Gravimetric Adsorption Studies of Hydrogen on Granular Metal Surfaces Using a Vacuum Microbalance
A Cahn RG microbalance has been incorporated into a high-vacuum gravimetric adsorption apparatus for hydrogen adsorption studies from 77 to 273 K on granular metal surfaces. A study was undertaken to eliminate or minimize the expected thermomolecular flow (TMF) effects and make gravimetric adsorption results meaningful under these conditions.
Pressure- and temperature-dependent TMF effects were found to be associated with the balance beam, hangdown wires, and sample container. The balance beam of the Cahn balance was found to exhibit a small reproducible pressure-dependent apparent weight change which, because of the design of the balance, could not be eliminated. Temperature gradients along the walls of sample and reference hangdown tubes were minimized by silvering the walls and by submerging the tubes to a depth of 55 cm in a well-stirred constant-temperature bath at the desired temperature.
The experimental arrangement used minimized but did not eliminate TMF. The remaining forces were found to be reproducible for a fixed geometry and were determined from blank runs made on the system. A sample of pure copper, which does not adsorb hydrogen at the temperatures investigated, was used to verify the calibration curve. Using these calibration curves, hydrogen adsorption studies were obtained for a reduced-oxide nickel alloy sample over the temperature range 77 to 273 K and the pressure range 10−6 to 10−2 torr.
KeywordsAdsorption Study Silver Film Balance Beam Thorium Oxide Granular Metal
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