Effect of liquid phase on the spark plasma sintering process of ZnO ceramic

Abstract:

ZnO ceramics were fabricated via spark plasma sintering (SPS) technology. The role of acetic acid solution on the SPS was mainly investigated. The results indicated that, with the addition of liquid phase (2 mol/L acetic acid solution) during SPS, the shrinkage and densification of ZnO ceramic samples were activated at 52 _^oC and 115 _^oC, respectively. The density of ZnO ceramic samples can be achieved to the value of more than 95% and then fully densified when the sintering temperature was further increased to 160 _^oC and 200 _^oC. The grain grows from 200 nm of the raw particle to 600 nm after sintering at 250 _^oC for 5 min. The X-ray diffraction results show that no obvious impurity phase can be observed, and the grain growth present a clear anisotropic orientation, preferentially growing along the vertical direction of applied pressure. With assistance of liquid phase in SPS, the grain growth activation energy was determined at only 78.8 kJ/mol, a third as large as that sintered in the conventional SPS. Impedance of ZnO ceramic samples was measured at room temperature. It was found that the grain boundary resistance decreases from 9.82×10_⁶ W to 2.75×10_³ W with the increasing sintering temperature from 120 _^oC to 250 _^oC.