Al合金中のSi迅速容量定量法

Abstract

Normally Si in Al alloy and Al-Si alloy is determined gravimetrically or, in certain cases, colorimetrically, but the former is a time-consuming method and the latter is not suitable for high silicon alloy. The method presented here consists of formation of K2SiF6 and its titration with alkali according to the following new analytical procedure. Transfer 0.2 to 0.5 g of the sample to a 300 mL polyethylene conical beaker. Add 60 mL of hot (1:1) HNO3 and 5 mL of HF. Dissolve the sample without heating and dilute with water to 100 mL. Cool rapidly to 20°C and add KNO3 until the solution is saturated. Filter through No. 5A filter paper with a polyethylene funnel. Wash with cold washing solution (dissolve 150 g. KNO3 in 850 mL of distilled water, add 150 mL of alcohol, and then cool to below 20°C until the washings are acid-free. Transfer the paper and the precipitate to a 500 mL conical beaker, add 200 mL of carbon dioxide-free boiling water, shake thoroughly, and titrate while still hot with NaOH solution, using 5 drops (3%) of phenolphthalein indicator, until a faint pink color appears. Deduct the blank from the main titration. 1 mL of 0.5 N NaOH\fallingdotseq0.3508%Si. With Al alloys, this method is only interfered by Ti, Ta and Zr; consequently, as long as these elements do not exceed 0.5% of the sample, succeessful results will be always obtained. Therefore this method can be applied to a number of Al alloys and Al-Si alloys, Furthermore, this method is more rapid, simple and accurate than the usual method and the whole procedure can be carried out within 50 minutes. Hence, this method is a very suitable method for the purpose of industrial routine analysis.