Ultrasonic-assisted hydrothermal synthesis of cobalt oxide/nitrogen-doped graphene oxide hybrid as oxygen reduction reaction catalyst for Al-air battery.

A persistent ultrasound-assisted hydrothermal method has been developed to prepare cobalt oxide incorporated nitrogen-doped graphene (Co3O4/N-GO) hybrids. The electrochemical behaviors and catalytic activity of the prepared hybrids have been systematically investigated as cathode materials for Al-air battery. The results show that ultrasonication can promote the yield ratio of Co3O4 from 63.1% to 70.6%. The prepared Co3O4/N-GO hybrid with ultrasonication exhibits better ORR activity over that without ultrasonication. The assembled Al-air battery using the ultrasonicated Co3O4/N-GO hybrid exhibited an average working voltage of 1.02 V in 4 M KOH electrolyte at 60 mA∙cm-2, approximately 60 mV higher than that using hybrid without ultrasonication. This should be attributed to large number density of fine Co3O4 particles growing on the dispersed GO sheets under the persistent ultrasonication. The related ultrasonic mechanism has been discussed in details.

Effects of synergetic ultrasound on the Sc yield and primary Al3Sc in the Al-Sc alloy prepared by the molten salts electrolysis.

In this work, ultrasound has been employed to help prepare Al-Sc alloys using the molten salt electrolysis. The effects of synergetic ultrasound on the Sc content and primary Al3Sc particles of Al-Sc alloys are specifically investigated. Ultrasound can strongly promote the Sc content of the electrolytic Al-Sc alloy and transform the large Al3Sc phase clusters into fine cubic particles. Meanwhile, it also homogenizes the distribution of Al3Sc phase. The Sc content increases by 74.4% up to 1.43 wt% when applying ultrasound during both electrolysis and solidification process. It also transforms the molten salts/liquid Al interface by enhancing the wettability. The huge primary Al3Sc phase clusters transform into fine cubic particles by ultrasound. The average particle size reduces from 77 ±â€¯36 µm down to 21 ±â€¯8 µm. The concerned mechanism have been discussed in detail.

Effects of radiator shapes on the bubble diving and dispersion of ultrasonic argon process.

In this work, three ultrasonic radiators in different shapes have been designed in order to investigate the effects of radiator shapes on the argon bubble dispersion and diving as well as the degassing efficiency on magnesium melt. The radiator shape has a strong influence on the bubble diving and dispersion by ultrasound. A massive argon bubble slowly flows out from the radiator with the hemispherical cap, due to the covering hemispherical cap. Using a concave radiator can intensively crush the argon bubbles and drive them much deep into the water/melt, depending on the competition between the argon flow and opposite joint shear force from the concave surface. The evolution of wall bubbles involves the ultrasonic cavities carrying dissolved gas, migrating to the vessel wall, and escaping from the liquid. Hydrogen removal can be efficiently achieved using a concave radiator. The hydrogen content can be reduced from 22.3 µg/g down to 8.7 µg/g. Mechanical properties are significantly promoted, due to the structure refinement and efficient hydrogen removal.

The role of ultrasound in hydrogen removal and microstructure refinement by ultrasonic argon degassing process.

In this work, the role of ultrasound in hydrogen removal and microstructure refinement by the ultrasonic argon degassing has been fully investigated by the experimental work in water and AZ91-0.4Ca magnesium melt, respectively. Ultrasound is able to break up argon gas into numbers of small bubbles and drive them diving deeply to the bottom of water, which are responsible for the efficient degassing regime of ultrasonic argon process. The argon flowrate plays a dominant role in promoting hydrogen removal effect. Meanwhile, the increasing argon flowrate can suppress the microstructure refinement, due to the subdued ultrasonic cavitation under a large argon flowrate. Mechanical properties of AZ91-0.4Ca alloy can be much promoted by the ultrasonic argon degassing process. Ultrasound is the key to achieve not only efficient degassing regime, but also microstructure refinement as well as mechanical properties promotion.