6 replies to this topic

[Freese]

Last night I attempted to do up a batch of zinc spreader stars, using Weingart's Granite Star formula:

KNO3 14
S 2.5
Char 7 (150 mesh)
Zinc 40
Dext 1

I planned on doubling the recipe but for some reason (like, say, I'm a moron) I doubled everything but the zinc dust (only put in 40g). Also, I don't have 150 mesh charcoal, so I used 7 grams of airfloat. Since I have been interested in seeing what lampblack does, I substituted lampblack for the other 7 grams of charcoal. Both provide carbon and make a tail effect, right?

The recipe calls for wetting with 25% alcohol. I used isopropyl alcohol, (about 35% (maybe a bit more but less than 50%), which is what I had in the spray bottle). I had to use isopropyl as the only ethanol I had in the house was 12 year old single malt scotch. (and NO, I wasn't drinking it or anything else!) I used as little as possible. Mixed the comp in a plastic Rubbermaid container. Ran the comp through a sieve three times before wetting.

As I was incorporating the alcohol into the comp, the bowl began to feel warm (now that's odd...). I put the bowl down and waited a few seconds and rechecked, the bowl was definately feeling warm, like a hot bath. This, I thought, cannot be good so I grabbed the fire extinguisher, threw half a cup of baking soda into the comp, went outside and dumped it on a patch of bare dirt then dumped a couple gallons of water on it. No further reaction took place.

So, what happened??? Did I hallucinate this? Should I have taken a wait and see approach? I never had that happen before. Is there something in the lampblack that could cause this? I have heard that KNO3 and Al powder can cause a reaction, but there was no Al in the comp and no ammonium perc either. I have made spreader stars before using a similar formula and had no problems. I really like spreader stars and would like to start making them again, but I'd rather not repeat last night, had a bit of a panic.

And can lampblack be used as a general substitute for charcoal?

Can someone tell me what happened.

Thanks.

[pyromaniac303]

I have an idea on what could have caused this.

Have you seen those instant hand warmers that are sold in camping shops? They contain a mixture of a metal powder (I think it is Iron but maybe zinc could take its place), and activated carbon (charcoal?). They are in sealed packages and when they are exposed to air they suddenly produce heat for several hours as the air reacts with them. Try just a mix of zinc powder and the same charcoal you used, wet it, and use a thermometer to see if theres any rise in temperature, then do the same with just zinc and lampblack.

I think it could be this effect that caused the heat. I have never known it get above 40 degrees C in commercial handwarmers but I am not sure what the leftovers of the reaction are, obviously not what you wanted in your formula so it may not have worked at all after it had cooled.

[pyromaniac303]

OK just found some more info, and a hand warmer contains the following:
*activated carbon
*iron powder
*sodium chloride
*vermiculite
*water

Hope this helps, it does seem like the only thing you have changed since your other zinc spreader stars is the source of carbon, and if iron powder behaves in a similar way to zinc then there is a good possibility this was your problem.

[Mumbles]

Zinc and KNO3 will react in a similar way to Al and KNO3.

[alany]

I've made that comp many times and never had any significant heating. Your water wasn't HCl was it? Are you sure it was pure Zinc powder? I've had uncoated Iron powder in a similar comp cause a reaction hot enough to start the comp steaming.

[Chyros]

Your water wasn't HCl was it?

LOL, I immediately thought of that too. It'Of course, HCl and zinc give of hydrogen gas; this would explain why the thing heated up (but of course, where would the acid come from? )

[cat]

Well two things happened here:
1) Your Zinc had a basic reaction with the KNO3, this is well documented. Some people believe that be controlling the acidity of the formula you can prevent the reaction (such as adding H3BO3 or other weak acid). This is partial untrue this will only slow the reaction. Zinc readily reacts with water and this is increased in both alkaline and acidic conditions.

2) Lampblack has an insolating effect that is not well documented. I?ve known several people who have substituted air float for lampblack and for the first time experienced heating of drying comp.

If a comp you are mixing begins to heat it should be abandoned and destroyed. It is foolish to risk ones wellbeing to try and save any amount of chemicals. Depending on the comp it may be possible to flood with water from a distance to prevent a flare-up. Do not pick up the material and try and move it. You have no way of knowing the internal temp or speed of the reaction. Chances are it will not ignite but rather render the mixture unusable.

I personally know two people who have been burned trying to rescue a batch of reacting comp. Understand you are working with energetic materials; when you deviate from tried and tested formulas extreme caution and planning is necessary to keep you safe.

-cat