US Patent 7674427 Rare earth metal member and making method

By using a rare earth metal having a minimal content of impurity metal element, machining it into a member and cleaning with an organic acid-base capping agent, there is obtained a rare earth metal member composed entirely of a rare earth metal and containing not more than 100 ppm of impurity metal element in a sub-surface zone, which member is characterized by a high surface purity, a large grain size, minimized grain boundaries, and improved halogen resistance or corrosion resistance.