Removing impurities from solid metals - by heating and ion bombardment in very hard vacuum

摘要

Impurities are removed from the interior of a metal which has a temp. region with negative segregation enthalpy below its m.pt. The metal is heated to below its m.pt. so the impurities diffuse to the surface, from where they are removed by sputtering a thin surface layer via ion bombardment. Only a part of the surface is pref. subjected to ion bombardment; and the pref. solid is (a) Nb, heated to 745-895 degrees K. to remove oxygen; or (b) iron or its alloys, heated to 535 degrees - 925 degrees K to remove carbon. Used also for the removal of H2, N2, O2, H2O, CO, CyHx, from e.g. Nb, Ta, Fe or Cu alloys. The temp. required is low when compared with conventional methods for removing impurities, so that e.g. properties obtd. by cold work are not impaired as the temp. is below the recrystallisation tmep.; and interstitial impurities are easily removed.