Ultrasound Assisted Electrodeposition of Zn-TiO2 Dispersion Coatings
When ultrasound is introduced into an electrolyte acoustic cavitation is likely to occur. The resulting effects are different phenomena such as acoustic streaming and micro-jetting, generation of shock waves, promotion of mass transport from/to the electrode, cleaning of the electrode surface and the reduction of the diffusion layer thickness, among others . Consequently, advantages such as such as increased deposition rates, reduced porosity and grain refinement have been reported for ultrasound-assisted plating [1,3].
Metal matrix composite coatings can be prepared by codeposition of micro and nano-particles during the electroplating process. One difficulty to overcome during the deposition has been particle agglomeration in plating bath medium due to the high ionic strength of the electrolytes. Regarding this aspect, ultrasound can be beneficially used to promote both deaglommeration of particles and acoustic streaming of the bath during the electrodeposition [4-5]. Depending on the application of such composite materials, ultrasound can be a powerful tool for the preparation of tailored composite coatings.
This work presents a comparative study of the influence of ultrasound on the electrodeposition of pristine Zn and Zn-TiO2 dispersion layers from additive-free chloride-based electrolytes. TiO2nano-particles (P25, Degussa) were used as second phase material. Different combinations of ultrasonic frequency and ultrasonic power have been studied by using two different electrochemical setups: ultrasound-bath-setup and horn-probe setup. Particle incorporation into the zinc matrix was investigated by Glow Discharge Optical Emission Spectroscopy (GD-OES). Furthermore, the morphological and structural properties of the layers were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Focused ion beam (FIB) assisted imaging.
The system Zn/TiO2 was selected due to its potential application as chromium(VI)-free protective layer and/or as functional coating with photocatalytic activity.
Acknowledgments: M.C. gratefully acknowledges support from the Deutscher Akademischer Austauschdienst (DAAD) through a PhD fellowship as well as the Gleichstellungsrat-TU Ilmenau.
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