DLM) of Flory and Ronca. The DLM allows rods to cross, enables rods to fit too easily into tight spaces, does not account for unoccupiable (wasted) space, and neglects the ingrowth of short-range order. Increasing resolution can eliminate the first two shortcomings from the DLM. To account for wasted space in the DLM, it will be necessary to derive a more complex expression for combinatorie entropy. To properly accommodate the effect of short-range order, the calculation of both combinatorie and orientational entropy must be improved.

Transitions to Ordered Phases in Systems Containing Rod-like Particles: II. Continuum Monte Carlo Approach versus Discrete Lattice Models

Abstract The predictions of the new continuous-placement Monte Carlo (CMC) approach described in the preceding paper are compared with the results obtained from the discrete lattice model (DLM) of Flory and Ronca. The comparison is made for two-dimensional, monodisperse, athermal systems. For this purpose, we have adapted the Flory-Ronca model to two dimensions, gaining additional insight into the justification for one of the numerical correction factors used in that model. The CMC and DLM approaches both predict that a uniform (flat) distribution of rod orientations in the anisotropic phase is associated with a first-order isotropic-to-nematic transition, while normally distributed orientations lead to a continuous transition with increasing rod concentration. The two models also agree qualitatively with respect to the relative free energies of different rod orientation distributions in the anisotropic phase. However, the DLM assigns disproportionately high entropy to short rods (especially at high conce...

Entropy of Rodlike Particles: Continuum versus Lattice Representations

Abstract The computationally tractable discrete lattice model is compared to a more realistic representation of rodlike particles, which allows continuous variation of rod position and orientation. This continuous-placement Monte Carlo method provides a measurement of the combinatoric entropy of rod configurations. Comparisons reveal that the discrete lattice model overestimates the entropy of short rods and of disordered phases. Three fundamental reasons for these predictive errors are discussed.

SOLID STATE ENERGY CONVERSION ALLIANCE DELPHI SOLID OXIDE FUEL CELL

The objective of this project is to develop a 5 kW Solid Oxide Fuel Cell power system for a range of fuels and applications. During Phase I, the following will be accomplished: Develop and demonstrate technology transfer efforts on a 5 kW stationary distributed power generation system that incorporates steam reforming of natural gas with the option of piped-in water (Demonstration System A). Initiate development of a 5 kW system for later mass-market automotive auxiliary power unit application, which will incorporate Catalytic Partial Oxidation (CPO) reforming of gasoline, with anode exhaust gas injected into an ultra-lean burn internal combustion engine. This technical progress report covers work performed by Delphi from July 1, 2003 to December 31, 2003, under Department of Energy Cooperative Agreement DE-FC-02NT41246. This report highlights technical results of the work performed under the following tasks: Task 1 System Design and Integration; Task 2 Solid Oxide Fuel Cell Stack Developments; Task 3 Reformer Developments; Task 4 Development of Balance of Plant (BOP) Components; Task 5 Manufacturing Development (Privately Funded); Task 6 System Fabrication; Task 7 System Testing; Task 8 Program Management; Task 9 Stack Testing with Coal-Based Reformate; and Task 10 Technology Transfer from SECA CORE Technology Program. Inmorexa0» this reporting period, unless otherwise noted Task 6--System Fabrication and Task 7--System Testing will be reported within Task 1 System Design and Integration. Task 8--Program Management, Task 9--Stack Testing with Coal Based Reformate, and Task 10--Technology Transfer from SECA CORE Technology Program will be reported on in the Executive Summary section of this report.«xa0less

Microstructural size effects on the dielectric response of inhomogeneous media

The microstructure of dielectric films is an inherent characteristic of the fabrication process, and imposes distinctive behavior on the electric field distributions in these inhomogeneous media. In this paper, we examine the size dependent problem for cubic defects for an Al2O3 dielectric material. Using the LOCALF method to analyze the electric field response, we have developed models for Al2O3 dielectric films of varying microstructure size and volume fraction, and compare these results with conventional effective medium methods. Besides the dielectric susceptibility and volume fraction dependencies, the physical size of the heterogeneities creates localized regions of high field intensity.