PREPARATION OF SILICON NANOPARTICLES BY MEANS OF DISINTEGRATION IN A CAVITATION WATER JET

High-energetic water jet (at cross-sectional velocity exceeding 660 ms(-1)) represents a liquid flow with cross-sectional power density about/or above 144 kWmm(-2). In the experimental Water Jet Mill (WJM) device, potent dynamics of disintegration of silicon microparticles develop during the passage of modified cavitation water jet through the microparticle dispersion. The main mechanism of this disintegration of solid microparticles is the extreme impact pressure of a water-hammer on particle surface in the termination phase of the implosion of vapor cavitation bubbles. Around the working temperature of WJM about 65 degrees C, cavitation erosion of solid materials in water reaches high intensity. Gradients of flow velocity in the disintegration zones of WJM rise up to 1000 ms(-1)/mm and generate markedly high tensile stresses in the liquid, resulting in the creation of vapor cavitation bubbles. The cavitation coefficient reaches values of 10(-4) rank and the cavitation intensity is very high. Moreover, a high value of specific surface of solid particles in the fine water micro-dispersion is manifest, thus fostering the process of heterogeneous nucleation of cavitation bubbles on individual particles. The impact pressure of liquid in the termination phase of the collapse of spherical bubbles reaches values as high as 5.7 GPa at normal pressure of the surrounding liquid, namely 0.1 MPa. Due to the rapid process of refinement, it is possible to expect a significant influence of crushing mechanisms on the overall process of disintegration with the given energy densities. Apart from fundamental specification of the disintegration process, the present paper has another major focus, i.e., the presentation of experimental results of disintegration of silicon microparticles into the nano-scale.