sbreheny
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Calcium Carbide impurities
Hi all,
I recently got some calcium carbide which is sold for "gun sight smokers" - little lamp black carbon generators to make gun sights as truly black as
possible to avoid glare. I noticed that the lumps of carbide are not of a uniform color and even the dry carbide smells strongly of a sulfurous or
garlic-like odor. I reacted two lumps (maybe 1 gram) with some water and the smell increased dramatically. The gas produced was flammable so I am
assuming that mostly acetylene was produced but there were definite impurities.
Given that these impurities are usually very toxic (arsine, phosphine, h2s, etc.), I am curious about the safety of using this carbide. I was planning
on trying it out on a homemade carbide lamp set-up but if the smell is that strong from such a tiny amount, I'm not so sure.
Thoughts? Is this typical for lamp-grade carbide?
Sean
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macckone
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I would be cautious.
Use it outside with good ventilation and don't breath the fumes.
Mostly this stuff is used for carbide cannons which ignite everything.
Used in a lamp, any of the nasty stuff should burn up.
But I would be concerned about breathing the fumes if it has an odd smell.
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IrC
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Along with the impurities you mentioned also consider Calcium Cyanide and Calcium Cyanamide. Common impurities in miners Carbide. I would not be all
that paranoid if you work with reason and common sense. Remember miners in years gone by spent every day for decades in tunnels with little airflow
and their greatest worry was black lung from coal dust. OK, also explosions and cave-ins but off topic. Anyway just don't work in a stuffy room with
no air flow, but not so bad I would be worrying about fume hoods if I was just burning the gas from water immersion as long as there was a decent
draft out of the room. The cyanide impurities obviously mean be careful with contact (and stop sniffing it to see what it smells like). I am sure the
amount is not that great but you know it takes little with any cyanide to be a concern.
"Science is the belief in the ignorance of the experts" Richard Feynman
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HgDinis25
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Technical Grade Calcium Carbide is only about 85% pure. However, most impuritis are Calcium Oxide and Calcium Hydroxide. In smaller amounts you have
Calcium Phosphide, Calcium Sulfide, Calcium Nitride and Silicon Carbide, this quoting wikipedia:
http://en.wikipedia.org/wiki/Calcium_carbide
I've never heard of cyanide contamination in calcium carbide. Could you please provide some references?
Despite wikipedia claimings, the following book gives a much scientific aproach on calculating carbide impurities:
http://books.google.pt/books?id=ElhD1jDVVqEC&pg=PA22&...
On page 28, one can see that the makority of impurities comes from Calcium Oxide. However, taking as true the information given by the book, I fail to
see how can Calcium Carbide of technical grade smell so bad (I have smelled it my self).
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woelen
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I only know of the following impurities:
- calcium phosphide
- calcium sulfide
- calcium hydroxide
- calcium oxide
- calcium carbonate
- organics (sulphurous compounds) in tiny and highly variable amounts
The phosphide is the most prominent impurity and it produces phosphine. This also is the main smell of calcium carbide. I actually find the smell of
H2S non-present in the many samples of calcium carbide I ever used. Some samples, however, had strong phosphine smell, mixed with some particular
organic smell.
In a few chemical experiments I also made pure phosphine and this has exactly the same smell as most of the samples of calcium carbide I used.
Phosphine and also organic sulphurous compounds have a strong and bad smell, even at very low concentration, so you certainly will smell it.
Fortunately, burning of the gas destroys all dangerous compounds completely (phosphine burns to phosphoric acid and sulphurous compounds burn to SO2).
If there were a small amount of cyanide in calcium carbide as well, then that would not worry me. Cyanide is not more toxic than phosphine and it also
will be destroyed completely when the gas is burned. However, at the decomposition of CaC2 with water you get strongly alkaline Ca(OH)2 and this will
prevent any cyanide to be released as HCN, the liquid simply is too alkaline and if any cyanide is present it will remain in solution when water is
added.
The only impurity which really would be BAD, VERY BAD, would be arsenic compounds. These give arsine with water and on burning these give arsenic
trioxide. Sulfide, cyanide and phosphide all are converted to harmless forms of the element, but arsenic has no harmless form. It will remain very
toxic.
I, however, never heard of arsenic impurities in calcium carbide. I strongly doubt their presence. If they were, then it would be absolutely 100%
forbidden where I live, but it is very common where I live (we have the habit of carbid-shooting for fun in the Netherlands) and such a habit
certainly would be prohibited if it introduced arsenic in the life-environment.
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IrC
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Did not get that info from any technical sources, no doubt my references have long ago passed on. I grew up in a mining community and it was one of
the warnings miners talked about due to the way carbide was made in kilns exposed to open air. The combination of C, Ca, and N2 from the air in the
conditions inside the kiln (glowing hot) lead them to consider the formation of CaCN and CaCN2. Just a bit of information I have always taken for
granted from my youth in the 50's. Never saw any reason to question it in the decades since. Your right it could be wrong but if so why the hell did
miners consider it? The other worry in confined areas in the mines was phosphine as woelen mentioned. woelen your the expert chemist, was that just an
old miners tale or is the reaction possible inside kilns the way carbide was manufactured many decades ago?
"Science is the belief in the ignorance of the experts" Richard Feynman
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woelen
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Formation of cyanamide certainly is possible when calcium carbide is made. At well over 1000 C, CaC2 reacts with N2 to give C and CaCN2:
CaC2 + N2 ----> CaCN2 + C
So, cyanamide certainly can be an impurity when the temperature in the kiln is not controlled very well and goes towards 1100 C or so.
This, however, is not the same as formation of cyanide. I see no easy way of forming Ca(CN)2 in a kiln, even in the presence of carbon and CaC2.
Maybe the miners mistook CaCN2 for Ca(CN)2 and mistook the name calcium cyanamide with the name calcium cyanide.
Calcium cyanamide is actual made from CaC2 in a process called Frank–Caro process. Wikipedia has a page on this process (just search for Frank Caro
inside wikipedia and I'm quite sure you get a hit).
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IrC
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Thanks woelen I would say that was highly likely. Doubtful if they understood the difference between the names. Also they were very sloppy in the use
of the language. I never really gave it further thought over the years, until the subject comes up such as this thread it's just one of those facts
that stay stuck from long ago. Like pet rocks.
"Science is the belief in the ignorance of the experts" Richard Feynman
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