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Strepta
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When I was actively working on this some years ago, I did a number of experiments with varying stoichiometry. My best results (~50%) yield were with a
slight excess (15%) of Al. What I recall vividly was that the mix had the rheology of a light weight oil--it would sway like a liquid when the test
tube was jostled and spurt up when the tube was rapped on the work table. This was the result of the use of pyro grade Al and extensive mixing (with a
coffee grinder) and drying of the mix prior to use.
Yes, the boria is a pain to powder--supposedly best due by vacuum heating of the boric acid. This results in a matrix of B2O3 with voids where the H2O
has vacated, and this is easily powdered.
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watson.fawkes
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Quote: Originally posted by Magpie  | 10Al + 6NaPO3 + 6B2O3 ---> 3Na2B4O7 + 5Al2O3 + 6P
My choice of Na2B4O7 (borax) as the end product is somewhat arbitrary. I'm assuming that since it is commonly found in nature it is a stable ground
state. |
There seems to be only one simple oxyanion of boron, the borate, with boron oxidation state 3+.
Borax has this same oxidation state, as do all the common polymeric borate relatives. A hypothetical borite ion, in oxidation state B1+,
might only exist in an excited state and transiently. So one potential advantage of using borate is that it's less likely to partially reduce. 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+.
Another advantage is that the melting point of borax is 743 °C. That might be a eutectic temperature for soda-boria. I haven't tried looking
up the data. Regardless, the product alumina will surely raise the melting point.
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White Yeti
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I know electrolysis is a pain in the ass to get to work, but has anyone contemplated the electrolysis of molten phosphoric acid? The idea is that
phosphate is electrochemically reduced sequentially from phosphate to phosphite to hypophosphite and finally to phosphorus, the allotrope remains to
be determined.
H3PO4(aq) + 2 H+ + 2 e− ---> H3PO3(aq) + H2O −0.276V
H3PO3(aq) + 2 H+ + 2 e− ---> H3PO2(aq) + H2O −0.499V
H3PO2(aq) + H+ + e− ---> P + 2 H2O −0.508V
O2(g) + 2 H2O + 4 e− ---> 4 OH−(aq) +0.40V
Hypophosphite disproportionates at around 250C to phosphine and phosphate, but if the temperature is kept around 60C this problem shouldn't arise.
If 85% phosphoric acid is used, would the water be electrolysed first instead of the phosphate? If so, is pure phosphoric acid conductive enough for
the electrolysis to proceed?
Due to phosphorus's tendency to form polymeric anions such as pyrophosphate, phosphorus pentoxide or escape as phosphine, I honestly have no idea what
the exact outcome of this electrolysis would be. Obviously due to the reactive nature of phosphorus, some method should be employed to ensure that the
phosphorus and oxygen are not allowed to mix.
What do you think? Is it worth a shot?
"Ja, Kalzium, das ist alles!" -Otto Loewi
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plante1999
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| Quote: Originally posted by garage chemist | Just some other experiment I found: a demonstration experiment to show that bones contain phosphorus:
Cleaned, boiled and dried chicken bones are burned with a bunsen burner on a fireproof surface and directly heated with the flame until they have
turned into white ash.
2g of this bone ash are mixed with 0,5g magnesium powder and 0,5g kieselgur.
The mix is heated in a test tube which is plugged with a glasswool plug. After the reaction has finished, it is left to cool and the glasswool plug is
removed in a darkened room and observed closely.
A glow is visible on the glasswool.
When the residue in the test tube is mixed with water, gas bubbles are evolved which self-ignite on contact with air. They are phosphine.
Reactions are on the site that I posted.
The important feature here is the use of magnesium instead of the often- used aluminium. Mg reacts at a much lower temperature than
Al.
The SiO2 must be finely dispersed in the mix, hence the use of kieselgur. Quartz sand is not fine enough, even after good grinding.
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I already made some P4 a few days ago with aluminium, NaPO3 and B2O3. I decided to try this experiment changing the Mg for a smaller amount of Al and
I was able to get very small amount of phosphorus at very high temperature for a long time, so it seam that with calcium phosphate Mg is better
suited.
I will try to find Mg then I will report my result here. As for the reagents, the bone ash is from chicken bones that I calcined to the white ash, and
the kielsegur is from insect killer which is suppose to be 91% SiO2 and ''chemical free'' which is obviously false since there is something in the
bottle.
I never asked for this.
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bbartlog
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| Quote: Originally posted by White Yeti | I know electrolysis is a pain in the ass to get to work, but has anyone contemplated the electrolysis of molten phosphoric acid? ...
What do you think? Is it worth a shot? |
I would expect it to be too poor a conductor. The dissociation constant is low; while there is water present I think the main products would be
hydrogen and oxygen, and once you get to the point where you have a glassy mass of 90something% phosphoric acid I don't think you'll have a lot of
moving ions. And even if you did I think you might find that P2O5 would be the end product.
The less you bet, the more you lose when you win.
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Magpie
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In preparing for a phosphorus run using B2O3 I became aware of an increase in weight of at least 3.2g on 50.0g of charge. I believe this is due to
the pickup of water by the hygroscopic B2O3 and to a lesser extent NaPO3. I believe I will have to reject this charge and start over. Based on the
following reaction every gram of water will kill 1.8g of P:
16P + 15H20 ---> 3P2O5 + 10PH3
(1g/18)(16/15)(31) = 1.8g
Since the theoretical yield of this charge is only 7.1g of P, this would be an unacceptable loss.
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 | In preparing for a phosphorus run using B2O3 I became aware of an increase in weight of at least 3.2g on 50.0g of charge. I believe this is due to
the pickup of water by the hygroscopic B2O3 and to a lesser extent NaPO3. I believe I will have to reject this charge and start over. Based on the
following reaction every gram of water will kill 1.8g of P:
16P + 15H20 ---> 3P2O5 + 10PH3
(1g/18)(16/15)(31) = 1.8g
Since the theoretical yield of this charge is only 7.1g of P, this would be an unacceptable loss.
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B2O3? Boric oxide? To what desired effect?
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Magpie
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Have you read upthread for background. The B2O3 serves as a sort of "sink" to prevent the formation of AlP which would otherwise consume half the P.
Same purpose as using SiO2 in the standard formulation...just a variant of this.
---------------------------------------------------------
I decided not to reject my prepared Al/NaPO3/B2O3 charge but to heat it to 350C in an attempt to dehydrate it prior to use.
The single most important condition for a successful synthesis is good mixing - Nicodem
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blogfast25
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Sorry, read most but must have missed that bit. My bad.
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White Yeti
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| Quote: Originally posted by bbartlog |
I would expect it to be too poor a conductor. The dissociation constant is low; while there is water present I think the main products would be
hydrogen and oxygen, and once you get to the point where you have a glassy mass of 90something% phosphoric acid I don't think you'll have a lot of
moving ions. And even if you did I think you might find that P2O5 would be the end product. |
I feared those potential problems, but would adding a small amount of sodium phosphate increase the conductivity of the solution? If the sodium salt
is soluble in molten phosphoric acid, the conductivity would increase dramatically.
On the other hand, I highly doubt that the phosphoric acid could be dehydrated all the way to phosphorus pentoxide via an electrolysis alone.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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Magpie
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I just finished cleaning up after my phosphorus run (#5) with boria substituted for silica according to the following assumed reaction:
10Al + 6NaPO3 + 6B2O3 ---> 3Na2B2O7 + 5Al2O3 + 6P
The charge was 50g.
I had noted that the charge had picked up 3.2g during grinding and handling due apparently to the aggressively hygroscopic nature of B2O3. I felt that
this water had to be driven off before firing because of the potential for a yield killing reaction below:
16P + 15H2O ---> 3P2O5 + 10PH3
Therefore I heated it for 2 hours at 350C. This did drive off the water but also melted the boria forming the charge into a hard monolithic disk 3"
in dia and 1/2" thick. Wrongly or rightly I felt this disk had to be pulverized so pounded it with a hammer in a plastic bag then ground it up
quickly in the coffee grinder.
I backfilled the retort ass'y with argon, started the argon bubbler, and turned on the furnace. When the temperature reached 700C nothing yet had
happened. So I set the thermostat to 800C. When the temperature reached 750C that's when the fun started.
The reaction took off. Some few drops of red and black P fell into the receiver as shown below:
first P discharged
(The weight P in the receiver is 0.5g.)
Then a large fire in the furnace occurred, indicating a breach of containment of the retort. I pulled the plug on the furnace and took a few steps
back. The generation of P2O5 smoke was voluminous, challenging my powerful fume hood.
After about a half hour I ran out of argon. Now a big goober of burning phosphorus dropped into the receiver. Oh well, all the exposed P in the
furnace had to burn off at some time.
You can perhaps see the added goober in the picture below:
after 2nd P discharge
After cooling overnight I open the furnace for inspection. Here's what was left of the retort:
run #5 (boria) retort
You can see the glassy slag in the bottom of the retort and around the inlet of the snorkel. A second picture shows the snorkel in more detail. The
inlet is about 1/2 closed off with glass.
run #5 (boria) snorkel
Discussion
My current retort is clearly not adequate for containing this reaction. However, I think the reaction has potential for producing a good yield of P.
All three reactants are liquid at the apparent firing temperature of 750C. And the slag has a very low volume: maybe 25% of the retort, and likely
has a low viscosity as there are very few vacuoles. There was much burning of P in the furnace indicating a potentially good yield.
Questions, comments, and recommendations are welcomed.
[Edited on 25-9-2012 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Strepta
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Excellent! As soon as you "harden" your retort, we should see some nice results. I never used a charge larger than 4 g, so I can only imagine the
magnitude of that conflagration. It will be interesting to see your yield and, then, whether further improvement can be made.
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watson.fawkes
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One thing I immediately noticed is how much higher
the initiation point was for this reaction, particularly since everything is liquid and the earlier mixture was powder. The answer, it seems to me, is
that there's a gaseous intermediary in all the powder reactions that's able to set off a chain reaction. A little digging, a candidate popped up:
P4O6, with boiling point 173 °C. I'd guess it reacts with Al, reducing to P4. In any case, since gas molecule
are more mobile that liquid ones, it could explain why the mixture ignites later.
I would have to guess that you've got phase separation at 700 °C, with a puddle of molten Al at the bottom, covered by a boron-phosphorus flux
on top. That would mean that at the time the reaction starts you've got a planar interface layer where the reaction occurs, at least before it gets
violent.
It's suspicious that the ignition temperature you report is just a few degrees above the melting point of borax, one of the putative products. It
looks like the aluminum, whether solid or liquid, might be passivated by borax, kinetically limiting the reaction below its liquid threshold.
What's the enthalpy of this reaction? I know aluminum burns hot, but that crucible is just totally wrecked. Notice how the very bottom of the can is
the one part that stayed partly attached. My guess would be that you can see the height of the molten Al in the secant across the arc of metal that's
left.
Any reaction that involve combustion of liquid Al is going to need something heavier than sheet metal to contain the heat. I guess it's more obvious
when you state it that way. From the photograph, it seems that the lid of the retort stayed on, and that the wall of the retort failed first. Confirm?
As a more engineering-oriented comment, there's a hot spot. You need adequate thermal mass in the wall of the container so that it doesn't rise above
its melting point at the surface level of the Al (where the reaction is happening) before the heat can dissipate outward.
You mention that the slag has volume about 25% of the retort. How did you measure that?
My one suggestion is to use carbon as part of the initial charge. I don't know that it ought to be the entirety of the reducer, but because its
oxidation product is a gas you might see a lowering of the ignition temperature (see first comment). If it lowers below the melting point of Al, then
the hot-spot problem will be alleviated. With liquid Al as a reagent, you've got the melting enthalpy of Al to dissipate as heat. I'd guess that the
Al powder might still settle at the bottom, but it would be an improvement over a puddle. The carbothermic industrial reaction I reported on is at
much higher temperature, but it's also reducing a Ca compound, not an Na one. It might be useful to run a small carbon-only reduction just to estimate
its ignition temperature. Also, with liquid salts as the other reagents, porous chunk charcoal might work better than fines that can settle more
easily.
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Magpie
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Thanks. Yes, it's back to the drawing board for a more robust retort. The beauty of the paint can is that it is a highly engineered item yet is mass
produced. So it is cheap and therefore, expendable.
The single most important condition for a successful synthesis is good mixing - Nicodem
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UnintentionalChaos
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| Quote: Originally posted by Magpie |
Thanks. Yes, it's back to the drawing board for a more robust retort. The beauty of the paint can is that it is a highly engineered item yet is mass
produced. So it is cheap and therefore, expendable. |
I have used a beefy retort made from black iron pipe parts that should hold up. The body is a piece of 2" pipe nipple with an appropriate cap on the
bottom. A few reducing adapters and an elbow later, I added a long piece of narrow iron tubing. I've used it for half a dozen benzene runs, though the
retort volume (and yield per run) is thus low compared to paint can approaches. It also takes a -long- time to get to temperature being several pounds
of steel.
I don't think that the entire thing ran me more than $20. If you can weld, sealing the bottom off properly (I did have some seepage out of the
threads) would help.
[Edited on 9-25-12 by UnintentionalChaos]
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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Magpie
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Sorry I can't easily confirm that as that can has been disposed. With some dumpster diving it would be retrievable, however.
The lid and bottom retained integrity. The lid did stay on. The sidewall was trashed, however, as you can see.
It's just an estimate by eye. It might be even less than 25%.
The only experience I have with carbon is an attempt to run the industrial reaction with Ca3(PO4)2, C, and SiO2. This was in a ceramic tube in a
tube furnace. There was no reaction. Maximum temperature was likely 1300C. I apparently did not record this experiment as I can't find it in my
notebooks.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Magpie
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Yes, I will probably have to go to some metal pipe for the boria reaction. That may be practical as the product is pretty much water soluble and
should allow for recovery of the retort with a reasonable amount of effort/risk.
I can't weld (don' have the equipment) but know a SCWIM who can for a reasonable price.
--------------------------------------------------------------
Another possibility is to use a ceramic tube/tube furnace with the boria formulation. Because of the vastly reduced slag the charge could be
considerably higher than when using silica, and thereby a decent yield could be achieved. I suppose there is a risk that the boria/borax would flux
the mullite ceramic retort and eat through the wall, however.
[Edited on 25-9-2012 by Magpie]
[Edited on 25-9-2012 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Dave Angel
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Hey Magpie - are you using something like this for your argon?:
I make use of these cylinders and I've just (very carefully after ensuring it was empty!) opened my last one up (for the Downs cell). Perhaps this
could be the beginnings of the heavy duty container you seek?
Oh, and nice work so far by the way! I've been silently following this as WP is a little way down the line for me, but I'll look forward to making use
of your learnings when I get to it.
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Magpie
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No, those don't seem to be available in the US. What I have is a much larger 40 cubic foot cylinder that I get refilled at my gas dealer. I have
thought of using an empty disposable propane cylinder that is about that size, however.
I just got back from a trip to my local scrap dealer where I purchased some 0.125" plate, and 3" tube, wall thickness 0.065", for $8.50. Both are
stainless steel. I will be visiting my SCWIM tomorrow to get these pieces fabricated into a new, much more beefy, retort. 
The single most important condition for a successful synthesis is good mixing - Nicodem
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Magpie
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| Quote: Originally posted by Magpie | ... I will be visiting my SCWIM tomorrow to get these pieces fabricated into a new, much more beefy, retort.
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I have put a hold on fabrication of a new, ss retort. It's design was predicated on being reuseable. Because of the hardness and insolubility of
some slag that hardened on the floor of my furnace during the previous run with boria that assumption may not be valid.
It is a dark, glassy slag. Dark because of unreacted aluminum I believe. The slag forms small bubbles in both HCl and NaOH but is otherwise
unaffected. It is difficult to chip using a chisel and hammer. It will grind difficultly under attack with a file. My Dremel with diamond wheel
even has trouble cutting it.
So, I have retrieved the slag mass from the dumpster. If I can't find a way to dissolve or otherwise break up this slag I will be forced to revert to
an expendable retort body for the boria formulation.
Any suggestions on how to deal with that slag will be appreciated.
The single most important condition for a successful synthesis is good mixing - Nicodem
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watson.fawkes
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| Quote: Originally posted by Magpie | So, I have retrieved the slag mass from the dumpster. If I can't find a way to dissolve or otherwise break up this slag I will be forced to revert to
an expendable retort body for the boria formulation.
Any suggestions on how to deal with that slag will be appreciated. |
Vycor glass starts life as a kind of
alkali-borosilicate glass. It's heat-treated to cause a phase separation into a high-silica (96%) phase and everything else. Then it's leached in
acid, which dissolves out the non-silica phase. According to this document, it's hot sulfuric acid 90 °C, concentration not specified. The result glass is micron-sized porous, and it either used
porous or heated again to shrink and seal the pores. So my guess is that the heat is a necessary driver to get the acid reagent into the reaction zone
by using thermal motion. You don't have a silica phase, but an alumina one. If you're lucky, your slag will leach out similarly.
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Magpie
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Thanks watson for the document. I will do some experimenting with the boria slag in hot sulfuric acid.
Another approach to this problem, which I like even better, is to cheaply harden the paint can. I have had some ideas on how to do this:
1. Using a removable mandrel cast a layer of plaster-of-paris internal to the can. Idea thrown out because water would be driven off during the
firing from CaSO4*2H2O.
2. Cast the internal surface with a clay based ceramic. Idea thrown out because of the 10-14% shrinkage expected.
3. Line with furnace cement.
4. Line with kaowool using waterglass as adhesive.
Other suggestions are welcomed.
The single most important condition for a successful synthesis is good mixing - Nicodem
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watson.fawkes
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Line with sand and fireclay. Perhaps some grog, or small amounts of
bentonite or ball clay. That's what I recall off the top of my head, without research, into one kind of shop-made crucible for small foundry work. The
principle is having sand as a body largely eliminates shrinkage. The fireclay sinters enough to hold everything together. Additives such as grog,
bentonite, and ball clay are used as shrinkage modifiers and cements (but you don't want very much cement at all in a fire clay mixture).
As I recall, the standard fire clay available on the US West Coast is Lincoln.
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Magpie
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This sounds like the right idea. What temperature is needed to sinter the fireclay? Wiki indicates 1600C for firing. My furnace will only reach
1000C.
[Edited on 28-9-2012 by Magpie]
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According to this link, a ceramic of 90%talc/10%clay, fired at 1040C, shrinks very little if at all:
http://www.pottery-magic.com/pottery/clay/low-shrink.htm#.UG...
[Edited on 28-9-2012 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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watson.fawkes
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| Quote: Originally posted by Magpie | | This sounds like the right idea. What temperature is needed to sinter the fireclay? Wiki indicates 1600C for firing. My furnace will only reach
1000C. |
That's the reason for the additives. I checked one reference; it recommends potassium feldspar
(orthoclase) at 2% or less. This is a mixture of K2O and alumina-silicate. The potassium content acts as a flux, lowering the melting point
at interfacial boundaries, so that the clay sinters at a lower temperature.
I mentioned fireclay because it's got relatively high alumina content and low alkali and alkali earth content. 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. You also want something that your reaction fluid won't simply dissolve.
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