Influence of hydrostatic pressure and sound amplitude on the ultrasound induced dispersion and de-agglomeration of nanoparticles

Abstract

In most applications, nanoparticles are required to be in a well-dispersed state prior to commercialisation. Conventional technology for dispersing particles into liquids, however, usually is not sufficient, since the nanoparticles tend to form very strong agglomerates requiring extremely high specific energy inputs in order to overcome the adhesive forces. Besides conventional systems as stirred media mills, ultrasound is one means to de-agglomerate nanoparticles in aqueous dispersions. In spite of several publications on ultrasound emulsification there is insufficient knowledge on the de-agglomeration of nanoparticulate systems in dispersions and their main parameters of influence. Aqueous suspensions of SiO2-particles were stressed up to specific energies EV of 10(4) kJ/m3 using ultrasound. Ultrasonic de-agglomeration of nanoparticles in aqueous solution is considered to be mainly a result of cavitation. Both hydrostatic pressure of the medium and the acoustic amplitude of the sound wave affect the intensity of cavitation. Furthermore, the presence of gas in the dispersion medium influences cavitation intensity and thus the effectiveness of the de-agglomeration process. In this contribution both, the influence of these parameters on the result of dispersion and the relation to the specific energy input are taken into account. For this, ultrasound experiments were carried out at different hydrostatic pressure levels (up to 10 bars) and amplitude values (64-123 microm). Depending on the optimisation target (time, energy input,...) different parameters limit the dispersion efficiency and result. All experimental results can be explained with the specific energy input that is a function of the primary input parameters of the process.

Executive Study of Hydrostatic Pressure Effects on Sludge Pretreatment by Sonication

“…Besides, the cavitation threshold increases linearly with the static pressure, thus the acoustic pressure amplitude required to reach the cavitation threshold also increases [17]. Yasui et al [18] showed the optimal static pressure which maximizes the acoustic energy increases as the acoustic amplitude increases or viscosity of liquid decreases, which qualitatively agrees with Sauter et al [19].…”

Ultrasound assisted dispersal of a copper nanopowder for electroless copper activation

“…One of the first papers published using this technique investigated the effects of high intensity ultrasound on micron-sized inorganic solids with powders of 60 -90 µm diameter being reduced to 5-10 µm in diameter after a few minutes of ultrasonic irradiation [12]. A number of nanomaterials that have been the subject of recent dispersion investigations include goethite [13,14] , silica [15][16][17][18][19] , haematite 3 [20], barium titanate [21], zinc oxide [22], carbon black [23], silver [23], alumina [24][25][26] and carbon nanotubes [27]. In many of these studies, high intensity ultrasonic processing was found to de-agglomerate and decrease the size of the starting materials.…”

Comparative performance of in-line rotor-stators for deagglomeration processes

“…Other process devices used by previous researchers include the sawtooth impeller (Xie et al, 2007), batch rotor-stator (Xie et al, 2007;Pacek et al, 2007), high pressure devices Sauter and Schuchmann, 2012), stirred bead mills (Kowalski et al, 2008, Schilde et al, 2011 and ultrasonicators (Sauter et al, 2006(Sauter et al, , 2008. Some of the studies included numerical modelling to develop both an understanding of the flows within process devices which are not accessible for measurements and also models describing the deagglomeration process (Baldyga et al, 2006(Baldyga et al, , 2007(Baldyga et al, , 2008(Baldyga et al, , 2009.…”