Al合金中のSi迅速容量定量法

抄録

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.