A contribution to the theory of cementation (metal displacement) reactions

Abstract

In this paper, cementation (metal displacement) reactions are discussed in terms of Evans diagrams, i.e. diagrams constructed by the superposition of cathodic and anodic polarization curves. The conditions under which the rate of a cementation reaction will be controlled by cation diffusion to the reacting metal surface or some chemical step at the surface are explored. It is found that for the case in which the effective cathodic and anodic areas are approximately equal, the cementation is likely to be diffusion-controlled when its two component oxidation-reduction reactions have standard electrodepotentials which differ by more than 0.36 V. The ratio of cathodic to anodic area is also found to be important in determining the reaction mechanism. The presence of an oxide film on the metal is shown to be another factor which influences the reaction mechanism. Evans diagrams are used to discuss the composition of the product layer formed during a cementation reaction.

Elemental metals for environmental remediation: Learning from cementation process

“…In essence, only a smooth, coherent deposit can inhibit the cementation reaction. According to Power and Ritchie [40], cementation reactions whose constituent half-reactions has electrode potentials which differ by greater than 0.36 V are likely to be diffusion-controlled (Table 1). As recalled above the diffusion is favoured by the porous nature of the metallic deposit which is additionally electronic conductive and constitute a path for electron transport.…”

“…(1)) is precipitated from solution and replaced by a metal higher in the electromotive series (M m+ 1 -Eq. (2)) [39][40][41][42][43][44][45]. Cementation, also known as contact reduction or metal displacement, is necessarily a spontaneous heterogeneous reaction ( G 0 < 0) that takes place through the galvanic cell M 0 1 /M m+ 1 /M n+ /M (Eq.…”

Improvement of a cementation process by ultrasound: case of the cadmium?zinc couple at a RDE

“…The limiting step can thus be determined by using techniques such as Evans' diagrams for corrosion reactions as proposed by Power and Ritchie [25] and recently used by Alemany et al [20] or Jeffrey et al [26]. In all cases the operating cementation point (E cem ; i ¼ 0) is located on the Cd(II) diffusion plateau of the reduction wave with and without US.…”

Removal of copper metal by cementation using a rotating iron cylinder

“…The first involves the recovery of metals from leach solution [2,3] and the second is concerned with the purification of electrolyte solution to remove metals that are more electropositive than the metal to be deposited, e.g., Co, Ni, Cd from ZnSO 4 electrolyte [4][5][6]. Many applications have been reported in industry [6][7][8][9][10] for the recovery of metals and purification of electrolyte solution. Almost all the authors have reported that the rate of the cementation reaction at room temperature is diffusioncontrolled [1,5,11].…”