High dielectric Al2O3-(20–30 wt%) HDPE composites processed via cold sintering

Abstract

In the present work, the dielectric properties of cold sintered alumina (Al2O3) reinforced with 20–30 wt% HDPE composite was investigated. The Al2O3-HDPE composites were successfully processed via cold sintering at extremely low temperature in the range of 80–120 °C for 120 min with the application of uniaxial pressure of 500 MPa under vacuum. In fact, cold sintering is a promising method to consolidate ceramic-polymer composites with very large difference in melting points and other thermo-physical/chemical properties. In the present work, high dielectric constant (ε’) of 11.73 and low dielectric loss (tanδ) of 0.0076 measured for Cold Sintering Processed (CSPed) Al2O3-20HDPE and a little low ε’ of 9.13 and low tanδ of 0.0066 was evident for CSPed-Al2O3-30HDPE at 1 MHz. Such differences in the dielectric properties of the Al2O3-20,30 HDPE composites depend on the crystallite size, dangling bond density and microstrain of the materials. Increase in ε’ with temperature is noticed for CSPed-A20H. Moreover, for CSPed-A20H at 1 MHz the temperature variation of dielectric constant (TCC) of 186.94 ppm/°C (or 0.018694 %/°C) was estimated and it reflects a marginal variation of ε’ with temperature. The coefficient of thermal expansion (CTE) of 87.25 × 10−6 °C−1 and 109.3 × 10−6 °C−1 was estimated for CSPed-A20H and CSPed-A30H, respectively. Overall, the cold sintered Al2O3-20HDPE composites exhibited comparable or better dielectric properties than Al2O3 based materials (as reported in the literature) processed by conventional sintering or cold sintering processes.