Overview
ISO 1118:1978 specifies a spectrophotometric method for determining titanium content in aluminium and aluminium alloys. The method employs the chromotropic acid spectrophotometric technique to measure titanium concentrations ranging from 0.005% to 0.3% by mass. This standardized procedure provides detailed instructions on reagents, apparatus, sampling, test execution, and result reporting, ensuring accuracy and repeatability in titanium analysis of aluminium materials.
This standard is not fully applicable to aluminium alloys containing more than 1% silicon and includes an annex addressing necessary modifications for such cases.
Key Topics
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Scope and Applicability
Applicable to aluminium and aluminium alloy products with titanium content between 0.005% and 0.3% (m/m).
Not fully applicable to alloys with silicon >1% (m/m).
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Principle of the Method
- Sample is attacked with sodium hydroxide, then acidified with nitric and sulfuric acids.
- Iron (III) is reduced by ascorbic acid.
- Titanium forms a colored complex with chromotropic acid at pH 2 - 2.5.
- The complex’s absorbance is measured spectrophotometrically at approximately 470 nm wavelength.
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Reagents and Solutions
High-quality analytical grade reagents are used including:
- Sodium hydroxide solutions
- Nitric acid and sulfuric acid of specified normalities
- Chromotropic acid solution
- Potassium permanganate and sodium sulfite for oxidation-reduction steps
- Ascorbic acid for iron reduction
- Buffer solution to maintain pH for optimal color development
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Apparatus Requirements
- Precision pH meter with minimum 0.02 unit sensitivity and glass electrode
- Spectrophotometer capable of measurements near 470 nm
- Standard laboratory glassware for controlled volumetric procedures
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Sampling and Sample Preparation
Samples should be prepared as chips or shavings with thickness ≤ 1 mm obtained by milling or drilling. Laboratory test samples of approximately 1 g are weighed with 0.001 g precision.
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Test Procedure
- Sample dissolution and pH adjustment guided by pre-established calibration curves.
- Establishment of calibration standards using titanium standard solutions.
- Addition of reagents following a precise sequence to develop the titanium-chromotropic acid complex.
- Spectrophotometric absorbance measurement and blank test for correction.
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Result Expression
Titanium content is expressed as a mass percentage derived from the absorbance of the complex relative to calibration standards.
Applications
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Quality Control in Aluminium Manufacturing
Ensures precise quantification of titanium in aluminium alloys to meet specifications in aerospace, automotive, and construction industries.
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Material Certification and Compliance
Supports standardized testing for alloy certification to international benchmarks, facilitating global trade.
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Research & Development
Used in metallurgical laboratories analyzing alloy compositions for new material development and process optimization.
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Environmental and Safety Monitoring
Verification of titanium content to ensure alloy stability and performance, indirectly contributing to safety and sustainability.
Related Standards
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ISO/R 1118-1969
The previous recommendation replaced by ISO 1118:1978, delineating earlier methodology for titanium determination.
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ISO Standards on Aluminium Alloys
Other ISO standards addressing chemical composition, mechanical testing, and analytical methods for aluminium and its alloys.
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Spectrophotometric Analytical Standards
Guidelines and methods on spectrophotometric determination of metals, useful for cross-reference in laboratory practices.
Keywords: ISO 1118, titanium determination, aluminium alloys, spectrophotometric method, chromotropic acid, titanium analysis, aluminium titanium content, spectrophotometry, metal alloy testing, chemical analysis standards.
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