Humidity sensor using sintered zircon with alkali-phosphate

Abstract

A ceramic humidity sensor using alkali phosphate (tribasic), phosphoric acid and zircon as raw materials was studied. The ceramic body prepared by doping with sodium phosphate consists of zircon, Nasicon and probably glassy sodium polyphosphate. The sensitivity for humidity can be improved by doping with sodium phosphate and phosphoric acid. The specimen in which the mole ratio (Na/P) is nearly equal to one is desirable for a humidity sensor with respect to sensitivity, and the impedance is 2×10⁶ Ωcm or below in a dry atmosphere. The formation of Nasicon explains the decrease of impedance in the low humidity region and a decrease of impedance in the high humidity region can be achieved by the formation of sodium polyphosphate.