Homegrown Oxidizers Part Eight
WSM

As a proof-of-concept demonstration of the conversion of sodium chlorate to sodium perchlorate, we will set up some trial cells. Sodium chlorate is much more soluble than potassium chlorate, so our starting electrolyte concentration will be about 600 grams per liter of water (600g NaClO₃/L H₂O) or about 5 pounds per gallon. Higher concentration electrolytes are easier on the electrodes during the electrolysis process.

To show proof of the presence of perchlorate, we’ll use an indicator, methylene blue solution, which turns from blue to purple in a perchlorate solution, but is unaffected by chlorates or nitrates.

We plan to use a platinized titanium anode in one test cell and a lead dioxide anode in another test cell to determine their differences in our perchlorate system.

Most amateurs who’ve gone on to make perchlorates have noticed a strong ozone (O₃) odor while running their cell. Our research suggests that this isn’t optimal. Ozone production appears to indicate the system is using too much current and overpowering the anode.

We intend to test this idea in our sample perchlorate cells with more tightly controlled power input. For our power source, we’ll use a power supply with constant voltage (CV) and constant current (CC) capability. We expect running the supply in CC mode will allow us to limit the amperage over time and not “over drive” the electrodes.


A small power supply with CV and CC capability

Running the cells in CC mode should also simplify current efficiency (CE) calculations, since the current won’t vary as the cells run from start to finish.

Before running our proof-of-concept cells, we need to finish preparing the components.

Electrode Design and Fabrication

We’ve described electrode schemes where the anode is sandwiched between the cathodes for higher performance and efficiency. Let’s take a closer look and view some details we’ve developed in our research.

The arrangement for simple setups like ours is to place the anode in the center and surround it with cathodes. This helps provide an environment where the electrical stresses on the anode are more evenly distributed. With cathodes on both sides, we hope to optimize the output and prolong the working life of the anode.

Electrode Diagram.doc
Diagram of an anode sandwiched between cathodes, showing manufacturing design details. Not shown are insulating spacers between the electrodes.

This could be done with three separate leads, connecting them electrically outside the RC, but we believe a more efficient design connects the double cathode plates inside the cell with additional CP titanium structures, essentially “boxing” the anode, and only requires two leads to connect the electrical power.

By using non-conductive, compatible spacers between the electrodes, they’re held tight in close proximity but without touching each other, which would cause an electrical short circuit. We’ve used materials like Viton rubber or Teflon tubing for the spacers, but industry has also used ceramic or glass insulating spacers for the same purpose.

Electrode Fabrication

We use a spot welder to fabricate our electrodes. It uses low voltage and high current to weld by the electrical resistance of the metals being bonded, and works quite well with CP titanium.


A spot welder like this is capable of permanently bonding titanium.

After the metal pieces are cut to size, cleaned and dried, we’ll spot weld them together to form our sandwiched anode and cathodes, matching (as best we can) the diagram above.

The length of the tubular titanium leads are determined by subtracting the length of the electrodes from the internal depth of the cell, plus it’s recommended to leave a two inch gap between the electrodes and the bottom of the cell tank (for ample fluid flow). Make sure enough of the top end of the tubular leads is left to more than clear the Kynar compression fittings in the lid of the cell, so they don’t overheat.

We tried the CP titanium solid round rod for pillars between the cathodes but they failed to withstand the spot welding without deforming. We changed to formed, CP titanium sheet metal straps and succeeded in assembling the cathode pair for the LD anode (shown below).


Separate components for the LD electrode set.


LD Anode and Cathodes.


End view of the electrodes (the anode is wrapped with foam to protect it).

We’ve got the electrodes prepared; now we need to set up the cells and run them.

In the next part, we’ll run the cells and show our results, plus discuss further options and possibilities for producing good quality, pyrotechnics grade potassium perchlorate.