Sciencemadness Discussion Board - Chlorate-Aluminum-Sulfur Chinese Firecracker Compositions & Storage Stability

Chlorate-Aluminum-Sulfur Chinese Firecracker Compositions & Storage Stability

Hennig Brand - 11-11-2012 at 07:57

I know that mixtures using Chlorates and Sulfur are notoriously dangerous, and are considered off limits all together by most professional fireworks producers. I also know that Chlorate-Aluminum-Sulfur type firecracker compositions have been used by the Chinese to produce firecrackers for much of the last century, and up to today in some cases.

Shimizu gives the following formula:
Potassium Chlorate 43%, Sulfur 26%, Aluminum 31%

Weingart gives this composition:
Potassium Chlorate 30%, Sulfur 30%, Aluminum 40%

And there are many other references using similar compositions as well.

What I have noticed is that these compositions, at least when I make them, have very poor storage stability. I have found that even in as little as 2-3 weeks, compositions of this type can become degraded to the point that they will not explode in a firecracker, even in quantities as large as 1/2 gram. Burn rate becomes dramatically reduced.

I have lately been trying to solve this stability problem.

According to, http://www.corrosionist.com/materials__aluminum_corrosion.ht... and many other references that are easily found.

"Acid waters containing chlorides are especially corrosive to aluminum. Although sulfate-containing waters of low pH are also corrosive to aluminum, they are less corrosive than chloride-containing acid waters."

Sulfur and especially flowers of sulfur has a certain amount of sulfurous and sulfuric acid present. This acidity can contribute to the decomposition of both chlorate and aluminum. These reactions can produce more acid or other corrosive products which can further accelerate corrosion and decomposition.

I have tried to buffer the sulfur by adding 2-3% of very finely powdered calcium carbonate to it. I noticed no, or very little, improvement to the storage stability of the composition.

I make my own chlorates and while it is very easy to recrystallize potassium chlorate from water there will always be a certain amount of chloride contamination. Chlorides are known to be bad from a corrosion perspective, especially in the presence of acidity.

The following is a copy/paste taken from the yarchive page but was originally a post made by Steven.R.Faber on the rec.pyrotechnics forum.

"Did you ever analyze any firecrackers? All the Chinese flashcrackers
I tested (not M-80s) use potassium chlorate, and I am pretty sure sulfur
also, although I don't remember if I tested for sulfur vs antimony
sulfide.
In a lecture by J. Conkling (professor and researcher on pyro. mentioned
here on the net before) he gave a formula for flashcrackers containing
potassium chlorate, aluminum, and sulfur and said he would'nt
touch the mixture himself but the chinese have been making
millions of them safely for years. I was a little surprized at
his aversion for the mix also since I had made hundreds of salutes
using the chlorate, sulfur, and magnesium and Al powder as a kid
without incident. I found that a KCl03, Mg, S mix M-80 type salute
would go bad after a couple weeks of stewing in its
juices(moisture). It would not get sensitive, but would burn more
slowly. The sulfur and Mg would react with water vapor to give H2S
which I detected from blackened Pb acetate paper. Maybe with the
reducing properties of Mg absent, using Al, that acid build up could
be a problem. My KCl03 may have been stabilized with some bicarbonate
as mentioned by Weingart which would reduce the problem.
There is also a factor of what type of sulfur is used.
Flowers of sulfur (sublimed) contains the monoclinic form which
is more active in the above regard than is the rhombic form (can
be made by heating the other forms for a period of time) which is
the recommended form for pyrotechnics. Do any of you have a source
or use the rhombic allotrope in your mixes?

Steve"

His experiences with these types of compositions are the same as mine.

I only make these compositions in very small quantities for small salutes. As of now they need to be used within a couple of weeks or so after making because of the lousy storage stability of the composition.

The Chinese obviously found ways of making these compositions reasonably storage stable.

I would appreciate it if someone could shed some light on the storage stability problems I have been experiencing. A solution to the problem would be wonderful.

Hennig Brand - 13-11-2012 at 00:37

Here is a report, based on a study of chlorate firecracker safety, done by the Chinese. The report examines the thermal stability of chlorate firecracker compositions, as well as friction and impact sensitivity. Perchlorate and nitrate compositions were also studied, in the same way, with the results being used for comparison purposes.

Attachment: Safety Study of the Chlorate Firecrackers.pdf (179kB)
This file has been downloaded 1839 times

[Edited on 13-11-2012 by Hennig Brand]

Hennig Brand - 22-3-2013 at 15:59

Well I substituted potassium perchlorate for the potassium chlorate, in a composition similar to the ones listed in the first post, and as expected the stability problem was solved. After 2 months of room temperature storage the paper crackers that contained the new mixture worked just like freshly made ones.

I haven't really solved the chlorate cracker composition stability problem, but I have developed more of an appreciation for some of the differences between potassium perchlorate and potassium chlorate.

It would still be nice to know some of the Chinese techniques for utilizing chlorate and not perchlorate in firecracker compositions.

[Edited on 23-3-2013 by Hennig Brand]

Bert - 24-3-2013 at 07:59

I've been to China several times, and we import their fireworks for our company.

I have never seen potassium chlorate used in a Chinese salute or firecracker strings made by the factories we deal with. (Chinese like to live to go home too!) I have a couple of times found Chlorate based flash used in small crackers used as reports in consumer aerial fireworks I tested. Items made for the Chinese market may be different- I don't have much access to such.

As far as stability, you will need to avoid chloride contamination, avoid "flowers of Sulfur" and use either Frasch process or oil refinery byproduct Sulfur instead. The grade used for vulcanizing rubber is good-

Chlorate based "cannon cracker" report mixes listed by Weingart and used before Aluminum became the fuel of choice had a reputation for settling and caking in the devices and rendering them sluggish, so were usually only loaded 1/2 full in the hopes that handling would keep the powder free flowing. Commercial perchlorate intended for pyrotechnic use is often milled with various agents to keep it free flowing.

Ral123 - 24-3-2013 at 08:33

Aren't all non sulphur containing compositions with chlorate with infinite storage life? It's interesting that it says that perchlorate flash is less sensitive to impact then nitrate flash. Why chloride contamination would be a problem?

Hennig Brand - 24-3-2013 at 14:39

Thank you Bert for the information, it sounds like you are well versed in the subject matter.

One thing I noticed regarding chlorate-sulfur-aluminum flash was that when stored in a pocket made from a piece of aluminum foil it would stay "fresh" 2 to 3 times longer than when in a paper casing. Is this because of the moisture bonded to the cellulose (paper) casing accelerated decomposition of the composition or is it that the cracker is mostly sealed allowing gaseous decomposition products to build up accelerating decomposition. I guess it could be both, or something else I haven't thought of.

BTW, the sulfur I use is an agricultural variety used on animals for certain ailments (I think). It is supposed to have a small amount of calcium carbonate already mixed in IIRC.

@Ral123 I am not an expert and Bert can probably give you a better answer. IIRC, chloride contamination results in greater sensitivity and lower storage stability of chlorate compostions. Contaminants in general lessen the storage stability of many compositions. But chlorides in this case are especially bad, especially in the presence of acidity from the sulfur. It must act to catalyze or facilitate decomposition in some way, but I am not exactly sure how.

[Edited on 24-3-2013 by Hennig Brand]

AJKOER - 3-4-2013 at 09:49

Perhaps one could improved the mix by adding a compound that would absorb moisture (it is after all the hydrogen from H2O that is contributing to the formation of acids), and was still explosive as a hydrate.

Perhaps anhydrous Oxalic acid, but separately wrapped, so as not to be in contact with the other ingredients to avoid contributing to the acidity issue. Apparently, even H2C2O4.2H2O can be detonated although, by itself, H2C2O4 is difficult to produce any significant explosion on heating. Source Bretherick, Vol 1, page 269, on Oxalic acid to quote:

"Surprisingly, even the dihydrate is apparently detonated by a 50 g tetryl booster,
the anhydrous acid is thermally less stable and thus probably more sensitive. There
is, however, no history of explosion."

[Edited on 3-4-2013 by AJKOER]

Hennig Brand - 28-3-2015 at 07:57

Quote: Originally posted by Hennig Brand

Well I substituted potassium perchlorate for the potassium chlorate, in a composition similar to the ones listed in the first post, and as expected the stability problem was solved. After 2 months of room temperature storage the paper crackers that contained the new mixture worked just like freshly made ones.

Found three of the same perchlorate crackers in storage which were all made at the same time as those discussed above over two years ago. I took one outside, lit the fuse and it worked perfectly. What a tremendous improvement in storage stability between this composition, with potassium perchlorate, and when potassium chlorate is used. I suppose I could have a contaminant in my chlorate that was causing a lot of trouble, but it was recrystallized from water twice, IIRC, and every sample I made formed large, well formed, clean looking crystals. It could just be the chlorate and sulfur issue, but I have noticed storage stability issues with chlorate comps, made with homemade chlorate, even without sulfur in the past IIRC.

Every component and chemical, except the sulfur and sugar for nitrate-sugar fuse, was home made. I had actually switched to using sugar carbon instead of sugar for fuel in fuses since it is very slow burning, non-hygroscopic and much hotter burning, though a bit of the old sugar fuse was lying around and ended up being used for these crackers. The paper fuse I make now is much better in a number of ways, apart from the improved fuel, since learning how to properly roll paper fuse and how to select paper which is more suitable.

[Edited on 28-3-2015 by Hennig Brand]

PHILOU Zrealone - 29-3-2015 at 09:56

The cardboard contains water but also chlorides...
The fact Al tubing helps storage prolongation might thus also comes from less chlorides from the container.

I have worked a lot in the past with chlorate mixes but usually without Aluminium.
For stability purposes I always added 1-2% CaCO3 (chalk/Calcite to write on black board) and the mixes were stable for years.

-NaClO3/NaCl/S/C
-NaClO3/NaCl/Suggar
-KClO3/S (flower of sulfur)/C (airborne black of fumes)

The last mix was the more brisant and less hygroscopic...it was a heavily deflagrating/detonating mix; an uncompressed coffee spoon of the free flowing light powder was able to pulverize a hard copper pipe (1mm wall thickness, 3cm diameter, 3 cm height OPEN ON BOTH ENDS and posed on the ground on one end!). A plastic straw fuse (2mm diameter) made with that mix burned in LESS THAN A SECOND/30 CM, while the same mix with NaClO3/NaCl took like 10-20 seconds for the same lenght!)

The presence of NaCl in the NaClO3 came from the brand "total weed killer 60% NaClO3", the rest was 40% NaCl...it was good for fuses, bengal fire, fumigenes and pipe bombs despite the high NaCl content! This was slighly more hygroscopic than KClO3 but not dramatically. It had the ability to corrode (rust formation due to NaCl) a little coffee tin cans and to a lesser extand glavanised pipe-bombs.

The effect of chloride and moisture upon aluminium is just like with iron, corrosion is enhanced via a galvanic cell effect.
In the presence of moisture and sulfur, some H2SO4 is present and will react with chloride to make HCl and with Al to make Al2(SO4)3 and H2.
H2SO4 with chlorate set some HClO3 free and explosive ClO2 gas; this can set the mix on fire and reduces the amount of available chlorate.
Chlorate and HCl makes Cl2 and H2O...this reduces the amount of chlorate and increases the humidity.
Cl2 and H2O makes HCl and HOCl...this increases the acidity and set some Cl2O free.
With Aluminium HCl is bad news because AlCl3 hydrolyses to make Al(OH)3 and HCl in a catalytic fashion drastically reducing the amount of active aluminium.

CaCO3 scavenge most of the H2SO4 as inert CaSO4 what catches also the water as CaSO4.xH2O (hydrated plaster of Paris), it only set inert CO2 gas free!

[Edited on 29-3-2015 by PHILOU Zrealone]

Hennig Brand - 29-3-2015 at 10:48

Thanks for the great description. I did notice that the KClO3/S/Al mixtures would get a bit damp and unreactive often even after just a few weeks of storage. Is there any special technique for adding the CaCO3, other than just finally powdered and well mixed in?

PHILOU Zrealone - 29-3-2015 at 12:09

I grind the CaCO3 as ultafine powder into an electric coffee grinder with the KClO3 or better with the Sulfur/C black of fume.
Maybe that for Al protection you may boost up the amount of CaCO3 to 5%.

markx - 3-4-2015 at 13:13

I did play around with chlorate based flash in the past....makes one hell of a salute header on rockets

Interestingly enough I never had any storage issues with the KClO3/Al/S mix. Some of the small rockets survived over a year in an unheated shed and still gave a healthy bang. I guess the key may lay in the Al powder that I used...it was "PAP-1" from the soviet era and it definately was coated with some kind of unearthly protective matter (paraffin, linseed oil like substance or some kind of silicon oil). It is just incredible how hydrophobic and stable that aluminum powder is. When I bought the drum from some "local yokels" over 10 years ago I noticed that water had seeped into the powder and there were big pockets of it through all of the powder mass and it probably had been stored like that for god knows how long. Yet there was not the slightest sign of any degradation. I did dry about half of the mass with great effort and then gave up on the rest. It is still stored separately outside in the original drum with the original water inside and still no signs of any degradation. The only thing that is able to destroy the PAP-1 powder is alkaline media (lime, lye, portland cement). Local autoclaved aerated concrete factories still use the PAP-1 grade to make Aeroc blocks even today.
I also made barium nitrate based green stars with it and the green stuff has now survived well over 5 years of storage without any degradation in performance.
Another interesting fact that I noticed was that the PAP-1 based chlorate flash (with or without sulfur) was quite inert towards mechanical manipulations. It was impossible to ignite by striking or friction...and boy did I beat the samples hard, alas, to no avail. I did use KClO3/C/(S) mixes in small percussion igniters and it worked like a charm, but add the PAP-1 aluminium and it became inert. Not to say that that this would be a cause to lower ones safety standards regarding chlorate based mixtures, but with this grade(or particular drumful) of aluminium powder the beneficial effect was quite undeniable.

[Edited on 3-4-2015 by markx]

Hennig Brand - 4-4-2015 at 05:04

Yeah, it is a lot of fun, I used to make rocket headers with chlorate flash too. Was your KClO3 homemade? Your observation about the aluminum powder is very interesting and I am going to look into it. I don't know much about it, but it shouldn't be that difficult to find a suitable coating material and to coat the aluminum powder that I have. The coating should probably be applied before or during milling not after however. I have never made stars, but I thought aluminum powder was not normally used when trying to make colors, other than white, because the intense white from the aluminum tends to drown out the other less intense colors.

My first thought is that my homemade KClO3 likely has a significant amount of chloride in it that is causing decomposition or degradation of the reactive aluminum, but I also seem to remember obtaining a small bottle of reagent grade KClO3 from a lab and having similar (maybe not quite as bad) storage stability issues when it was used. It has been a while, but that is what I remember.

Having a look at a few chemical compatibility charts online, that use an A,B,C,D rating system, potassium chlorate and aluminum were always given a B which represents minor effects on contact in normal storage such as discolouration. However, this minor effect seen on an aluminum storage tank could be a big problem when it happens with extremely high surface area aluminum powder which requires that its surface be as reactive and oxide free as possible. I also noticed that small firecrackers would be the first to lose performance and eventually not work at all, while a 3g salute would still work reasonably well for many times longer (not as sharp a report as when fresh, but still pretty good). Strong confinement seemed to counteract a lot of the reduced reactivity as well. It would seem that loss of reactivity of the aluminum is likely the biggest contributing factor to degradation of these compositions.

[Edited on 4-4-2015 by Hennig Brand]

markx - 5-4-2015 at 23:33

If I remember correctly, linseed oil was used to coat magnalium powders....so perhaps this could be a good starting point, although I trust that there might be better alternatives out there nowadays.
Yes, the KClO3 was homemade, but carefully recristallised. KClO3 electrosynthesis was a big personal success for me back these days....it was extremely difficult to acquire anode materials and knowledge was limited. I used all kinds of graphite like abominations derived from old batteries etc. In fact I went as far in my desperation as to find a brand of charcoal (for grilling) that was conductive and could be used as a primitive anode material for chlorate cells. Not to mention that this stuff really gave new meaning to high erosion rates