PREPARATION OF POROUS BATIO3 PTC THERMISTORS BY ADDING GRAPHITE POROSIFIERS

Using an ordinary ceramic processing technique, a new method of prepar ing porous BaTiO3 PTC thermistors is introduced. Adding proper graphit e powders into calcined BaTiO3 powder can increase porosity and enhanc e the PTC effect of the sintered sample. When the graphite addition is about 1.0 wt%, the resisivity of samples from low-purity raw material s decreases to 20 OMEGA . cm at room temperature, while the PTC resist ivity ratio is over 10(5) and 1-2 orders higher than that of samples w ithout the porosifier. The porosifier has increased the reproducibilit y of resistivity from 60% up to 90%. In addition, the porous thermisto r has a fast response to overcurrent and shows some improvement in hea t resistance. With the aid of the Heywang model and the Kuwabara concl usion, the influence of graphite on grain surfaces is discussed. The e xperimental results show that this method is a useful technique to pre pare good PTC thermistors from low-purity raw materials.