m1tanker78 - 10-3-2011 at 15:32
Sorry, I didn't get a pic but I might try to reproduce and take a pic or vid...
Why is it that after sodium is allowed to very slowly burn in air, a very light blue flame appears around the resulting oxide/peroxide? By 'slowly
burn' I mean to raise the temp enough to where it begins to oxidize rapidly enough to give off a little incandescence but not so fast that it quickly
burns and puts off a lot of smoke. The flame is very faint - almost looks like plasma. I have observed this 2 or 3 times and each time it has appeared
at a slightly elevated temp (sorry, didn't measure) and after the initial "burn". Each time has been in open air.
Is this free hydrogen that's recombining or reoxidizing? The temperature is way too low to be a thermal blue...
Tom
m1tanker78 - 10-3-2011 at 16:01
I guess it is hydrogen combining with oxygen and burning (same color and faintness of space shuttle main engine).
I must be losing my touch with google... 
Tom
Sedit - 10-3-2011 at 16:22
Someone else will more then likely chime in here but I believe I remember someone mentioning that the peroxides of alkali metals was phosphorescent. I
could be wrong because I can't remember where I read this mind you.
a_bab - 10-3-2011 at 22:30
Sedit, you must have read this: http://www.sciencemadness.org/talk/viewthread.php?tid=13400
I personally believe the blue may have something with the temperature of the flame. If it was hydrogen burning if would be chocked by sodium ions.
[Edited on 11-3-2011 by a_bab]
m1tanker78 - 11-3-2011 at 12:44
These flames are visible in a moderately well lit room (but just barely). There are no other components to the blue. It looks like a blanket of faint
blue with a few very short peaks coming up randomly. Like a lava lamp from what I remember. I never noted any smoke at all. I don't think it's
phosphorescence but I may have a new set of experiments on my to-do list; had no idea alkalis could produce phos. effects. The temperature was low
enough that it didn't create a large convection.
I came across this old book while searching the net. It mentions phosphorescence of alkalis and respective oxides and peroxides. It also addresses the
blue glow as being the slow oxidation of sodium though I'm pretty sure the sodium had already all oxidized so it was likely the oxide going to
peroxide.
Here's the link if anyone's interested:
http://books.google.com/ebooks/reader?id=2SjzAAAAMAAJ&nu...
Tom
m1tanker78 - 24-12-2012 at 08:25
I've been looking over my notes and remembered this thread. The blue flames that I observed on a few occasions were most likely burning CO. I was able
to reproduce this a while back by 'burning' sodium in an atmosphere of CO2 and air. Initially, the sodium begins to burn in the usual
manner - glowing bright yellow and putting off dense smoke. After a few seconds, this subsides and a smokeless light blue flame can be seen.
Originally, the CO2 atmosphere was provided by thermal decomposition of sodium carbonate, which the pool of sodium was sitting on top of. I
didn't make the connection until I investigated another set of puzzling observations which was the formation of iron carbonyls around the steel
cathode of a Downs cell.
What do you think? I envision an apparatus in which a gentle dry stream of CO2 is passed over (or bubbled through) hot sodium to generate
CO. This CO is passed through hot steel wool or nickel powder which should react to form Mx(CO)y. The carbonyl is condensed and
collected for a demonstration of a nickel mirror (as an example). If the condenser is borosilicate glass tubing, I surmise that part of it would,
itself, become a mirror. Although dangerous (toxic), this would be a nice demonstration as well as proof of concept. I wish I had some boro glass
tubing and the skills to construct this thing.
Every attempt to photograph the blue flames has ended in failure because the camera picks up wavelengths of light that my eyes don't (infrared). As a
result, the blue flame is completely washed out with the 'thermal' component.
As a final note, I'm aware of the fact that CO can be generated by dehydration of formic acid.
Tank
Endimion17 - 24-12-2012 at 08:58
I've seen such flame.
Sodium used in demo experiments is always wet. It's the protective liquid it was in, iin most cases kerosene.
I wouldn't be surprised if that had something to do with the blue light. After all, sodium is a strong reducer and would, at sufficiently elevated
temperatures rip apart hydrocarbons. Therefore some elemental carbon might form which could be in the form of a surface phase. It might end up as
carbon monoxide.
To test this hypothesis, sodium should be cut, washed with ether, cut again in dry ether and evacuated for a few hours. Then it can be allowed to
burn. If no blue flame is present, then it has to be connected to the kerosene layer.
m1tanker78 - 24-12-2012 at 09:19
E17: The sodium was virgin; it was residual sodium that remained on top of the
solidified salt melt after running the Downs cell and pulling off the collection apparatus. The salts were also very pure. The cell continues to
release CO2 until it cools to a certain point. If I had some pressurized CO2 gas, I'd try this a different way.
Tank