Mass-Transport versus Charge-Transfer Limitation

Mass-Transport versus Charge-Transfer Limitation 

Cu-plating with an add bath containing H2SO4 and CUSO4), and migration is viewed favorably, as an additional mode of mass transport. 

Convective mass transport is caused by the movement of the solution as a whole. 

Mass transport by diffusion can be regarded as the last resort. When movement of the electroactive species is not promoted by the input of external energy, either electrical (migration) or mechanical (convection), diffusion takes over. The driving force in this case is the gradient in chemical potential caused by the gradient in concentration. It is a relatively slow process, with diffusion coefficients for small molecules in dilute aqueous solutions at room temperature, in the range of 2 X 10 -8 X 10 cm s-  

We alluded to the Nernst diffusion layer thickness, 6, in the first chapter. This quantity is related to the mass-transport-limited current density through the equation 

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Mass Transport Versus Charge-Transfer Limitation... 

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