The Lead Dioxide (PbO2) Anode

An insoluble anode that is relatively cheap, easy to make, reliable, and long lasting for the manufacture of Chlorate's and Perchlorate's has long been sought after by the non-professional. The Lead Dioxide Anode (the Poor Mans Platinum) is one way to go.
There are a number of different types and methods of construction of the Lead Dioxide anode that have found use in industry. The usual type of Lead Dioxide anode that was used in the past by the big producers of Chlorate's and Perchlorate's were Graphite substrate and Titanium substrate Lead Dioxide anodes. The Graphite substrate Lead Dioxide (GSLD) anode requires a high quality thick coat of Lead Dioxide to protect the Graphite from the Chlorate/Perchlorate electrolyte. It also needs a high quality , hard and dense Graphite (although home producers have used battery carbons) in order to have a high reliability. Gouging rods are NOT acceptable.
The original patent that was used by a major Chlorate and Perchlorate manufacturer to make Graphite Substrate Anodes is US 2,945,791 and is available in the 'further reading section'. (see also US 3,463,707) It uses a well controlled setup.
Amateurs have been finding it difficult to obtain a GSLD Anode that has lasted long in an electrolytic cell. The Anodes appear to be OK when plated but fail after a time when used. That's not to say that it cannot be done.

The Ti substrate anode needs an precoat between the LD and the Ti as LD will oxidize Ti metal. A reasonable adherent coating of Lead Dioxide is also required. Ti substrate Lead Dioxide anodes that have been successful in industry have had a coating of Platinum metal or Pt Oxide applied to the Ti before being coated with Lead Dioxide. An alternative to the Pt/Pt Oxide is a semiconductor coating of doped Tin Oxide. This is applied by painting and thermal decomposition.
Massive Lead Dioxide anodes (anodes having no substrate) have also been proposed and are a good long lasting anode once a successful anode has been produced. The problem here is that it is difficult to make massive anodes of the required size that have no flaws, a tiny flaw or crack will cause the hard brittle anode to fail by breaking.
Plastic and ceramic substrate anodes were proposed in order to obtain anodes that did not require a perfect coating of Lead Dioxide. The ceramic substrate anode was not a success as the porous substrate conducts salts up to the connection when it goes into service. It also requires a reasonably good coating of Lead Dioxide in order to carry the heavy currents when used in a (Per)Chlorate cell. The plastic substrate anode has the same problem of requiring a good coat of Lead Dioxide to carry heavy currents.

Anodes that have an inert reinforcing fibre mesh as a substrate are being tried. The type of anode will be 'forgiving', unlike anodes with Graphite as the substrate where a less than perfect coating of Lead Dioxide gives inevitable failure of the anode once it goes into service. They are comparable to massive anodes but with the added reinforcing of the inert fiber mesh or other substance. A valve metal could also be used so long as the electrical connection is not made to the valve metal.

The current state of thinking is this:

Graphite substrate made correctly using a good grade of graphite. No corner cutting on temperature control. Steady Lead Ion concentration in the electrolyte (use large bath) and not too much pH/Nitric acid concentration variation (use large bath). Use surfactant and put on a thick coat (min. 3mm) of LD. See US Pat. US 2945791

Ti substrate Anodes using the doped Tin Oxide precoat or a purchased MMO precoat. Ti substrate is a mesh or drilled flat sheet. First an Alpha then a Beta Lead Dioxide coating is applied. Good control of plating baths. Since Ti is readily available this may be the best way to go.

Inert mesh reinforced massive Anodes are a viable alternative for the Amateur. Good success has been reported using plastic domestic 'pot scrub' material as the reinforcing mesh.

The Magnetite substrate Lead Dioxide anode may be workable. It appears that when a solid piece of Lead Dioxide is simply attached to a piece of Magnetite and placed into a (Per)Chlorate cell it will function as a successful anode. See here for details.

See here for more info on Lead Dioxide types.

Electro depositing Lead Dioxide
Titanium Substrate anodes
Inert cloth reinforced anodes
Installing anode in a cell
Graphite Substrate Lead Dioxide anodes
Inert Porous Substrate anodes
Plastic Substrate anodes

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