Electrodeposition Theory and Practice
Topics in Number 48 include: Effects of codeposition of hydrogen on the structure of electrodeposited copper New classes of electrode materials introduced by spontaneous deposition of Ru and Os on Au(111) and Pt(111) single crystal surfaces Recent develop
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Electroless Deposition: Theory and Applications Stojan S. Djoki´c1 and Pietro L. Cavallotti2 1 Elchem Consulting Ltd., Edmonton, AB, Canada T5X 6B3 2 CMIC, Dept. Politecnico, Via Mancinelli, 7, 20131 Milano, Italy
I.
INTRODUCTION
Electroless deposition is a process that has been used in practice for centuries. Although not recognized as such, electroless deposition of noble metals, e.g., silver or gold was known to the ancient civilizations. In spite of very slow developments throughout the centuries, significant scientific results have been achieved in the second part of the twentieth century.1–3 The research achievements in the area of electroless deposition have contributed to tremendous applications and developments in various industries. In general terms, for the electroless deposition no external current is required. Coatings produced by electroless deposition are uniform and continuous, which makes this process very attractive for different applications. Applications of electroless deposition are related to electronics, energy conversion, aerospace, and biomedical and automotive industries. In addition, new applications in the area of metallization of polymers, ceramics, and fabrics, production of
S.S. Djoki´c (ed.), Electrodeposition: Theory and Practice, Modern Aspects of Electrochemistry 48, DOI 10.1007/978-1-4419-5589-0 6, c Springer Science+Business Media, LLC 2010 251
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various powders, corrosion and wear-resistant coatings, decorative and catalytic surfaces, etc. are being developed. The aim of this chapter is to discuss the recent research, developments, and applications of electroless deposition.
II. GENERAL CONSIDERATIONS OF ELECTROLESS DEPOSITION Studies and practices of plating of different types of coatings from aqueous solutions without an external current source were described in the literature as electroless deposition. The research was predominantly related to the deposition of metals and/or alloys. However, it seems that the deposition of compounds without an external current source was in a way neglected. It is to be noted that electroless deposition of oxides, salts, polymers, etc. is also possible. Metal electrodeposition, where the reduction of metal ions takes place, is always a cathodic reaction. In most of the cases electrodeposition of oxides is the anodic process resulting from the oxidation of metals. In the analogy, for the electroless deposition of metals, the presence of reducing agents is needed, while for the electroless deposition of compounds, oxidizing agents are usually required. In terms of kinetics and mechanisms, electroless deposition processes have many similarities. In an attempt to analyze the electroless deposition, several mechanisms such as atomic hydrogen, hydride ion, metal hydroxide, electrochemical, and universal have been proposed.1–3 It is important to note that these mechanisms were developed for cases of nickel and copper electroless deposition, which were the most widely studied metals in this respect. Based
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