GB/T 223.8-2025 Iron,steel and alloy—Determination of aluminium content—Titrimetric method and spectrophotometric method English, Anglais, Englisch, Inglés, えいご
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ICS 77.080.01
CCS H 57
National Standard of the People's Republic of China
GB/T 223.8-2025
Replaces GB/T 223.8-2005,GB/T 223.9-2008
Iron, steel and alloy - Determination of aluminium content - Titrimetric method and spectrophotometric method
Issue date: 2025-08-29 Implementation date: 2026-03-01
Issued by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China
the Standardization Administration of the People's Republic of China
Contents
Foreword
1 Scope
2 Normative References
3 Terms and Definitions
4 Method 1: Sodium Fluoride Separation-EDTA Titrimetric Method
5 Method 2: Potentiometric Titration Method
6 Method 3: Spectrophotometric Method (Sodium Carbonate Separation-Diphenylcarbazide Spectrophotometry)
7 test method
Iron,steel and alloy - Determination of aluminium content - Titrimetric method and spectrophotometric method
Warning—Personnel using this document shall have practical laboratory experience. This document does not address all potential safety issues. Users are responsible for implementing appropriate safety and health measures and ensuring compliance with relevant national regulations.
1 Scope
This document describes methods for determining aluminum content in iron, steel, and alloys using:
Method 1 (Sodium Fluoride Separation-EDTA Titrimetric Method): applicable to iron, steel, and alloys with aluminum content of 0.50%–10.00%.
Method 2 (Direct Chromazurol S Photometric Method): for acid-soluble aluminum in iron, steel, and alloys (0.050%–1.00%).
Method 3 ( Cupferron Separation-Chromazurol S Spectrophotometric Method): for aluminum in iron, steel, and alloys (0.015%–0.50%).
2 Normative References
The following referenced documents are indispensable for the application of this document. For dated references, only the cited version applies; for undated references, the latest version (including amendments) applies.
GB/T 6379.1: Accuracy (Trueness and Precision) of Measurement Methods—Part 1: General Principles and Definitions.
GB/T 6379.2: Accuracy (Trueness and Precision) of Measurement Methods—Part 2: Basic Methods for Repeatability and Reproducibility of Standard Measurement Methods.
GB/T 6682: Water for Analytical Laboratory Use—Specifications and Test Methods.
GB/T 7729: General Rules for Spectrophotometric Methods in Chemical Analysis of Metallurgical Products.
GB/T 12805: Laboratory Glassware—Burette.
GB/T 12806: Laboratory Glassware—Volumetric Flask.
GB/T 12808: Laboratory Glassware—Pipette.
GB/T 20066: Steel and Iron—Sampling and Preparation of Samples for Chemical Composition Determination.
3 Terms and Definitions
No terms or definitions require clarification in this document.
4 Method 1: Sodium Fluoride Separation-EDTA Titrimetric Method
4.1 Principle
The sample is dissolved in acid. Iron, chromium, nickel, manganese, and other elements are complexed with ammonium citrate and ammonium oxalate. Aluminum is precipitated as aluminum fluoride using sodium fluoride at pH 4–5, separating it from other elements. The precipitate is dissolved in a hydrochloric acid-boric acid mixture, then treated with nitric acid and perchloric acid to destroy filter paper and remove fluoride.
Excess EDTA is added to the slightly acidic solution.
At pH 6, using xylenol orange as an indicator, the excess EDTA is titrated with a zinc standard solution.
Fluoride ions react with aluminum to release EDTA, which is then titrated with zinc standard solution.
Interference:
Zirconium (Zr), cerium (Ce), and rare earth elements (REEs) do not interfere if their total content in the solution does not exceed 50 mg.
4.2 Reagents and Materials
Unless otherwise specified, only analytically pure reagents and Grade 2 water (or equivalent purity) as per GB/T 6682 shall be used.
4.2.1 Sodium (or potassium) pyrosulfate.
4.2.2 Sodium fluoride.
4.2.3 Hydrochloric acid (HCl), ρ ≈ 1.19 g/mL.
4.2.4 Hydrochloric acid (1+1). Prepared by diluting HCl (4.2.3).
4.2.5 Nitric acid (HNO₃), ρ ≈ 1.42 g/mL.
4.2.6 Perchloric acid (HClO₄), ρ ≈ 1.67 g/mL.
4.2.7 Sulfuric acid (H₂SO₄), ρ ≈ 1.84 g/mL.
4.2.8 Sulfuric acid (1+1). Prepared by diluting H₂SO₄ (4.2.7).
4.2.9 Sulfuric acid (2+100). Prepared by diluting H₂SO₄ (4.2.7).
4.2.10 Hydrofluoric acid (HF), ρ ≈ 1.15 g/mL.
4.2.11 Ammonium hydroxide (NH₄OH), ρ ≈ 0.90 g/mL.
4.2.12 Ammonium hydroxide (1+1). Prepared by diluting NH₄OH (4.2.11).
4.2.13 Sodium fluoride solution (35 g/L). Store in a plastic bottle.
4.2.14 Sodium fluoride solution (5 g/L). Store in a plastic bottle.
4.2.15 Complexing agent solution: Mix 400 g/L ammonium citrate and 50 g/L ammonium oxalate in equal volumes.
4.2.16 Hydrochloric acid-boric acid mixture: Mix saturated boric acid solution, HCl (4.2.3), and water in a (15+25+60) ratio.
4.2.17 Acetic acid-ammonium acetate buffer solution (pH 5.0–5.5): Dissolve 200 g ammonium acetate in 500 mL water, add 25 mL glacial acetic acid (ρ ≈ 1.05 g/mL), and dilute to 1 L. Mix well.
4.2.18 2,4-Dinitrophenol solution (2 g/L): Dissolve 0.2 g 2,4-dinitrophenol in ~50 mL ethanol (1+1) (1 part ethanol + 1 part water), then dilute to 100 mL with ethanol (1+1). Mix well.
4.2.19 Xylenol orange solution (2 g/L): Prepare freshly in summer; store for ≤1 week in winter.
4.2.20 Disodium ethylenediaminetetraacetate (EDTA) solution (0.02 mol/L): Dissolve 7.4448 g EDTA in water, transfer to a 1000 mL volumetric flask, and dilute to volume. Mix well.
4.2.21 Zinc standard solution (cZn = 0.0200 mol/L): Dissolve 1.6276 g zinc oxide (pre-dried at 110°C to constant weight) in 20 mL HCl (4.2.4), add ~200 mL water, adjust to pH ~7 with NH₄OH (4.2.12) using congo red paper, cool, transfer to a 1000 mL volumetric flask, and dilute to volume. Mix well.
4.3 Apparatus
All glassware shall comply with Class A requirements as per GB/T 12805 and GB/T 12806.
4.4 Sample Preparation
