Determination of Microamounts of Carbon in Various Metals and Alloys by the Combustion-Nonaqueous Titrimetric Method

Abstract

Microamounts of carbon (7∼600 ppm) in ferrous and non-ferrous metals and alloys were determined by the combustion-nonaqueous titrimetric method.
The carbon dioxide liberated by the combustion of a sample was absorbed with dimethyl-formamide (DMF) containing monoethanolamine and then the absorbent was titrated with the standard benzene-methanol solution of tetra-n-butylammonium hydroxide (0.007–0.002 M). The end point of the titration was located either visibly by using thymolphthalein as an indicator or potentiometrically by using a couple of platinum and calomel (containing DMF) electrodes. Pure benzoic acid was used as the standard substance for the standardization.
Many improvements were given on both the conbustion apparatus and the procedure.
Microamounts of carbon in various samples were determined by the proposed method. The are: plain carbon and high purity ferritic stainless steels (0.05∼0.002%C), Inconel X-750 (0.027%C), copper alloys (20∼30 ppm C), tantalum powder (40 ppm C) and high purity metallic uranium (7 ppm C). All results were quite satisfactory and indicate that the proposed method was adaptable for the determination of carbon less than 100 ppm in various samples without use of any standard samples or calibration curves.