The Platinum Anode


In industry, the Platinum or Platinum alloy Anode is nowadays used for converting Chlorate into Perchlorate. MMO(DSA) being used for Chlorate production. Most Pt Anodes are Platinum clad, the base metal is usually a 'valve' metal such as Ti. An alloy of Pt/Ir (70/30) is extensively used as it is superior to Pt alone, it has greater catalytic effect. Platinum is expensive ($40/gram year 2006) and heavy. It has a density of 21.4 g/cc.
The surface properties of Pt are very important to the operation of the material giving the metal a range of different characteristics. Smooth Pt (solid Pt, and electro deposited) has been favoured in Chlorate and Perchlorate production as it's wear rate is low. Other Pt surfaces can be formed by depositing the Pt using thermal decomposition, 'Paints' or in combination with other metals (Ir). Theses surfaces have better catalytic activity which have better overpotential figures etc.

Anode current densities used vary widely. They range from 100mA/square cm to 700mA/square cm. Use about 300mA/square cm. Pt will increasingly erode if used in a Chlorate cell with a low concentration of Chloride. Keep above 80 grams per litre Chloride. Pt will also increasingly erode if used in a Perchlorate cell if the concentration of Chlorate is low, though the extra erosion appears to be little.
There is some information regarding wear rates of Pt in US Patent No. 3,475,301.
The wear rate of Platinum is 0.5 grams per ton of Chlorine produced when used in Chlorine cells with coating depts of 0.05 to 0.1 mil (Metals handbook).

Pt wire and coins (bullion) is readily available. Platinum clad Anodes are available from corrosion control companies. Platinum plated (usually Ti) are also available from companys supplying electroplating supplies. They tend to be expensive considering the amount of Pt that is actually on the Anode. There have been good reports of Platinum plated Ti anodes being used for Perchlorate production using pure or nearly pure Chlorate. See Alan Yates page for reports on Pt anodes.
When purchasing Platinum bullion or wire is should be noted what the ratio of weight to surface area you are getting. If you are going to manipulate the Pt physically after you purchase then this is not so critical. The same goes for Pt clad Anodes, know what surface area you are getting for your buck. You should go for a Pt coating thickness of 70 micron or so.
Platinum clad anodes are sometimes available which have thicker coats of Pt than the electroplated anodes.
The Platinum coated Ti anode used for electroplating applicatios have very thin coatings of Pt on them (10 micron or less) but they hold up OK when making Perchlorate from pure or nearly pure (recrystallized at least twice) Chlorate.
Below are two Pt clad Anode manufacturers.
http://www.telprocompanies.com
http://www.lidaproducts.com

Pool chlorination anode are sometimes Pt based. The bipolar anodes (AFAIK) are Pt based.
An example at this address: http://www.directpoolsupplies.com.au/prod646.htm
A picture is below. It should be noted that it is not certain if this anode is MMO or Pt.

[Pool chlorination anode]

.
The ratio of weigh(price) to surface area for Pt wire is important from a cash and current carrying (heat dissipation per cm) point of view.
This is discussed in Resistance and power calculation for Pt wire.

Figures I have seen with people who actually used 0.5mm Pt wire said that 4 amps was the max. current that was sensible to put through wire. I have seen as high as 7 amps. This was far too high IMHO.

You can cut a given length of wire into a number of Anodes to lessen the resistance problem if you need, as discussed in link to Resistance and Power calculation.
You could also flatten wire to give it more surface area per buck. Watch out for the current needed to run your new flattened Anode. You cannot flatten the wire too much and expect the wire at the top to be able to carry a huge current. Platinum is very malleable.
With an infinitely flattened wire you will have infinitely large surface area costing an infinitely small price per cm squared, with an infinitely high ................... You need to decide where the sensible point is.

Pt wire can be attached to a Copper wire and sealed in a glass tube to save on Platinum.

If you use Chromates in your Perchlorate cell this will help protect Pt from corrosion as it stops Chloride from forming. See this thread by GarageChemist(or see Na Perchlorate section):
http://www.sciencemadness.org/talk/viewthread.php?tid=5050&page=2#pid60758
Since Chromates stop Chlorate and Hypochlorite being reduced at the cathode back into Chloride this will protect the Pt as Chloride in the Perchlorate cell will corrode Pt.
SMALL amounts of Chloride in a Perchlorate cell are a Platinum anode eroder.
If using homemade Chlorate, you should recrystallize the Chlorate at least twice to get the Chloride concentration low and save on anode erosion. Persulphate or NaF would probably help protect the Pt as well. They may not.
According to Encyclopedia of Chemical Processing and Design, Vol 51, 1995 page146, Barium is a poison to Noble Metal or Noble Metal Oxide anodes and may even reduce there lifetimes.

Another possible way to make Pt anodes is to use Potters Platinum .
See here for some info on plating Pt onto Titanium.

The price of Platinum in coins is much lower per gram than wire or foil.

You can look up the price of Platinum on the international markets by doing a search for precious metal dealers/brokers.
Coins can also be bought from similar sources.
Try the following for Pt wire, coins and Anodes.

Farwest corrosion control.

Thomas Register.

http://www.alfa.com/

There's plenty of further reading regarding Platinum Anodes (and its cousins) in the Platinum Metals review journal.
There is an article depicting the development of the Pt Anode in PMR 1998 (42) 1 (available at above link) and here (local PDF, 600k).

HIT THE BACK BUTTON ON YOUR BROWSER