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Student
Abstracts at Ames:
An Exploration of Ternary Compounds in RE-T-In, RE-T-Ge, and RE-T-Al Systems
(RE = Ce, Nd, Lu; T = Pd, Pt, Ni): A New Ternary Indide
and a Symmetry Question. JOSHUA WEBER (Grinnell College, Grinnell, IA, 50112) GORDON J. MILLER AND SRINIVASA THIMMAIAH (Ames Laboratory, Ames, IA, 50011)
Ternary indides containing
rare-earth (RE)
and transition (T)
metals, RE-T-In, have exhibited unique properties, yet the characteristics
of many RE-T-In
systems remain unknown. This exploration initially focused on novel
Ce-T-In systems, with T = Pd, Pt, and Ni. The focus then expanded to include ternary
indides with the RE metals
Nd and Lu and to include ternary compounds from RE-T-Ge and RE-T-Al
systems to study the effects of varying atomic size and valence electron
count. All samples were synthesized by arc-melting. A Guinier powder
X-ray diffractometer was used for phase identification, and select
samples were further analyzed using a Bruker single crystal X-ray
diffractometer. Only select crystals were analyzed because most products,
including
all Ce-T-In systems, contained multiple phases instead of the desired
complex-structured phase. The most interesting results have come from the Lu-Ni-In
and Ce-Pd-Al systems, from the phases Lu10Ni10.08(1) In19.0(1) and CePd0.93(1) Al3.08. Lu10Ni10.08(1) In19.0(1) is a new phase. It crystallizes in the tetragonal crystal system,
space group P4/nmm,
adopting the Ho10Ni9In20-type
structure, with
unit cell parameters a =
13.128(1) Å and c =
8.977(1) Å,
and unit cell volume of 1547.2(3) Å3 for Z = 2. Single-crystal analysis indicates that CePd0.93(1) Al3.08 belongs
to space group I4/mmm,
but it has been reported (as
CePd0.75Al3.25)
in space group I4mm. While electronic structure calculations seem to suggest this
reported solution as well, the space group is still undetermined. The RF values of the refinement were 5.13% for Lu10Ni10.08(1) In19.0(1) and
4.75% for CePd0.93(1) Al3.08.
Physical measurements and electronic structure calculations will be used to study
the new Lu-Ni-In compound and to resolve the space group problem of the Ce-Pd-Al
compound. In
future explorations, RE-T-In
systems
containing Nd, Lu, and other RE elements and additional RE-T-Ge
and RE-T-Al
systems, those systems which yielded the most interesting results, will be further
investigated.
Bio-Oil Stability Increase by Minimizing Ash through Pretreatment. DUSTIN BALES (University of Missouri-Rolla, Rolla,
MO, 65401) JUSTINUS SATRIO (Ames Laboratory, Ames, IA, 50011)
Bio Oil is created through
the fast pyrolysis of biomass process, and can be used for production of commodity
chemicals and is being researched as a fuel. Bio-Oil is preferable over biomass
as a fuel because it is much more energy dense and easier to transport. Bio-Oil
created by fast pyrolysis tends to be unstable in long term storage because
the fast pyrolysis process has a short reaction time, which does not allow
thermodynamic equilibrium to be reached immediately after production. It has
been determined that this is partly due to high alkali ash content. Alkali
metals (ash) act as a catalyst in the destabilizing reactions. Hence, alkali
reduction causes increased stability. It is hypothesized that certain biomass
pretreatments could reduce this alkali content before the sample is pyrolized
into bio-oil, specifically boiling water and boiling acid. The objective of
this research is to discover what effect these biomass pretreatments have on
alkali content. Experiments have been designed to test the ash reduction properties
of boiling corn stover for 60 minutes in water and 1%, 2.5%, and 5% phosphoric
acid solutions with corn stover biomass feedstock. Samples that have gone through
the torrefaction process then the boiling pretreatment will also be used to
discover any affect torrefaction has on alkali content. Torrefaction is a low-temperature
thermo-chemical pretreatment that breaks down hemi-cellulose in an inert atmosphere
and also acts as an excellent drying process. Phosphoric acid is used because
of its ability to breakdown hemi-cellulose, hypothetically releasing locked-in
alkali and increasing Levoglucosan content. Simple ash analyses of the untreated
and treated biomass show a maximum of 52% reduction with 5% phosphoric acid
treatment with rinse. Torrified biomass showed a maximum of a 72% ash reduction
after a 2.5% acid treatment. Scanning Electron Microscope with Energy Dispersive
X-Ray Spectrometry gives a breakdown of the components of biomass ash, char
ash, and bio-oil ash. Largest percentages other than oxygen were Silicon, Silicon,
and Iron, respectively. Fiber analysis shows a steady decrease in hemi-cellulose
with increasing acid concentration. Future work must be done to discover the
mechanism by which the Phosphoric Acid removes ash, and to test the pretreated
biomass in the actual pyrolysis process.
Coarsening of Superconducting Froths. ANDREW
FIDLER (Albion College, Albion, MI, 49224) RUSLAN PROZOROV (Ames
Laboratory, Ames, IA, 50011)
The structure and dynamics
of foams and froths has been a subject of intense interest due to the desire
to understand the behavior of complex systems, when topological complexity
prohibits exact derivations based on minimum energy arguments. Though exact
solutions have proven unattainable, general laws that govern the overall
structural evolution have been developed. This is particularity true in the
case of two-dimensional foams consisting of arrays of polygonal shaped cells
with three edges per vertex. The mathematics for describing the cellular
evolution in this system has proven to be surprisingly simple in form, and
it applies only to the system as a whole. This gives a hope that, while the
behavior of individual cells may be difficult to analyze, the overall system
can be described by relatively simple rules. Using magneto-optical imaging,
it was recently demonstrated that the intermediate state in superconducting
lead exhibits patterns that appears to be very similar to soap foams. While
visually alike, physically these systems are quite different. In conventional
foams the foaming agent is always some form of matter, while in the intermediate
state in lead the structure is characterized by superconducting and normal
state regions. In this project, we have investigated these analogies and
seen whether the general equations mentioned above apply equally as well
to magnetic superconducting foams. It has been determined that laws describing
foam evolution, such as von Neumann's law, work remarkably well for superconducting
froth, but some parameters are different when compared to conventional foams.
The biggest difference between these two systems is the agent that provides
the foaming in superconducting lead, the superconducting region, decreasing
as the field evolves, whereas in conventional soaps the amount of the foaming
agent is constant. Nevertheless, the statistics of the polygons and structural
dependence on the applied magnetic field and temperature have proven to be
analogous to time. Topological transformations of the cells have also proven
to be identical to conventional foams. This new type of superconducting foam
could prove to help greatly to the insight into the general physics of foams,
since the structure can be controlled to a greater extent by reversible manipulation
of magnetic field and temperature, which is impossible in case of conventional
foams where
time cannot be reversed.
Effect of Chemistry on the Life and Performance of High-Power Lithium-Ion Cells. MAGDALENA FURCZON (University of Illinois at Chicago,
Chicago, IL, 60680) DANIEL ABRAHAM (Ames Laboratory, Ames, IA, 50011)
High-power battery technology
is key to the commercial success of hybrid electric vehicles (HEVs). These
vehicles combine the advantages of the extended driving range and rapid refuelling
capability of a conventional vehicle with the increased fuel economy and reduced
exhaust gases of an electric vehicle. The relatively high specific-energy and
specific-power characteristics of rechargeable lithium-ion batteries make them
an attractive alternative to the nickel metal-hydride batteries used in hybrid
vehicles currently in the market. The goal of this project is to determine
the suitability of various electrode-electrolyte combinations for HEV applications.
The cells typically contain a layered oxide-based positive electrode, a graphite-based
negative electrode, and an electrolyte containing an organic solvent and lithium-bearing
salts (such
as LiPF6). Project activities to date have involved investigation of
the effect of alternative salts, such as LiF2B(C2O4) and LiB(C2O4)2,on cell cycling performance. Experiments were conducted on ~2
mAh coin cells and on ~35 mAh cells containing a lithium-tin reference electrode.
The cells were electrochemically cycled or subjected to above-ambient temperatures
(up to 55 °C). Capacity and impedance measurements were made periodically to
determine the deterioration of cell performance with age. Initial data indicate
that cells containing the LiF2B(C2O4)
salt show better long-term
performance than do cells containing the LiPF6 and
LiB(C2O4)2 salts.
Effects of Elemental Impurities on TiNiSn Solution Growths. THOMAS
BRENNER (Carleton College, Northfield, MN, 55057) PAUL CANFIELD (Ames
Laboratory, Ames, IA, 50011)
The intermetallic compound
TiNiSn has been of interest to researchers because of its semiconducting and
thermoelectric properties. We attempted to determine the effects of constituent
element purity
on the growth and electrical properties
of TiNiSn single crystals. We grew TiNiSn single crystals from a Sn flux, each
time varying the purity of our constituent elements. In order to test the hypothesis
that chlorine impurities affect the crystal formation and electrical properties
of TiNiSn, we added nickel chloride powder to the starting elements for several
growths. Qualitative differences in crystal growth were observed, and secondary
compounds were identified by x-ray diffraction whenever possible. Resistivity
measurements were made between 2 and 375 K on TiNiSn crystals from each growth,
so that the effect of elemental purity on resistivity could be determined. Using
the resistivity data, we calculated the semiconducting gap for each sample. Lower
purity Ti led to variation in growth products, but changing Sn and Ni purity
did not produce variation. The addition of nickel chloride produced several changes
in the growth. For all samples room temperature semiconducting gaps were between
110 and 180 meV. No trends were observed in either gap energy or resistivity
with respect to elemental purity.
Functionalized Particles As Templates for Nanoparticles Self-Assembly. CHRIS KNOROWSKI (Virginia Tech, Blacksburg, VA, 24061)
DR. ALEX TRAVESSET (Ames Laboratory, Ames, IA, 50011)
Block copolymer solutions
or melts exhibit an amazing variety of phases and structures with vast possibilities
for the design of novel materials A promising design strategy is the transfer
of a polymer structure to an inorganic component present in solution, where
the goal is to obtain a self-assembled inorganic crystal exhibiting the mesoscopic
order imposed by the polymeric phase, which serves as a template. Establishing
general conditions for successful templating is therefore a major theoretical
challenge, with fundamental implications for both basic and applied science.
In this paper we investigate general conditions leading to successful templating
by considering a generic pluronic coexisting with inorganic particles, which
herein will be referred as nanoparticles. We assume that nanoparticles tend
to crystallize and thus attract each other with a characteristic attractive
energy N. We also functionalize the ends of the polymer with an affinity for
the nanoparticles to facilitate templation thus introducing a new energy scale
F, which is the energy gain for nanoparticles to bind to the functionalized
group. We use a short ABA triblock copolymer where the A blocks are hydrophilic
and the B blocks are hydrophobic, and model the water implicitly. Using course
grained MD simulations we investigate the region where this triblock copolymer
forms a hexagonal phase. When the nanoparticles are added to the system an
extraordinary variety of exotic phases are realized as we vary the attractive
N and F forces. Over a large range we see a double gyroid with the nanoparticles
forming one gyroid (space group 1a3d) and the hydrophobic blocks forming another
gyroid which interlock around each other. Over a small region we see a perforated
lamellar with hexagonal ordering, with the nanoparticles and the hydrophobic
blocks forming alternating planes. The hydrophobic forming the perforated lamellar
and the nanoparticle Lamellar connecting through the perforations in the hydrophobic
plane. As we continued to increase both values of N and F we see a noncentrosymetric
double gyroid (space group I4_132). There are also several areas where coexistence
between phases occur and many regions where further exploration could reveal
new phases
of the diagram.
High Activity Fuel Cell Catalysts via Mesoporous Nanocomposite Polymers. GREGORY BAKER (Pennsylvania State University, University
Park, PA, 16802) ERIC COCHRAN (Ames Laboratory, Ames, IA, 50011)
Hydrogen fuel cells have
the potential to improve the way we propel our vehicles. Catalyst particles within
cathode catalyst layer (CCL) promote the reaction of protons, electrons, and
oxygen, producing water, which must be removed. The current CCL design suffers
from poor mass transport properties, limiting the efficiency of the present-day
hydrogen fuel cell. The current structure is a combination of different materials
put together to achieve these goals but lacks the order needed to achieve the
desired efficiency. In this research, we investigated the development of a novel
CCL design that will significantly increase the transport of reactants to active
catalyst sites. The first step towards this design was the synthesis of a new
catalyst support, based on single-wall carbon nanotubes (SWCNTs), that integrates
electon and proton conductivity into a single particle. First, pristine SWCNTs
were functionalized with an aniline derivative compound using a solvent free
technique. Then, azide-terminated polystyrene was “click-coupled” to the alkyne
group. This SWCNT-graft-polystyrene was then sulfonated; this created negatively
charged regions in the polymer, which facilitated the deposition of platinum
nanoparticles through the reduction of platinum salts. After sulfonation the
polymer is also proton-conductive. Thermogravimetric analysis analyzed the effectiveness
of the grafting reactions. Nuclear magnetic resonance spectroscopy demonstrated
that the proper products were prepared during the synthesis of the aniline derivative
and also to ensure that azide terminated polystyrene was achieved. Transmission
electron microscopy determined the effectiveness of the decoration
with platinum.
Novel reduction of monosaccharides and disaccharides using palladium-carbon
catalysts. FIONA MILLS-GRONINGER (Manchester College, North
Manchester, IN, 46962) GEORGE KRAUS (Ames Laboratory, Ames, IA, 50011)
Mixtures of sugars as by-products of
industrial processes are difficult and expensive to separate. This will be increasingly
important in the emerging cellulose ethanol industry in which large volumes of
carbohydrates will be produced. By reducing the different sugars in a mixture
to a single product in a single-step reaction, the resulting carbohydrate can
be easily used in further processes. Reductions of carbohydrates using palladium-catalyzed
reactions are documented in literature, typically with lengthy reaction times.
In this study, mono- and disaccharides are reduced using a novel combination
of palladium-carbon catalyst, formic acid, and concentrated sulfuric acid heated
to 80°C, producing the reduced form of the simple carbohydrate after one hour.
Reaction progress was determined using 300 and 400 MHz proton NMR. After successful
production of the reduced sugar, the compound was acetylated using acetic anhydride
and purified using TLC and flash column separation. Various acetylation conditions
were attempted, and reaction efficiency was determined using the NMR spectra
as well as qualitative TLC comparison. Reduction was confirmed by comparing the
spectra of the carbohydrate starting material with spectra after reduction. The
spectra of a-methyl-D-glucopyranoside (methoxy glucose), dextrose, D-cellobiose,
and sucrose showed distinct differences from the starting material indicative
of reduction. Furthermore, comparison of the spectra of reduced forms of methoxy
glucose, dextrose, and cellobiose showed almost identical peaks consistent with
production of a single reduced product. The complex carbohydrate cellulose acetate
was unable to be reduced using this method. Future work will include optimizing
conditions for acetylation as well as determining conditions for effective reduction
of complex carbohydrates.
Production of Pure Phase Multiferroic Materials by High Oxygen Pressure Annealing
Processes. MATTHEW CROMWELL (Brigham Young University-Idaho,
Rexburg, Idaho, 83460) DR. R. W. MCCALLUM (Ames Laboratory, Ames,
IA, 50011)
This study aims to form
multiferroic materials from Rare Earth compounds and Manganese oxides. The
desired composition
is RMn2O5 (R = Rare Earth). Multiferroic materials import stems from simultaneous
ferromagnetic and ferroelectric characteristics. Because of their dual nature,
multiferroic materials could be utilized in various technologies. Understanding
the properties and behavior of their crystal systems is critical to the eventual
application of such materials, yet producing a pure single phase is still problematic.
This must be done by reacting highly stable R2O3 with Mn-O, which remain
stable in air to 1200 ºC. Existing phase diagrams for the given system indicate
that increasing partial pressure of Oxygen
(PO2)
greatly improves the kinetics of the phase transition. However, at such temperatures
and pressure, standard materials soften and fail. Oxygen also presents a problem,
being highly corrosive in nature. A furnace chamber maintaining up to 1000 ºC
with 10 bar PO2 was built from Hainesalloy-230, a high-nickel superalloy. This
pressurized system was installed and various safety considerations and procedures
were negotiated in bringing this into operation. A series of experiments varying
annealing conditions were then performed to study the effect of changing PO2. Two sets of samples were made from the same mixture and run
at 900 ºC and 1000 ºC for twenty hours. Within each set, four pressures (in bar)
were applied- 9.3, 3, 1 and 0.2. Results were examined by X-Ray Diffraction (XRD)
to determine composition. XRD showed the content of desired phase increased significantly
at higher temperature and also with increasing PO2.
Increasing temperature by 100 ºC produced double the desired phase over the 20
hour test. Still significant was the increase due to PO2 which
lifted the desired
phase from 60% to 72%. This affirms the importance of PO2 in
this phase system.
In further study, the effect of PO2 over greater time intervals and elevated temperatures may be
instructive in obtaining pure phase materials.
Protein-Assisted Magnetite Nanoparticle Synthesis. TIMOTHY
PICA (University of California
at Berkeley, Berkeley, CA, 94709) TANYA PROZOROV (Ames Laboratory, Ames, IA, 50011)
Uniform magnetite nanocrystals were
synthesized in the presence of the biomineralization protein mms6 involved in
the biomineralization of magnetite in bacterial magnetosomes. Several recombinant
mms6 proteins were tested: polyhistidine-tagged full-length mms6 protein (his-mms6),
a 25 amino acid segment from the C-terminus of this protein (c25-mms6), and a
glutathione s-transferase enzyme-tagged mms6 protein (GST-mms6). The his-mms6
protein was reported to facilitate formation of ~30 nm, single-domain, uniform,
isomorphic magnetite nanocrystals in aqueous polymeric gel, as verified by transmission
electron microscopy analysis and magnetization measurements. Conjugating the
proteins to activated Pluronic polymer allowed further control over particle
growth. Similarly, the c25-mms6 protein was also shown to promote shape-selective
formation of magnetite nanocrystals. Preliminary fast protein liquid chromatography
(FPLC) studies indicated that both his-mms6 and c25-mms6 proteins were present
in solution as multimers, thus potentially forming extended surfaces suitable
for nucleation of magnetite. The significantly larger GST-mms6, which was found
in a monomeric state and did not form multimers in solution, exhibited poor magnetite
templating ability, and produced small nanoparticles lacking specific shape.
This suggests that the ability of the protein to form multimers could play an
important role in magnetite crystal formation, with larger numbers of protein
molecules in the multimer resulting in the formation of larger magnetite nanoparticles.
To test this hypothesis, we conducted magnetite synthesis in solution with various
protein concentrations. In addition to synthesis in solution, we attempted synthesis
on surfaces using both chemical ink-jet printing of protein solution on silicon
wafers, as well as stamping the protein solution onto the surface of functionalized
silicon. It was found that magnetite growth was limited to locations on the silicon
wafer where protein had been stamped. The structure and placement of the formed
magnetite nanoparticles were analyzed through electron microscopy and magnetic
measurements. Additional magnetic analysis will offer further insight into the
magnetic characteristics of mms6-assisted
magnetite nanocrystals.
Simulation of Shearing in Dense Granular Flows. BRIAN
LANGSTRAAT (Central College, Pella, Iowa, 50219) SHANKAR SUBRAMANIAM
(Ames Laboratory, Ames, IA, 50011)
Understanding the response of granular
matter to mechanical loading is essential to many applications in science and
engineering, such as avalanches and hopper flows. The constitutive behavior of
pure solids or fluids is well understood by researchers. However, the mechanical
response of granular matter, which can exhibit fluid-like or solid-like behavior
depending on the loading conditions and volume fraction, is not well understood.
In this work, computer simulations of interactions between individual particles
that constitute the granular matter are used to test continuum models of granular
flow. We use the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS)
which was developed at Sandia National Laboratories to simulate the dynamics
of a large number of particles. The response of granular matter to plane shear
between two parallel plates is chosen as a canonical test problem. The LAMMPS
simulation data is analyzed to understand the evolution and steady-state profiles
of volume fraction, average velocity, granular temperature, and stress. Glass
beads are simulated with a volume fraction of 0.46. Three shear rates are tested
corresponding to the slow frictional, transitional, and intermediate regimes.
The sheared particles tend to form striated layers in planes parallel to the
shearing surfaces. The simulations reveal that the center layers are very dense
with high stress and a linear change in velocity. Also, the granular temperature
is low within the center layers. We conclude that in the dense, central layers
of the sheared granular flow there are less velocity fluctuations. This research
is part of a larger project that will help to further the understanding of dense
granular flows.
Uniform Height, Self-Organized Pb/In Islands Grown on Si(111) 7 X 7 Interfaces. GEORGE SCOTT (Northwestern University, Evanston, IL,
60201) MICHAEL TRINGIDES (Ames Laboratory, Ames, IA, 50011)
The ability to grow uniform height
self-organized nanostructures is made possible by Quantum Size Effects (QSE)
and could have applications in the technology sector. Pb deposited epitaxially
onto different Si(111) interfaces ( (7 X 7), Beta Phase-sqrt(3)xsqrt(3), Alpha
Phase-sqrt(3)xsqrt(3) etc) produced islands of uniform heights but In on Si(111)
7 X 7 did not. These initial Si(111) interfaces are prepared by depositing small
amounts of Pb or In under ultra-high vacuum (UHV) conditions. After these initial
2-D phases are prepared, deposition is followed by the element of interest (Pb
or In) to form epitaxial nanostructure islands. Good height uniformity was found
when In was deposited on the Pb Alpha Phase-sqrt(3)xsqrt(3) phase when fcc In(111)
islands are present. In order to gain insight into the kinetics that could lead
to similar behavior in other Pb-In mixed systems, Pb was deposited on In sqrt(31)xsqrt(31).
Spot profile analysis – low-energy electron diffraction (SPA-LEED) was the primary
method used in the uniform height experiments because of the ability to observe
a large sample area. From the diffraction intensity profiles, uniform heights
existed only when Pb was present in the system. Scanning tunneling microscopy
(STM) was also used to build height histograms and verify
the diffraction results.
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