Elaboration and electrical characterization of varistors based on zinc oxide by microwave sintering
摘要
The experiments were carried out on sintered varistors such that the percentage of raw materials used is as follows: 98 mol% ZnO, 0.5 mol% Bi2O3, 0.5 mol% Sb2O3, 0.5 mol% Co2O3, 0.5 mol% MnO2 was sintered in a single-mode microwave cavity without susceptor at a frequency of 2.45 GHz, at a heating rate of 150 °C min−1 to the temperature of 900 °C for four sintering times (10, 30, and 60 min) in two steps. At the end of the first step of the microwave process, the samples have too high an electrical conductivity. Annealing under O2 was carried out as a second phase at a temperature well below the sintering temperature, allowing satisfactory electrical characteristics. The second heat treatment step of microwave sintering under O2 made it possible to increase and improve the non-linearity coefficient in a very encouraging manner, particularly for the two samples produced at temperatures of 900 °C-30 mn and 900 °C-60 mn where the non-linearity coefficient reaches the value of 27.84 and 31.6, respectively. The effect of different sintering temperatures (1000, 1100 and 1200 °C) was also measured during the optimal sintering time of 60 min where very encouraging results of α 20.63, 29.96, 30.35 were found better than those that we obtained for the model 900 °C-60 mn. In addition, the results of the microstructures show that (densities reached 98.6%, Grain size (µm) increases sintering temperatures from 7.0, 11.4 to 14.3 (µm) with decrease in leakage current from Jl(Ma cm−2) 0.119, 0.012 to 0.01, the nature of the secondary phases by X-ray diffraction, the grain size by scanning electron microscope) are studied.