I'll admit that pure quartz can't melt in lava based on temperature, but not all of sand is quartz (most of it is however).
Second, melting temperature can be lowered with additives.
Third, sand doesn't need to melt to bend, stretch, and fuse.That's how glass was once made (otherwise, glassmaking in the middle-ages wouldn't be possible).
Despite physical facts, AkaInu will own Crocodile completely if they fought.
So Akainu going to add somthing to Crocodile to make him melt him?