Evaluation of the Role of the Activating Application Method in the Cold Sintering Process of ZnO Ceramics Using Ammonium Chloride.

The influence of the method of applying the activating additive ammonium chloride and its concentration on the density and microstructure of zinc oxide ceramic obtained by cold sintering at 244 °C was investigated. The activating agent was applied by two methods: impregnation and subsequent autoclave treatment. When the powder was activated by the impregnation method, the crystal sizes remained at the initial level of 0.17-0.19 µm. After the autoclave treatment, the crystal sizes increased to 0.31-0.53 µm. Samples of cold sintering ZnO with relative density up to 0.96 and average grain sizes 0.29-0.86 µm were obtained. ZnO powders and ceramic samples were analyzed using SEM, TGA/DSC, and XRD to reveal the effect of the powder activation method and cold sintering conditions on the material microstructure. The effect of ammonium chloride concentration on grain growth and microstructure of ceramic samples is shown. It was found that the average grain size of ceramic samples with an increase in additive concentration passes through a minimum. In cold sintering of the autoclave activated powder, the effect of reducing the average grain size was observed. The results of this work are discussed on the basis of the idea of the solid-phase mobility of the crystal structure arising when interacting with an aqueous medium.

The Fabrication and Characterization of BaTiO3 Piezoceramics Using SLA 3D Printing at 465 nm Wavelength.

The additive manufacturing of BaTiO3 (BT) ceramics through stereolithography (SLA) 3D printing at 465 nm wavelength was demonstrated. After different milling times, different paste compositions with varied initial micron-sized powders were studied to find a composition suitable for 3D printing. The pastes were evaluated in terms of photopolymerization depth depending on the laser scanning speed. Furthermore, the microstructure and properties of the BT ceramic samples produced through SLA 3D printing were characterized and compared with those of ceramics fabricated through a conventional die semi-drying pressing method. Three-dimensional printed samples achieved relative densities over 0.95 and microhardness over 500 HV after sintering, nearly matching the relative density and microhardness attained by the pressed samples. Upon poling, the 3D-printed samples attained acceptable piezoelectric module d33 = 148 pC/N and dielectric constants over 2000. At near full density, BT piezoceramics were successfully fabricated through SLA 3D printing at 465 nm wavelength, achieving photopolymerization depth of more than 100 microns. This work paves the relatively low-cost way for 3D printing of piezoelectric ceramics using conventional micron-sized powders and high printed layer thickness.