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Author: Subject: Preparation of elemental phosphorus
Zan Divine
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[*] posted on 14-5-2012 at 06:22




[/rquote]

On the contrary, reaction of phosphorous with bromine or chlorine will give rise to phosphorous trichloride/phosphorous pentachloride, which can be used when wanting to synthesize custom phosphine donors, or when wishing to synthesize acyl halides or anhydrides. [/rquote]

Couldn't agree with you more, Steve. The heavy duty chlorinating and brominating agents commercially available to hobbyists are approximately none. While sulfur halides and boron halides can be made, they are nowhere near PCl3 & PCl5 in utility.
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[*] posted on 18-5-2012 at 18:34


Introduction & Background
Recently I performed a high temperature phosphorus experiment using a ceramic tube retort and a tube furnace as first proposed by garage chemist (ref 1). This is the second such experiment that I have performed (ref 2). The main purpose of this experiment was to evaluate 2 equipment changes designed to improve safety and reduce costs. The changes are:

1. A tubulation was added to the 24/40 borosilicate glass tailpipe to allow a slight argon overpressure per the method of Gruson (ref 3). This was to prevent suckback of water into the retort.

2. A new luting compound, made of zirconium silicate/waterglass/water, was to be tried. This cement can be destroyed by soaking in hot 10% NaOH thereby allowing recovery of the glass tailpipe.

As before, the phosphorus making chemistry is represented as:

6NaPO3 + 10Al + 3SiO2 ---> 5Al2O3 + 3Na2SiO3 + 6P

Stoichiometric amounts were used. Basis was 5g of P.

The reactants were ground together in a mortar to a fine powder then poured into the retort. The new cement was then applied to the tapered open end of the retort and the glass tailpipe pressed into place. The cement was allowed to dry overnight at room temperature.

Apparatus Set-Up
The retort was inserted into the tube furnace and the open areas at each end of the furnace tube were plugged with Kaowool. A 12” x 1/8” type K thermocouple was inserted alongside the retort from the back end. The opening of the tailpipe was submerged about ½” below the water surface in the product receiver beaker. A clamp-on ammeter was used to monitor the current to the 220VAC furnace.

IMG_1049 (2).JPG - 106kB

1. Apparatus in mid-run

Run Log
t= 0 minutes: The furnace current was set at 6.7a, initiating heat-up. There was a steady issuance of large bubbles into the product receiver water as the air in the retort heated up. At furnace temperature T= 245C some water condensate could be seen in the tailpiece. More will be said about this water later.

t= 33 minutes: T = 351C and the bubble rate was a steady 1/s.

t=40 minutes: T=400C and the bubble rate was slowing. Turned up current to 7.5a. Turned on hood exhaust fan.

t= 51minutes: Started constant flow of argon (1-2 bubbles/s) as retort gas bubble rate had become very slow. T=516C.

t= 56minutes: T= 550C. Temperature was increasing fast. Suspect the P reduction reaction is taking place. A lot of burning phosphine was issuing at the tailpipe.

t=60 minutes: T=600C. A lot of white smoke was issuing at the tailpipe. Suspect this is P2O5.

t=73 minutes: T=696C. White P has dribbled down tailpiece to within ½” of end. Phosphine stopped 10 minutes or so ago. Keeping argon at 2 bubbles/s. The new luting compound is holding a seal and is only slightly penetrated by red tinted P!

t=85 minutes: T=766C. I = 7.5a.

t=92 minutes: T=800C. Turned off furnace.

t=150 minutes: T=538C. Cut off argon supply and removed product receiver beaker.

t=170 minutes: Removed retort from furnace to cool. Turned off hood fan.

As can be seen in the picture below a film of red P sublimed onto the inside of the glass tailpiece.

The yield of white P in the water receiver was very small, ie, less than 1 g, and this had to be melted with a heat gun to get it to drain into the receiver.

IMG_1050 (2).JPG - 100kB

2. Apparatus at end of run

Examination of the Slag
After the ceramic tube had cooled to room temperature the ceramic tube was circumcised with a Dremel diamond cut-off wheel about ¾” from the tapered female end of the glass tailpiece. The ceramic tube was then crushed in two places using a pair of channel locks. This opened up the tube and allowed examination of the slag. The slag was a black, almost vitreous, vacuoled mass that had expanded to within 2” of the beginning of the taper of the ceramic tube. A small piece of slag was placed into a beaker of water to see if it contained any phosphide as indicated by the generation of phosphine bubbles. There were none generated. The slag floated easily as can be seen in the pictures below.

IMG_1051 (2).JPG - 98kB

3. Slag in retort

IMG_1052.JPG - 95kB

4. Close-up of slag

There was a small amount of sublimed red P in the closed end of the ceramic tube.

Recovery of the Glass Tailpiece
During my screening tests for a suitable luting cement I had found that the cement could be destroyed by soaking in 10% aqueous NaOH overnight. Therefore I placed the tailpiece with ceramic stub in a bath of this solution as shown in the picture below.

IMG_1053.JPG - 84kB

5. Tailpiece cleaning in 10% NaOH

However, after soaking for 40 hours the stub was still cemented tightly to the glass. However, this soaking did remove and dissolve nearly all of the film of sublimed red P as can be seen in the photo. No evidence of phosphine bubbles was noted.

This solution was then discarded and a fresh solution of 10% NaOH was prepared and heated to near boiling. The stub was immersed in this solution and within an hour it had destroyed the cement, and the stub was removed as shown below.

IMG_1054.JPG - 84kB

6. Recovered tailpiece

During the soak in the fresh, hot 10% NaOH many tiny bubbles were being released for 5-10 minutes as the solution penetrated the cement. Suspecting that this might well be phosphine the hood fan was tuned on. The following equation may have been occurring.

3NaOH + P4 + 3H2O ---> PH3 + 3NaH2PO2 (ref 4)

Conclusions and Discussion
It was clear from the run log that the reaction initiates at about T = 550C as indicated by a fast rise in temperature and the sudden presence of burning phosphine and smoky vapors. Therefore, this confirms that when using the above reactants only a moderately high temperature is required.

The 2 new equipment design features have been proven effective by this experiment. The argon purge allowed for an easy shutdown without worrying about a possible catastrophic suckback of water into the retort. The successful glass/ceramic seal and the recovery of the tailpiece are important to safety as well as economic viability.

Although a mass balance was not possible it seems likely that complete or nearly complete conversion of the NaPO3 to phosphorus was achieved. The slag had no apparent white P as would be evidenced by smoking in air. The slag also did not appear to contain phosphide as would be evidenced by its bubbling in water. (Grinding some before water immersion would have been a better test.) However, very little P was actually captured as the desired product, white P: at best 20%.

Some of the product left the reactor as phosphine, PH3. This was simply due to an oversight on my part, ie, the reactants and apparatus should have been well dried before use.

A small amount of phosphorus was converted to a sublimed film of red P. Even if this could be avoided it does not seem of much consequence.

The major loss, as indicated visually, may well have been uncondensed P4 vapor which promptly converted to P2O5, P4O10, and/or H3PO4 as it left the water surface of the receiver. This problem should be mostly solvable by increasing the residence time in a temperature controlled condenser.

Slowing down the reaction rate would also make it easier to condense the P4 vapor. But with an exothermic reaction and the present apparatus that doesn’t seem possible.

References
1. http://www.sciencemadness.org/talk/viewthread.php?tid=65&...
2. http://www.sciencemadness.org/talk/viewthread.php?tid=65&...
3. http://www.sciencemadness.org/talk/viewthread.php?tid=65&...
4. College Chemistry, 7th ed (1984), by Holtzclaw et al, p. 686.

As always, questions, comments, and suggestions are welcomed.




[Edited on 19-5-2012 by Magpie]

[Edited on 19-5-2012 by Magpie]




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thumbup.gif posted on 19-5-2012 at 06:57


In celebration of <b>10 years of Sciencemadness</b> I have put together a summary of this thread. Unfortunately the summary does not include any of the information from the brilliant post from Magpie directly above this post. Great work!

The file is being attached to this post however how people further off in the future who are pages away will know this post is even here is debatable. Especially considering I wrote this for people who are too impatient to even skim the thread :P

Attachment: Phosphorus Summary.pdf (204kB)
This file has been downloaded 841 times

PS- This is not meant to be a living document. It will not be updated. It is merely here to get people up to speed on what has been attempted and how things have panned out in those attempts. I am also attaching the HTML version which I created the PDF from in case someone in the future want's to tinker with it. I have been told by others that the internal links within the HTML file may not work on all systems.

Attachment: Phosphrous Summation.htm (112kB)
This file has been downloaded 914 times

[Edited on 5/19/2012 by BromicAcid]




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[*] posted on 24-5-2012 at 05:46


Quote: Originally posted by blogfast25  
Quote: Originally posted by Myfanwy  
could phosphine and hydrogen peroxide yield some P4?

2PH3 + 3H2O2 -> 6H2O + 1/2 P4



Possibly but why go to the trouble of making a highly toxic, highly inflammable gas when you can make P from Calgon tablets, some fine sand and some Al powder?


Sorry to bring up an old post, but many people seem to make phosphine inadvertently, as a result of accidental production of phosphide sideproducts.

Yes I know phosphine is notorious, but what if we tried to make a phosphide on purpose and then convert the phosphine into P4?

Does phosphorus react with H2O2?




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[*] posted on 24-5-2012 at 08:11


@ magpie: beautiful work sir! glad you were able to recover the fitting. i wonder that using a gas for positive pressure may have contributed to the early cooling of the P4 gas inside the glassware? is it possible to inject the gas from the other side of the heat source so that your yield stays hot until it reaches the water? the general form of a tube furnace suggests much difficulty in the proposition... what alterations do you have in mind for future runs?

@bromic acid: your effort in compiling and efficient pruning of this thread will be a great help to anyone new who may wish to take up the torch and run. it is visually appealing as well. excellent work!




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[*] posted on 24-5-2012 at 13:01


Quote: Originally posted by Rogeryermaw  
@ magpie: beautiful work sir! glad you were able to recover the fitting. i wonder that using a gas for positive pressure may have contributed to the early cooling of the P4 gas inside the glassware? is it possible to inject the gas from the other side of the heat source so that your yield stays hot until it reaches the water? the general form of a tube furnace suggests much difficulty in the proposition... what alterations do you have in mind for future runs?


Thank you. Injecting the argon from the back end would be possible but would take some extra work and expense. When the retort is in the green stage a mullite tube, such as a thermocouple sheath, could conceivably be attached to the back end. But I'm skeptical that this would be of much help. Also the argon would then have to move through or around the molten slag. This might or might not be a problem. Although from my picture it seems as though there is a lot of P in the tailpipe, it is just a sublimed film so I don't think it amounts to much P.

I'm working on a prototype of a 12" air condenser that would extend down to the water receiver. I'm expecting that the P will condense in the tube and freeze. But the tube is vertical so I can keep it moving down to the receiver using a heat gun.

I spent some time reviewing your excellent work, specifically looking for indications of yield. The numbers I found indicate that your typical yield was about 6.5g. This was on a charge of 102g of NaPO3 which would give a theoretical amount of P = 31g. So your yield was ~ 21%. Please correct me if my figures are wrong.

I'm hopeful that as we research this method that we can find ways to increase the yield as there is obviously a lot of P not being captured.





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[*] posted on 24-5-2012 at 19:11


your figure seems about correct. i have been thinking a lot about this lately and i wonder how much the yield of this sort of method can really be increased. is it really possible to stop or even reduce the formation of PH3? when i have done this at night i have also noticed (the setup has a glass receiver with a loose fitting lid) a bluish-white glow around the area where the pipe passes the lid which indicates a loss of P4 to inefficient cooling caused by fear of suck-back related catastrophe (shallow immersion giving the extremely hot P4 gas little time to cool to the condensation point). there are numerous possibilities to consider . all in all, considering the state of the world, i'm happy to be able to experiment with phosphorus at all, even if procuring it is, as yet, inefficient.

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[*] posted on 24-5-2012 at 19:15


Quote: Originally posted by Magpie  
The yield of white P in the water receiver was very small, ie, less than 1 g, and this had to be melted with a heat gun to get it to drain into the receiver.

That could be because phosphorous, in a finely divided state, might actually react with water.
http://www.sciencemadness.org/talk/viewthread.php?tid=20064

This could potentially explain your low yields passing hot phosphorous vapor to condense in water.


[Edited on 25-5-2012 by AndersHoveland]
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[*] posted on 24-5-2012 at 20:33


Quote: Originally posted by Rogeryermaw  
...is it really possible to stop or even reduce the formation of PH3?


The formation of PH3 requires the presence of hydrogen. None of the reactants contain this. So if we can get the bulk of the P4 condensed to a liquid before it hits the water there should be little phosphine produced.

Quote: Originally posted by Rogeryermaw  

...all in all, considering the state of the world, i'm happy to be able to experiment with phosphorus at all, even if procuring it is, as yet, inefficient.


Amen.




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[*] posted on 24-5-2012 at 23:34


I really do not know, but I do not think that elemental phosphorous readily reacts nitrogen directly. There seems to be very little information about this available.

http://www.sciencemadness.org/talk/viewthread.php?tid=20208#...

[Edited on 25-5-2012 by AndersHoveland]
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[*] posted on 26-5-2012 at 12:37


yes specific information is hard to find but there are some syntheses using elemental phosphorus that recommend nitrogen as an inert atmosphere so i rather doubt they react directly.
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[*] posted on 28-5-2012 at 07:13


We know, from existing literature, that P & N probably don't react at these low temperatures. We also know that leading hot P4 vapors into H2O is not generally problematic in that it's been done that way for a long time and still is.

I'll be the first to admit that when all factors are considered, it's way, way easier said than done, but the mass change of the reactor/tailpiece (once P is melted out) could be hugely indicative of the nature of the problem. For instance, you may have to pre-bake the reactor, reactants, & luting to get a reliable starting weight.

I'm not sure I'd automatically assume that you released all the missing P as PH3 or as P that oxidized to P4O10. You'd have really noticed a lot of smoke and/or stench. I'm more inclined to worry about incorporation into the slag as red P or possible incomplete reaction due to some reactant segregation.

A long standing practice in leading hot vapors into water is to use a wide tube to avoid suck-back of water into the reactor. You want the tube to be a significant volume compared to the volume of the reactor. Your new vertical tailpiece may be very appropriate if wide enough.

I've been handling a lot of molten P recently, and the thing that amazes me is the simplicity of operations and ease of handling.
I was a little surprised to find that 1 or 2 gram samples of commercial white P can be placed on a room temperature surface outside and they just sit there, emiting an occasional wisp of smoke and liquify and after 5 minutes will not ignite.

It's time to end some of the widely held ideas that P is a fearsome thing too dangerous to play with. It's really this simple: Keep it underwater, work in a ventilated area. You can easily move it through air with forcepts to its next watery location. No fire. I was amazed to find that this dragon was, in reality, a docile pet when just the simplest precautions are taken.

This doesn't take away from the inherent level of risk you faced with P vapor @ >500 C. That may well be the dragon.;)

When I lit it, it burned fiercely with mountains of the oxide billowing away. I'd guess that a gram of P being liberated as this was would totally fill a room with thick smoke. Your aerosol size many vary, of course.

You really took some time with your work & presentation, Magpie, and your work has all the hallmarks of a career scientist.



[Edited on 28-5-2012 by Zan Divine]




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[*] posted on 28-5-2012 at 09:15


Quote: Originally posted by Zan Divine  
... We also know that leading hot P4 vapors into H2O is not generally problematic in that it's been done that way for a long time and still is.


Agreed.


Quote: Originally posted by Zan Divine  

I'll be the first to admit that when all factors are considered, it's way, way easier said than done, but the mass change of the reactor/tailpiece (once P is melted out) could be hugely indicative of the nature of the problem. For instance, you may have to pre-bake the reactor, reactants, & luting to get a reliable starting weight.


Agreed. I plan to do just that.

Quote: Originally posted by Zan Divine  

I'm not sure I'd automatically assume that you released all the missing P as PH3 or as P that oxidized to P4O10. You'd have really noticed a lot of smoke and/or stench. I'm more inclined to worry about incorporation into the slag as red P or possible incomplete reaction due to some reactant segregation.


Agreed. In reviewing some of Rogeryermaw's work it is apparent that a relatively small amount (I'm assuming <6g) of burning P emits a huge amount of white smoke. See his video where he burns P on top of a wood post on his patio.


Quote: Originally posted by Zan Divine  

A long standing practice in leading hot vapors into water is to use a wide tube to avoid suck-back of water into the reactor. You want the tube to be a significant volume compared to the volume of the reactor. Your new vertical tailpiece may be very appropriate if wide enough.


It's not very wide and I'm hoping that this will not become a problem. It may be an Achilles heel, unfortunately - not from a suckback standpoint as I will be using an argon purge, but from a plugging standpoint.


Quote: Originally posted by Zan Divine  

I've been handling a lot of molten P recently, and the thing that amazes me is the simplicity of operations and ease of handling.
I was a little surprised to find that 1 or 2 gram samples of commercial white P can be placed on a room temperature surface outside and they just sit there, emiting an occasional wisp of smoke and liquify and after 5 minutes will not ignite.


My observation, also.


Quote: Originally posted by Zan Divine  

It's time to end some of the widely held ideas that P is a fearsome thing too dangerous to play with. It's really this simple: Keep it underwater, work in a ventilated area. You can easily move it through air with forcepts to its next watery location. No fire. I was amazed to find that this dragon was, in reality, a docile pet when just the simplest precautions are taken.


Agreed.


Quote: Originally posted by Zan Divine  

This doesn't take away from the inherent level of risk when you faced with P vapor @ >500 C. That may well be the dragon.;)

Most assuredly.


Quote: Originally posted by Zan Divine  

When I lit it, it burned fiercely with mountains of the oxide billowing away. I'd guess that a gram of P being liberated as this was would totally fill a room with thick smoke. Your aerosol size many vary, of course.


Yes - see Rogermyermaw's video.


Quote: Originally posted by Zan Divine  

You really took some time with your work & presentation, Magpie, and your work has all the hallmarks of a career scientist.


Thank you. Unfortunately the career scientist thing is all behind me now.

It's good to have this body of work critiqued by a fresh set of experienced eyes.




[Edited on 28-5-2012 by Magpie]

[Edited on 29-5-2012 by Magpie]




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[*] posted on 28-5-2012 at 20:31


many of your observations are spot on. a couple of points if i remember right...the molar mass of phosphorus is close to 31 grams. i based my experiments on 1 mole of sodium hexametaphosphate. when i measured, i had a rough starting mass of 217 grams with all reactants combined (after drying in oven) and a post run weight of 199.8 grams. even with a conservative estimate (owing some loss to the brittle nature of the slag) the reactant mass lost in the neighborhood of 15-17 grams. with the collection of 6+ grams of P4, that is an anus load of product to account for. the weight is not there so we can rule out P4 being trapped in the reaction mass. i know for a fact that some burns away from performing this experiment at night. there is no mistaking the ghostly glow of phosphorus vapor. it is possible that we don't see as much of the P4O10 as we should think; perhaps it is absorbed into the receiver water forming phosphoric acid. a post run pH test of the water may confirm this but, even if positive, this does not explain all the losses. the thought of the mass containing some red phosphorus had not occurred to me and certainly bears investigation but i have a feeling that the answer to this will only be solved through trial and error. we will chip away little by little at the imperfections of this process until the yields increase and then there will be some sore foreheads after the mass *facepalm* of realization.

only one thing bugs me here. please do not get comfortable with the safety of phosphorus. she is a wicked, backstabbing bitch that will only bite you when you stop looking. the reason that it sometimes fails to auto-ignite is that even the slightest breeze can carry enough heat away from it to slow the process. if it is sunny out and the wind stops, it will go eventually. don't handle it with your hands too much, even in gloves. not only can your body heat do the job, a residue can rub off on your hands that may contaminate other things. the lowest known lethal dose of P4 is in the neighborhood of 15mg (i know the LD50 is closer to 50 mg). mostly, however, you are correct. with the safeties in place, phosphorus has been a pussycat to handle. i just don't want the young bucks to get it in their heads that the dangers are imaginary.

for those interested, some health and safety info can be found here: www.atsdr.cdc.gov/toxprofiles/tp103-c2.pdf

[Edited on 29-5-2012 by Rogeryermaw]
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[*] posted on 29-5-2012 at 09:25


Has anyone tried powdered iron as a reducing agent? Perhaps the lower melting point of its oxide as compared to those of aluminium and magnesium may allow for better mixing and a more complete reaction.



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[*] posted on 29-5-2012 at 13:17


iron readily forms phosphides with P4 in high heat.

that is actually involved in one of the industrial methods to produce P4 (well sort of. the iron is from impurities and undesirable). iron in the crucible will form iron phosphide from which PH3 is produced and then burned away to yield P4. however, the handling of that much PH3 is too scary for me.

[Edited on 29-5-2012 by Rogeryermaw]
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[*] posted on 30-5-2012 at 11:03


Excellent work, Magpie.
I also have a selfmade ceramic retort at home, but haven't been willing to use it for this synthesis because I knew that it would be a single-use item, with no possibility of reuse because of the hard glassy slag that cannot be removed from the retort.
With the amount of work and time that goes into making a ceramic retort, I don't think of this as a good way to make phosphorus, though at least it DOES work, which sets it apart from so many of the theoretical methods posted here.
I also haven't been able to attach a glass tube to my retort, which you were able to do.



[Edited on 30-5-2012 by garage chemist]




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[*] posted on 30-5-2012 at 12:26


Quote: Originally posted by garage chemist  
Excellent work, Magpie... With the amount of work and time that goes into making a ceramic retort, I don't think of this as a good way to make phosphorus, though at least it DOES work, which sets it apart from so many of the theoretical methods posted here.

Thank you. Yes, it does work, but still needs a lot of development.

The tube materials are very cheap (<$1) but the time required is considerable. Also, one must have a 1300C furnace for firing, as you know. It takes me about a week, working on and off, to make one. At least now I have a sure-fire procedure and don't get any failures. The last tube I made was #21.

Quote: Originally posted by garage chemist  

I also haven't been able to attach a glass tube to my retort, which you were able to do.


Yes, I tried a lot of formulations before finding one that works. Here's the formula:

*10g pottery grade ZrSiO4
*17 drops "as received" pottery grade waterglass
*add just enough water to get good fluidity

I make mine in a small beaker using a stirring rod.

The bond can then be destroyed with near boiling 10% NaOH.

I have used it twice now, both times with good results.

[Edited on 30-5-2012 by Magpie]

[Edited on 30-5-2012 by Magpie]




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[*] posted on 30-5-2012 at 15:37


Quote: Originally posted by Rogeryermaw  
many of your observations are spot on. a couple of points if i remember right...the molar mass of phosphorus is close to 31 grams. i based my experiments on 1 mole of sodium hexametaphosphate. when i measured, i had a rough starting mass of 217 grams with all reactants combined (after drying in oven) and a post run weight of 199.8 grams. even with a conservative estimate (owing some loss to the brittle nature of the slag) the reactant mass lost in the neighborhood of 15-17 grams. with the collection of 6+ grams of P4, that is an anus load of product to account for. the weight is not there so we can rule out P4 being trapped in the reaction mass.

[Edited on 29-5-2012 by Rogeryermaw]


Forgive me if you've already said so, but was the phosphate really dry? Unless you dry it by fusion, or to constant weight in a drying pistol at high temp with P2O5 in the other end, you can be sure that some of the weight loss was water. You really have to work to get it dry. I melted it in an electric furnace and got a hard glassy solid that is real work to powder.

[Edited on 30-5-2012 by Zan Divine]




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[*] posted on 31-5-2012 at 08:36


Reduction of sodium hexametaphosphate with a sufficiently active metal such as pyrotechnic aluminum or powdered magnesium and either silica or boria is relatively straight forward. The reactants, when thoroughly mixed and sufficiently heated, will combust to provide the required reaction heat. If the reaction tube is long enough, you should have no difficulty segregating the free P from the reaction slag using heat.
Pure magnesium is a bit too fast ( I used 100 mesh powder in my one experience with it) as it blew out the stopper of the reaction tube with a loud bang although it did not destroy the test tube reactor. Perhaps a powdered magnalium (Mg/Al, 50:50) would work a bit better. In the US at least these materials are readily available, particularly at this time of year.
The best I could do in efficiency was about 50%, however. It would indeed represent some advancement if someone could positively identify where and in what form the other 50% of theoretical P was.
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[*] posted on 31-5-2012 at 09:06


Quote: Originally posted by Strepta  
Reduction of sodium hexametaphosphate with a sufficiently active metal such as pyrotechnic aluminum or powdered magnesium and either silica or boria is relatively straight forward.


What differences did you notice when boria was substituted for silica?




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[*] posted on 31-5-2012 at 09:24


When heating the reaction mix with boria, it began to noticeably shrink and curl before combustion onset as boria fuses at a lower temp than silica. Also, I obtained by best yield with boria (52%) although it was not significantly greater than with silica (48-50%). Does the lower melting point of boria mean it provides a better flux?
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[*] posted on 31-5-2012 at 09:49


I'm not sure of the mechanics of boria vs silica. I just know that boria has a much lower mp (450C or 510C) than silica (1600-1725C). This should mean that it is a liquid at the reaction temperature, where silica might not be. Boria should promote a more efficient reaction, as all reactants would then be liquid.

We are already fighting a lack of any stirring or agitation.

It is known by potters that alumina increases the viscosity of a melt. So I assume this is working against us. Alumina, however, is a by-product in both cases when aluminum is used as the reductant.

If boria produces a less viscous less voluminous slag this might also be an advantage.

[Edited on 31-5-2012 by Magpie]




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[*] posted on 31-5-2012 at 12:10


Quote: Originally posted by Zan Divine  


Forgive me if you've already said so, but was the phosphate really dry? Unless you dry it by fusion, or to constant weight in a drying pistol at high temp with P2O5 in the other end, you can be sure that some of the weight loss was water. You really have to work to get it dry. I melted it in an electric furnace and got a hard glassy solid that is real work to powder.



as dry as i could get it by conventional means. about 2+ hours in the oven at over 350f. it was partially fused and had to be broken up before loading the vessel.

Quote: Originally posted by Strepta  
When heating the reaction mix with boria, it began to noticeably shrink and curl before combustion onset as boria fuses at a lower temp than silica. Also, I obtained by best yield with boria (52%) although it was not significantly greater than with silica (48-50%). Does the lower melting point of boria mean it provides a better flux?


if it swells less then a larger charge could be used. this doesn't change efficiency but would allow one to produce more P4 per run thereby requiring less runs to produce the product needed. definitely an advantage.



[Edited on 31-5-2012 by Rogeryermaw]
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[*] posted on 2-6-2012 at 12:25


I'm not sure if this has already been discussed, but is trisodium phosphate a suitable replacement to sodium hexametaphosphate?



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