Dr. Flanagan came to Vermont in 1961 after receiving his Ph.D. at the University of Washington with B.S. Rabinovitch and doing postdoctorate research at Queen's University, Belfast, and Brookhaven National Laboratories He has twice been a Fulbright Research Scholar, and was selected the University Scholar in the Physical Sciences 1985-86. He was awarded Doctor of Philosophy "honoris causa" from Uppsala University (Sweden), 1992.
Emeritus Professor — Physical & Solid State Chemistry
Research and/or Creative Works
Our major research effort is centered about the behavior of hydrogen and its isotopes in metals, alloys and intermetallic compounds. We are especially interested in the thermodynamics of these systems. With the aid of thermodynamic data, statistical mechanical descriptions of these systems may be given. Although the investigation of hydrogen in metals may appear to be a rather specialized research area, the results help in the understanding of phenomena which are rather widespread, e.g., phase transitions, ternary phase diagrams, hysteresis in solid reactions, etc.
Palladium dissolves large amounts of hydrogen. A characterization of the Pd-H system is by the measurement of hydrogen isotherms at different temperatures, i.e., relations between the equilibrium P(H2) and the corresponding H content of the Pd. These isotherms can be used to obtain thermodynamic data for the system. Any modification of the Pd causes changes in the isotherms. For example, the Pd can be modified by substitutional alloying. We have a continuing research program on the characterization of Pd alloy-H systems by isotherm measurements and reaction calorimetry, i.e., measurement of the heat evolved when H2 is absorbed by the alloy. In addition to alloying, the Pd lattice can be modified to a lesser extent by introducing defects such as dislocations and vacancies. These can be detected by changes in the H2 solubility. This type of research is currently underway.
Another modification of the Pd lattice is by the internal oxidation of Pd-rich alloys. Internal oxidation occurs when there is a small amount of readily oxidized solute in a less oxidizable solvent metal. For example, a Pd/Al (3%) can be internally oxidized in an oxygen atmosphere at 800 ºC to give a Pd matrix containing nano-size alumina precipitates. This is a convenient method to prepare metal/oxide composites. The solubility of hydrogen in the Pd matrix is modified slightly by the presence of the non-hydrogen dissolving precipitates. There is a segregation of H to the Pd/alumina interface and also to the stress field about the precipitates. The solubility can be used to probe the properties of metal/oxide interfaces.
In addition to the use internal oxidation to prepare composites such as Pd/almina, it is also possible to prepare composites where the oxide dissolves H. For example, the internal oxidation of Pd/Mo (3%) yields Pd/MoO3, the MoO3 dissolves H to form a hydrogen-bronze. These systems are currently under investigation using measurements of hydrogen solubility and reaction calorimetry. In addition some physical analytical techniques such as SEM (scanning electron microscopy), SANS (small angle neutron scattering) and TEM (transmission electron microscopy) are being employed to complement the thermodynamic studies of the hydrogen dissolved in the Pd/oxide composites.
Studies are underway to characterize LaNi5-xSnxH systems for hydrogen storage. The substitution of Sn for some of the Ni decreases the plateau hydrogen pressure making the parent compound, LaNi5, more suitable for some applications. In addition, the substitution of Sn makes the intermetallic compound more stable towards many cycles of hydriding/dehydriding needed for applications.
Wang, D.; Flanagan, T.B. "Hydrogen Permeation of Partially Internally Oxidized Pd-Al Alloys in the Presence and Absence of CO", J. Membrane Sci., 2005, 253, 165.
Wang, D.; Flanagan, T.B. "Diffusion of Oxygen in Palladium", Scripta Mat., 2005, 52, 599-601.
Wang, D.; Flanagan, T.B.; Balasubramaniam, R. "Insights into Internal Oxidation of Binary and Ternary Pd Alloys Using Hydrogen Solubilities, J. Alloys Compounds, 2004, 364, 105-12.
Wang, D.; Flanagan, T.B.; Shanahan, K.L. "Permeation of Hydrogen through Pre-oxidized Pd Membranes in the Absence and Presence of CO", J. Alloys Compounds, 2004, 372, 158-64.
H. Noh, D. Wang. S. Luo, T. Flanagan, R. Balasubramaniam, "Hydrogen Bronze Formation within Pd/MoO3 Composites", J. Phys. Chem. B., 2004, 108, 310.
Park, C.-N.; Luo, S.; Flanagan, T.B. "Analysis of Sloping Plateaux in Alloys and Intermetallic Hydrides. I. Diagnostic Features", J. Alloys Compounds, 2004, 384, 203-7.
Luo, S.; Park, C.-N.; Flanagan, T.B. "Analysis of Sloping Plateaux in Alloys and Intermetallic Hydrides. II. Real Systems", J. Alloys Compounds, 2004, 384, 208-16.