Terfenol-D powder is a magnetostrictive material that consists of a rare earth metal (terbium), iron, and dysprosium. The material is known to be sensitive to oxidation and can corrode in air. Therefore, it is recommended to handle the Terfenol-D powder in an inert atmosphere such as a glove box or a nitrogen-filled chamber to prevent any oxidation. Keeping it in an air-tight container may not provide adequate protection from oxidation.