luminous emissions from high-speed sand impacts

Factual Questions
1

Question prompted by this thread regarding light emissions from sand impacting helicopter rotor blades.

The assertion at the photo page is that this phenomenon is related to static electricity. While there is no disputing the fact that static electricity does build up on helicopters, I’m suspicious of the claim that static electricity is responsible for this luminous phenomenon; the color doesn’t seem to match the bright blue/white in the static discharges I’ve seen before. Electrical-discharge sparks are pretty damn hot, the result being a preponderance of high-energy photons that tend toward the blue end of the spectrum.

Out of curiosity, a few minutes ago I turned off the lights in the basement and fired up the sandblaster. I saw the same luminous emissions seen on the heli rotor - same color even - but here’s the interesting thing. I saw them on the sand (aluminum oxide) as it was being ejected from the nozzle. It was visible for a distance of maybe 6-8 inches before fading away. Directing the blast sand onto a part didn’t affect things at all; emissions didn’t particularly increase upon impact with a piece of angle iron. Did not seem like discrete static sparks, the particles were glowing continuously as they moved away from the blaster nozzle. Possibly something to do with the impact of the alox with the blaster nozzle (tungsten carbide)?

Is this phenomenon triboluminescence, rather than static electricity?

2

“sand” is aluminum oxide? That’s news to me.

I always thought it was mostly silicon dioxide.

3

Most sand is silicon based, however there are lots of types of sand. Small scale sandblasting usually usually corundum sand because it’s harder and less toxic than silica sand. And corundum is aluminium oxide.

4

Lots of sandpaper uses aluminum oxide as well.

5

If you are on a beach at dusk, and throw a chunk of quartz (silicon dioxide apparently) onto the pebbles, you’ll see a flash, presumably through the compression creating a piezoelectric charge. So I would guess that the flashes could be from the tiny sand crystals being compressed by the rotor blades.