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garage chemist
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The commercial carbide is not prepared by the pyrophosphoric acid method, otherwise it would be more expensive (phosphoric acid isn't that cheap
since it needs white phosphorus as a precursor).
The garlic odor of the carbide results from PH3, thats clear, but the origin of the calcium phosphide is from impurities in the used calcium oxide. It
contains small amounts of phosphorite or apatite which get reduced to phosphide in the arc furnace.
In the arc furnaces, the CaC2 leaves the furnace in a molten state at over 2000°C.
Imagine how bright that must be...
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IrC
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I have CaO at 1,100 C about every other day, and it is bright with #6 welding glasses. I wish I had a kiln that would do over 2,000 C. So that makes
sense but then I wonder how the PH3 stays in there at those temperatures. It would seem it would all be up in smoke before the stuff cooled down. Or
maybe it forms while cooling but then I don't know where it would get the hydrogen from. Just doesn't seem that stuff would still be in
there while that hot.
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12AX7
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Well uh.. it's kind of anhydrous at that temperature, so it tends to stay bound as phosphide (reduced from phosphate by carbon, just as Na2SO4 +
4C = 4CO + Na2S). 
1100C, pffbt that's nothing, I was at that temp just the other day inside some kaowool. Calcined some lime while I was at it, too.  Now blinding white hot...that's when you get into molten iron and steel. 
Tim
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IrC
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I use oxy/gas (various) for even higher temperatures but I was referring to the inside of my electric kiln. 2,200 F may not sound like much but it is
when you have several pounds of material inside several square feet of firebrick all at this temperature. But I understand now, the hydrogen to make
PH3 is coming from the water when you put CaC2 in H2O. Don't know why I didn't think of that earlier. So there are a few more reactions
going on in there than I realized.
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12AX7
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| Quote: | Originally posted by IrC
I use oxy/gas (various) for even higher temperatures but I was referring to the inside of my electric kiln. 2,200 F may not sound like much but it is
when you have several pounds of material inside several square feet of firebrick all at this temperature. |
Ah, not a bad size for ameteur work. But...still.. I'll have to show
pics here of the 3.2 cubic foot gas kiln I'm building.
H2S, PH3, CH4 and etc. also grace the presence of my nose when breaking up (salt) slag left from melting aluminum or magnesium.
Tim
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jimmyboy
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calcium carbide simply doesnt have any demand anymore - why its pretty uncommon to find it - i would still like some to mess with though
An excellent detailed writeup on making it a few grams at a time can be found in Brauer (Inorganic Prep) - i also remember having a pdf that detailed
using carbon rods and a high wattage electric heater as a DC source to provide enough amperage - anyone done all this already? any success stories?
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IrC
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I would think a variable core Lincoln arc welder would be perfect for that. 12AX7, how hot does a gas kiln get, and what temperature can the fire
brick kilns are made of take? I still don't know how hot is safe in my kiln, at 2,400 F my meter pegs, light was shining through the brick clear
to the outside. Scarey looking when it is sitting on the floor inside the house.
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12AX7
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Depends on the firebrick...some day I want to fire some high alumina insulating bricks and make a cone 30 kiln. Yes, that's hot enough to pretty
near melt platinum, and titanium if it didn't burn like hell.
Bricks with high flux content like calcium and potassium might melt lower than 2100F, or lower.
Tim
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garage chemist
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I can still buy CaC2 OTC in most home/garden stores as "Wühlmausgas", as a means of getting rid of moles and "Wühlmäuse"
(don't know the english name for them).
It is sold in rather fine granulated form, about 4-7 mm grain size.
The normal means of use is to throw a spoon of it into a mole nest and close it. The humidity of the soil causes the hydrolysis of the carbide with
the evolution of PH3 stink, which should make the moles move out of the garden.
It is sold in metal cans of 250g or 500g content. On the label, it says "contains 800g/kg CaC2", which is just technical grade carbide.
However, you can't just walk into the store and buy it. It is locked in a safe cabinet and can only be got on request for the specific product.
I don't know if you can get it outside of germany, at least I've never heard of it being available in the US.
If there's interest, I could post a picture of the product and label.
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woelen
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In certain parts of the Netherlands you can buy it at kilogram quantities just before new year's eve. It is used as an alternative for fireworks.
It is called 'Carbid' and it is technical quality, containing quite some phosphide.
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stygian
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For those who can't obtain CaC2
This may be of interest to those wanting/needing acetylene, but cant obtain CaC2 for some reason (it's also cool, just found it digging around
for info on phorone).
Electrolysis of Salts of unsaturated organic acids leads to a combination of acetylene, methylacetylene, propadiene, CO, and CO2.
Source: http://jagor.srce.hr/ccacaa/CCA-PDF/cca2002/v75-n1/CCA_75_20...
[Edited on 21-11-2005 by stygian]
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kazaa81
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Isn't that a Kolbe electrolysis?
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stygian
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Read the document. Kolbe theory says that unsaturated acids 'dont work' supposedly. The truth seems to be that they produce the
unsaturated hydrocarbons mentioned. One such acid, crotonic (oxidize crotonal, made from acetaldehyde)
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DeAdFX
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Calcium carbide is used for fertilizers...
CaC2 + N2 = CaNCN
Calcium carbide reacts with nitrogen to produce calcium cyanamide(sp)...
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neutrino
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How would one then go about obtaining this carbide? I've only ever heard of the cyanamide sold for fertilizer.
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DeAdFX
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| Quote: | Originally posted by neutrino
How would one then go about obtaining this carbide? I've only ever heard of the cyanamide sold for fertilizer. |
To be honest I have no clue. It was a use for CaC2. You could try asking someone who works at a fertilizer plant for CaC2? Other than that no clue.
This reminds me in my schools chemical storage area I saw a container for CaC2. I don't remember any specifics of the container but if it is
still there I wouldn't mind taking picturs of it.
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chemoleo
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What do you mean, 'this carbide'?
Calcium cyanamide is widely used. .. as a lawn fertiliser. If it's used here, it most certainly will be in the US... you just have to find it.
The reaction of CaC2 and N2 requires high temperatures (>700 deg C IIRC) to work however. Might be easier to just play with the fertiliser (one
project that is, one day, on my to do list).
Anyway. Is someone going to try the purported route of C/CaO/pyrophosphric acid /pressure, as mentioned above?
Although unlikely to work, don't you think it's worth a try?
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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S.C. Wack
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No, the cyanamide is not used as fertilizer over here. You would have seen mention of this if it was.
http://hazmap.nlm.nih.gov/cgi-bin/hazmap_generic?tbl=TblAgen...
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BromicAcid
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Over the last several years I have tried to find calcium cyanamide in my area with no sucess, as far as I can tell it is no longer avalible in the
states except from scientific suppliers such as Spectrum (although you can never tell what smaller specialty shops may still be carrying). I was at
one time tempted to even purchase it form here as I belive one can produce carbon tetrachloride from it.
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Picric-A
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Sorry to bring up and old post.
I used to be able to buy CaO in 25Kg sacks for around £6.
Now by garden centre has stopped selling them and i have had to buy Ca(OH)2 from a chemicals supplier at £3 for 1kg.
Can calcium hydroxide be used to make calcium carbide in an arc Furnace?
In response to the calcium cyanamide question, normally when one is making calcium carbide in a home built arc furnace fair amounts of calcium
cyannamide are formed as hot carbide reacts with atmospheric nitrogen. Yet aother impurity in 'home made' CaC2 
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Formatik
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| Quote: | Originally posted by Picric-A
Sorry to bring up and old post.
I used to be able to buy CaO in 25Kg sacks for around £6.
Now by garden centre has stopped selling them and i have had to buy Ca(OH)2 from a chemicals supplier at £3 for 1kg.
Can calcium hydroxide be used to make calcium carbide in an arc Furnace? |
CaCO3, CaO, Ca(OH)2 will all work. Though it would be better to dehydrate the Ca(OH)2 first, since it requires only moderate heat to dehydrate.
[Edited on 29-8-2008 by Schockwave]
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Picric-A
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If i didnt dehydrate it (heat to 550C) would this ruin the carbide produced?
Would you have to run the one with CaCO3 longer?
thanks,
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12AX7
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Hydroxide and carbonate require additional heat and carbon to decompose.
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Picric-A
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cool thanks,
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ScienceSquirrel
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Calcium carbide comes up for sale on www.ebay.co.uk quite frequently.
I would just store a search and leave it for few months.
Cavers and collectors of antique carbide lamps use it.
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