ISO 4829-1:2018

Overview

ISO 4829-1:2018 - Part 1 of the ISO 4829 series - specifies a reduced molybdosilicate spectrophotometric method for the determination of total silicon in steel and cast iron. The procedure is applicable for silicon mass fractions between 0.05 % and 1.0 %. It describes sample dissolution, treatment of insoluble residue, colour development, calibration and spectrophotometric measurement of the reduced blue silicomolybdate complex.

Key topics and technical requirements

• Scope and range: Determination of total silicon in steel and cast iron for 0.05–1.0 % Si.
• Analytical principle: Dissolve sample → oxidize to form yellow molybdosilicate → selectively reduce to a blue complex with ascorbic acid → measure absorbance at about 810 nm.
• Sample preparation: Test portion ~0.5 g of fine chips/turnings; sampling per ISO 14284.
• Dissolution & residue treatment: Use sulfuric/nitric or hydrochloric/nitric acid mixtures for dissolution; fuse acid‑insoluble residue with sodium peroxide and return to the filtrate.
• Interference control: Oxalic acid is added and sulfuric acid concentration increased to limit interferences (e.g., phosphorus, arsenic, vanadium).
• Reagents & water quality: Analytical grade reagents; water per ISO 3696 (grade 2); avoid demineralized ion-exchange water that can contain colloidal silica.
• Apparatus & measurement: Class A volumetric glassware (ISO 648, ISO 1042), polypropylene or PTFE containers, zirconium crucibles, and a spectrophotometer with spectral bandwidth ≤10 nm, wavelength accuracy ±2 nm and measurement at ~810 nm.
• Quality controls: Blank tests with high‑purity iron, freshly prepared standards, and establishment of a calibration curve using silicon standard solutions.

Practical applications and users

• Quality control laboratories in steel mills, foundries, and metallurgical plants for routine silicon analysis.
• Independent materials testing and chemical analysis laboratories verifying alloy composition.
• Research labs conducting comparative studies of silicon in ferrous alloys.
• Procurement and inspection teams ensuring compliance with material specifications that specify silicon limits.

Benefits:

• A standardized, validated spectrophotometric method for consistent, comparable silicon results.
• Clear guidance on reagents, apparatus, and interference management for reliable routine analysis.

Related standards

• ISO 14284 - Sampling and preparation of samples for chemical composition analysis (steel & iron).
• ISO 3696 - Water for analytical laboratory use.
• ISO 648 / ISO 1042 - Laboratory glassware (pipettes and volumetric flasks).

Keywords: ISO 4829-1:2018, silicon determination, steel, cast iron, spectrophotometric method, reduced molybdosilicate, silicon 0.05–1.0%, metallurgical quality control.