National Center for Physical Acoustics

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Materials Physics

The Materials  Physics group, currently lead by Dr. J.R. (Josh) Gladden, uses various acoustic methods to better understand a variety of novel materials.  The primary tool is resonant ultrasound spectroscopy (RUS) which uses the mechanical resonance spectrum (think of the tones produced when tapping a wine glass) to very precisely determine the elastic constants of the material.  These elastic constant are an excellent probe into the atomic environment and very sensitive to any changes due to temperature, pressure, or magnetic field for instance.  They have used RUS to study novel thermoelectric materials at high temperatures, layered ceramics for use in hydrogen fuel cells, and metallic hydrides near a critical temperature and pressure point. Current interests include structural phase change materials with applications in vibration energy harvesting and designing a new type of laser based RUS method to extend our current temperature and pressure range from 1000 oC and 1200 psi to 1800 oC and 2500 psi.

The Materials Physics group also has an interest in soft, structured materials.  They have been studying visco-elastic wormlike micellar fluids which support shear waves over long distances.  These shear waves can be detected with a simple optical technique due to the birefringence of the material (demonstrated in the photo).  Acoustics is being used to better understand possible structural phase transitions in the fluid at particular concentrations and temperatures.

Research Programs

  • Novel thermoelectric materials
    Over the past few years we have been working with the Jet Propulsion Laboratory, a branch of NASA, to study new types of thermoelectric materials.  These materials can convert a temperature gradient directly into electric power and will be a component in the energy source portfolio of the future.  To date we have investigated nanostructured silicon germanium, lanthanum telluride, and Zintl phase YMS materials.  We are beginning a study of lead telluride and skutterudites.
  • Metal-hydrides
    It has been long known that hydrogen gas can insert itself into the spaces between atoms in many types of metals.  This is one approach to hydrogen storage.  A detailed knowledge of the hydrogen absorption and desorption process is crucial to the design and optimization of hydrogen storage units.  The Materials Science group at NCPA is in the process of studying the elastic constants of palladium hydride at high temperatures and hydrogen pressures.  We have plans to study non-metalic hydrogen absorbers such as graphene sheets and ways to speed hydrogen absorption/desorption rates using acoustic resonances.
  • Novel ceramics for hydrogen fuel cells
    Ceramic based hydrogen fuel cells require high temperatures for operation and require strong, thermally robust structural components.  We are beginning a study into several types of novel layered ceramics at high temperatures which are being developed for next generation fuel cell technology for use in automobiles.
  • Lead-free solder alloys
    New types of solder alloys avoid the use of lead for environmental and health reasons.  A current problem with these alloys however is excessive brittleness, which can lead to failure of solder joints in electronics.  We have a current study to measure the elastic moduli in polycrystalline lead-free solder alloys up to the melting point for samples at various degrees of aging.  Additionally, we are measuring crystallite growth dynamics by monitoring acoustic resonances over time.

About Materials Science Group:

The materials science group at the NCPA has focused on characterization of mechanical properties and structure of novel materials. Elastic constants of a crystal are a measure of the curvature of the energy binding atoms together and, as such, they are sensitive probes into changes in the atomic environment.  Because elastic constants are relevant to both microscopic and macroscopic properties of a material, they are important to both fundamental solid state physics as well as materials and mechanical engineering.  Our group has focused to elastic constant measurements in extreme environments including both high temperatures (up to 1000 oC) and high pressures (vacuum to 140 atmospheres).  The types of materials we are primarily interested in are energy related materials which will eventually become components of clean, carbon free energy systems in the future.

Collaborators and Sponsors

  • Jet Propulsion Laboratory
  • Los Alamos National Laboratory
  • Oak Ridge National Laboratory
  • Cisco Systems Corp.
  • Delphi Corp.
  • U.S. Army