Scientific Publications 2004
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2004. "Gas-Phase Database for Quantitative Infrared Spectroscopy." Applied Spectroscopy 58(12):1452-1461. Abstract The National Institute of Standards and Technology (NIST) and the Pacific Northwest National Laboratory (PNNL) are each creating quantitative databases containing the vapor-phase infrared spectra of pure chemicals. The digital databases have been created with both laboratory and remote-sensing applications in mind. A spectral resolution of ≈0.1 cm-1 was selected to avoid degrading sharp spectral features, while also realizing that atmospheric broadening typically limits line widths to 0.1 cm-1. Calculated positional (wave number, cm-1) uncertainty is ≤0.005 cm-1, while the 1σ statistical uncertainty in absorbance values is <2% for most compounds. The latter was achieved by measuring multiple (typically ≥9) path length-concentration burdens and fitting a weighted Beer’s law plot to each wave number channel. The two databases include different classes of compounds and were compared using 12 samples. Though these 12 samples span a range of polarities, absorption strengths, and vapor pressures, the data agree to within experimental uncertainties with only one exception.
2004. "Synthesis of Hierarchical Titanium Carbide from Titania-Coated Cellulose Paper." Advanced Materials 16(14):1212-1215. Abstract An aqueous-based, inexpensive, TiO2 precursor, Tyzor-LA, and cellulose paper have been used to prepare TiC via carbothermal reduction in an Ar flow. The hierarchical cellulose structures were also completely maintained through the agglomeration of 10-50nm TiC nanoparticles, and the lattice parameter of TiC increased with the increase of reaction temperature, while the oxygen content in the sample decreased (0.24wt% at 1500oC).
2004. "Room Temperature Ferromagnetism in Ion-implanted Co-doped TiO₂(110) Rutile." Applied Physics Letters 84(22):4466-4468. Abstract Ferromagnetic Co-doped rutile TiO₂ singel crystals were successfully synthesized by high temperature ion implantation and charaterized by a variety of techniques. Co is uniformly distrubuted to the depth of ~300nm with an average concentration of ~2 at. %, except in the near-surface region, where the concentration is ~3 at. %. Magnetic measurements reval ferromagnetic behavior at room temperature with an effective saturation magnetization of ~0.6 ub/Co atom. The Co formal oxidation state is found to be +2 throughouth the implanted region, and no Co(0) is detected.
2004. "Room-Temperature Ferromagnetism in Ion-Implanted Co-Doped TiO₂(110) Rutile." Applied Physics Letters 84(22):4466-4468. Abstract Interest in diluted magnetic semiconductros (DMS) is growing rapidly within the emerging field of spintronics. For example, the ability to efficiently inject spin-polarized carriers into nonmagnetic semiconductor heterostructures creates new and exciting possibilities for utilizing DMS materials in spin-based devices. Several III-V and II-VI semiconductor materials doped with magnetic transition metal elements have been explored. Although these materials show promising behavior in some cases, most exhibit Curie temperatures of ~170 K or less. It has recently been shown that certain oxide semiconductors doped with magnetic transition elements show room-temperature ferromagnetism.
2004. "Using CrAIN Multilayer Coatings to Improve Oxidation Resistance of Steel Interconnects for Solid Oxide Fuel Cell Stacks." Journal of Materials Engineering and Performance 13(3):295-302. Abstract The requirements of low cost and high-tempurature corrosion resistance for bipolar interconnect plates in solid oxide fuel cell stacks has directed attention to the use of metal plates with oxidation resistant coatings. We have investigatedt he performance of steel plates with multilayer coatings consisting of CrN for electrical conductivity and CrAIN for oxidation resistance. The coatings were deposited usin large area filterd arc deposition technolgy, and subsequently annealed in air for up to 25 hours at 800 degrees celsius. The composition, structer and morphology of the coated plates were characterized using RBS, nuclear reaction analysis, AFM and TEM techniques. By altering the architecture of the layers within the coatings, the rate of oxidation was reduced by more than an order of magnitute. Electrical resistance was measured at room temperature.
2004. "NRA and ERDA Investigation of Helium Retention in SiC as a Function of Irradiation and Annealing." Nuclear Instruments and Methods in Physics Research. Section B, Beam Interactions with Materials and Atoms 219-220:631-635. Abstract Silicon carbide has been proposed for coating applications in advanced reactor designs, so studies of its behavior in the presence of ion irradiation and fission products are of Interest. We investigated the retention of He in single crystal 6H SiC as a function of irradiation dose and annealing temperature using both nuclear reaction analysis (NRA) and time-of-flight elastic recoil detection analysis (ToF ERDA). Ions of 3He⁺ were implanted at 40 keV in SiC to a depth of ~200 nm at room temperature. NRA was performed using 1.0 MeV D⁺ and the 3He(D,α)1H reaction. No change in the He profile was seen for irradiation dose up to 6.8x1017 D⁺/cm₂ at room temperature. Isochronal annealing of the SiC between 300 and 1200 K also showed no significant helium loss. Subsequently, a sample was irradiated with D⁺ at 900 K and again at 1100 K. No loss of 3He associated with irradiation was seen for a dose up to 5x1017 D⁺/cm₂. Annealing the sample above 1200 K resulted in thermally activated loss of He. ToF ERDA measurements were performed using 44 MeV 127I10⁺ for both irradiation and analysis. Depth profiles of the He distribution showed no significant change under I bombardment with an ion fluence up to ~1014/cm₂ at room temperature. NRA was performed on the implanted sample subjected to ERDA. The 3He profiles for regions subjected to I irradiation were similar in shape to those with no I irradiation.
2004. "Reaction of Hydroquinone with Hematite I. Study of Adsorption by Electrochemical-Scanning Tunneling Microscopy and X-ray Photoelectron Spectroscopy." Journal of Colloid and Interface Science 274 (2004)(2):433-441. Abstract The reaction of hematite with quinones and the quinone moieties of larger molecules may be an important factor in limiting the rate ofreductive dissolution, especially by iron-reducing bacteria. Here, the electrochemical and physical properties of hydroquinone adsorbed on hematite surfaces at pH 2.5–3 were investigated with cyclic voltammetry (CV), electrochemical-scanning tunneling microscopy (EC-STM), and X-ray photoelectron spectroscopy (XPS). An oxidation peak for hydroquinone was observed in the CV experiments, as well as (photo)reduction of iron and decomposition of the solvent. The EC-STM results indicate that hydroquinone sometimes forms an ordered monolayer with ∼1.1 H₂/nm², but can be fairly disordered (especially when viewed at larger scales). XPS results indicate that hydroquinone and benzoquinone are retained at the interface in increasing amounts as the reaction proceeds, but reduced iron is not observed. These results suggest that quinones do not adsorb by an inner-sphere complex where adsorbate–surface interactions determine the adsorbate surface structure, but rather in an outer-sphere complex where interactions among the adsorbate molecules dominate.
2004. "The Growth Morphology of the {100} Surface of KDP (Archerite) on the Molecular Scale." Journal of Physical Chemistry B 108(47):18284-18290. Abstract No abstract for this publication is available at this time.
2004. "Reaction of Hydroquinone with Hematite II: Calculated Electron Transfer Rates and Comparison to the Reductive Dissolution Rate." Journal of Colloid and Interface Science 274(2):442-450. Abstract Reaction of hydroquinone with hematite II: Calculated electron transfer rates and comparison to the reductive dissolution rate
2004. "Copper Sorption Mechanisms on Smectites." Clays and Clay Minerals 52(3):321-333. Abstract Abstract– Due to the importance of clay minerals in metal sorption many studies have attempted to derive mechanistic models that describe adsorption processes. These models often include several different types of adsorption sites, including permanent charge sites and silanol and aluminol functional groups on the edges of clay minerals. The edge sites have similar pH-dependent adsorption properties as many oxide minerals. To provide a basis for development of adsorption models it is critical that molecular level studies be done to characterize sorption processes. In this study we conducted XAFS and ESR spectroscopic experiments on copper (II) sorbed on smectite clays using suspension pH and ionic strength as variables. At low ionic strength, results suggest that Cu is sorbing in the interlayers and maintains its hydration sphere. At high ionic strength Cu atoms are excluded from the interlayer and sorb primarily on the silanol and aluminol functional groups of the montmorillonite or beidellite structures. Interpretation of the XAFS and ESR spectroscopy results provides evidence that multinuclear complexes are forming on the edge sites. Fitting of EXAFS spectra revealed that the Cu-Cu atoms in the multinuclear complexes are 2.65 apart, and have coordination numbers near one. This structural information suggests that small Cu dimers are sorbing on the surface. These complexes are consistent with observed sorption on mica and amorphous silicon dioxide, as well as the Cu-bearing silicate minerals plancheite and shattuckite, yet are inconsistent with previous spectroscopic results for Cu sorption on montmorillonite. We hypothesize that the differences in sorption mechanisms on the edges of the montmorillonite are due to loading level. The results reported in this paper provide mechanistic data that will be valuable for modeling surface interactions of Cu with clay minerals, and predicting the geochemical cycling of Cu in the environment.
2004. "The Effect of Water on the Adsorption of NO₂ in Na- and Ba-Y,FAU Zeolites: A Combined FTIR and TPD Investigation." Journal of Physical Chemistry B 108(12):3746-3753. Abstract The adsorption of NO₂ was investigated and compared on Na- and Ba-Y,FAU zeolites both in the absence and presence of adsorbed water using FTIR and TPD techniques. The same ionic NOx species (NO⁺, NO⁺:NO₂, NO₃-), formed by the disproportionation of NO₂, were observed to form on both materials under dry conditions at room temperature. The thermal stabilities of these species, however, were vastly different on the two materials. Room temperature evacuation was sufficient to decompose the NO⁺NO₂ adduct in Na-Y, while this species was stable up to 350K over Ba-Y. The adsorbed NO⁺ was also much more stable over Ba-Y than on Na-Y. Water significantly affected the adsorbed NOx species on both materials. In the presence of water the IR signatures of adsorbed NO+ were eliminated from both catalysts, however it did not affect the IR feature of the NO⁺NO₂ species on Ba-Y. In the TPD spectra the NO₂ desorption peak shifted from 350K to 520K on Na-Y pre-exposed to water. In Ba-Y the high temperature NO₂ desorption feature of ~470K shifted to ~620K as a result of adsorption on the water containing sample, while the low temperature peak remained unchanged.
2004. "Adsorption, Coadsorption and Reaction of Acetaldehyde and NO₂ on Na-Y,FAU: an in situ FTIR Investigation." Journal of Physical Chemistry B 108(44):17050-17058 . Abstract The adsorption of acetaldehyde and its co-adsorption and reaction with NO₂ were investigated on a Na-Y, FAU zeolite using in situ FTIR spectroscopy. Acetaldehyde adsorbs strongly over Na-Y and desorbs molecularly at around 400K with very limited extent of condensation or polymerization. Reaction between CH₃CHO and NO₂ takes place in co-adsorption experiments even at 300K. In the initial step, acetaldehyde is oxidized to acetic acid accompanied by the formation of NO, which can be observed as N2O₃ formed via a further reaction between NO and NO₂. The key intermediates in the overall NOx reduction in this process are nitro- and nitrosomethane, which form in the next step. Their decomposition and further reaction with adsorbed NOx species lead to the formation of HCN, HNCO, N₂O, CO₂ and organic nitrile species identified by their characteristic IR vibrational signatures. At 473K, the reaction between adsorbed CH₃CHO and NO₂ is very fast. The results seem to suggest a mechanism in which N-N bond formation takes place among ionic nitrogen containing species (NO⁺ and CN⁻ or NCO⁻). No evidence has been found to suggest the participation of NHx⁺NOy⁻ type species in the N⁻N bond formation under the experimental conditions of this study.
