I know of this precedure. You can speed up the procedure by adding some chloride (e.g. dilute HCl). The chloride ions have a catalytic effect on this
reaction.
I have made some of this red Se, cleaned it with distilled water, and dried it. The dry material I put in an ampoule. But unfortunately, the material
is not stable. Over the weeks, the material turns dark grey and half a year later, you hardly can see the red color anymore. The saturation of the
color decreases over time, just to be left with zero saturation, being a dull gray material.
I have seen samples of red selenium for sale, not the amorphous material, made from reduction of a selenite or selenous oxide, but by dissolving the
thus obtained red selenium in some solvent and then very slowly letting the solvent evaporate, so that you get a crystalline solid. These crystals are
dark red and apparently they are more stable. I never purchased some of that red selenium though, because it is very expensive (several euros per
gram), and I still have severe doubts on its long-term stability. I want some for an element collection, stable for years in a display, which is in
daylight. |
