Original Research Paper Dynamics analysis of cavitation disintegration of microparticles during nanopowder preparation in a new Water Jet Mill (WJM) device Richard Dvorsky a,⇑ , Jiri Lunacek a , Ales Sliva b a Institute of Physics, VSB-Technical University of Ostrava, 17. listopadu 15, 708 33 Ostrava – Poruba, Czech Republic b Institute of Transportation – Laboratory of Bulk Materials, VSB-Technical University of Ostrava, 17. listopadu 15, 708 33 Ostrava – Poruba, Czech Republic article info Article history: Received 17 April 2009 Received in revised form 8 September 2010 Accepted 13 September 2010 Available online 25 September 2010 Keywords: Nanoparticle Cavitation Implosion Disintegration Milling Grinding abstract A physical analysis of cavitation-based implosive breakage of solid particles focusing on practical appli- cation during fine particle disintegration in a liquid suspension is submitted in the present paper. The physical source of the cavitation dynamics phenomena involved is an extreme velocity gradient induced by an ultrahigh-energy liquid jet mixing together with a slow liquid suspension of milled particles. Extreme tensile stresses occurring at velocity gradients over 1000 ms 1 mm 1 at the operating tempera- ture of 65 °C generates high-intensity pure vapor cavitation in the degassed water dispersion with extreme values of impact pressure in the final of bubble implosions on particle surfaces. Preparation of silicon nanoparticles with median diameter approximately 148 nm using a newly devel- oped ‘‘Water Jet Mill” (WJM) device is demonstrated in the present article as an example of application of the aforementioned disintegration method as well as of theoretical analysis of this method. The disinte- gration method is characterized by a high potential for milling of submicron particles with high efficiency. Ó 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved. 1. Introduction At present, effective preparation of submicron powders and nanopowders for industrial applications is a major practical issue in nanotechnology processing. Key challenges in most current meth- ods of nanotechnology processing using ‘‘top-down” particle prepa- ration include optimization of time effectiveness of the milling process, and optimization of milling size limits in the technological procedure [1–7]. Besides, for many technological applications, parti- cle contamination by spin-off material from the milling parts of the milling device and its inner walls poses a significant problem, con- sidering that the disintegration occurs mostly in direct contact with these parts [6–9]. Extreme dynamics of cavitation disintegration of solid materials [10,11] represent an excellent opportunity to opti- mize milling parameters with the application of fine particle disinte- gration processes in a liquid suspension. Apparently, an important factor of the cavitation process is the dominance of particle disinte- gration by the dynamic impact of liquid on particle surface without a direct contact with milling bodies and inner surfaces, as is the case for all other equipment, including aerodynamic jet mills. Physical analysis of cavitation disintegration of fine solid particles in a liquid suspension along with the presentation of preliminary experimental results of ‘‘top-down” nanoparticle preparation in a newly developed device called the Water Jet Mill (abbreviated form: WJM) [12] have been carried out in the paper. 2. Theoretical background and rationale 2.1. Generation of cavitation bubbles in the Water Jet Mill There are two parallel mechanisms generating cavitation zones in the WJM. The first source of cavitation is a special ultrahigh en- ergy water nozzle, e.g. the system described in [13], that injects cavitating water jet directly into the mixing chamber input in the upper part of the WJM. The second source of cavitation is an inter- action of the ultrahigh energy cavitating water jet with a slow-flow water suspension [11] of fine solid particles in the top abrasive and lower cavitation tubes. In the current experimental regime, the system WJM is kept at an operating temperature by inflowing water from the primary nozzle. During 180 s of disintegration experiment the primary cold water jet is able to keep a milling sus- pension at a constant operating temperature 65 °C. Extreme tensile stresses occurring at velocity gradients over 1000 ms 1 mm 1 cre- ate high intensity of nucleation of pure vapor cavitation bubbles in the degassed water dispersion [10]. 0921-8831/$ - see front matter Ó 2010 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved. doi:10.1016/j.apt.2010.09.008 ⇑ Corresponding author. E-mail address: richard.dvorsky@vsb.cz (R. Dvorsky). Advanced Powder Technology 22 (2011) 639–643 Contents lists available at ScienceDirect Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt