Effect of thermal plasma heating on the dielectric properties of Al-Zr composites

Abstract

A low-cost extended arc thermal plasma heating (EATPH) source has been used for the sintering of Al-Zr high-temperature ceramic oxides, and their dielectric properties have been studied. Pellets of Al-Zr composites were sintered using optimum sintering parameters such as sintering time, plasma power and plasmagen gas flow rate in an EATPH reactor. Samples of similar composites were also sintered using a conventional resistive heating furnace at 1500°C for 20 h, and their dielectric properties were studied and compared with the plasma sintered sample. Sintered pellets were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and dielectric measurement, carried out as a function of frequency and temperature. Highly dense sintered products were obtained by the plasma heating route within a very short sintering time compared with the conventional sintering schedule. Dielectric measurements (both dielectric constant and loss factor) showed a significant reduction in the dielectric constant, K, at room temperature under different test frequencies and also as a function of temperature. However, the change in dielectric loss factor, tan Δ, was not as pronounced as the change in K. The behaviour of the K and tan Δ curves changes drastically compared with the conventional sintered material. The reduction in K and the crossover behaviour of tan Δ in the plasma sintered specimen may be due to the action of non-reactive Ar plasmagen gas during plasma sintering, which favours mobile oxygen for the polarization network under the influence of frequency and temperature.