Solids with lowest autoignition temperatures?

[dbooksta]

I've been trying to determine whether any solids have an autoignition temperature under 200C. Supposedly "oily cotton" autoignites as low as 120C, but I ran a bunch of tests with cotton patches and none of them ignited before a control patch saturated with sulfur (which went right around 200C). They certainly smoke, but to clarify: The "auto ignition" I'm interested in is where the substance, exposed to an ambient atmosphere, spontaneously begins to burn at a significantly hotter temperature than the ambient.

 

So what substances auto-ignite between 100C and 200C? (Sulfur would barely satisfy this, although it has actually melted well before it auto ignites.)

[Mumbles]

What sort of oil did you use? There are plenty of stories about linseed oil soaked rags auto-igniting. That is a little different situation, but higher ambient temperatures accelerates the auto-ignition. It's just an idea, not sure if it'd suit your needs.

 

Otherwise all of my ideas are not really all that air stable or that easy to come by. Things like boranes, silanes, and white phosphorous all have notoriously low auto-ignition temperatures.

[dbooksta]

Right, something as volatile as white phosphorous wouldn't qualify: way too low an auto-ignition temp. Didn't say it has to be easy to come by, just that it has to be solid and auto-ignite to flame between 100C and 200C. Actually I'd be interested in anything down to 50C. I'll just be surprised if there's such a wide temperature chasm of non-reactivity at these "hot but not fire-hot" temperatures.

 

I actually tested four different oils on cotton: 2-cycle, 3-in-1, WD-40, and Kroil.

 

My understanding of the linseed oil phenomenon is that it undergoes some sort of exothermic process when it's left on the rags, so it doesn't really count: It will generate some heat, which might be enough to ignite, but once it has evaporated or done whatever it does it will no longer ignite.

Edited October 11, 2015 by dbooksta

[Peret]

Perhaps something involving glycerine? Everyone knows that glycerine auto-ignites with permanganate but I don't know if anyone tried other oxidizers.

 

Potassium chlorate, charcoal and manganese dioxide ignites at a very low temperature - I don't know how low, but below boiling point.

[Mike]

Other question, what do you wanna do with it?

[dbooksta]

I don't know. Initially I was reviewing some storage safety guidelines and I began wondering why temperature wasn't specified. Then I began looking and thought, "This is weird: I can't find anything south of sulfur (and north of phosphorus)."

 

I could probably come up with some interesting applications. Temperature fuses? Reactive targets that have to be hit a certain number times within a short period before they will trigger?

[rogeryermaw]

My experiments indicated that white phosphorus isn't a solid when it ignites. It melts at about 45C and ignites when the liquid surface is exposed to an oxidizer including the halogens (bromine, chlorine, iodine and, I'm assuming fluorine as I've never had access to fluorine and don't really want to)

[alvin001]

Did you consider that most chemicals don't pose any real danger on their own?

Also every chemical has a msds you can get e.g. from Merck or Aldrich that tell you how to store it.

[ORMDale]

Any solid that will auto-ignite reliably at those temps is considered pyrophoric as far as I know, and I imagine the exact temp would depend on how finely divided it was,

[dbooksta]

Interesting: Pyrophoric solids (here's a good list) oxidize even at very low temperatures but, like you say, they do so more quickly at higher temperatures and higher surface areas. Since exothermic "oxidizing" is a slow "burning" I would imagine that the "auto ignition" temperature of pyrophoric solids is technically below standard temperature.

 

That's sort of what I was observing with the oily cotton: it smokes at far lower temperatures than it "combusts,"

 

But there must be some distinction between "burning" and what I'll call "combusting," because with some chemicals like sulfur (I think) you can leave them out below their autoignition temperature indefinitely and they will not oxidize.

 

Assuming what I've said here is correct, then "pyrophoric" chemicals are not what we're looking for because their auto ignition temperature is actually below 0C.

[Mumbles]

I can't find a solid definition of pyrophoric. One source says anything that ignites spontaneously below 13C (55F), and another says 55C (130F). Given the similarities of the numbers, I suspect there is a typo in one of them. My gut says 55C/130F. It just feels less arbitrary and more reasonable. The source they reference, SEMI F6-92, is not openly available.

 

I had a thought though. What about coating a pyrophoric material with oil or low volatility solvent and painting onto cotton? The oil could be boiled or vaporized off at the temperature you desire. Maybe something like very fine iron. You can make it at home by heating iron (II) oxalate with a torch flame for test tube quantities. You'd need to find a way to protect the iron while it cools though.

[FloridaCracker]

I have a feeling that the smoking oily cotton was not smoke from something about to burn. But an oil particulate fog from the transition from liquid to vapor. In essence, oil "steam".

[Matchless]

The beginning of Ellern's 1968 Book Military and Civilian Pyrotechnics (Part 2 chapters 3-10) covers spontaneous ignition (also called self-ignition or pyrophoricity). He covers a lot of ground in a short space and has excellent endnotes for additional research. He discusses elemental pyrophoric substances like phosphorus and the alkali metals and your issue of exothermic auto-oxidation of unsaturated oils, drying hay, dust explosions, and even a case of smoldering laundry. No mention of spontaneous human combustion though. One of my favorite items is an 1865 patent for pyrophorus, a substance that was to be sprinkled on the bowl of a pipe and brought to red heat by suction, thus lighting the pipe. An excerpt from the patent http://www.google.com/patents/US47335 follows:

 

 

My powder consists of the following substances: potash, forty parts; burned alum, thirty parts; powdered charcoal, twenty parts; rye-flour, ten parts; total, one hundred parts, After these ingredients in the given quantities are perfectly fine powdered and thoroughly dried they must be well mixed together. This substance is then put into an iron cylinder, which must be hermetically sealed. The mixture should be filled into said cylinder without pressing it, and without having an empty space in it. After all this is done the cylinder is to be placed into the fire, allowing In this state it is to be kept in the fire for forty minutes. This time having elapsed, the cylinder is to be removed from the fire and put on a place where it will slowly cool off. After six hours the cylinder can be opened at one end by removing the screw-bolt; but put immediately a cork in the mouth of it,which has a hole through the middle, through which a strong wire can pass. With this wire the substance inside of the cylinder, which has formed into a crust, must be thoroughly stamped, so as to powder it. After this is done the powder must be filled, by means of a funnel, into bottles or tin cases, which can be closed with a cork or screw. The bottles or cases must be perfectly dry before being filled. This being done, is ready for use. The proper proportions of the ingredients, and the adding of the rye-flour in particular, prevent the aluminium and carbonas calium to draw the oxygen contained in atmosphere immediately; hence the ignition of the powder only after breathing at it. Should a greater quantity of rye-flour be added than above given, the powder would light only slowly,and if added too much it would not light at all.

The advantages which this powder offers to smokers are very great. He can light his pipe or cigars by simply putting a little of the powder on his pipe, then to breath on it, and the tobacco will burn. The smoker can use it in any kind of weather, no matter whether windy or rainy, and when the use of matches are of no avail a farmer, any one being in the open air can light his pipe or cigar with this powder when he. cannot use matches, they having become damp from some cause, or it being too windy.

Perhaps if USA Pyro Supply will run a special on hermetically sealed iron cooking cylinders and burnt alum we can cook up a batch?

He is a wonderful writer and I recommend the book for any proper pyro library. Another passage from Ellern about the oxidation of unsaturated oils goes:

A person understanding the principles of this mechanism can deliberately set a fire that not only leaves no incriminating evidence but also has a delayed action feature that can be determined experimentally beforehand with some degree of accuracy and that depends on the ambient temperature; the type, amount, and dispersion of the oil; contact with other combustibles; and the control of air access in a specific arrangement.

For further reading on this topic he refers to: Unconventional Warfare Devices & Techniques, Incendiaries, Department of Army, Technical Manual, TM31-201-1 (1966)

This is a better site to see the actual patent without all the errors and omissions in the google translation: http://pdfpiw.uspto.gov/.piw?Docid=00047335&homeurl=http%3A%2F%2Fpatft.uspto.gov%2Fnetacgi%2Fnph-Parser%3FSect1%3DPTO1%2526Sect2%3DHITOFF%2526d%3DPALL%2526p%3D1%2526u%3D%25252Fnetahtml%25252FPTO%25252Fsrchnum.htm%2526r%3D1%2526f%3DG%2526l%3D50%2526s1%3D0047335.PN.%2526OS%3DPN%2F0047335%2526RS%3DPN%2F0047335&PageNum=&Rtype=&SectionNum=&idkey=NONE&Input=View+first+page

[taiwanluthiers]

speaking of smoking... when I was a kid there was a toy that consists of a small stick of composition. The composition is placed inside a cigarette and when lit (or when it reaches the stick) it causes the cigarette to explode...

[Mumbles]

speaking of smoking... when I was a kid there was a toy that consists of a small stick of composition. The composition is placed inside a cigarette and when lit (or when it reaches the stick) it causes the cigarette to explode...

 

 

Which has what to do with this thread? You really need to stop trying to drag threads off topic. It's very tiresome.

[edbrown]

Phosphorous Sesquisulfide (P2S5) if my memory is correct. Very sensitive with KCLO3. Used in tip of SAW matches in the past.

Ed

[dbooksta]

Phosphorous Sesquisulfide (P2S5) if my memory is correct. Very sensitive with KCLO3. Used in tip of SAW matches in the past.

Ed

 

Yes, used in strike-anywhere matches, but that ignition requires friction. It appears its autoignition temperature is no lower than 275C.

[edbrown]

Autoignition temperature is 212F if memory is correct. From experience if the same sheet of paper is used for weighing KCLO3 and P2S5 and is dropped on the floor after completing weighing and is then picked up, the friction between the floor and paper was sufficient to create a small explosion. Not recommended.

Ed