Comparing Lead Alloy Anode and MMO Coated Titanium Anode for Electro Galvanizing

Comparing Lead Alloy Anode and MMO Coated Titanium Anode for Electro Galvanizing

The growing importance of high-speed electroplating and electro galvanizing has led to the careful consideration of the processes occurring at the anode as well as the cathode. A soluble anode appears advantageous because metal ions in the solution should be maintained at the desired concentration. However, non-uniform dissolution, passivation, and faradaic inefficiency are known to occur. The inter-electrode gap necessarily increases and the anodes must frequently be replaced, which complicates the design and operation of an electrolytic system with soluble anodes.

Gas evolves at insoluble anodes. Chlorine evolution from a chloride electrolyte would pose significant problems in cell design and operation and safety. Thus insoluble anodes are presently used with sulfate solutions. Two types of insoluble anodes are: (1) lead or lead alloys such as lead-silver and load-calcium and (2) a precious metal or catalytic type consisting of a valve metal such as titanium or tantalum coated with a metal or metal oxide usually selected from the platinum group. A valve metal forms a nonconducting surface during electrolysis if not protected by a barrier.

This mixed metal oxide coated titanium anode is characterized by a high surface area, high electronic conductivity, long term stability, or low cost in addition to its catalytic function. Viable catalytic electrodes are typically a compromise between activity, stability, and cost.

For electrolytic processes involving the anodic evolution of oxygen, catalytic anodes such as the MMO coated titanium electrode are capable of stable, extended performance over a wide range of current densities. The fabrication process and its impact on the electrochemical activity and stability of a catalytic anode are most important. Experience has shown that passivation is the primary failure mode, not loss of the catalyst when the anode is used to evolve oxygen at high current densities.