GB/T 20975.21-2020 in English
VALIDMethods for chemical analysis of aluminium and aluminium alloys—Part 21:Determination of calcium content
- Issued on:2020-09-29
- Implemented on:2021-08-01
- File Format:PDF
- Delivery:Via email within 1~3 business days
$156.00
《GB/T 20975.21-2020铝及铝合金化学分析方法 第21部分：钙含量的测定》由TC243（全国有色金属标准化技术委员会）归口，TC243SC1（全国有色金属标准化技术委员会轻金属分会）执行，主管部门为中国有色金属工业协会。
Introduction
Interpretation of the core content of the standard
| Method | Measurement range | Precision (repeatability) | Main improvements |
|---|---|---|---|
| Flame atomic absorption spectrometry | 0.010%-1.00% | 0.002%-0.07% | Acid dissolution replaces alkali dissolution, extending the measurement range |
| Na2EDTA titration | 4.00%-30.00% | 0.24%-0.40% | Adding a secondary separation step |
Evolution of key technologies
Compared with the 2008 version, the main improvements of the new version of the standard include: expansion of the measurement range (the upper limit of the flame method is increased from 0.30% to 1.00%), standardization of safety warnings, optimization of sample pretreatment (using acid dissolution method to reduce blank value), and update of precision data (flame method RSD≤1.0%).
Key points of experimental operation
Key steps of flame atomic absorption spectrometry
1. Use copper salt-8-hydroxyquinoline composite masking system
2. Eliminate matrix effect by standard addition method
3. Use air-acetylene rich flame at 422.7nm wavelength
Precautions for Na2EDTA titration
1. Two separations are required (sodium hydroxide precipitation + copper reagent complexation)
2. The endpoint is determined by calcium carboxylate indicator (pH≥12)
3. Strontium content needs to be determined separately and corrected (coefficient 0.4574)
Implementation suggestions
1. For low calcium content (<0.1%), flame atomic absorption method is preferred
2. For high calcium content samples, gradient dilution verification is recommended
3. The laboratory should establish a traceability system for calcium oxide standard substances
4. Regularly calibrate the atomic absorption spectrometer's characteristic concentration (≤0.20μg/mL)
Standard application scenarios
This method is applicable to the quality control of aluminum alloy castings, aerospace materials and electrical aluminum materials, especially for the process monitoring needs of calcium as a grain refiner or deoxidizer.
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