Continuous synthesis of nanostructured inorganic powder using supercritical water medium

ABOL/O/F/2004-001

Abstract

A French university laboratory has developed a new technology to synthesize nanostructured powder in a continuous way, using supercritical water medium. A continuous production prototype was developed which shows that a continuous flow production can be achieved. The laboratory is looking for manufacturers, industrial companies interested in a technical cooperation and willing to benefit from the know-how background to improve the prototype and bring it at the industrial scale.      

Description

Nano size grain materials draw industry and scientist attention because of their electrical, magnetic, optical properties depending on grain size. Many synthesis technologies of powdery precursors were studied and used but these technologies do not produce a huge volume and cannot be developed at the industrial level. Continuous synthesis technologies, allowing a production of several tens or hundreds of grams per hour are then very interesting.

This French lab has developed a method and a prototype which use a technology working under thermodynamic conditions ranging from hydrothermal up to supercritical water conditions (temperature > 374°C ; pressure > 221 bar). Indeed, supercritical water behaviour is between gas and liquid states; by modifying temperature and pressure, it will be easy to modify the viscosity and the diffusion coefficient of the reaction fluid. At high temperature and constant pressure, the solubility of ionic compounds is thus almost zero.  The evolution of water properties allows obtaining metallic oxides from metallic cations aqueous solutions by a two step thermo-hydrolysis reaction. Instantaneous formation of a large number of hydroxide nucleuses, which are immediately dehydrated, leads to nano particles. 

Different kinds of ferrites can be synthesized but also several oxides such as Co3O4, ZrO2, TiO2, CeO2, NiO.

Innovative Aspects
Water in its supercritical state is more difficult to achieve than the well known supercritical carbon dioxide but the advantage is the high solubility of the precursors. The “Chemistry” is the same but supercritical water has a lower viscosity, a higher diffusivity and inorganic compounds have a very low solubility in this fluid. High crystal nucleation speed, lower time response, and limited growth allow to get nano size grains.

Main Advantages
The present technology has also the main advantages to be easy to use compared to closed reactor and to have a high productivity. Besides, synthesized oxide powders in supercritical water have two interesting qualities :

· they are “well” crystallised

· unlike nanopowders achieved by different wet methodologies showing surface polluted with ions of the reaction, hydrothermal and supercritical powders have clean surface grains.

Current Stage of Development : available for demonstration

Organisation/Company Type:  university - research Institute

Organisation/Company Size: 11- 50

Collaboration

- technical cooperation

- type of partner sought: company, industry
- specific area of activity of the partner : any type of company producing powders (for cosmetics, magnetics, electronics industries)  
- task to be performed : technology integration and industrialization