Ceramic Humidity Sensors for Environmental Parameters Monitoring

Despite many types of sensors are available commercially, they do not satisfactorily meet the specific needs of the country, since they are designed for different conditions. In environmental parameters monitoring, the climatic differences in Brazil should be considered, which make necessary the development of sensors for each region of the country. Thus, researchers of the Environmental Technologies Group (TECAMB) integrated to the Associate Laboratory of Sensors and Materials (LAS) of the National Institute of Space Research (INPE) have well established themselves, for the last 20 years, in the elaboration of diagnosis techniques, characterization and development of porous ceramic. In this work, porous ceramic was manufactured from mechanical mixture of ZrO2 and TiO2 powders, compacted and sintered at different temperatures, for application as air humidity sensing elements in the Project "Development and Application of Network of Geosensors for Environmental Monitoring", into a co-operation programme under the Microsoft Research-FAPESP Virtual Institute for IT Research, for tropical forests monitoring. Ceramic materials applied as sensing elements of humidity, specifically metallic oxides, have shown advantages in terms of their mechanical strength, their resistance to chemical attack and their thermal and physical stability in, mainly, hostile environments. It is noteworthy that the ceramics exhibit a unique structure, consisting of grains, grain boundaries, surfaces and pores, what make them appropriate to be used as humidity sensors, since they have microstructures able to be controlled and suitable chemical compositions. The characterization of the sintered ceramics were carried out through X-ray diffraction (crystalline phases), scanning electron microscope, SEM (microstructure) and measurements of B.E.T. (specific area of porous). The porous ceramics characterization as air relative humidity sensor element was accomplished through capacitance variation meas- rements, using a RLC bridge coupled to a climatic chamber, in function of the air relative humidity range.