GB/T 4702.1-2016 in English
VALIDChromium metal—Determination of chromium content—The ammonium ferrous sulfate titrimetric method
- Issued on:2016-08-29
- Implemented on:2017-07-01
- File Format:PDF
- Delivery:Via email within 1~3 business days
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《GB/T 4702.1-2016金属铬 铬含量的测定 硫酸亚铁铵滴定法》由TC318（全国生铁及铁合金标准化技术委员会）归口，主管部门为中国钢铁工业协会。
Introduction
GB/T 4702.1-2016 Standard Overview
This standard specifies the method for determining the chromium content in metallic chromium by ammonium ferrous sulfate titration, which is applicable to the determination of chromium content in metallic chromium with a vanadium content of ≤0.20%, and the range is ≥97.00% (mass fraction). This method dissolves the sample in dilute sulfuric acid, uses silver nitrate as a catalyst under appropriate acidity, oxidizes trivalent chromium to hexavalent chromium, and titrates using ammonium ferrous sulfate standard titration solution.
Standard Background and Technological Evolution
GB/T 4702.1-2016 replaces the original GB/T 4702.1—1997. The main technical changes include:
- Added safety warnings and normative references
- Optimized the sample processing process: use dilute sulfuric acid to dissolve the sample, adjust the sample amount to 0.200g (accurate to 0.0001g), and directly oxidize and titrate
- Replace potassium permanganate solution with manganese sulfate solution
- Use sodium chloride solution instead of hydrochloric acid to decompose permanganate
- Adjust the concentration of ammonium ferrous sulfate standard titration solution to 0.13mol/L
Reagents and Instrument Requirements
All reagents used in the analysis are analytical grade, and water must meet the purity of grade 3 or above as specified in GB/T 6682. The key reagents include:
| Reagent name | Concentration/purity | Preparation method |
|---|---|---|
| Ammonium ferrous sulfate standard titration solution | About 0.13mol/L | Preparation: Weigh 50.98g of ammonium ferrous sulfate and dissolve it in 1000mL of sulfuric acid (5+95) and mix well. |
| Potassium dichromate standard solution | c(1/6 K₂Cr₂O₇)=0.1000mol/L | Preparation: Weigh 4.9040g of dried potassium dichromate standard material and dissolve it in a 1000mL volumetric flask. |
Detailed analysis steps
Sample preparation:Samples should be prepared according to GB/T 4010. The sample should pass through a 1.68mm sieve.
Titration process:After adding sulfuric acid, phosphoric acid and an indicator, boil the chromium oxide and then titrate to the endpoint. Key data include:
- Sample amount: 0.200g
- Titration volume: record the volume of ammonium ferrous sulfate standard titration solution consumed in the titration sample solution and blank test.
Result calculation and allowable difference
Calculate the chromium content (mass fraction) wCr according to formula (2):
wCr = (c₂ × (V₆ - V₀₁) × 0.01733 / m₀) × 100
| Chromium content (%) | Allowable difference |
|---|---|
| ≥97.00 | 0.40 |
Implementation suggestions
To ensure the accuracy of the analysis results, it is recommended that:
- Perform the experiment in strict accordance with the standard operating procedures
- Use reagents and instruments that meet the requirements
- Calibrate burettes and analytical balances regularly
- Perform blank tests and compare results
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