The plastic substrate Anode has been difficult to get to work for the Amateur. It is difficult to obtain a good heavy coat of Lead Dioxide that will adhere well to the plastic substrate and give a good reliable connection at the top for the heavy, long term connection required for the (Per)Chlorate cell.
The advantages of the plastic substrate
it that it is easy to obtain and is non porous and therefor will not suffer to a
great extent from the problem of the salts from the Chlorate/Perchlorate cell
getting to the current connection by cappillary action. Not all plastics will
stand up to the harsh conditions in a Chlorate/Perchlorate cell and there you
must know what type of plastic you have. Plastics that are suitable for the task
are polyester, polypropylene, polyethylene, teflon, ployvinylchloride (PVC) and
polystyrene (...and counting).
If you have a plastic and you wish to see if it is up to the task, you can test it by setting up a chlorate cell using a graphite anode (or lead dioxide) and placing the plastic to be tested in the cell close to the anode for a few days. If the plastic remains intact then it is probably ok for to use as a substrate for an anode. Plastic bars can be purchased from your supplier of raw materials for lathe work. Engineering supply firms should carry it. Get PVC if you can.
To make the plastic conductive it is painted with a solvent that melts a
layer of the plastic and it is then rolled in a excess of dry lead dioxide
powder. You should use plenty of dry powder at this stage. Don't be tempted to
rub off the excess from the anode at this stage. The excess can be removed when
the solvent is fully dry. Try not to 'disturbe' the layer of solvent/melted
plastic when applying the powder. A handy solvent that will melt most plastics,
including PVC, is plumers glue which is available at the hardware store. It is a
mixture of MEK, and Tetrahydrofurvan.
Connections are applied as described elsewhere on this page and it is plated. Metal connections will not give as many problems as with the porous ceramic substrates when the anode goes into service as there will be no conduction of salts up the plastic substrate.
The anode is plated in the usual manner, as per the ceramic substrate anodes. There can be a problem with the plating solution creeping up the powered anode and corroding the connection that is make to the anode for to plate it. This will not be a problem if you are using a graphite connection when you are plating the anode. If not, the best method is to plate about one inch of one end of the anode and then turn the anode upsidedown and make a good connection to this small (inch long) plate and then plate the rest of the anode.
For getting a connection to the anode see Metal/graphite connections..