Electroplating in the Presence of Ultrasound

Recent studies have demonstrated that simultaneous ultrasonic irradiation of electrochemical systems significantly improve electrochemical reactions [10,11]. Ultrasound has been used extensively in the electroplating industry for many years, and the literature contains many articles reporting the advantages of ultrasound in electrodeposition and plating which include  

Whilst there may be different origins for the variety of these effects, one well-characterised consequence of ultrasonic irradiation is the generation and subsequent collapse of cavitation bubbles within the electrolyte medium and near to the electrode surface of the electrochemical cell. The electrode surface causes asymmetrical collapse of a bubble which in turn leads to the formation of a high velocity jet of liquid 

Let us now discuss examples of the use of ultrasound in the electroplating of such metals as chromium, zinc, iron, copper, silver and nickel (electro and electroless). 

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Another example of where ultrasound influences the discharge rate of chromium is in the chromium electroplating of steel plates. When cold-rolled steel plate is elecUo-lytically chromated from a silent aqueous solution containing chromates and dichromates, a chrome coating of 13 mg m is obtained after 1 s, whilst in the presence of ultrasound a coating of 45 mg m is obtained [25] in the same time. The product is also accompanied with an increase in the brightness of the metal. Similar results have been found by other workers [26]. 

Ratajewicz and co-workers have also studied the effect of a ultrasonic field on electrode polarization and activation energy in zinc electroplating [96], The conclusion from their work was that the zinc electrochemical reduction reaction was influenced by the presence of organic additives, especially CN ions, and that in the presence of ultrasound the cathode fouling is reduced. 

One promising area of investigation is the use of ultrasound to speed up the operating rates of existing aqueous electroplating systems which were not economically viable in the past. These systems can then become feasible and Fitch [102] has described the use of aqueous based compounds such as sodium salts (e.g. hydroxide, silicate, phosphate, carbonate, and borate) as an alternative to the more toxic materials commonly used. These inorganic compounds are inexpensive, readily available, and highly effective in the presence of ultrasound. 

Ultrasound has also been successfully employed for the production of novel inorganic compounds such as Si semiconductors in which case it is found that ultrasound increases yields of products and in some cases influences the reaction mechanism itself. For the traditional electrochemical process of metal electroplating the presence of ultrasound increases the thickness of the material deposited, as well as increasing the efficiency of the reaction. Ultrasound has also been successfully employed in the machining of complex electronic circuitry using electrochemical etching techniques. A majority of papers published in the literature still... 

Electrochemistry Almost any electrochemical process benefits from the presence of ultrasound with improved current efficiency and the prevention of electrode fouling. These advantages are particularly evident in electroplating but can be also beneficial in electrosynthesis and electroanalytical chemistry. 

The electroplating of metals invariably involves gas generation at one or other of the electrodes and the physical presence of the gas acts as a barrier to efficient passage of current (discharge of ions). One of the ways in which ultrasound can improve electroplating—and indeed general electrochemical processes—is by the removal of this gas barrier [76]. 

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