Sciencemadness Discussion Board - Preparation of elemental phosphorus

... In the reaction you're using it for, I'd worry about the mineral content of a ceramic acting as a reagent. For example, I wouldn't use talc, because it's a hydrated mineral. I'd have to guess that hot gaseous phosphorus would dehydrate it, reducing your yield.

Talc is (OH)2Mg3(SiO5)2. According to Norton's Fine Ceramics - Technology and Applications, p.250, talc dehydrates at 900-950C to protoenstatite and glass. Therefore water should not be present after firing of the vessel, preliminary to use in the phosphorus reaction.

You also want something that your reaction fluid won't simply dissolve.

I don't know if that would be a problem with the protoenstatite. Do you?

watson.fawkes - 28-9-2012 at 09:51

Ah. I had been thinking that you could find a mixture that you could ram up and then fire in place the first time it was used, rather than pre-firing it. It would save a step. Sorry; I hadn't thought to say that.

I'd guess a magnesia-silica ceramic would be fairly resistant to molten boria. But as with all these ideas for ceramic liners, it'd need to be tested. It might be a good idea to run a test with just melting boria without reaction first, in case there's some rampant incompatibility.

Magpie - 28-9-2012 at 12:49

I have just finished preparing a paint can lined with 90%talc/10%EPK kaolin. It will take a day or two to dry then I will fire it to as high as my furnace will go - likely ~1000C.

@ watson: I will make a second lined can using a red fireclay as a base as you proposed. I also have on hand nepheline syenite (K2O/Na2O), custer feldspar (K2O), EPK kaolin, alumina, and a fine grog. What ingredients and in what proportions would you recommend?
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Edit: I suspect that the red fireclay is not what I should be using. What I think you are suggesting is a high alumina fireclay, which I would guess is either the Lincoln that you mentioned or a Hawthorne (Missouri) fireclay. I will research this. Let me know if my assumption is correct.

Today I prepared a 2nd paint can lined with Rutland's "Chimney Sweep" furnace cement. This rammed in nicely.
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2nd edit: After 48hr in NaOH at room temperature the boria hard-as-a rock slag has disintegrated to a brown floc. I will test a piece of slag in boiling NaOH tomorrow.
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3rd edit: A small piece of boria slag completely disintegrated in boiling 10%NaOH in less than 1/2 hr. Initially, as before, there was a great quantity of small bubbles emitted - likely due to unreacted Al.

[Edited on 29-9-2012 by Magpie]

[Edited on 29-9-2012 by Magpie]

[Edited on 29-9-2012 by Magpie]

[Edited on 29-9-2012 by Magpie]

[Edited on 29-9-2012 by Magpie]

blogfast25 - 28-9-2012 at 13:07

Reading back the last pages I came across this:

And it seems thermodynamically unfavorable to reduce to B instead of P. There's still the issue of the Al not completely oxidizing. But if you're lucky, the borate might further oxidize to perborate with oxidation state B⁵⁺.

B(V)? The (simplified) electron configuration of boron (Z = 5) is 1s2 2s2 2p1. For the pentavalent state the inner electrons 1s2 would have to get involved! The structure of ‘perborate’ (e.g. NaBO3) doesn’t involve pentavalent boron.

Also, has it occurred to anyone that both SiO2 and B2O3 are reducible by Al? For SiO2 the reduction with Al is exothermic by about – 200 kJ/mol (Standard Enthalpy of Reaction). For B2O3 I don’t know but I know AlB12 is synthesised by reaction of boric oxide and aluminium.

So, are we sure that it is ‘thermodynamically unfavorable to reduce to B instead of P’?

[Edited on 28-9-2012 by blogfast25]

[Edited on 28-9-2012 by blogfast25]

Edit: based on NIST Webbook HoFs, for B2O3 + 2 Al ===> 2 B + Al2O3 the SEoR is 1273 – 1676 = -403 kJ/mol. Methinks you might be producing boron in there! And thus of course also less P4…

I think it might be worth running a test without any slagformers like SiO2 or B2O3, you might get surprisingly high yields...

[Edited on 28-9-2012 by blogfast25]

White Yeti - 28-9-2012 at 18:13

Perhaps you could consider a mix of carbon and aluminium powders. The aluminium would warm up the reaction enough for the reduction with carbon to take place.

Magpie - 28-9-2012 at 19:53

Edit: based on NIST Webbook HoFs, for B2O3 + 2 Al ===> 2 B + Al2O3 the SEoR is 1273 – 1676 = -403 kJ/mol. Methinks you might be producing boron in there! And thus of course also less P4…

This might be at least a partial explanation for the poor yield of P when using SiO2.

We don't know yet what the yield of P would have been with the boria due to the blowout of the retort. Hopefully we will soon find out with a hardened paint can retort.

I think it might be worth running a test without any slagformers like SiO2 or B2O3, you might get surprisingly high yields...

The slag could contain significant AlP. One would have to be careful not to let that contact water due to PH3 generation.

blogfast25 - 29-9-2012 at 06:02

The slag could contain significant AlP. One would have to be careful not to let that contact water due to PH3 generation.

The HoF of AlP is referenced by Wolfram Alpha as a mere – 166.5 kJ/mol, not a lot.

I think that in a stoichiometric mix (NaPO3 + Al) the formation of AlP isn’t very likely, for that reason. And AlP doesn’t react very fast with water, so the risk of phosphine generation is fairly small too.

I don’t recall this entire lengthy thread but I’ve a feeling the SiO2 kind of got carried over from the initial Ca triphosphate + cokes + silica very high temperature method. I’m not sure whether in the lower temperature reduction using aluminium silica still has a role to play. I’ve seen great strides forward being taken (by Magpie) in terms of reactor/condenser design that haven’t really materialised in great gains in yield. Maybe we’re overlooking something?

[Edited on 29-9-2012 by blogfast25]

Rogeryermaw - 1-10-2012 at 20:52

magpie, in some of my experimentation, i have ground up my slag and tested it with water and HCl and noted no gas generation. this has been quite some time ago (over a year) but the test was negative, all the same. that is not to say that the formation of AlP is not possible given differing ratios of reactants and differing grain sizes ect. but only that i personally did not encounter it. also, i wonder if it is possible at all for alumina to form as part of this reaction...would not the heat required to form alumina render the reaction vessel completely destroyed on the first run?

Magpie - 1-10-2012 at 21:39

Roger, I usually see some bubbles emitted when cleaning up the condenser in 5% NaOH. I keep the hood fan on then place the bath outside for a couple days. I also see bubbles when placing the boria slag in HCL or NaOH. I think these bubbles are most likely due to unreacted aluminum. So whether PH3 is a real problem or not I cannot say. I will assume it is a potential problem until I'm convinced otherwise. I do not see any PH3 burning, however - but this may be because everything is at room temperature.

I know we talked about the need for SiO2 way upthread to allow complete conversion to elemental P and prevent the formation of AlP. I need to reread those posts.

I made a run with boria today (#6), which was successful. I'll report the results tomorrow.

blogfast25 - 2-10-2012 at 04:08

A deeper search for the HoF of P2O5 yielded two values, one of – 3382 kJ/mol (which sounds inordinately high compared to other pentoxides!) and one derived from:

3 Ca + 3/2 O2 == > 3 CaO ….. 3 x – 635 kJ/mol (NIST)
2P + 5/2 O2 == > P2O5 …. Say, X
3 CaO + P2O5 == > Ca3(PO4)2 …. Say, Y

Sum:

3 Ca + 2P + 4 O2 == > Ca3(PO4)2 ….. – 4132 kJ/mol (Wiki)

So according to Hess we’d have – 4132 = 3 x (- 635) + X + Y

Assuming Y to be small compared to the other values, then X ≈ - 2227 kJ/mol.

That’s also a real whopper but significantly smaller than the – 3382 value. The latter would make the reduction of P2O5 with Al endothermic, the - 2227 value would make it exothermic, so really I’m still none the wiser. High temperature and the escape of one of the reaction products would always push the reduction equilibrium to the right but if highly endothermic then yield could be small and other reduction reactions (silica, boria) might be favoured. But right now that can’t be stated with any certainty…

It all does seem to indicate that the HoF of P2O5 (and hence also of phosphates) is very high and that it might be very difficult to reduce it to P with high yield in relatively low temperature conditions. The carbothermic reduction has two gaseous reaction products and is carried out well above Magpie's temperatures.

[Edited on 2-10-2012 by blogfast25]

[Edited on 2-10-2012 by blogfast25]

Another thing that puzzles me is that thermodynamically speaking Na2O is quite easily reduced by Al, so that the reduction of NaPO3 (well, (NaPO3)6) should go all the way: NaPO3 +2 Al == > Na + P + Al2O3. This is not the case with Ca phosphates because CaO is not reducible by Al.

[Edited on 2-10-2012 by blogfast25]

watson.fawkes - 2-10-2012 at 06:48

Unlike percarbonate, perborate isn't an adduct. See Wikipedia on sodium perborate. So apparently the 1s electrons do hybridize. Boron is a complete outlier here. The hybrid only seems possible because there is no "1p" electron state that would have energy between 1s and 2s. Apparently the ion is tetrahedral, though I can't cite a definitive reference (I looked; nothing very handy).

The peroxocarbonate ion CO₄^2- has one oxygen in the configuration O-O-C and the carbon atom coordinates its bonds with three oxygen atoms, as with carbonate. It's certainly conceivable that a tetrahedral CO₄^2- ion exists at high pressures, after a phase change.

blogfast25 - 2-10-2012 at 08:48

@watson:

Interesting, very much 'outside the box'.

Any thoughts on my other musings?

arsphenamine - 2-10-2012 at 09:41

re: aluminothermic boron reactions: a calculated exothermic heat of reaction doesn't tell you about the energy of the transition state,i.e., that it can be initiated. Luckily, boro-thermite reactions are an empirical fact.

re: 1p orbital classification: for consistency with prior nomenclature, its absence is a convention by decree, right up there with motion of (+) charges in electrical circuit analysis.

I'll get back to you on Boron 1s involvement once I see the Lowdin charges.

arsphenamine - 2-10-2012 at 10:46

Expired equine flagellation:

The optimized geometry with VanDerWaals spacing is shown below.

The overall electron density plot is very similar.

Ab initio calcs on Li2perborate.trihydrate show very slight Boron 1s involvement. Non-involvement would give a 1.99 or 2.00 Lowdin charge, as you'd expect. I get 1.96. (Lithium computations don't take as long as sodium, isoelectronic valence shells, etc.)

Renderings using Jmol show spherically symmetric boron 1s orbitals, meaning either a full or half-full shell. 1.96 Lowdin charge sez full.

While you're at it, grab a copy of JMOL for molecular rendering and editing.

Structure was optimized using Mopac2012 at the PM7 level; orbital groveling was at 6-31++G(dp) with GAMESS May2012(Rev.1).

[Edited on 2-10-2012 by arsphenamine]

Magpie - 2-10-2012 at 11:53

A 25g charge using boria was run yesterday (run#6). The paint can retort was lined with 1cm of Rutland’s “Chimney Sweep” furnace cement. After ramming the cement in place the retort assembly was heated slowly to 260C per Rutland’s instructions to cure the cement. The assembly was then heated to 750C to burn off the tin plating on the can and to drive off remaining water from the cement. The finished pieces are shown below:

Retort with furnace cement

Ground Boria was mixed with the aluminum and ground NaPO3 by mixing in a capped bottle to keep out moisture. The mix was placed in the retort, previously back-filled with argon. The assembly was placed in the furnace, the thermostat set for 750C, and heating was begun. When 750C was reached there was as yet no reaction so the temperature was held there for 15 minutes. The thermostat was then set for 800C. Shortly thereafter the reaction began and a steady, slow production of P, burning PH3, and white smoke occurred. The P was of very good quality, ie, white and uncontaminated. The weight of P was 1.0g for a yield of 27.8%. The P is shown in the picture below:

Run#6 phosphorus

Today the retort was removed from the furnace. It was covered with velvet colored rust as shown here:

Run#6 fired can with rust

The fired weight of the assembly was 2.9g heavier than the unfired weight. This could be due in part to the formation of that rust. Also, the ~530g weight of the assembly is at the upper limit of my scale’s capability, which may be introducing some inaccuracy.

The assembly was then opened. This was done with difficulty as the lid was stuck to the can. You can see that the slag vacuoles are very large. The inlet to the snorkel was again about 50% plugged with slag. The opened assembly is shown here:

run#6 retort assembly opened.JPG - 131kB

Run#6 retort assembly opened
The final picture shows the snorkel and lid being removed from the condenser. The technique shown here is now routine:

removal of snorkel & lid from condenser.JPG - 136kB

Removal of snorkel & lid from condenser

Discussion
I decided to cut the charge in half from the previous run because the furnace cement lining had consumed nearly half of the can’s available volume. I believe this lining width (1cm) could be cut at least in half for future runs. The cement is a very tough material and was completely undamaged by the firing.

The 27.8% yield is the best I have achieved with any of my phosphorus making runs. It is also noteworthy that the production was slower and steadier than that of any of my previous runs.
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In rereading the posts of not_important and Strepta I find that they assumed a different borate reaction product and therefore used 1/2 the boria that I've been using. Also, Strepta recommended a 15% excess of aluminum.

So my next run (#7) will use Strepta's assumed reaction (p.14 upthread) and the 15% Al excess. I will cut back the thickness of the retort lining to 0.5cm, and increase the charge size to 35g. I know this is poor experimental technique in regard to changing too many variables at one time, but at this point I'm after production.

Questions, comments, and recommendations are welcomed, as usual.

[Edited on 3-10-2012 by Magpie]

watson.fawkes - 2-10-2012 at 22:08

Any thoughts on my other musings?

I can't make much sense of the thermodynamic figures by themselves. It's clear that activation energies are at play, given that Magpie has reported "ignition" temperatures, very indicative of overcoming an activation energy level with thermal excitation. But upon mulling over one of your observations, there's like more energies yet at work.

Another thing that puzzles me is that thermodynamically speaking Na2O is quite easily reduced by Al, so that the reduction of NaPO3 (well, (NaPO3)6) should go all the way: NaPO3 +2 Al == > Na + P + Al2O3.

Molten boria and phosphorus oxides form a solvent system for Na⁺ ions. There's almost certainly something like a heat of solvation happening here. If the Al can't reach an Na⁺ ion because of steric hindrance from coordinated B and P oxides, it can't reduce it. And even if it could, it's not clear to me that taking the Na⁺ ion out of solution doesn't turn the net Al-Na redox reaction endothermic.

blogfast25 - 3-10-2012 at 07:28

@Magpie:

Nice work, even though yield still isn't great. One has to wonder what it would do on scaling up...

One banal question: how do you remove the slag from your improved retort? That stuff must be rock hard, no pun intended!

Magpie - 3-10-2012 at 07:49

Nice work, even though yield still isn't great. One has to wonder what it would do on scaling up...

Thanks. Yes, I think %yield should increase with increasing charge size. I have to cautiously sneak up on the upper limit as I don't want another blowout and consequent furnace fire.

I am limited to a 1/2 pint (250mL) paint can due to the size of my furnace box. The box is wide enough to double that size but expendable cans with compression seals don't come in that shape.

One banal question: how do you remove the slag from your improved retort? That stuff must be rock hard, no pun intended!

I don't. The can is expendable ($2.50 ea). That, and the lid's compression seals, are the keys to this particular technology. Only the condenser, spacing washer, and snorkel are reuseable. The condenser is fairly expensive ($30) as I had to hire a welder/machinist to make it.

m1tanker78 - 3-10-2012 at 15:50

I've been following along and have a few questions. Apologies if this has been covered - long thread!

1. Thermodynamically, what is the probability of formation of sodium phosphide(s) in this reaction?

2. What do you expect would result from addition of an alkali metal (say, sodium) to the mix?

3. What of the effects of pressure/vacuum on the reaction and outcome?

4. Could the reaction be carried out in a vertical reactor with some sort of check valve at the top. After reaction and cool down, back fill the reactor with water and collect WP manually?

I've never messed around with WP so I don't know if it tends to stick to steel (referring to #4). As for #2, my thinking is that the alkali metal could help to sop up some additional oxygen and possibly 'flux' the reactants. If Na3P formation is strongly favored then this would obviously be counter-productive.

I want to take a shot at this but need some fresh ideas.

Tank

p.s. Magpie, thanks for taking the time to illustrate your experiments. Nice work so far!

Magpie - 3-10-2012 at 16:29

...
4. Could the reaction be carried out in a vertical reactor with some sort of check valve at the top. After reaction and cool down, back fill the reactor with water and collect WP manually?

The phosphorus is generated as a gas at over 500C. It's going to move right out of the reactor as soon as it is generated. It won't condense until it is cooled below its bp which is 280.5C.

I've never messed around with WP ...I want to take a shot at this but need some fresh ideas.

Just remember the words of Rogeryermaw..."Phosphorus is a back stabbing bitch," or something like that. It's not only potentially lethal if inhaled or ingested, but WP will ignite on contact with air, making it very much a fire hazard!

p.s. Magpie, thanks for taking the time to illustrate your experiments. Nice work so far!

You're welcome, and thanks.

[Edited on 4-10-2012 by Magpie]

blogfast25 - 4-10-2012 at 06:38

Ooops. It does make for rather a lot of slag piles for relatively little product.

watson.fawkes - 4-10-2012 at 06:47

It does make for rather a lot of slag piles for relatively little product.

<voice actor="Raul Julia" character="Gomez Addams">It's research!<voice>

Magpie - 6-10-2012 at 07:57

Phosphorus run #7 was made yesterday using a charge of 35g based on the following stoichiometry:

6NaPO3 + 10Al + 3B2O3 ---> 6NaBO2 + 5Al2O3 + 6P

This is ½ the boria used in the previous run #6. To this was added 1.3g of Al for a 15% excess. This formulation is based on a report of success by Strepta (p.14, this thread).

This run was unusual in that at first glance it seemed to be a failure. That is, only a couple of small drops of white P fell into the receiver upon initiation of the reaction, which was quickly over. Then I noticed that the outlet of the condenser was nearly plugged. Digging with a steel rod with a hooked end I pulled this plug out. It can be seen as the dark object on the right in the picture below:

Contaminated P plug

At first I wasn’t sure what this plug was composed of as it was so dark. However, upon warming to above 40C in the receiver it liquified, as would be expected for white P. It weighed 2.5g for a yield of 41.7%! Although some of this weight is due to contamination, based on its melting and solidifying behavior, I think it is a minor amount.

The furnace cement lining for this run was reduced from the previous run and targeted at a thickness of 5mm. This thickness, however, was an estimate, as I had no convenient way to measure it. The dried weight of the lining was 57.9g vs 141.9g for the previous run.

The ingredients were prepared and loaded into the retort as in the previous run. The furnace was set for 750C, which was reached in 47 minutes. I planned to hold it at this temperature for 15 minutes but the reaction initiated after about 5 minutes and was over in a few seconds. After digging out the aforementioned plug the reactor was allowed to cool. After a few minutes I lowered the water bath and shut off the argon. I did this to allow any residual P in the condenser and retort to burn off. This is an efficient and safe way to get rid of residual WP. Some small pieces fell onto the water, floated, and burned with flaming. The rest just burnt off to a white smoke in the condenser as air creeped in. I attempted to take a picture of this but was a little late and not much smoke can be seen:

Burning off residual P

Today the retort assembly was removed from the furnace and weighed. It weighed 455.5g vs an unfired weight of 457.9 for a weight loss of 2.4g. This compares well to the P yield of 2.5g. The assembly was then opened for inspection of the slag and recovery of the condenser. Shown below is a picture of the glassy slag, which is grayer than before:

Opened retort run #6

Discussion
It is apparent from the results of this run that the receiver water needs to be kept > 45C to keep the P from solidifying at the outlet of the condenser. I’ve been thinking about providing for this over the last few runs as a small amount of solid P has always deposited near this outlet.

Although the product of this run is contaminated I am very pleased with the apparent increase in %yield. If this contamination is intrinsic to the conditions of this run hopefully it can be eliminated, or at least minimized, in the future. At this point I don’t know its origin or cause.

Comments, questions, and recommendations are welcomed.
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Pieces of slag were placed in 14% NaOH at 50C in a 6" test tube. Profuse bubbling ensued. This gas was shown to be flammable. Surely this is hydrogen generated from unreacted aluminum powder:

2Al + 2(OH)- + 6H2O ----> 2Al(OH)4- + 3H2

[Edited on 7-10-2012 by Magpie]

watson.fawkes - 6-10-2012 at 10:46

Shown below is a picture of the glassy slag, which is grayer than before

What strikes me about these new photos is the way that gas is nucleating in the reaction mixture. There are very large, spherical voids visible. What this means to me is that the mixture is fairly viscous with respect to the gas production rate. (It's just like over-leavened baked goods.) So it doesn't surprise me that it seems to have boiled over into the condenser neck. I'd guess that the bulk of the contamination is simply the boria medium, mostly post-reaction.

Another aspect that interests me is that the refractory lining seems to prevent a chemical reaction with the steel liner. For whatever reason, something about the way the intermediaries work was attacking the iron directly; I don't have any particular idea why.

Magpie - 6-10-2012 at 12:28

These reactions seem, once initiated, to be extraordinarily fast, like a thermite reaction. At first I thought the contamination of the P plug could be Al powder. But I'm not all sure about that. Once melted, the color was almost like milk chocolate. Perhaps I can test some of the product. Mostly though, I just hope I can clean it up.

With the retorts lined with furnace cement I have had no steel wall blowouts. During the preparation of the last lining, after bringing the temperature up to 750C to burn off the tin plating and drive out the residual water in the cement (a couple ml), I found that the liner had separated from the can at the floor, forming a sort of dome. I assume that this was due to gas generation from tin vaporizing under the liner. I didn't like the look of this but decided to use the retort anyway. This apparently caused no problems as the liner seemed to be intact following the reaction.

I want to say a little about the hazards of making and handling phosphorus. Some may think I'm being melodramatic when referring to WP as "a backstabbing bitch." Well, Rogeryermaw and Endimion17 probably don't, as they have found out the hard way. My 2 encounters, fortunately, have not caused me bodily harm. In one instance I was cleaning up after a run using a damp paper towel. All of a sudden it caught fire. The fire was vigorous and totally unexpected. Fortunately I was working over my steel sink so just dropped the flaming towel and let it burn out. The 2nd encounter occurred this morning when I had separated out what I thought was all red P from the receiver water using a small sieve. As I was suspicious of this residue I placed it in the open spent paint can retort from yesterday's run. Then I took this outside and placed it in the sun on my concrete patio. In about half a minute there was a spontaneous roaring fire in that retort! The water had evaporated away and the sun had warmed it up. Exposed to oxygen of the air the WP had everything it needed to burst into flame. Phosphorus is a very interesting element to make and experiment with, but if you become complacent in handling WP you may pay dearly.

[Edited on 6-10-2012 by Magpie]

[Edited on 7-10-2012 by Magpie]

blogfast25 - 7-10-2012 at 05:43

Very nice work and reporting, Magpie, as usual. At near 50 % yield that becomes a more viable way to produce some P.

Am I right in saying the retort internal volume (bearing in mind also the liner) is slightly larger than say, a can of pop? 35 g of charge shouldn’t take up more than say 20 ml, so the content of the retorts must expand hugely during reaction.

Thermite like behaviour, probably self-sustaining, would be in line with my own single data point contribution here (p.17): once ‘lit’ it ‘burned’ furiously for about 30 seconds.

Re. using warmer water for the condenser to avoid P solidifying in the retort’s outlet, that was mentioned in one of the many cited papers on reduction of phosphates, very high up in the thread (I was re-reading the bulk of it last night)

Have we any certainty that in the slag a borate is formed, instead of aluminate?

6 NaPO3 + 10 Al == > 6 NaAlO2 + 2 Al2O3 + 6 P

Then the low melting boric acid would really be just a (important) slag fluidiser.

Banal question: what’s your source of (NaPO3)n?

Magpie - 7-10-2012 at 08:14

Thanks. Yes, this last yield is starting to make all this R&D look worthwhile.

Am I right in saying the retort internal volume (bearing in mind also the liner) is slightly larger than say, a can of pop? 35 g of charge shouldn’t take up more than say 20 ml, so the content of the retorts must expand hugely during reaction.

A can of "pop" (US slang - also used in UK?) here is 355mL. I measured my nominal 1/2 pint paint can at 270mL, as received. But, yes, the slag takes up a lot of volume. And since I don't like furnace fires I tend to load it conservatively - at least the first time around with a new formulation. There was a fair amount of freeboard in the fired can of the last run as you can see in the photo. So this formula could probably be loaded safely to 45g, maybe even 50g. The formation of P vapor and the high viscosity of the molten slag expand the volume of the slag greatly. During this last run there was no slag in the inlet of the snorkel for the first time.

Have we any certainty that in the slag a borate is formed, instead of aluminate?

6 NaPO3 + 10 Al == > 6 NaAlO2 + 2 Al2O3 + 6 P

Then the low melting boric acid would really be just a (important) slag fluidiser.

I'm really not sure about the chemical makeup of the slag. It does tend to dissolve after a few days sitting outside in a bath of 5% NaOH. When I placed some in 14% NaOH at 50C there was rapid bubbling. This gas was flammable and I take it as H2 generated by unreacted Al.

Boria seems to present a distinct advantage over SiO2 in reduced slag volume and viscosity. I'm not sure yet about its effect on yield.

Banal question: what’s your source of (NaPO3)n?

Dharma Trading.

m1tanker78 - 7-10-2012 at 08:28

I want to say a little about the hazards of making and handling phosphorus. [...] Phosphorus is a very interesting element to make and experiment with, but if you become complacent in handling WP you may pay dearly.

Good timeout reminder Magpie. There's a lot of info here that one generally won't come across on the net or Wiki concerning the personal dangers and encounters with WP.

I plan to do a few trials with TSP as that's the easiest for me to obtain. I plan to substitute the silica portion of the charge with a slight excess of 'food grade' diatomaceous earth (very fine powder).

I'm still not sure whether all or part of the Al/Mg can be replaced with an alkali metal (specifically, sodium). I see a few potential problems with this:

*Sodium probably won't mix intimately with the reactants.
*Na3P formation. I gather that in theory, the phosphides of Al/Mg can form in this reaction as well so that may be a non-factor.
*Sodium boils at 800+ degrees C. From Magpie's reporting this is slightly above the temp at which the reaction kick starts but the reaction (if any) might drive off sodium.

The TSP and DE would be roasted prior to the trials. I'll likely try using Mg powder well before I experiment with other reducing metals. I won't be attempting to collect WP at first. Mostly observing (at small-ish scale) if and how the reaction proceeds. These trials will be done outside and upwind.

Can anyone comment on possible drawbacks of using DE as well as feasibility of using sodium in the reaction mix?

Tank

blogfast25 - 7-10-2012 at 09:21

@m1tanker78:

There are indications that orthophosphates (like TSP) are much harder to reduce than metaphosphate, upthread. Still, it would be nice to confirm/inform that. Start with a test tube test?

DE isn't pure silica. That doesn't mean it won't work though.

Metal phosphide as by-products doesn't really seem to be an isuue in the strepta/magpie method.

Magpie - 7-10-2012 at 09:58

I think one advantage of the use of Al/B2O3/NaPO3 is that all reactants are liquid prior to reaction initiation, which seems to be about 750C. This is not true when using silica as the reaction fires off at around 550C, where all ingredients may still be solids. Lack of mixing is surely a hindrance in these reactions so it seems that having all or even some of the reactants in the liquid state would be an advantage.

orthophosphate as precursor
There are some references to the fact that the main P producing reaction is:

P2O5 + reductant ---> P + oxide

So, the easier the phosphorus bearing ingredient can be converted to P2O5, the easier for the above reaction to occur.

For NaPO3 we have:

2NaPO3 + high heat ---> P2O5 + Na2O

For the P2O5 generating reaction to occur in the industrial reaction with an orthophosphate (PO4---) like Na3PO4, a temperature of 1200-1500C in an electric arc furnace is required.

sodium as reductant
Sodium is a powerful reductant and more reactive than even magnesium, I presume. And it would definitely be a liquid at the reaction temperature. And as you say it would very possibly be a vapor at the reaction temperature. This would cause havoc coming into a water receiver, let alone contaminating your product. And how would you keep it from reacting with oxygen - you would surely have to have a cover gas in the reactor.

The above are just my thoughts, as per your request. In the end, as BromicAcid's signature so eloquently states: "Theory guides, experiment decides."

[Edited on 7-10-2012 by Magpie]

m1tanker78 - 7-10-2012 at 10:29

I performed a small test. I combined Mg, TSP and DE (in slight excess) in a small stainless steel cup. I placed an inverted SS cup over this and secured it with a brick. The total charge was just over 1g. I didn't bother roasting the reactants in this test...

I used a propane torch to create a hot spot right at the bottom of the container (from the side). After ~ 5 minutes, there were 2 consecutive pops and accompanying flame exited between the shell halves. I moved the torch around the bottom just to make sure the reaction had completed. I noted no further reaction so I allowed everything cool for a few minutes.

When I removed the top shell half, the side walls immediately became engulfed in a thick white smoke. I dunked this in a container with water I had prepared before the reaction even though I don't expect to recover any WP just yet. This all took place in a split second so no chance for a pic.

I did this outside and was upwind the whole time. I also put some distance between me and the 'reactor' whenever possible since I didn't know how swift the reaction would be.

I hope to build upon this since apparently TSP + DE worked well although it's hard to say if it will scale up well. I'm also eager to try this reaction with sodium or lithium instead of Mg/Al. In the meantime, I'll stick with Mg..

+++++++++++++++++++++++++++

EDIT:[/B]

Thanks for the reply Magpie. I inspected the spent mixture and noted no expansion nor bubbles. In fact, the mixture doesn't look like it liquefied - presumably because I used DE (silica) rather than boria as you've been doing. I hope to be able to replicate the above experiment with sodium instead of Mg. Should I use a lower molarity of sodium??

Tank

[Edited on 10-7-2012 by m1tanker78]

Magpie - 7-10-2012 at 11:27

stead of Mg. Should I use a lower molarity of sodium??

I don't know what to tell you here. I think you are in uncharted territory! Be careful and have fun.

Maya - 11-10-2012 at 09:21

Do you think that 96% Na6O18P6
would give a better yield than the commercial stuff?

Magpie - 12-10-2012 at 10:28

Phosphorus run #8 was carried out yesterday with the following objectives:

1. Evaluate the effects of a larger batch size (45g vs 35g).
2. Evaluate the effects of a heated water receiver (55-60C).

As in run #7, boria and a 15% excess of aluminum were used. The water receiver was kept heated using a hotplate.

The retort was loaded into the furnace and brought up to 750C. At this time a 15 minute soak was started. However, after about 3 minutes the reaction initiated and was quickly finished. There was less burning phosphine and smoke than before. The P came nicely into the receiver. Again it was chocolate brown, as can be seen in the photo below:

Run #8 product

The yield was 3.2g for a %yield of 42.0%. That for run #7 was 41.7%.

Although the outlet of the condenser was at all times heated to around 55-60C by the water in the receiver there was some P deposits found in the end of the condenser. They would catch fire as I pulled them out with a spatula.

The retort was difficult to open and was found to be full of slag. The disassembled retort is shown in the photo below:

Attachment: phpqQu8nV (129kB)
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Disassembled retort ass’y for run #8

The snorkel and condenser inlets are plugged solid. This is shown in more detail in the photo below. The condenser inlet is shown at the top; the snorkel inlet is shown at the bottom.

plugged snorkel & condenser inlet run#8.JPG - 126kB

plugged snorkel and condenser inlets for run #8

This is due in part to a charge that is apparently too large. A 2nd factor is the inadvertent use of too much furnace cement lining. The lining weighed 189.3g vs 57.9g for the last run. Also, this lining had bulged out in several places thereby decreasing working volume. This is thought to be due to the addition of too much water to the cement, which was added to improve workability. Actually the cement can be rammed into place without the addition of water.

Discussion
It appears that 45g is a tad high for charge size. If the lining had been correctly sized and installed this might not have been a problem. In addition, the yield would probably have been greater if plugging had not occurred.

The heated receiver definitely facilitated the flow of P by keeping it liquid.

Questions, comments, and suggestions are welcomed.

[Edited on 12-10-2012 by Magpie]

blogfast25 - 14-10-2012 at 05:16

It seems you're approaching the outer limit of the capacity envelope of your set up.

Magpie - 14-10-2012 at 10:33

It seems you're approaching the outer limit of the capacity envelope of your set up.

With the present formulation, yes. There are a couple of variations I have been considering, however:

1. Ball mill the mixed reactants (under argon)
2. Substitute pyro grade flake Al for my currently used spherical, 100-200 mesh Al, per Strepta's recommendation
---------------------------------------------------------------------------

Would it be safe to ball mill a mix of NaPO3/Al/B2O3 in the ratio 1.00/0.51/0.34 using steel balls?

In general, can thermite mixtures be ball milled using steel balls?

[Edited on 14-10-2012 by Magpie]

Magpie - 17-10-2012 at 15:58

Phosphorus run #9 was completed today. The charge was 35.6g, using boria, and aluminum in 15% excess. The purpose of this run was to evaluate the effect of ball milling the mixed reactants.

The NaPO3 was first ground in a coffee grinder for 2 minutes. This was then mixed with boria and Al in a capped bottle. This mix was then ball milled with ½” chromed steel balls for 6 hours.

The paint can retort was lined with 75.1g of furnace cement, an apparent minimum for complete coverage. The liner was slowly cured up to 500F. Then the assembly was heated to 750C to burn off the tin plating on the can and remove liner water. There was no bulging of the liner.

The charged retort assembly was placed in the furnace and the thermostat set at 750C. Just before reaching this temperature the reactants ignited. There was some burning phosphine and smoke and then chocolate colored P came rapidly into the receiver, which was heated to 47C. The weight of this dirty P was 3.7g, for a %yield of 62.9%.

Weight loss of the reactor assembly was 412.9 – 409.5 = 3.4g.

The opened assembly is shown in the pictures below:

Opened retort for run #9

snorkel, run #9

I was ready to stop this series of testing, then mirabile dictu, on opening the retort I found that there was hardly any slag! The can was mostly empty! So, it seems that at least one more test should be run, ie, that with a much larger ball milled charge.

Discussion
I’m not sure what is responsible for the contamination of the P that is giving it a chocolate color. Most likely it is just finely divided reactants and/or slag carryover blown out with the rush of P vapor. This coloration first started back on run #7, which was the first successful boria run using the larger (35g) charge. Hopefully the P can be cleaned up to remove this contaminant. I will try the cleaning methods using chromic acid and HNO3 used by Endimion17.

The 62.9% yield is significantly higher than my previous best at 42.0% for run #8. So apparently the improved mixing and possibly finer particle size provide significant advantage. Since all reactants should be liquid at 750C it seems that improved mixing would be the main factor responsible for the increased yield.

Comments, questions, and recommendations are welcomed.

DJF90 - 17-10-2012 at 16:11

I haven't really been paying attention too much to this thread but nice work Magpie. It definately seems as though ball milling the mixture has had a positive effect on the progress of the reaction. I guess this is kind of what you'd expect, although I'm suprised it isnt more subtle given that at the reaction temp of 750*C its no longer a solid state reaction (everything should melt?!). Hopefully your chocolatey phosphorus will clean up nicely without too much of a loss.

Strepta - 20-10-2012 at 06:00

Magpie: Once again, nice job! you appear to be producing evidence that intimate mixing is the key to better yield, along with the unexpected slag reduction. I'm very interested to see your next attempt (larger charge). Will you also ball-mill for 6 hours? You'll have to decide whether the extra effort/time is worth the 20% increase or if it makes more sense to quickly mix and run a few morebatches at 42%. (U2U reply sent)

watson.fawkes - 20-10-2012 at 06:43

The 62.9% yield is significantly higher than my previous best at 42.0% for run #8. So apparently the improved mixing and possibly finer particle size provide significant advantage. Since all reactants should be liquid at 750C it seems that improved mixing would be the main factor responsible for the increased yield.

One thing I find significant is that with finer particle size the character of the bubble boundaries left in the slag is quite different. It seems to my eye that there's an interesting phase change happening. My guess is that with the finer sizes the mixture becomes something like a colloid when it all melts, that is, having much higher interfacial surface area and significant boundary energy. In such a mixture, the excess of Al you've been using may not need to be so large.

I would also caution directly comparing yield percentages between these later runs before purification. If indeed some of the initial reagent mixture gets carried over, either unreacted or partially reacted, then it shouldn't count properly as yield. Determining that at this stage isn't obvious, clearly. The first thing I'd try, assuming an infinitely equipped analytical lab (clearly an assumption contrary to fact), is to put the yield into a heated centrifuge and see what separates.

blogfast25 - 20-10-2012 at 07:23

Magpie:

6 h of ball milling the reagent mixture must be a pain in the proverbials, but it does seem to have paid off very nicely: the increase in yield (I second Watson’s motion, though) and spectacular decrease in slag volume do seem to open up the way to larger charges and better yields. Will soon we see you produce 10 g (or more) of crude P per run? :-)

Since as the brown contamination seems to loosely correlate with the introduction of boria into the mix, could part of the contamination be amorphous boron?

Another thought just occurred to me. Was the heating cycle used in all of the recent runs held rigorously the same? My reasoning is as follows. Clearly the much larger volume of slag in the previous runs is due to foam. But if you maintain heat post-reaction, eventually and as long as the material remains liquid the foam should collapse (faster so if the melt was of lower viscosity), even though that could take some time. If on the other hand you shut off heat abruptly after reaction you’d ‘freeze’ the foam and prevent any possibility for it to collapse. Maintaining heat post-reaction might thus be a way of reducing slag volume…

[Edited on 20-10-2012 by blogfast25]

Magpie - 20-10-2012 at 17:59

I'm very interested to see your next attempt (larger charge). Will you also ball-mill for 6 hours? You'll have to decide whether the extra effort/time is worth the 20% increase or if it makes more sense to quickly mix and run a few morebatches at 42%.

Yes, I will ball mill for 6 hr. For routine production it's value would be a time & effort decision. At this point I'm mostly after the knowledge of what works and what doesn't work. Actually ball milling is easy - the mill does all the work. You just have to babysit it a little - while doing your regular activities. You just want to make sure it doesn't overheat or stop I guess, and I've never had any problems. I've already proven this mix won't explode on me. You do have to pick the balls out (quickly, to keep moisture absorbtion to a minimum) and then clean and dry everything when finished.

I would also caution directly comparing yield percentages between these later runs before purification. If indeed some of the initial reagent mixture gets carried over, either unreacted or partially reacted, then it shouldn't count properly as yield. Determining that at this stage isn't obvious, clearly. The first thing I'd try, assuming an infinitely equipped analytical lab (clearly an assumption contrary to fact), is to put the yield into a heated centrifuge and see what separates.

Yes, that last batch was very dirty - I would even call it crusty. Right now I'm cleaning it up and have removed the bulk of the contamination using chromic acid. This will definitely decrease the yield from my reported 62%. I like your idea of the heated centrifuge. I will try just heating it up to say 60C then giving it a spin in my unheated centrifuge.

Magpie:
Will soon we see you produce 10 g (or more) of crude P per run? :-)

I haven't dared hope for anything that large.

Since as the brown contamination seems to loosely correlate with the introduction of boria into the mix, could part of the contamination be amorphous boron?

I suppose it is the right color. You know better than I whether that is thermodynamically possible or even likely.

Another thought just occurred to me. Was the heating cycle used in all of the recent runs held rigorously the same? My reasoning is as follows. Clearly the much larger volume of slag in the previous runs is due to foam. But if you maintain heat post-reaction, eventually and as long as the material remains liquid the foam should collapse (faster so if the melt was of lower viscosity), even though that could take some time. If on the other hand you shut off heat abruptly after reaction you’d ‘freeze’ the foam and prevent any possibility for it to collapse. Maintaining heat post-reaction might thus be a way of reducing slag volume…

The heating cycle is somewhat rigorous up to the time of ignition as it is controlled by the furnace and retort characteristics, ambient temperature, and when I turn on the hood fan. When I turn off the furnace has been pretty much right after ignition since I started using boria. There's no point in beating a dead horse.

blogfast25 - 21-10-2012 at 05:29

"There's no point in beating a dead horse."

Except perhaps as I suggest, to 'kill' the foam and obtain only a small amount of (more or less non-porous) slag.

Magpie - 26-10-2012 at 10:32

I finished cleaning the crude phosphorus of run #9. I first used a chromic acid wash (K2Cr2O7/H2SO4) on a magnetic stirrer. Improved but still a bit crusty, I heated the P to 65C then centrifuged it for 1 minute. This gave no separation. Finally, I heated the P in 6M HNO3 with agitation on a magnetic stirrer/hotplate. This further cleaned it to where, although still off color, it now looks like phosphorus. This is shown below:

phosphorus from run #9, cleaned

Loss of weight due to cleaning was from 3.7g to 2.8g. %yield then decreased from 62.9% to 47.6%. This is still my best yield so far.

Magpie - 27-10-2012 at 16:00

The P from runs #7 and #8 was also quite dirty so I decided to clean it also. My plan was to use a chromic acid wash followed by a 6M HNO3 wash, as I did with the P from run #9. To my surprise the P was clean enough after just one wash with the chromic acid as can be seen below.

The reagent consisted of 20mL water + 20mL con H2SO4 + 2.25g K2Cr2O7. This was heated and stirred on a magnetic stirrer/hotplate, and the dirty P added to it. This reagent turned from orange to a murky green/brown during the cleaning process.

White Yeti - 30-10-2012 at 07:22

Just as a random query, wound zinc be a good reducing agent for this reaction? I'm thinking that it would be a strong enough reducing agent to reduce phosphorus, but not silicon, thus potentially increasing yields. There's always the problem of producing zinc phosphide, but zinc phosphide has a relatively low melting point, as does zinc metal itself, so if phosphide were to form, it would remain molten and available, perhaps for an oxidation back to phosphorus. Perhaps it's worth a try; the reaction may even take place at lower temperatures owing to the lower MP of zinc.

blogfast25 - 31-10-2012 at 09:03

Zn? It’s not very likely. Such aluminothermic reduction reactions are really driven by the huge heat of formation (HoF) of alumina (- 1676 kJ/mol). The HoF of ZnO is only – 350.5 kJ/mol (NIST value). To be fair we have to compare 3 mol of ZnO with 1 mol of Al2O3, so 3 x (-350.5) = - 1051.5 kJ/3 mol. That’s still a lot lower than the competing value of - 1676 kJ/mol. From it can be deduced that the reduction with Al is much, much more exothermic than with Zn (about 600 kJ difference is a huge difference).

Magpie - 1-11-2012 at 15:00

Phosphorus run #10 was completed today. The charge was 52.7 g, with boria as slag former, and aluminum in 15% excess. The purpose of this run was to evaluate the effect of running a larger ball milled charge vs the 36.3g ball milled charge of run #9.

The NaPO3 was first ground in a coffee grinder for 2 minutes. This was then mixed with boria and Al in a capped bottle. This mix was then ball milled with ½” steel balls for 6.45 hours.

The paint can retort was lined with 87.1g of furnace cement. The liner was slowly cured up to 500F then the assembly was heated to 750C to burn off the tin plating on the can and remove liner water. There was no bulging of the liner.

The loaded retort assembly was placed in the furnace and the thermostat set at 750C. At about 710C the reactants ignited. This resulted in an explosive reaction – a scary event. The products shot out of the condenser, causing some water and bits of burning phosphorus to get knocked out of the receiver. There was also the usual burning phosphine, and quite a lot of smoke. The silver solder rebuild on the condenser was virtually ruined, apparently due to the intense heat developed. This can be seen in the picture below:

Fired retort, run #10

As on run #9, on opening the retort I found that there was hardly any slag. This confirms the much reduced volume of slag that occurs with the ball milled charge.

Retort slag, run #10

The slag, although sparse, did plug the snorkel, as shown below:

Plugged snorkel, run #10

Additional slag deposited on the outside of the snorkel is shown here:

Slag on snorkel, run #10

The product was a very dirty looking rust colored P, as shown below:

Dirty P, run #10

The P was cleaned in heated chromic acid followed by cleaning in heated 6M HNO3. The yield is 2.0g of P for a %yield of 23.0%. The cleaned P is shown below:

P, run #10

Weight loss of the reactor assembly was 445.4 – 442.3 = 3.1g.

Discussion
The results of run #9 showed that ball-milling increases the efficiency of the reaction. However, as shown by the results of run #10 the reaction of a larger charge size is too powerful to be conducted safely.

Additionally, the yield and %yield were decreased due to the explosive discharge of the reaction. Much of the P was apparently deposited in the condenser as I had to burn off a lot after the reaction during cleanup. I believe that much of the rust colored crud in the receiver is red P, further contributing to the loss of yield.

A further danger was noted in that examination of the snorkel showed that it was plugged, or very nearly so, for this larger run.

Comments, questions, and suggestions are welcomed.

12AX7 - 1-11-2012 at 18:26

Larger charges are better ran with coarser reactants, is this the case here as well?

The boria with excess aluminum may've contributed some exotherm.

Tim

Magpie - 1-11-2012 at 18:41

Larger charges are better ran with coarser reactants, is this the case here as well?

See the results for run #8 above.

[Edited on 2-11-2012 by Magpie]

Strepta - 2-11-2012 at 08:32

Magpie: Concerning run # 10: the fact that the entire charge was at reaction temperature and the point of origin of first ignition is uncertain is probably key to understanding what happened. It may be possible to effect a more controlled flame front by preheating the mix to, say, 500 deg C and then igniting it’s top surface in some manner, probably electrically. This would be in pursuit of a planar flame front where nearby regions need the reaction heat to initiate rather than the nearly instant ignition of the preheated bulk charge.

When I was doing my experiments with a test tube, I heated the entire tube to a point and then concentrated the burner flame near the top surface of the charge. Ignition was always at this top surface and progressed rather uniformly down the length of the charge. I realize that this is probably not practical for your present fixturing. If an electrical igniter (perhaps assisted with a small pyrotechnic mix) was tried, it may take a few trials to work out the amount of pre-heating and igniter size; or maybe you can work out some more clever way to control the point of ignition.

Magpie - 2-11-2012 at 09:17

Strepta: I think you have a good point, and it is backed up by your observations. I would like to try this if we could come up with a practical way to do it by modifying my present retort assembly.

Edit: One thought: Place a thin layer of hypergolic (at 500C) mixture on top of the ball-milled charge.

[Edited on 2-11-2012 by Magpie]

blogfast25 - 2-11-2012 at 10:48

So a preheat to about 500 C with one ignition point, huh? That would be worth experimenting with, using a small open crucible and some suitable hypergolic. Causing auto-ignition more or less throughout the whole mass at once (as you seem to be doing here) may cause the ‘explosion’ when charges become larger. And blocked snorkels in these conditions make me shiver!

12AX7 - 2-11-2012 at 19:51

Larger charges are better ran with coarser reactants, is this the case here as well?

See the results for run #8 above.

[Edited on 2-11-2012 by Magpie]

What about it? In #8, the charge was slightly smaller than #10; it produced much more slag (give or take how much got blasted out by the rapid ignition

). As scale continues to rise, it doesn't seem like ball-milled reactants are all that great an idea. At least not loose. A pressed charge may burn nicely rather than deflagrate, particularly if ignited on the top.

Tim

Magpie - 2-11-2012 at 20:24

What about it? In #8, the charge was slightly smaller than #10; it produced much more slag (give or take how much got blasted out by the rapid ignition

You indicated that a coarser charge would give a slower burn rate. Yes, but run #8, which is not ball milled, looks to be the upper limit for charge size due to the large amount of slag. Using ball milled material pointed a way to larger charge sizes due to the large drop in the quantity of slag (run #9). Thus, this line of experimentation was followed to its natural end: run #10.

As scale continues to rise, it doesn't seem like ball-milled reactants are all that great an idea.

Now that we've seen the results of run #10, yes.

At least not loose. A pressed charge may burn nicely rather than deflagrate, particularly if ignited on the top.

The use of briquettes is an idea that has intrigued me also. There's a patent for using these for the industrial production of P using the usual raw materials. However, I can't remember all of the claimed benefits. P vapor passing out of the retort easier was one of them IIRC.

Strepta - 3-11-2012 at 03:29

Pelletizing, graining and/or pressing are all good ideas, but only after you have ball-milled the bejesus out of the reactants to ensure their most intimate contact- unless you wish to abandon yield as a primary objective. Some advantage may also be gained from increasing the mixture's opacity with a small amount of carbon black to reduce infrared penetration.

blogfast25 - 3-11-2012 at 07:32

Some advantage may also be gained from increasing the mixture's opacity with a small amount of carbon black to reduce infrared penetration.

Do you have any evidence or references citing that technique?

Interestingly, some years ago I mixed in a very small amount of fine graphite into a ferric oxide thermit mixture and couldn’t get it to ignite for love nor money. I didn’t pursue the line of inquiry.

Magpie - 3-11-2012 at 08:00

... If an electrical igniter (perhaps assisted with a small pyrotechnic mix) was tried, it may take a few trials to work out the amount of pre-heating and igniter size; or maybe you can work out some more clever way to control the point of ignition.

Yes, a material that is stable until a high temperature (like 500C) is reached whereupon it ignites providing a higher temperature to ignite the mix might work. This might be as simple as placing a thin layer of ground up match heads on top of the mix.

I have electrical fuse wire. Of course this would be ideal as the mix temperature at ignition could be controlled exactly. Providing the one-time use insulated wire terminals would require extra work, however.

Strepta - 3-11-2012 at 10:02

Blogfast: My notion of the use of carbon black to opacify probably came from an article in Journal of Pyrotechnics, by Ken and Bonnie Kosanke, to which I had a subscription a few years ago. Currently, I have no access to those issues. The idea is also mentioned here: http://en.wikipedia.org/wiki/Opacifier

Magpie: Couldn't you drill two holes (3-4mm) in the paint can and lead the wires troughholding them in place wih a dab of furnace cement?

Magpie - 3-11-2012 at 12:27

Magpie: Couldn't you drill two holes (3-4mm) in the paint can and lead the wires troughholding them in place wih a dab of furnace cement?

Yes, that is what I was thinking also. I could use 2 regular copper wires as terminals. They would be insulated from the lid and sealed with furnace cement. The fuse wire would then be terminated at those 2 copper stubs, internal to the paint can.

This fuse wire is 34 ga Nichrome. It works well and I have used it to set off Mg in a bomb calorimeter. Fuse length is 4cm and I fire it with 24VAC.

Magpie - 19-11-2012 at 17:10

As a followup to my last post in this thread I fabricated a paint can retort with a Nichrome wire heating element. The wire was 0.56mm in diameter and 11cm long. When 9.7VAC was applied to the wire it would glow bright orange in 3 seconds. If the burn time was kept to 5 seconds or less multiple firings could be attained without the wire severing due to excessive heating.

Two holes, ~3mm in diameter, were located in the bottom of the wall of the paint can, diametrically opposed. The Nichrome wire was centered in these holes and cemented in place using furnace cement such that the wire was electrically insulated from the can. See pictures below:

A charge of 34.5g of Al/Bi2O3/NaPO3, with 15% Al excess, was placed in the can, covering the wire element. Using ss crimps 2 lengths of copper wire were extended from the retort. The retort was then loaded into the furnace as shown below:

copper terminals for retort

Heating was started. At temperatures of 500C, 550C, 600C, and 650C, a 5 minute soak was applied then the heating element activated for 5 seconds. After each firing the element would be checked for electrical continuity to assure that it had not severed.

This plan was accomplished, but at no temperature did the charge react to produce phosphorus. The retort was allowed to cool to room temperature then opened for inspection. The charge had sintered and could only be removed with with a hammer & chisel.

Conclusion This method for initiating the charge was not successful. I believe that the sintering was normal and unrelated to the element firings.

blogfast25 - 20-11-2012 at 14:30

Thanks Strepta.

Magpie: it's both a pity and a bit of a mystery as to why ignition wasn't achieved... Perhaps longer firing times of the wire to increase the temperature of the charge immediately surrounding the NiCr wire is needed? In that case you'd probably need sturdier wire... 5 seconds is not a long time to reach a high temperature locally, because there's not much time for heat transfer. And your wire also takes a couple of seconds to get to peak temperature.

[Edited on 20-11-2012 by blogfast25]

[Edited on 20-11-2012 by blogfast25]

Magpie - 20-11-2012 at 16:27

Blogfast thanks for your interest but I really don't have a clue as to why the reaction didn't ignite. When I inspected the sintered charge I could see a small volume of solidified melt around the wire on one end. So there was some melting. I'm under the impression that liquifaction is necessary for ignition.

Strepta - 20-11-2012 at 17:01

Peculiar indeed. In your previous run explosive ignition occured at 710 deg, while in this case you took the reactants to 650 deg and then attempted to push over the threshold with a very localized high temperature source. This does not mirror my own experience, the most obvious difference being the use of pyro Al. Are you still "all in" for this reaction or growing weary? If not, as we discussed before, a small pyrotechnic booster may help. Also, if you kept the pieces of reactants you had to break up to remove from the retort, you may reheat a small quantity of those to ignition again, carefully monitoring the temperature.

Magpie - 20-11-2012 at 18:49

I am growing weary of experimenting with phosphorus so will stop for now. I will save the sintered charge fragments, however, for some possible future testing.

blogfast25 - 21-11-2012 at 02:52

I am growing weary of experimenting with phosphorus so will stop for now. I will save the sintered charge fragments, however, for some possible future testing.

You've done a lot and come a long way but this is not easy (and not cheap either) research to be carried out in from a hobbyist capacity.

Magpie - 21-11-2012 at 09:31