Efforts in Expanding Abner Brenner's Paradigm of Alloy Electrodeposition Research

Alloy electrodeposition (ELDP), industrialized in the 1840s mainly by Elkington & Co. in England, has been an interesting research topic in history. Contemporary alloy electrodeposition research focuses on its application at novel substrates, with novel electrolytes, for novel applications, observed with novel characterization techniques. However, most of the works can be considered to be built and extended from Abner Brenner’s research paradigm on alloy electrodeposition in the 1960s, in which more than 100 binary and more than 20 ternary and higher-order alloy ELDP systems were summarized (see Modern Electrodeposition, 700 pages). The main ideas of Brenner’s paradigm are (1) identifying all the 13 general control parameters of alloy ELDP, (2) classifying the alloy ELDP systems based on its concentration-composition relationship, and (3) generalizing the behavior of 5 alloy ELDP classes into 6 principles of composition control.

To extend Brenner’s paradigm, there should be a better understanding of the concentration-composition relationship. For designing novel electrolyte systems, a guideline on how to predict the stability of alloy deposition baths should be available. With better predictability on the concentration-composition relationship, the complexity of the system can be reduced so that phenomena like the phase selection behavior, the chemistry variation inside the diffusion layer, the nucleation exclusion effect, the impact of the waveform on the deposit properties, and the reaction intermediate species can be investigated and controlled.

This thesis will observe the underpotential co-deposition and phase separation behavior. To improve the predictability of an alloy ELDP system, several simple models have been proposed in terms of composition control, electrolyte design, initial deposit properties, diffusion layer structure, and quantification of spatial features. The structure of this thesis has been listed below:

1. Presenting the impact of alloy thermodynamics on alloy ELDP kinetics and the Phase separation behavior in alloy ELDP (Chapter-2, Ag-Pd ELDP system)
2. Using mixed-potential theory as a guideline to prepare and stabilize alloy ELDP baths and using the limiting current composition behavior to design electrolytes for deposits with specific compositions (Chapter-3, Ag-Fe ELDP system).
3. Classifying and characterizing electrodeposited phases in the Cu-Sn alloy system, and the occurrence of metastable phases during its ELDP (Chapter-4).
4. Demonstrating the full complexities in the estimations of the rate of concentration drop, the initial deposit thickness, the initial stage duration, and the potential-composition curve (Chapter-5, Cu-Ag ELDP system).
5. Reviewing and discussing different models for estimating the diffusion layer thickness in ELDP systems. Presenting the full complexity of estimating the diffusion layer thickness of alloy ELDP with the stagnant diffusion layer model (Chapter-6)
6. Discussing the nonlinearity, reproducibility, and the impact of surfactant (suppressor) on the deposit morphology (Chapter-7, CuCoFeNi-based ELDP systems).
7. Reviewing and discussing the quantification of spatial distributions in electrodeposited particles (Chapter-8, Cu-Ag ELDP system).

I hope that this thesis can offer an overview of those topics related to the extension of Brenner’s paradigm of alloy ELDP in the 1960s. Furthermore, I hope that those simple models could offer some predictability in alloy ELDP when investigated with advanced characterization techniques or used in novel applications.