Scientific and Technical Aerospace Reports Volume 38 July 28, 2000

20000065655 Ames Lab., IA USA
Fundamental studies of supported bimetallic catalysts by NMR spectroscopy
Savargaonkar, N.; Oct. 17, 1996; 68p; In English
Report No.(s): DE97-002922; IS-T-1794; No Copyright; Avail: Department of Energy Information Bridge
Various hydrogenation reactions on transition metals are important commercially whereas certain hydrogenolysis reactions
are useful from fundamental point of view. The kinetics of hydrogen chemisorption was studied by means of selective excitation
NMR on silica supported Pt, Rh and Pt-Rh catalysts. The activation energy of hydrogen desorption was found to be lower on silica
supported Pt catalysts as compared to Rh and Pt-Rh catalysts. It was found that the rates of hydrogen adsorption and desorption
on Pt-Rh catalyst were similar to those on Rh catalyst and much higher as compared to Pt catalyst. The Ru-Ag bimetallic system
is much simpler to study than the Pt-Rh system and serves as a model system to characterize more complicated systems such as
the K/Ru system. Ag was found to decrease the amounts of adsorbed hydrogen and the hydrogen-to-ruthenium stoichiometry. Ag
reduced the populations of states with low and intermediate binding energies of hydrogen on silica supported Ru catalyst. The
rates of hydrogen adsorption and desorption were also lower on silica supported Ru-Ag catalyst as compared to Ru catalyst. This
report contains introductory information, the literature review, general conclusions, and four appendices.
NTIS
Bimetals; Catalysts; Spectroscopic Analysis
20000066592 Department of the Navy, Washington, DC USA
Fiber-Optic Pipette (FOP) for Rapid Long Pathlength Capillary Spectroscopy
Stellman, Christopher, Inventor; Bucholtz, Frank, Inventor; Ewing, Kenneth, Inventor; Jul. 30, 1998; 13p; In English
Patent Info.: Filed 30 Jul. 1998; US-Patent-Appl-SN-09-126,221
Report No.(s): AD-D019713; No Copyright; Avail: Issuing Activity (Defense Technical Information Center (DTIC)), Microfiche
Capillary spectroscopy is frequently used in the analysis of small-volume liquid samples. Traditionally, optical spectroscopy
of samples in capillary tubes has been achieved by using simple lenses to excite the sample and collect the resulting signal of interest,
Figure la. More recently, these standard optical arrangements have been replaced with fiber-optics, Figure 1b. Coupling of
a fiber-optic probe to the end of a capillary tube has provided a much simpler means of sample excitation and signal collection.
In addition, this arrangement has allowed for the excited and collected light to be efficiently waveguided throughout the sample
medium over a long pathlength. Thus, a larger sample is interrogated (opposed to traditional capillary or non- capillary measurements)
and significant signal enhancements have been achieved.
DTIC
Optical Properties; Spectroscopy; Capillary Tubes; Fiber Optics
20000067641 NASA Marshall Space Flight Center, Huntsville, AL USA
Exploiting the Temperature Dependence of Magnetic Susceptibility to Control Convection in Fundamental Studies of
Solidification Phenomena
Seybert, C. D., California Univ., USA; Evans, J. W., California Univ., USA; Leslie, Fred, NASA Marshall Space Flight Center,
USA; Jones, W. K., Jr., Motorola, USA; [2000]; 2p; In English; Microgravity Materials Science, 7 Jun. 2000, Huntsville, AL,
USA; No Copyright; Avail: Issuing Activity; Abstract Only
It is well known that convection is a dominant mass transport mechanism when materials are solidified on Earth’s surface.
This convection is caused by gradients in density (and therefore gravitational force) that are brought about by gradients in temperature,
composition or both. Diffusion of solute is therefore dwarfed by convection and the study of fundamental parameters, such
as dendrite tip shape and growth velocity in the absence of convection is nearly impossible. Significant experimental work has
therefore been carried out in orbiting laboratories with the intent of minimizing convection by minimizing gravity. One of the best
known experiments of this kind is the Isothermal Dendritic Growth Experiment (IDGE), supported by NASA. Naturally such
experiments are costly and one objective of the present investigation is to develop an experimental method whereby convection
can be- halted, in solidification and other experiments, on the surface. A second objective is to use the method to minimize convection
resulting from the residual accelerations suffered by experiments in microgravity. The method to be used to minimize convection
relies on the dependence of the magnetic susceptibility of a fluid on temperature or composition (whichever is driving
convection). All materials experience a force when placed in a magnetic field gradient. The direction and magnitude of that force
depend on the magnetic susceptibility of the material. Consequently the force will vary if the susceptibility varies with temperature
or composition. With a magnetic field gradient in the right direction (typically upward) and of the right magnitude, this variation
in the magnetic force can be made to exactly cancel the variation in the gravitational force. Expressed another way, normal buoyancy
is exactly countered by a ”magnetic buoyancy”. To demonstrate the principle, a solution of MnC12 in water has been used.
First the variation of the susceptibility of this paramagnetic solution with temperature and concentration was measured. Then a
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