Gary D. Maupin

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.

Combustion synthesis of YBa2Cu3O7−x: glycine/metal nitrate method

Abstract A combustion synthesis method has been developed to simply and rapidly prepare YBa2Cu3O7−x and YBa2Cu3O7−x/Ag from an aqueous solution of the metal nitrates and glycine. Glycine served both as the fuel for combustion and as a complexant, important to prevent inhomogeneous precipitation of individual components prior to combustion. Ash collected following combustion consisted of well-mixed, soft agglomerates of barium carbonate, yttrium oxide, cupric oxide, and/or copper metal, depending on the ratio of fuel to oxidant. This mixture was calcined at 900°C for 4 h to convert the product to YBa2Cu3O7−x. Samples sintered at 950°C for 8 h and annealed in oxygen at 450°C for a like time showed a Tc (midpoint) of 92.5 K with a width of 1.4 K and a high degree of phase-purity. This synthesis method is well suited to the preparation of a wide variety of multicomponent ceramics.

Evaluation of Perovskite Overlay Coatings on Ferritic Stainless Steels for SOFC Interconnect Applications

Conductive oxide coatings are used to improve electrical performance and surface stability of metallic interconnects, as well as to mitigate or prevent chromium poisoning in solid oxide fuel cells (SOFCs). To further understand materials suitability and shed light on mass transport, two conductive perovskites, were taken as examples and applied as dense coatings via radio frequency (rf)-sputtering on three stainless steels.

Synthesis and crystallization of yttrium-aluminium garnet and related compounds

Amorphous oxide combustion products with compositions corresponding to Y4Al2O9, YAlO3, and Y3Al5O12 were synthesized by the glycine-nitrate process and heat-treated to induce crystallization. The crystalline structure of the resulting powders was determined by powder X-ray diffraction techniques. The phase stabilities of the crystalline phases were investigated as functions of the glycine-to-nitrate ratio, the yttrium-to-aluminium ratio, and the heat-treatment conditions. Heat treatment for short durations resulted in incompletely crystalline powders that consisted of a mixture of Y4Al2O9, YAlO3, and Y3Al5O12 phases, regardless of the chemical composition of the amorphous combustion product. However, heat treatment for longer durations or higher temperature generated both pure-phase, monoclinic Y4Al2O9 and Y3Al5O12 with the garnet structure. Prolonged heat treatment at high temperature failed to generate pure-phase orthorhombic YAlO3. Subsequent analysis revealed a sluggish, complex crystallization process involving the formation and decomposition of several phases.

Amorphization in Gd2Ti2O7 and CaZrTi2O7 irradiated with 3 MeV argon ions

Abstract Irradiation of Gd2Ti2O7 and CaZrTi2O7 with 3 MeV Ar+ ions results in the simultaneous expansion of the unit-cell volume and radiation-induced amorphization. The damage cross sections for amorphization, which were determined hy X-ray diffraction, are 0.023 nm2 and 0.014 nm2, respectively. These damage cross sections are relatively low and suggest some inherent resistance of these structures to amorphization, in agreement with previous studies. Transmission electron microscopy and electron diffraction confirmed the amorphous character of both materials at high fluences. Raman spectroscopy indicated a decrease in scattered intensity with ion fluence for the Raman-active vibrational modes of Gd2Ti2O7 and CaZrTi2O7. In the case of Gd2Ti2O7, increases in both linewidth and wavenumher with ion fluence also were observed.

Glycine-nitrate synthesis of a ceramic-metal composite

Abstract A ceramic-metal composite material, consisting of NiO, NiFe 2 O 4 and Cu metal, was prepared by the glycine-nitrate combustion synthesis process (GNP). The synthesized powder consisted of intimately mixed nanometer size crystallites. This GNP powder was cold-pressed and solid-state sintered, which produced a dense cermet with micron size grains. The scale of the microstructure in the GNP material was about one order of magnitude smaller (linear basis) than that for samples fabricated by mechanical mixing of single phase powders followed by sintering at a temperature above the melting point of the metal phase. The paper also discusses synthesis of powders containing a single metal, Ni, Cu, or Fe, and the two-metal system containing Ni with Cu. The phases produced by oxidizing versus reducing combustion conditions are explored.

Electrochemical Performance and Stability of the Cathode for Solid Oxide Fuel Cells: III. Role of Volatile Boron Species on LSM/YSZ and LSCF

Boron oxide is a key component to tailor the softening temperature and viscosity of the sealing glass for solid oxide fuel cells (SOFCs). The primary concern regarding the use of boron-containing sealing glasses is the volatility of boron species, which possibly results in cathode degradation. In this paper, we report the role of volatile boron species on the electrochemical performance of LSM/yttria-stabilized zirconia (YSZ) and LSCF cathodes at various SOFC operation temperatures. The transport rate of boron, ~3.24 × 10 -12 g/cm 2 sec was measured at 750°C with air saturated with ~3% moisture. A reduction in power density was observed in the cells with the LSM/YSZ cathodes after the introduction of boron source to the cathode air stream. A partial recovery of the power density was observed after the boron source was removed. Results from post-test secondary-ion mass spectroscopy (SIMS) analysis showed that the partial recovery in the power density correlated with the partial removal of the deposited boron by the clean air stream. The presence of boron was also observed in the LSCF cathodes by SIMS analysis; however, the effect of boron on the electrochemical performance of the LSCF cathode was negligible. The coverage of triple phase boundaries in LSM/YSZ was postulated as the cause for the observed reduction in the electrochemical performance.

Simulation of radiation damage in zircon

Abstract Radiation damage in natural zircon minerals due to alpha decay over geologic time has been simulated in laboratory studies extending over 5.5 years using Pu-doped synthetic zircon. These studies confirm for the first time that laboratory testing of actinide-doped materials can accurately predict the radiation-damage behavior of radioactive waste forms over geologic time and also provide new insights into interpretation of radiation damage in natural minerals.

Optimizing the Advanced Ceramic Material for Diesel Particulate Filter Applications

This paper describes the application of pore-scale filtration simulations to the ‘Advanced Ceramic Material’ (ACM) developed by Dow Automotive for use in advanced diesel particulate filters. The application required the generation of a three dimensional substrate geometry to provide the boundary conditions for the flow model. An innovative stochastic modeling technique was applied matching chord length distribution and the porosity profile of the material. Additional experimental validation was provided by the single channel experimental apparatus. Results show that the stochastic reconstruction techniques provide flexibility and appropriate accuracy for the modeling efforts. Early optimization efforts imply that needle length may provide a mechanism for adjusting performance of the ACM for DPF applications. New techniques have been developed to visualize soot deposition in both traditional and new DPF substrate materials. Loading experiments have been conducted on a variety of single channel DPF substrates to develop a deeper understanding of soot penetration, soot deposition characteristics, and to confirm modeling results.

Non-Thermal Plasma System Development for CIDI Exhaust Aftertreatment

There is a need for an efficient, durable technology to reduce NOx emissions from oxidative exhaust streams such as those produced by compression-ignition, direct injection (CIDI) diesel or lean-burn gasoline engines. A partnership formed between the DOE Office of Advanced Automotive Technology, Pacific Northwest National Laboratory, Oak Ridge National Laboratory and the USCAR Low Emission Technologies Research and Development Partnership is evaluating the effectiveness of a non-thermal plasma in conjunction with catalytic materials to mediate NOx and particulate emissions from diesel fueled light duty (CIDI) engines. Preliminary studies showed that plasma-catalyst systems could reduce up to 70% of NOx emissions at an equivalent cost of 3.5% of the input fuel in simulated diesel exhaust. These studies also showed that the type and concentration of hydrocarbon play a key role in both the plasma gas phase chemistry and the catalyst surface chemistry. More recently, plasma/catalyst systems have been evaluated for NOx reduction and particulate removal on a CIDI engine. Performance results for select plasma-catalyst systems for both simulated and actual CIDI exhaust will be presented. The effect of NOx and hydrocarbon concentration on plasma-catalyst performance will also be shown. SAE Paper SAE-2000-01-1601 {copyright} 2000 SAE International. This paper is published on this website with permission from SAE International. As a user of this website, you are permitted to view this paper on-line, download this pdf file and print one copy of this paper at no cost for your use only. The downloaded pdf file and printout of this SAE paper may not be copied, distributed or forwarded to others or for the use of others.