1. R. Höhn, etc., Met A 7, 230477 (Bi, Cd, Ga, In, Tl in Z.R. Al)
2. M. B. Altman, Met A 7, 430194 (Impurities removal)
3. J. Kaczor, etc., WAA 8, 240001 (Z.R. with Ag tracer)
4. A. Tutelea, etc., Met A 8, 430110 (Electrorefined Al)
5. W. D. Hannibal, etc., WAA 8, 240007 (Zone refined)