Separation and Determination of Small Quantities of Aluminum in Steel

A method is described for determining small amounts of aluminum (0.01 to 0.3 percent) in stainless and carbon steels. A perchloric-sulfuric acid solution of the steel is electrolyzed in a mercury cathode cell to remove most of the iron, and an extraction with chloroform is made to remove elements such as aluminum, residual iron, and titanium as cupferrates from a solution buffered at pH 3.5. These elements are converted from cupferrates to perchlorates; all except aluminum are then extracted as cupferrates with chloroform from 4 N hydrochloric acid. Aluminum in the acid solution is determined photometrically with aluminon (ammonium aurintricarboxylate) at a wave length of approximately 540 millimicrons. An accuracy of ± 0.005 percent aluminum is indicated.