Sonoelectrochemical Synthesis of Nanocrystalline Materials

Reisse and co-workers [147-149] were the first to describe a novel device for the production of metal powders using pulsed sonoelectrochemical reduction. This device exposes only the flat circular area at the end of the sonic tip to the electrodeposition solution. The exposed area acts as both cathode and ultrasound emitter, named by Reisse et al. as sonoelectrode . A pulse of electric current produces a high density of fine metal nuclei. This is immediately followed by a burst of ultrasonic energy that removes the metal particles from the cathode, cleans the surface of the cathode, and replenishes the double layer with metal cations by stirring the solution. In [145], a list is given of chemically pure fine crystalline powders, mostly metals or metallic alloys, prepared by this method, with particle sizes varying between 10 and 1000 run depending on deposition conditions. 

In the sonoelectrode design, a titanium horn acts both as the cathode and the ultrasound emitter. The electroactive part of the sonoelectrode is the planar circular surface at the bottom of the horn. This sonoelectrode produces a sonic pulse that is triggered immediately following a current pulse. One pulse driver is used to con- 

The sonoelectrochemical deposition of CdSe nanopartides is carried out from an aqueous solution of CdS04, complexed with potassium nitrilotriacetate (N(CH2C02K)3) NTA as a source for Cd, and a selenosulfate solution, (Na2SeS03), as source for Se. The CdSe crystal size could be varied from X-ray amorphous up to 9 nm by controlling the various electrodeposition and sonic parameters. The effects of various electrodeposition and sonic parameters on the properties of CdSe nanopartides are presented in Table 6.3. 

The fundamental basis of the sonoelectrochemical technique to form nanoparticles is massive nucleation using a high current density electrodeposition pulse (ca. 150-300 mA cm ), followed by removal of the deposit from the sonoelectrode by the sonic pulse. Removal of the particles from the electrode before the next current pulse prevents crystal growth. Overall there are many experimental variables involved in sonoelectrochemical deposition electrolyte composition and temperature, electrodeposition conditions including current density (le), pulse-on time (te(on)) and ratio between pulse-on time and pulse-off time (te(off)) (the duty cyde) sonic probe conditions sonic power (Is), sonic pulse parameters, fs(on) and ts(off). 

The effects of the various sonoelectrochemical parameters on crystal size can be rationalized, in general, as follows  

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