Palladium chloride films have been found to be useful as alternatives to the gold films heretofore used to detect airborne elemental mercury at concentrations of the order of parts per billion (ppb). Somewhat more specifically, when suitably prepared palladium chloride films are exposed to parts-per-billion or larger concentrations of airborne mercury, their electrical resistances change by amounts large enough to be easily measurable. Because airborne mercury adversely affects health, it is desirable to be able to detect it with high sensitivity, especially in enclosed environments in which there is a risk of leakage of mercury from lamps or other equipment.

Four PdCl2-Film Sensors were exposed to various concentrations of Hg in air at a temperature of 25 °C and a relative humidity of 31 percent.
The detection of mercury by use of gold films involves the formation of gold/ mercury amalgam. Gold films offer adequate sensitivity for detection of airborne mercury and could easily be integrated into an electronic-nose system designed to operate in the temperature range of 23 to 28 °C. Unfortunately, in order to regenerate a gold-film mercury sensor, one must heat it to a temperature of 200 °C for several minutes in clean flowing air.

In preparation for an experiment to demonstrate the present sensor concept, palladium chloride was deposited from an aqueous solution onto sets of gold electrodes and sintered in air to form a film. Then while using the gold electrodes to measure the electrical resistance of the films, the films were exposed, at a temperature of 25 °C, to humidified air containing mercury at various concentrations from 0 to 35 ppb (see figure). The results of this and other experiments have been interpreted as signifying that sensors of this type can detect mercury in room-temperature air at concentrations of at least 2.5 ppb and can readily be regenerated at temperatures <40 °C.

This work was done by Margaret Ryan, Abhijit Shevade, Adam Kisor, Margie Homer, and April Jewell of Caltech; Kenneth Manatt of Santa Barbara Research; Julia Torres and Jessica Soler of Glendale College; and Charles Taylor of Pomona College for NASA’s Jet Propulsion Laboratory.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:

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Refer to NPO-44955, volume and number of this NASA Tech Briefs issue, and the page number.

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Detecting Airborne Mercury By Use of Palladium Chloride

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This article first appeared in the July, 2009 issue of NASA Tech Briefs Magazine.

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