387 replies to this topic

[raketpeter]

Raketpeter what voltage do you run your 3.3amp cell?..Does your perc perform well with making colours?...how many times do you have to recrystalize?

Alany mentions his first batch was not as good as his commercial  perc(obviously he can purify the product more)..Also what size PT anode are you using and what method of control are you using for current..

I am intrested in what that Black coating is on alany's Pt anode  very wierd?.. i have made small test batch's using my Pt Anode mesh and had no black coating..

.I have nearly made all my Lead Dioxide anodes...

My first Graphite anodes were 13 mm( 1.5mm PbO2 coating) diameter 15 cm long but these are made to use a current of about 10 amps each (Surface area approx 49 cm x 200 milliamps)..

I made these small electrodes because from what i have read passing large currents through a big anode tend to over heat the connections..etc..

    So i thought make small electrodes and share the current between them, so each electrode only has to take a small current..
From my experiments these GSLD anodes can easily take 10 amps so i scaled up my next batch and Now the ones i will be using are much bigger  ..

They are 34mm Diameter( 1mm PbO2) 15 cm long can take 25 amps (128 cm Surface area x 200 milliamps)..
I will post some pictures later .. very rare to see PbO2 anodes on the Net?..i have read lots but no photos ..

The actual coating on the rods is superb.. very smooth no pits or pinholes..much easier than i thought to make them..
The secret in making them is do it properly..I have read lots of people on the Rec.pyro ..were there PbO2 anode peel or dont last long..Also use Graphite not Carbon!! i tried Carbon gouging rods..Rubbish... dont bodge.. get Graphite...

The end result is well worth it...Rock hard Black crystaline PbO2 coating Sounds like ceramic when you tap it..

I am running in each electrode at about 25 amps in a Brine solution to test each one.. for a week or two .this also serves to leech out any chemicals that may have been absorbed by the PbO2 coating ..
The best test for the Anode is when the Chloride concentration gets really low even a Pt electrode dont like low levels of Chloride..

The only problem i have is when adding PbO to lower my Ph of my plating tank .. even though i have added lots of excess PbO and have left it stirring overnight at 60 centigrade.. it never reaches PH 7..?.. baffled me..
Also when PbO is added the colour of the solution is not the same pale blue as it was to start.. this worried me until i added a small amount of Nitric acid.. the colour then changed Back from a greenish blue to a nice pale blue...

To be continued....

Sorry for taking a while to respond - was out of town.
My cell runs at a voltage between [5.25;5.55]V.
The overvoltage for my Pt anode is higher than for PbO2 ditto.
The anode itself is essentially a Pt wire - about 100cm long and 0.4mm in diameter.

Haven't used the product for making colours (yet).
I have done a fair bit of experimentation with (re)crystallization and in short - I think it's a pain:
You must crystallize at minimum 52 deg C in order for nice crystals of anhydrous Perc. to form. Lower temperatures yields the mono- (or di-) hydrate which drains the mother liqour very poorly.
I have used centrifugation to separate the fluid (which is recyc'ed) from the anhydrous crystals. Works well - but VERY labour intensive.
Beware - product is LOST when you boil to concentrate to create the supersaturated solution for crystalization - losses are SIGNIFICANT - try placing a propane flame in the "steam" leaving your boiling vessel and the sodium colouration of the flame will demonstrate my point.

Bottom line - I'm dropping the step of crystallization of the sodium salt.

Btw. veeery nice work on your PbO2 sasman - congrat's!

Peter

[alany]

The crystalisation at an elevated temperature to avoid occluded water only applies to Ammonium Perchlorate. Potassium Perchlorate has no hydrates and is quite trivial to seperate thanks to its very low solubility. It crystalises out so fine and dries so well you almost don't need to mill it. If you grow it very slowly by controlled cooling it forms long thin needles that form a loose mat in the bottom of the vessel - but to achieve that I had to cool it over 5 hours.

As an experiment last night I seperated a mixture of Sodium Chloride, Sodium Chlorate, Sodium Perchlorate and Potassium Perchlorate by recrystalisation *alone*. It took three recrystalisations, but I got very pure Potassium Perchlorate out with no measurable Chloride or Chlorate. It is easier (and safer) to destroy the Chlorate, but it is quite feasible to get the Chloride, Sodium and Chlorate levels very low by repeated recrystalisation and loose no intermediate Chlorate.

Loss due to misting is not significant in my experence. I use boiling chips so it doesn't bump and it evapourates quite nicely leaving little if any fall out around the hotplate. It might colour the torch flame, but what's a few mg? Also you might not want to have a flame near an acidified electrolyte for Chlorate destruction, Chlorine Dioxide is very violently explosive.

[raketpeter]

I was referring to the crystallisation of the sodium salt only this salt is hard to crystallise out. I disagree that " it evapourates quite nicely" - I had to make a special concentrator for this purpose. Problems include: Boiling point is about 145 dec C (forget about std. hotmelt glue, polystyrene insulation, etc.), a thin crust of crystals from on the surface effectively preventing evaporation.

Regarding loss I estimate I lost some two kilograms of product (out of about 15kg total) due to aerosol losses. Also It does not take a flame to see that product is being lost - you can SMELL the perchlorate in the air (don't inhale ).

[alany]

Yes Sodium Perchlorate is very soluble and likes to crust on top of a saturated solution, you can make a almost syrupy yellow slime out of it before it will crystalise. I think it is best not to try an extract it by evapouration to dryness, its solubility slope is steep enough to get a 20-40% yield by cooling if you really want it.

I can't think of a reason why I'd want solid Sodium Perchlorate anyway? Sodium Chlorate, sure it is quite useful to charge your perchlorate cell with, but the Perchlorate is so deliquescent and essentially useless for pyro, why would you bother extracting it from the liquor?

[gilbert pinkston]

NaClO4 crystalizing out of a warm gilbert cell (half gallon size) about two weeks running time
http://eseephoto.com...9294_189348.jpg
more can be had by sticking it in the freezer
it may be a good way to separate O3 from O4 for pyrification
the liquid of course is returned to the cell for futher O3 to O4 electrolysis late in the next run

[alany]

Did you know that a "gilbert cell" is a kind of double balanced mixer topology formed from six identical transistors? It was invented by Barrie Gilbert at Analog Devices back in the late 1960s, since then many Si and GaAs implementations have been founded, and devices that operate into the SHF region are available.

[gilbert pinkston]

yeah i like em that's why i added (electrolytic) in an earlier post i use several in the form of the MC1496 in my tranciever that was a popular ic in the 70s and my rig is old technology

[sasman]

Alany i got my graphite from http://www.olmec.co.uk/ . They have a minium order of 35 GBP..

I started making another electrode to day..but after about 15 minutes we had a power cut ..Now once you have started plating PbO2 you cannot stop the current,if you do restart the current the deposit may not adhere well..So i took it out of its holder to remove the coating .

I placed it in my lathe and started to sand it down with emerypaper( yes i was wearing a safety mask)..Usually graphite sands down very rapidly even with 1000 grit paper..There was no way would the emerypaper touch this leaddioxide.. i tried 240 ,120,80,60 grit it just didnt make a mark on it!!..All it did was polish the surface.. i was gobsmaked as to how hard the coating was ..I ended up having to use a File to get the coating off..even then i had to use the corner of the file..the flat part of the file wouldnt touch it.

The coating can't have been very thick i estimate a few thousands of an inch..This little lesson gives me more confidence that my GSLD anode's are built to last!! ..

[alany]

You could probably heat the electrode to above 300 C and decompose the lead peroxide to make it easier to remove? How much damage that might do to the underlying graphite I am not sure.

[sasman]

I have read lots about making Anodes and making ClO3 ClO4 etc... but very little on the destruction of Chlorate..Those members who make Perc how do you destroy the ClO3?...
I am intrested in the use of Sulfites..I would rather avoid boiling the solution with HCl.. i can find no reference on how much sulfite,acid etc.. is needed to destroy say 10 g of Chlorate?. any body know?..

cheers

[alany]

According to that Geocities site the sodium metabisulfite reaction is:

3(Na2S2O5) + H2O + 2(NaClO3) => 3(Na2SO4) + 3(H2SO4) + 2(NaCl)

Which means you need at least 1.5 moles of metabisulfite for each mole of chlorate:

Na2S2O5 190.106
NaClO3 106.441

So 2.67 times as much metabisulfite by mass, 26-30 g should do it for 10 g of chlorate.

The lowered pH really helps I don't recommend you try sulfite treatment at elevated pH, it probably won't be very effective. The exact amount of chlorate is typically not known so acidifying and then adding sodium metabisulfite until the liquor tests free of chlorate is probably the safest. The acidification alone will take out the bulk of the chlorate - well that is my experence anyway, but the sulfite is more rapid and agressive at cleaning up the last of it.

Edit:

Before I tried it I was a bit worried, but I found the process quite straight forward. Having the Indigo Carmine test available really boosts your confidence, especially if you have tested it carefully with known solutions. Of course a pH meter is very handy too.

Edited by alany, 01 April 2005 - 12:54 AM.

[sasman]

Thanks for that alany..I dont want to add too much excess sulphite , i dont want contaminate the final product to much..

? but you will NEVER get VERY PURE product. The connection to the anode will corrode ? the dust in the area with contaminates the cell etc, etc. If you get 94-95% pure product with no chlorate then consider yourself a happy men.

Now if you look Patent 2,392,769 it mentions the end result of using SO2 to destroy the chlorate the final dried product contained the following ..There is no mention of fluoride contamination.. which i will be using about 2g litre..


Sodium Perchlorate 98.70 %
Sodium Sulfate 1.00 %
Sodium chloride 0.04 %
Sodium Carbonate 0.32 %

Now if i produce NaClO4 solution at near that 98% or even 95% worst case.. and add pure 99% KCl and the precipitated KClO4 is washed with ice water..Then i would have thought due to the low solubility of KClO4 then the final product should be very very pure?..Most of the other dissolved impurities have a far higher solubilty than KClO4..so most of the contaminants would remain in solution?.. leaving very pure product?..

I have ran my 36 mm GSLD anodes now for over 2 weeks and there are no signs of corrosion. I know its not very long but im sure there ok so when i get my bigger Titanium Cathodes i will be able to put them all in a big cell and put 125 + amps through it and see what i get..Not sure to use a sealed cell design or open cell.. i like the evoporation losses i can top up with concentrated chloride solution..

I will use Deionised water for making the electolyte.. i always thought Tap water was pretty pure but i noticed when i washed one of my freshly etched anodes(etched in NaOH) directly with Tap water i could see a white cloudy precipitate form.. this does not happen with Deionised water...I assume it might be Calcium Hyroxide? ppte..

Sofar everything is going pretty smoothly .. so i expect something to go wrong soon.. something always pops up and tries to knock you down. i am starting to get excited..Once i have sorted this liitle Perc Problem out i can get back to making some pyro.. Not made any since the 5th..

[alany]

It is fairly easy to get quite pure Potassium Perchlorate out in the first extraction. Its low solubility makes recrystalisation a larger scale operation than for Potassium Chlorate, you need big beakers and longer boil times, but after two cycles of recrystalisation your product will be very pure.

I have no practical way to essay the exact purity, except maybe a careful gravimetric oxygen determination. It doesn't precipitate AgCl from AgNO3 solution, doesn't discolour boiling acidic Indigo Carmine and flame tests just as purple as my twice recrystalised KNO3. That's pure enough for practical purposes I think.

You do loose a little in the recrystalisations, maybe 10 grams per litre. You can boil down the solutions and return them to the mother liquor if you want, but I generally don't. I am a little concerned about impurity build-up in the mother liquor.

I've been thinking over the DI vrs tap Water decision myself. DIW is about $1 AUD litre unless you make it yourself - a high capacity still or deioniser is yet another expense in an already expensive project and it will get used very little to justify the expense. Tap water seems to work fine, but I've been doing my top-ups using DIW to limit the concentration of impurities in the liquor. The local tap water is pH about 6, contains significant Chlorine and some Calcium. I could take out the Calcium with Sulfates, and then take out the Sulfates with Barium Chloride or something. I think the milkyness I saw from the chlorate destruction was probably Calcium Sulfate coming out. It didn't seem to otherwise effect the process. I think I'll run my big cell on tap water to start with, if the Calcium and other crap in it proves to be a problem then I'll try DIW instead.

I like running the cell refluxing, it cuts down on level changes and reduces the need for top-ups. I don't bother cooling the condenser, so it isn't 100% efficient, but it works fairly well and requires no additional water or energy. The reaction itself consumes about 165 ml of water per kg of (sodium) perchlorate and produces at least 91 litres of hydrogen.

Edit:

I know what you mean about getting back to Pyro. I've made very little since I started this (per)chlorate adventure, just some rockets and little tuning tests.

Edited by alany, 03 April 2005 - 05:41 AM.

[sasman]

You can get Deionised water at about ?2.50 for 5 litres..from car spares shop i think thats pretty cheap..if i get it from a lab supplier it way more costly..

I got up at around 5 am this morning to make another anode.. ..I like to keep an eye on the cell while it spinning away at 1400rpm..I made a few small alterations to the plating tank .
1) i added another copper cathode 2) i placed the cathodes on either side of the Anode ,the anode to cathode gap was about 7 cm..

All the other anodes were made using one copper cathode bent in a U shape and the anode was placed in the centre of the U this however made the bottom of the U very close to the anode.Now beacause it was closer at the bottom there is a tendency to for the Lead dioxide to grow faster.. which caused a slight bulging at the end..

So i made the Graphite anode more of a rounded V shape rather than a smooth U shape...

I wasnt sure how good the throwing power of the plating solution was but im very happy with the results..

New shaped anode

There is no noticable bulge but the centre of the anode was approx .5 mm thinner in the middle than at the ends... this did not happen on my other anodes..But i am fairly sure it was due to the bent cathodes( i bent the cathodes so that they would grip the Tank better).. my original cathodes were dead straight..

The anode weight was 209.3 g before plating and was 495.7 g after plating
thats about 286g of PbO2..The coating is about 2mm thick,Length of coating approx 13 cm overall Diameter 36 mm so its effective Surface area is 135cm which equals approx 27 amps..

I used approx 11 amps at 5 v but as the Nitric acid levels built up the current goes up to about 14 to 15 amps at 60 Centigrade.

Plating was for approx 12 hours
Which works out at about 150 amp hours
I made another anode on saturday so the palting solution was only allowed to stand for 2 or 3 days which may not be enough for any nitrites to oxidise?..I have read that only a 6% nitrite level can make the cell efficiency run at 20% instead of the near 100% .So i am thinking of adding a bit of hydrogen peroxide to oxidise the nitrites back to nitrates..

I only have one more Big anode to make and hopefully my cell will be up and running next week..

[Pretty green flames]

Finally got my cell up and running but there are strange things happening in it.

I have been running my cell for about 25 hours right now.
On the 17th i ran the cell for about 12hours then left the cell out for the night, on the 18th i got some cube like crystals (Chlorate maybe) then i ran it the whole day yesterday and then left it overnight (again), this morning i got some needle shaped crystals on the electrodes and on the bottom of the cell (perchlorate ???? )

what could it be.

EDIT: I used saturated KCl solution for the electrolyte.

Edited by Pretty green flames, 19 April 2005 - 07:17 AM.