Synthesis of nanosized zinc oxide
Zinc oxide (ZnO) is a unique material that exhibits multiple semiconducting, piezoelectric, and pyroelectric properties. Major industrial applications concern electronic devices, like gas sensors, or varistors. This last application requires multiple dopants, whose role is not well-understood. In this study, it is proposed to synthesize ZnO with a good control of the size and the size distribution, in order to get higher properties, and limit the number of dopants.
Zinc oxide nanoparticles were produced by precipitation in mild hydrothermal conditions (90°C). Regular roundish particles of well crystallized material were obtained, with a very narrow size distribution centred on 200 nm. Then the influence of organic species added as soft templates in order to control particle size and particle size distribution in the final product was studied in detail. Anionic additives, such as poly(acrylic acid) (PAA Mw 2000), Dispex A40 (commercial PAA from CIBA Mw ~ 10000), and sodium dodecylsulfate (SDS) allowed a significant decrease of the particle size towards 100 nm, while conserving a very narrow size distribution. The influence of the pH was also investigated with PAA. By increasing the pH from quasi neutral to basic conditions, the morphology was spectacularly modified from roundish nanoparticles to micronic branched flower-like particles, with elongated primary crystal morphology.
|pH = 5.6
|pH = 5.6
PAA 0.05 %
|pH = 11.2
PAA 0.05 %
SEM pictures of different nanosized ZnO obtained in a mini-batch reactor
Transfer to the SFTR (Segmented Flow Tubular Reactor) (link to Reactor development (SFTR)) has been done producing 30 g batches of powders (mini-batch: 200mg, SFTR 3 g/h), . By generating identical micro-reactors giving a homogeneous mixing of the reactants, the SFTR avoids poor mixing and reaction conditions often encountered in classical large batch reactors. We showed that this process allows the production of high-quality nanopowders (dv50=70 nm), a very narrow particle size distribution (PSD) (dv90<90nm), and no agglomeration. The synthesis is very stable over time, leading to a powder with high reproducible characteristics. The powder could also be dried and redispersed without any loss of powder quality.
|PSDs of ZnO powders during 12 hours of continous precipitation using the Segmented Flow Tubular Reactor (SFTR)||PSDs of ZnO powders synthesized with the SFTR in suspension after the reaction, after drying 24h, 70°C, and after freeze-drying|
Then Spark Plasma Sintering (SPS) has been used used to produce dense ceramic at lower temperature (900 °C), in order to both limit and control grain growth, and preserve “nanosized” properties.
A. Aimable, M. T. Buscaglia, V. Buscaglia, P. Bowen, Polymer-assisted precipitation of ZnO nanoparticles with narrow particle size distribution, Journal of European Ceramic Society (2009), in press.
- Vincenzo Buscaglia, Maria-Teresa Buscaglia, Institute for Energetics and Interphases (NRC Genoa, Italy)
- Witold Lojkowski, Institute of High Pressure Physics of the Polish Academy of Sciences (Warsow, Poland)
- Zhe Zao, Arrhenius Laboratory, Stockholm University (Sweden)
· Aimable N. Jongen, A. Testino, M. Donnet, J. Lemaitre, H. Hofmann and P. Bowen, “Precipitation of nanosized and nanostructured powders: process intensification using SFTR”, applied to BaTiO3, CaCO3 and ZnO – Chem. Eng. & Techn., 34(3) 344-352 (2011).
· Aimable, T. Strachowski, E. Wolska, W. Lojkowski, P. Bowen, Comparison of two innovative precipitation systems for ZnO and Al-doped ZnO nanoparticle synthesis, Processing and Application of Ceramics 4  (2010) 107–114
· Aimable, M.T. Buscaglia, V. Buscaglia, P. Bowen, Polymer-assisted precipitation of ZnO nanoparticles with narrow particle size distribution, J.Eur. Ceram.Soc. 30(2) (2010), 591-598