ISO 11436:1993

Overview

ISO 11436:1993 specifies a curcumin molecular absorption spectrometric method for the determination of total boron content in nickel and nickel alloys. The method covers boron concentrations in the range 4 g/t to 240 g/t (ppmw). The analytical principle is dissolution of a test portion, thermal decomposition of resistant boron compounds by fuming with phosphoric and sulfuric acids at ≥290 °C, formation of a boron–curcumin complex in an acetate/sulfuric medium, and absorbance measurement at 543 nm.

Key topics and technical requirements

• Scope: Applicable to nickel and nickel alloys with total boron 4–240 g/t.
• Sample prep: Typical test portions 0.25–0.5 g depending on expected boron level; millings/drillings normally used; cleaning recommended if contaminated with oil.
• Chemical digestion: Dissolve in hydrochloric and nitric acids; decompose boron nitrides and other resistant compounds by fuming with phosphoric + sulfuric acids at not less than 290 °C for 30 min.
• Colour development: Form boron–curcumin complex in buffered acetic/sulfuric medium (acetate buffer + curcumin reagent); timing and reagent order are critical for reproducible colour.
• Spectrometry: Use a molecular absorption spectrometer set to 543 nm, 2 cm cells, spectral bandwidth ≤10 nm, wavelength accuracy ±2 nm. Blank and compensating solutions are required; sodium fluoride is used for compensation.
• Calibration & quantification: External calibration using boron standards; net absorbance plotted vs. micrograms of boron.
• Precision & validation: Method validated by interlaboratory testing (nine laboratories) and evaluated per ISO 5725. The absorbance repeatability for the highest-absorbance solution is specified (relative deviation ≈ 0.3% or better).
• Apparatus: Quartz conical flasks, optional aluminium alloy heating block (examples in informative Annex A), volumetric plastic flasks, and typical lab glassware rinsed with acetic acid.

Applications

• Quality control and chemical analysis in nickel metallurgy, stainless and specialty alloy production.
• Certification and verification of boron content in raw materials, finished alloys and reference materials.
• Research laboratories studying trace boron effects on alloy properties or corrosion behavior.

Who should use this standard

• Analytical chemistry laboratories in metal production and testing.
• Metallurgists and process control engineers responsible for alloy specification compliance.
• Accreditation and certification bodies needing a recognized method for boron determination in nickel alloys.

Related standards and notes

• References ISO 5725 for precision (repeatability/reproducibility) evaluation.
• Prepared by ISO/TC 155 (Nickel and nickel alloys), Subcommittee SC 4 (Analysis).
• Note: possible chemical interference from rhenium is identified in the standard; users should consider matrix interferences during method application.

Keywords: ISO 11436:1993, boron determination, nickel alloys, curcumin spectrometric method, 543 nm, molecular absorption spectrometry.