Cold Sintering Process of Zinc Oxide Ceramics: Powder Preparation and Sintering Conditions Effects on Final Microstructure

Abstract

Although the activating effect of an acetate medium in the cold sintering process of zinc oxide ceramics is well known, some problems need to be solved on the effect of process conditions and the initial powder’s preparation methods on the ceramic’s density and microstructure. This article describes an effect of the zinc acetate introduction method, its concentration in zinc oxide powder as well as that of the die sealing configuration on the density and microstructure of zinc oxide ceramics obtained by the cold sintering process at 244 °C. The activating additive of zinc acetate was applied in two ways: (1) impregnation in aqueous solution and (2) impregnation with subsequent treatment in water vapor. Zinc oxide powders and ceramics were analyzed using SEM, TGA/DSC/MS and XRD to reveal the effect of powder pre-treatment and sintering conditions on the material microstructure. Cold sintered ZnO ceramics samples with a relative density up to 0.99 and with average grain sizes from 0.28 to 1.71 μm were obtained. The die sealing by two Teflon sealing rings appeared to be the most effective.

Direct Cold Sintering of α-Al₂O₃ Ceramics in a Pure Water Medium

“…The boehmite grains of both rounded and plate-like morphologies under the CSP conditions tend to perform coalescence and finally transform homogenously into αalumina modification (Figure 7c). Earlier, the coalescence of the particles was also demonstrated for the CSP of ZnO [47], CaCO3 [3], and Na2Mo2O7 [48]. Regardless of the phase composition, the obtained ceramics possessed a relative density in a range of 58-65 %, which is close to the density of the conventionally pressed compacts.…”

Water-Assisted Cold Sintering of Alumina Ceramics in SPS Conditions

“…A disadvantage of the currently used mold was connected to an insufficient reproducibility of its sealing. Previously, the importance of the mold sealing system and the choice of appropriate materials for it was demonstrated in the cold sintering of ZnO ceramics [84]. The improvement of the mold design would allow for the preservation of the CSP-SPS conditions for a longer exposure and open prospects in obtaining dense α-alumina ceramics by a novel ecologically pure and energy-saving technique.…”

Structural Designs of Transparent Polyimide Films with Low Dielectric Properties and Low Water Absorption: A Review

“…Furthermore, millimeter-wavelength radio waves suffer from high attenuation, leading to significant signal-quality losses [ 14 , 15 ], which can be overcome by installing a large number of beamforming antennas (an array of antennas that controls the direction of the wavefront), but this requires high-quality insulating materials with low D k , low D f , poor water absorptivity, and good adhesiveness to maintain high-level substrate wiring (referred to as “flexible copper-clad laminates”). A few materials are suitable for 5G/6G applications, including polytetrafluoroethylenes (PTFEs), some ceramics, and liquid-crystalline polymers (LCPs) [ 16 , 17 , 18 ]. However, these materials suffer from their own drawbacks: for instance, ceramic materials require high-energy procedures (longer, high-temperature processing).…”

“…However, these materials suffer from their own drawbacks: for instance, ceramic materials require high-energy procedures (longer, high-temperature processing). Even though the cold sintering process consumes less energy, it decreases the density and degrades the microstructure of the ceramic [ 17 ]. PTFEs exhibit good heat and corrosion resistance, as well as optimal dielectric properties; however, they suffer from high costs and environmental regulatory restrictions [ 16 ].…”