Field relaxing materials: production temperature and relaxation effectiveness

To prevent breakdown in the insulation of electric equipment requires the development of new materials and the control of electric fields. The authors have previously been engaged in the manufacture of functionally graded materials (FGMs) based on titanium oxide and barium titanate. These FGMs possess structured properties that cause a graded change in relative permittivity. It has been found that a change in the manufacturing temperature causes the relative permittivity to vary. The present paper describes an attempt to discover optimal conditions for field control by manufacturing FGMs at a range of temperatures from 673 K to 1273 K and investigating the properties of the resulting materials. The FGM studied was composed of barium titanate and kaolin. The highest values for relative permittivity were obtained at 1273 K. Investigations with a scanning electron microscope (SEM) showed that in comparison with the materials produced at lower temperatures, the pores between the grains were smaller. Similarly, the porosity and water absorption properties showed minimal values for material manufactured at 1273 K. It was concluded that this was because this material contained less air. The smaller the porosity, the larger the value for relative permittivity.