Jdurg - 22-10-2006 at 15:57
Well my photography booth FINALLY is set up properly and I'm able to take some great shots of my element samples. I now have the lighting just how I
want it and the images come out quite clear with quite a bit of detail. Attached to this post is an image of my potassium metal lump. The side you
are looking at is the freshly cut side as of about 1.5 to 2 years ago. During that time, I have had the potassium stored in the same container and it
is VERY air-tight. Still, you can readily see the golden-yellow peroxides and superoxides that have covered the surface. What's puzzling to me,
however, is the deep blood-red compound forming on the cut surface. I have absolutely no clue what that could be and it has been bugging the hell out
of me. It doesn't meet the criteria for any type of oxide that I know of, and I wonder if it is just an ultra thin, regular potassium oxide layer
akin to the thin colorings you can see on metals like niobium or silver? This piece is very beautiful and I'll never get rid of it even when my oxide
free piece arrives, but I just want to know what this is. (I also plan on re-shooting all of my elements now that I have the photography setup just
right).
Odyssèus - 22-10-2006 at 17:02
Could it be something else from the atmosphere? The sulfide is listed on MSDSs as redish brown.
That is a very nice sample.
[Edited on 23-10-2006 by Odyssèus]
Jdurg - 22-10-2006 at 17:25
You know, I never really thought too much about it being a sulfide but that would kind of make sense. However, I just do not know where the sulfide
came from. There is a chance that it came from the mineral oil the potassium is being stored under as oils have a large sulfur content in them. It
would then make sense that as the peroxide coating (which you can see is pretty heavy on this sample) slowly decomposed the presence of oxygen made it
turn that red color. I almost wish I had access to an analytical lab close to me so I could take the lump with me and have them analyze it
spectroscopically.
Odyssèus - 22-10-2006 at 18:18
You could try taking a small scraping of the red stuff and dissolving it in water. You might be able to smell the H2S as its formed.
Nerro - 23-10-2006 at 02:44
coult it be that the oil contains a tiny amount of some contaminant that is very very very slowly reacting with the K and producing a layer of KX (or
whatever) that is extremely thin and regular that can distort light in such a way that it produces red light?
I'm going out on a limb here though because if my hypothesis were true you'd probably see all colours.
There wasn't any glyme in your oil by any change? 
-edit-
I didn't think of this at first but could it be a scattering effect caused by mixed oxides, peroxides and cabonates/sulfides?
Also, I've read about non-stoichiometric oxides of some alkalimetals, maybe the colour of a certain KOn ( 0 < n < 1 ) is deep red?
[Edited on Mon/Oct/2006 by Nerro]
12AX7 - 23-10-2006 at 03:06
Yea if it were interference it would react with the whole thing and look iridescent, none so specific as that red. Although it's weird that it's only
red in places, not over the whole cut or something.
Tim
Jdurg - 23-10-2006 at 04:30
I have thought about cutting off a small piece and reacting it with water, but with all of the heavy peroxidation I'd rather not mess around with
pieces of it in fear of the entire lump going up in smoke. (Corrosive smoke at that. 
).
The red speckling exists all around the piece of metal, but it's most noticeable on the side that I took the picture of. Everywhere else the
metallic, crystalline red "dots" are covering any part of the metal that appeared to have been exposed. (It looks as if there were some spots of
heavy peroxidation and as those peroxides decomposed this red compound took its place).
I too have thought that perhaps it's just a layer of oxide on the surface that has grown just thick enough to produce that distinct red-metal color
but not any further due to the tight seal of the lid. Personally, I think this is pretty neat looking and somehwat goes against what one would expect
from potassium metal. Although I'll be getting a nice, clean, oxide free sample of K within the next couple of months I'm definitely going to hold on
to this thing.
woelen - 25-10-2006 at 05:50
Jdurg, first I want to tell that the picture of your potassium sample is really cool. Very good!
I have been reading in my book on the chemistry of the elements, and it mentions that potassium is capable of forming the compound KO3, so-called
potassium ozonide. Ozonide ion is very unstable, and it is deep red, at very high dilution it is yellow.
You can make ozonide from a persulfate salt by adding solid NaOH or KOH to solid persulfate and then wetting the stuff slightly. A white humid puddle
is formed, but this soon turns orange. After a short time it starts bubbling, giving off oxygen. This orange color is due to small amounts of ozonide,
which quickly decompose.
It _might_ be that the red material is potassium ozonide.
[Edited on 25-10-06 by woelen]
Jdurg - 25-10-2006 at 06:15
Thanks for the kind words. Once I got my photography area set up properly I was able to start taking some incredibly good pictures of my samples.
That mention of potassium ozonide is VERY interesting. I took a look and yes, KO3 is a deep red color but the compound is very unstable in the
presence of moisture. However, due to how well this sample is protected from moisture I don't think there is any H2O vapor present in the mineral oil
to decompose the KO3. The only way to truly test this would be to open the jar, cut some potassium off, then mist some water vapor on it to see what
happens. I will not, however, be doing that as I think that would be quite dangerous and I don't want to alter my lovely sample now.