Cyrus
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Uses for sheet rock (gypsum) ?
Hello all,
What can I do with gypsum, which is hydrated CaSO4 ? When heated it turned grey from white, and smelled like sulfur. What reaction is this?
Practically anyone who lives in a newer house has tons of this stuff, so it would be great to find a good use for it, besides
walls!
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darkflame89
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Smelled like sulfur? Maybe the gypsum decomposed to form sulphur dioxide? But CaSO4 decomposes at 900 degrees C. Just how hot was your heat?
Ignis ubique latet, naturam amplectitur omnem.
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I am a fish
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When you post a question, be precise. Include every piece of information that could possibly be of relevance. As darkflame89 pointed out, the term
"heated" is not very helpful.
CaSO4 is not a particularly interesting chemical. Building materials are generally inert, which makes them not particularly useful as reagents.
The only interesting reaction I can think of is:
3CaSO4 + 8Al -> 3CaS + 4Al2O3
Ignite a mixture of anhydrous calcium sulphate and aluminium powder with thermite, and it burns with a bright white light.
1f `/0u (4|\\| |234d 7|-|15, `/0u |234||`/ |\\|33d 70 937 0u7 /\\/\\0|23.
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acx01b
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nice reaction
but thermite whats that ?
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Cyrus
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I wish I could tell you the exact temperature, but I can't. The test tube was heated in a flame from my burnz-o-matic propane burner for
sweating copper
pipes. I know that bunsen burners get to
around 1500 C, but it was not that hot,
because the glass didn't melt. The m.p. of pyrex is about 800 C. I should note that
it let off whitish fumes that didn't look like
water.
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Quantum
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acx01b:
Thermites are extremly exothermic(hot) redox reactions. Some examples are:
Al/S
CuO/Al
Fe<sub>3</sub>O<sub>4</sub>/Al(most popular and well known)
A thread about thermite analogs
Ignore my post on the 3rd page on that thread; back then in my 'early days' I didn't even know what redox was! Now I have some text books and am becoming educated rapidly.
What if, what is isn\'t true?
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axehandle
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No, no, no, no no!
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I wish I could tell you the exact temperature, but I can't. The test tube was heated in a flame from my burnz-o-matic propane burner for sweating
copper
pipes. I know that bunsen burners get to
around 1500 C, but it was not that hot,
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No way, my biggest propane burner only goes up to 1100-1200ish, and that's with the air intake blower at full blast.
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because the glass didn't melt. The m.p. of pyrex is about 800 C. I should note that
it let off whitish fumes that didn't look like
water.
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More like 1000..1200 for borosilicate glass.
But it is almost certainly SO2 from decomposition of CaSO4. I once used a (dehydrated) CaSO4 block as a crucible plint in my furnace, and the whole
apartment was SO2:ed. Very nasty, but I suppose it could be used in a controlled manner to generate SO2.
What's interesting about CaSO4 as a construction material is that it acts as a firewall in case of a fire. To "burn through", i.e.
become so hot as to propagate the fire to the next room, all the water has to be driven out first.
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Cyrus
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Yes Yes Yes No No
I wholeheartedly disagree about bunsen burner max temperatures, and with good reason! According to The Flinn Chemical and Biological Catalog
Reference
Manual 2002 their bunsen burners with propane reach the temperature (at the hottest part of the flame) of 1560 C, and their Meker burners reach a
scorching 1775 C!
Maybe thats a good excuse to charge so much. Flame me all you want for mentioning a burner hotter than your mighty one
As for the m.p. of boro. glass, you may be right, but the number 812 C sticks in my head, and the test tubes seem to melt quickly.
This does seem like a great method for small amounts of SO2
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axehandle
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Is that catalog online? Link, please..... I'd like a spec. The only way to reach that flame temp with propane would be to pre-heat the air to
500C.
Edit: MP of borosilicate glass: 1250C.
Reference: http://www.mellesgriot.com/products/optics/mp_3_4.htm
[Edited on 2004-5-13 by axehandle]
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BromicAcid
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It might not make a difference but bunsen burners in my geographic location burn with methane but you specifically say "The only way to reach
that flame temp with propane would be to pre-heat the air to 500C." Like I said, it might not make a difference, I am not going to pull out
'the book' to get the numbers for a quick and dirty thermodynamic calculation.
Hawley's Condensed Chemical Dictionary lists the softening point of borosilicate glass at 593C, I easily bend it using the burner on my gas stove
to heat it. Vycor, the pure silica glass softens at a respectable 1482C!
[Edited on 5/13/2004 by BromicAcid]
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axehandle
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Methane you say? I'll do some research.
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Mumbles
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I'd think the only way one could acheive those temperatures would be with preheated air. Preheated pure oxygen is more like it. You have to
remember those are ideals. One readily does not acheive those temperatures. I give a normal LP bunsen burner 1200 tops under normal conditions.
As for the SO2. I don't know the name(pyrolyse maybe). When you heat Sodium Bicarbonate it goes to Na2C2O5 or whatever it may be. Do you think
this might be happening?
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axehandle
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My guess when heating CaSO4 to decomposition is:
CaSO4 + heat --> CaO + SO2 + 1/2 O2
at higher temps I wouldn't be surprised to see
CaSO4 + LOTS heat --> CaO + SO3
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Cyrus
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I think if you go to
http://www.flinnsci.com/Sections/Ordermaker/flinnOrdermaker....
you might get a downloadable catalogue which might have this info in it under burners, but this is 2004, not 2002.
I just did a google search and found at
http://66.102.7.104/search?q=cache:tAGbuZs2U64J:www.ams.usda.gov/nop/NationalList/TAPReviews/CaSO4.pdf+decomposition+of+calcium+sulfate+to+&hl=en&
amp;ie=UTF-8
quite an address, but it says that calcium sulfate decomposes to SO3, which might be more useful- sulfuric acid.
Other sites say it decomposes into sulfur oxides.
To mumbles, do you mean it decomposes into sodium oxalate? Na2C2O4? This doesn't sound right, as the oxalate ion will decompose at higher
temperatures too.
[Edited on 13-5-2004 by Cyrus]
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axehandle
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quite an address, but it says that calcium sulfate decomposes to SO3, which might be more useful- sulfuric acid.
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It's certainly worth some experimentation. A test could be made using a furnace and a copper tube crimped at one end containing anhydrous CaSO4.
I'll try it out once my new furnace had cured.
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I am a fish
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Another interesting reaction I've just found out about is:
CaSO4 + SiO2 → CaSiO3 + SO3
Apparantly, when global supplies of sulphur were running low, this was seriously considered as an industrial method of sulphuric acid production.
However, now that sulphur is routinely extracted from fuels, there is a great abundance of it and so the process was never used industrially.
Unfortunately, I don't know the temperature required.
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frogfot
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In another industry process they heat CaSO4 with coal at 1500*C:
CaSO4 + C --> CO + SO2 + CaO
I thoat this could be done on small scale with simple bunsen burner since temp can be simply achieved by burning excess coal in air. Gonna experiment
on this.. my primary goal is to make Na2SO3 by SO2 + Na2CO3..
Another more simple use is:
CaSO4 + Na2CO3 --> CaCO3 + Na2SO4
weee.. making own Na2SO4 to dry stuff with. I tested this on small scale, boiled water soln with Na2CO3 and excess of CaSO4 for several hours. pH of
soln drops to like 10 but it never goes further.. so neutralisation of ubtained Na2SO4 is required (by H2SO4), and then purification by recryst..
Should give pure enough drying agent..
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S.C. Wack
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While looking for ammonium sulfate > sulfuric acid patents a while back, I found these patents. The usefulness is questionable, if you had CO2 and
NH3 tanks you would not be scrounging for H2SO4. But you could of course generate these yourself and lead them simultaneously into an ammonium sulfate
solution and obtain the carbonate. Alleged in GB191302002 and WO9609248:
The reaction is: CaSO4 + 2NH3 + CO2 + H2O = CaCO3 + (NH4)2SO4.
The gases are added to a saturated solution of ammonium sulfate so that 40-45 g/L NH3 is absorbed. The temp. is below 25C to prevent volatization. The
gypsum is added in equimolar amount, and the mixture is heated with stirring to 40C for 5-6 hrs. They claim that only 5% of the ammonium carbonate is
unconverted. The CaCO3 is of course solid, and also most of the ammonium sulfate. Upon cooling, they say, pure ammonium sulfate precipitates.
I have plenty of ammonium carbonate to test this, but I threw out, apparently, the CaSO4 I had. I must have thought that it was useless.
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Mumbles
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No, sorry, I posted a bad example. I still cant find the term. I did get a better example.
2 NaHSO<sub>4</sub> ---> Na<sub>2</sub>S<sub>2</sub>O<sub>7</sub> + H<sub>2</sub>O
Then you can heat this(Sodium Pyrosulfate), it produces Sodium Sulfate and Sulfur trioxide.
Now that I think about it, I have no clue what I was talking about when I posted it the first time.
By the way, I wasn't trying to make the oxalate group. It was supposed to be the pyrocarbonate group.
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Cyrus
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Sorry to dredge up an ancient topic, but I have found 3 new uses for sheetrock
1-it is a great general protection material, as it is fireproof, reactions can be done on sheetrock to save the garage floor, or you can hide behind
sheetrock if the reaction is violent enough or splatters molten metals, or you can build a box out of sheetrock and do the reaction in it.
2- An easy source of CaO and Ca(OH)2 (by heating of course), and I suppose if the solution sat out for long enough, CaCO3 would be obtained, all from
sheetrock.
3- As a source of plaster of paris- heat the hydrated calcium sulfate until it turns into calcium sulfate hemihydrate, then powder it. Now use this
plaster as a lost wax mold for your Pt/Au/Ag castings.
Calcium sulfate also reacts with borax, but I do not know the reaction.
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