Synthesis and Sintering of ZnO Nanopowders

Abstract

Nanopowders are continuously under investigation as they open new perspectives in numerous fields. There are two main challenges to stimulate their development: sufficient low-cost high throughput synthesis methods leading to a production with well-defined and reproducible properties, and for ceramics, conservation of their nanostructure after sintering. In this context, this paper presents the synthesis of a pure nanosized powder of ZnO (dv50 ~ 60 nm, easily redispersable) by using a continuous Segmented Flow Tubular Reactor (SFTR), which has previously shown its versatility and its robustness, ensuring a high powder quality and reproducibility over time. A higher scale of production can be achieved based on a "scale-out" concept by replicating the tubular reactors. The sinterability of ZnO nanopowders synthesized by the SFTR was studied, by natural sintering at 900 °C and 1100 °C, and Spark Plasma Sintering (SPS) at 900 °C. The performances of the synthesized nanopowder were compared to a commercial ZnO nanopowder of high quality. The samples obtained from the synthesized nanopowder could not be densified at low temperature by traditional sintering, whereas SPS led to a fully dense material after only 5 minutes at 900 °C, while limiting the grain growth and thus leading to a nanostructured material.

Influence of processing parameters on the densification and the microstructure of pure zinc oxide ceramics prepared by spark plasma sintering

“…Aimable et al [14] reported that synthesized powder could not be densified by traditional methods, though using SPS they could densify to 99.5% with grain size of 0.2 ± 0.8 μm at 900 °C. Whereas, com mercial powder could only be densified to 95.1% with grain size of 1 ± 0.5 μm using similar SPS conditions.…”

“…There is an increase in the grain size from initial size of 193 nm to 5.5 ± 2.2 μm, when sintering is performed at 700°C, 250 MPa. According to Aimable et al [14] such grain growth is controlled by the diffusion rate of zinc ions within the crystal structure [14]. Hence, the neighbouring grains diffuse into each other at the grain boundaries causing grain growth during sintering [36].…”

Grain growth kinetics and magnetic properties of a V-doped ZnO dilute magnetic oxide

“…The elaboration of ZnO-based ceramics has a wide variety of technological applications in optoelectronics [1,2] photoluminescence [3,4], varistor fabrication [5], magnetism [6,7] and transparent conductive contacts [8,9]. The V2O5-doped ZnO system is of interest in its bulk form as it exhibits varistor behavior, i.e., a non-linear voltage dependence on the current, due to the segregation of the dopants at the grain boundaries forming an electric barrier.…”