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Author: Subject: Preparation of elemental phosphorus
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[*] posted on 18-10-2002 at 16:45


It mustn't be too difficult to reduce phosphates with metals - this is what my chemistry book says about it.

The pure acid is a colorless crystalline solid (mp 42.35C). It is very stable and has essentially no oxidizing properties below 350-400C. At elevated temperatures it is fairly reactive toward metals, which reduce it, and it will attack quartz.

It seems that the phosphate anion is reduced by metals at temperatures over 400C.




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[*] posted on 19-10-2002 at 17:27


Someone suggested CaP might be electrolysed to Ca metal and P. This sounds somewhat unlikley, is acetone even an ionising solvent?

Phosphate salts + silica is only the way to go for much higher temperatures, avoid salts alltogether, and you dont have to melt the silica or even use it at all.

Orthophosphoric acid is easy to reduce, but not the goal. Orthophosphoric acid and ammonium phosphates on strong heating pass through the pyrophosphate stage to the metaphosphoric stage. This is the annoying glassy solid you cant dissolve easily. Empirical formula HPO3 its actually a polymer. The smart money is on reducing this I'm almost sure, less hydrogen means less P lost as phosphine. Theres no cation to form a phosphide, so the only way youd get one is using excess aluminium.

Aluminium sounds rather excessive for this anyway, the reaction might be specitaculaly energetic, maybe a mixture of a small amount of aluminium with a larger amount of carbon would be pratical, the excess thermal energy from the aluminium forcing the mixture to a temperature where the carbon is effective.

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[*] posted on 19-10-2002 at 21:08


You're right that calcium phosphide can't be electrolyzed in acetone (or any other solvent for that matter). Acetone will dissolve some ionic compounds. I had discussed an old article I found on the production of lithium metal by electrolysis of anhydrous solutions of lithium chloride in various solvents, acetone among them. I believe that's what prompted the idea that one might electrolyze calcium phosphide in the same fashion.

As mentioned a bit upthread, I've already tried using aluminum with diammonium phosphate. Aluminum foil was placid, even sluggish - very manageable. Aluminum dust was much more vigorous; I wouldn't want to try heating large quantities of it with phosphates. The idea of using a mixture of carbon and aluminum sounds good. And, of course, I've never gotten around to trying Vulture's suggestion of using calcium carbide to perform the reduction. One more thing to put on my to-do list...
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sad.gif posted on 30-1-2003 at 02:47
aluminium and silica


earlier in the thread it says any phosphate can be used for the aluminium reduction, and cilica may be added for a more complete reduction, but heres a hang up i have about that:

If you used a phosphate like mono-calcium phosphate, wouldnt that require much higher temperatures anyway? (defeating the purpose of using the Al for lower reduction temperature)

Same with the silica, wouldnt this require higher temps too?

Would the addition of silica, stop phosphite from being a product? I hope so personally! i know the "carrier gas" would stop any steam from coming in to contact with it, assuming its condensed in to water as polverone suggested. But I'd be more concerned with the carrier gas blowing the phosphite product in to the water, even though it is only a gentle flow of gas.

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[*] posted on 1-2-2003 at 19:03


can too much heat decompose a phosphide of an unreactive metal?
for example 2Cu3P2 => 6Cu + P4
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[*] posted on 1-2-2003 at 21:45


Great idea! I think that at the very least the following will occur, considering that cupric chloride decomposes relatively easily into cuprous chloride and chlorine:

4Cu3P2 ----> 4Cu3P + P4




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[*] posted on 2-2-2003 at 07:06
But...


How would you make the phosphide? I can't think of a good method without elemental phosphorus...
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[*] posted on 2-2-2003 at 08:54


Igniting a composition of aluminum powder and copper phosphate. If the stoichemitry is done right, the aluminum should be fully oxidized, leaving cupric phosphide, which should decompose as it is formed due to the heat previously liberated by oxidation of aluminum.



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[*] posted on 2-2-2003 at 09:33
Good plan.


That's the kind of thing I've been thinking about, a method that doesn't require an external heat source once the reaction has started. I was just going to try various Al/C/(HPO3)n mixtures, to see if I could get a self-sustaining reaction that wasn't too vigorous. I can't at the moment see any advantages of using copper phosphate over metaphosphoric acid, but maybe experimentation will prove me wrong.
I couldn't find pure ammonium phosphate in any local shops, only mixtures with sulphates and other crap, so I've bought some by mail order. It should be here within a week, so I'll be able to experiment soon. Also on order is some clay, to make a specially designed cell for making sodium. It's not too special, but would keep air out and help to keep the products seperate. I'll talk about it in the right topic when I actually have something to talk about...
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[*] posted on 3-2-2003 at 00:20


I don't know if this will be of any use, bt while I was browsing about the internet, i chanced upon a little article.
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[*] posted on 4-2-2003 at 19:29
caution


copper phosphide Cu3P2.
Properties: Grayish-black, metallic powder. Insoluble in water; soluble in nitric acid; insoluble in hydrochloric acid. Sp. gr. 6.67.
Derivation: By heating copper and phosphorouse.
Hazard: Dangerous; spontaneously flammable and toxic phosphine is evoloved on reaction with water. May explode when mixed with KNO3.
Use: Manufacturing phosphor-bronze.
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[*] posted on 30-3-2003 at 17:24


In a book called "Lange's Handbook of Chemistry" somewhere in the book it says "The chief sources of the element is phosphate rock, generally Ca3(PO4)2, which is treated with sulfuric acid to convert it to phosphoric acid which is then heated with carbon, the crude phosphorus being removed by distillation."



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smile.gif posted on 10-4-2003 at 01:40
My plans


On the Sunday I plannig to prepare P from H3PO4 + C = H20 + CO + P. :)
I have real 600-650C in my glove :D

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[*] posted on 25-4-2003 at 13:41


Maybe I will try this method to make the oxide of phosphorus.
Ca3(PO4)2+3 SiO2= 3 CaSiO3+P2O5.
This does need alot of heat. My idea is CaSiO3 have a melting point of 1540*C and P2O5 sublimbs at 340*C I may be able to distill off the P2O5.

Then the isolateing of P is P2O5+5 C=2P+5 CO2.
The problen is white phosphorus is very reactve and may explosve in contact with air.
And I doubt theres much of a yield of P4. I calculated that out of 310grams of Ca3(PO4)2 you will get around 15 grams of P4 as yield.
I don't really think creating the oxide is too much of a challange. But reducing the oxide and provideing a inert enviorenemt is th biggest challange.




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thumbup.gif posted on 24-7-2003 at 08:00


Hmmm... I think that whatever phosphate you have, it's a good idea to convert it to H3PO4 by boiling in conc. H2SO4, then convert it to trisodium phosphate by reacting it (a melt is better than solution - - H3PO4 melts at 44C) with CALCINATED soda - water is highly undesirable.
It's melting point is 73 - 77 C.:)
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thumbup.gif posted on 24-7-2003 at 09:13


And the equation for the reaction:
3Na3PO4+5Al+2SiO2=3P+5NaAlO2+ +2Na2SiO3
The sodium salts left over could be used as either alkalis (the corresponding insoluble oxide precipitates - sometimes as a gel:() or as sources of the corresponing chemically active oxide.
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[*] posted on 24-7-2003 at 21:39
maybe I have to revise my statement


that the Castner-Tiegel is the best way for electrolytic sodium production.

The following is quoted from a post a certain "Polverone" made at the HIVE whereby he quotes somebody he correspondended with in usenet. A quote of quotes so to say. ;)
Quote:
As for the sodium, I regret to inform you that I did not make it in my own castner cell I used the most ingenious and safe way that I could find, melt sodium nitrate, obtain a closed container made of soda lime glass and seal it with a wire touching the inside, use that as the electrode where the sodium forms and the ions will migrate though the glass and sodium will be deposited inside, it actually works reasonably well, although more recently I just buy my sodium from eBay.

I always had another opinion on the conductivity of glass, but there maybe a trick. No temperatures nor voltages or currents given. Somebody ever heard of this?

[Edited on 25-7-2003 by Organikum]




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[*] posted on 27-7-2003 at 21:41


I've heard of the method before on Usenet... it's been mentioned as appearing in kids' science fair projects. The person who I corresponded with on these topics is now a member of this forum... care to speak up, You Know Who You Are?
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[*] posted on 28-7-2003 at 08:45


Why wouldn't it work? You don't necessarily need two wires, although I know it's hardwired into our brains that you do. The electrode on the inside is one path for the current, while the migration of ions through the glass is another path for the current.

Your body cells, for example, use the potential difference created by ion pumps to perform biochemical work.

There are many electrodes for quantitative analysis that use the migration of ions through glass. Especially sodium ions can be exchanged on glass surfaces.

[Edited on 28-7-2003 by vulture]




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[*] posted on 28-7-2003 at 16:54


Okay, I'll speak up, I didn't want to post in response because this is the Phosphorus topic, not the Sodium but I will. The basis for the procedure came from an off hand mention to it's production mentioned in an eBook on glassware manipulation, it can be found at Rhodium, the text relevant is as follows:
[ Diffusion through Glass
The mobility of sodium atoms in a soda-lime-silica glass at elevated temperatures is fairly high; if an evacuated bulb of such a glass is dipped into molten sodium nitrate and electrolysis is brought about by bombarding the inside of the bulb with electrons, the circuit being completed with an electrode in the sodium nitrate, then metallic sodium appears in the bulb. By immersing the bulb in other molten salts the sodium ions can be replaced by ions of silver, copper, thallium, and vanadium. ]
The name of the book, etc., were not copied so I cannot give credit where it is deserved.
I am fairly new to electrolysis so there was a lot of trial and error, I have no volt meter so Amps were not measured, I carried out experiments with a big 9V battery for a lantern and some wall adapters, greater then the 9V and some other side reactions seemed to dominate like NO2 formation otherwise it appeared to be N2 and O2 being formed. The glass MUST be thin, I got soda-lime glass from eBay and my first try was an antique bottle, way too thick. Also the vessel must be evacuated, it helps to pull the sodium in I guess keeps the equilibrium favored, and the wire must touch the inside of the bulb below the liquid sodium nitrate line but not at the bottom, if sodium pools around the wire the reaction will go to something else. It doesn't make a whole lot of sodium at a time 5 - 20 g but I'm sure someone could tinker with it and get more approximated values and increase yields, etc. The sodium is liquid at this temperature.

On the topic of phosphorus, just out of curiosity I looked it up in a book of electrode potentials to see if there was an electrolysis procedure for elemental phosphorus manufacture. As I just stated my electrochemistry needs some tweaking, here is what I found.

Electrically conducting phase P(red)
Solvent Water
Temperature 25C
Pressure 760 Torr
Electrode reaction HPO4(2-) + 7H(+) + 5e(-) <---> P + 4H2O
Standard Value -0.288V

There are numerous listed but all the electrically conducting phases are either red phosphorus or white phosphorus and all the solvents are water, how would such a reaction be run?
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[*] posted on 26-12-2003 at 17:50


Wow, I was the last one to post here, and off topic. Anyway, I don't know much about alloys but I know that they use a copper-phosphourus alloy in welding.

Often copper is refined by using a copper cathode and an impure copper anode, the anode dissolves in solution and replates on the cathaode and the sludge of impurites ends up below it in a puddle.

I know that when making red phosphourus by mixing white with molten lead and heating for several days you take the left over lead and electrolyze it similarly to revcover the bulk of the red phosphourus formed.

This copper-phosphorus alloy is readily availible, so would it be possible to isolate the phosphorus in this way?




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[*] posted on 3-1-2004 at 06:59


If you can get hold of a phosphide and acidify it you get PH3. This will decompose on heating to give P4.
Reduction of phosphate by a reactive metal should give the phosphide.
Sulphur reacts with phosphorus so I doubt polysulphide would work as a reductant

[Edited on 3-1-2004 by unionised]
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[*] posted on 5-1-2004 at 20:11


veeeeery interesting unionised. can you give more details? specially the dec temperature. does it completely decompose to P4 and hydrogen or some higher phophines form too?



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[*] posted on 5-1-2004 at 23:00


BromicAcid,

Interestesing post about sodium, it matches what Ive read with a few alterations though....

One book it is mentioned in is Shakashiri's Chemical demonstrations. A bulb is partially immersed in molten sodium nitrate, its powered from an isolating transformer and 2kv is placed between the filement and the container which can be AC or DC the right way round. The hot filment turns the bulb into a vacuum tube and the current flowing through the glass (sodium ions) produces in a short time a mirror coating to the inside of the bulb.

Seeing as it needed 2kv I dismissed the idea, I'm very curios how you got it to work with only 9v and with such large amounts of sodium produced......

Aparently a lot of other ions will replace sodium, but the glass tends to get very brittle and shatters.

The phosphorous by electrolysis looks very strange. I was under the impression Red P or White P didnt conduct electricity. I dont follow either why the acid would be reduced and not the water....
I think perhaps the reaction was measured in reverse to provide a value and that the reaction cannot be run preperativly.

[Edited on 6-1-2004 by Marvin]
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[*] posted on 14-1-2004 at 15:25


For some reason I'm always thinking of phosphorus.... I was going through my notes today (The book is now over 150 pages long with tons of photocopies and handwritten things on 3 x 5 cards jammed in it) and came across:
Quote:

....and R.A. Brooman heated a mixture of silica, iron, coal, and calcium phosphate so as to form a fusible slag and iron phosphide. The latter when heated with sulphur, hydrogen sulphide, carbon disulphide, etc., furnished phosphorus.

Inorganic and Theoretical Chemistry: pg 740 (That's all I have on where it came from, neglected to write down the authors name on the photocopy:( )

All it has for the R. A. Brooman reference in the index was i.b., 2294, 1864 I wish I could track it down because it seems interesting in that it could be carried out by heating with sulfur, I assumed that any kind of sulfur reduction would result in sulfur-phosphorus compounds, I guess their low decomposition temperature got them and in addition such a reaction seems like it would run at a low temperature... well hopefully.

Also I dug up my references from Gmelin for "Labratory Preparation (of phosphorus)" I've looked it over, it's in German of course but I believe there is nothing new there, if someone wants to look at it I can scan it in, it covers Reduction of CaHPO4 with carbon, reduction under HCl or Cl2, Reduction of Hg6(PO4)2, and reduction of sodium hexametaphosphate by aluminum powder, by the way, sodium hexametaphosphate is made by decomposing NH4NaHPO4.

Finally, I talked with one of my teachers about electrolysis of aqueous solutions to yield phosphorus, he told me it can be done with degassed water at temperatures just above the melting point of white phosphorus. He said it melts off and sinks to the bottom, but when I asked which salts could be used he gave one of those "Well it was back when I was in school..." speeches and expected me to forgive him for not remembering, I felt like ringing his neck! :mad:




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