Conference Proceeding

Ultrasound assisted preparation of Nanomaterials

Dr. Christos Argirusis,
National Technical University of Athens, Greece

Dr. Ing Christos Argirusis is a Chemist with PhD in Chemical Engineering. He is working in the area of materials engineering with special interest in preparation methods of nanomaterials, using ultrasound and hydrodynamic cavitation, microwaves etc. He has graduated and received the doctoral degree in engineering from Clausthal University of Technology, Germany. Presently he is working with National Technical University of Athens, Greece, as associate professor and director of the Laboratory of Inorganic Materials Technology at the School of Chemical Engineering. His research group works currently on the preparation of nanomaterials both metallic and ceramic as well as metal-ceramic composites for various applications such as catalysts, metal organic frameworks for gas storage or drug delivery, activated electrodes for energy conversion devices etc. Other research interests focus on electrophoretic deposition, transport properties in condensed matter and sono-electrochemistry. He has published 85peer reviewed journal papers and more than 120 conference papers. He is the treasurer of the European Society of Sonochmistrye.V., vice president of the Greek Ceramic Society and visiting scientist in TU Clausthal, Germany.

Sonication of liquids with ultrasounds leads to numerous chemical reactions of high energy. The actual chemical impact of ultrasounds is not a result of direct interaction of sound waves with the molecules of a given chemical substance. As a matter of fact, ultrasounds cause a series of physical phenomena to the liquid phase which, in turn, create such conditions that will trigger and accelerate chemical reactions. One of the most important phenomena is acoustic cavitation, the creation, inflation and finally collapse of one bubble somewhere in the liquid phase. During the collapse of a bubble there is extremely high energy production on site. Collapse happens so rapidly that the heat produced at the core area of the bubble cannot diffuse through the collapsing bubble boundaries. On the contrary, the surrounding liquid medium which finds itself at a relatively lower temperature, cools rapidly the shrinking cavity of the collapsing bubble. This is the mechanism after which the topical hot spots are created within the liquid. It is remarkable that in such spots the pressure reaches a magnitude of more than 1000atm, a temperature of at least 5000 °C, a heating/cooling rate larger of >109 °C/s, and lifetime of <1μs. Hot spots work as tiny reactors of temperature and pressure. Some organometallic compounds, soluble in the solvent, may be volatile and thus pass from solvent to the vapor cavity of the bubble. In this case, after bubble collapse, a chemical reaction takes place in the gas phase. Free metal atoms are created within the bubble due to bonds breaking with the help of high temperatures and thus lead to a phenomenon called shockwave impact. Basics on sonochemistry followed by an overview of ultrasound assisted reactions as well as the preparation or modification of catalytic active materials by means of ultrasound, sonochemical and sono-electrochemical methods will be presented and explained, in this lecture.

Published: 27 April 2017