Anti cake causing problems

[NeighborJ]

I'm not exactly sure where to post this but since most of my problems now are revolving around whistle rockets, it is getting posted here.

The initial problem started with a new batch of whistle. My motors were suddenly weaker than previous batches and the only change I had made was to a perc with anti cake. This wasn't a big problem because all I needed to do was use a longer spindle and I had just as much thrust and with a longer burn. The adjustments were made and life continued as normal. But today I pulled out what was left of that batch and made three 1# motors. Every one of them catoed. It had been evident while pressing those motors that moisture had made its way into the mix, and had evaporated. I believe the anti cake was buffering the catalyst from doing it's job and when the moisture got into the mix it allowed the catalyst to make full contact with the perc. This fuel is suddenly just as reactive as the original fuel I was using.

So my question is can the caking agent be removed so I can enjoy consistent rockets once more? It seems to me that it could be dissolved in water, decanted off and dried before I make any new batches of fuel. What is anti cake made of? How much should have been needed to coat x amount of 325 mesh perc? Is there a proper method for removing it? Any ideas or experiences are welcome.

[DavidF]

NeighborJ, I have only used homemade, quite pure perc. I initially had many CATOs with all my whistle rockets on anything longer than anemic tooling. This led me to think that part of the reason for the success of D. Thames' Super Whistle Fuel was the inhibiting effect of the anti-cake in the HP-140 spec'd in the formula. I think the anti-cake has a smoothing effect on the burn. But I don't know that for a fact or anything. Here's an old paper that addresses your purity concerns, at least somewhat.

http://www.pyrobin.com/files/perchloratenotes.pdf

[ddewees]

http://2.bp.blogspot.com/-q2j0V-lXEOA/TdPSgnhuieI/AAAAAAAAAao/kgdhMsVukJU/s1600/cake.jpg

[NeighborJ]

DavidF I agree with you 100% about that smoothing effect you spoke of. I made some insane motors with and without cat, all worked awesome with the anti cake. It would seem that I could use almost any length spindle I desired without Catos.I just want some reliability, the anti cake is still in the mix but it is not insulating the perc any longer. This wet then dried mix is only working with the original short spindle. So it could be as simple as wetting the entire batch of perc then letting it dry. This should give me consistency. I thought something seemed wrong on Saturday when my uncatalyzed whistles sounded like a long-winded ass blast, and my 2oz cat rockets way over lifted their 3" ball shells. The fuel was wet. This could be the reason for many people's Catos but it's blamed on anything else.

I will do some more experimenting with hot vacuum filtered perc and only wetted perc I have a feeling they will perform very close to each other. Thanks for the linc.

[NeighborJ]

OK I admittedly have no idea what I am doing with this filtering process but I don't think I am supposed to get two separate layers of material from the filtered solution.

When I heat the solution while stirring I get a foamy frothy layer on top of the water. I skimmed this waxy material off before filtering. Then poured the 212f solution thru the filter and found most of the material fills the filter and plugged it up immediately. The solution recovered once again forms a waxy layer on top of the solution in the fridge and the perc on the bottom is a very small amount likely 15% of the original perc weight. The bulk of the material is caught in the filter. I plan on trying to dissolve all material floating on top and caught in the filter and try to get it to pass the filter again.

I just don't think it should have two different layers. I'm questioning everything about this process and don't have much time to fool with failed experiments while working 70 hrs a week. It seems either the anti cake is a wax or I'm just doing something way wrong here. When my small amount of recovered perc is dry, I will test it. It seems to me that I need to use a solvent of some kind to remove this waxy stuff.

[DavidF]

I am only saying this from the perspective of the teenage boy I was when I used to grow crystals, not as any kind of authority. I found that when you crystallize something from a dirty solution, the crystals are clean. The 'crap' in the solution sits on top of the clean crystals. If my logic is right, you should be able to make a supersaturated perchlorate solution with boiling water, let it cool to almost ice cold, remove the crystalline mass, rinse it briefly in ice water, and have almost all of the pure perchlorate.

 

I posted the link because it addressed the impurities that can be found in potassium perchlorate. The method of separating those impurities, I dunno about. A highly respected pyro did it that way, so I thought he knew something I didn't. Personally (as a non-chemist) I wouldn't do it his way. Maybe Mumbles has a pointer or two for us on it?

 

EDIT: when I say 'dirty solution', I mean a solution that is 'dirty' with insolubles.

Edited September 26, 2016 by DavidF

[Mumbles]

My first inclination would be to investigate your solvent for making whistle mix. It could be wet or have some lower volatility components in it. Either one would slow the evaporation past where it seems dry or would normally be dry with typical solvents.

 

Anti-cake can be removed, but it helps to know what it is first. Most typical anti-cakes are insoluble in water, so they can be removed by recrystallization. A bit of a pro tip with regard to filtering fine particulates by the way. Try using celite on top of the filter paper. It helps catch stuff and prevent it from clogging the filter. If the top gets "clogged" it can be gently scraped or stirred to expose a "fresh" surface.

 

Based on Eric's testing I did some testing of my own actually for sodium and calcium contamination. I was more concerned with color purity than rocket performance. He gave me samples of a number of perchlorates, as well as some of the alleged large amount of insoluble mass. All I can say with regard to that, is that when I did it there wasn't much if any insoluble portion, though I was working with fairly low concentrations. Unfortunately I only got reliable data for sodium concentration of the perc. This was about 8 years ago, so I don't recall the issue with calcium, but it was an instrumental or calibration issue. These numbers come from an ICP-AES instrument. I also forgot the domestic material and insoluble material at home that day, so I don't have data for those either, which probably would have been the most telling. The moral of the story is that all the available perc is fine with regard to sodium contamination at least.

 

KClO4 Std Chinese - 1.16ppm Na 0.116 mass %

KClO4 Spanish - 1.29ppm Na 0.129%

KClO4 Swedish 1 - 0.64ppm Na 0.064%

KClO4 Swedish 2 - 1.02ppm Na 0.102%

KClO4 Taiwan - 3.19ppm Na 0.319%

KClO4 High Purity Chinese (HP-140) - 1.14ppm Na 0.114%

Sr(NO3)2 (Service Chemical) 2.48ppm Na 0.248%

Sr(NO3)2 (Barium & Chemicals) 0.57ppm Na 0.057%

Ba(NO3)2 (Service Chemical) 0.28ppm Na 0.028%

Ba(NO3)2 (Barium & Chemicals) 0.21ppm Na 0.021%

I was able to analyze some barium and strontium carbonates for calcium carbonate concentration and came up with around 0.3% for standard grade ceramic stuff or the material from Service Chemical (likely the same general source), and again Barium & Chemicals material was notably better, around 0.06-0.08%

[Arthur]

I used to think "anticake" was a fumed silica based product. As to origin of perc, I once saw a bag in a factory, the outer bag was labelled in Spanish (supplier of the perc) but the inner bag had Mandarin characters on the label -so I guess that Spanish perc is probably Chinese perc in disguise.

Edited September 26, 2016 by Arthur

[NeighborJ]

Without going into details about my methods of discovery, I can safely say the problems I am having are caused by the anti cake for sure and not contaminants or moisture in my acetone. It seems to encapsulate the perc grains causing them to be less reactive. The perc itself is not of questionable purity, 99.2%. The whole purpose of these questions are to discover what the anti cake is and utilize the best method to remove it. Without a real lab, I have only my five senses and ingenuity to determine what it is. So what I can determine so far is that it is much lighter than water and is insoluble. It can be removed by floating it off in water however it carries with it much of the encapsulated perc. The recrysyalization method will unlock most of it but filtering it has been a problem and will plug even a 20 mesh screen due to its waxy nature.

I had hoped someone here had run into this and would have answers already worked out.

Edited September 26, 2016 by NeighborJ

[Arthur]

Cab-O-Sil is chemically known as fumed silica or SiO2. Is one of the anticake agents.

[Mumbles]

A clarification from my results from before. 1000ppm KClO4 solutions were tested, which is how the mass results were calcuated. Also this particular batch of Spanish perc, from NitroParis, was actually from Brazil. Chino or Chico brand IIRC. It came from Firefox, but I know the original importer of this material.

 

Have you tried asking the supplier what anti-cake is in the product? If they don't know they might be able to find out for you. The 99.2% (alleged) purity is the standard chinese green drum stuff for anyone curious.

[NeighborJ]

OK I think I've finally made some headway on removing the anti-cake. I believe I should have described the texture of the anti cake as more of a soapy lather. I skipped the hot filter process and went directly to the cold wash. I kept flushing until the floating residue stopped appearing in the batch. It took a lot of washes but I believe I got most of it out. I'm still waiting to hear from the supplier to find out what it is. Tomorrow I plan on doing the hot filter to the washed perc. This time I don't foresee any unusual problems.

[Sparx88]

I get this issue with kno3 I use. I only put up with it because it's local and cheap. Heating a saturated solution slowly will float some of it and whatever else, skim it off. Boil down a bit and re-crystal at room temp nice and slow. Check back after 12 hours and you should have skyscrapers forming nice. At the bottom will be the remaining junk settled just pour off the remaining "clean" solution back into the pot and discard the bottom junk, not the crystals. Or filter it all. Then boil crystal remaining solution again. It's something I do automatically with most salts now.

[NeighborJ]

I'm told by the supplier that the anti cake in question is indeed cabosil.

[DavidF]

So it sounds like the hydrophobic type of fumed silica. Some guys on FW were just talking about how it made their magnalium flash weak when mixed with the perc.

 

Considering the solubility curve of potassium perchlorate, I just can't see the value of filtering the solution. 1 litre of water dissolves 220 grams at boiling temperature. When cooled to almost freezing, the same litre will hold less than 10 grams in solution. Since the anti-cake (or whatever it is) floats, that makes it easy. Discard the whole of the ice cold solution, and lose only 1% of the perc. A quick rinse with ice water and you're done. Does anybody see a problem with this method?

 

If you really wanted to save the crud, you could filter the liquid remaining after 99% of the perc has been precipitated by cooling. If you let it warm up to room temp first, the only thing that could blind the filter is the contaminant.

[NeighborJ]

You read my mind David, I checked the batch in the fridge this morning and it was one layer on the bottom of the tub only a few floaters were hanging around on the surface. I'm planning on dumping the water from the top and letting it warm up then filter, then heat the liquor to reduce down what is left in the water. It sounds like a great plan. Now I need to clean all 35# of it.

[Mumbles]

If you are planning to do multiple batches, you could save the perchlorate saturated wash water and use it for the next batch. The cabosil should still float to the top, and you'll have next to no perchlorate loss from subsequent batches.

[OldMarine]

I have batches of perc from various sources. Would dissolution of small samples in water tell me if any contain cabosil? It would be handy to know for future projects.

[Arthur]

While I do know a seller who will add cabosil on request as anti -cake there is no certainty that all contaminants will be cabosil. As Cabosil is a silica there is no chance of it being truly soluble, it is however so fine that it may well pass through filter media freely.

[DavidF]

OldMarine, I don't know if you want to open that Pandora's box! I know what I would do. And it's not what most would do. I would clean up all my perc and mix it all together and get reliable results from all of it. One thing I have never had to worry about as a factor in pyro mysteries is if my perc was different from batch to batch. Perc formulas are generally too vivacious to not be concerned about the quality of such an important ingredient, IMHO.

 

NeighborJ, when I crystallize mine I chill it to ice cold- not fridge cold. And I have saved the supernatant liquid and crystallized it. It made good blue stars so I knew the rest was good. BUT, what a lot of energy expended boiling off all that water, for that little bit of good stuff! Each of us has his own way

[OldMarine]

Dave, I'm not worried about my perc much except for the fact I don't need more variables in my processes as yet. I use chinese stuff for most everything but save the Swedish for my perc-blues. Chi-com stuff has worked well for all else.

[NeighborJ]

I suppose I should explain the complete cleaning process due to some misunderstanding.

This first batch I cleaned was 3000g. I put it in a 5 gallon bucket with about 1gallon of room temp distilled water. I then stirred it until I had a thick layer of cabosil/foam on the surface. I used a 20 mesh kitchen strainer to skim off this layer. I then repeated this stirring and skimming process until this foam no longer develops. Then the perc and water solution is chilled in the fridge overnight, then poured thru a 30micron filter paper and left over a bucket to drip dry for an hour. The perc on top of the filter paper is set on a drying screen in my star drying box. The water is saved for the next batch so it is not important to crystallize at freezing temps until all the perc I plan to wash has been processed. I may take all my collected cabosil and wash it all together just to collect any residual perc. After which I plan to set the gallon of saturated liquor in the drying box which is almost always on any way and collect any perc left in it after it evaporates. The drying box is powered by a explosion proof 400w HPS lighting fixture cycled by a thermostat set at 160degrees f. A fan and a few hi/lo vent holes provide air exchange.

[NeighborJ]

This cabosil removal project is proving to be more problematic than I originally thought. I have further refined my process and discovered it still retains much of the anti cake in the perc.

The cabosil seems to fall to the bottom of the bucket but when air is introduced to the wash solution it attaches to the bubbles and rises to the surface. I have found that an aquarium aerator works well for this purpose however it still needs constant relocation in the bucket to expose new cabosil to the bubbles. It seems to me that a lot of the perc also attaches to these bubbles and ends up getting skimmed off the top with the AC. I have not yet done any testing of the skimmed foam buy I have made a test batch of whistle with the cleaned perc and the results have been unsatisfying.

It seems to me that it will need to be recrystallised to get the purity I am looking for. That will need to wait for a time when I'm not working so much. I've pulled my chest freezer out of storage so I can chill the supper saturated solution down to near freezing.

[OldMarine]

Honestly, I'd buy some new perc from Pyrochemsource.com or Hobbychemicalsupply.com and save the shitty stuff for color pots, saxons and whatnot.

[NeighborJ]

I agree with you OM and I'd give the same advise to someone else. This isn't going to defeat me, I will figure it out. It would be too easy to go and buy it, and I do have other good perc, but this is kind of a stepping stone for me. The ultimate goal is the perchlorate cell. This is a learning experience, and these impuritys are not the ones which a cell will create, the things I learn here about recrystalization will only help me in the future when I am ready. I have a long way to go before I'm ready to try a cell again but if I set my goals high, I can relax and enjoy the journey and not be discouraged by setbacks. I have anticipated unforeseen problems and am willing to accept them.