The determination of mobile nitrogen in steel using an ammonium ion-selective electrode

Abstract

An absorption cell containing an ammonium ion-selective electrode has been constructed and used for the determination of mobile nitrogen in steel; this nitrogen is released as ammonia when the steel is heated at 500 °C in a stream of hydrogen. The cell was used in conjunction with a digital voltmeter and a recorder in order to obtain a continuous record of the progress of the reaction between mobile nitrogen and hydrogen. Results are presented for the determination of 0·0005–0·0108 per cent. of mobile nitrogen in 10 steels using the new equipment and are compared with those obtained by using a spectrophotometric finish based on indophenol blue. The method, with relative standard deviations of 0·0001–0·0003 per cent., is more precise than that with the spectrophotometric finish, with relative standard deviations of 0·0002–0·0006 per cent.