Overview
ISO 7693:1984 specifies a cinchonine gravimetric method for the determination of tungsten content in ferrotungsten. The method is applicable to ferrotungsten materials with tungsten contents between 70 and 90 % (m/m). The standard defines principle, reagents, apparatus, sample preparation, step‑by‑step procedure, expression of results and requirements for the test report. An annex provides a spectrometric procedure to determine molybdenum, which can interfere with the gravimetric result.
Key topics and technical requirements
- Scope: Designed for ferrotungsten alloys with 70–90% tungsten by mass.
- Principle: Dissolve sample (HF, HNO3, H2SO4), evaporate, fuse residue with sodium carbonate and diboron trioxide, dissolve fused mass and precipitate tungsten as a cinchonine–a‑benzoin oxime complex; ignite to impure tungstic oxide and weigh.
- Interference correction: If molybdenum is present, determine it spectrometrically (annex) and correct the tungstic oxide mass. Spectrometric measurements are made near 460 nm.
- Reagents & apparatus: Standard specifies reagent grades and concentrations (HF, HNO3, HCl, H2SO4, cinchonine, a‑benzoin oxime, tin(II) chloride, ammonium thiocyanate, etc.) and typical lab equipment including spectrophotometer/spectrometer.
- Sample & test portion: Powder passing 160 µm sieve prepared per ISO 3713; typical test portion ~1.000 g.
- Quality controls: Includes blank and control tests, and procedures for filtration, ignition (temperature limit to avoid volatilization), fusion, and calculation.
- Result expression: Tungsten content calculated from mass differences of impure tungstic oxide and residues with a conversion factor (standard gives the formula and factor).
- Reporting: Test report must reference ISO 7693, identify sample, report result and method, note unusual features and any deviations from the standard procedure.
Applications and users
- Who uses it: Metallurgical analysts, quality control chemists, ferroalloy producers, independent testing laboratories and regulatory bodies assessing ferrotungsten composition.
- Practical uses:
- Certification and quality control of ferrotungsten batches.
- Incoming material inspection for steel and alloy manufacturing where tungsten content affects performance.
- Dispute resolution or validation testing when compositional accuracy is required.
- Benefits: Provides a standardized, reproducible gravimetric approach with defined controls and a correction path for molybdenum interference-useful where instrumental methods are not available or for confirmation of spectrometric results.
Related standards
- ISO 3713 - Ferroalloys: sampling and preparation (referenced for sample preparation).
- Developed by ISO/TC 132 (Ferroalloys); consult current ISO catalog for any revisions or newer analytical standards covering tungsten determination or instrumental alternatives.
Keywords: ISO 7693:1984, ferrotungsten, tungsten determination, cinchonine gravimetric method, molybdenum interference, spectrometric determination, tungsten content.