SURFACE-ACOUSTIC-WAVE MERCURY-VAPOR SENSOR

A sensor for the in situ detection and measurement of low concentratio ns of gaseous mercury is presented. The sensor is based upon a dual de lay line SAW oscillator with a gold-coated delay path. Gaseous mercury interacts rigorously with the gold film, forming an amalgam. The resu lting increase in film mass is manifested as a decrease in oscillation frequency, Measurement of gas concentration is achieved by differenti ating the sensor response at room temperature or by operating the sens ing element at a temperature where gas-film reaction kinetics result i n equilibrium rates of mercury amalgamation and desorption, This equil ibrium value of amalgamated mercury is highly dependent upon the gas c oncentration. Thus, the delay line oscillation frequency is a sensitiv e measure of gaseous mercury concentration. Responses of this sensor t o gaseous mercury concentrations in the ppb range are presented. The s ensor response features are analyzed in terms of response shape, respo nse magnitude, response time, and linearity at 25 degrees C and 200 de grees C.