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Author: Subject: Thoughts On Anodes
yobbo II
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[*] posted on 12-3-2018 at 19:16

I have been running the above anode for some weeks now. Works perfect.
I hammered the platinum bar so that it has twice the area of its original area and current is run at 3 amps. This makes about 130 grams perchlorate from chlorate per day.

I hope to substitute the Ti with W welding electodes as the W is more OTC. Don't know if it will work or not.
Details below:
Some pictures attached.

Platinum Anode from 1g bullion bar

On the board '' there was described by a poster, PDFBDQ, a way to attach MMO to a piece of Titanium so that the MMO would be completely submerged and therefor no MMO area being used as a current runner and wasting good MMO real estate! This connection was a rivet make from Titanium and worked well, even though the connection was rather sloppy, so long as the connection was underneath the surface of the liquid in the chlorate cell. Having seen this it was decided to try a similar connection between a piece of Platinum bullion and a flat piece of Titanium as a current runner. This allows all of the Platinum to be submerged and therefor almost all of its surface area to be utilized for chlorate or/and perchlorate production.
It would be unrealistic to use a small Pt bullion bar in a cell and expect some of the Pt to be used as a current runner from the anode connection (whatever metal that may be) and the surface of the cell liquid. Most of the bar would be used up and still the connection would be exposed spray/gasses etc. You would need a piece of Pt a few centimeter$ lonĀ£.
A similar electrode is also called the "bi-electrode" as described in Platinum Metals Review 1960, 4 (1) Ti-Pt and Ti-Pt Bi-Electrodes.
A one gram PAMP Suisse bar of Platinum was obtained. It measures 14.7 by 8.9 by 0.36mm, giving a surface area of approx. 2.6cm squared. At one Amp this give a current density on the anode of 385 mA per square cm. which is a reasonable CD. I have seen Platinum run at higher CD's. This gives around 44 grams of Na perchlorate per day (from chlorate) at around 80% CE.
A constant current supply was used for all (one and three Amp) runs.

The Platinum bar is held in a bent piece of flat Ti by a Ti bolt. The cathode is held in place by bolting it to the anode current runner using a piece of perspex as in insulator and spacer which is not visible in the picture. The bolt screws into a hole in the Ti which was threaded using a simple threader.
The cathode in the vicinity of the anode is like a large blunt fishing hook. All Titanium including the bolt is grade one. Grades 2, 3 or 4 would be ok. Grade 5 which contains Aluminium would likely corrode. The weigh of the piece of Platinum was weighed at 0.98 grams using a cheap, two decimal point scales. I guess the scales was out by 0.02 grams?

The electrode was put to the test in a 'jam jar' cell containing dissolved sodium perchlorate (no chlorate or chloride) at one Amp for 15 days. Cell temperature was around 30C and cell Voltage around 6 Volts. There were no noticeable problems or weight loss from the Platinum.
Brown deposit on Pt in the picture is from just after a run in a K perchlorate cell (see below) BTW.

New cell liquid which contained 424 grams sodium chlorate per litre of solution was added to the cell. No chloride. Cell volume was around 360ml giving a total weight of sodium chlorate of around 153 grams. Current efficiency was around 75% when chlorate concentration was sensibly high. Five days later chlorate concentration was measured at 0.5 grams per liter of solution. Platinum seems to be very good at rapidly reducing the chlorate concentration to very low levels. No noticeable weight loss on Pt bar.
The anode makes around 44 grams of Na perchlorate from chlorate per day.

Another cell was started up with 500g/l Na chlorate and run for about 5.5 days. Chlorate at the end of run was measured at 0.08 grams per litre. There was a smell of ozone from the cell at the end of run. No weight loss for the Platinum. The cell pH was not measured.

Potassium Perchlorate cell
Another cell run was performed this time using potassium chlorate as starting material at 168 grams per litre. The cell was kept warm at around 60C using a hot plate as potassium chlorate is not very soluble when temperature is low. CE was lower than Na cells at around 50 to 60%. The formed perchlorate was inclined to accumulate on the anode/cathode electrode and had to be brushed off two or three times.
The cell was run to a point where there would be very little chlorate left in the cell liquor. Serious corrosion of the Titanium current runner going to the Platinum bar occured just below the water line and this caused a deposit of grey Ti compound in the cell as the end of run approached. Something to be watched if running K perchlorate cells but this problem did not occur on the next cell run. The actual cause of this corrosion is unknown. See picture. BTW the Ti in question was not 'heat damaged' as in strontium cell below.
The Pt bar was not effected.

Another K cell was started up similar to the last one. 161 g/l K chlorate. Cell volume 372ml (60g K chlorate total). 60 hours later the cell was stopped. Chlorate (in liquid) was around 1.6 grams per litre. Perchlorate was on the cell bottom. The was a brown deposit, see picture at top, on the Pt which cold oxalic acid did not remove. The serial number on the Pt was getting hard to read and the surface of the Pt was getting a 'scrubbed' look. There was no measurable weight loss on Pt bar with a cheap 2 decimal point scale.

Lithium Cell
Another cell was started using Lithium chloride as the starting material. The chloride was obtained from ceramic grade carbonate + HCl acid. 96.5 grams of Li chloride was dissolved into the cell giving around 261g/l in a 360cc volume. Current was one Amp using a constant current supply. A trace of perchlorate showed up in the cell after some hours but only a trace. Twenty five days later perchlorate stared to form as the chloride level went down to around 25 grams per litre. The chlorate run give around 50% CE. There was no attempt made to control pH. Chlorate making with a small anode like this is very slow. Seven days later the cell was shut down. Chlorate level was measured at around 0.03 grams per litre and chloride level was measured at less than 0.36 grams per litre. The cell contents was heated to around 150C for 6 hours to obtain the anhydrous perchlorate salt which (I believe) in not possible to get without vacuum, so I probably had a mixture of the trihydrate and the anhydrous. Lithium perchlorate is the only perchlorate with a known definite melting point. It does not decompose at its melting point.
Total weight of the perchlorate when it went solid was 217 grams. There was no weight loss on the Pt, it still weighed 0.98 grams.
Modified anode
It was decided to attempt to make the anode larger by hammerng the Pt bar and making it thinner. Pt leaf is made professional by placing the Pt between layers of velum (light leather) and hammering. Two pieces of ordinary leather were obtained and an approx. 250g hammer with one side flat was obtained and hammering began on a solid steel slab with the Pt between the two pieces of leather. The Pt flattened easily enough, its area was increased to twice what is was. The area of the Pt was now 2.62cm squared per side. The anode/cathode assembley was simplified with the platinum now being clamped between two flat pieces of Ti not unlike a pair of pincers with a very broad nose. The Ti bolt (grade one) together with a Ti washer, the Ti with the threaded hole and the Ti current runner was used to do the clamping. Current was run at three Amps, which is a cd of 575 mA per square cm, quite high. The same cathode was used as before. This 3 Amp anode will give around 130 grams sodium perchlorate (from chlorate) per day at 80% CE.

Strontium Cell

A Strontium chlorate/perchlorate cell was set up using Strontium chloride obtained by adding 276 grams pottery grade Sr carbonate to HCl. There was approx. 2 grams insoluble stuff which was filtered out giving a clear solution of 296.3 grams chloride which is 1.87 moles (calculated from carbonate). The purity of carbonate from the ceramics store is not known. It is best to leave some unreacted carbonate behind as metal impurities are inclined to stay behind when this is done. A new 'jam jar' was obtained which contained 770ml solution giving 385 grams chloride per litre.
The anode was run at three Amps using a constant current supply for approx. 15 days. There was a problem with (I presume) insoluble strontium hydroxide building up on the cathode which caused the cell voltage to rise and the current to go to zero. A stirrer bar about one inch long and a magnetic stirrer at 800rmp was used to stop this happening. The temperature of the cell was around 38 centrigrade. pH was controlled be adding 1 or 2 cc of 12% HCl acid to the cell per day. This is very little acid compared to a sodium cell. pH was measured with a pH probe that was calibrated with a buffer solution. Cell pH stayed around 6.8 for the chlorate stage and was at 1.8 at the run end. Acid was not added for the last few days.
The cell ran in the region of 38C. Cell voltage was inclined to move around a bit and varied from 5.5 to 7.5 Volts during the chlorate stage. The cell voltage would start to rise immediately after the stirrer was stopped.
Perchlorate appeared in the cell soon after it was started. I did not measure how much but it was a significant amount judging by the addition of methylene blue to a cell sample. 156 hours later (6.5 days) or 468 Amp-hours later perchlorate started to form in earnest. Chloride concentration was around 200 g/l at this stage, seems very high.
Acid still needed to be added to cell for 5 more days to keep pH around 6.8. At this stage (day 12) there was a very 'mild' smell coming from the cell which indicates the chlorate stage is over. Chloride concentration on day 12 was 44g/l with 7.7 Volts accross cell and a pH of 6.7.
At the start of the run there was a ss bolt holding the cathode just above water line which had corroded and discoloured the solution. This discolouration had now deposited onto the side of the jar leaving the liquid clear. It was decided to empty the container and wash the deposit off the jar inside. This was done using a tooth brush and the anode/cathode was also washed and scrubbed with the tooth brush. When the cell was started again with the stirrer as before the voltage accross the cell started to rise and the current went to zero. The rpm on the stirrer had to be increased to 1100rmp to keep cell current going at 8.6 volts. The voltage accross the cell reduced after a while and the stirrer was lowered back to 800rmp. I think this problem was caused by the cell cooling down and when it got heated up again it ran in its usual fashion as something similar happened a few days later. The solubility of the strontium hydroxide is greater in the warm cell and, I guess, builds up on the cathode less.
On day 12 the cell contents went grey as there was Titanium corrosion happening. It happened on the current runner as outlined in the picture. It was not the usuall pitting corrosion that occures but a much larger area of the Ti was etched. pH of the cell was measured at 6.2. This piece of Ti (Grade one) was subjected to high heat sometime in its past that made it very brittle. When placed in a vice and struck with a hammer it would snap as opposed to bend. Perhaps its corrosion resistance was compromised? The other pieces of Ti (not high heat damaged) did not corrode. The cell at this point had sizable concentrations of both chloride and chlorate which is a potential region for Pt to erode, and perhaps Ti too! (as described elsewhere).
The cell was stopped, contents filtered and the anode/cathode washed and the cell started again. There was no more serious corrosion problems. The cell had to be warmed up using the hot plate to stop the voltage rising too much and causing the current to go to zero even at 1100 rpm (up from 800). The cell ran OK but it was noticed that the rpm of the stirrer had to be kept at the increased rate of 1100 rmp to stop the voltage from rising too much accross the cell. This problem stopped when the cell warmed up (hydroxide has greater solubility?). The actual junction between the Ti and Pt was not the problem because when anode and cathode where shorted together the current ran at 3 Amps.
Day 13, chlorate was measured at 161 g/l. Day 14, chlorate was measured at 56g/l and the chloride was at 12g/l.
The solution was getting a bit cloudy (corrosion?) with the pH at 1.8. The voltage accross the cell was 8 volts with the cell at 38C and decreased to 6.4 volts When the cell was warmed to 56C using the hot plate (cc of 3 Amps and 1100 rpm). The end of day 15 saw chloride at 4.7g/l and chlorate at 0.3g/l. The chloride seems to be higher that the chlorate? There is small amount of white Ti corrosion compound visible between the Ti and the perspex piece holding anode and cathode apart but nothing too serious.
The Pt piece was removed and weight at 0.97 grams, down from 0.98 grams. Some Pt erosion it would seem. It is hard to say as the scales I have are just too crude for the job. A three or four place scale would be required. When the scales was taken to a warmer place it was inclined to read 0.98 again.

The cell was let settle for three days to allow cloudyness to deposit on cell bottom. Clear liquid was decanted off and the rest filtered. Liquid was dried off by placing the cell contents in a flat glass tray in an oven and heating to 170C for about 24 hours. It was very difficult to get rid of the water. A total of 474 grams (1.65 moles) of Sr perchlorate was obtained, there should be 535g (1.87 moles)). Some grams product would have been lost when doing titrations etc. The amount of product does not correspond to the amount of starting Sr carbonate. There is approx. 60 grams missing? I have no idea where it could have gone or what error was made. Total Amp-hours into cell was 1049Ah which is 39.14 moles of electrons. Having 1.65 moles of product gives 1.65 x 2 x 8 = 14.952 moles of electrons needed, giving a current efficiency of 56.6 percent.

A larger cathode could be used to stop the low solubiltiy of strontium hydroxide causing cell voltage problems.
To end Ti corrosion problems a more 'valve' valve metal could be used like Niobium. This will cost more but if the cell is being stirred the anode only needs to go below the surface of the electrolyte and therefor you would need very little valve metal.

Barium Cell
Note that barium is toxic. Barium perchlorate can be useful for making perchloric acid and other perchlorate salts as the sulphate is insoluble. To make perchloric acid you just add sulphuric acid and remove insoluble Barium sulphate.
A barium chlorate/perchlorate cell was started up. Chloride was obtained from 500g ceramics store carbonate + HCl acid. Not all of the carbonate would dissolve with perhaps 10% left over. The mixture was left overnight to get as much to dissolve as as possible. Perhaps heating might have helped? The purity of the carbonate is unknown. HCl was 12% concrete cleaner (no additives). It is best to leave some unreacted carbonate in the system as this has the effect of removing metal impurities.
The cell and anode/cathode was the same as the last cell above. Current was 3 Amps, constant current supply, with V at 5.76 and temperature at 38C. Stirring was not required but was used anyways. The solubility of barium hydroxide is higher that strontium hydroxide. pH control was attempted and about 2cc 12% HCl was added per day to keep pH around 6.2 during chlorate stage. The pH of the cell at shut down was around 2. The cell was cloudy from the start due to some carbonate that was not properly removed and turned a nasty brown colour after a few days. The cell was shut down for two days to allow the cloudyness to settle and the clear liquid was decanted off.
Cell restarted and was run until chlorate concentration was 0.76g/l. There was a black discolouration in the cell at the end of the run together (after black stuff had settles) with a very slight haze of gray (titanium erosion product?). The cell was let settle for about a week as it took that long for the gray to settle to the bottom and the clear liquid was decanted off. The solution was placed in a flat glass baking tray in an oven and dried at 130C for about six hours. It was much easier to dry than the Sr perchlorate above. Total weight of product was 533g or 1.585 moles.
Total Amp-hours into cell was 1191Ah or 44.44 moles of electrons.
The current efficiency (ce) was 57%. Final weight of Platinum bar was now 0.95, down from 0.97 grams so there was some loss of Platinum. Thats 37.5 grams of Platinum per ton of perchlorate produced. I have seen figures for platinum lost (sodium perchlorate production) of 2 to 7 grams per ton.
Sodium Perchlorate cell using 'poor' starting solution
The jam jar cell was started up again using a solution containing 95g/l sodium chloride and 496g/l sodium chlorate and around 600ml. This is not a sensible starting solution for Platinum anode perchlorate cells as chloride causes anode erosion. This cell could be called a chlorate cell for the first day or two I suppose. Stirring was not used as the anode was close to the jar bottom and bubbles kept all of the solution moving.
No pH control was attempted. The cell was run at 3 Amps for 3 days and chlorate level was above 15g/l. The pH of the cell was measured at around day 4 and found to be high at around 9. Cell contents were titrated for chlorate level on the seventh day of operation and found to be 5.14g/l Twenty four hours later the chlorate concentration was below 1g/l. The pH at this stage was measure with a high quality probe at a value of 11.5 but you can measure the pH OK using pH paper (only when cells have high pH it would seem, see cell No. 2 below) as there is no bleaching effect as you have in a chlorate cell due to the presence of hypochlorite (bleach!).
Cell contents was evaporated and dried at around 150C for some hours. Total product (presume anhydrous) was 446grams perchlorate. Total Amp-hours into cell was 576Ah AFAICR.

Two more sodium cells
No. 1
Two cells were run using the same starting solution as above, 97g/l chloride and 496g/l chlorate. Cells contained 770ml liquid. Current was 3 Amps. Stirring was used. Chloride was not monitored except to note what the starting concentration was. No pH control was used for the first cell. (Cell No. 2 had acid added)
pH when the chloride became low (cell became a perchlorate cell) was around 9. At 360g/l chlorate, pH was 9.5. Current efficiency was measured at 94% when chlorate concentration was between 360 and 188 grams per litre.
When chlorate concentration was between 188 and 53g/l CE was around 70% with pH around 9.
When chlorate concentration was between 53 and 2.3g/l CE was around 24.5% with pH around 9.6.
Cell was stopped around 14 hours later with chlorate concentration around 0.11g/l.
The cell was run for a total of 7 days.
No. 2
The next cell was the same as above but 12% HCl acid was added to keep pH at around 7 or so for the first few days (chlorate stage). pH control was a bit hap-hazzard. Stirring was used. The pH of the cell was measure at the start and was around 9.8. 2cc acid was added and cell went to pH 7. A few hours later the cell was at pH 9 and it took 19cc of acid to take the pH to 6.8. The next day 7cc of acid was added to keep cell around a pH of 6.8. Next day 7cc acid added. Next day 4cc added very early in the day with no more acid additions needed to keep pH around 6.8. pH drifted down slightly later in the day and chlorate concentration was measured at 400g/l. Later in the day chlorate concentration was at 349g/l. The cell had now ran for 78 hours, 234 Amper-hours had passed in.
When the chlorate concentration was betweeen 349 and 184g/l the CE was 86% with pH around 6.8.
When chlorate concentration was between 184 and 8.8g/l the CE was close to 100% with pH around 4.7. (suspiciously high CE!)
Twelve hours later the chlorate concentration was 0.53g/l with pH now at 1.7. You cannot use pH paper for to measure this low pH for
some reason or other. It gives a false reading of neutral.
This cell had run for 5.5 days to take chlorate concentration to a low level. The last cell ran for six days to take chlorate concentration to a low level.
There was no sign of titanium erosion in the last three cells. All liquor at end of runs was clear.
The Platinium bar now weighed in at 0.91 grams, down from 0.95 three cells/batches ago. That's approx. three batches of 440 grams sodium perchlorate made from a 'not-to-be-recommended' starting solution taken all the way to very low chlorate levels. This equated to 30.3 grams Pt per ton of Na Perk. produced. Ferocious erosion compared to commercial production cells. The starting solution contained chloride. Making perchlorate with chloride in the cell is erosive to platinum according to various sources. Also keeping chlorate concentration high in the cell will give greater CE and probably reduce Pt wear. Using the Pt to reduce the chlorate concentration to very low levels (chlorate scavenging) as opposed to letting the Na Perk. crystallize out of solution (my adding chlorate to cell as the cell progresses) saves lots of work and is easy to do.

corr_pt.jpg - 16kBdisassam.jpg - 82kBkp_on_anode.jpg - 47kBetched_sr.JPG - 54kB
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