Low temperature sintering of zno-based ceramics and investigation of their varistor applications

Cold sintering process (CSP) is a promising ultra low-temperature sintering method that needs an aqueous solution for transition of atoms along with formation of dissolution-precipitation process under high pressures. In this thesis, technical and scientific investigations of the CSP were discussed by using ZnO as model material. ZnO bulk ceramics with >99.00 % theoretical density (T.D.) were obtained under 540 MPa pressure, at 140˚C temperature after 50 minutes dwell time and 7.00 wt % liquid with pH 5.5 via CSP. Change of liquid film thickness was evaluated during CSP. For detailed interactions of the sintering variables, responce surface methodology (RSM) using Minitab software was used with Cental Composite Design (CCD) method. pH was obtained as the most effective parameter of the CSP for the given experimental conditions and in the five experimental varibles of temperature, pressure, pH, liquid amount and the time. In the final part of the thesis, ZnO-Bi2O3 and ZnO-Bi2O3-Co2O3 varistor systems were produced by CSP method. Threshold voltage was expected to be increased for high voltage applications based on fine grains and higher amount of grain boundaries due to CSP. ZnO-Bi2O3-Co2O3 varistors with > 95.00 % T.D. were produced at 250˚C via CSP. α value obtained as 27 and thereshold voltage was 2200 V/mm, that are compatible with conventionally produced high voltage varistors.