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Substituting Ba nitrate for Sr nitrate

rubber stars

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#1 rellim

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Posted 15 April 2018 - 05:48 PM

I want to make green rubber stars per Skylighter "How to Make Screen-Sliced, Briliant-Red Rubber Stars" by Ned Gorsky. In the article he says to substitute barium nitrate for strontium nitrate to get green stars but gives no amount.  Molecular weight ratio for the 2 salts is 1.24 so I think that I should multiply the amount by 1.24. Is this correct?

 

#2 bobd

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Posted 15 April 2018 - 07:19 PM

I have simply replaced the Sr nitrate with the Ba nitrate 1-for- and gotten good results.

b


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#3 OldMarine

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Posted 15 April 2018 - 08:25 PM

Yup, 1 for 1 in weight works perfectly!


Edited by OldMarine, 15 April 2018 - 08:26 PM.

Come on! Name one other hobby in which you cheer as your money and hard work go up in smoke!

#4 bobd

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Posted 15 April 2018 - 10:12 PM

Thanks, Pat.  I missed the edit.


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#5 Mumbles

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Posted 16 April 2018 - 10:12 PM

I agree with the 1 for 1 swap.  They colors are always great, but my burn rates tended to differ a bit between the two colors.  Just something to keep in mind.  


Just so you guys quit asking, here is the link to the old forum. http://www.xsorbit2....forum/index.cgi

The sky is my canvas, and I have 2,113 pounds of powdered paint in the workshop.

#6 greenlight

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Posted 18 April 2018 - 12:00 AM

They should be able to be swapped 1 for 1 because they both have the same decomposition equations but I have noticed a difference in burn rate too.

@ mumbles..Which one do you notice burns slower. I think it is the barium comp for me. I think I know the reason too but I will wait to see what your opinion is on the slower burning first.

Edited by greenlight, 18 April 2018 - 12:00 AM.


#7 Baldor

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Posted 18 April 2018 - 12:21 AM

Could the slower burning be due to diferent molar mass? To be precise, having the same equations, the correct substitution should be mol by mol, not gram for gram. There is a 25% difference, as Rellim mentioned: Sr(NO3)211,63 g/mol , Ba(NO3)261,337 g/mol You should use 0.81g of Sr(NO3)2 to substitute 1g of Ba(NO3)2 , or 1.24 of of Ba to substitute 1g of Ba.



#8 greenlight

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Posted 18 April 2018 - 12:55 AM

Thats exactly what I was thinking.

I took the percent ratio for Sr(NO3)2 which is 53 for the red rubber formula and calculated the stoichiometric equivalent of Ba(NO3)2.
It does add up to be more oxygen rich with the Sr than the Ba.

To substitute, I got a different result than you. I got an excess of exactly 12.5% Barium nitrate to be equivalent to strontium nitrate.

My result is probably becaise i used the 53% in the original formula to work it out which is nearly half of 100% so half the result

Edited by greenlight, 18 April 2018 - 01:09 AM.


#9 Baldor

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Posted 18 April 2018 - 01:42 AM

Don't trust my calculations. I made them  just out of bed and in a hurry before heading for work. Percentages should not change regardless the starting cuantities.



#10 greenlight

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Posted 18 April 2018 - 07:37 AM

Yes, I think it is 12.5% extra barium nitrate. 25% seems a bit much and you would get a very diminished burn time result if you substituted 1 for 1.

#11 Baldor

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Posted 18 April 2018 - 09:38 AM

I repeated the calculations and stand by my results. 25% was an approximation, in reality is 23.487%. Just use the 0.81 and 1.24 factors mentioned above.

 

But this is not the end of the history regarding the slower burning composition. Energy of the reactions should be accounted too, and my chemistry is too rusty for this.

 

All in all, if you are happy with an slower composition, a 1:1 substitution by weight seems Ok, as are attesting more experienced pyros.



#12 Mumbles

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Posted 19 April 2018 - 07:29 AM

For me, it was always the red that burned slower.  There are a few factors that probably went into this though, so I can't say it's a rule across the board.

  1. I have no idea which compound the formula was "optimized" for.
  2. My strontium nitrate could have been slightly damp.  I never tried this with my higher purity stuff, or took great steps to dry anything.  
  3. My barium nitrate is listed as X-Fine, which could mean a different particle size between the two.
  4. Could very well be the molar ratios.  This is something I've wondered about too, but would need to know the answer to point one to make the correct substitution. 

While I'm not entirely sure, I suspect the composition was optimized for red which makes this all the more odd.  


Just so you guys quit asking, here is the link to the old forum. http://www.xsorbit2....forum/index.cgi

The sky is my canvas, and I have 2,113 pounds of powdered paint in the workshop.

#13 kaotch

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Posted 20 April 2018 - 09:29 AM

Baldor, your approach to calculate on basis of g/mol is interesting. There is noway that you can substitute ingredients on a 1:1 basis. This subject has always puzzled my mind and therefore would advise , get a copy of A.A.Shidloskiy's book Principles of Pyrotechnics , where these matters are explained in depth.



#14 Baldor

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Posted 20 April 2018 - 09:46 AM

Substituting mol for mol is only the start, Kaotch and only in this case in which the formulas of the nitrates and the reactions are exactly the same.  Energy needed to decompose the nitrates, and energy released should be taken in account too.



#15 bobd

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Posted 20 April 2018 - 07:24 PM

The empiricist's response to this question is to make red and green stars from the same composition with Ba Nitrate substituted for Sr nitrate.  If the results are pleasing, there is your answer.  The academic maundering is interesting, but the proof is in the sky.

$0.02

Bob


Edited by bobd, 20 April 2018 - 07:24 PM.

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#16 rellim

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Posted 29 April 2018 - 11:15 AM

I made green stars with +.24 Barium Nitrate and fired them in a half red half green 2" shell. See attached video. 

 

Interesting tidbit from Russel:

 

In practice, both red and green star compositions are formulated to have a negative oxygen balance (i.e. there is an oxygen deficiency) since the presence of a reducing atmosphere in the flame inhibits the oxidation of MCl to MO (where M is Sr or Ba), thus enhancing the colour purity of the flame


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#17 rellim

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Posted 29 April 2018 - 11:17 AM

Try to attach again.

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