10 replies to this topic

[Pretty green flames]

I've been experimenting with a nice blue color recently and came up with this formula for a blue/green star

It's quite nice and it ignites easily ( no prime necessary)

Here's da formula

6 grams of KNO3
4 grams of Sugar
0.5 grams of Charcoal
4.5 grams of Sulphur
3.5 grams of Aluminium powder (i used 50 micron)
9.5 grams of Zinc powder


Please tell me what you think of this.

Thnx for your thoughts

Take care

[paul]

The use of sugars in stars is not very recommendable. It is hygroscopic and thus the stars wouldn?t keep up very long.

But I?ll give it a go and test this stuff :D

[Pretty green flames]

maybe try adjusting the formula a bit.
I only have a 0.5g accuracy scale so try adding a little less of everything

I'll do further test in the near future.
Right now i'm waiting for my Zinc powder.
I'll let you know how i get on

Take care

[alany]

Try this, it burns significantly blue/green coloured:

http://www.vk2zay.ne...ition.php?id=38

It makes an interesting match when the slurry is coated onto cotton string. It burns fairly slowly as match but very hot and deliberately. Some of the residue glows under black light, it must be zinc sulfide activated by impurities.

I'll try and get some videos of some stars of this stuff tonight, the wind has to die down first.

[cat]

Try this, it burns significantly blue/green coloured:

http://www.vk2zay.ne...ition.php?id=38

Alan: A few safety notes:

Some people use to add KNO3 to Zn+S propellant to get a better yield and a higher ISP however they learned the hard way why granite stars contain (alkaline reaction) boric acid, or why spreader star contain di/bichromate and usually recommend treated metal fines. Zn is a very reactive metal (well at least in its common crystal forms) and will readily react with both oxidizers in this formula. Stored Zn fuel grains are known to be hard to light because the surface area is usually zinc sulfide or sulfate. This eventually spreads through the comp resulting in junk. The worst case is that the zinc can heat up while drying. As for the speed of combustion, try reducing the S content.

ADDED: Just wondering why add the KNO3 at all?

Edited by cat, 08 January 2005 - 06:26 PM.

[alany]

I use the Potassium Nitrate to make it easier to ignite.

Zinc + Sulfur is hard to ignite. The sulfur tends to burn off before it ignites if you just hit it with the torch. It seems to need the containment and low oxygen environment inside a device to reliabably take fire. The high thermal conductivity probably tends to cool hot spots too. Practical micrograin rockets often use a burst disk to get the motor pressurised because it is so damn hard to ignite.

Boric acid is never used in granite stars. While the borate might help protect the Zinc the slight acid buffering would tend to increase any corrosion. Zinc is less prone to corrosion in alkaline conditions, unlike say Aluminium. In Carbon rich environments Zinc Carbonate forms on the surface of the Zinc. Zinc Carbonate is insoluable and very robust. Zinc Sulfide is similar and better than the Oxide in protecting Zinc but not as good as the Carbonate. Sulfate production is not favoured IIRC, the Zinc will reduce it if it forms. That is probably why granite stars are relatively 'safe'.

The Dichromate in spreadersis mainly a catalyst for the Chlorate, and as an additional oxidiser. It will help protect the Zinc a bit though, but I've never seen that mentioned as its purpose in that composition.

[cat]

I use the Potassium Nitrate to make it easier to ignite.

Understood, that makes a lot of sense

Boric acid is never used in granite stars.

Though it may not be listed in Weingart formula, the more I search the more references to its use I find.
Refer to Cardwell's article on zinc stars, Pyrotechnica #1

The Dichromate in spreadersis mainly a catalyst for the Chlorate,

Umm, actually you?re probably right (another good point). Though this comp is know to create substantial heat while drying and pre-treating the zinc can help eliminate this, though it slows the vigor of its combustion.

[BurlHorse]

Since we are on the topic of this. Can anyone help me as to why my granite stars never work? When I used to cut stars many moons ago I dried them in direct sunlight straight after cutting (bad I know). They burnt great. But now I am rolling them I have had over 3kg of granite comp not take fire. The finished stars when first rolled would burn better than they do now! I have kept them anyway... I can get them to light from a shimizu falls star thats about it! Even then they just smoulder.

Anyone got an answer or a solution?

 

Daniel my first guess would be that your over wetting when rolling as opposed to the amount of water you use in cakes for cut stars. Granites are tempermental anyway. what is the Comp, Perhaps we can drill it down by looking at that.

Stay Green,

Best Regards,

Bear