Activation Studies in the Oxidation of Graphite.
MASSACHUSETTS INST OF TECH CAMBRIDGE FLUID DYNAMICS RESEARCH LAB
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One aspect of the oxidation of isotropic graphite has been studied using molecular beam - mass spectroscopy techniques. The measurements considered the hysteresis behavior in CO reaction probability which results upon cycling the surface temperature from 900 K to 1700 K back. A room temperature effusive O2 beam was employed with intensities at the graphite surface varying from 6.8x10 to the 14th power to 2.7x10 to the 15th power moleculessq. cm. sec. The beam impinged at an angle of 45 degrees relative to the surface normal. Reaction measurements were made in the principle plane normal to the graphite surface. A tuning fork chopper was utilized to modulate species desorbing from the surface and the signal was extracted using a digital phase sensitive detection scheme. The major findings are summarized below 1 The hysteresis behavior in CO reaction probability is a manifestation of surface adjustment times which are long compared to usual periods of data taking. 2 If brought to 1400K on the lower level of the hysteresis curve, the surface will adjust to a higher equilibrium value of reaction probability corresponding to the upper hysteresis level provided sufficient time of exposure to an incident O2 beam is allotted. 3 The pertinent quantity in the activation adjustment process is the cumulative number of oxygen particles impinging upon the target surface. Activation did not occur in the absence of an incident O2 beam. 4 A cumulative impingement of 2x10 to the 20th power O2 moleculessq. cm was necessary to fully activate the surface. This corresponds to the removal of 3x10 to the 17th power carbon atomssq.cm.
- Atomic and Molecular Physics and Spectroscopy