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In-situ monitoring of vanadium dioxide formation using high-temperature XRD

Powder Diffraction

Rodriguez, M.A.; Bell, Nelson S.; Griego, James J.M.; Edney, Cynthia E.; Clem, Paul G.

The monoclinic-to-tetragonal phase transition (∼70 °C) in vanadium dioxide (VO2) strongly impacts the infrared properties, which enables its use in applications such as smart window devices. Synthesis of VO 2 can be challenging due to the variability of vanadium oxide phases that may be formed. We have employed high-temperature X-ray diffraction (HTXRD) to monitor the reaction process of vanadium oxide precursor powders to form the desired tetragonal VO2 phase. Single-phase tetragonal VO2 was formed within 30 min at 420 °C in flowing N2 gas (∼50 ppm O2). The monoclinic-to-tetragonal phase transformation was observed via HTXRD at ∼70 °C with the typical ∼10 °C hysteresis (i.e. approached from above or below the transition). © International Centre for Diffraction Data 2014.

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TYPE Conference YEAR 2014
OSTIScopus

The influences of excess sodium on low-temperature NaSICON synthesis

Journal of the American Ceramic Society

Bell, Nelson S.; Edney, Cynthia E.; Ingersoll, David I.; Spoerke, Erik D.

Controlling the materials chemistry of the solid-state ion conductor NaSICON is key to realizing its potential utility in emerging sodium-based battery technologies. We describe here the influence of excess sodium on phase evolution of sol-gel synthesized NaSICON. Alkoxide-based sol-gel processing was used to produce powders of Na3Zr2PSi2O12 NaSICON with 0-2 atomic % excess sodium. Phase formation and component volatility were studied as a function of temperature. NaSICON synthesis at temperatures between 900-1100C with up to 2% excess sodium significantly reduced the presence of zirconia, sodium phosphate, and sodium silicate secondary phases in fired NaSICON powders. Insights into the role of sodium on the phase chemistry of sol-gel processed NaSICON may inform key improvements in NaSICON development.

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TYPE Journal Article YEAR 2014
OSTIScopus

Improved flywheel materials :

Boyle, Timothy J.; Bell, Nelson S.; Ehlen, Mark E.; Anderson, Benjamin J.

As alternative energy generating devices (i.e., solar, wind, etc) are added onto the electrical energy grid (AC grid), irregularities in the available electricity due to natural occurrences (i.e., clouds reducing solar input or wind burst increasing wind powered turbines) will be dramatically increased. Due to their almost instantaneous response, modern flywheel-based energy storage devices can act a mechanical mechanism to regulate the AC grid; however, improved spin speeds will be required to meet the necessary energy levels to balance these green energy variances. Focusing on composite flywheels, we have investigated methods for improving the spin speeds based on materials needs. The so-called composite flywheels are composed of carbon fiber (C-fiber), glass fiber, and a glue (resin) to hold them together. For this effort, we have focused on the addition of fillers to the resin in order to improve its properties. Based on the high loads required for standard meso-sized fillers, this project investigated the utility of ceramic nanofillers since they can be added at very low load levels due to their high surface area. The impact that TiO2 nanowires had on the final strength of the flywheel material was determined by a three-point-bend test. The results of the introduction of nanomaterials demonstrated an increase in strength of the flywheels C-fiber-resin moiety, with an upper limit of a 30% increase being reported. An analysis of the economic impact concerning the utilization of the nanowires was undertaken and after accounting for new-technology and additional production costs, return on improved-nanocomposite investment was approximated at 4-6% per year over the 20-year expected service life. Further, it was determined based on the 30% improvement in strength, this change may enable a 20-30% reduction in flywheel energy storage cost ($/kW-h).

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TYPE SAND Report YEAR 2013
DOIOSTI

Electrospinning of nanofiber Chevrel phase materials

Journal of Materials Chemistry

Woan, Karran V.; Scheffler, Raymond H.; Bell, Nelson S.; Sigmund, Wolfgang M.

A modified sol-gel synthesis for non-oxide sulfide ceramics is presented. Sols are electrospun into continuous nanofiber precursors and then heat treated to obtain Chevrel-phase sulfide materials. In particular, the Mg-Chevrel fibers formed have average diameters of 230 ± 57 nm with grain sizes of 10 ± 3 nm after heat-treatment. © 2011 The Royal Society of Chemistry.

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TYPE Journal Article YEAR 2011
ScopusOSTIDOI
Results 51–75 of 120
Results 51–75 of 120