TIL (today i learned) that Teflon isn't always inert.

[unclejed613]

while reading through https://archive.org/download/Chemis...ics-_Basic_Principles_and_Theory_Conkling.pdf because tomorrow is the 4th of July, and it's become a family tradition that i make some of the fireworks, i came across a table of "photoflash" mixtures in this chart:

i thought i was seeing things, but the third compound uses Teflon as the oxidizer (in this case it's fluorine (F) that is the oxidizing element, and fluorine is the most reactive of the halogens). i've always considered Teflon to be stable and mostly inert, although it does have a habit of poisoning soldering iron tips. it's the same release of fluorine at high temperatures that makes it an oxidizer in pyrotechnic compounds. one potential hazard when using teflon in a mixture is that due to it's electrical insulating properties, Teflon can take on static charges very easily, and when mixing pyrotechnic compounds that's the LAST thing you want.

 

[gophert]

The fluorine in "Teflon", (actually, poly(perfluoroethylene) ) is not the oxidizer. Fluorine atoms start out in the reduced state (aka, fluoride) so they cannot grab electrons from other atoms. Fluorine IS the most reactive halogen but generally is already reduced to fluoride ion to make it the most stable

This reaction is driven by (1) the instability of hot magnesium in the presence of ANY oxidizer, and (2) the great stability (heat of formation) of magnesium fluoride, and (3) the great crystallization energy of magnesium fluoride and (4) the ability of carbon of Teflon to accept electrons.

Ultimately, the carbon is the oxidizing agent and the white flame generated by the reaction is so bright that it masks the soot (lamp black) co-product and even the white MgF2 produced by this reaction.

 

[Ylli]

Teflon can take on static charges very easily, and when mixing pyrotechnic compounds that's the LAST thing you want.

That's for sure! You play with flash mixtures and you still have all your fingers and eyes?

Flash mixtures are like off-line switching power supply - It is much easier and SAFER to buy ready made than to try and make yourself.

 

[gophert]

That's for sure! You play with flash mixtures and you still have all your fingers and eyes?

Flash mixtures are like off-line switching power supply - It is much easier and SAFER to buy ready made than to try and make yourself.

But then you don't have visible conversation starters at dinner parties or good stories to tell.

Would you rather have a boring conversation like...

FRIEND: hey, what did you do on the Fourth?
YOU: oh, not much. I lit some Walmart fireworks with the kids. They got bored and played video games while I finished off all the sparklers by myself so they didn't sit in the garage until next year.

Or, a highly interesting and detailed conversation like this...

FRIEND: hey, what's with the eye patch and bandages?
YOU: (let your imagination run a bit)

 

[unclejed613]

That's for sure! You play with flash mixtures and you still have all your fingers and eyes?

Flash mixtures are like off-line switching power supply - It is much easier and SAFER to buy ready made than to try and make yourself.

first of all i have experience with flash powder in live music shows, and even designed a very reliable capacitive discharge controller to set off the igniter wires for one show.

i mix gram and sub-gram quantities, and don't use any plastic instruments.. i also don't store them in mixed form, and the only time the mixture is enclosed is when they are in the paper tube. i also don't mix tools, the tool i use to place fuel on the weighing pan is not the same tool i use for oxidizer, etc... i don't have fuel and oxidizer containers open simultaneously. after a first experiment using a paper tube i scaled back the amount of powder a lot. i've only used plastic 35mm film cans before and they had so much "give" to them the reaction was mostly a bright flash, and not much thump. the paper tubes are something i was trying for the first time, and were definitely louder than i expected. i've cut back the size from the 10 grams i used in the plastic cans to less than a gram in the paper tubes (which i had to cut in half). i might experiment with "slowing" down the mixture to compensate for the smaller confinement volume of the paper tubes.


one thing i remember in high school chemistry is one of our teachers told us how he had used a mortar and pestle to grind some sulfur. he then a few weeks later was grinding some kind of chlorate, with the same mortar. he said he had heard popping noises when he was grinding, and then had a really loud pop and the mortar cracked in half. then he remenbered using the same mortar for sulfur. so he was making a point to be careful with instruments and tools not getting them mixed up into dangerous combinations.

 

[Ylli]

i mix gram and sub-gram quantities, and don't use any plastic instruments........

Sounds like you do it right. Back when I was in high school and stupid, I make home made firecrackers out of KClO4 and Mg. Put in hand wound paper tubes, they were **loud**. Knowing what I do now, I think I'm lucky to still have all my fingers.

Back in the chem lab,we also made small quantities of NI3. That stuff would get everywhere. Snap/crackle/pop/purple smoke........

 

[Nigel Goodwin]

I'm not sure if I've mentioned this before or not? - but back in the 70's I used to help run a small rock club - and at one point we did a bit of a refurb, and reopened a couple of weeks later.

So for the opening night the main DJ and I (I was second DJ) decided to make a spectacular opening stunt - so I made a tape up (by splicing 1/4 inch tape together) of the theme from 2001 AD, where it builds up to a crescendo, then I spliced the explosion off Dark Side of the Moon in, recorded with the VU needles bouncing off the end stops - so nice and loud.

Bearing in mind we were poor, and had little access to anything - so we decided to 'make' some flash powder

So we obtained some magnesium powder (I'm not sure where from?), broke some fireworks open, and mixed the gunpowder in to the magnesium - what could possible go wrong?.

To fire it we ran a piece of fuse wire through the mixture, connected it to a mains lead and plug - so all we had to do was plug it in at the right moment - bear in mind, we didn't test ANY of this

So on the night we placed a metal tray on top of one of the speakers, placed the pile of mixture on top running the fuse wire through it.

So we played the tape, we were the only two who knew what was going to happen, so I went to the far side of the room, turned my back on, closed my eyes, and put my hands over my eyes as well.

The crescendo reached it's peak, the explosion from Pink Floyd rang out, and EVERYTHING went bright white

It seemed like a miniature Hiroshima, I expected to find shadows printed on the walls - but luckily no one was hurt - the speaker was a bit blistered through the metal tray though, and we disposed of the tray before the barman could see it.

Perhaps we should have tested it first?, and adjusted the quantities? - but no money, we couldn't afford to do it twice!.

 

[Pommie]

Perhaps we should have tested it first?, and adjusted the quantities? - but no money, we couldn't afford to do it twice!.

Sounds like you had enough to do it four times.

Mike.

 

[Nigel Goodwin]

Sounds like you had enough to do it four times.

Mike.

Probably - but we didn't want to take the risk

 

[shortbus=]

Back in the chem lab,we also made small quantities of NI3. That stuff would get everywhere. Snap/crackle/pop/purple smoke........

Similar to me. Was making some and waiting for the percipate to form (never doing it before thought it would be much more that it was) And the cat knoked the beacer over. Every time the wind would blow in the window you could see and hear little pops.

 

[unclejed613]

some flash pots i used once were made using quick cement poured into styrofoam coffee cups, and the pan in the top formed by pushing another coffee cup down into the cement. two nails were then punched through the second coffee cup and became the tie points for the nichrome wire as well as the wires from the controller. to fire, the nichrome wire was tied across the nails about 1/8" above the bottom of the pan, and flash powder was poured in until it covered the nichrome. the controller was a 40V power brick from an old printer, a 10k resistor and a very large electrolytic cap. charge on the cap was indicated by an LED and some zeners, and the firing switch was an old relay with a plastic button on top of the actuator. the flash pots were wired in parallel (there were two of them) so that as the nichrome wire on one burned open circuit, it would set off the other one too... the two flash pots went off almost simultaneously with one on each side of the drum kit. when testing mixes for the show, we went off to an unused office in another part of the building... the mix we ended up using didn't have a loud thump, but had a really bright flash (i think it was probably 35% chromate and 65% Mg). one of the mixes (50/50) blew a bunch of ceiling tiles up into the suspended ceiling with a very loud thump. the chemical kit came with a bottle of iron filings to add sparkle to the mix, so we used some of that in the show too....
there were also 4 stage crew with fire extinguishers ready in case of an accident, but everything went off without a hitch that night. just a few weeks earlier a band back east (CN or RI) had the club they were playing in burn down because they got careless with flash pots.

 

[unclejed613]

Ultimately, the carbon is the oxidizing agent and the white flame generated by the reaction is so bright that it masks the soot (lamp black) co-product and even the white MgF2 produced by this reaction.

you kind of contradicted yourself there... the reaction is 2CF2+2Mg=2MgF2+C::C it's a replacement reaction ad the fluorine is the oxidizer. the empty valence slot on the fluorine has a higher affinity for the Mg with 2 valence electrons than it does for the C with 4 valence electrons (the formula says CF2 because the other two bonds form the polymerization chain, but regardless, the affinity for Mg outweighs the affinity for the carbon and polymer bonding)...

secondary to interest in electronics as a kid, was chemistry... my grandfather was a chemist who dabbled in electronics, i'm an EE who dabbles in chemistry.

 

[shortbus=]

i'm an EE who dabbles in chemistry.

And Gopher is a chemist that dabbles in electronics.