Reactive spark plasma sintering of Si2N2O ceramic: Reaction process, microstructure, mechanical and dielectric properties.

Dense Si 2 N 2 O ceramic was successfully prepared through the spark plasma sintering method at 1750 °C with nano-sized amorphous Si 3 N 4 powder as raw material. The reaction sintering process, mechanical and dielectric properties of the Si 2 N 2 O ceramic were investigated in detail. The results revealed that the amorphous Si 3 N 4 was initially crystallized to β-Si 3 N 4 , then oxidized to Si 2 N 2 O during the sintering process. With prolonging the dwell time, the grain orientation of Si 2 N 2 O gradually developed to the c-axis direction of the orthorhombic crystal. Meanwhile, the density of as-sintered ceramic was improved significantly, which greatly influenced the mechanical and dielectric properties of Si 2 N 2 O ceramic. In this work, the optimal dwell time of sintering process was 20 min, which is obviously shorter than the ordinary sintering methods. The Si 2 N 2 O ceramic fabricated at the above conditions exhibited the most favorable mechanical and dielectric properties with a bulk density of 2.80 ± 0.01 g cm−3, Vickers hardness of 13.1 ± 0.1 GPa, flexural strength of 214.1 ± 15.8 MPa, fracture toughness of 2.8 ± 0.3 MPa m1/2, and combined with low dielectric constant of around 3.5 to 4.5 at 8.2−12.4 GHz. Thus, the spark plasma sintering method is potentially regarded as a rapid way to prepare Si 2 N 2 O ceramic used as the structural and wave-transmitting functional material. [ABSTRACT FROM AUTHOR]