Patents

This invention relates to a process of making dense lead zirconate titanate ceramics showing low-frequency dispersion behaviour with a consequent variation of capacitance with the ambient humidity. The PZT [Pb(Zr0.52Ti0.48)O3] powder was synthesized by a mixed route of the citrate nitrate gel method followed by solid-state mixing and calcination. PZT pellets (with 1-5 wt% excess PbO as a sintering aid) were made by pressing the powder with a pressure of 64 MPa. The PZT pellets (kept on a dense 8YSZ plate) were inserted inside a furnace preheated to a temperature in the range of 900 - 950 °C. The pellets were kept inside the furnace maintained at that temperature for 30-120 min and allowed to cool inside by switching off the furnace. The two surfaces of the fast-fired PZT pellets were ground to remove the surface layers and to keep the thickness of the pellet in the range of 0.4 - 0.5 mm. The pellets, after polishing were ultrasonically cleaned and electrodes on both sides by silver paste, followed by curing at a temperature in the range of 600 - 650 °C for a time in the range of 30 - 45 min. The humidity sensing behavior of the electrode PZT pellets was studied by placing them in a closed desiccator maintained under different relative humidities by using saturated salt solutions. As the sensor material is & primarily nonporous, the response/recovery of the sensors is very fast. In comparison to porous humidity sensors, these nearly nonporous sensors are supposed to be more rigid and should show a low hysteresis and drift.