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Leuven, Belgium

Jordens J.,Catholic University of Leuven | Jordens J.,Researchgroup Lab4U | Gielen B.,Catholic University of Leuven | Gielen B.,Researchgroup Lab4U | And 2 more authors.
Chemical Engineering and Processing: Process Intensification | Year: 2014

This paper presents a study on the effect of ultrasonic frequency on both the nucleation and the degradation of paracetamol under sonication. The effect of ultrasonic irradiation was investigated for frequencies ranging from 41 to 1140. kHz. The results obtained in this paper show that the lower ultrasonic frequencies are preferable, both to enhance the nucleation rate and to limit degradation. A reduction of the metastable zone width was observed in all experiments when applying ultrasound. The highest reduction was achieved at a frequency of 41. kHz and a decrease of the reduction was observed with increasing ultrasonic frequencies. Degradation was limited at a frequency of 41. kHz, while significantly higher levels of degradation are observed at higher frequencies. Radical formation seems to be the main degradation mechanism for all frequencies. © 2014 Elsevier B.V. Source

Jordens J.,Catholic University of Leuven | Jordens J.,Researchgroup Lab4U | De Coker N.,Catholic University of Leuven | Gielen B.,Researchgroup Lab4U | And 2 more authors.
Ultrasonics Sonochemistry | Year: 2015

The influence of ultrasonic frequency and intensity on particle shape, tap density and particle size distribution was investigated during the precipitation of manganese carbonate. For the first time, a broad frequency range of 94 till 1135 kHz was studied in one single reactor setup. Smaller and more spherical particles were observed during sonication compared to silent conditions. Lower frequencies and increased intensities result in smaller and more spherical particles. The most spherical particles with superior tap densities are obtained at the lowest frequency and most elevated intensity. Moreover, the results indicate that a particle size threshold exists, below which the particle size cannot be reduced by a further increase of the ultrasonic intensity or reduction of the frequency. Sonication of already formed spherical powders resulted in particles with smaller sizes but unaffected shapes. Finally, one test with pulsed ultrasonic irradiation resulted in equally sized particles with similar sphericity as the ones produced under continuous sonication. © 2015 Elsevier B.V. Source

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