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r1dermon

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i see colored motors all the time now..."green gorilla" "red line" ...etc...are these motors using the traditional coloring agents? such as barrium for green and strontium for red? or are they also using composite coloring agents?
 

bjmcder

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For the most part, "traditional" colorants like those seen in fireworks are used. Barium for green, Strontium for red, etc. Typically, the temperature of the flame needs to lowered so that the color does not get washed out and appear white. This typically results in a loss of efficiency which may or may not be tolerable depending on the application.

Faster propellants like "blue thunder" have a small percentage of copper oxide to increase the burn rate, and the copper also produces the blue color.

The color reactions are the result of the excitation/relaxation processes occuring with the electrons on the metal atoms. An electron becomes energized and occupies a higher energy level, then, upon returning to its ground state, emits a photon of a discrete wavelength which we see as a color. I don't know offhand what the actual reactions are (they usually involve chlorine), but Terry McCreary wrote an article on the process in Extreme Rocketry awhile back.
 

Ryan S.

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Originally posted by bjmcder


Faster propellants like "blue thunder" have a small percentage of copper oxide to increase the burn rate, and the copper also produces the blue color.

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As far as I know, Copper Oxide is not used in Blue Thunder Propellant, Copper Chromate is. Most Copper Oxide formulations have Aluminum in them to increase the brightness of the blue, but this increases smoke.

Do a little research online and you will see what chemicals make what colors.

copper oxide is a burn rate catalyst as well. Most chemicals that change flame color do not do this. For example; Strontium Nitrate slows the burn down slightly, same with Barium.
 

bjmcder

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I stand corrected. But many amateur fast propellants use CopperII Oxide as a catalyst. I can see why aerotech would use copper chromate, as Chromium compounds (including the CrO4 (-2) and Cr2O7 (-2) ions) typically have better catalysing properties.

Like you said, Thermic agents like Mg and Al make the flame much brighter and add a bit of metal oxide smoke, but the incandescance will wash out any color due to black body radiation if you use more than a few percent metal in a composition. It can be quite a delicate balance, especially with Barium salts.

On another note, I notice that everybody posting to this thread thus far is from Massachusetts. We've probably met in the past at various launches.
 

Ryan S.

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true, though I have heard of blue motors using Al percentages up to 8% without any color problems, only thermic ones.

We probably have met, I launch at CMASS and used to fly at Frontier
 

r1dermon

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i know what chemicals make what colors, the thing i was wondering about was if those basic chemicals are also used in aerotech colored propellants. i was wondering if they use some kind of artificial means of coloring. i think bjmcdr laid out a good post. thanks.:D
were you at the last cmass launch? saturday? man, that wasnt a great day. lol. i lost two rockets and my LOC broke two fins on every flight, 5 minute epoxy rules.
 

bjmcder

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I haven't been to a launch in a while, I've just been really weighed down with work and various other eratta for a while. I'm making it a priority to start flying again this spring.
 

r1dermon

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well, there's still two november launches left. doug never fails to provide entertaining crashes.:D sorry doug, i had to say it.
 
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