Overview
ISO 5997:1984 specifies two standard methods for the determination of silicon content in chromium ores and concentrates: a molecular absorption spectrometric method (Method A) and a gravimetric method (Method B). The standard defines scope, principle, required reagents and apparatus, detailed procedures, spectrometric measurement (Method A), calibration and expression of results. It is intended to provide repeatable, validated laboratory techniques for reporting silicon (Si) content in chromium raw materials.
Key topics and technical requirements
- Two methods, by Si range
- Method A - Molecular absorption spectrometric method: applicable to samples with 0.05 to 0.5 % (m/m) Si. Measurement wavelengths: 810 nm or 620–640 nm.
- Method B - Gravimetric method: applicable to samples with 0.5 to 15 % (m/m) Si.
- Analytical principle
- Method A: fusion of sample, dissolution, reaction of silicic acid with ammonium molybdate to form silicomolybdate, reduction to a blue complex and spectrometric measurement.
- Method B: sample decomposition (fusion with sodium peroxide or wet digestion with acids), separation and ignition of silicic residues, treatment with HF/SO4 and reweighing.
- Reagents and standards
- Defined reagents such as fusion mixture (sodium carbonate/sodium tetraborate/potassium nitrate), ammonium molybdate, hydrochloric/perchloric/hydrofluoric acids, and a silicon standard solution.
- Apparatus
- Platinum crucibles, spectrometer with selectable wavelengths, pH meter, muffle furnace and appropriate fusion equipment.
- Calibration, blanks and expression of results
- Calibration graph preparation for Method A; blank tests through all stages; formulae for converting absorbance or mass difference to percent Si. Method B includes prescribed permissible tolerances for duplicate determinations.
- Safety and handling
- Explicit cautions for toxic and corrosive reagents (perchloric acid, hydrofluoric acid, chromyl chloride) and requirement for fume cupboards and protective equipment.
Practical applications and users
- Laboratories performing chemical analysis of chromium ores and concentrates for quality control, mine output certification, smelter feedstock assessment and metallurgical process control.
- Industrial quality assurance teams in mining, ferrochrome production and alloy manufacturing where accurate Si specification affects processing and product properties.
- Regulatory and inspection bodies requiring standardized test methods for material certification and trade.
Related standards
- ISO 5997 refers users to other standards for context and sampling: ISO 6629 (methods of chemical analysis) and notes that sampling/sample preparation standards (e.g., ISO 6153, ISO 6154) are relevant. Users should consult these documents when implementing ISO 5997 procedures.
Keywords: ISO 5997:1984, chromium ores, silicon determination, molecular absorption spectrometric method, gravimetric method, spectrometric measurement, fusion, ammonium molybdate, calibration.