A SELECTIVE SOLID-STATE GAS SENSOR FOR HALOGENATED HYDROCARBONS

This paper is concerned with a solid-state gas sensor having a selective response to halogenated hydrocarbon vapors, especially to chlorinated hydrocarbons. The halogenated hydrocarbon (HH) sensor is fabricated from a temperature-controlled bead of a sintered mixture of lanthanum oxide and lanthanum fluoride with two embedded electrodes. The current through the bead is measured at a constant imposed potential between the electrodes. The conductivity of the HH sensor bead is sensitive only to the presence of halogenated organic vapors, such as chlorobenzene, bromobenzene, iodobenzene, chloropropane, bromopropane, iodopropane, chloropentafluorobenzene, dichloromethane and 1,1,1-trichloroethane, but not to air, CO, NO2, hexane, benzene or phenol. The sensor device is controlled by a minicomputer for automatic control of the sample injection and data acquisition; this makes ambient air measurements automatic. A chemical mechanism for gas-sensor response is proposed to explain the analytical characteristics and high degree of selectivity of the sensor.