Sciencemadness Discussion Board

Nice carbide making experiment

metalresearcher - 11-11-2017 at 11:43

Today I repeated an experiment making CaC2 by putting CaO and charcoal in a graphite crucible and putting carbon rods to a DC welder (127 A) onto it. I let the arc running for 5 minutes which indeed generated immense heat (> 2000 C) and athen I let it cool down.
After cooling down (05:12) I poured some water in the crucible and it started bubblimg immediately. I ignited it and it catched a bright sooting flame which means that it is really acetylene gas (C2H2).
And there was a typical 'carbide smell' which is actually PH3 according to some sources, as C2H2 or CaC2 are completely without any smell.
But why does phosphine occur in carbide ? The source of my CaO is lime from the hardware store which is Ca(OH)2 which I have burnt. And the carbon is charcoal, so where is the PH3 (or other bad smell) from ?
Here the video.

https://www.metallab.net/jwplayer/video.php?v=L2NsaXBzL01ha2...

GrayGhost- - 11-11-2017 at 14:39

Hi I buy calcium carbide in hardward store ( in my country) for welding with acetylene and oxygen torch, and yes smell very bad. Is sell in rocks of variable size for kilograms.

I dont know exact origin of bad smell but is like sulfured.

Bezaleel - 14-11-2017 at 09:10

If this is indeed phosphine, I expect to be from calcium phosphate. Calcium phosphate containing rock is industrially processed for the phosphate. I guess lime is a side product and tiny amounts of phosphate are left in it.

Bert - 8-12-2017 at 04:41

Nice experiment. I am interested in a couple of group IV carbides lately as fuels.

Where did the Phosphorus and/or Sulfur contaminants that gives acetylene from Calcium carbide the phosphine or sulfide odor come from?

Limestone

Cheap sources of Calcium for industry are often of organic origin- Limestones in particular. Sedimentary rocks formed from ocean floor deposits of corral, shells and calcerous skeletons of microscopic organisms. Organic debris of that type always contains some Phosphorus (everything living on earth does), plus limestones generally contain odd bits of other minerals such as pyrites (which are sulfide minerals).

Acetylene

Quote:

industrially, the gas is mostly produced from the cracking process used to break down large hydrocarbons in oil refineries, and by the partial combustion of methane. In this pure form, the gas has what the US National Institute for Occupational Safety and Health describes rather beautifully as a ‘faint, ethereal odour’, though particularly when obtained from calcium carbide, which often has impurities, it tends to have a strong, unpleasant garlicky smell from phosphine derivatives, or the unmistakable rotten eggs stench of hydrogen sulphide.