| RESEARCH |
temperature. J. Karl Johnson, an associate professor of chemical and petroleum engineering at the University of Pittsburgh, says that a number of theoretical modeling studies, including his own, are consistent with Eklund's experimental observations. If you assume that the intact hydrogen molecules physically adsorb to the nanotubes--a process known as physisorption--and you make reasonable assumptions for the molecular interaction potentials, Johnson says, the modeling indicates that "nanotubes are not capable of storing large amounts of hydrogen at room temperature and moderate pressures." The simulation results agree fairly well that only about 1 to 2 wt% of hydrogen is stored in nanotubes at room temperature and reasonable pressures, he adds. But the modeling results are only as good as the assumptions used in the modeling, theorists point out. If something more than physisorption is occurring in Heben's experiments--as Heben has suggested--then the results of the studies modeling physisorption of hydrogen may be misleading. "I don't think my simulations prove that Mike Heben's results are wrong," Johnson says. "I think they indicate that his results cannot be explained through simple physisorption." Heben's results are so intriguing, Johnson remarks, that they "make me think there's something else going on. I think you have to keep an open mind." |
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