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This page was translated automatically using artificial intelligence (DeepL). The German version is binding. More information about automatic translation
Electrolytic gold plating is an established method for finishing components, owing to the chemical resistance of this precious metal. In the electronics sector in particular, properties such as good electrical conductivity and temperature resistance are important, and electrolytic gold plating is therefore indispensable. Gold electroplating is based on cyanide electrolytes, as these are characterised by high stability and reliable deposition. Potassium gold cyanide, K[Au(CN)₂], is used as the starting component for a cyanide-based gold electrolyte. However, cyanides pose a potential hazard due to their high toxicity. This means that stringent safety requirements must be met. Furthermore, complex wastewater treatment processes and regulatory inspections are required. Consequently, there is significant economic and environmental interest – particularly amongst small and medium-sized enterprises (SMEs) – in conducting research into the further development of cyanide-free gold electrolytes.
One possible alternative is the new dithio-urea-gold(I)-methanesulphonate complex. This new starting compound has already been used successfully to carry out electroless gold plating. In galvanic deposition, undesirable side reactions are observed, which manifest as a brown coating on the substrate. Current research at Mittweida University of Applied Sciences, in collaboration with Chemnitz University of Technology, is focusing on the synthesis of new cyanide-free gold salts, which are to be used as the basis for the development of new electrolytes, as well as on the addition of additives to these electrolytes.
For the electrochemical synthesis of new gold compounds, an H-cell is used with separate anode and cathode compartments, which are separated by an ion-selective membrane. The anolyte contains the complexing agent, methanesulfonic acid and the gold anode. The catholyte contains an acidic solution and the platinum cathode. This setup allows the gold to be dissolved electrochemically and stabilised using a complexing agent. As the reaction compartments are separated by the membrane, the gold that has been dissolved is not immediately deposited back onto the cathode.
In this way, various complexing agents – ranging from phosphonates and xanthogenates to selenourea, which is very similar to thiourea – have already been tested. However, a successful substitution for thiourea has not yet been achieved; consequently, the replacement of methanesulphonic acid with various other acids has, for the time being, been successfully carried out.
Experiments are currently being carried out with tetrachloroauric acid as the starting compound for the synthesis of new cyanide-free gold compounds. Cysteine (an amino acid) and 5,5-dimethylhydantoin (DMH) have emerged as promising complexing agents. Initial gold layers have already been deposited from a solution of the gold acid with the addition of DMH (see Figure 2).
The gold-DMH complex and the gold-cysteine complex are to be isolated and subsequently characterised in further detail. In addition, the effects of other parameters on the galvanic deposition of gold will be investigated.
About
Tobias Schürer: He studied nanotechnology on the Master’s programme at West Saxon University of Applied Sciences in Zwickau, graduating in 2020. Since October 2021, he has been working at Mittweida University of Applied Sciences in the Faculty Engineering Sciences as a research assistant on the GaGoKom project within Professor Frank Köster’s Surface and Electroplating Technology research group. His responsibilities include the synthesis of new gold complexes and the characterisation of the gold layers deposited using these complexes.