The development of a rotating electrochemical quartz crystal microbalance for the study of leaching and deposition of metals

Despite the widespread use of the electrochemical quartz crystal microbalance (EQCM). there is still no commercially available instrument of the rotating type. The first reported rotating EQCM (REQCM) was built in the authors' laboratory in 1994 and, in 1997, a second generation instrument was designed to overcome problems with stability and sensitivity. This paper describes the design and construction of a rotating EQCM, detailing how these problems can be minimized. The advantages of this equipment are its high sensitivity (< 10 ng), the ability to study reactions over relatively short time intervals and the possibility of studying electrochemical reactions which occur simultaneously with the evolution of gas. In this paper, the benefits of the REQCM are illustrated using two simple examples: the deposition of copper from cyanide solutions; and the leaching of copper in cyanide solutions. For deposition reactions, the REQCM effectively extends the electrochemical window, allowing the reaction to be studied simultaneously with evolution of hydrogen. Use of the REQCM is the only technique capable of achieving this. For leaching, use of the REQCM is the quickest, simplest and most accurate method of measuring reaction kinetics and determining whether a reaction is chemically or diffusion controlled.