Dispersive coating on electroceramic particles for fabrication of flexible sheet

Abstract

Particles dispersively coated with other material is a kind of composite particles, i.e., core particles are dotted with other material. Two methods have been developed for such the composite particles. One is a forced electrification method and the other a rotating drum method. The former utilizes the electrostatic force, i.e., positively electrified core particles and negatively electrified child particles are mixed. The latter is a mechanical method as follows. Core particles and child particles are charged into a cylindrical vessel, and mixed by rotating the vessel for several hours. We prepared composite particles of PTCR (Positive Temperature Coefficient of Resistivity) barium titanate and the junction metal such as indium and solder. When the composite particles are filled, the junction metal always exists between the neighboring core particles. The PTCR property of the filling is almost the same with that of the sintered barium titanate. We fabricated a PTCR thin sheet by packing the composite particles between two sheet electrodes. If the composite particles are electrically connected but fixed not firmly, the sheet shows PTCR property and can bend by rearrangement of the particles. Thin ceramics sheet is practically impossible because of the brittleness. However, flexibility can be given to the sheet of the PTCR-junction metal composite particles. The composite particles are fixed by enveloping in an evacuated bag or by embedding in a heat resistant resin. Advantages and disadvantages of the preparation methods and fabrication methods are discussed. Preliminary experiments for a new approach to the PTCR sheet are introduced.