Abstract
A rapid and accurate method was developed for the determination of silicon by diffusion method. The recommended procedure is presented as follows.
To a weighed sample (Si :075μg) in platinum crucible, minimum of nitric (1+1) or hydrochloric acid (1+1) is added, followed by 1.0 ml of sulfuric (1+1) or perchloric acid. After the reaction and decomposition is accomplished, evaporate until white fumes appear. The crucible is cooled to room temperature, and 1.0 ml of water is added, followed by 0.6 ml of 25% hydrofluoric acid. The crucible is immediately covered with a platinum lid coated with 1.0 ml of 70% sodium hydroxide solution and kept at 110120°C for 90 minutes. During this period, silicon is volatilized as the tetrafluoride from a perchloric or sulfuric acid medium and absorbed in the sodium hydroxide on the inner surface of the lid. The sodium hydroxide solution which has absorbed the silicon is dissolved in 40 ml of 4% boric acid solution and neutralized with sulfuric acid (1+3) using pH test paper and further 1.0 ml of sulfuric acid (1+3) is added. The solution is diluted to about 50 ml with water, and 5.0 mlof 8% ammonium molybdate solution is added, and keep it about 25°C for 10 minutes. To the resulting solution, 3 ml of 20% tartaric acid solution is added, the solution is mixed, and 3 ml of ANS reducing solution is added. The solution is diluted to 100 ml with water. After the molybdenum blue color is developed, the absorbency is measured at 815 nm using 1-cm cells. After deducting the absorbency of a corresponding blank, the silicon content is calculated from the standard calibration curve.
The recovery of silicon was about 95% by this method and the relative errors stood within 4%. The present method was applied to the determination of 0.0080.17% silicon in aluminum and steels, and the analytical results obtained agreed with the standard values within experimental error. The elimination of most interfering ions in the analysis of silicon was accomplished by this procedure.
