Overview
EN 24159:1989 (identical to ISO 4159:1978) specifies a potentiometric method for the determination of manganese content in ferromanganese and ferrosilicomanganese alloys. The procedure is designed for high‑manganese ferroalloys (typical manganese content 55–95 % m/m) and uses a controlled redox titration with potassium permanganate in a pyrophosphoric medium, with the endpoint detected potentiometrically.
Key topics and technical requirements
- Analytical principle: oxidative titration of manganese in a pyrophosphoric medium; potentiometric detection of the KMnO4 endpoint (sudden potential increase ≥ 100 mV).
- Sample preparation: precise test portion (small, highly weighed sample) is attacked/dissolved using a combination of hydrochloric, hydrofluoric and perchloric acids (procedures differ slightly for ferromanganese and ferrosilicomanganese).
- Reagents: analytical‑grade acids, potassium permanganate (recrystallized and standardized), sodium pyrophosphate (pyrophosphoric medium), and controlled dilutions of HCl for pH adjustment.
- Apparatus: volumetric glassware, reflux condenser, sintered‑glass filters, magnetic stirrer, pH meter, and potentiometer or equivalent electrometric setup (platinum and calomel electrodes).
- Procedure highlights:
- Acid digestion with controlled heating until perchloric fumes/oxidation products form.
- Dilution and pH adjustment to about 6.5–7 using diluted HCl.
- Potentiometric titration with standardized KMnO4; a blank determination and parallel standardization of KMnO4 are required.
- Quality and reporting: recommended duplicate titration on a second aliquot; stated reproducibility for experienced operators: 95% confidence limits ≈ ±0.20 %.
- Safety note: special precautions with perchloric acid when heated (fuming) and with hydrofluoric acid.
Applications and users
- Practical for and composition verification in ferroalloy production and processing.
