sintering conditions of piezoelectric ceramics(2)

 The effect of pre-firing temperature. When the calcination temperature of piezo ceramic crystals is low, the particle size is fine but the difference is small, the accumulation in the green body is not tight, and the contact points are not much, which is unfavorable. When the calcination temperature is high, the particle size is coarse, the activity is poor, and the sintering power is small. In addition, an unsuitable calcination temperature will increase the free oxide of the ceramic material, which is causing a large amount of PbO to be volatilized, resulting in an increase in the sintering temperature. Only with a suitable pre-firing temperature, the porcelain material has both active and wide particle size distribution, and has many deposition contact points and high density after sintering. Therefore, the selection of the correct pre-firing temperature is a key factor in achieving good sintering. (5) The influence of porcelain properties and molding density is that the finely ground porcelain has fine grain size, large activity and large sintering power; the particle size of piezoelectric column piezoelectric ceramic is wide, and the compacted parts in the formed blanks are less, and the parts of the blank are as much as possible. Uniform densification is beneficial to the improvement of ion density and uniformity of ceramic density during sintering.

 Effect of sintering conditions. The degree of perfection of solid phase sintering depends mainly on the sintering temperature and holding time in the sintering conditions. Increasing the sintering temperature will increase the ion diffusion capacity and accelerate the sintering process. However, if the temperature is too high, there will be bond deformation of the piezo ceramic parts, secondary grain growth of density decrease, lead loss and performance degradation. If the temperature is too low, there will be a phenomenon of high porosity, low density, and poor electrical properties. The holding time is an important condition to ensure that the temperature of each part of the PZT piezoelectric ceramics cylinder is uniform during the sintering process and that the crystal is densified into a ceramic. The length of the holding time has a certain effect on the grain size and uniformity. (7) Effect of sintering atmosphere.

The sintering atmosphere of Pzt ceramic disc refers to an atmosphere in the furnace and inside the crucible during the sintering process. The general atmosphere is divided into three types: oxidation, reduction and neutrality. Its role is to form a protective sintering environment to control the solid phase reaction and form the desired tissue structure. In general, the PZT-based ceramic component should be sintered in an oxidizing atmosphere because the reducing atmosphere will metallize the metal oxide and reduce the valence ion, thereby lowering the insulation resistance of the ceramic member, increasing the tg δ, and deteriorating the performance. Sintering is carried out in the air to form an oxidizing atmosphere. A high temperature furnace in which a silicon carbon rod is used as a heating element is generally a weak oxidizing atmosphere. Sintering under the combined conditions of the two basically ensures that the porcelain high powder piezo cylinders are not reduced. La2O3, Bi2O3, Nb2O5, Ta2O3, Sb2O3 and other oxides are added to the formulation. At the time of sintering, attention should be paid to the problem of insufficient oxygen. After burning, the piezoelectric properties of the products after burning will be significantly improved. The plastically shaped blanks are stored in the air with high humidity for a long time, and will adsorb carbonate, nitrate, chloride or hydroxide ions, which is not conducive to the contact of the ceramic particles and hinder the sintering. Therefore, the storage conditions and time of the plastic blank should be controlled.

The effect of PbO volatilization of soft PZT piezoceramics in sintering is that the proportion of PbO in PZT ceramics is large, and the melting point of PbO is low, which is volatile during sintering, especially for high Zr/Ti formula. PbO vapor pressure is increased and volatilization is more serious. PbO volatilization will deviate from the stoichiometric ratio, increasing the difficulty of sintering into porcelain, and failing to achieve the material properties of the design.