Research in
The Barron Group
- Overall Goals and
Concepts
- Why
aluminum?
- Why an
interdisciplinary approach?
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- Research Areas -
Highlights and Present Topics
- Group 13 Organometallic
and Coordination Compounds
- Alumina nanoparticles:
from sol-gel to composites to hybrid materials
- Chemical control
over materials formation
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- Undergraduate
research
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- Collaborative
research
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- Stop the Presses: This
month's results!
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Overall Goals of the Research in the Barron
Group
- As highlighted by a joint appointment in
the Department
of Chemistry and Department
of Mechanical Engineering and Materials
Science, research in the Barron
group focuses on the chemistry and materials science of aluminum
and its related elements in the periodic table.
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- Research within the Barron Group is aimed
at understanding the relationships between the structure and
bonding within a compound or material with its physical and/or
chemical properties. With such an understanding it is possible to
control structure at the both the nanometer and Angstrom level.
The control of nanometer structure is aimed at allowing for the
design macroscopic structure and/or properties. Thus, it should be
possible to design new materials (whether molecular or not)
through an understanding of these relationships.
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Why Aluminum?
- Or rather why aluminum, gallium, indium
(and occasionally boron)? Since the focal point of the research
within the Barron group is not a single topic or a specific
technique, but a group of elements, some explanation is warranted:
aluminum is the most abundant metal in the earth's crust, and is
one of the most important elements in the modern world.
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- Aluminum oxides are an ubiquitous part of
modern technology. Applications include: precursors for the
production of aluminum metal, catalysts, and absorbents;
structural ceramic materials; reinforcing agents for plastics and
rubbers, antacids, and binders for the pharmaceutical industry;
and as low dielectric loss insulators in the electronics industry.
Although the applications for aluminum oxides themselves are
extensive, doped and mixed metal systems and non-oxide materials
are of increasing importance, e.g., the III/V (13/15)
semiconductor materials.
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- Organoaluminum compounds are of industrial
importance in processes for making a wide variety of chemical
products and as highly selective reagents in organic synthesis.
More recently organometallic compounds of aluminum, gallium and
indium have become important as precursors to electronic materials
and ceramics.
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- Each of the areas described above provides
significant challenges for a multidisciplinary approach to
scientific research, both at the level of basic science and that
of direct technological application.
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Why an interdisciplinary approach?
- Given the interdisciplinary nature of
modern science, techniques traditional to chemistry can be used to
solve real problems in materials science and, as is often
overlooked, materials science can aid in the development of new
areas or answer questions in chemistry. The diversity of research
interests within the Barron Group enables members of the group to
not only gain a broad range of knowledge, techniques, and views,
but to leverage off of the expertise of other group members in
creatively approaching scientific questions. Interdisciplinary
collaborations are for the mutual benefit of both parties.
Individual expertise, which separately cannot solve specific
problems, jointly brings novel approaches to the fore.
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- It is important that researchers use a
combination of appropriate characterization methods depending on
the problem being tackled. Equally, it is important for
researchers to bring techniques to an area where they have not
been traditionally employed. In addition to the tools traditional
to inorganic chemistry (Schlenk techniques, NMR and IR
spectroscopy, TG/DTA, X-ray crystallography, computational
methods, etc.) members of the Barron Group have the opportunity to
become knowledgeable in the use of more unusual methods (e.g., gas
phase photoelectron spectroscopy, BET, XAFS, etc. ) and those
often associated with Material Science (SEM, TEM, AFM, XPS, etc.).
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Research Areas - Highlights and Present
Topics
- The research undertaken in the Barron Group
may be described by three thrust areas, summarized below.
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- Where appropriate, links are provided to
give more details of specific research areas. Sub-links are also
provided for "Figures" (which would slow downloading of the main
text). Abbreviated references to specific publications are
provided (Journal, year, volume, page) in the links, however,
complete citations are provided in the full publication
list.
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Group
13 Organometallic and Coordination Compounds-
- This area involves a study
of relationships between the structure
and bonding in Group 13 compounds.
We have extensively studied several fundamental reactions
of Group 13 organometallics (i.e., their oxidation
and hydrolysis)
as well as investigating the factors that control physical
properties such as
volatility.
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- The Lewis
acidity of Group 13
compounds is well known. We have investigated the extent to which
Group 13 Lewis acids activate
small molecules and other metals upon coordination. Recent work in
the Group is aimed at using the chemistry of the Lewis acid-base
interactions as a route to solid state chemical switches.
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- An industrial important
class of catalysts are the alkylalumoxanes, in particular
methylalumoxane (MAO). We have discovered the structure of
alkylalumoxanes,
and demonstrated that their activity is dependent on their Latent
Lewis acidity. Recent work in the group has been aimed at
developing new routes to active catalyst compounds.
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- A recent project is the use
of Group 13 compounds as ligands
for transition and main group metals.
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Alumina
Nanoparticles: from Sol-Gel to Composites to Hybrid Materials
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- The acid hydrolysis of aluminum compounds
as a route to ceramics has been known since the 1950's, but the structure
of the sol-gels
was unknown. We have shown that alumina sol-gels (also called alumoxanes)
have a structural
core of the mineral boehmite. This allowed us to create a route
to these alumoxanes directly
from the mineral. Our investigations into the carboxylate-substituted alumoxanes
(carboxylate-alumoxanes) have shown them to be alumina
nanoparticles which are surface
stabilized by carboxylate groups.
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- Having developed a large scale, environmentally
benign, synthesis we have investigated the application of the carboxylate-alumoxanes
as ceramic
precursors. Their nanoparticle
nature allows for superior processing of composites and coatings. In addition,
the pore size of the resulting ceramic is controlled
by the identity of the carboxylate group which has led to our fabrication
of alumina ultra-filtration membranes.
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- Given the wide range of carboxylic acids
available and their ease of chemical modification, we have investigated the
application of chemically functionalized
carboxylate-alumoxanes as catalysts
and the key components in composites for automotive and aerospace applications.
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Chemical
Control over Materials Formation
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- Several efforts have been
directed towards the development of mild and/or highly controlled
chemistry-based approaches to the formation of inorganic solid
materials. These methods, loosely grouped under the name "chemie
douce" (soft-chemistry),
pay close attention to the structure, stability, and mechanisms of
product formation.
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- We have demonstrated the
principle of molecular control over the phase of a CVD film. Not
only can meta-stable phases be grown, but a new cubic
phase of GaS is only
formed from a precursor with a cubic Ga4S4
core. The control exerted by the molecular core was demonstrated
by a step-by-step analysis of the reaction pathway. This chemistry
has been expanded to other Group 13 chalcogenides and led to the
fabrication of a new class of GaAs
transistor.
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- Other chemically controlled
reactions we have explored include: the first formation of
InP
nanoparticles by
Me3SiCl elimination; a room
temperature metal exchange
with alumina nanoparticles allowing a route to mixed metal oxides;
and the microwave synthesis of semiconductors.
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- The formation of chemically
(functionally) graded
interfaces has been
an area investigated by the group. In particular, we have been
interested in the "reaction bonding" of dissimilar materials such
as metal:ceramic or ceramic:carbon.
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- Two recent projects involve
the control and inhibition of cement
formation and the
catalyzed aqueous
synthesis of ceramic thin films
under ambient conditions. These are part of a new research area
aimed at developing bio-materials mimics.
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Undergraduate
Research
- The importance of research
in an undergraduate degree cannot be quantified. It is often the
experience that shapes a student's future interest in science.
Undergraduates that undertake research within the Barron Group are
given their own distinct projects that are closely allied with an
ongoing project within the Group.
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- For a list of publications
with undergraduate researchers in the Barron Group
click
here.
Collaborative
Research
- Since no scientist works in
isolation, the development of meaningful collaborations are an
important part of the research program in the Barron Group.
Interactions are fostered within both academia and industry,
either to bring new expertise to the research group, or,
alternatively, in order to tackle problems of interest to the
group in new ways. Collaborations are intended for the mutual
benefit of both parties. Individual expertise, which separately
cannot solve specific problems, jointly brings novel approaches to
the fore.
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- For a list of publications
that have resulted from outside collaborations click
here.
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- For publications resulting
from our on-going (and extensive) collaboration with Professor
Simon G. Bott (U of Houston) for X-ray crystallography, see
full
publication list.
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