Bedlasky
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Pyrophosphate preparation
Hi.
I plan to prepare few pyrophosphates in muffle furnace.
Firstly I want to prepare disodium and tetrasodium pyrophosphates by heating NaH2PO4 at 250°C and Na2HPO4 at 450°C. Have you experience with it? How
long I would heat it? Is half an hour long enough?
After this I want to prepare some transition metal pyrophosphates. I decide between Mn, Co, Ni and Cu pyrophosphates - I'll probably make two of them
(I will prepare it on afternoon shift in work because I don't have muffle furnance in home and there isn't time for making all of them). Firstly I'll
precipitate ammonium-metal phosphate from neutral solution, filtrate it, wash it few times with water, wash it two times with methanol and let it dry
at 65°C. After that I heat it at 1000°C for 30-60 minutes (this is only estimated time, I didn't find any article about its preparations,
temperatures and pH of solutions I found in article about gravimetric determinations, but there isn't detailed description).
Later in home I'll compare colour of metal pyrophosphates with metal phosphates and ammonium-metal phosphates which I'll precipitate from solutions.
I'll also try precipitation of pyrophosphates from solutions using tetrasodium pyrophosphate. Finally I'll use disodium pyrophosphate as complexing
agent for preparation of solution of Mn(III)-pyrophosphate complex.
My questions are: Do you think that heating times are long enough to complete transformation of phosphates in to pyrophosphates?
Is there any possibility of formation of phosphine, phoshides or another decomposition products?
In the case of Ni and Co pyrophosphates I am little concerned about their carcinogenicity. Is there possibility of dust swirling in furnace during
heating?
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woelen
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I would not worry about formation of phosphides and other dangerous lower oxidation state phosphorus compounds. If your starting materials are
phosphates, then I do not expect any of these.
Comparing colors may be quite difficult. The compounds you prepare at home are from aqueous solution and most likely are hydrous compounds. This can
greatly affect the color. You also get the material in very finely divided state. I expect the material from the furnace to be much coarser, maybe
even single globules if the material melts at 1000 C.
Whether you get dust I do not know. I do not expect much turbulent air motion in the oven, but can't you put the material in a loosely closed crucible
or something like that, so that there is no possibility of free moving dust through the oven?
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rockyit98
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i also redid my 5L electric furnace that can get to 1200C.in future i'm thinking of making P by heating Cu(ii) Pyrophosphate or polyphosphate with
carbon . i have Ca(H2PO4)2 thinking of adding Con H2SO4 and Na3PO4 to make NaH2PO4 by removing CaSO4
heating it fast will make Sodium trimetaphosphate.and go from that. woelen is right you need an electric furnace for this.keep in mind this will make
hot H3PO4 vapor.
"A mind is a terrible thing to lose"-Meisner
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Bedlasky
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I found today some articles about thermal decomposition of different ammonium-metal phosphates and copper phosphate.
There is very similar behaviour between different ammonium-metal phosphates:
1. step (50-100°C) - NH4MPO4.6H2O --> NH4MPO4.H2O + 5H2O (this applies in particular to NH4MgPO4, some phosphates of transition metals are
precipitate as monohydrate)
2. step (100-250°C) - NH4MPO4.H2O --> NH4MPO4 + H2O
3. step (250-350°C) - NH4MPO4 --> MHPO4 + NH3
4. step (350-550°C) - 2MHPO4 --> M2P2O7(amorphous) + H2O
5. step (600-700°C) - M2P2O7(amorphous) --> M2P2O7(crystalline)
This is only general overview, temperatures for different phosphates may be little bit different, but not too much.
In gravimetric determination of Mg as Mg2P2O7 is NH4MgPO4.6H2O heated at 1100°C for 1 hour, so this seems to be good conditions for formation of
other pyrophosphates.
Copper phosphate decomposes as follows:
1. step (130-290°C) - Cu3(PO4)2.3H2O --> Cu2(PO4)(OH) + CuH(PO4)2.H2O + H2O (but this look like mistake, probably CuH(PO4)2.H2O is CuHPO4? I don't
know.)
2. step (330°C) - Cu2(PO4)(OH) + CuHPO4 --> Cu3(PO4)2(amorphous) + H2O
3. step (605°C) - Cu3(PO4)2(amorphous) --> Cu3(PO4)2(crystalline)
So I suppose for making anhydrous metal phosphates would be the same conditions as for preparations of pyrophosphates.
Woelen: Thanks for reminders. I don't know if phosphates melt around 1000°C, but pyrophosphates definitely not. I once prepare in school magnesium
pyrophosphate as described above and it was fine crystalline powder. For example: calcium pyrophosphate have melting point 1353°C. I don't know if
are in work some crucibles with cap and I don't have any crucible. In work we have ceramic bowls, but tommorow I'll look at the cups. I will work in
small scale, I don't need lots of these phosphates. On your advice I prepare phosphates in more ways:
1. ammonium-metal phosphates by precipitation from solutions
2. hydrated metal phosphates by precipitation from solutions
3. anhydrous metal phosphates by dehydrating hydrated metal phosphates
4. metal pyrophosphates by thermal decomposition of ammonium-metal phosphates
5. metal pyrophosphates by precipitation from solutions
6. if will be results from preparations of phosphates and pyrophosphates interesting, I'll buy sodium triphosphate and precipitate metal triphosphates
from solutions
rockyit98: I don't want to make phosphorus or phosphides, but only anhydrous phosphates and pyrophosphates. This preparations also make hot H3PO4
vapor?
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Tsjerk
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Quote: Originally posted by Bedlasky  |
rockyit98: I don't want to make phosphorus or phosphides, but only anhydrous phosphates and pyrophosphates. This preparations also make hot H3PO4
vapor? |
No I don't think so. Not when you use anhydrous phosphates, probably not even when there is water in there.
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rockyit98
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| Quote: Originally posted by Tsjerk | | Quote: Originally posted by Bedlasky |
rockyit98: I don't want to make phosphorus or phosphides, but only anhydrous phosphates and pyrophosphates. This preparations also make hot H3PO4
vapor? |
No I don't think so. Not when you use anhydrous phosphates, probably not even when there is water in there. |
what i do before i try something is think of what could go wrong here. it have saved my life! when i need to make rust proof some steel i put some
Ca(H2PO4) in a can and SLOW heat it with piece of iron or steel. which give 3Ca(H2PO4)--->Ca3PO4 +2H3PO4 and phosphoric vapor react with iron
oxide to make protective coating. i do this way because you can't heat it with glass beaker and for good coating it need high temperatures. so if you
need pyrophosphates need to move quickly with heating.
"A mind is a terrible thing to lose"-Meisner
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BaFuxa
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| Quote: Originally posted by Bedlasky | Hi.
I plan to prepare few pyrophosphates in muffle furnace.
Firstly I want to prepare disodium and tetrasodium pyrophosphates by heating NaH2PO4 at 250°C and Na2HPO4 at 450°C. Have you experience with it? How
long I would heat it? Is half an hour long enough?
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I have, I just left it in for 30 minutes at the target temperature. I tested with the PH according to some data I found online, it all checked up.
Potential counts for nothing until realized.
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