The effect of liquid phase chemistry on the densification and strength of cold sintered ZnO

Assessment of flaws in cold‐sintered ZnO via acoustic wave speed and attenuation measurements

“…25,26 Aside from the bimodal density distribution, the grains shown in Figure 4C are fairly isometric with an average grain size of 200 nm, which is consistent with previously reported results showing grains with sizes on the order of the particle size used. 6,9,26 Large regions of missing data in the wave speed maps are visible in the top Figure 2F and the right of Figure 2G. In these regions, a reflection was not detected in the narrow, predetermined time window placed at the expected arrival time for the back surface reflection.…”

“…However, some cold-sintered parts do not reach comparable mechanical or functional properties to those obtained via conventional sintering, even when high relative densities are achieved. [6][7][8][9] These degraded properties are presumed to be in part a result of macroflows that arise from poor die-filling, pressure gradients in the die, inhomogeneous distributions of the fluxes, or temperature gradients during the process. Densification can be further compromised in the case of inhomogeneous removal of transient phases or inability to reach the proper cold sintering temperatures and pressures everywhere in the part.…”

“…ZnO is used in semiconductor, thermoelectric, and varistor applications and is a model ceramic system for cold sintering studies. 7,24,25 Previous studies on coldsintered ZnO have investigated sintering mechanisms at elevated 24,25 and near room-temperatures, 26 effects of different transient phases, 9,27 and mechanical and functional properties. 6,7,9,28 Gonzalez-Julian et al 24 investigated the mechanisms of cold sintering ZnO and demonstrated the critical role both water and zinc acetate play in densification.…”

“…7,24,25 Previous studies on coldsintered ZnO have investigated sintering mechanisms at elevated 24,25 and near room-temperatures, 26 effects of different transient phases, 9,27 and mechanical and functional properties. 6,7,9,28 Gonzalez-Julian et al 24 investigated the mechanisms of cold sintering ZnO and demonstrated the critical role both water and zinc acetate play in densification. Adsorbed water and zinc acetate increase defect formation within ZnO grains and in the grain boundary area which reduces the activation energy for atomic diffusion and promotes densification.…”

“…In contrast, Nur et al 7 reported similar elastic modulus and hardness in 99% dense cold-sintered ZnO, which used deionized water as the transient liquid phase, relative to conventionally sintered ZnO samples. Jabr et al 9 investigated effects of transient phase chemistries on the densification and mechanical strength of cold-sintered ZnO. Relative densities above 95% were obtained at 125 • C using formic acid and acetic acid, but acetic acid samples showed significant grain growth, whereas formic acid samples retained their initial grain size.…”