The Conradi group uses nuclear magnetic resonance to study solids. A primary focus is the motion of H and D atoms in metal-hydrides and deuterides. These materials will play an important role in future energy systems. For example, automobiles and trucks can be run on H2 with very little pollution (and greater efficiency, using fuel cells instead of internal combustion engines). On-vehicle storage of the H2 by dissolving it into an appropriate metal will allow large vehicle range (distance between re-fuelings), considerably superior to compressed gas storage. We note that some metals absorb up to 3 H atoms per metal atom, resulting in very dense storage of hydrogen. The scientific issues surrounding metal-hydrides are our focus. Where in the metal lattice do the H (or D) atoms reside? How rapidly do they diffuse and what is the pathway and mechanism by which they diffuse? How do the interstitial H atoms change the structure and electronic behavior of the host metal ?
Current research is on ZrBe2(H,D)x, with x near 1.5. This material undergoes a phase transition at 200 K (240 K in the deuteride) which we believe to be an ordering of the vacancies (1 in 4 H,D sites are vacant). Deuterium NMR has been used to study the change in D-atom mobility at the transition. Be-9 NMR provides the best evidence of the structural changes at the transition. Nanoscopic PdHx is being examined as well. This small-grain material (~10 nm diameter) has different hydriding characteristics than traditional large-grain PdHx. In particular, proton NMR shows two well-resolved lines, indicating two distinct sites. The nature of these sites is a goal of our work.
The Conradi group uses laser-polarized rare gases (He-3 and Xe-129) to study lungs in humans and small animals. Helium-3 can be polarized to an absolute nuclear spin polarization of about 50% in 0.5 liter STP quantities. Compared to typical Boltzmann equilibrium polarizations, hyperpolarized gas yields NMR/MRI signals bigger by 100,000. This sensitivity increase more than offsets the very low spin densities of gases, 1000 -10,000 smaller than water.
The human lung imaging effort routinely images the lungs of healthy volunteers and patients with emphysema. By measuring with MRI the diffusivity of the gas, the integrity or destruction of the lungs alveolar walls is determined. The combination of diffusivity images with ventilation images creates a high-resolution and thorough depiction of the status of the lungs. The human effort is an on-going collaboration with our group in Physics, the Department of Radiology, and the Lung Volume Reduction Surgery effort at the W.U. Medical School. The imaging of small-animal lungs is under development. The aims are to use this new technology as a tool to follow longitudinally the development of lung disease in animal models.
Mark Conradi received a B.S. in 1973 and Ph.D. in 1977, working in Prof. R. E. Norberg's nuclear magnetic resonance (NMR) lab at Washington University. A postdoc stint as a Wigner Fellow at Oak Ridge National Laboratory's Chemistry Division was an exposure to electron spin resonance and chemistry. From 1979-1986, Mark was an assistant and then associate professor in the Department of Physics at the College of William and Mary, Williamsburg, VA. The research developed there was solid-state NMR of molecular solids and gases. In 1986 Conradi moved to Washington University where he is now (full) Professor. The research includes solid-state NMR spectroscopy and relaxation measurements in metal-hydrides and deuterides. Laser-polarized rare gases are being used for MR imaging of lungs in humans and small animals. Also, routes to ultra-high sensitivity 'routine' NMR of solutions using laser-polarized xenon are being explored.