The Carbon Armor is my own creation - it has never appeared in any Iron Man comic book. Basically it was an excuse for me to paint an Iron Man Minimate in dark colors, but I didn't want to call him "Night Operations" or "Darkness Attack" or "Twilight Camouflage" Iron Man. Then I started thinking carbon is sort of like a metal, and so the Carbon Armor was born.
If this armor were going to appear in a comic, I would think that origin would go something like this: While researching the Vision's density-changing abilities, Tony Stark discovered a way to reverse-engineer those abilities. To harness those abilities, Tony Start recreates an older version of his Iron Man armor with special carbon-composite materials. The resulting armor allows Iron Man to change the armor's density - while it can't go immaterial, he can increase the armor's density to the point of diamonds, allowing never-before-seen levels of protection!
Yeah, none of this is supported by real science, but it's from a comic book where someone flies around with jet-boots. Real science doesn't apply here.