The selection of materials from which certain parts of the cells were made, is also very important. Thereby, maybe the most important parts are the anodes. They need to be resistant to chlorine which is generated on the surface of the anodes. The almost ideal material for the anodes is platinum, which corrodes at a very low rate (compared to the graphite, about which I will say more later). Thanks to the negligible corrosion of platinum, at the end of the reaction one gets a solution with very little impurities, and because of that, the further refinement of the electrolyte is greatly simplified. The only drawback of platinum is its very high price, which is the only reason why I didn't use this material. There are various alternatives to this material. The most well known are lead(IV) oxide and graphite. The first of the mentioned is also used in lead batteries, and in this case, it is useful because it is relatively ressistant to corrosion, even when the eleytrolysis is done at higher temperatures (which increases the yield of the electrolysis). Because of the unavailability of anodes made of this material, I used graphite which was the most simple solution at the time. Graphite is cheap and can easily be found. Unfortunately, it has a few drawbacks - it is not completely resistant to the conditions in the cells during electrolysis, so it corrodes at a relatively high rate. That creates an additional problem, it pollutes the electrolyte, and that can create even more complications later, so it is necessary to filter the electrolyte after the process is complete. In spite of the mentioned drawbacks, by keeping the conditions as close to ideal, the corrosion of the graphite anodes can be reduced to a minimum.
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After 160 hours have passed since the start of the electrolysis, the process is finished. The electrolyte is filtered a few times with the help of a medicinal gauze, in order to filter out larger unwanted particles. After that, the electrolyte was further filtered through cotton wool placed in a bottleneck (of a larger two-liter bottle) that was cut off. Gradually, by repetitive filtration, a yellow colored clear solution was obtained. Since the filtration was progressing at a very slow rate, I took a smaller amount of the already filtered solution, and the rest of the solution was slowly filtered for a few more hours. In the filtered solution, along with sodium chlorate, there was also some sodium hypochlorite. Because of that, the solution was heated until the boiling point was reached, and was kept at that temperature for about 15 minutes. Thanks to this step, all the sodium hypochlorite converted to more sodium chlorate (which is also the basis of the hypochlorite method of chlorate synthesis). After heating for 15 minutes, I checked the pH of the solution, and added a bit of sodium hydroxide solution so that the pH would get close to 8. If one assumes that all the NaCl passed into NaClO3, that would mean that from the starting 350 grams of sodium chloride, one could get around 627 grams of sodium chlorate, which is only possible in theory (the yield of this type of homemade cells is mostly around 50%). Although the yield of the process was surely much less than 100%, I calculated the amount of needed potassium chloride for the reaction of the ion exchange by taking into account the theoretical yield of 100%. That way, I was sure that all of the sodium chlorate passed into potassium chlorate. However, some of the potassium chloride remained unused (which is not a problem because thanks to its high solubility, it remains in the solution and doesn't cause problems when extracting potassium chlorate).
Because of that, graphite can still be used with relatively good results. In addition, as I already mentioned, another advantage of this material is its low price. In this experiment I used graphite electrodes that are normally used for welding, and can be found in shops that sell welding equipment. These electrodes were covered with a thin layer of copper, but it was fairly simple to peel this copper off. After that, the anodes were shortened a bit, and were placed in the holes that were made through the lids of the cells. As for the cathodes, one can use a wide range of materials, because to a certain extent, they are protected against the corrosion caused by the anodes, and that allows a much wider choice of materials. A good material is stainless steel which is cheap and can be found easily. This, among other things, was also the reason I used it in this experiment. All other parts of the electrolytic cells were home made, and with these parts, care was also taken about the materials that were used - the anode fixture was made of polypropylene (PP), the gas exit tubes were made of glass, and most of the bolts were also made from stainless steel. The rubber insulation material is also resistant to corrosion.