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Strepta
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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.
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Magpie
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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]
The single most important condition for a successful synthesis is good mixing - Nicodem
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blogfast25
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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!
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12AX7
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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
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Magpie
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Quote: Originally posted by 12AX7  |
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.
| Quote: Originally posted by 12AX7 |
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.
| Quote: Originally posted by 12AX7 |
At least not loose. A pressed charge may burn nicely rather than deflagrate, particularly if ignited on the top.
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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.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Strepta
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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.
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blogfast25
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| Quote: Originally posted by Strepta | | Some advantage may also be gained from increasing the mixture's opacity with a small amount of carbon black to reduce infrared penetration.
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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.
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Magpie
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| Quote: Originally posted by Strepta | ... 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.
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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.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Strepta
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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?
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Magpie
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| Quote: Originally posted by Strepta |
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?
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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.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Magpie
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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.
The single most important condition for a successful synthesis is good mixing - Nicodem
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blogfast25
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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]
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Magpie
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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.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Strepta
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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.
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Magpie
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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.
The single most important condition for a successful synthesis is good mixing - Nicodem
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blogfast25
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| Quote: Originally posted by Magpie | | 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.
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Magpie
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Not really. The charge was subjected to unusual handling. Here's the tedious details:
The charge was initially standard in preparation including 6 hours of ball-milling. It was loaded into the retort. But when the heating element was
tested for electrical continuity it failed. The connections were just twisted wire and were inside the retort. So, the powder was poured back into a
capped jar. An improved method for the electrical connections using ss crimps was installed.
The powder seemed to clump due to absorbed moisture so the bottle was placed in the drying oven. This is when the Hg thermometer broke so there was
more fussing with that problem. The charge was lightly sintered so was dug out of the bottle and lightly ground in a mortar. It was then charged to
the retort. From there on the standard procedure was followed.
So, all this extraneous handling, moisture absorbtion, drying, and poor grinding very possibly compromised the charge and prevented the ignition.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Neodymium
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Hi Magpie,
I’ve been recently following your phosphorus adventures for which I highly commend your skill, creativity and persistence. I have some
familiarity with industrial processes as a professional chemist and I appreciate the difficulty of getting solid state reactions (or liquid mixtures
containing insoluble solids) to start smoothly and run to completion. Your efforts to very finely grind and mix the reactants and dry them has, I am
sure, been an important element in your success by creating as much active surface contact area as possible from which the reactions can occur.
In the real world kinetics often trumps thermodynamics in determining whether or not a particular chemistry may be practically employed. Please
consider the possibility that the erratic production rates and yields which you have experienced may be due to the difficulty of the reductant
(aluminum) physically reaching beyond the surface of the phosphate particles at these “low” temperatures. When the aluminum first melts it may
wet and react with the phosphate particles’ surfaces giving a burst of reduced species, i.e. phosphorous, which then ceases since the liquid
aluminum forms a skin which impedes further, deeper reaction and results in low yields. The aggregated liquid aluminum film with its low total
surface area and sequestering surface ‘crud’ has an aluminum vapor pressure of only 5 x 10^-8 mm at 800C. This is far too low a concentration for
it to be a kinetically useful vapor phase reductant (the vapor could penetrate the passivating barrier film if there were only enough of it). The
vapor pressure of magnesium is a billion times higher, 10 mm, at 800C and it may prove to be a useful adjuvant to the aluminum reductant. Try
starting out by supplementing the aluminum with a SMALL amount (10%?) of magnesium and see if this makes the reaction start more smoothly at lower
temperatures and reliably go further towards completion. I look forward hearing of further experimental adventures from you!
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Magpie
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Thank you Neodymium, for your interest and suggestions. At some time I may give them a try. Right now I need a good, long rest from the labors of
phosphorus research.
The single most important condition for a successful synthesis is good mixing - Nicodem
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elementcollector1
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I hate to pose an OT question, but it is phosphorus-related. I scraped the red P off of some matchboxes after a soak in some acetone. However, it
looks like paper particles are still a major contaminant. Is there any way I can remove these, leaving only the P behind?
Elements Collected:52/87
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Erbium_Iodine_Carbon
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I was thinking of a relatively low temperature method of phosphorus production that could be done in standard glass equipment. I'm not certain if it
will work and I don't currently have the means to try.
The idea would be to first produce phosphine and then oxidising it to phosphorus using a halogen.
The first step would be to dehydrate phosphonic acid (HP(OH)2 / H3PO3) (also called phosphorous acid, purchased as a pool chemical) and then decompose
it at 200 degrees C to phosphoric acid and phosphine.
The second step would be to lead the phosphine into either a solution of iodine in varsol or KI3 in water. I don't know if iodine is a strong enough
oxidising agent to oxidise the PH3 but I've read it can oxidise H2S to elemental sulfur so I'm assuming the same can be done for phosphorus. The
reaction would be:
2 PH3 + 3 I2 --> 2 P + 6 HI
The idea being the phosphorus would precipitate out of solution.
However, one problem is that P and I react to form PI3 which then decomposes in water to form H3PO3 and HI. Can anyone think of a way to avoid this?
Wikipedia says PI3 is usually made from both elements in solution but the reaction might happen before the phosphorus can precipitate. The fact that
this procedure works with sulfur is that there are no stable compounds of sulfur and iodine.
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elementcollector1
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After reading the summary of this thread, I'm tempted to try the microwave reaction between H3PO4 and C. I do have questions, as always:
-I have ground-glassware. Will this be suitable as a container? For example, a flask connected to a stoppered distillation adapter connected to a
(receiving) flask?
-What sources of carbon are adequate for this? For example, if I took some burnt plants, leached out the soluble stuff, and dried the result, is that
an acceptable carbon source for this reaction?
-Most conventional pathways to P from phosphates mention SiO2 in use. Will the glass fulfill this purpose, and if so, to what extent?
-Is an inert atmosphere necessary to prevent phosphorus oxides?
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aliced25
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Could I make an uneducated suggestion here? If the purpose is to liquify the charge with a high phosphorus content, why not use ammonium dihydrogen
phosphate? It would melt fairly low (I used to use it to generate fairly dry NH3 in glass) and it forms a polyphosphoric acid glass. The NH3 would
sweep the oxygen (and anything else out of the reaction vessel in short order and could be collected in water/HCl prior to the main event.
Even Nicodem, on p16 of this blown-out thread suggested ammonium phosphates
| Quote: | Maybe something too obvious, but shouldn't ammonium phosphate react with aluminium powder to give phosphorous at proper conditions? This would make
the use of silica unnecessary and the reaction should proceed at lower temperatures than with any of the sodium (poly)phosphates. The gasses forming
in the first stage of calcination (A; where aluminium polyphosphate forms) should purge the air from the reaction vessel protecting the mixture from
oxygen. Since the reaction enthalpy of the reduction stage (B) is considerably higher than with the analogous reaction of sodium phosphates, no
additional "acid" like SiO2 or Al2O3 should be necessary to smooth the reaction.
A: 3 (NH4)H2PO4 + Al => Al(PO3)3 + 3/2 H2 + 3 NH3 + 3 H2O (at < 300°C ?)
B: Al(PO3)3 + 5 Al => 3 P + 3 Al2O3 (at >900°C ?)
Or was this already tried and is not working? |
Now monoammonium (ammonium dihydrogen phosphate) melts in the Microwave to give copious amounts of NH3 fumes and a polyphosphoric acid glass (due to
expansion differences it will break just about whatever you melt it in). What would happen if carbon were added to the mixture prior to melting? Would
we get evolution of carbon oxides, and reduced phosphorus? I've got an old MW now, I'll scrape up the $$$$ to buy some soluble MAP crystals online and
trial it (I just have to work out how to push the fumes into water/HCl to stop the neighbours freaking out).
PS Although, I must confess, I'm much more interested in Phosphine production for both PCl5 and P2O5/POCl3 production via Len's writings.
[Edited on 20-4-2013 by aliced25]
[Edited on 21-4-2013 by aliced25]
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elementcollector1
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And yet, H3PO4 melts at a stunning 40 degrees C - 20 if it's the hydrate. Much better for microwave purposes. (And fortunately, I happen to have a
spare microwave).
Still, I need some experienced advice on this - I'm not too willing to go charging into a reaction scheme without knowing what'll happen.
Anyone ever done the 'microwave route' before?
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aliced25
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What? To polyphosphoric acid from Ammonium Dihydrogen Phosphate? Too many times to count. My suggestion, get a cheap quartz container/crucible because
the fucker is likely to shatter when cooling (I've lost some expensive cookware).* The polyphosphoric acid glass is probably able to be ball-milled or
just broken up into a fine powder.
I wonder how it would go in the Tarbutton et al experiment, mix the powder with NaCl in a steel can, with a steel pipe leading out of it (as a
condenser) and collect what comes over. According to Len1 (and Tarbutton, et al) the reaction gives POCl3 in good yield, so I'd be VERY interested in
seeing what happens with polyphosphoric acid.
* Also consider how to extract the fumes from the MW reaction, I've got a little rotary-vane pump and am considering running it at just enough
pressure to pull the fumes through a small outlet hole in the MW into an acid solution, as a trap before the pump. As long as the air is being sucked
into the MW (ie. it is at just under 1atm), the only escape route for fumes is through the trap.
[Edited on 21-4-2013 by aliced25]
From a Knight of the Realm: "Animated movies are not just for kids, they're also for adults who do a lot of drugs." Sir Paul McCartney
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