Orange flame and blue flame: what causes the difference? metal vapors?

pa5tabear

What causes flame color? I know light color corresponds to photon energy which is related to electrons relaxing from a high to low energy state.

I'm not sure how to conceptualize this situation though.

My professor was heating a 0.8 wt% carbon steel rod, in austenite phase, with a blow torch until it started glowing. I assume it was still in the austenite phase.

During the heating, the flames from the blow torch were blue until the metal started glowing orange. At this most of the flames changed color to orange. There were still some blue flames at the outlet of the blow torch but those that were past the piece of metal were all orange.

chill_factor

it may be that metal atoms or clusters are being vaporized from the surface by the hot gas flow across it, at which point they'll start emitting light at their characteristic frequencies. this is actually an analytical technique for trace metals in organics or solutions called atomic emission spectroscopy.

joseamck

Blue means hotter than orange flame. That is why blue stars are hotter than yellow/orange stars just like Betelgeuse (red giant) which is located in the orion constellation. The cause of the blue flame is just that is coming out really hot due to the introduction of more hydrogen or oxygen atoms (I think), you can tell by the color of the flame. Also remember from the spectrum, visible blue light has shorter wavelengths than red and thus the energy is higher. photons with shorter wavelengths have more energy than photons with longer wavelengths. That is why radio waves don't kill you, but Gamma rays and x-rays are dangerous.

AlexLAV

I also think the orange glow is due to admixtures originated from heated steel surface. It may be any solid particles such as ferrum oxide, or may be soot. Moreover Fe atoms have a lot of emission spectral lines within the visible range, and there may be some other admixtures, such as Na atoms which have very intense orange emission lines.

Different metals give different colors to the flame. For example Cu gives green or blue color (I dont remember exactly), Co - blue, and Cr - green.