Publications

Clem, Paul G.; Voigt, James A.; Siegal, Michael P.

Abstract not provided.

2005 AIChE Spring National Meeting, Conference Proceedings

Sounart, Thomas L.; Bickel, Jessica E.; Tallant, David T.; Matzke, Carolyn M.; Voigt, James A.; Michalske, Terry A.

The synthesis of cysteine-capped CdS quantum dot nanocrystals (CdS-cys) between two interdiffusing reagent streams in a continuous flow microfluidic reactor was investigated. Spatially resolved fluorescence imaging and spectroscopy of the microreactor at various reactant concentrations and flow rates was used to study nucleation and growth of these particles. The laminar flow of the impinging streams allowed for controlled diffusional mixing of the reacting cadmium and sulfide ions at the boundary between the two solutions, while the capping agent was present in one or both of the solutions in excess. The results show that the photoluminescence of these particles grown under these microfluidic conditions differs from those grown in batch reactors.

Hsu, Julia W.; Simmons, Neil C.; Voigt, James A.

Abstract not provided.

Voigt, James A.; Hsu, Julia W.; Criscenti, Louise C.; Cygan, Randall T.; McKenzie, Bonnie B.

Abstract not provided.

Voigt, James A.; Hsu, Julia W.; McKenzie, Bonnie B.; Spoerke, Erik D.

Abstract not provided.

Sounart, Thomas L.; McKenzie, Bonnie B.; Spoerke, Erik D.; Voigt, James A.

Abstract not provided.

Voigt, James A.; Michalske, Terry A.; Hoyt, Jeffrey J.; Tallant, David T.

Abstract not provided.

Voigt, James A.; Phifer, Carol P.; Sipola, Diana L.; Zschiesche, Dale Z.

Abstract not provided.

Tuttle, Bruce T.; Voigt, James A.; Sipola, Diana L.

Abstract not provided.

Spoerke, Erik D.; Voigt, James A.; Hsu, Julia W.

Abstract not provided.

Bunker, B.C.; Bachand, George B.; Voigt, James A.

Abstract not provided.

Hsu, Julia W.; Spoerke, Erik D.; Sounart, Thomas L.; Simmons, Neil C.; McKenzie, Bonnie B.; Chang, Nolanne A.; Voigt, James A.

Abstract not provided.

Criscenti, Louise C.; Spoerke, Erik D.; McKenzie, Bonnie B.; Cygan, Randall T.; Voigt, James A.

Solution-based synthesis is a powerful approach for creating nano-structured materials. Although there have been significant recent successes in its application to fabricating nanomaterials, the general principles that control solution synthesis are not well understood. The purpose of this LDRD project was to develop the scientific principles required to design and build unique nanostructures in crystalline oxides and II/VI semiconductors using solution-based molecular self-assembly techniques. The ability to synthesize these materials in a range of different nano-architectures (from controlled morphology nanocrystals to surface templated 3-D structures) has provided the foundation for new opportunities in such areas as interactive interfaces for optics, electronics, and sensors. The homogeneous precipitation of ZnO in aqueous solution was used primarily as the model system for the project. We developed a low temperature, aqueous solution synthesis route for preparation of large arrays of oriented ZnO nanostructures. Through control of heterogeneous nucleation and growth, methods to predicatively alter the ZnO microstructures by tailoring the surface chemistry of the crystals were established. Molecular mechanics simulations, involving single point energy calculations and full geometry optimizations, were developed to assist in selecting appropriate chemical systems and understanding physical adsorption and ultimately growth mechanisms in the design of oxide nanoarrays. The versatility of peptide chemistry in controlling the formation of cadmium sulfide nanoparticles and zinc oxide/cadmium sulfide heterostructures was also demonstrated.

Ceramic Engineering and Science Proceedings

Yang, Pin; Voigt, James A.; Rodriguez, Marko A.; Moore, Roger H.; Burns, George B.

The impacts of small niobium additions to processing, microstructure, and electrical properties in the Zr-rich lead zirconate titanate ceramics (PZT 95/5) were investigated. The influence of niobium content on dielectric responses and the characteristics of ferroelectric behaviors, as well as the relative phase stability and the hydrostatic pressure induced ferroelectric-to- antiferroelectric phase transformation are reported. Results indicate that increasing the niobium concentration in the solid solutions enhances densification, refines the microstructure, decreases dielectric constant and spontaneous polarization, and stabilizes the ferroelectric phase. The stabilization of ferroelectric phase with respect to the antiferroelectric phase near PZT 95/5 composition dramatically increases the pressure required for the ferroelectric-to-antiferroelectric phase transformation. These observations were correlated to the creation of A-site vacancies and a slight modification of the crystal structure. The importance of these composition-property relationships on device application will be presented.

Bell, Nelson S.; Lockwood, Steven J.; Voigt, James A.; Tuttle, Bruce T.

Chemically prepared zinc oxide powders are fabricated for the production of high aspect ratio varistor components. Colloidal processing in water was performed to reduce agglomerates to primary particles, form a high solids loading slurry, and prevent dopant migration. The milled and dispersed powder exhibited a viscoelastic to elastic behavioral transition at a volume loading of 43-46%. The origin of this transition was studied using acoustic spectroscopy, zeta potential measurements and oscillatory rheology. The phenomenon occurs due to a volume fraction solids dependent reduction in the zeta potential of the solid phase. It is postulated to result from divalent ion binding within the polyelectrolyte dispersant chain, and was mitigated using a polyethylene glycol plasticizing additive. Chemically prepared zinc oxide powders were processed for the production of high aspect ratio varistor components. Near net shape casting methods including slip casting and agarose gelcasting were evaluated for effectiveness in achieving a uniform green microstructure achieving density values near the theoretical maximum during sintering. The structure of the green parts was examined by mercury porisimetry. Agarose gelcasting produced green parts with low solids loading values and did not achieve high fired density. Isopressing the agarose cast parts after drying raised the fired density to greater than 95%, but the parts exhibited catastrophic shorting during electrical testing. Slip casting produced high green density parts, which exhibited high fired density values. The electrical characteristics of slip cast parts are comparable with dry pressed powder compacts. Alternative methods for near net shape forming of ceramic dispersions were investigated for use with the chemically prepared ZnO material. Recommendations for further investigation to achieve a viable production process are presented.

Voigt, James A.; Tuttle, Bruce T.; Sipola, Diana L.; Rodriguez, Marko A.; Watson, Chad S.; Burns, George B.

Abstract not provided.

Proposed for publication in Desalination.

Nenoff, T.M.; Pless, Jason D.; Voigt, James A.; Sipola, Diana L.; Krumhansl, James L.

An environmentally friendly method and materials study for desalinating inland brackish waters (i.e., coal bed methane produced waters) using a set of ion-exchange materials is presented. This desalination process effectively removes anions and cations in separate steps with minimal caustic waste generation. The anion-exchange material, hydrotalcite (HTC), exhibits an ion-exchange capacity (IEC) of {approx} 3 mequiv g{sup -1}. The cation-exchange material, an amorphous aluminosilicate permutite-like material, (Na{sub x+2y}Al{sub x}Si{sub 1-x}O{sub 2+y}), has an IEC of {approx}2.5 mequiv g{sup -1}. These ion-exchange materials were studied and optimized because of their specific ion-exchange capacity for the ions of interest and their ability to function in the temperature and pH regions necessary for cost and energy effectiveness. Room temperature, minimum pressure column studies (once-pass through) on simulant brackish water (total dissolved solids (TDS) = 2222 ppm) resulted in water containing TDS = 25 ppm. A second once-pass through column study on actual produced water (TDS = {approx}11,000) with a high carbonate concentration used an additional lime softening step and resulted in a decreased TDS of 600 ppm.

Proposed for publication in International Journal of Applied Ceramic Technology.

Siegal, Michael P.; Overmyer, Donald L.; Richardson, Jacob J.; Voigt, James A.; Clem, Paul G.

A variety of solution deposition routes have been reported for processing complex perovskite-based materials such as ferroelectric oxides and conductive electrode oxides, due to ease of incorporating multiple elements, control of chemical stoichiometry, and feasibility for large area deposition. Here, we report an extension of these methods toward long length, epitaxial film solution deposition routes to enable biaxially oriented YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO)-coated conductors for superconducting transmission wires. Recent results are presented detailing an all-solution deposition approach to YBCO-coated conductors with critical current densities J{sub c} (77 K) > 1 MA/cm{sup 2} on rolling-assisted, biaxially textured, (200)-oriented Ni-W alloy tapes. Solution-deposition methods such as this approach and those of other research groups appear to have promise to compete with vapor phase methods for superconductor electrical properties, with potential advantages for large area deposition and low cost/kA {center_dot} m of wire.

Hsu, Julia W.; Simmons, Neil C.; Voigt, James A.

Abstract not provided.

Proposed for publication in Nature Materials.

Hsu, Julia W.; Simmons, Neil C.; Voigt, James A.

The ability to precisely place nanomaterials at predetermined locations is necessary for realizing applications using these new materials. Using an organic template, we demonstrate directed growth of zinc oxide (ZnO) nanorods on silver films from aqueous solution. Spatial organization of ZnO nanorods in prescribed arbitrary patterns was achieved, with unprecedented control in selectivity, crystal orientation, and nucleation density. Surprisingly, we found that caboxylate endgroups of {omega}-alkanethiol molecules strongly inhibit ZnO nucleation. The mechanism for this observed selectivity is discussed.

Nenoff, T.M.; Sattler, Allan R.; Pless, Jason D.; Krumhansl, James L.; Voigt, James A.

The need for fresh water has increased exponentially during the last several decades due to the continuous growth of human population and industrial and agricultural activities. Yet existing resources are limited often because of their high salinity. This unfavorable situation requires the development of new, long-term strategies and alternative technologies for desalination of saline waters presently not being used to supply the population growth occurring in arid regions. We have developed a novel environmentally friendly method for desalinating inland brackish waters. This process can be applied to either brackish ground water or produced waters (i.e., coal-bed methane or oil and gas produced waters). Using a set of ion exchange and sorption materials, our process effectively removes anions and cations in separate steps. The ion exchange materials were chosen because of their specific selectivity for ions of interest, and for their ability to work in the temperature and pH regions necessary for cost and energy effectiveness. For anion exchange, we have focused on hydrotalcite (HTC), a layered hydroxide similar to clay in structure. For cation exchange, we have developed an amorphous silica material that has enhanced cation (in particular Na{sup +}) selectivity. In the case of produced waters with high concentrations of Ca{sup 2+}, a lime softening step is included.

Proposed for publication in Nano Letters.

Sounart, Thomas L.; Voigt, James A.; Tallant, David T.

Abstract not provided.

Ceramic Transactions

Yang, Pin Y.; Voigt, James A.; Lockwood, Steven J.; Rodriguez, Marko A.; Burns, George B.; Watson, Chad S.

The electrical properties of lead zirconate titanate ceramics near the 95/5 composition are extremely sensitive to the chemical composition and processing conditions. To precisely control the lead stoichiometry in a solid solution has been a challenge because of lead volatility during high temperature sintering. In this study, we investigated the effect of the amount of lead in the solid solution on crystal structure, dielectric behavior, and phase transformation characteristics for chemically prepared niobium modified PZT 95/5 ceramics. Implications are important for process control and assurance of material performance.

Yang, Pin Y.; Yang, Pin Y.; Moore, Roger H.; Lockwood, Steven J.; Tuttle, Bruce T.; Voigt, James A.; Scofield, Timothy W.

The hydrostatically induced ferroelectric(FE)-to-antiferroelectric(AFE) phase transformation for chemically prepared niobium modified PZT 95/5 ceramics was studied as a function of density and pore former type (Lucite or Avicel). Special attention was placed on the effect of different pore formers on the charge release behavior associated with the FE-to-AFE phase transformation. Within the same density range (7.26 g/cm3 to 7.44 g/cm3), results showed that ceramics prepared with Lucite pore former exhibit a higher bulk modulus and a sharper polarization release behavior than those prepared with Avicel. In addition, the average transformation pressure was 10.7% greater and the amount of polarization released was 2.1% higher for ceramics with Lucite pore former. The increased transformation pressure was attributed to the increase of bulk modulus associated with Lucite pore former. Data indicated that a minimum volumetric transformational strain of -0.42% was required to trigger the hydrostatically induced FE-to-AFE phase transformation. This work has important implications for increasing the high temperature charge output for neutron generator power supply units.

Proposed for publication in Journal of the American Chemical Society.

Tian, Zhengrong R.; Voigt, James A.; McKenzie, Bonnie B.

We report for the first time a one-step, templateless method to directly prepare large arrays of oriented TiO{sub 2}-based nanotubes and continuous films. These titania nanostructures can also be easily prepared as conformal coatings on a substrate. The nanostructured films were formed on a Ti substrate seeded with TiO{sub 2} nanoparticles. SEM and TEM results suggested that a folding mechanism of sheetlike structures was involved in the formation of the nanotubes. The oriented arrays of TiO{sub 2} nanotubes, continuous films, and coatings are expected to have potentials for applications in catalysis, filtration, sensing, photovoltaic cells, and high surface area electrodes.