Substituting Ba nitrate for Sr nitrate

[rellim]

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?

[bobd]

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

b

[OldMarine]

Yup, 1 for 1 in weight works perfectly!

Edited April 16, 2018 by OldMarine

[bobd]

Thanks, Pat. I missed the edit.

[Mumbles]

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.

[greenlight]

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 April 18, 2018 by greenlight

[Baldor]

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)₂ 211,63 g/mol , Ba(NO₃)₂ 261,337 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.}

[greenlight]

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 April 18, 2018 by greenlight

[Baldor]

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.

[greenlight]

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.

[Baldor]

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.

[Mumbles]

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.

[kaotch]

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.

[Baldor]

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.

[bobd]

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 April 21, 2018 by bobd

[rellim]

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

[rellim]

Try to attach again.