Silicon for hot primes

[pyrogenius007]

I want to make a hot prime for my crackling stars. I have till now primed them with un milled BP mixed with coarse mg/al. They performed quite well on the ground but when I put them in a shell many of them were blown blind. I want to prime them with a hot prime which contains silicon. When I looked up on the net I came across some sites which mention elemental silicon while one site mentioned "fused" silicon, which type of silicon is best suited for a hot prime ? Even in this forum many people simply referred to it as silicon. Can anyone please enlighten me as to which type of silicon is used ? Since I do not have a dedicated pyro supplier in my city I have to buy this stuff from chemical suppliers, I do not want to end up buying something which has no use for my project.

Regards.

 

[Uarbor]

Go to fireworks cookbook.com. or pyro chem source or hobby chemical Supply. My favorite is fireworks cookbook. They all have relatively High shipping but if you order a bunch of other stuff you'll be needing all from the same supplier it ain't so bad. It is definitely silicon. Not silicone not silica. I think it's the same stuff microchips are made from. Although it is important to note that black powder plus silicon is a good Prime it's not technically a hot Prime. Edited July 9, 2022 by Uarbor

[Arthur]

A quick caveat;

Silicon is a metal and exists in all shapes that metals can be. (Dust, granules, lumps and sheets) It's flammable.

Silica is an oxide and is often called sand, or quartz It's sometimes melted to make crucibles (called fused silica) it doesn't burn.

Silicone is a polymeric oxide linked material that burns a little

 

You are looking for Silicon and probably 20 to 40 mesh. The good property of silicon that makes primes HOT is that it burns to silica and at that temperature silica (the oxidation product) is a sticky liquid so the heat of fusion is passed to the star as well as just radiated energy

 

As well as silicon primes there are two layer primes that may help you.

[Arthur]

One technique that may help is to prime the stars first with a mixed ingredients bp prime then over prime with BP. The milled and corned BP takes fire well, the "BP ingredients mix" burns more slowly and passes more fire to the star.

 

Also remember that hard breaks can be the cause of blind stars. The stars leave the flame so quickly that they do not light, perhaps to tame the burst would solve your problem.

[Richtee]

 

Also remember that hard breaks can be the cause of blind stars. The stars leave the flame so quickly that they do not light, perhaps to tame the burst would solve your problem.

Or...yer busting it soo hard ya shatter the stars. It always amazes me with the big crys shells...how they get such good even ignition and bust ‘em like it had a nuclear core gone south in it.

[Arthur]

IF your stars are smooth primed, consider rolling the primed star in 2/3/4F powder to give the surface some roughness to help them catch the first fire.

[cmjlab]

Just to echo the above information already posted in response, I use the Silicon (yes it is elemental metal powder, but it's just not labelled that way) and it looks like a dark grey metallic powder, comes in -325 mesh.

I've bought it from Tim at pyrochemsource.com (but fireworks cookbook.com is also a reputable source). I've found chucks of it fro time to time, but it was easily crushed between the fingers into a fine powder/dust, so maybe you could find it elsewhere and crush it up yourself (**careful of he dust, it's toxic**)

As for use, I agree with everyone else, it makes an excellent "hot" prime additive either in one like Lloyd's Pinball Prime (just add +5% - +10% to the formula), or added to a "scratch" mix BP / 75-15-10 +Binder (sieved, not milled) in same +5% - +10% proportions). Between those two primes, I've not had any issues lighting stars with a hot B.P. and SFB boosted break. Good Luck!

[cmjlab]

Question- for Crackle, what comp are you using and what binder?

 

I ask because of my own initial frustrations similar to yours. I could make outstanding Dragon Eggs with both Lloyd's formula and the 37.5/37.5/25 formula that worked individually with a piece of fuse, a bunch balled up in a piece of paper with B.P. and a fuse - but NOT very well in a burst.

My issues worked out to be two issues:

1. needing a shot shell double base smokeless powder, or similar fast burning NC, not the double base ball pistol powder that when burned in a small pile burned VERY slow.

2. A thin layer of Hot Prime with Silicon, but a thick layer of sieved B.P. prime with Silicon that would stay ignited during initial high velocity of burst, then ignite Hot Prime as they slow - initiating DE effect (crackle effect).

[pyrogenius007]

A big thanks to all who replied to my query, now I know what to purchase. I may have to do a bit of trial and error with the prime composition and settle for one that gives the best result. As for burst charge I am using the same amount of BP coated rice hulls (I am making 3" shells) which I use for color stars. I have had no problems with them, but then crackling stars may require a bit of tweaking, I will have to do a bit of trial and error with them. Anyway, with a hot prime I will have to see how they perform with my usual quantity of burst charge and make necessary changes if required. Thanks

[pyrogenius007]

Question- for Crackle, what comp are you using and what binder?

 

I ask because of my own initial frustrations similar to yours. I could make outstanding Dragon Eggs with both Lloyd's formula and the 37.5/37.5/25 formula that worked individually with a piece of fuse, a bunch balled up in a piece of paper with B.P. and a fuse - but NOT very well in a burst.

My issues worked out to be two issues:

1. needing a shot shell double base smokeless powder, or similar fast burning NC, not the double base ball pistol powder that when burned in a small pile burned VERY slow.

2. A thin layer of Hot Prime with Silicon, but a thick layer of sieved B.P. prime with Silicon that would stay ignited during initial high velocity of burst, then ignite Hot Prime as they slow - initiating DE effect (crackle effect).

NC lacquer was a big problem for me too, it is very difficult to get nitrocellulose powder where I live. I solved the problem by making my own gun cotton, dissolved it in acetone and made my own NC lacquer. There are many sites on the internet which give detailed instructions on how it is prepared. However, be very very careful while making it, use proper protective gear while making it especially if you are using sulfuric and nitric acids. The trick in making stable and good quality nitrocellulose is the washing process, make sure that no traces of acid remain in the cotton, you have to wash it in a large quantity of water for at least 7 to 8 times to get rid of any acid, test the last batch with litmus paper, the result should be neutral or slightly alkaline.

[cmjlab]

I've been doing the same, making guncotton via 2:1 Sulfuric to Nitric Acid. The first couple times I used hardware store Sulfuric Acid and KN03, though it worked great, I felt it was not as highly nitrated as it could be. So then I used Sulfuric Acid from Duda Diesel (concentrated) and distilled my own red fuming nitric acid - the gun cotton was night and day difference in potency (I have no way to determine nitrogen content, other than it would only dissolve in Acetone, not Ethyl Alcohol). I also used a repeated boil/rinse/repeat and sodium carbonate bath, followed by a 2% Urea soak to slow degradation. It seems to work unless left in high summer heat or direct sunlight in a sealed container. *I still wouldn't use it on any chlorate containing comps just to be safe*

[cmjlab]

One final point to add to that rambling on in my prior post - there are quite a few knowledgeable folks who believe the N.G. in double base smokeless powder helps with the flammability and performance of the crackle/Dragon Eggs. All I can say is that the Crackle/Dragon Eggs worked better for me with the double base vs. my own N.C., not really sure why. Best of luck!

-Charles

[pyrogenius007]

Could be. Since I have no way of getting double based smokeless powder I will have to make do with my homemade stuff. I have got fairly satisfactory results with it. Would like to see if any member with more knowledge could throw more light on this subject. They could also give me some advise on how to make better dragon eggs/crackle using gun cotton dissolved in acetone as I am doing at present

Thanks.

[Arthur]

SOME guitar lacquers are NC based and ideal, trouble is that you will have to find it in your home area and test it for NC

 

--bay.co.uk/itm/371589760466 is just one example in one country

Edited July 10, 2022 by Arthur

[Smokelvr]

Diatomaceous Earth works too, it's an inert additive and pretty much a very fine silica powder, so it doesn't burn and just makes dross

Also consider adding an oxide like red or black iron, or even black copper oxide which works as both a speed catalyst and dross maker

which helps to transfer heat to the star, that seems to be the basis of most hot primes.

[a_bab]

When silicon (the element) burns it does it very hot so that energy goes into the molten silica.

Using straight silica in a star priming composition would likely not work. But I may be wrong.

 

Meal powder mixed with 10% silicon would ignite any kind of star.

[Pyrophury]

Try this prime:

 

Potassium Perc. - 70

Redgum/Phenolic resin - 10

Silicon (-400#) - 10

Silicon Dioxide (-400#) - 5

Dextrin - 5

 

Unlike with silicon powder alone, which just forms molten droplets that don't stick to the star, with the addition of the silicon dioxide it forms a slaggy crust that envelopes the star, and stays in contact even with hard FP breaks. Like any hot prime it will still need step priming with BP.

[Mumbles]

cmjlab mentioned something that I think is worth highlighting. The thickness of the prime matters. If your stars are lighting fine on the ground, but not the air, this is usually a pretty good indicator you might need more thickness. Stars have what some refer to as a critical wind velocity. In short, if the stars are moving too fast, they can blow themselves out or at least prevent the flame from propagating. If you video your shells, you can sometimes see dim orange stars coming out of the burst, and then nothing or only some of the stars light. Charcoal stars are probably the least effected by this. It's part of the reason charcoal streamer or glitter transitioning into colored cores is fairly common. It's not just pretty, but also there for function. Crackle stars by virtue of their delay before initiating are probably some of the most sensitive to critical wind velocity. You may notice you almost always see crackle used in matrix comets, with a slaggy delay composition over the top, at the center of a shell burst, or as the final core effect in a color changing star.

 

The thicker prime doesn't actually light them any better, just burns longer and gives them a chance to slow down some before lighting the intended star effect.

[Soloserly]

I agree that thickness of the prime is often critical, especially for comps that burn at lower temps - like most blue stars.  As mentioned, they can be blown out by the pressure of the burst charge and/or wind velocity if the prime is not thick enough to give them some time to slow down.  

Since we're on the topic of Silicon, one of the most consistent primes I've used is the Veline prime formula with the potassium dichromate omitted and replaced by elemental Silicon powder.  

The description of the silicon powder sold on the Fireworks Cookbook site actually says it is a "dark gray powder called 'fuzed' silicon" but that's inaccurate.  The dark gray powder is elemental silicon and "fuzed" (fused) silicon is known as silicA; it is the pure silicon dioxide found in glass.  The last time I bought Silicon was from Pyro Chem Source for around $8 a lb. and it works great.  Skylighter also has it, although at more than twice the price the last time I checked.

[Arthur]

It's possible that a star needs multi layer primes. Some layers as a buffer between incompatible comps, some layers to catch fire easily from the burst, some layers to pass really hot fire to the star. Sometimes a star will have an outer prime of meal slurry with 2FA dusted over to make a ragged surface that takes fire well.