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.
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:
Innovative Technology Assets Management
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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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Overview
The document discusses the development and application of palladium chloride (PdCl₂) sensors for detecting airborne mercury vapor, particularly in the context of NASA's Jet Propulsion Laboratory (JPL) and its Third Generation Electronic Nose (ENose). The ENose is designed for real-time air quality monitoring in crew habitats aboard spacecraft, such as the International Space Station (ISS), where the detection of toxic chemicals, including elemental mercury, is critical for astronaut safety.
Elemental mercury is a concern in space environments due to its potential release from certain lighting and its adverse health effects when inhaled, even at low concentrations. NASA has identified the need to detect mercury vapor at concentrations as low as 3 parts per billion (ppb) to ensure the safety of astronauts. Traditional methods for mercury detection, such as using gold films, have shown sensitivity but require high temperatures for regeneration, which is not ideal for the ENose's operational conditions.
The document outlines the synthesis and testing of novel inorganic sensing films made from palladium chloride, which have demonstrated excellent sensitivity and regeneration capabilities at lower temperatures (below 40 °C). These sensors can detect mercury vapor at concentrations starting from 2.5 ppb, making them suitable for the stringent requirements of the ENose.
The PdCl₂ sensing films are created by depositing a solution of palladium chloride onto gold electrodes and sintering them in air. The resulting sensors exhibit good sensitivity and reproducibility, even in humidified air, which is essential for their application in the variable conditions of space.
The document also references various studies and previous works related to mercury detection, highlighting the evolution of sensor technologies and the importance of developing diverse sensing materials to enhance the reliability of detection systems. The innovative approach taken by JPL in utilizing palladium chloride represents a significant advancement in the field of environmental monitoring, with potential applications extending beyond aerospace to other industries concerned with air quality and toxic substance detection.
In summary, this document emphasizes the critical role of advanced sensing technologies in ensuring astronaut safety and the ongoing efforts by NASA to develop effective solutions for monitoring hazardous substances in confined environments.
