A simple and reliable method has been developed for the state analysis of small amount of aluminum in steel. The procedure is as follows: 1. Separation of aluminum compound
(a) The steel sample covered with close-texture filter peper as a diaphragm, connected as an anode, is dissolved into 130ml of 1% NaCl-5% EDTA electrolyte (pH 6-7) with current density of 50mA/cm2 for 2hr. Remove the anode, and residue is collected into filter paper using methanol. Add 50ml of 4% iodine methanol solution to the residue and warm at 60× for 30 min.
(b) Filter and wash with methanol. Add 10ml of HNO3 and 10ml of HClO4 to the filterate and evaporate to dense white fumes. Cool, dilute to 100ml, and determine aluminum in cementite in accordance with section 2.
(c) Transfer a fifth parts of the electrolyte to a beaker. Add 15ml of HNO3 and 10ml of HClO4 and evaporate to dense white fumes. Cool, dilute to 100ml, and determine aluminum as solid solution in accordance with section 2.
(d) Transfer the paper and residue (paragraph (b)) to a beaker, add 30ml of HNO3 (1: 1) and 5ml of H2O2 and boil for 10min.
(e) Filter and wash with water. Add 10ml of HClO4 to the filterate and evaporate to dense white fumes. Cool, dilute to 100ml, and determine aluminum as AlN in accordance with section 2.
(f) Transfer the paper and residue (paragraph (e)) to a platinum crucible, heat until the carbon is gone. Add 1g of Na2CO3 and ignite for 20min at 900 to 1000×C. Cool, dissolve in 30ml of water containing 5m/ of HCl. Add 10m/ of HClO4 and evaporate to dense white fumes. Cool, dilute to 20ml. Filter through into a 100ml volumetric flask, and wash with water until to the mark, and determine aluminum as oxide in accordance with section 2.
2. Photometric determination of aluminum.
Transfer 5ml of each of the solutions of section 1 (b), (c), (e) and (f) to 50 ml volumetric flasks. To each, add 10 ml of water and 5 ml of 0.1% Eriochrome Cyanine R solution and allow to stand for 2 to 3 min. Add 3 ml of 2% mercaptoacetic acid and 10 ml of buffer solution and dilute to 50 ml. Warm at 80×C for 1min. Cool and measure the absorbance against blank solution at 590 mu.