Improved compaction of ZnO nano-powder triggered by the presence of acetate and its effect on sintering

Abstract

The retention of nanocrystallinity in dense ceramic materials is still a challenge, even with the application of external pressure during sintering. The compaction behavior of high purity and acetate enriched zinc oxide (ZnO) nano-powders was investigated. It was found that acetate in combination with water plays a key role during the compaction into green bodies at moderate temperatures. Application of constant pressure resulted in a homogeneous green body with superior packing density (86% of theoretical value) at moderate temperature (85 °C) in the presence of water. In contrast, no improvement in density could be achieved if pure ZnO powder was used. This compaction behavior offers superior packing of the particles, resulting in a high relative density of the consolidated compact with negligible coarsening. Dissolution accompanying creep diffusion based matter transport is suggested to strongly support reorientation of ZnO particles towards densities beyond the theoretical limit for packing of ideal monosized spheres. Finally, the sintering trajectory reveals that grain growth is retarded compared to conventional processing up to 90% of theoretical density. Moreover, nearly no radial shrinkage was observed after sinter-forging for bodies performed with this advanced processing method.

Geologically-inspired strong bulk ceramics made with water at room temperature

“…While the use of nanoparticles to accelerate the densification process of ceramic materials has been utilized for several decades2225 and have recently also been exploited for pressure-assisted sintering at milder temperatures down to 150–200 °C (refs 26, 27, 28) or for binding at room temperature29, no evidence was shown thus far that this effect can also be harnessed to densify a sparsely soluble ceramic material into strong bulk compacts with water at ambient temperature.…”

Unveiling the mechanisms of cold sintering of ZnO at 250 °C by varying applied stress and characterizing grain boundaries by Kelvin Probe Force Microscopy

“…Furthermore, the incorporation of zinc acetate promotes larger dissolution of Zn 2+ and O 2-ions into the water boundary layer, as well as more Zn 2+ ions by the dissolution of the zinc acetate. According to the information provided by KPFM, XRD and the obtained microstructure, and previous investigation by some of the authors [24][25], epitaxial grain growth on the surface of the ZnO particles takes place when zinc acetate is incorporated. The crystals grow in the preferential (002) crystallographic plane, which may be related with precipitation mechanisms.…”

“…All these studies suggest that the presence of water can, under given conditions, strongly reduce the sintering temperature of oxide powder compacts, by partial dissolution of the particles and subsequent precipitation, synthesis reaction or the diffusion of ions from the water molecules into the crystal structure [17][14] [24]. Nevertheless, more fundamental investigations are required that is also the scope of the present paper.…”

Demonstration of the cold sintering process study for the densification and grain growth of ZnO ceramics

“…There are also previous reports showing that zinc oxide powder can be obtained from zinc acetate in high humidity, 37 the growth of the ZnO nanocrystal with water and residual acetate was enhanced at 85°C, 38 and the pressed nano-particles with acetated water have high density. 39 CSP is an attractive solution to apply these phenomena efficiently.…”