18 replies to this topic

[digger]

I was trying out win#2 this evening. I tried two different binders red gum and dextrin as the formula calls for. The first one I tried was the red gum bound using alcohol. I noticed that the formula seemed to heat up a little for a short while, but nothing to serious. The second batch I tried dextrin with water and the composition started to get hot and when it had reached about 45C I decided to dump it into a bucket of water.

Has anyone else had this problem with this comp?

Cooperman I believe that you had a problem with a glitter blooming, does this sound like the same problem? How did you end up solving it?

[digger]

Oh well tried again with the addition of 1% Boric acid. The mix warmed up a little but not as bad as the first batch so I went ahead and tried to make a few stars from it.

I left them for 20 minutes and went to check them. mmm a very strong smell of H2S and the 2 1" stars I pumped were getting very hot maybe up to 60C on the surface so once again I have dumped them into a bucket of water.

Does anyone have any Ideas what is going on?

For reference the formula is Win #2
Potassium Nitrate 40
Charcoal Airfloat 13
Magnalium, granular, -200 mesh 12
Strontium Nitrate 10
Sulfur 10
Antimony Trisulfide, Chinese needle 10
Dextrin 5

[pyrotrev]

There could be two possibilities: firstly check the pH of a strong solution of your KNO3 - it does vary a lot, if it's much past 7.5 could be a problem. Secondly if strontium nitrate is anything like the barium salt that could be a problem too, again check the pH. If in doubt, bind with an organic binder! Full marks for being safety conscious anyway.

[digger]

There could be two possibilities: firstly check the pH of a strong solution of your KNO3 - it does vary a lot, if it's much past 7.5 could be a problem. Secondly if strontium nitrate is anything like the barium salt that could be a problem too, again check the pH. If in doubt, bind with an organic binder! Full marks for being safety conscious anyway.

Right then I suppose a bit more info is needed.

I tested the PH of the kno3 and that was bang on 7 (I used recrystallised stuff for this), the sulphur was slightly acidic, I have not tested the other components.

The reaction must at least involve the antimony trisulphide or sulphur along with the metal.

The only thing that I am thinking is could it be the MgAl? When I bought this I also bought Mg and looking at the powders they look identical. Could they have been mixed up at source?

What would the best test be to prove if it was MgAl or Mg?

[digger]

Ok I have tried another batch with a new batch of MgAl. The same reaction occurred so I dumped it again (this is starting to get annoying) except for a small amount that I put in a beaker and topped up with water.

I tested the water with a Ph strip and it instantly went off scale at 9 (my strips are a 5 - 9 range).

Well after this I went on to check all or the ingredients separately

strontium nitrate 6.5
potassium nitrate 6.5 - 7
Sulphur 6.5
Antimony Trisulphide 9 eventually. Now this is the interesting one, I did not expect this.

It took a while for the Ph strip to react to the Antimony Trisulphide for what ever reason. So I assume that it is obviously an alkaline reaction with the al part of the mgal.

Has anyone had this happen to them? Is this normal for Antimony Trisulphide?

[digger]

Ok I have done some more work and there seems to be some strange things happening so I will report more information as it becomes available. It may not be the Antimony Trisulphide after all.

[Frozentech]

Ok I have done some more work and there seems to be some strange things happening so I will report more information as it becomes available. It may not be the Antimony Trisulphide after all.

Not certain if anyone has asked you, but are you using distilled water as your solvent to moisten the comp ? There have been cases of water with high levels of carbonates, etc causing unwanted reactions in pyro comps.

[digger]

Not certain if anyone has asked you, but are you using distilled water as your solvent to moisten the comp ? There have been cases of water with high levels of carbonates, etc causing unwanted reactions in pyro comps.

I have posted on Passfire too, someone did mention that the water could possibly be the issue. So to answer your question I am using tap water. We analyse the local water at work on a daily basis so I will dig out a copy of the report today along with getting a big bottle of distilled water from the lab.

Interesting though. What sort of unwanted reactions have been reported from these carbonates?

Edited by digger, 13 August 2008 - 09:28 AM.

[digger]

Ok I have done a little more checking of things.

The water I used was fairly high in calcium carbonate 35ppm, chlorine at 8ppm with no other significant contaminants.

I have repeated adding the chems to demineralised water tonight and the same reaction.

So I did the pH tests again with the inclusion of the magnalium this time.

The addition of the magnalium to water gave a strong alkali. Does anyone have any further insight into this reaction. All I can think of is the production of magnesium hydroxide and then becomes an auto catalytic reaction. Any input from you chemistry bods out there would be a great help.

I have done a bit of reading and it would appear that it is not recommended to use boric acid in compositions containing magnailium (Pyrotechnic chemistry by kosanki, shimizu et al). Even still I did add some boric acid to the aqueous mixture and it did neutralise the alkali, but there may have been an acidic reaction that started instead.

So where should I go next? Should I coat the magnalium with linseed oil or potassium dichromate?

Edited by digger, 13 August 2008 - 07:19 PM.

[digger]

does this sound like the same problem?

linky

[digger]

Ok then I have done some more testing and here is what I found:-

When I put the magnalium in the water there was no obvious reaction, but as I raised the ph to about neutral with boric acid it started to bubble slightly.

To determine if I had been sold magnesium instead of magnalium I have checked the density of the material using a volumetric flask a set of lab scales and a burette filled with alcohol.

The density turned out to be 1.96g/ml which when using a density of mg at 1.74g/ml and 2.70g/ml for aluminium gives an alloy at about 75% magnesium. So that could very well be the answer.

I will double check these results tomorrow to make sure I managed to remove all the air from the sample when doing the density experiment.

So it would appear that it could be a reaction triggered by a high mg content alloy. So I will have to get some fresh stuff and dichromate treat this stuff.

D

[Frozentech]

The density turned out to be 1.96g/ml which when using a density of mg at 1.74g/ml and 2.70g/ml for aluminium gives an alloy at about 75% magnesium. So that could very well be the answer.

I will double check these results tomorrow to make sure I managed to remove all the air from the sample when doing the density experiment.

So it would appear that it could be a reaction triggered by a high mg content alloy. So I will have to get some fresh stuff and dichromate treat this stuff.

D

Makes sense. It seemed like it was acting more like Mg than MgAl alloy. I have dichromate treated MgAl myself, for use in lance comps that contain Ammonium Perchlorate. Even though MgAl is "less reactive" according to all sources, it heats up dramatically when mixed with the NH4ClO4. Treating with Potassium Dichromate as if it were straight Mg, following the procedure from Shimizu took care of that. I saw that your on Passfire; Kyle has an article in the archive there on it as well.

[pyrotrev]

Gareth: how about a little detective work? - make up small quantities of the mix but omit suspicious components, from what you said the Sb2S3 and maybe the strontium nitrate would be the first suspects.

[digger]

Gareth: how about a little detective work? - make up small quantities of the mix but omit suspicious components, from what you said the Sb2S3 and maybe the strontium nitrate would be the first suspects.

I think I have cracked it now. It would appear to be the MgAl that is causing the problem as it turns out it is about 75% mg. Hence it is acting as if it is mg.

I did do some tests by adding different components to the water one after another. When I started with the mg there was an instant reaction with the mg which changed as each different component was added.

To give you an idea of how reactive this stuff is after I did the volumetric analysis I left the stuff in the alcohol for about 20 minutes. When I came back it was violently bubbling away. So it must have been reacting to the water content of the alcohol which is probably no more than 4% and most likely much less.

Makes sense. It seemed like it was acting more like Mg than MgAl alloy. I have dichromate treated MgAl myself, for use in lance comps that contain Ammonium Perchlorate. Even though MgAl is "less reactive" according to all sources, it heats up dramatically when mixed with the NH4ClO4. Treating with Potassium Dichromate as if it were straight Mg, following the procedure from Shimizu took care of that. I saw that your on Passfire; Kyle has an article in the archive there on it as well.

Yep I am over on Passfire too, although I am a pretty passive member as a general rule.

I have read the article by Kyle and I have coated mg in that way with some success so it looks like this MgAl will get the same treatment and be slowly worked off into formula as and when possible.

I may not be quite at the end of this yet, but it does feel like I have found the cause of the problems.

[Frozentech]

I think I have cracked it now. It would appear to be the MgAl that is causing the problem as it turns out it is about 75% mg. Hence it is acting as if it is mg.

Now, the next interesting thing will be to see what effect the high Mg percentage has on the glitter delay