The Cosmic Rust gun is a weapon in Dark of the Moon.
The Cosmic Rust gun is a weapon weilded by Sentinel Prime. When fired, the gun discharges a powerful blast that rips through the chasis of an enemy, or Comrade in Sentinel's case, causing devastating external damage. But, discharge leaves behind the Cosmic Rust virus which slowly eats away at the victim, alive. Luckily, some victims don't survive the blast, and don't feel the pain of being eaten.
When Sentinel Prime and the Autobots regroup at the NEST base, when Sentinel Prime tells him that he made a deal with Megatron. Therefore, he uses the gun to shoot at Ironhide multiple times; two times in the back and one in the front. When Bumblebee combat Sentinel alone. After retreating, Sentinel Prime goes to the backdoor of the NEST Base and destroy every weapons that stands in his way and the Director asks him what is he doing. After answering the Directors question he destroys many helicopters as possible. When he left the NEST Base, Ironhide crumbles to dust.