16 replies to this topic

[GMetcalf]

Finally got round to putting up my first post on the forum!

 

So while I await my application for an Aquire & Keep to be processed (the Greater London ELO said he received over 100 applications after Christmas so it could be a while) I figured I needed something exciting to keep me busy which won't disturb the neighbours too much. Hence I felt some colour experimentation coming on!

 

Now the supply of perchlorate has basically dried up and I've got to make my left over stock last (so only using it for nice stars for special occasions), I was wondering if it was possible to make coloured stars using old fashioned potassium nitrate, of which I have plenty.

Some background to my nitrate star project:

• The reason perchlorates are used for coloured stars is because they burn at relatively high temperatures. This varies from around 2200^oC when used with organic fuels and 3500^oC when used with metallic fuels.
• A hot flame is required to put the metal ions which produce colour into a gaseous state in the flame, the necessary temperature has to be roughly over 2000^oC although it does vary slightly between metals.
• Nitrates burn at much cooler temperatures! When used with an organic fuel the temperature is roughly 1750^oC while with a metallic fuel it is around 2500^oC.
• Addition of organic material or an inert metal salt (such as a carbonate) to a metallically fuelled flame reduces the temperature dramatically, this includes adding chlorine donors such as parlon and PVC.

Now to create a hot enough flame using potassium nitrate as the oxidiser is clearly going to require a metallic fuel to get the flame temperature up to a high enough temperature to achieve a colourant in the gaseous phase. The choice of metallic fuel is going to be aluminium, magnesium or magnalium. Some basic chemistry research reveals that the metal with the highest heat of combustion (the heat given off when it is combined with oxygen from its elemental form) is aluminium, so that answers that question. So we have so far:

• The stars must be metallically fuelled.
• Aluminium is the hottest metallic fuel for this purpose.
• The quantity of colourant and chlorine donor must be kept to a minimum to keep the flame heat high enough to produce colour.

So for my first test I'm going to simply try to see if I can get the composition to get hot enough to produce the basic colour from an added metal salt (without a chlorine donor). These colours vary slightly from what we usually take to be the classical colours produced by various metals. Thanks to Shimizu's book here are the colours I'm looking for:

• Calcium: Orange.
• Copper: Pale Green.
• Strontium: Orange Red.
• Barium: White.

Now to the ingredients. I have most things available to me but to make it easy for people to use the formulae, I'd like to keep it down to easily accessible chemicals. Clearly an aluminium flame is necessary so I'm thinking to base the formulae on a basic nitrate flash (relatively insensitive and burns nice and hot). To make the formulae even more insensitive and because it's easily bought from art stores, the aluminium I'm using is the atomised variety. Obviously nitrates and aluminium have the potential to react so I'm adding 2% boric acid (which annoyingly affects the flame temperature but is necessary). The metal colourants I'm going to use are all carbonates as these can be bought from pottery supply stores and they're easy to work with and relatively non-toxic.

 

I'm simply going to test unconfined piles of composition (I know, making them into stars changes the burning characteristics but baby steps first!) first using the following general formula, by weight, with everything except the aluminium mixed by passing through an 80 mesh screen, then the aluminium diapered in:

• Potassium Nitrate - 41%
• Sulphur - 17%
• Atomised Aluminium - 25%
• Metal Carbonate - 15%
• Boric Acid - 2%

The calcium carbonate composition burnt a bright orange colour, the copper carbonate composition burnt a bright white with tinges of very pale green at the edges, the strontium carbonate composition burnt a white with tinges of orange at the edges and lastly the barium carbonate composition burnt a bright white colour. Nitrate based flash on its own of course burns a nice white so can't really say much about the barium, but the others seem to have worked somewhat! Now to work out compositions which include some chlorine donors...

 

As with any good science, the key to good results is lots of repetition! So if anyone out there would like to give these a crack, then please do, and report back what colour you get (and feel free to change the formula if you need to, i.e. use flake aluminium or copper oxide instead of carbonate etc). Happy experimenting!

[Vic]

Adding aluminium to potassium nitrate stars will give you sliver streamers or glitters it will wash out any real chance of coloured stars, in my view.

[starseeker]

Firstly, welcome to the forum and and may i say what a great and interesting first post , 

 

I look forward to seeing how your experiments go ,

[Arthur Brown]

Yes well thought out first post.

Colours largely came into fireworks with the development/discovery of chlorates, then perchlorates. However there are just a few comps listed in  http://www.thegreenm.../pfp/stars.html which use nitrate for colours, some as you say needing magnesium -a hot burning metal- to be hot enough to make colour.

 

As (per)chlorate colours are currently beyond you for lack of the chemical, then perhaps experimenting with all the available charcoal stars would be fun.

[GMetcalf]

Now for the chlorine donor tests! I've made up some formulae utilising a base of nitrate flash plus some extra oxidiser and parlon as a chlorine donor to give the following formulae for basic colours (plus I swapped to using copper oxide for the blue because the chemistry is a bit simpler):

Red:

• Potassium Nitrate - 54%
• Atomised Aluminium - 10%
• Sulphur - 12%
• Strontium Carbonate - 13%
• Parlon - 11%

Blue:

• Potassium Nitrate - 54%
• Atomised Aluminium - 14%
• Sulphur - 10%
• Copper Oxide - 8%
• Parlon - 12%

Green:

• Potassium Nitrate - 54%
• Atomised Aluminium - 14%
• Sulphur - 10%
• Barium Carbonate - 11%
• Parlon - 9%

All stars were bound with acetone and pumped. The results were as follows:

The blue and green stars burnt white, so no luck there, but the red star burned an orangey red, so if none else, we might have a potassium nitrate based red star on our hands!

 

I'm going to try and substitute in some magnalium for the aluminium and see if that takes away some of the white from the flame (magnesium doesn't add a white colour to flames), although I suspect the barium star won't be hot enough to produce a green colour regardless of ingredients.

[RichardH08]

Hats off to anyone who is prepared to tackle a project like this, which may prove to be both long and challenging. Given the current UK need for an explosives precursors licence in order to purchase (and, within a year, to possess) potassium perchlorate, coupled with increasing concerns in the USA and elsewhere regarding the environmental impact of perchlorates, it seems to be well timed.

 

However, I suspect it may be a mistake to concentrate so much on the issue of flame temperature. Work in the past, for example by Clive Jennings-White, has shown that it is possible to create red and green nitrate-based mixtures that are relatively cool burning and contain no metals. His formulae – on his own admission – burned slowly and were not suitable for making stars, but are an indication of what may be possible. I believe that good quality nitrate-based stars are not unknown in commercial products.

 

From general considerations of the physics and chemistry of pyrotechnic mixtures, reasonable reds and greens should be possible. Blue may prove more difficult, if only because there are so few suitable copper-containing compounds.

[GMetcalf]

So an update on how this is going. I have some formulae which when I finally get them ignited, burn with a very small but coloured flame - interestingly the blue being the easiest to get to give some colour. They still need a little tweaking so once I'm happy I'll post them for everyone to have.

 

My current problem is that the ignition temperature has to be very high (Black Powder prime isn't quite cutting it and a loose pile of composition doesn't seem to ignite full stop). The formulae currently contain Potassium Nitrate, Sulphur, PVC, Aluminium and metal carbonates. I think the best call would be to incorporate some Red Gum but without an empirical formula for it, I've no idea where to start working out the ratio between Nitrate and Red Gum I'm going to need to have it burn adequately. I know Red Gum is a very complex mix of compounds so an empirical formula would be a massive over simplification, but it's at least a starting point, if anyone knows a close enough formula?

 

Anyone have any other ideas how I can reduce the ignition temperature without adding too much extra fuel to the stars? I'm starting to get the feeling maybe I'll just have to settle for having to prime stars with a silicon prime to get them to ignite.

 

I'll be having a go at some adjusted formulae for the red tonight so I'll let you know how it goes.

[GMetcalf]

I've tested a new red formula, as a loose pile, with some adjustments to try and get it to ignite at a lower temperature.

 

The formula is currently:

• Potassium Nitrate - 57%
• Strontium Carbonate - 16.5%
• PVC - 14%
• Sulphur - 8.5%
• Charcoal - 4%

It was mixed by passing through an 80 mesh screen. The composition burned an orangey-red colour with a pretty good flame, however it did burn very sluggishly and sort of stopped and started (a bit like a strobe mix?). I get the feeling this is mainly due to the PVC, which isn't melting during the reaction and so heat isn't propagating through the composition. I'm going to try and mill the PVC powder I have with some Charcoal or some Red Gum and see how this affects its ignitability in a Potassium Nitrate mix. I'm also aware there's a high carbonate content which is going to be a flame retardant so I'm going to try a formula with less Strontium Carbonate and more oxidiser and see how that affects it.

 

I'm also going to try a variety of formulae tomorrow to ascertain what the optimal amount of added aluminium should be.

[GMetcalf]

An update on the Aluminium experiments. I tested a bunch of formulae containing different proportions of Aluminium to ascertain what gave the best burning characteristics and lowest ignition temperature. So far my best formula has been:

• Potassium Nitrate - 56%
• Sulphur - 14.5%
• Aluminium - 15%
• Strontium Carbonate - 5.5%
• PVC - 5%
• Charcoal - 4%

It was mixed by passing through an 80 mesh screen and diapering in the Aluminium. Of all the formulae I tried this gave the best flame envelope burning quite bright but still retained an orangey-red tinge to the flame. I suspect the carbonate is only decomposing to Strontium Oxide in the flame and no Strontium Monochloride is forming, hence no deep red is seen. I'm going to see what happens if I make adjustments to this formula to try and increase the temperature by lowering the Charcoal and Sulphur content and keep you all posted. I'm also working on some Copper Oxide containing formulae so I'll let you know how that goes.

[GMetcalf]

An update on how things are going:

 

I've been working on the Copper Oxide blues formula and I've been having a lot of trouble with it. The formula is based on Copper Oxide thermite to attempt to get enough heat into the mix to produce some colour. However, regardless of what organic fuel compositions I mix it with, I can't get it to reliably ignite and burn through. In fact in half the tests I've done, the Aluminium doesn't seem to have ignited at all. I'm going to see if I can work out a formula based on Nitrate Flash which might burn hot enough to decompose Copper Oxide and allow it to react with Aluminium, thus producing some Copper in the flame which I can try and get to react with some chlorine. If anyone has any suggestions, that would be lovely!

[digger]

I have not read this thread properly, so excuse me if I missed it. What type of aluminum are you using and what is the particle size?

[digger]

OK I have done a better search through the thread.

 

Try reducing the particle size of the atomisied aluminium to as fine as you can get. -600 mesh is available.

Try moving to a more reactive type of aluminium such as bright flake then more reactive again with dark flake.

Whilst magnalium may not have the highest heat of combustion it is far more reactive, so should be worth a try.

Turquoise should be possible if you move to Barium Nitrate (can be made from barium carbonate, acetic acid (vinegar) and potassium nitrate easily, if you are up for a bit of chemistry).

 

P.S. it is good to see someone doing some experiments again.

[GMetcalf]

I have switched to using Flake Aluminium now (250#), I only started with Atomised as I have bags of the stuff. I don't have much Dark Aluminium, and since Oliver Brown closed down I don't have a good source for more, but ideally I would be using that.

 

I do have some Magnalium, which was next on my list to try as a fuel, but I'm not sure about the reaction with Copper Oxide. As far as I understand it makes a mean thermite which is almost as fast burning as Flash Powder, so I'm not sure how a star with that mix in it would react, maybe somewhat like a Dragon's Egg?

 

On the subject of the greens, I don't have access to Barium Nitrate (and never needed it as I've been able to achieve pretty acceptable greens using only Barium Carbonate). The main problem with a Barium Carbonate green is you need something in the flame to react with the Barium Oxide produced by decomposition of the carbonate and this requires flame temperatures above 2000^oC to decompose the Barium Oxide. Using Potassium Perchlorate combined with Aluminium this is easy (I've also had some success with organically fuelled Barium Carbonate stars), but a lot trickier using only Potassium Nitrate, however in theory not impossible!

[digger]

I don't think it will go thermite like with the nitrate and other component levels you have in your compositions.

 

I am following you research with some interest, as you are searching for the Holy Grail. No mean feat, to which I sincerely hope you succeed.

 

I always found barium carbonate greens to be a little washed out personally. Barium chlorate and barium salicyclate is nice and works many ratios to alter luminosity / burn rate for a nice emerald green.

 

Barium nitrate greens are excellent with every shade of green possible from yellow green through emerald green to turquoise.

Edited by digger, 01 May 2015 - 01:00 PM.

[GMetcalf]

Well I'll give the Magnalium a go this weekend when I have some time and feedback the results!