Publications

Results 101–150 of 231
Skip to search filters

Mechanically-induced degradation of metallic sliding electrical contacts in silicone fluid at room temperature

Electrical Contacts, Proceedings of the Annual Holm Conference on Electrical Contacts

Dugger, Michael T.; Groysman, D.; Celina, Mathias C.; Alam, Todd M.; Argibay, Nicolas A.; Nation, Brendan L.; Prasad, Somuri V.

The degradation in electrical contact resistance of a contact pair sliding while submerged in silicone fluid has been investigated. While the contamination of electrical contacts by silicone vapors or migrating species at elevated temperature due to decomposition in electric arcs is well known, the present degradation mechanism appears to arise from chemical reactions in the silicone fluid at room temperature, catalyzed by the presence of the freshly-abraded metal surface. As a result of these reactions, a deposit containing Si, C and O forms in the vicinity of mechanical contact. The specific contact metals present and the availability of dissolved oxygen in the fluid have a dramatic influence on the quantity of reaction product formed. The chemistry of the deposit, proposed formation mechanisms, the impact on electrical contact resistance and mitigation strategies are discussed.

More Details
TYPE Conference Poster YEAR 2015
ScopusOSTIDOI

Exploring the role of phosphate structural distortions on the sodium jump dynamics in NASICON phases

Materials Research Society Symposium Proceedings

Alam, Todd M.; Bell, Nelson S.; Wheeler, Jill; Spoerke, Erik D.; Cygan, Randall T.; Ingersoll, David I.

High temperature solid state sodium (23Na) magic angle spinning (MAS) NMR spin lattice relaxation times (T1) were evaluated for a series of NASICON (Na3Zr2PS12O12) materials to directly determine Na jump rates. Simulations of the Ti temperature variations that incorporated distributions in Na jump activation energies, or distribution of jump rates, improved the agreement with experiment. The 23Na NMR T1 relaxation results revealed that distributions in the Na dynamics were present for all of the NASICON materials investigated here. The 23Na relaxation experiments also showed that small differences in material composition and/or changes in the processing conditions impacted the distributions in the Na dynamics. The extent of the distribution was related to the presence of a disordered or glassy phosphate phase present in these different sol-gel processed materials. The 23Na NMR T1 relaxation experiments are a powerful tool to directly probing Na jump dynamics and provide additional molecular level details that could impact transport phenomena.

More Details
TYPE Conference Poster YEAR 2015
ScopusOSTIDOI

Characterization of free, restricted, and entrapped water environments in poly(N-isopropyl acrylamide) hydrogels via 1H HRMAS PFG NMR spectroscopy

Journal of Polymer Science, Part B: Polymer Physics

Alam, Todd M.; Childress, Kimberly K.; Pastoor, Vevin; Rice, Charles V.

Different water environments in poly(N-isopropyl acrylamide) (PNIPAAm) hydrogels are identified and characterized using 1H high resolution magic angle spinning (HRMAS) nuclear magnetic resonance (NMR). Local water environments corresponding to a "free" highly mobile species, along with waters showing restricted dynamics are resolved in these swollen hydro-gels. For photo-initiated polymerized PNIPAAm gels, an additional entrapped water species is observed. Spin-spin R2 relaxation experiments support the argument of reduced mobility in the restricted and entrapped water species. By combining pulse field gradient techniques with HRMAS NMR it is possible to directly measure the self-diffusion rate for these different water environments. The behavior of the heterogeneous water environments through the lower critical solution temperature transition is described.

More Details
TYPE Journal Article YEAR 2014
ScopusOSTIDOI

Development and Investigation of NMR tools for chiral compound identification

Alam, Todd M.; Dernov, Vitaliy D.

The goal behind the assigned summer project was to investigate the ability of nuclear magnetic resonance spectroscopy (NMR) to identify enantiomers of select chiral organo-fluorophosphates (OFPs) compounds which are analogs of chemical warfare agents (CWAs, e.g. Sarin). This involved investigations utilizing chiral solvating agents (CSAs) and characterizing the binding phenomena with cyclodextrins. The resolution of OFPs enantiomers using NMR would be useful for research into toxicodynamics and toxicokinetics in biological systems due to the widely differing properties of the CWA enantiomers [1]. The optimization of decontamination abilities in the case of a CWA events, with this method’s potential rapidity and robustness, as well as the development of models correlating chiral compounds with CSAs for optimal resolution are all rational benefits of this research.

More Details
TYPE Other Report YEAR 2014
OSTIDOI

Development of alkaline fuel cells

Alam, Todd M.

This project focuses on the development and demonstration of anion exchange membrane (AEM) fuel cells for portable power applications. Novel polymeric anion exchange membranes and ionomers with high chemical stabilities were prepared characterized by researchers at Sandia National Laboratories. Durable, non-precious metal catalysts were prepared by Dr. Plamen Atanassovs research group at the University of New Mexico by utilizing an aerosol-based process to prepare templated nano-structures. Dr. Andy Herrings group at the Colorado School of Mines combined all of these materials to fabricate and test membrane electrode assemblies for single cell testing in a methanol-fueled alkaline system. The highest power density achieved in this study was 54 mW/cm2 which was 90% of the project target and the highest reported power density for a direct methanol alkaline fuel cell.

More Details
TYPE SAND Report YEAR 2013
OSTIDOI

Ab Initio Calculations of Possible γ-Gauche Effects in the 13C-NMR for Methine and Carbonyl Carbons in Precise Polyethylene Acrylic Acid Copolymers

Molecules

Alam, Todd M.

The impacts of local polymer chain conformations on the methine and carbonyl 13C-NMR chemical shifts for polyethylene acrylic acid p(E-AA) copolymers were predicted using ab initio methods. Using small molecular cluster models, the magnitude and sign of the γ-gauche torsional angle effect, along with the impact of local tetrahedral structure distortions near the carbonyl group, on the 13C-NMR chemical shifts were determined. These 13C-NMR chemical shift variations were compared to the experimental trends observed for precise p(E-AA) copolymers as a function acid group spacing and degree of zinc-neutralization in the corresponding p(E-AA) ionomers. These ab initio calculations address the future ability of 13C-NMR chemical shift variations to provide information about the local chain conformations in p(E-AA) copolymer materials.

More Details
TYPE Journal Article YEAR 2013
OSTIDOI

Enhanced Micellar Catalysis LDRD

Betty, Rita B.; Glen, Crystal C.; Alam, Todd M.; Taggart, Gretchen S.; Tucker, Mark D.; Rivera, Danielle R.; Kinnan, Mark K.

The primary goals of the Enhanced Micellar Catalysis project were to gain an understanding of the micellar environment of DF-200, or similar liquid CBW surfactant-based decontaminants, as well as characterize the aerosolized DF-200 droplet distribution and droplet chemistry under baseline ITW rotary atomization conditions. Micellar characterization of limited surfactant solutions was performed externally through the collection and measurement of Small Angle X-Ray Scattering (SAXS) images and Cryo-Transmission Electron Microscopy (cryo-TEM) images. Micellar characterization was performed externally at the University of Minnesotas Characterization Facility Center, and at the Argonne National Laboratory Advanced Photon Source facility. A micellar diffusion study was conducted internally at Sandia to measure diffusion constants of surfactants over a concentration range, to estimate the effective micelle diameter, to determine the impact of individual components to the micellar environment in solution, and the impact of combined components to surfactant phase behavior. Aerosolized DF-200 sprays were characterized for particle size and distribution and limited chemical composition. Evaporation rates of aerosolized DF-200 sprays were estimated under a set of baseline ITW nozzle test system parameters.

More Details
TYPE SAND Report YEAR 2012
OSTIDOI
Results 101–150 of 231
Results 101–150 of 231