A Rapid Volumetric Method for Determination of Si in Al-alloy (Quinoline Method)

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  • Al-Al合金中のSi迅速容量定量法（キノリン法）
  • Al-Al ゴウキン チュウ ノ Si ジンソク ヨウリョウ テイリョウホウ キノリンホウ

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Abstract

The use of (C9H7N)4H4 (SiO4·12MoO3) was studied for precipitation of Si as quinoline complex by Wilson, Duval and Brabson for the first time. But the extremely attractive new method based on the precipitation is not widely applied to the routine analysis even now. Hereupon, I made studied in order to apply the method to the determination of Si in Al-alloy. Namely, Si in Al-alloy is first converted into Na2SiO3 by attacking with NaOH, and then made acidic with HCl. Practically all of the Si remains in the solution as H4SiO4, which reacts with Na2MoO4 to form a yellow H8[Si(Mo2O7)6] in pH 1.10 acid solution as follows: H4SiO4+12MoO3+3H2O=H8[Si(Mo2O7)6]·H2O. The solution, made more acidic with HCl to prevent the precipitation of quinoline molybdate, is treated with C9H7N, and the precipitate of quinoline complex (C9H7N)4H4(SiO4·12MoO3) is quantitatively determined. When this complex is dissolved in excess NaOH, it is broken down to C9H7N, H4SiO4 and H2MO4. C9H7N and H4SiO4 are too weak to react with NaOH, and so only H2MoO4 reacts with NaOH according to the following equation: (C9H7N)4H4(SiO4·12MoO3)+24NaOH=4C9H7N+H4SiO4+12H2O+12Na2MoO4. The excess of NaOH may be determined, and each equivalent of NaOH used in reaction corresponds to 1/24 of the molecular weight of Si. This method is more rapid in the procedure than JIS gravimetric method, because the whole procedure may be carried out within 70 minutes. Furthermore, it was found that the standard deviation was 0.006 to 0.02, which favorably compares that (0.016 to 0.060) in JIS gravimetric method, when the similar samples of about 0.40 to 13.0%Si were used. In the case of alloyed Al, only interference by P, As and Ge has to be considered, so it can be applied to analysis of most of Al-alloys. Therefore, this method is very suitable for industrical routine analysis.

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