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Author: Subject: Preparation of elemental phosphorus
Polverone
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[*] posted on 26-6-2002 at 12:50
Preparation of elemental phosphorus


Historical and modern preparations of elemental phosphorus from phosphates are straightforward yet inconvenient for an amateur chemist because they require very high temperatures, provided by charcoal/coal fired furnaces in old methods and by electric arcs in newer ones.

In the 1800s and earlier, phosphorus was prepared by a number of processes. The earliest was that of Brandt, who prepared it from human urine and charcoal. Later methods were variations on the theme of "heat bone ash with charcoal at high heat." The ashes of bones contain considerable phosphorus, combined with calcium and oxygen, that can be reduced to the elemental state with enough heat and a suitable reducing agent (carbon).

I will summarize the method given in Muspratt:

Animal bones are strongly heated in air until all organic matter has been destroyed. The bones are powdered and to every 3 parts of powder are added 2 parts concentrated sulfuric acid and 16 to 18 parts water. This causes some of the calcium in the bones to be converted to calcium sulfate, which can then be removed by decantation/filtration.

The liquid thus obtained is evaporated to a thick, sirupy consistency. It is mixed with one-fourth its weight of charcoal powder, and then it is raised to near-red heat to make it perfectly dry. The mass is transferred into a stoneware or iron retort in a furnace. The retort has a copper tube connected to a heated underwater receiver where the phosphorus can condense without oxidation (and without solidifying and blocking the tube); the gases that bubble to the surface are sent back to the chimney of the furnace by a second, smaller copper tube. The furnace temperature is gradually increased to white heat.

First comes off steam, then hydrogen and carbon monoxide and dioxide, and finally, at bright red heat, phosphorus begins to come over, accompanied by phosphine and CO/CO2 (it is difficult to be sure about some of the exact products because of the archaic and sometimes inaccurate terms used in the text).

Muspratt does not say precisely how long all of this takes, but Wagner's Chemical Technology (1872) indicates that heat was maintained for a long time, up to 48 hours.

And here's a summary of the modern method:

Ca3(PO4)2+3 SiO2+5 C = 3 CaSiO3+5 CO+2 P

Sadly, this reaction requires 1000-1500 C to operate. It's done in an arc furnace. Building a suitably airtight, nonconducting, refractory vessel for an arc furnace is something well beyond my current engineering skills/resources (any brilliant suggestions?)

I have, a couple of times, tried straightforward phosphate reduction with charcoal and heat. The vessel is a steel pipe with a screwed-on cap at one end and a screwed-on nipple at the other. The nipple has a section of copper pipe inserted in it and sealed with furnace cement. I filled the pipe with a mixture of diammonium phosphate and charcoal on the (admittedly dubious) premise that the ammonium salt would have a lower decomposition temperature and might help the reaction along. Plus it was the only pure phosphate I could find on short notice.

I heated the apparatus with a large gas laboratory burner and had a vessel of warm water to dip the copper pipe into. On my first attempt, I got a lot of strange/unpleasant smelling gases and water condensation at first (I wasn't going to submerge the tube until I was sure something interesting would come out). I also saw some gas leakage around the threads on the pipe. When it looked like the reaction wasn't going anywhere, I removed the nipple/copper tube assembly. I then heated the tube some more just for curiosity's sake. Toward the end I started to see something interesting. The mixture was melting and bubbling out of the tube a bit. I could heat this portion directly with the gas burner, and when I got it red hot I started to see a rather distinctive flame come out of voids in the material. It looked like the flames I'd gotten by igniting red phosphorus (obtained from match box strike strips) and it had the same smell.

After that minor encouragement I figured I'd clean things out and try again, more patiently this time. However, it turns out that whatever hot diammonium phosphate and charcoal turn into, it is hard, insoluble, and tenacious. I had to painstakingly chip/smash slag out of the pipe with a metal rod.

On my second attempt, much later, I kept the copper tube underwater the whole time and tried to be patient with the heating. The gas burner took a while (15 minutes?) to heat the tube up to red heat, and even then could maintain that heat only where the tube directly contacted the flame. It never got hotter than a medium-red. There was a considerable amount of junk deposited in the water - mostly copper salts created by hot/moist exit gases - but no phosphorus that I could see.

I have not yet made a third attempt. I have recently been considering (along with madscientist) alternate ways of preparing phosphorus, ones that might use cleverness to get around the high heat requirement.

Electrochemical methods? I haven't found any, nor do I particularly expect to. The one wacky idea I had was to try electrolyzing phosphides in non-aqueous media (since they react with water) but phosphides are hardly household chemicals and phosphorus is nonconductive, so it would soon block passage of current if it were deposited.

Another wacky idea was to try electrolyzing molten phosphates with carbon electrodes and hope that the intimate contact of phosphate ions and carbon would promote reduction, but this would require temperatures and apparatus similar to the arc furnace.

More active reducing agents? Perhaps aluminum or magnesium powder could be substituted for carbon. I don't know if this would be safe or practical. Would it yield elemental phosphorus or magnesium/aluminum phosphide? Again, I'm not sure.

I AM sure that I want to crack this problem. Phosphorus and its compounds are invaluable reagents for a variety of laboratory procedures, and it's also just plain nifty. Five years ago I could have just ordered some from a chemical supplier, but I didn't have that foresight, and now it cannot be obtained in the United States without a DEA permit.

Such a simple substance, and such simple chemistry, that should pose such challenges...

[Edited on 26-6-2002 by Polverone]
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[*] posted on 28-6-2002 at 11:52
An interesting patent...


Wow, don't everybody try to answer at once. Anyway, I've just found a very interesting document: US Patent 6207024 (accessible through www.uspto.gov) describes the production of elemental phosphorus from pyrolytic carbon and phosphoric acid, using microwaves to heat the reactants. The reaction takes place at much lower temperatures than the conventional arc furnace process. The problem (or problems), of course, is that the phosphorus still needs to be protected from oxidation, you need a relatively heat-resistant and microwave-transparent reaction vessel, and it's going to be tough to condense and collect the phosphorus if you're trying to come up with something using a domestic microwave oven. Microwave ovens are cheap at thrift stores, but there are still obstacles to overcome for performing this reaction at home...
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[*] posted on 8-8-2002 at 08:05


This is not entirely on the topic but hey.

I found a few mole gassing pyrotechnics.
You light them and put em in the hole where they produce highly toxic PH3.

They contain Ca3(PO4)2 and Al. In order to release PH3, Ca3P2 has to be formed by the following reaction:

3Ca3(PO4)2 + 16Al -> 3Ca3P2 + 8Al2O3

I wonder if one could produce elemental phosphorus from calcium phosphide?
Maybe by substitution with a halogen?

Ca3P2 + 3Cl2 -> 3CaCl2 + 2P

Although somehow this doesn't *feels* right.

Substitution with a non-metal with a lower electronegativity seems more promising, but then you have another problem: How would one get elemental Silicon, Germanium, Antimony or Tellurium?
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[*] posted on 24-8-2002 at 16:50


Vulture mentioned in another thread that CaC2 would make a good reducing agent in such a reduction as phosphate reduction.

I suspect that sodium polysulfide would work well in a phosphate reduction.

4Na3PO4 + 2Na2S2 ----> 8Na2O + 4SO2 + P4

Calcium phosphide would probably be useful. It probably could be electrolyzed in, say, acetone, with graphite electrodes, which would yield calcium metal (useful) and white phosphorous (holy).




I weep at the sight of flaming acetic anhydride.
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[*] posted on 24-8-2002 at 21:35
Wait a minute...


I thought I posted information here on using aluminum and silicon dioxide for low-temp reduction of phosphates. I guess that was on other forums, though. Ahh, yes, here it is, from the E&W Forum:

Oooh, I like that idea Vulture! And here's another gem.

Donald J. Haarmann was kind enough to post this on Usenet in sci.chem as part of a very long post on thermites and Goldschmidt reactions:

Quote:

Aluminium as a Reducing Agent, &c.
L. Franck. Chem. Zeit. 1898, 22, [25], 236-245.
In:- The Journal Of The Society Of Chemical Industry. 17, [6], 612-613.
June 30,1898

Action of Aluminium on Phosphorus Compounds—Phosphorus vapour when led over powdered aluminium, heated to a dull red beat in a current of hydrogen, combines with it with incandescence, forming a dark greyish-black unfused mass, which is decomposed in contact with moist (normal) air, forming PH3, and leaving a greyish-white powder. It is decomposed also by water, aluminium also by water, aluminium hydroxide and a brownish-black residue being left ; and by acids and alkalis, which dissolve it almost completely with evolution of PH3. The compound remains unaltered when heated in air.

At more or less elevated temperatures, all phosphoric, acid compounds (meta-, pyro-, and ortho-salts alike) are decomposed by aluminium. Metaphosphates, however, undergo the most complete change, according to the equation—

6NaP03 + 15AI = 6NaAl02 + 2Al203 + Al5P3 + P3

The addition of silica effects the release of the remaining phosphorus, thus :—

6NaPO3 + 10AI + 3Si02 = 3Na2Si03 + 5Al203 + 3P2

Calcium and magnesium salts are as efficacious as those of sodium, but the superphosphates of commerce are not available for the production of phosphorus in this manner. If, however, bone ash be decomposed by hydrochloric acid instead of by sulphuric acid, a material suitable for the purpose is obtained.

Hence phosphorus may be produced, with almost quantitative completeness of yield, at relatively low temperatures...


Now the real question is: what is meant by a "relatively low temperature?" One of these days I may just have to find out!
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[*] posted on 24-8-2002 at 21:43
I hit


I meant to address this also.

Quote:
Calcium phosphide would probably be useful. It probably could be electrolyzed in, say, acetone, with graphite electrodes, which would yield calcium metal (useful) and white phosphorous (holy).


Mmmm, the holy white phosphorus! Do not approach the glory too closely or you may be hurt! But I think you are jumping a little ahead of yourself. Calcium phosphide may or may not be soluble in acetone, and phosphorus is a non-conductor, so it may be a problem keeping the current flowing even if it is soluble.

Oh, and as long as we're on this topic, in that E&W Forum thread that I've copied part of here, PrimoPyro mentioned that
Quote:
Also, phosphates can be reduced to elemental phosphorus with catalytic hydrogen around 750C (upper limit) and lower down to around 350C.


He didn't provide any more information than that. Care to enlighten us, Primo?

I think the most straightforward method is to build a charcoal furnace and do it the old-fashioned way, but I don't have a furnace nor the room for it. So let's bring on the wacky Rube Goldberg methods!
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shocked.gif posted on 26-8-2002 at 22:52
Damn that post was hard to find!


I don't have any info to add to that. I referenced that from a post at The Hive. The user "UTFSE" posted it under post no. 210542, in the Stimulants forum, under the thread called, "The Philes on Phos...(so far)".

You should really read that thread, it contains a huge wealth of info and sources. The source for that statement was said to be:

"Mellor's Comprehensive Treatise on Inorganic and Theoretical Chemistry" Vol 3 Supplement 3; Wiley 1971

Wow! $720 for a used copy! Damn! Check it at:

http://www.amazon.com/exec/obidos/tg/detail/-/0471593095/qid...

I'll message this user (haven't seen him in awhile, hope he's still around) and ask for a copy of the full reference, word for word.

PrimoPyro
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[*] posted on 28-8-2002 at 09:07


Would that just be a simple high temperature reduction with a hydrogenating catalyst like platinum?



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[*] posted on 28-8-2002 at 18:13
Very likely


That is very likely. I am very very interested in nickel hydrogenolysis catalysts, especially Urushibara prepared nickels, as opposed to Raney Nickel, which is highly pyrophoric. (Jeeze, it can actually erupt into flames by simple filtration induced friction!)

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[*] posted on 29-8-2002 at 07:58
Pyrophoric Nickel...


When I read that in my chemical book I was a bit stunned, you would only expect that with highly reactive metals like Mg.

Did you know Hydrogen autoignites in contact with very fine Pt powder?

I wonder if there is no chemical way to oxidize the P-3 to P from Ca3P2?




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[*] posted on 21-9-2002 at 04:50
Red to White Phosporus


I succeeded in heating red phosporus in a CO2 atmosphere and distilling the phosporus vapour which condensed to white phosporus and looked like candle wax.
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[*] posted on 21-9-2002 at 09:36
Nifty


I would try the same thing if I had ready access to red phosphorus. However, thanks to the War on Drugs, it is now impossible for somebody who is not licensed by the DEA to buy elemental phosphorus in the United States. Actually, it's illegal to make and own as well. Nevertheless, I am always interested in possible routes to this fascinating element. Phosphorus and its derivatives have so much use in the laboratory that I can't resign myself to saying "oh, that's off-limits."
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[*] posted on 21-9-2002 at 14:09


It seems that I'm a lucky bastard as I have both red and white P. And it's really nice to play with these. Not talking about Na, K, Li, Br.
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[*] posted on 21-9-2002 at 14:14


bummer, I haven't recently tried to get anything exciting. I suspect it's harder nowadays. In Victoria, they had a crackdown on 'chemical' waste and storage as we've had a few fires over the years. Also there is more caution on chemicals related to explosives such as Ammonium nitrate from garden suppliers etc.
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[*] posted on 22-9-2002 at 01:07


I would advise caution in the distillation of phosphorus... especially white phos.

Since it is toxic and u can get a nasty case of phosphorus jaw [jaw slowly rots away]. Not nice eh?
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[*] posted on 22-9-2002 at 17:21


I distilled it in an atmosphere of CO2 and it doesn't burn as long as the CO2 is provided. No real hazard. The P4 just condenses in a test tube in ice water. Because it's always cold it doesn't burn.
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[*] posted on 10-10-2002 at 05:01


Hey polv!("186" has) missed ya, didn't know you had a forum. Our 19th century muspratt conversation got cut short so I couldnt reply to your note at 'The [bought] Hell' (speculating..uh). I wasn't going to use your email at your college site just in case...

It sounds like you got close with the first attempt, I was under the impression it was a failure altogether from what you had told me, but well done. I'd be very cautious about the Al route, check this out [http://www.uow.edu.au/eng/bmh/explosion.htm] I stumbled on it accidently while trying to source Al powder in australia. The hydrogen gas too.

This diammonium phosphate you played with decomposses at 155C right? You can make it work you already have had success it just needs fine tuning.
I want you to consider the following for your pipe experiment, I think it could get you there.

- Buy a few small pieces of ceramic fibre board. its VERY easily cut. Arrange them like so
here's a cross-section of labtop CF arrangement:
________
| |
| |

use it as an insulating enclosure for your tube, you'll get fantastic temperautures, certaininly in excess of 200C with your torch across the tube. Remember you can easily cut holes in this fibre with a kitchen knife. So you could make a box with it, with a hole at either end to support tube, and a hole for the flame entry.

You know the chemistry of this more than me, so now solve the problem of how to get it under water without oxidizing first. Brainstorm: a bend on the nipple end of tube as it exits the pipe, a longer tube. Also remember the charcoal never reached a temp that would have removed the oxygen would it?

On that note, I'm going to zap the reactants first in microwave to rid of any moisture.
MONOPOTASSIUM PHOSPHATE (Tradename: MKP) KH2PO4)
decomposition point for this one slightly higher at :~250C
This will mean that your C will have reached a higher energy level when its ready, and more of a glow, less oxygen.

Are you sure you want to go the arc route? Already got the tools for it except for refractory cement? What about a cheap electric kiln? they have a vent hole at top and front door. This my intended route,

The refractory vessel shape is basic, I know you can work that out!

Either an upright cone with a flat hem ("lips" sitting on a casserole pot with lips around rim)
|
/\
/ \
= =
|_|
Bad ascii art I know but thats option one.

Option 2 is more ingenius, and I thought it up (heh.. surprising I know)

...cut a kinda tall triangle out of a piece of paper, slice it diagonally from one lateral to the counter-lateral. Now rotate the top piece on the slice axis... the rest is the same as above with lips and casserol [retort].
It should appear like the design above but with the point of the triangle now coming out of the side -- I call it the Muspratt 2002 PDT.
Cone construction in a flash:
http://www.flyingacesclub.net/volare/cone.htm

Construction :
Scrapped the stoneware pot idea. Just make a nice accurate carboard version, pour refractory cement over each of the two pieces in a thoughtful fashion, thats what I'm leaning towards, itll work, ill burn the cardboard off.

Email me if you like polve I have digital images of mine ... and measurements, of everything, and kiln photos if your interested in that option. The tubing could be a winner though!
Have you had time to re-scan that page of muspratt containing the reciever yet? Maybe ill check out your site and see if its updated, you could well have...
The pressure black flow on cooling needs thought.

I have a few questions that may or may not need to be answered (I've forgotten them so I dont know LOL), I must be in a giving mood.

Recent finds I've bookmarked on this topic since we last spoke ...

Fun stuff ...
http://boyles.sdsmt.edu/phosox/oxidation_of_phosphorus.htm

On aluminum as reducing agent.
http://cdl.library.cornell.edu/gifcache/moa/manu/manu0026/00...

More descriptive version including a labtop... in tubing.
http://cdl.library.cornell.edu/gifcache/moa/manu/manu0026/00...


http://cdl.library.cornell.edu is top notch by the way for OLD articles and reference spanning 1815 - 1926, kept it with you in mind two days prior to now.


This post was longer than I intended, but hopefully you'll have a decent read. ttysih.

pRO :)

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[*] posted on 11-10-2002 at 11:46
Hello again, and GOOD INFO!


It's nice to see you here. When you suggest ceramic fiber board as an insulating material, did you really mean "you'll get fantastic temperautures, certaininly in excess of 200C with your torch across the tube"? Because I can top 200C with a hotplate... I'm hoping you meant to add another zero in there.

Anyway, the problem isn't decomposing the diammonium phosphate so much as it is reducing the decomposition product. I do believe I produced some small amount of phosphorus near the end of my run, but as I've stated in previous posts, I couldn't heat the whole assembly enough to make this method viable. Perhaps with better insulation or a better heat source I could.

But it doesn't look like I even need to do that! That document you turned up on the Cornell site is great. I'll reproduce the text here for folks who don't want to download a gigantic GIF.

Quote:
Aluminum for the Preparation of Phosphorus

The applications of aluminum in the arts multiply with much the same rapidity as do those of electricity. The Berichte describes a new method of preparing phosphorus by its use as a reducing agent. The process is so simple that it can easily be illustrated on the lecture table. Hydrogen ammonium sodium phosphate is fused in a porcelain crucible until it is changed into sodium metaphosphate; aluminum turnings are then dropped into the liquid, and the freed phosphorus bursts into flame. Now, if the experiment is tried with a glass tube, instead of a crucible, a slow current of hydrogen being passed over the mixture of the salt and aluminum, the phosphorus distills into the cooler part of the tube without the formation of any phosphoretted hydrogen. The residue consists of alumina, sodium aluminate, and a phosphide of alumina - Al2P2.

By these steps in the process only 30 per cent of the phosphorus in the mineral used can be obtained; but the phosphide is decomposed entirely by heating it with silica, and this may be added at the beginning of the experiment and the reaction proceeds without difficulty and without loss.

It is advised that for the lecture table a combustion tube a yard long be used; two and a half parts of aluminum, six parts of sodium metaphosphate (obtained from heating previously the hydrogen ammonium sodium phosphate) and two parts of finely pulverized silica are placed in the tube, a slow current of hydrogen is passed through, and heat is applied until the reaction begins. This is shown by sudden incandescence, and phosphorus is seen to condense in globules on the cooler part of the tube, at the end where hydrogen escapes.

Instead of this phosphate, any ordinary phosphate may be used, but experimenters are warned not to use the superphosphates containing calcium sulphate mixed with them, such as are used for fertilizing purposes, because the sulphate is suddenly decomposed by the aluminum with an explosion when a certain temperature is reached.


I doubt that any of us really want to have to use hydrogen gas connected to a burning-hot tube. I would presume, however, that any non-oxidizing gas would serve as a carrier. Nitrogen, argon, helium, and maybe even propane and natural gas might be used in place of hydrogen. Or it may be possible to distill the phosphorus with no carrier gas at all, simply vaporizing it and condensing it in water. However, I would be very careful of suckback with this method, because you certainly don't want a steam explosion in the midst of molten salts and phosphorus.

Really nice news from the above quoted material is that A) the aluminum need not be finely divided; if turnings work, you can use sweepings from a machine shop! and B) silica improves yields greatly but isn't absolutely required. In any case, I think that fine ceramic grade silica powder would be the ticket here.

Be careful when cleaning up your residue if you try this. Aluminum phosphide will, I think, yield phosphine gas on contact with water, and phosphine is very flammable and very poisonous.
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[*] posted on 12-10-2002 at 15:09
Another useful tidbit


I was searching for phosphates with relatively low melting points. I found that sodium hexametaphosphate melts at 550 C and is used as a water softening agent, so it should not be at all difficult or suspicious to acquire. Diammonium phosphate, the material I previously used for my phosphorus preparation attempts, also has a relatively low melting point, though it partially decomposes as it melts, into what products I'm not sure. The diammonium phosphate was obtained as a nutrient for use in beer/wine brewing.
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[*] posted on 12-10-2002 at 15:52


polverone

Did u already think of using a mix of phosphates?

You could make a mix with another phosphate as this would further decrease the melting point.

The same is used in industry for melt electrolysis in the production of aluminum and alkali metals.
The fact that impure solid substances have lower melting points, is well known in organic chemistry, where it is used for testing the purity of synthesized substances.
Pure substances have a sharp melting point and usually higher melting points than impure.

HLR




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[*] posted on 13-10-2002 at 02:29
some updated info


When creating Ca3P2 by reducing calciumtriphosphate with Al, the fused mass of Ca3P2 and Al2O3 can't be separated. This leaves only oxidation from PH3 as an option, which is extremely dangerous, because of it's auto-inflammability and it's high toxicity.

Maybe Zn or Mg powder would work?




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[*] posted on 13-10-2002 at 02:34
Something to keep in mind


When directly trying to isolate phosphorus from phosphates or P2O5, you'll have to reduce it, but when isolating form phosphides you'll have to oxidize.

I'm confident that one of the two will show as the most viable method.




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[*] posted on 13-10-2002 at 10:50


Hoffman: I did think of using a eutectic mixture of phosphates, but I didn't really want to because I'm sure there's some minimum temperature at which the reaction proceeds, and I can easily achieve temperatures up to 800 C or so.

Vulture: Did you see the information from the Cornell site? You'll get a lot of phosphides if you just mix the aluminum and phosphate, but powdered silica will decompose the phosphide to yield phosphorus.

Yesterday, despite needing to do so many other things, I just had to see what I could achieve with a molten phosphate + aluminum. I melted diammonium phosphate in a stainless steel dish with a propane burner until the decomposition bubbling slowed down. Then I added a ball of shredded aluminum foil and mixed it into the viscous liquid in the dish. As the temperature rose, flammable bubbles began popping to the surface and igniting. A steady stream of flammable gas/vapor was produced for a couple of minutes as the foil got hot enough to melt.

I also tried mixing a small quantity of 300 mesh aluminum powder into the melt. After a delay of about half a minute, the whole region where the powder had gone experienced a sudden incandescent ignition. I couldn't tell if this reaction generated further flammable gas because of the intensity of the light. After a few more minutes of heating I turned the heat off and stirred the thick mass with a spoon so that it became crumbly, loose chunks as it cooled (instead of one huge mass stuck in the bottom of the dish).

There were many small bright droplets of unreacted aluminum left in the mix after cooling. This morning, the mixture had adsorbed some water from the air and smelled a bit like garlic (phosphine forming?)

I would like to try this with sodium hexametaphosphate instead because it was hard to tell, with this last attempt, whether I was producing phosphorus vapor or hydrogen. By eliminating all hydrogen sources, a second run could be much more instructive. Also, I think the reaction may go more easily with a sodium compound as the aluminum forms sodium aluminate with it. I would of course *also* like to try adding powdered silica to the mix and seeing how that affects the reaction. Finally, I'd like to try using aluminum turnings/filings instead of powder and foil, since I think they may be more suitable forms (more vigorous than foil, but not dangerously so).

Anyway, I hope that someone else can try this out, as I am extremely busy and I don't know the next time I'll get to make an attempt at this.
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[*] posted on 15-10-2002 at 19:51
This is a possiblity......


Instead of using Na, NH4, etc... PO4's I was thinking of using Pb3(PO4)2, made by using the pH downer in Hydroponics stores and PbO. In the patent I came accross, they used Pb3(PO4)2 prepared from the oxide, and reduced by H2 at about 400*C. The products were P4, Pb and H2O. I guess the same thing can be applied with C as the reducant. Maybe the temp would need to be a little higher, the mix would yeild P4 in a fire place, but I think its worth a shot, I need to make a Cu flask though.
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[*] posted on 16-10-2002 at 00:06
That's a possibility...


I think the main difficulty, though, is freeing the phosphorus from oxygen, not from whatever cation it's attached to. I could be wrong. I would certainly be interested in hearing of your results in any case. Consider trying aluminum foil/filings/turnings as well, and (if you can) also try adding powdered silica, as it seems to be beneficial in all of the phosphorus-producing methods I have read of...
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