VAPOR ADSORPTION ON REFRACTOMETER SENSORS.
Annual rept. for Nov 63-Oct 64,
UNIVERSITY OF WESTERN ONTARIO LONDON DEPT OF PHYSICS
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An earlier study of refractometer response to a humid environment has indicated that the observed refractivity exceeds the true refractivity at relative humidities greater than 60 percent, at least for temperatures in the range 8 to 50 C. The present work defines more clearly the physical processes causing the refractivity error and assesses methods of reducing the error. The refractivity error for relative humidities exceeding 70 percent is greater when vapor is injected into the air as steam than when evaporated slowly from an open water surface. Quartz in the sensing element, whether in the region of strong electric field or in the fringe-field region, causes large errors at high relative humidities. The depth of the adsorbed layer is 3 microns on untreated invar and 1 micron on quartz at a relative humidity of 90 percent, as observed in the wind tunnel, but only about one-ninth of these when studied gravimetrically. An optical ellipsometer has shown the onset of microscopic condensation at relative humidities exceeding 70 percent on untreated invar the size of the condensation droplets increases until they become visible at humidities approaching saturation.