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Fulmen
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Don't really have much K2CO3 left, and no real source either. Found some KOH-based paint stripper, but I don't know if it's pure or not.
As for the risks of cyanides I've found several vague references to cyanates breaking down to cyanides at elevated temperatures, but nothing definite.
I guess it should be OK as long as I avoid extreme temperatures or reducing conditions.
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Fulmen
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I spent some time reading up on the hydrolysis in water to see if it's possible to recrystallize. It seems like it's most stable above pH9, but I also
realized that purification isn't really needed. I now have two uses for cyanates, as a precursor to thiocyanates and as a C-N-source for
nitrocarburization. Neither will require high purity, in fact both uses will require addition of more carbonate. So as long as the yields are good I
should be able to use the product as-is.
The next real hurdle will be a reaction vessel. Due to the scale I will be aiming for I need to deal with the ammonia gas. Using carbonates would
produce a mixture of ammonia and and ammonium carbonate I guess, not really that useful. So the hydroxide-route seems like a good choice, unless I'm
missing something.
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Fulmen
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I might be on to a cleaner reaction. From the attached PDF:
A method of preparing pure NaCNO is described, based on isomerisation of urea to NH4CNO under anhydrous conditions. Sodium metal is dissolved in dry
butanol and urea is then added in eqnimolecular quantities; the mixture is refluxed. Insoluble NaCNO separates in almost theoretical yield.
The conversion rate is temperature dependent, so a high-boiling alcohol should be used. Glycerol or perhaps a glycol should be viable solvents. One
problem is the formation of carbonates due to hydrolysis with the water produced by the reaction.
The article mentions the use of sodium butoxide as a water scavenger, obviously I need something a bit more OTC. Or perhaps the high bp. of glycerol
is enough to drive out the water fast enough to reduce the problem?
Attachment: 1150-THE-PREPARATION-OF-PURE-SODIUM-CYANATE-FROM-UREAae22.pdf (398kB)
This file has been downloaded 1419 times
Edit: Perhaps something like CaO could work?
[Edited on 22-4-18 by Fulmen]
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Melgar
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Okay, first of all, you're making wrong assumptions all over the place. The best way to purify alkali cyanate salts is to use the fact that
everything that isn't an alkali cyanate salt will BURN when you get it to the salt's melting point. Do you know what ammonium carbonate does when
heated to 400˚C? It's a trick question, ammonium carbonate can't exist at those temperatures. Unless maybe you're somewhere near the core of
Jupiter.
The advantage of K2CO3 is that first, the cyanate salt melts at a lower temperature, so your reaction vessel is more likely to hold up. Second,
sodium salts have an annoying tendency to damage most things when they're molten, and potassium salts are somewhat better in that respect. K2CO3 is
very cheap, and much cheaper than KOH. And certainly a fuckton cheaper than sodium metal.
The disadvantage of making the sodium salt is that at the higher melting point, the cyanide salt is more likely to form in significant amounts. It's
not hard to separate them using standard chemistry methods, but those are problems that can be avoided by just using K2CO3 in the first place.
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S.C. Wack
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You may want to read what the Inorganic Syntheses entry for the cyanates has to say. IIRC it's in the second volume that can be found at a libgen or
archive.org.
Perhaps I should mention that when I tried urea to cyanate, something sublimed, blocking the ammonia outlet, and the container failed inside the
furnace.
[Edited on 22-4-2018 by S.C. Wack]
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Melgar
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Quote: Originally posted by S.C. Wack  | You may want to read what the Inorganic Syntheses entry for the cyanates has to say. IIRC it's in the second volume that can be found at a libgen or
archive.org.
Perhaps I should mention that when I tried urea to cyanate, something sublimed, blocking the ammonia outlet, and the container failed inside the
furnace.
[Edited on 22-4-2018 by S.C. Wack] |
That'd be isocyanic acid, which would then trimerize to cyanuric acid or polymerize to some other random crap:
https://en.wikipedia.org/wiki/Isocyanic_acid
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Fulmen
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Melgar: K2CO3 might be cheap in theory, but that doesn't help me when the availability is fuck-all. It wouldn't be a major
issue if I wanted to make 10g, but I might need as much as a kilo of the stuff. Also, the sodium salt seems to be the preferred salt for
nitrocarburization (not sure why yet).
S.C Wack: Thank you for that reference. It basically confirms and expands on what my other sources tell me.
But I must admit the solvent-based route seems to be more promising if I am to make any significant quantities. First of all the temperatures will be
much lower, allowing the use of standard glassware:
"The rate of reaction appears to be determined by the boiling point of the solvent. Thus there is a steady increase in the series methanol (b.p. 65°;
3o% conversion in 4o h), ethanol (b.p. 78°; 4o% conversion 4° h), propanol (b.p. 97°; 52% conversion in 15 h), butanol (b.p. 117°; 72% conversion
in 2 h), isoamyl alcohol (b.p. 131°; 8o% conversion in 1 h)."
The question is if one can get decent yields without using sodium metal. One idea is to use boiling glycerin or glycol at reduced pressures.
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Melgar
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| Quote: Originally posted by Fulmen | | Melgar: K2CO3 might be cheap in theory, but that doesn't help me when the availability is fuck-all. It wouldn't be a major
issue if I wanted to make 10g, but I might need as much as a kilo of the stuff. |
Oh, well why didn't you say so? Are you familiar with cream of tartar? Commonly used for cooking? It's potassium bitartrate. A pound of it costs
about $7 where I am. So what you do is, you take that shit and burn it, making sure there's plenty of oxygen available. If you have KNO3, (probably
not, but I figured I'd mention it) then you can mix that in too, since it'll release oxidizing radicals while latching onto the CO2 that's produced.
Keep the heat on until there are no traces of brown or black left, and it's all white. That's K2CO3.
Although I mentioned potassium bitartrate, any other potassium salt of an organic acid will work. Potassium sorbate, for example. Potassium
benzoate, even. It's just a matter of how much crap you have to burn off. Even potassium chloride will form potassium carbonate if you mix it with
charcoal and burn it. Even some dishsoaps can be burnt to leave a K2CO3 residue. And all you have to do to isolate it is dissolve it in water and
filter it. Even wood ashes can be soaked and filtered to get K2CO3, since that's the only carbonate in wood ash that's water soluble.
I guess I just never would have thought that lack of K2CO3 could be a problem for anyone.
BTW, it helps us here if you put your country or state in the "location" field, so we can figure out what laws you're having to deal with.
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Fulmen
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There is virtually no OTC source of potassium at all around here except low-sodium salt. And considering the amounts I might need it's not really
practical to make it from alternative sources like ashes/soap etc.
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Melgar
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Just curious: where exactly do you live? I'm trying to think of a place where you have access to sodium metal and butanol, but not eBay.
Not sure if you have access to black powder or road flares, but they typically produce potassium carbonate. Potassium nitrate and potassium
perchlorate are used in flares, and are usually mixed with some carbon-based fuel, as well as a bit of strontium nitrate to make them red. Edit: The
white smoke is potassium carbonate though, and I guess you'd need a way to capture that.
Even failing that, they sell 20-pound bags of potassium chloride to regenerate water softeners for people on low-sodium diets. Pulverize that up with
charcoal in a trash can with holes in the bottom, light it, and leach the ashes.
I'm not trying to be mean, I'm just trying to keep you from thinking that sodium metal is somehow going to be more cost-effective.
There's actually an expired patent that details a cost-effective way to produce potassium carbonate with very little in the way of resources.
Interestingly enough, it's US Patent #1:
https://motherboard.vice.com/en_us/article/pggjyb/the-first-...
[Edited on 4/22/18 by Melgar]
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Fulmen
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LOL! I didn't say I had sodium metal, but around here the range of useful OTC chems is pretty limited. Doesn't really matter where I live, I prefer to
keep a low profile as this is an open forum. I also avoid ordering chems if possible, and importing is completely out of the question. It does limit
my options but does keep the storm troopers off my doorstep.
I actually did try to extract K from ash once, I was helping a friend with a soap project. It was messy and the yield was low. Producing larger
quantities that way doesn't really get my juices flowing.
I don't think sodium butoxide is required, it's primary function is as a water scavenger. From the article: "In one experiment with alcoholic NaOH the
final preparation contained 75% NaCNO, and approximately 25% Na2C03." I could probably live with this yield if I have to, but I also think it must be
possible to overcome this problem somehow.
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Melgar
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You certainly CAN use sodium carbonate, if you had no other choice, but I've used both, and 200˚C difference between the melting points makes a
pretty huge difference, as far as how much of a pain in the ass it is. Potassium cyanate melts at a lower temperature, and acts as a solvent for the
reaction to continue, whereas sodium cyanate is much harder to melt, and meanwhile all the isocyanic acid is vaporizing and making a mess.
Homebrewing stores and bakery supply stores will certainly carry either the carbonate or bicarbonate salt of potassium. Potassium bicarbonate is used
instead of baking soda for people who are on a low-sodium diet, for example. It's just so ubiquitous that it's hard for me to imagine not being able
to source it. Like not being able to source wax or copper or something. Just seems weird to me. But I guess I'll let it go now.
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Fulmen
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It is what it is. That's part of the reason I'm looking at the solvent route, if one can limit the presence of water it should be able to produce a
fairly clean product with decent yields. And at only 150°C. I don't see why you're so hell-bent on the thermal route.
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Melgar
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Because the thermal route is so easy! You just mix stoichiometric amounts of urea and potassium carbonate in a cheap glass beaker with thick walls,
put some foil over the top loosely so the ammonia and CO2 can escape, then heat it from underneath with a hand torch or something. (I used a hose
clamp to hold the beaker to the side of a metal workbench.) All the impurities either vaporize or pyrolyze, and you're left with potassium cyanate
that barely requires any purification. With potassium as your alkali, you can do it in glass, since the damage to the glass is minimal, and it only
needs like 400˚C. Sodium attacks glass much more already, and when you add to that the fact that you need to get it to like 600˚C, it's really not
safe at all to use glass, and you need some special crucible.
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Fulmen
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OK, you do have a fair point. I don't really like pushing glass to 400°C, but that's not a deal breaker. It just sounds a bit impractical once you
start scaling it up.
I will do another search for potassium salts, they are always useful to have around and I could at least make enough cyanate for some initial tests.
The solvent method certainly has it's own set of challenges, the primary being it's sensitivity to water: "With butanol containing 0.04% moisture,
1-2% carbonate was generally present in the sample. With butanol containing 0.3% moisture, the carbonate content rose to 10%.". Then again these
numbers are probably from running the reaction over night, with a higher bp a few hours should be enough. Nor should it be necessary to run the
reaction to completion, especially if one performs multiple batches.
I also realize that the sodium butoxide isn't a scavenger but rather an oxygen-free source. If a method for removing water from the reaction is found
it might be possible to use sodium hydroxide. Reducing the pressure could work, an aspirator should be enough to prevent water from condensing back
out. That also takes care of the ammonia, eliminating the need for a fume hood or doing the reaction outside.
Another benefit of this method is that it produces a powdered product, grinding down large quantities of fused salt isn't exactly done in 5 minutes.
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Fulmen
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I have found a source for K2CO3, but it's not local. I might be able to stop by in a few weeks time, but being impatient I decided to give NaOH a try.
I started by melting 20g in a hotplate in a stainless cup. The assumption was that if I could melt the NaOH I could dispense with the propane. I then
added 35g of urea (5g in excess) in portions, not really the best idea I've had. Even outside with good ventilation the ammonia was a problem, and the
mixture foamed severely. Before half the urea was added I was left with a tan, powdery solid, so I ground it up as best I could with the remaining
urea and left it for 10 minutes.
The product was then broken up and washed twice with EtOH. The wash was yellow and tested strongly alkaline.
Net product: 32,65g (100,1% yield).
Now obviously this shouldn't produce perfect yields, so I might try another wash tomorrow. Or not, it doesn't really matter for now. I'll probably use
this for making thiocyanate.
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Fulmen
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Next was a test to see if thiocyanate would form from cyanate and elemental sulfur. 10g of the crude sodium cyanate and 6g of sulfur was mixed
together and heated on a hotplate. Initially some NH3 was produced, as the temperature increased SO2 began to escape. After 30 minutes the reactants
had barely fused together, so I increased the temperature with a blowtorch. Once the mix melted it seemed to be self-sustaining, producing a lot of
bubbling and some sparks that resembled burning charcoal. After the reaction had subsided the container was cooled and the product dissolved in warm
water.
This produced a large portion of black insoluble matter and a yellow liquid with a very faint "sulfurous" smell. From what I could find thiocyanate
should produce a blood-red complex with Fe(III) and a blue with Co(II), sadly I only got a red/brown precipitate with Fe and a whitish ppt with Co.
Could it be polysulfides interfering?
I also tried the cyanate reaction with NaOH and urea again, this time with the ingredients finely ground and blended. The foaming was even worse this
time, possibly due to more aggressive heating, so the reaction had to be stopped early. I assume it's because sodium cyanate is solid at the reaction
temperature. Hopefully a larger reaction vessel and adding the reactants in portions will help.
This time the product was grey, understandable as the stainless steel was also blackened from the heat.
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Fulmen
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I also got around to test the sodium cyanate for nitrocarburization, and it shows real promise. Even a few minutes of heating with a blowtorch did
produce a significant increase in surface hardness, next step will be to make enough for a test bath. Not sure how I should test the hardness, I do
have a Rockwell tester but it's not well suited for this use.
Perhaps some sort of abrasive test would be easier to jerry-rig?
I should also try something like a salt spray test, the coating is supposed to improve corrosion resistance.
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VSEPR_VOID
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If you find a source of thriocyanates or ferrocyanides make sure to add it to the List of Chemicals and Materials Made by Sciencemadness.org Users
https://docs.google.com/document/d/1AoI2VA5L4bmFw2HwXS2OVYTV...
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Fulmen
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Yet another messy reaction with NaOH. This time I started with 1/3 of the urea mixed with the NaOH, it still foamed over making a righteous mess. I
believe the production of solid NaOCN that's the problem, even with a blowtorch I could only get the material touching the sides of the vessel to
melt. So while it's good enough to test nitrocarburization (shows real promise) it's not suited for large scale production. Guess I will have to get
some K2CO3 after all.
The solution from the thio-reaction has started ppt out a yellow substance (I think, hard to tell as the solution is yellow as well), this will
require more investigation. In theory it could be sulfur from polysulfides oxidizing in air, but there is barely any H2S evolved so I don't really
think so.
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Fulmen
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Persistence pays off. I solved the foaming problem simply by adding the mixed reagents in small portions, I just use several stainless beakers and
work slow. I can easily make 200g in an afternoon, so I should have more than a kilo in no time. I expect I will need some potassium salt as well, but
I can at least start with the sodium salt.
I still need to figure out a suitable composition for the nitrocarburization bath. I can find examples for cyanide baths, but little on cyanate-based
ones. The odd thing is that the baths are used in the 4-600°C range, and most ingredients have a melting point above this. Here are two examples of
cyanide baths:
1: • NaCN, 30% • KCl, 39% • Na2CO3 or K2CO3, 25% • Moisture, 2%
2: • NaCN, 60% • KCl, 24% • K2CO3, 15% • Moisture, 1%
I'm suspecting some eutectic effects are in play, this could complicate the search a bit.
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Melgar
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If you're interested in OTC alkali cyanides, a popular preparation of mixed sodium/potassium cyanide (circa 1800s, anyway) used to be adding
stoichiometric amounts of sodium carbonate to potassium ferrocyanide, then melting the mixture down. Supposedly iron oxide precipitates out, CO2 is
released, and the molten salt is a mixture of sodium and potassium cyanide, which has a lower melting point than either one by itself.
Obviously, this is not one to fool around with, and should initially only be done at the smallest scale possible. But alkali cyanides are really not
bad to work with at all, as long as you're very careful about having good ventilation and never exposing them to acids. (Unless you take all necessary
precautions and know exactly what you're doing, anyway)
Cyanides tend to be used a lot in metallurgy because of how well they work for certain purposes. If you can't find any information on the use of
cyanates, there's a very good chance it's because cyanides work a lot a better.
The fact that every preparation uses both sodium and potassium salts indicates it's definitely a eutectic type of molten salt mixture. If you feel
comfortable attempting it, you could even do a one-pot preparation from potassium ferrocyanide, once you've ensured that this reaction does actually
produce alkali cyanides.
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Fulmen
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I'm staying clear of cyanides. While they are more common (or at least have been around longer) it's actually the cyanate (formed in situ by
oxidation) that provides the nitriding action. Cyanide-free baths exist and seems to be replacing cyanide, so I can't find any reason why it should be
inferior.
The info I have found only mentions cyanates and carbonates, for all I know it could be as simple as that. The two cyanide baths I listed only contain
30-60% CN, but as the MP of all the constituents are above 550°C I suspect it's formulated to produce an eutectic. But it's also possible that the
cyanate concentration must be kept low for optimal results.
And as I'm typing this I found data on the Sursulf-process (sulfur added for lubrication purposes):
CN-: <0,8%
CNO-: 36±2%
CO32-: 19±2%
K+: 24,5±2%
Na+: 20±2%
Li+: 1,25±0,2%
S2-: 2-10PPM
The Li is a catalyst and reduces MP, the Na/K-balance seems to be to reduce bath viscosity.
Then there is patent 4019928:
The bath preferably contains 25-57 weight % of cyanate calculated as cyanate ion, 0 to 30% alkali metal chloride and the balance carbonate and alkali
metal ions. Preferably cyanide is omitted, but it can be present in an amount up to 5%. Without removing the waste salt, the bath is regenerated by
adding melon, melam, or melem.
Now I'm getting somewhere.
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Fulmen
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I had a faint hope of finding a carbonate-free composition. Since the cyanate breaks down to carbonate during use a carbonate-free bath could simply
be regenerated with an excess amide after use. But I assume there is a reason for it, so I think it's better to stick with something true&tested
for starters. The Sursulf-bath ends up at 30% NaOCN, 30% KOCN, 20% Na2CO3, 20%K2CO3, I think this will be my starting point. I still need to get hold
of some K2CO3, in the mean time I will research bath analysis.
There are 3 components of interest, CN-, OCN- and CO32-. The cyanide should oxidize to cyanate, but I
might have to test for the buildup during testing. Aeration of the bath is generally required, but I have a faint hope that a small bath can work
without it.
With a straight cyanate/carbonate-bath I should be able to balance the ratio simply by analyzing one, and the carbonate seems like the obvious choice.
"Practical Nitriding and Ferritic Nitrocarburizing 2003" by David Pye lists a method where the carbonate is precipitated with BaCl2, filtrated,
dissolved with HCl and titrated with NaOH.
I would like to avoid the barium, perhaps calcium would work? And with a precipitate a gravimetric method should work as well, saving me a titration
setup. A direct titration would be nice of course, but I assume there is a reason why it's not mentioned.
Analyzing cyanate seems too complicated for my taste, Pye's method is based on disassociation to ammonia and a Kjeldahl-type distillation.
As for regeneration urea will likely be a poor choice due to the baths operating temperature. Patent 4019928 mentions "melon, melam, or melem", but I
can't find too much info on these. Cyanuric acid might work, I'll have to look into that.
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eesakiwi
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I can get Potassium Ferrocyanide as a case hardening powder from a hardware store.
US$35 for 500gms (lb)
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