This is an amusing line of inquiry. Sapphire is growing in popularity for microchips. I found a source for single-crystal sapphire ingots... they only go up to 8 inches (~20cm) in diameter, about 60mm long. This tank was about 11 meters in diameter, 25m long. Scaling that up would be quite the project.

I mean, you could probably do chemical vapor deposition, but it wouldn't be a single crystal so what's the point?