Electrochemical Formation of Nano-structured Metal Deposits and Anodic Oxide Coatings by Applying (DC + AC) Pulses and Using Drag Reducing Polymer Additives

摘要

Two competing factors control the grain size of the electrodeposits: the nucleation of new crystals and the growth of existing crystals. Nanocrystal formation requires set of operating parameters that promote the nucleation of new crystals. If all other conditions stay the same, this process takes place when the concentration of the reacting species (metal and other ions) in the diffusion layer adjacent to the substrate is as high as that in the bulk solution. Therefore, thinner diffusion layers are related to faster rates of restoration by diffusion of the bulk concentration of ions consumed during the pulse on-time. The present paper presents a new approach in the production of nano-structured metal electrodeposits and anodic oxide coatings that combines (DC+AC) pulse application with the addition in electrolytes small quantities of drag reducing polymers (DRP). Typically used to diminish the skin-friction drag of the turbulent flow, these polymers can be also added into flowing electrolytes to reduce the thickness of the boundary and diffusion layers. In support of the advantages and efficiency of the proposed electrochemical technology this paper offers three examples of (DC+AC) pulse formation: 1) nickel deposits, 2) aluminium, and 3)titanium anodic oxide coatings. In all three cases the coatings' nano-structure determines their excellent functional properties.