The schools of magic of most spells are mixed up to say the least. The idea is that Acid is a physical material and as some think of evocation as only energy, they then put physical things like acid in conjuration. But that is if you ignore the second part of the evocation description where it says "or tap an unseen source of power to produce a desired end. In effect, they create something out of nothing". And then just in the core spells you have evocations that create wind and ice.
Now my evocation fox has always been that any spell that creates force/pressure/kinetic energy is evocation. And that evocations can create 'matter' for short times as per 'creates something out of nothing'. So summon sand pile is a conjuration, but to blast sand out of your hand at 300 miles an hour is evocation.
I also add [Acid], [Air], [Water] and [Earth] as energy types for evocation spells. So waterblast is [Water] semi matter/energy 'created out of nothing'.
The base effect of rusting would be transmuation, of course....but there is no reason an evocation spell could not cause it as a secondary effect.
And when you 'apply energy to air' you get spells like gust of wind...