Sciencemadness Discussion Board

Unusual primary

Yamato71 - 4-12-2012 at 16:49

Several years ago, I was attempting to create a reliable electric thermite igniter for use with CadWeld copper thermite based welding charges. I purchased a pound of CuO from a local ceramics supply and several pounds of paint grade aluminum powder. After washing the aluminum in acetone and mixing the two in a 4.42:1 ratio (CuO to Al), i added enough nitrocellulose lacquer to create a mixture having the consistency of pancake batter. I then dipped in several electric matches previously coated with SbS3 + KClO3 first fire mix. I used a paper cup as the dipping vessel and then set the squibs aside for a couple of days to dry. When dry, I dipped each into NC lacquer to seal and waterproof them. A layer of thermite mix about an inch thick had dried in the cup, so I decided to try to ignite that with one of the squibs as a test.

Initially, I decided to do the test in my back yard. Luckily, I thought better of it and drove out to a friends ranch instead. I paid out about 20 feet of wire and used a small WWII surplus twist blaster to fire one of the squibs in the cup of dry thermite-NC lacquer mix. I was not expecting what happened when I twisted the handle. Instead of going up in a shower of sparks and flame, the mass detonated with the characteristic sharp report of a high order detonation. The blast left a foot wide crater in the caliche soil and propelled a piece of gravel into my thigh with enough force to draw blood.

I was stunned at the force of the blast. My ringing ears confirmed that it was definitely a DDT. I tested each of the remaining squibs without the additional dried material in the cup and each time was rewarded with the sharp crack of the dried NC lacquer detonating. One squib placed into a beer can turned it into aluminum confetti.

I have never heard of low nitrogen content nitrocellulose being detonated by heat alone, but there it was. It was either the thermal pulse alone, or the aluminum powder sensitizing the NC to the point that the heat detonated it. This material, which I call "CuTherm 442" is the basis of the electric squibs that I used to detonate half-pound Tannerite charges for my WWII reenactment gigs. This stuff is easily detonated by flame. Visco fuse will reliably initiate DDT and simply dipping the fuse into the wet mix until a blob of dried material remains on one end is an easy way to make detonators. Substituting pyro aluminum for the paint grade aluminum makes initiation easier and more powerful.

Has anyone here run into this?

Poppy - 4-12-2012 at 17:02

What about shittier grade milled aluminium? Do you think it would also work for a small detonator device?

Yamato71 - 4-12-2012 at 17:48

Don't know, never tried it. I doubt it though. CadWeld uses granular flaked aluminum and CuO and the burn rate is very slow compared to copper thermite made with pyro aluminum. The aluminum I used was paint grade, wetted with mineral spirits. Prior to mixing, I stripped the mineral spirits with acetone and allowed it to dry.

hyfalcon - 4-12-2012 at 17:57

The CuO/Al mix is sensitive enough to be set off with just a .22 rimfire round, as long as there is a metal backing plate.

franklyn - 5-12-2012 at 02:20

Copper Oxide / Aluminum , has ten years of practical investigation in the
Exotic thermites & analogs thread , beginning with _
The video is here _ Attachment: copperdet.mpg (1.7MB)
This file has been downloaded 781 times

The fineness of the powder determines the rate of reaction.


Yamato71 - 5-12-2012 at 06:01

Yes, I've read every word of those threads and then some. The purpose of my post was to point out that apparently, when this thermite mixture is converted from a powder into a hard solid with NC lacquer as a binder, it changes from a sensitive energetic deflagrant into a powerful primary explosive mixture. I haven't seen this fact mentioned in the literature before and wanted to share it with the group.

[Edited on 5-12-2012 by Yamato71]

Swede - 5-12-2012 at 08:56

I find this to be pretty interesting, and thanks for sharing.

The question I have is how sensitive is the hardened or dried material, the stuff you described in the OP in the cup? Is handling dangerous?

The notion of a cast detonator is intriguing. Wouldn't the NC form a "skin" that would keep the deep interior somewhat laden with solvent?

Yamato71 - 5-12-2012 at 10:04

I really haven't had enough experience with this mixture to be able to classify it with respect to its sensitivity. I would have to say that, as a primary, it probably falls somewhere in the middle of the pack. It is flame sensitive, but not so much as the fulminates or azides, which are powders. I've never attempted to pulverize this material once it has set hard. I suspect that doing so would be inviting disaster. A smooth solid chunk of CuTherm 442 is difficult to ignite with anything smaller than a torch flame simply because of its thermal mass. A thin ribbon of it made by pouring the liquid onto a flat surface and allowing it to dry will easily cook off in a match flame, but it usually only deflagrates. A piece of visco or an electric match dipped into a hot burning first-fire mixture will reliably initiate the mixture, although thicknesses greater than 1/4" are usually required to assure DDT.

I have demonstrated that the mixture is also cap sensitive. Any amount of confined azide or fulminate will reliably detonate the cast mixture. BP or flash will also do the trick. I never tried using peroxides because I've never trusted them. For obvious reasons, I have not tried hammer or drop tests either. Once I got the mixture to reliably detonate with an electric match, I had accomplished what I had set out to do and did very little followup experimentation with it. Shortly thereafter I lost my hands and all experimentation on CuTherm 442 came to a halt. Ironically, that happened when I was making ETN that I had planned to add to the NC lacquer in an attempt to get more reiable boosting of my Tannerite charges from smaller squibs.

Yes, because this mixture contains a high proportion of VOC's (mostly acetone), it will quickly skin over and slow the drying process, but not by much. Drying outdoors in the sun seems to work best and minimizes the risk of solvent vapor flash fires. If I needed to make thick pieces, I did so by repeated dipping and drying, usually on a primed electric match. A quarter inch (6.35mm) or greater thickness would reliably undergo DDT when the match was fired.

If allowed to completely dry in a cup, the resultant copper-colored puck will have a concave top, which brings up the possibility of easily making shaped charges out of this material without the need for risky sawing or grinding. I also suspect that cast pucks of CuTherm 442 would make wonderful exploding targets for rimfire ammo.

Have fun experimenting with this material but please do so carefully.

[Edited on 5-12-2012 by Yamato71]

[Edited on 5-12-2012 by Yamato71]

Rosco Bodine - 5-12-2012 at 17:41

Has anybody tested the magnalium stoichiometric analogue using fine mesh (50/50 Mg/Al alloy) to see if such mixture using magnalium as the fuel and reductant may be even more energetic ? That substitution of magnalium could make an interesting and even more energetic mixture for thermites in the same way as it does for flashpowders.

Yamato71 - 6-12-2012 at 15:17

I have not compounded this material with anything more reactive than German dark pyro aluminum. The resulting mix is very flame sensitive. One part Al and 4.42 parts CuO were wetted with acetone and stirred together as a slurry to minimize the possibility of accidental ignition. 10-25% NC lacquer was stirred into the wet slurry prior to dipping or casting operations. Once dry, the mixture was ready for use. Dry acetone can be used to thin the material as needed. Water or halogenated solvents MUST NOT be used as they will exothermically react with the Al/Mg, igniting the mixture. As if that wasn't bad enough, chlorinated solvents such as CCl4, CH2Cl2, CHCl3, etc will evolve phosgene gas prior to ignition.

Rosco Bodine - 7-12-2012 at 02:38

This composition could also be interesting to pyrotechnists as a cheaper crackling microstar formulation, but it would seem like the granules would need to be coated and inhibited with some sort of a slow fire primer / inhibitor coating that would act as a split second time fuse to delay ignition of the core particle. Loading the star particles matrix mix with coarser flake or chips of titanium or zirconium or even possibly magnesium or ferosilicon could make for a "super sparkler" kind of energetic incendiary star effect. These could also make for an interesting "star core" where the star coating itself acts as the fuse and the star finshes with a bang. That would be useful in a starburst where each star in the first big starburst ends in its own mini starburst.

AndersHoveland - 7-12-2012 at 03:46

If what I suspect is true, you might want to see what happens if you just use CuO and the nitrocellulose together, without the Al powder.

[Edited on 7-12-2012 by AndersHoveland]

Rosco Bodine - 3-6-2013 at 21:27

Here is a link to a post regarding related art

Antiswat - 4-6-2013 at 10:24

thats pretty interesting..
so easily ignited material then over to CuO Al then to NC Lacquer (i suppose this wasnt ping pong balls but rather pyrotechnics grade NC lacquer)
ive seen nitrocellulose lacquer sold for guitars also if it would be of interest for any who doesnt have NC laying around
i guess this would also work with CuO MgAl which by my experience if heated well enough in 1:1 volume ratio go loudly bang (very sharp bang)

improving this could be done with rubbing some ETN powder on the surface of the still not completely dried NC lacquer

i have actually tested CuO + GD Al 4:42 1 some time ago by weight and found it to not even ignite, so i guess ill go with MgAl instead
definately something that needs to be tried

Antiswat - 5-6-2013 at 09:22

i have done some tests with this described mixture..

i tried both 1:1 CuO MgAl by volume and 4.42 CuO 1 Al (1-3┬Ám Al)
both was mixed with a premade solution of nitrocellulose lacquer from pure acetone and NC prills (fireworks grade)
it was let dry out on a steel plate and what was seen was nothing more but a green star composition.. :S

there must of happened something you didnt think about when you mixed those things up man.. im very sure of that, because i saw no potential of detonation or even going towards it

i tried with different ratios of NC lacquer aswell

could it be that KClO3 or SbS3 could have had influence on this perhaps?

Rosco Bodine - 5-6-2013 at 12:23

Not certain but I would think that the OP was providing ratios by weight. See how the stoichiometry reconciles with that.

Also uncertain is what is the nature of the visco, the nitrocellulose lacquer which was used, was this a low nitration NC composition, or was it a commercial IMR single base powder having been thinned with acetone, or was it perhaps a double base powder like bullseye which had been liquified with acetone. The higher nitrated grades of NC and especially the double base powders liquified with NC would be much more liable to a "cookoff" detonation from a thermite mix. So I would think this parameter about the visco would definitely be a factor. The alumninum which the OP described using is also a paint grade flake which is a bright Al made as a paste with naptha or mineral oil, and would tend to be more chemically reactive than a supplied dry powdered Al which has a protective oxide coating. These are some factors about the composition described by the OP which likely have bearing upon the properties of the composition which he described.

Hopefully the OP can address some of these details more fully, because such details probably do have peculiar effect which makes his described composition very specific in its requirements. I haven't experimented with this type thermite, bindered or unbindered.

Nitrocholine perchlorate reportedly is cookoff sensitive, and could make a good transfer charge, loaded over a base charge of trimethylamine perchlorate. Trimethylamine n-oxide perchlorate is another candidate transfer charge material. Betaine perchlorate is another possible candidate as a component of such a firing train.

[Edited on 5-6-2013 by Rosco Bodine]

Bert - 8-2-2014 at 11:47

A question for Yamato san?

Could you state the source of the NC lacquer used for the experiment? Was this a commercialy supplied product or a home made one- If home made, the source materials?

In a later post, you state that dark pyro Aluminum was tried? Did this perform in the same way as what I assume to be a bright flake Aluminum supplied in a (mostly removed by acetone washing) hydrocarbon base? If not, could you also give a name brand or product # for the paint grade Aluminum-

Enquiring minds want to know!

Bert - 10-2-2014 at 11:20

As a first attempt:

13.2g Black Copper oxide (ceramic glaze material, passes 100 mesh)

3g German blackhead Aluminum

7g of a 25% by weight NC lacquer (home made from the fastest burning, highest NG content double base smokeless powder I have access to- it's approx. 30% NG + 75% acetone/25% ethanol)

10g acetone as processing aid

Slurry coated onto commercial electric matches by repeated diping and drying until a teardrop shaped "blob" approximately 1/2" in the smallest Dia. was formed.

I tested 3 devices about 2 hours after making these. Mixed results- One burned like a very bright fireworks star. One made a high pitched crack similar to a large pistol primer being fired, along with a quick bright flash. One made a slightly quieter crack, and left a few burning pieces afterwards. I did not test these against a witness plate, or with any containment. Test was outdoors over snow and in darkness so presence of any unreacted composition could not be confirmed.

I guessed that the acetone might not have fully evaporated from the core of the "blob", so I put the remaining devices in a warm place with a fan on them and tried again 12 hours later. 3 of the devices were also dipped in straight NC lacquer to provide a surface coating.

The next day, I fired 3 of these, taped against Aluminum soda cans and inside a large cardboard box to retain any pieces generated.

Behavior was uniform. A "snap" about like a toy roll cap gun, no dammage to the can, and the coating of thermite was merely broken into pieces and thrown around in the box- very little if any was consumed, no coating from vaporized Copper was visible on the target. The devices coated with lacquer had fewer pieces generated, 1/2 of the blob stayed adhered to the e-match lead. The collected fragments burned like a fireworks star when a torch flame was played over them.

I'll take the remaining mixture and allow it to dry in a paper cup with visco inserted...

From the results he reported, Yamato san was doing something different. I notice he's been absent for about 10 months now.

The ingredients of this mix are somewhat similar to a dragons egg granule- and I've seen single 3/16" Dia. grains of that comp blow a hole in an Aluminum beverage can in a fashion similar to a granule of dextrin bound lead azo clathrate.


On re-reading the OP:

The OP specifies an e-match with a chlorate/Antimony sulfide "first fire". Wonder if that's applied over a bare bridge wire in a home made e-match, or if it's applied over a finished e-match. My e-matches are commercial US made. No chlorates are used in these- They are quick acting but rather quiet, producing a nice shower of Titanium sparks designed to ignite black powder rather than a shock. Chlorate and Antimony trisulfide are pretty snappy, and it would probably be bound with yet more NC lacquer.

Also interesting from the OP is this bit:

If allowed to completely dry in a cup, the resultant copper-colored puck will have a concave top

Copper colored? DID HE USE RED COPPER I OXIDE and not specify?! No pure Copper is present to give the mix a Copper color if he's accurately described his mixture... But WHO would use the red oxide for a thermite? With 1/2 the Oxygen of the black Copper II oxide, that doesn't make sense to me.

[Edited on 10-2-2014 by Bert]