Question

What is formed when a diamond is heated in vaccum?

Answer 1

If you heat it in air, it just burns up. If you heat it in a vacuum or other inert low-pressure environment, it first turns to graphite and then at higher temperatures sublimes straight to vapor. Calculations suggest that if you heat it to 5000 K (almost the temperature of the sun) at 10 GPa of pressure (the pressure 200 km or so below the earth's surface) it might melt.