Abstract:Technologie in Pfinztal für die Bestimmung der Tropfengröûenverteilung mittels Laserstreuung und der Volkswagen-Stiftung für die finanzielle Unterstützung (I/75 682).
“…The high Re shows that the capillary flow is highly turbulent. The data follow well the pressure drop in turbulent pipes: with λ being the friction factor according to the Blasius resistance formula 26 6 Characteristic capillary Re for measurements at different Δ p and corresponding values of the turbulent pipe flow model (Re at Δ p ≤ 200 from the study of Wengeler et al). Δ p is correlated with mean hydrodynamic stresses on the interparticle bonds.…”
Section: Liquid Dispersion and Fragmentationsupporting
The influence of primary particle diameter and the degree of agglomeration of flame-made silica agglomerate suspensions in aqueous solutions is studied by high-pressure dispersion (up to 1500 bar) through a nozzle with a 125 microm inner diameter. These particles were produced (4-15 g/h) by oxidation of hexamethyldisiloxane (HMDSO) in a coflow diffusion flame reactor. Their average primary particle size (10-50 nm) and degree of agglomeration were controlled by varying the oxygen and precursor flow rates. The particles were characterized by nitrogen adsorption, electron microscopy, and small-angle X-ray scattering. Hydrodynamic stresses break up soft agglomerates and yield hard agglomerate sizes in the range of 100-180 nm, as characterized by dynamic light scattering. Soft agglomerates exhibited decreasing light scattering diameters with increasing dispersion pressure, while hard agglomerates were insensitive.
“…The high Re shows that the capillary flow is highly turbulent. The data follow well the pressure drop in turbulent pipes: with λ being the friction factor according to the Blasius resistance formula 26 6 Characteristic capillary Re for measurements at different Δ p and corresponding values of the turbulent pipe flow model (Re at Δ p ≤ 200 from the study of Wengeler et al). Δ p is correlated with mean hydrodynamic stresses on the interparticle bonds.…”
Section: Liquid Dispersion and Fragmentationsupporting
The influence of primary particle diameter and the degree of agglomeration of flame-made silica agglomerate suspensions in aqueous solutions is studied by high-pressure dispersion (up to 1500 bar) through a nozzle with a 125 microm inner diameter. These particles were produced (4-15 g/h) by oxidation of hexamethyldisiloxane (HMDSO) in a coflow diffusion flame reactor. Their average primary particle size (10-50 nm) and degree of agglomeration were controlled by varying the oxygen and precursor flow rates. The particles were characterized by nitrogen adsorption, electron microscopy, and small-angle X-ray scattering. Hydrodynamic stresses break up soft agglomerates and yield hard agglomerate sizes in the range of 100-180 nm, as characterized by dynamic light scattering. Soft agglomerates exhibited decreasing light scattering diameters with increasing dispersion pressure, while hard agglomerates were insensitive.
“…Several studies have shown that the energy density (measured in J/mL) serves as a well-suited parameter for obtaining a largely identical degree of USD of nanomaterials among different laboratories [ 23 , 36 , 37 ]. Of note, the application of different ultrasonic dispersing methods (e.g., variation of the sonotrode geometry) and parameter settings (e.g., sonication time and vibration amplitude) requires the application of the energy density concept, applicable to ultrasonication, rotor-stator systems [ 37 , 38 ] or high-pressure dispersing [ 39 , 40 , 41 ]. In all these cases, the ultrasonic dispersing energy density can be used as a main parameter for comparing available and new sample preparation protocols or SOPs.…”
The granulometric characterization of synthetic amorphous silica (SAS) nanomaterials (NMs) still demands harmonized standard operation procedures. SAS is produced as either precipitated, fumed (pyrogenic), gel and colloidal SAS and these qualities differ, among others, with respect to their state of aggregation and aggregate strength. The reproducible production of suspensions from SAS, e.g., for biological testing purposes, demands a reasonable amount of dispersing energy. Using materials representative for each of the types of SAS, we employed ultrasonic dispersing (USD) at energy densities of 8–1440 J/mL and measured resulting particle sizes by dynamic light scattering and laser diffraction. In this energy range, USD had no significant impact on particle size distributions of colloidal and gel SAS, but clearly decreased the particle size of precipitated and fumed SAS. For high energy densities, we observed a considerable contamination of SAS suspensions with metal particles caused by abrasion of the sonotrode’s tip. To avoid this problem, the energy density was limited to 270 J/mL and remaining coarse particles were removed with size-selective filtration. The ultrasonic dispersion of SAS at medium levels of energy density is suggested as a reasonable compromise to produce SAS suspensions for toxicological in vitro testing.
“…Die unterschiedlichen Homogenisierungsdrücke konnten durch variierende Versorgungsdrücke am Homogenisator (0,2 – 0,6 MPa) und den Einsatz unterschiedlicher Blenden (0,1 mm und 0,2 mm Durchmesser) realisiert werden. Nach Wengeler et al entspricht der erfolgte Energieeintrag in J mL −1 direkt dem Homogenisierungsdruck.…”
Die Auswirkungen einer mittels Hochdruck‐Homogenisator induzierten Scherbehandlung auf die Separationseigenschaften von Exopolysaccharid‐bildenden bakteriellen Starterkulturen wird untersucht. Neben Änderungen seitens der Medienviskosität und der Sinkgeschwindigkeit der Bakterienzellen konnten auch deutliche Unterschiede bei der Kompaktheit des Sediments festgestellt werden. Zusätzlich wird die Skalierbarkeit der im Labor mittels analytischer Zentrifugation gewonnenen Ergebnisse in den Technikums‐Maßstab mit einem Tellerseparator gezeigt.
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