Overview
EN 27520:1991 specifies a standardized method for the determination of cobalt content in ferronickel using flame atomic absorption spectrometry (AAS), based on ISO 7520:1985. This method applies to cobalt concentrations ranging from 0.025% to 2.5% by mass. It provides a detailed procedure including reagents, apparatus, sampling, sample preparation, and calculation of results. EN 27520:1991 facilitates precise and reproducible chemical analysis critical for quality control in nickel alloy production.
Key Topics
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Scope and Range
The standard covers ferronickel samples with cobalt content between 0.025% and 2.5% (m/m).
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Analytical Principle
Cobalt is measured using flame atomic absorption spectrometry at a wavelength of 240.7 nm with an air-acetylene flame. Samples are dissolved using a nitric acid-hydrochloric acid mixture, with silica removed by perchloric acid treatment and filtration. Lanthanum solution is added to eliminate interference effects for accurate measurement.
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Reagents and Solutions
Utilizes high-purity chemicals such as nitric acid, hydrochloric acid, perchloric acid, hydrofluoric acid, and lanthanum chloride. Standard cobalt solutions and nickel plus iron matrix solutions are prepared to calibrate the spectrometer.
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Sample Preparation and Sampling
Samples are typically millings, drillings, or granules requiring no further preparation, though cleaning is prescribed if contamination by oil or grease is suspected. The test portion size is typically around 4 grams.
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Apparatus Requirements
Includes an atomic absorption spectrometer equipped with a cobalt hollow cathode lamp, standard laboratory glassware per ISO specifications, and PTFE beakers for high silicon samples.
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Calibration and Measurement
Calibration curves are established from standard solutions prepared with nickel-iron matrix. Measurement involves aspirating test solutions, blanks, and calibration standards into the flame to record absorbance. Calibration graphs ensure results fall within linear response ranges.
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Calculation and Expression of Results
Cobalt content is calculated from absorbance readings using a formula accounting for dilution factors, blank corrections, and sample mass. Results are expressed as a mass percentage, providing essential data for metallurgical quality assurance.
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Precision and Repeatability
Interlaboratory testing confirmed the method’s reliability, showing consistent repeatability and reproducibility across cobalt concentration ranges typical of ferronickel.
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Safety Notes
Handling of hazardous reagents like hydrofluoric acid and perchloric acid requires caution and use of proper fume hoods due to their corrosive and oxidizing properties.
Applications
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Quality Control in Ferroalloy Production
Ensures consistent cobalt levels in ferronickel alloys, critical for performance in stainless steel and specialty alloys.
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Chemical Analysis Laboratories
Provides a validated procedure for routine cobalt testing in ferronickel samples, enabling traceability and comparability of results worldwide.
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Regulatory Compliance
Supports compliance with material specifications requiring precise cobalt quantification, aiding in certification and quality assurance processes.
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Research and Development
Used in metallurgical research to characterize alloy compositions and optimize manufacturing processes involving ferronickel.
Related Standards
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ISO 7520:1985
The international standard upon which EN 27520:1991 is based, specifying the cobalt determination method in ferronickel.
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ISO 385/1, ISO 648, ISO 1042
Standards covering laboratory glassware essential for accurate volumetric measurements in the analytical process.
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ISO 5725
Defines the precision and repeatability requirements for chemical test methods, relevant for method validation and quality control.
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ISO 6352
Details determination of nickel content in ferronickel by gravimetric method, often performed in conjunction with cobalt analysis.
By following EN 27520:1991, laboratories can ensure accurate, repeatable, and internationally comparable cobalt content measurements in ferronickel. This standard supports quality assurance and material verification throughout the ferroalloy industry, enabling reliable control of alloy composition critical to downstream metal production.