I think there are lots of disintegration fx in anime… of my head I can think of:
Trigun (when he become hyper mode or whatever - and blasts away a city)
Gundam 0083 Stardust Memory - GP02 blasts away the entire fleet…
Zoids Chaotic Century - Charged Particle Canon. So much melted metal…
Others to consider:
FF Advent Children also has some scenes, perhaps adaptable? For example, Kadaj and his two flunkies melting away during the rain.
Dropping a cookie into a bowl of milk. The cookie usually disintegrates after a few minutes of intense pain.
GW