Nitrate / Mg / PVC stars

[Powderman]

Hello, lately I have been working on nitrate based color stars. I am using Na, Sr and Ba nitrates with Mg and PVC. PVC also acts as a binder activated by THF. At the moment the stars are kind of working, but there is definitely a lot to sort out.

So, at the moment I am nowhere close to building shells, but I would like to shoot solo stars from my star-guns with confidence (of not going blind) and perhaps try to make a roman candle. Actual problems are:

 

1. Priming. It has to be nitrate-based prime (no chlorate/perchlorate to use for priming available), and I am avoiding using sulfur. Sulfurless BP + silicon works with very small cut stars (3-5mm), but there are fails with spherical or pumped shapes (the prime burned off and the star did not light). Should I try BP + Si + MgAl as inner layer? It will be water/dextrin bound.

 

Actual composition is:

 

KNO3 3

charcoal 1

Si 0,45

dextrin 0,25

 

2. Speed of burning - mostly slowing down the green. Considering altering formula proportions or adding something like a bit of carbonates...

 

Actual compositions:

 

Red

Sr(NO3)2 55

Mg 28

PVC 17

 

Green

Ba(NO3)2 50

Mg 32

PVC 18

 

Amber

NaNo3 50

Mg 25

PVC 25

 

And this is how it looks. Stars are different in size and there are mixed or altered formulas, but two last are exactly as the formulas stated. Video is cut, each star is loaded separately. Camera has problems with in-between colors, red and green are well rendered.

https://youtube.com/shorts/XHbC20kxHxw

 

[cmjlab]

I thought the colors looked pretty good. Probably even better from more of a distance, as a mine, or in a shell.

 

Why are you avoiding Sulfur? Most primes include some Sulfur to reduce the ignition temperature as I understand it, and of all the fancy primes (of which most work well), sometimes that screen mix B.P. works best (with Sulfur).

 

It also looked like you had good consistency and ignition, unless the blind stars were cut from the video?

Edited January 31, 2023 by cmjlab

[Crazy Swede]

As stated above you do not have to avoid sulphur in the prime.

A good way of slowing down nitrate/magnesium stars is to make sure they are fuel rich and adding some dextrin as a secondary fuel. Dextrin will partly decompose into water vapour that will react with the excess magnesium in the flame.

If you are not using dichromate for corrosion protection of the magnesium, pre-treating the magnesium with linseed oil works well with nitrates and will slow down the combustion rate.

For a nicer looking yellow, combine strontium and barium nitrate at a suitable ratio. Or at least, do not combine chlorine donors and sodium since it will produce the ugly street lamp hue of dirty yellow.

If you can find or make the oxalates of Ba and Sr, they are good additives to slow down this type of formulas. The carbonates are less effective since they somewhat act as oxidizers with magnesium.

Edited January 31, 2023 by Crazy Swede

[Powderman]

Thank you very much for your suggestions, I will incorporate it in my next tests and post it here...

 

I am avoiding sulfur for two reasons. It smells, and my pyro work is done in my living space. I work with small amounts, mostly few grams at a time so no big mess, but the smell would be annoying. And there is some chlorate waiting to be incorporated in pursuit for blue stars, so I do not want to compromise my tools with sulfur. I think that most of the basic goals could be achieved withou sulfur, so I will try.

 

In the video no star went blind, I have used what proved to work (thicker priming, less charge, well dried stars). I would like to shoot the stars higher, but with more charge they go blind. I had no problems with pumped charcoal streamers, they went pretty high with a bang, of course the shape worked like a bullet in a gun, fully utilizing the gasses from charge. Now the stars are sub-caliber so it spits them weak.

 

At the moment Mg is only coated with paraffin - the reason is because it is easy and fast to do, and binding with PVC without water should also help. No real production at the moment, using tiny amounts to perform tests so shelf life is not of a concern now. But I have some linseed oil coated Mg so I will try it and see if it slows the burning a bit, that might be good to know for the future.

 

I am definitely going to try Sr-Ba mixtures for different hues and yellow. Combinations of Sr-Na seems to work but Ba-Na not so much.

 

I have dextrin and also strontium oxalate (for which I did not find any use so far), and barium oxalate seems easy to prepare, so I can try it.

[Powderman]

Today I took a video of the same plus some other stars, but this time with proper camera. Definitely better picture/colors. Really helpful with evaluating performance.

 

https://youtube.com/shorts/OBOp9cFkvn4

[cmjlab]

From my viewpoint, those colors/brightness look good. I'm not sure how you get to the right star shape though, without a Sulfur containing prime, if you can't get the stars to light when pressed or cut. Usually cut stars are the easiest to take ignition.

 

*An idea for keeping fire on the star longer while in the tube, so they have a better chance to ignite - perhaps a cardboard disc / paper wad packed down on top of the star? (Like a Chinese consumer cake). The disc appears to maximize lift power, keep a little rextra pressure / heat longer, and keep fire in the tube a bit longer.

 

I've not heard of anyone using THF solvent and PVC as the binder for stars anytime recently. Probably related to its reduced availability in the U.S. I wonder if that's plays a factor in burn speed.... Maybe one of the more experienced folks could chime in. Appears to work though.

 

Are those stars in the videos actually 3 - 5 mm (1/8" to 13/64")?

 

If so, for burn speed from myperspective:

- The Blue & Green stars seem to burn about right for 1/8".

- The Red & Orange / Yellow seem to burn slow for a 1/8" star (but for me, is common with SrNO3 formulas)

Edited February 1, 2023 by cmjlab

[SharkWhisperer]

Thank you very much for your suggestions, I will incorporate it in my next tests and post it here...

 

I am avoiding sulfur for two reasons. It smells, and my pyro work is done in my living space. I work with small amounts, mostly few grams at a time so no big mess, but the smell would be annoying. And there is some chlorate waiting to be incorporated in pursuit for blue stars, so I do not want to compromise my tools with sulfur. I think that most of the basic goals could be achieved withou sulfur, so I will try.

 

In the video no star went blind, I have used what proved to work (thicker priming, less charge, well dried stars). I would like to shoot the stars higher, but with more charge they go blind. I had no problems with pumped charcoal streamers, they went pretty high with a bang, of course the shape worked like a bullet in a gun, fully utilizing the gasses from charge. Now the stars are sub-caliber so it spits them weak.

 

At the moment Mg is only coated with paraffin - the reason is because it is easy and fast to do, and binding with PVC without water should also help. No real production at the moment, using tiny amounts to perform tests so shelf life is not of a concern now. But I have some linseed oil coated Mg so I will try it and see if it slows the burning a bit, that might be good to know for the future.

 

I am definitely going to try Sr-Ba mixtures for different hues and yellow. Combinations of Sr-Na seems to work but Ba-Na not so much.

 

I have dextrin and also strontium oxalate (for which I did not find any use so far), and barium oxalate seems easy to prepare, so I can try it.

Your colors look fine. Like others mentioned, you might want to sub sodium with something else for yellows (and for hygroscopicity concerns if storing or water-based binding). Check out some cryolite-based yellows perhaps.

 

Sulfur has such wide use for very good reason. You're the first fireworker I've ever heard to omit it because of the smell. Sulfur in your hand smells like pretty much nothing, and BP with sulfur burning smells like pyro heaven. It'll definitely improve your prime ignition and help sustain the burn. Sulfur on your tools rinses off--trace amounts will not turn chlorate comps into nitroglycerin. BP primes are not necessarily contra-indicated on chlorate comps--that little bit of mixing at the interface is not going to turn your stars into mini bombs that explode on launch. Chlorate-sulfur interactions are real and to be respected, but current concerns may be a bit overblown.

 

Also, check your dextrin quality. Is it possible that your prime is flaking off from the launch violence? You've got an organic-to-plastic binder interface, which might not meld together as closely as if the prime and comps used similar binders. This is usually not an issue, but it could become one if your dextrin isn't great to begin with.

 

You're certain that your prime is completely dry? That's by no means a hot prime to begin with, even with the silicon addition, and even a little remaining water might impact ignition reliability. This is often the reason why folks early on have issues with charcoal-based star comps--they look, feel, and sound dry but they are actually still somewhat damp. If you're testing them right after priming you might want to consider this possibility.

 

Is your prime screen-mixed? You could heat it up a little if you mill your KNO₃ with charcoal first and then screen in the silicon and dextrin. Adding a small amount of metal might help, too. But avoid changing more than one thing at a time or you'll never really learn what worked.

 

Your vids show decent star ignition--they're useful for color assessments but not so much ignition trouble-shooting.

 

Last, and this is kind of nit-picky, but if you provide your formulations for prime as percentages, like you did for your star comps, then the reader doesn't need to bust out a calculator to obtain your actual silicon and dextrin percentages...

 

You're on your way.

[Powderman]

I am really thankful for all your insight and tips.

 

*An idea for keeping fire on the star longer while in the tube, so they have a better chance to ignite - perhaps a cardboard disc / paper wad packed down on top of the star? (Like a Chinese consumer cake). The disc appears to maximize lift power, keep a little rextra pressure / heat longer, and keep fire in the tube a bit longer.

I've not heard of anyone using THF solvent and PVC as the binder for stars anytime recently. Probably related to its reduced availability in the U.S. I wonder if that's plays a factor in burn speed.... Maybe one of the more experienced folks could chime in. Appears to work though.

Are those stars in the videos actually 3 - 5 mm (1/8" to 13/64")?

 

Good idea with the wadding, in the beginning I have tried it without success, but I believe there were other problems back then which are sorted now. Should try again.

 

THF works really nice with PVC, it evaporates as fast as acetone and smells not much different. It is not very cheap but readily available in store here (used for gluing PVC foils for swimming pools I think...) When only a little is used the comp can be pressed, a bit more makes a dough-like stuff and even more creates honey-like fluid. It is not stringy. When drying it first becomes rubbery and at the end it feels like hard plastic. I like the idea of Mg and nitrate encapsulated in plastic. Might help with shelf life.

 

I have measured the stars and most of them are 4-6mm without priming. In the first video there were some smaller a bit and last two bigger. In the second video they were more size consistent.

 

 

Your colors look fine. Like others mentioned, you might want to sub sodium with something else for yellows (and for hygroscopicity concerns if storing or water-based binding). Check out some cryolite-based yellows perhaps.

 

Sulfur has such wide use for very good reason. You're the first fireworker I've ever heard to omit it because of the smell. Sulfur in your hand smells like pretty much nothing, and BP with sulfur burning smells like pyro heaven. It'll definitely improve your prime ignition and help sustain the burn. Sulfur on your tools rinses off--trace amounts will not turn chlorate comps into nitroglycerin. BP primes are not necessarily contra-indicated on chlorate comps--that little bit of mixing at the interface is not going to turn your stars into mini bombs that explode on launch. Chlorate-sulfur interactions are real and to be respected, but current concerns may be a bit overblown.

 

Also, check your dextrin quality. Is it possible that your prime is flaking off from the launch violence? You've got an organic-to-plastic binder interface, which might not meld together as closely as if the prime and comps used similar binders. This is usually not an issue, but it could become one if your dextrin isn't great to begin with.

 

You're certain that your prime is completely dry? That's by no means a hot prime to begin with, even with the silicon addition, and even a little remaining water might impact ignition reliability. This is often the reason why folks early on have issues with charcoal-based star comps--they look, feel, and sound dry but they are actually still somewhat damp. If you're testing them right after priming you might want to consider this possibility.

 

Is your prime screen-mixed? You could heat it up a little if you mill your KNO₃ with charcoal first and then screen in the silicon and dextrin. Adding a small amount of metal might help, too. But avoid changing more than one thing at a time or you'll never really learn what worked.

 

Your vids show decent star ignition--they're useful for color assessments but not so much ignition trouble-shooting.

 

Last, and this is kind of nit-picky, but if you provide your formulations for prime as percentages, like you did for your star comps, then the reader doesn't need to bust out a calculator to obtain your actual silicon and dextrin percentages...

 

You're on your way.

 

NaNO3 is the cheapest, and I have super dry environment inside during winter. I have observed moisture attacking only fertilizer grade ammonium and calcium nitrates. I will give it a try for now, no cryolite or oxalate at hand. First star in second video was tiny bit of KNO3/bright Al mixture, bound with phenolic resin and IPA. It works well also with NaNO3. I like the effect and will experiment more with it. The Al is coated and with phenolic/IPA it seems to be stable.

 

It is not that I absolutely do not like sulfur smells, but I definitely hate smells in my room except when I am working on something. And sulfur smell likes to persist longer than I would like. Burnt gunpowder has its magic, but anyone knows it and the neighbours might not like it. Sulfurless BP has nice smell too but it disappears after few metres :-) I should mention that this hobby is somewhere between gray zone and illegal here...

 

I have commercial dextrin and it works fine, but I too have suspicion how well it adheres to the star. Definitely will investigate into this. This problem may worsen with the size of the star.

 

I made a hot plate with 90°C surface and the stars rest there for many hours. Stars this small should be dry in reasonable time I think.

 

Prime is mixed with mortar and pestle in a bit damp state. No dust and better incorporation. Metals are added after grinding is finished.

 

I was primarily eager to see the colors :-) Now I have to work on the ignition... Here is slow-motion video of stars going blind:

 

https://youtube.com/shorts/L5RxW6Ii7QQ

 

There were some round 7-8mm blind stars before this and I managed to find them on the floor and it seems the prime burned off without igniting the stars... I have suspicion that in that case layer of prime was not thick enough. I re-primed them better and will test them again.

 

I have realized it too late, will definitely use proper % in formulas :-)

[SharkWhisperer]

I am really thankful for all your insight and tips.

 

 

Good idea with the wadding, in the beginning I have tried it without success, but I believe there were other problems back then which are sorted now. Should try again.

 

THF works really nice with PVC, it evaporates as fast as acetone and smells not much different. It is not very cheap but readily available in store here (used for gluing PVC foils for swimming pools I think...) When only a little is used the comp can be pressed, a bit more makes a dough-like stuff and even more creates honey-like fluid. It is not stringy. When drying it first becomes rubbery and at the end it feels like hard plastic. I like the idea of Mg and nitrate encapsulated in plastic. Might help with shelf life.

 

I have measured the stars and most of them are 4-6mm without priming. In the first video there were some smaller a bit and last two bigger. In the second video they were more size consistent.

 

 

 

NaNO3 is the cheapest, and I have super dry environment inside during winter. I have observed moisture attacking only fertilizer grade ammonium and calcium nitrates. I will give it a try for now, no cryolite or oxalate at hand. First star in second video was tiny bit of KNO3/bright Al mixture, bound with phenolic resin and IPA. It works well also with NaNO3. I like the effect and will experiment more with it. The Al is coated and with phenolic/IPA it seems to be stable.

 

It is not that I absolutely do not like sulfur smells, but I definitely hate smells in my room except when I am working on something. And sulfur smell likes to persist longer than I would like. Burnt gunpowder has its magic, but anyone knows it and the neighbours might not like it. Sulfurless BP has nice smell too but it disappears after few metres :-) I should mention that this hobby is somewhere between gray zone and illegal here...

 

I have commercial dextrin and it works fine, but I too have suspicion how well it adheres to the star. Definitely will investigate into this. This problem may worsen with the size of the star.

 

I made a hot plate with 90°C surface and the stars rest there for many hours. Stars this small should be dry in reasonable time I think.

 

Prime is mixed with mortar and pestle in a bit damp state. No dust and better incorporation. Metals are added after grinding is finished.

 

I was primarily eager to see the colors :-) Now I have to work on the ignition... Here is slow-motion video of stars going blind:

 

https://youtube.com/shorts/L5RxW6Ii7QQ

 

There were some round 7-8mm blind stars before this and I managed to find them on the floor and it seems the prime burned off without igniting the stars... I have suspicion that in that case layer of prime was not thick enough. I re-primed them better and will test them again.

 

I have realized it too late, will definitely use proper % in formulas :-)

Excellent. Four more thoughts come to mind.

 

1) If your red's having difficulty igniting, perhaps try drying out your strontium nitrate before storage. All mine arrives granulated, gets ground in a coffee grinder and then baked in the oven for an hour or so at around 220-250F (105-150C) before storage with a desiccant packet in a well-sealed container (same with all charcoal and all KNO₃ I use). Even though you're using organic binding that won't introduce water to your red comp, the dispersed PVC might lock in any moisture that your strontium nitrate may have picked up. I've noted granules fresh from the vendor to lose around 2+% water weight after baking. My routine is grind/bake/store. Only consideration would be if you're using a gas oven because water is a combustion product. In that case, just heat it a little hotter and open the door to vent water while it's cooling down some. You don't have to worry about thermal decomposition at those low temps. You can even bake it hotter without concern, but I just don't because I'm more likely to burn my fingers on the baking pan...

 

2) The KNO₃ is only at around 64% in your final prime mix, which might be a bit low. Consider upping it to 70-75% and see if you get a hotter/faster burn with better star ignition.

 

3) Faster charcoal makes hotter primes.

 

4) For rubber/plastic stars, my perc prime usually contains 5% Si and 5% Al or MgAl to help it along (and straight BP on the outside to get that going). Many use 10% Si to good effect, but I wonder how much of that is actually melted to slag and then oxidized in a cooler prime like yours--it might just be coming along for the ride and possibly working against you. You pretty much know Al/MgAl will ignite at slower sulfurless BP temps, though. Si? I wonder...

 

More priming always better than too little, especially with semi-stubborn plastic- or rubber-bound stars.

 

Maintenance/preventative stuff like drying chems could be routine. But only change a limited number of chem components at one time so it's easy to see what works (and what doesn't, or what makes things even worse...).

 

Keep on experimenting--you're pretty close to where you want to be!

[Powderman]

1. I did not notice reds being harder to ignite... But I will test moisture content in my Sr(NO3)2 just to know. My oven is electric, but I think the sample could also be heated on hotplate (thin layer) and I have IR thermometer to check the temperature easily (such a handy thing!)

 

2. Good point, upping the KNO3 content to 75% in my inner prime. Also testing samples with FeSi (Fe alloy with 14-16%Si).

 

3. I bake my own charcoal, there are trees everywhere, and a lot of different willows. So I use willow. I have blender milled charcoal with particles from dust to fractions of mm and some ball milled very fine.

 

4. I am going to perform tests of different base layers of prime on small water/dextrin bound red stars made last winter, they are dense and definitely not too easy to light. PVC bound are less dense so this may proof the prime enough to work. I will record how the star ignites inside my wood stove so I can work without going to cold and snow. Inspecting frame to frame should reveal how the prime works and how long it takes from igniting the prime to igniting the star...

Edited February 3, 2023 by Powderman

[Powderman]

I think no more priming tests inside, the prime acted like rocket and just now I saw my impossible crazy "piece of Mg ribbon" star flying like devil from the stove, and the most crazy is that the Mg ribbon actually got lit on the floor... Lucky I have no carpets :-)

Seems to me that this prime should be able to light some stars...

[SharkWhisperer]

 

2. Good point, upping the KNO3 content to 75% in my inner prime. Also testing samples with FeSi (Fe alloy with 14-16%Si).

 

3. I bake my own charcoal, there are trees everywhere, and a lot of different willows. So I use willow. I have blender milled charcoal with particles from dust to fractions of mm and some ball milled very fine.

2 FeSi seems like an experimental series all on its own. Might just overcomplicate uncomplicated current matters with your prime...

 

3 Wasn't referring to charcoal creation. Was referring to baking the accumulated moisture out of charcoal that acts as a water magnet by nature. Charcoal can hold a great deal of water weight and still appear bone dry. All my charcoal, homemade or purchased, gets ground, baked, and stored tightly sealed with silica packets if not used right away. Charcoal I haven't used in awhile get re-baked before use. I've seen dry-looking charcoal release 10% of water weight after baking; others have reported an even higher percentage of adsorbed water and I believe them... And, good that you make your own willow charcoal.

 

Testing flammable comps inside your house is never a good idea...

 

[Powderman]

Initial test with FeSi sample turned out unconvincing. But it might be good for sparklers after watching the video of the prime burning :-)

 

I have made more different stars, half is primed and ready and the other half is drying and then will be primed. It was snowing quite a lot here recently, but it is over now. It is going to be sunny/frosty weather for at least a week so testing will be possible. I like snow acting like a white canvas ready to be colored with stars :-)

 

I was referring to the "Faster charcoal makes hotter primes"

I know about charcoal being thirsty, it changes its "flow" and "dustiness" a bit as it becames more damp but aside that looks the same. If it goes into wet process composition I measure its water content and calculate correction. No need to dry something going to be wetted :-)

 

Testing at home anything that could go airborne after igniting is definitely a bad idea. I will take care to not repeat that mistake.

[cmjlab]

Some people believe the opposite about faster charcoal being a hotter prime. When I first started, I used hot charcoal (Willow / erc/) and the primes would burn off hard to ignite stars before the star ignited. I don't hink it much matters for a fast burning charcoal star, but I've never had much luck using anything but hard wood charcoal / screen mixed b.p. for primes on hard to ignite comps. Just another perspective to consider.

[Arthur]

Remember the white paper test for BP Slow powder scorches the paper, fast powder does not.

 

A good prime can be screen mixed ingredients with some coarse powder. The coarse powder has a big surface to take fire, the screen mixed ingredients burn slowly to pass fire.

[cmjlab]

I should clarify 2 things from my comments above:

 

1. that the slower screen mix B.P. works best when including Sulfur, but I've never made it into a sulfurless prime.

 

2. The faster charcoal certainly still works for a lot of people, my comments aren't to rule out what SharkWhisperer provided, only that it's never one answer / solution fits all situations.

[cmjlab]

Also, I strongly agree with the drying of charcoal regardless of intended use. Once it's mixed it can't easily be dried out going forward and if it contains significant moisture could cause your other components to clump, a double displacement reaction, or some other issue during storage/etc.

[Kalifireworks]

Sulfur shouldnt smell like anything by itself. It only smells when combined with water. Since you are not binding with water it shouldnt smell like anything.

 

Even if I use Water as a binder I never noticed any sulfur smell.

 

Is your sulfur maybe slightly wet?

[dangerousamateur]

So you feel a slower charcoal produces a better prime?
A slow prime might act longer on the star, but not hotter.
How about using a hot charcoal that burns clean and fast and rather slow the composition down with additives like silicon or thermite, so that there is more fuel than oxygen?

I feel a hotter charcoal usually takes fire more easily, an advantage a least for the outer layers, what do you guys think about that?

[SharkWhisperer]

. No need to dry something going to be wetted :-)

 

 

Really?

 

If you make two batches of 75/15/10 BP, one with dry charcoal and one with charcoal containing 10% moisture, will they behave the same way? Not exactly. The damp-charcoal batch will be over-oxidized and the actual comp will be approx 75/13.5 C/10 S/1.5 Water to start with before adding water for granulation/compaction, etc. Taking water out of the comp, your actual starting formulation is not 75/15/10, it is instead 76/14/10. Not a big difference. But charcoal can easily hold 20%+ water and look the same as dry. Then your starting comp is 77.3/12.4/10.3, not 75/15/10. You're starting off with a slightly different recipe than you intended.

 

For primes and star comps I would not be so concerned. When troubleshooting BP for lift/burst and especially for dialing in rocket/firearm propellant, the few % of error can become an issue. One batch of fuel burns fine and another batch cato's your motors or squibs your pistol. "But I used the same recipe and the same chems...".

 

Charcoal containing 10% water is pretty usual. But charcoal can easily adsorb much more moisture than that, especially when ground fine and with a large surface area. That's why many, myself included, bake their charcoal dry before use and store it well-sealed with desiccant packets.

 

For charcoal stars? Nah, it's a non-critical app so just grab that old bag of airfloat that's laying around. For tuning BP for rocket fuel or firearm propellant? Yeah, you want to start with the right proportions. Baking the sometimes substantial water mass out of your coal is cheap insurance for maintaining formula accuracy and batch-to-batch consistency.

 

Unless it's coming straight out of the retort, I bake my coal dry before storage or use. Can you get away without doing so? Of course. Usually.

[Powderman]

I also wrote that I take a sample first, measure how much moisture it contains and calculate correction to maintain proper ratios. It is much easier than drying it all. And I use charcoal for streamers, primes and lift, all of it is going to be wetted... Lately I have dried charcoal before ballmilling because it was laying quite some time around...

I just got an idea, marking whole package with dry weight can instantly show how much moisture it gained by simple weighing...

 

I think that inner prime should burn hot and perhaps leave some molten slag. It is not intended to make a lot of gases which take heat and material away. Outer prime should be easy to light and be able to propagate flame to the inner prime fast. That is how I imagine it working. At the moment it seems that I need to work on priming techniques to get compact, well adhering layers. And I have made batch of lift with 3:1 nitrate/charcoal instead of 2:1 I have used until now. It should burn cleaner and with higher temperature - both having positive effect on star ignition.

When shooting charcoal streamers it seems to work with anything, but the difference is also in shape (pumped barrel shape) and of course weight. Heavy "projectile" means hotter gases at higher pressure for prolonged time...

[cmjlab]

So you feel a slower charcoal produces a better prime?

A slow prime might act longer on the star, but not hotter.

How about using a hot charcoal that burns clean and fast and rather slow the composition down with additives like silicon or thermite, so that there is more fuel than oxygen?

 

I feel a hotter charcoal usually takes fire more easily, an advantage a least for the outer layers, what do you guys think about that?

If you were referring to my comments,

 

- "better prime?" - No I don't believe that it's better. I've had the most consistent ignition when using scratch mixed prime with a commercial mixed hardwoods charcoal (no metals usually).

- When I tried milled B.P. dust with a willow or ERC charcoal, the prime frequently flashed off, especially with nitrate strobes and KCLO4 based colored stars.

 

- "a slow prime may act longer on the star": yes, this is what I believe to be a contributing factor.

 

- "but not hotter": I'd agree that it does NOT burn hotter, but it also does NOT burn cooler. The only difference between Screen mixed B.P. & milled B.P. is the rate at which it burns.

 

- Lastly, I agree a hotter prime would have a better chance of igniting a tough composition, but that requires either a different oxidizer with a higher heat output (but also an ignition temp increase) OR a fuel that increases the heat output (i.e. AL, Mg/AL).

- this would be describing the use of a hot igniter prime (oxidizer with higher heat output / higher ignition temp) as the first layer, and requires a second layer to help ignite the hotter prime - usually a screen mix or perhaps a milled B.P. prrime (milled quickly ignites all over to quickly get the hotter prime going)

- i.e. "critical wind velocity"

 

Again, my only point was that sometimes there is not a "one size fits all" prime, in my relatively newcomers opinion. There are times where a milled B.P. prime is appropriate too.

Edited February 9, 2023 by cmjlab

[nordicwolf]

About baking charcoal...I get mine from a local guy who makes his own from ERC pet bedding. Should I bake that prior to ball milling? I suppose "yes" if I am milling all 3 comps at once for BP.

 

But if I am just milling the charcoal by itself, should I bake it? So far it mills into a fine airfloat, but I have no idea about moisture content.

 

Maybe I should mill it, bake it, then store it with desiccant in a well sealed container?

 

So many variations on one variable...thanks for making me think about it...good stuff here. Thanks

[Powderman]

It may be easier and less messy to bake before milling. But if it is not used or moisture-proof storaged afterwards it would be perhaps unnecessary. I am not sure how big of an impact moisture in charcoal has when ballmilling, it may or may not be a benefit to have certain moisture content... But too much might cause problems I think.

[cmjlab]

I've always thought of it as - if you're ball milling charcoal only, it may be more efficient to dry it afterwards, that way it dries faster and more completely since it's harder to dry completely when individual pieces are still large in size.

 

I don't really consider the weight concern until after it's milled and I'm ready to make B.P. or stars. My 2¢.