“Hydrogen generation via hydrolysis of zinc in a high pressure fluidized bed”

The goal of my research is the investigation of a viable means to split water and recover hydrogen as a renewable fuel source.  In the realm of thermo-chemical water splitting technology, an attractive approach is the two-step Zn/ZnO redox cycle:

            ZnO → Zn + ½ O2  ( high-temperature solar decomposition)  (1)

            Zn + H2O →ZnO +H2 (low temperature water splitting)          (2)

My work focuses on the low temperature water splitting portion of this cycle where hydrogen is generated.  My investigation includes: determining fluidization behavior of zinc nanopowders; designing and implementing a fluidized bed reactor of zinc nanopowder to carryout the water splitting reaction at high pressures; modeling the reactor to determine the kinetic properties and transport contributions of the reaction.

"Surface modification of nanoparticles
via Atomic Layer Deposition"

My main project goal is the application of ultrathin films on the surface of nanoparticles via Atomic Layer Deposition using a fluidized bed reactor. This technique allows for modifying the surface of ultrafine particles while maintaining their bulk properties.  Applications of this development range from microelectronics and high-performance materials to targeted-drug delivery and advanced cosmetic products.

This is a very novel development since conformal, non-granular, pinhole-free coatings had never been applied to bulk quantities of nanoparticles before. I am also interested in studying the new physical and chemical properties provided by the thin films as well as the effect of such films on interparticle forces.  

Luis is now at Applied Mcaterials in San Jose, CA.

Publications:
Hakim, L.F., C.L. Vaughn, H.J. Dunsheath, C.S. Carney, X.H. Liang, and A.W. Weimer, “Synthesis of Oxidation-resistant Metal Nanoparticles via Atomic Layer Deposition,” Nanotechnology, 18, 345603 (2007).

Hakim, L.F., J.H. Blackson, and A.W. Weimer, “Controlling the Interparticle Forces of Nanoparticles Using Atomic Layer Deposition,” Chemical Engineering Science, 62, 6199-6211 (2007).

Hakim, L.F., D.M. King, Y. Zhou, C.J. Gump, S.M. George, and A.W. Weimer, “Nanoparticle Coating for Advanced Optical, Mechanical and Rheological Properties,” Advanced Functional Materials, 17, 3175-3181 (2007).

Hakim, L.F., J.A. McCormick, G.-D. Zhan, P. Li, S.M. George, and A.W. Weimer, “Surface Modification of Titania Nanoparticles Using Ultrathin Ceramic Films,” Journal of the American Ceramic Society 89 (10), 3070-3075 (2006).

Hakim, L.F., S.M. George, and A.W. Weimer, “Nanocoating Individual Silica Nanoparticles by Atomic Layer Deposition in a Fluidized Bed Reactor,” Chemical Vapor  Deposition, 11,420-425 (2005).

Hakim, L.F., S.M. George, and A.W. Weimer, “Conformal Nanocoating of Zirconia Nanoparticles by ALD in a Fluidized Bed Reactor,” Nanotechnology, 16,  S375-385 (2005).

Hakim, L.F., J.L. Portman, M.D. Casper, and A.W. Weimer, “Aggregation Behavior of Nanoparticles in Fluidized Beds,” Powder Technology, 160 (3), 149-160 (2005).

Simulation, efficiency calculation and optimization of a solar reactor, which is used for the endothermic, high temperature step of the zinc/zinc-oxide redox cycle to produce hydrogen.

Sophia is currently a PhD candidate at ETH in Zurich.

Publications:
Haussener, S., D. Hirsch, C. Perkins, A. Lewandowski, A. Steinfeld, and A.W. Weimer, “Modeling of a Multi-tube High-temperature Solar Thermochemical Reactor for Hydrogen Production,“  Journal of Solar Energy Engineering, 131, 024503 (2009).

"Silica-coated Boron Nitride Particles
for Microelectronics Packaging"

Selectively coating only the edges (not the basal planes) of BN particles is desirable for increased wettability and interfacial adhesion of the BN edges within a polymer matrix while maintaining a high thermal conductivity via direct BN basal plane stacking. This project provides for the development of improved boron nitride (BN) filler materials for electronic thermal management applications. Novel Atomic Layer Deposition (ALD) nanocoating is used to selectively functionalize edges only and edges/basal planes to improve wetting of BN platelets with resin encapsulants. The improved wetting allows for significantly reduced viscosity (~ 5 times less) of BN/resin mixtures during processing and improved interfacial adhesion in the cured composite. These improvements are realized by placing an ultra-thin (nm thick), conformal, pin-hole free, chemically bonded SiO2 nanofilm on individual BN particles. 

James is now a Ph.D. student in Materials Science at University of Virginia

"Production of oxidation-resistant fine metal powders"

My project focuses on the use of a Thermal Gravimetric Analyzer to determine the feasibility of production of fine metallic powders via the reduction of their oxides.  By measuring the dynamic mass loss of the oxide sample during reaction (time, temperature), it is possible to calculate the activation energy and other kinetic rate parameters for the reduction reaction. The synthesized powders are then characterized by X-ray diffraction, oxygen content, microscopy, and surface area.  

Some of  the critical parameters that define optimum reduction process are the gas environment, the ultimate reaction temperature, and the ramp temperature program.   Ultimately, the fine metals will be passivated by coating the particles with a ceramic layer using Atomic Layer Deposition. This process creates a very conformal film on the surface of the particle that acts as a barrier for diffusion of oxygen, thus, increasing the oxidation-resistance of the powder.

"Atomic Layer Deposition Nanomaterials Synthesis, Characterization, and Applications "

My research interest is focusing on the design, synthesis, characterization, and properties of ultrathin films and nanostructures via the atomic layer deposition (ALD) technique. I am currently working on a number of projects and topics including ALD of ultrathin, conformal nanocoating on particles such as ALD on fine copper particles for quantum tunneling applications, ALD of inorganic films on polymers such as ALD on carbon nanotubes, fabrication and properties of nanolaminate composite materials and bulk nanocomposites from ALD coated powders, thin film growth, and various technological applications such as application of Particle-ALDTM and Polymer-ALDTM to phosphor particle functionalization and the fabrication of luminescent devices.

Guodong is currently at Smith International in Houston, TX.

Publications:
Zhan, G., X. Du, D.M. King, L.F. Hakim, J.A. McCormick and A.W. Weimer, "Atomic Layer Deposition of Bulk Quantities of Surfactant - modified Single-walled Carbon Nanotubes," Journal of the American Ceramic Society, 91 (3), 831-835 (2008).

"Production of Nanosized Metal Particles"

The interest in ultrafine metal nanoparticles has been increasing in the past few decades. However, due to their high surface area, nanosized metal particles rapidly oxidize when exposed to air. Metal nanoparticles can be produced from the decomposition of their oxalates. However, optimization of the particle size of the oxalate particles is required before the decomposition step.  A novel method to reduce the particle size of the oxalate particles was developed. Sub-micron particles were obtained after only a few hours of processing. Further reduction of particle size was observed during the decomposition of the metal oxalates.

"Thermophoretic Deposition of Aerosol Particles
in Laminar Flow Tube with Mixed Convection"

Thermophoresis is the term describing the fact that small particles suspended in a gas will acquire a velocity in the direction of decreasing temperature.  This phenomenon is important in a variety of applications such as the production of ceramic powders in high temperature aerosol flow reactors, and production of optical fiber performs. The gas molecules coming from the hot side of the particles have a greater velocity than those coming from the cold side.  The faster moving molecules collide with the particles more forcefully.  This difference in momentum leads to the particle developing a velocity in the direction of the cooler temperature. 

Jennifer is currently at Composite Technology Development in Lafayette, CO.

Publications:
Walsh, J.K., A.W. Weimer, and C.M. Hrenya, “Thermophoretic Deposition of Aerosol Particles in Laminar Tube Flow with Mixed Convection,” Aerosol Science, 37, 715-734 (2006).

Walsh, J.K., A.W. Weimer, and C.M. Hrenya, “An Experimental Study of Thermophoretic Deposition of Aerosol Particles in Laminar Tube Flow with Mixed Convection,” Aerosol Science and Technology, 40 (3), 178-188 (2006).

"Development of Rapid Reaction Technology"

My research involves the understanding and development of an aerosol flow transport tube reactor for various advanced materials.  The reactor is capable of operating at up to 2673 K (graphite reacton tube) and allows for the rapid heating (~ 1 million degrees/sec) of reactant particles to form fine powdered products.  We have successfully synthesized carbide (B4C, TiC, Mo2C), nitride (AlN), and intermetallic (NiAl, Ni3Al) materials as well as composites of those materials.  The product powders are typically submicron in size since the short residence time at temperature limits grain growth.  For most of these materials, the very properties that make them desirable (high hardness, high strength), make the synthesis of powdered forms by other techniques very difficult.

Chris is now a Senior Design Engineer at ALD Nanosolutions.

"Atomic Layer Deposition on polymeric materials"

My project is focusing on depositing thin film layers of alumina on polyethylene particles using ALD. These materials can later be used in improved barrier films and property enhanced plastics. 

Joe is now a Lead Process Engineer at ALD Nanosolutions.

Publications:
Spencer, J.A. II, X.H. Liang, D.M. King, S.M. George, A.W. Weimer, K.J. Buechler, C.J. Wood, and J.R. Dorgan, “Fluidized Bed Particle ALD Process for Producing HDPE/Alumina Nanocomposites”, in Fluidization XII – New Horizons in Fluidization Engineering, Engineering Conferences International (ECI) (Brooklyn, NY)(Edited by Xiaotao Bi, Franco Berruti, and Todd Pugsley), 417-424 (2007).

"Fluidization behavior and nanocoating
of ultrafine particles"

The focus of my research project is the study of the fluidization behavior of nanosized particles at low pressures. Determining parameters such as the superficial gas velocity and bed voidage at minimum fluidization give us insight on the special flow characteristics of nanoparticles in a fluidized bed. The ultimate goal is to coat nanoparticles using Atomic Layer Deposition at low pressures. The study of the effect of ceramic films on the fluidization characteristics is also relevant.

"Atomic Layer Deposition on fine copper particles for quantum tunneling applications"

My research currently involves the Atomic Layer Deposition (ALD) of alumina onto Cu particles.  The fluidization behavior of the Cu powders is investigated and the powders are then coated by ALD.  The resulting coated particles have an ultrathin conformal and chemically bonded layer of an insulating material (i.e. alumina) on the electrically conductive Cu particles.  The nanocoated Cu powders will be electrically pulse tested to determine if a non-linear quantum tunneling response can be obtained.  This type of response provides for an ability to reduce high voltage (electrical surges) threats to electrical equipment very effectively.

Les is now a Ph.D. graduate student in chemical engineering at Northwestern University.

"Rapid solar-thermal decarbonization of methane"

The objective of my thesis is to thermally dissociate methane to carbon black and hydrogen using a solar-thermal aerosol flow reactor. The most successful reactor design to date includes three vertical tubes. The outer tube is quartz, which serves as a window through which concentrated sunlight passes. The middle tube is a solid graphite tube that absorbs the solar radiation and heats the reactant gas stream. The innermost tube is a porous graphite tube through which argon is fed in order to create a “gas blanket” to protect the inner tube wall from deposition of the carbon black particles. The methane stream is fed into the center of the porous tube. Using concentrated sunlight from a 10 kW solar furnace, the reactor wall can achieve temperatures as high as 2100 K. At that temperature and a residence time on the order of 10 ms, 90% conversion of methane to hydrogen can be achieved. This is the first solar-thermal aerosol flow reactor designed to dissociate methane at high temperatures and low residence times. 

Jaimee Dahl is now employed with BP in Anchorage, Alaska, carrying out R&D in a Gas to Liquids Development Plant.

Publications:
Dahl, J.K., A.W. Weimer, A. Z’Graggen, and A. Steinfeld, “Two-dimensional Axi-symmetric Model of a Solar-thermal Fluid-wall Aerosol Flow Reactor,” Journal of Solar Energy Engineering, 127, 76-85 (2005).

Dahl, J.K., A.W. Weimer, A. Lewandowski, C. Bingham, F. Bruetsch, and A. Steinfeld,“Dry Reforming of Methane Using a Solar-thermal Aerosol Flow Reactor,”Industrial and Engineering Chemistry Research, 43 (18), 5489-5494 (2004).

Dahl, J.K., K.J. Buechler, A.W. Weimer, A. Lewandowski, and C. Bingham, “Solar-thermal Dissociation of Methane in a Fluid-wall Aerosol Flow Reactor,” International Journal of Hydrogen Energy, 29 (7), 725-736 (2004).

Dahl, J.K. W.B. Krantz, and A.W. Weimer, “Sensitivity Analysis of the Rapid Decomposition of Methane in an Aerosol Flow Reactor,” Int. Journal of Hydrogen Energy, 29 (1), 57-65 (2004).

Dahl, J.K., K.J. Buechler, R. Finley, T. Stanislaus, A.W. Weimer, A. Lewandowski, C.Binghman, A. Smeets, and A. Schneider, “Rapid Solar-thermal Dissociation of Natural Gas in an Aerosol Flow Reactor,” Energy, 29 (5-6), 715-725 (2004).

Dahl, J.K., V.H. Barocas, D.E.Clough, and A.W. Weimer, “Intrinsic Kinetics for Rapid Decomposition of Methane in an Aerosol flow Reactor,” International Journal of Hydrogen Energy, 27, 377-386 (2002).

Dahl, J.K., J. Tamburini, A.W. Weimer, A. Lewandowski, R. Pitts, and C. Bingham, “Solar-thermal Processing of Methane to Produce Hydrogen and Syngas,” Energy and Fuels, 15, 1227-1232 (2001).

"Study of fluidization and agglomeration behavior of nanosized particles for ALD processing"

Atomic Layer Deposition (ALD) allows modifying the surface of particles while keeping their bulk properties. Recent interest has been shown in applying thin films on nano-sized particles via ALD thru a fluidized bed processing. At very small scales (submicron) interparticle forces become very important and fluidization may become difficult. One of my project goals is to develop an understanding of all the interparticle forces involved in fluidization of nanoparticles. The use of multiple fluidization aids allows for reducing the natural agglomerating behavior of ultra fine particles. Therefore  conformal, non-granular, pinhole-free coatings can be applied on primary nano-sized particles. 

"Coating Particles with Alumina Nanolayers Utilizing Atomic Layer Deposition in a Fluidized Bed Reactor"

Jeff now works for HP in Corvallis, Oregon.

Publications:
Wank, J.R., George, S.M., and A.W. Weimer, “Nanocoating Individual Cohesive Boron Nitride Particles in a Fluidized Bed by ALD,” Powder Technology, 142 (1), 59-69 (2004).

Wank, J.R., K.J. Buechler, L. Hakim, S.M. George, and A.W. Weimer, “Coating Fine Iron Particles with an Oxidation-Resistance g-Alumina Nanolayer Using ALD in a Fluidized Bed Reactor,” in Fluidization XI - Present and Future of Fluidization Engineering, ECI International (Brooklyn, NY)    (U. Arena, R. Chirone, Ml. Miccio, and P. Salatino, editors), 603-610 (2004).

Wank, J.R., S.M. George, and A.W. Weimer, “Coating Fine Nickel Particles with Al2O3 Utilizing an Atomic Layer Deposition Fluidized Bed Reactor (ALD-FBR),” J. Amer.Ceram. Soc., 87 (4), 762-765 (2004).

Wank, J.R., S.M. George, and A.W. Weimer, “Conformal Ultrathin Non-conducting Coatings on Conducting Fine Metal Particles, "Proceedings of the 2002 Int’l Conference on Functionally Graded Materials  (Metal Powder Industries Federation), Princeton, NJ, 26-33 (2002).

Wank, J.R, A.W. Weimer, J.D. Ferguson, and S.M. George, “Conformal Encapsulation of Fine Boron Nitride Particles with Oxide Nanolayers,” in Functionally Graded Materials 2000, Ceramic Transactions, 114, 441-449 (K. Trumble, K. Bowman, I. Reimanis, and S. Sampath (editors), The American Ceramic Society, Westerville, OH (2001).

Wank, J.R., S.M. George, and A.W. Weimer, “Vibro-fluidization of Fine Boron Nitride Powder at Low Pressure,” Powder Technology, 121, 195-204 (2001).

"Direct electrochemical conversion on a carbon fuel cell"

My research is on a direct carbon converision fuel cell.  The direct electrochemical conversion of carbon black to electrical energy can be accomplished using a fuel cell design.  The use of a Direct Carbon Fuel Cell (DCFC) is attractive because of its near 100% thermodynamic efficiency.  This provides a substantial improvement over the production of electrical energy via burning carbon to provide turbine driving steam. This device is of interest because it could work in conjunction with the solar-thermal transport reactor under development in Dr. Alan Weimer’s research group.  The transport reactor thermally dissociates methane, producing hydrogen gas and nano sized carbon black powder.  This fine carbon black powder has been found to be highly reactive in a molten carbonate salt fuel cell, and my research investigates the reactivity in a direct oxidation type fuel cell.  The fuel cell was found to produce an open circuit voltage of 0.8 V at 800 oC, and a closed circuit current of 1-2 mA/cm2.

Houston is now a Ph.D. graduate student in chemical engineering at Northwestern University.