Ok i think i have cracked making Large Graphite Substrate Lead Dioxide Anodes (GSLD)..If you want to make Chlorate(ClO3) or Perchlorate(ClO4) you can use various Anodes Platinum is the probably the best ...Lead Dioxide (PbO2) is next best...
I have gone for the PbO2 anode because you can run the cell right from Chloride(Cl) to Perchlorate(ClO4)..if you used Platinum to do this then you will get excessive corrosion on the Platinum Anode due to the low Chloride concentration stage..
I tried plating PbO2 on to 13 mm Carbon Gouging rods because they were very cheap and looked like graphite!!.but i found it didnt take the coating very well so i Binned the idea..Graphite works realy well..
I got some Fine grained 10 mm Graphite 500mm long rod
Graphite rodsAlso after making Good 10mm Anodes i got some larger 32 mm x 500mm graphite rod
32 mm Graphite rodsYou need to treat the graphite so that the PbO2 adheres well.. To do this you simply electolyse the anode in a 10% Sodium hydroxide solution i applied 3 volts at about .0.05 Amps per square Decimeter..that works out at about 1.5 to 1.75 amps For the 10 mm Anode and about 6 to 7 amps for the 32 mm Anode..
Anode being etched
Close up of etched anode surface Etching AnodeWhen electroplating the PbO2 tiny oxygen bubbles form,If theses bubbles are allowed to stay on the coating these bubbles will form pits which will allow the corrosive salt solution through and thus destroy the substrate which in turns destroys the Anode..
In industry surficants are used which eliminates this problem..I spinn the electrode the centrifugal force throws off the bubbles leaving a nice smooth coating...
The plating tank was a 3 litre pyrex beaker .the plating solution was 333 g a litre Lead Nitrate + 50 g litre Copper Nitrate ..To spin the electode i used a Small 240v electric motor from a Fan..Mounted on plank of wood..To lower and raise the electode i used my camera tripod ..
The plating tank operated at approx 60 centigrade i used an electric hotplate with magnetic stirrer to agitate the solution..
Tank set up Spinning graphite? Spinning electrode side view.... Here is a close up of the finished product
13 mm GSLDI tried the electrode in a Sodium Chloride solution and it took 9 amp with no sign of errosion or heating.. So i Started making 32mm anodes..
I had to use a larger electric motor the Small fan motor siezed up when spinning the larger electode..Because the motor wieghed much more i had to use Aluminium bar to mount the motor on ...the extra weight helped reduce vibration..
32 mm In tank 32 mm In tank close up Close up of Electrode before coating Close up of Electrode after coating After plating the tank is replenished with the addition of Lead Dioxide (PbO) a bright yellow powder ..
Plating tank with an excess of PbO added i leave it stirring over night then filter the solution.. and leave it to stand for a few days before use so that any nitrites formed (which lowers the plating tanks efficiency).are oxidised back to nitrate..I acidify the solution to PH 1 with Nitric acid and its ready for use.
.I could have used a surficant to eliminate the bubbles, but continued use of the plating tank ends up that the breakdown products of the surficant makes a poor PbO2 coating...and to eliminate the breakdown products required the use of amly alcohol and distillation equipment...
Here are a few more pictures
Some more anodes Platinum mesh anode First graphite anode 36 mm Anode made to take at least 27 ampsThe 13 mm Anodes can take 9 amps with no signs of errosion so far..its been in the test tank nearly 2 weeks..The 36 mm Anodes has been in testing tank nearly a week and no signs of errosion with 27 amps through it....
The power is supplied for the 100 amp Chlorate cell is a Power Ten P62B 325 amp 5 volt power supply This is rated for continous use and weighs over 20 kg so hopefully should be up to the job..
To be Continued...