Abstract
The simultaneous determination of copper, lead and zinc in high purity aluminum was carried out by a square-wave polarographic method.
A square-wave polarographic method which can be carried out simply and rapidly and can avoid the contamination from the reagents has been developed for the determination of impurities such as copper, lead and zinc in high purity aluminum. A squarewave polarograph of Yanagimoto Mfg. Co. type PA 201 was used and the mercury pool at the bottom of the electrolysis cell was used as the anode. The mercury flow-rate and drop time of the capillary were 2.70 mg sec-1 and 4.05 sec, respectively. The span voltage was 2.0 V, the gate range was -3 to 8 and the time constant was 5-5.
The procedures and the results of each method were as follows;
Method A : 1.0 g of high purity aluminum (99.99% or 99.999%) was heated and dissolved in a mixed solution containing 40 ml of 6N hydrochloric acid, 2 ml of 3% hydrogen peroxide and 8 ml of 0.1% mercury (II) chloride.
It was found that a 1.0 g amount of sample could be dissolved within 913 min. After the metal was dissolved, the solution was transferred to a 100 ml volumteric flask diluted with distilled water to the mark, and a portion of this solution was used as the sample. Well-defined waves which corresponded to these metals were observed. Copper, lead and zinc could be determined from the wave which appeared at - 0.26 V, 0.48 V and -1.05 V, vs. Hg-pool respectively.
Method B: 1.0 g of the sample metal was heated and dissolved in 15 ml of 15% sodium hydroxide solution, and then 35 ml of nitric acid (1:1) was added. The solution was transferred to a 100 ml volumeteric flask and made up to the volume with distilled water. A portion of this solution was used for the polarographic experiments. In this method, the waves of copper, and zinc were observed at the same potentials as in method A, but the wave of lead appeared at -0.65 V. It was concluded that these metals in high purity aluminum can be also determined by this method. The analysis by method B was prepared to compare with method A. The analysis by method A could be carried out within 40 min. The impurities determined by method A and method B are given in the accompanying table.
