Can armament haki be used when in Logia form When a Logia devil fruit eater alters his shape to his type of fruit (like ace becoming fire) can he cover himself with armament haki?

We know that it can be used on the body and weapons, is it usable on the Logia form itself?
Yes. That kind of haki works independent from devil fruit however if something "generated" by devil fruit you can use enhance it with armament haki.