GB/T 8454-2020Reduced ilmenite powder for welding rob—Determination of ferrous iron content—Potassium dichromate titrimetric method (English PDF)

4.12 Ferric chloride solution, 100g/L

Weigh 100.0g of iron trichloride (FeCl3 · 6H2O) to dissolve in 1000mL of water.

Mix well. If the solution is turbid, it shall be filtered before use.

4.13 Ferrous ammonium sulfate solution, about 0.03mol/L

Weigh 11.8g of ferrous ammonium sulfate [(NH3)2Fe(SO4)2 · 6H2O] to dissolve in 500mL of sulfuric acid (5+95). Use sulfuric acid (5+95) to transfer and dilute to 1000mL. Mix well.

4.14 Potassium dichromate standard titration solution, c(1/6K2Cr2O7) =

0.05000mol/L.

Weigh 2.4518g of the reference reagent potassium dichromate, which has been dried at 150°C for 1h and cooled to room temperature in a desiccator. Dissolve in 500mL of water. Transfer to a 1000mL volumetric flask. Use water to dilute to the scale. Mix well.

4.15 Sodium diphenylamine sulfonate indicator solution, 2g/L

Weigh 0.20g of sodium diphenylamine sulfonate to dissolve in 100mLof water.

Mix well. If the solution is turbid, it shall be filtered before use.

5.2 Adjustable speed magnetic stirrer

5.3 Non-magnetic sample spoon

6.1 Laboratory specimen

Conduct sampling and sample preparation according to GB/T 10322.1. The particle size of the laboratory specimen for analysis shall be less than 74µm. standard titration solution consumed, V2. Add 10.00mL of ferrous ammonium sulfate solution to the solution again (see 4.13). Use potassium dichromate standard titration solution (see 4.14) to titrate till stable purple. Write down the titrated volume V3. (V2-V3) is the blank of the total amount of ferrous iron and metallic iron.

7.4 Determination of metallic iron

7.4.1 Weigh 0.50g of sample, to the nearest of 0.0001g. Place in a dry 150mL Erlenmeyer flask. Add 30mL of ferric chloride solution (see 4.12). Add the magnetic core. Plug the rubber stopper. Stir on the electromagnetic stirrer for 60min.

7.4.2 Remove. Use medium speed filter paper to filter into a 250mL volumetric flask. Wash the conical flask 5 times and filter paper 5 times. Dilute to the scale.

Mix well. Pipette 50.00mL of solution into a 300mL Erlenmeyer flask.

7.4.3 Add 15mL of sulfuric acid-phosphoric acid mixed acid (see 4.10) to the solution obtained in 7.4.2. Add 3 drops of sodium diphenylamine sulfonate indicator solution (see 4.15). Use potassium dichromate standard titration solution (see 4.14) to titrate till stable purple as the end point. Write down the volume of potassium dichromate standard titration solution consumed V4.

7.4.4 Into the blank solution accompanying with the sample, accurately add

10.00mL of ferrous ammonium sulfate solution (see 4.13), 15mL of sulfuric acid-phosphoric acid mixed acid (see 4.10), and 3 drops of sodium diphenylamine sulfonate indicator solution (see 4.15). Use potassium dichromate standard titration solution (see 4.14) to titrate till stable purple. Write down the volume of potassium dichromate standard titration solution consumed V5. Add 10.00mL of ferrous ammonium sulfate solution to the solution again (see 4.13). Use potassium dichromate standard titration solution (see 4.14) to titrate till stable purple. Write down the titrated volume V6. (V5-V6) is the blank of metal iron.

9.4 Acceptance of analysis values

The acceptance of analysis values is verified using certified reference materials (CRM) or standard samples (RM). Compare the final laboratory results with the standard value Ac. If

a), then there is no significant difference between the reported result and the standard value;

b), then there is a significant difference between the reported result and the standard value. Where, µc - CRM or RM measured value; Ac - CRM or RM standard value;

C - Its value depends on the type of CRM/RM used.

The C value of the certification standard sample (CRM) or standard sample (RM) determined by multiple laboratories is calculated according to formula (5):

Where, R - Inter-laboratory reproducibility limit; r - Repeatability limit in the laboratory; n - Number of repeated determinations of the standard sample; u - Uncertainty of CRM/RM sample standard value.

9.5 Calculation of final result

The final result is the arithmetic mean of the acceptable values of the specimen, or the value measured according to the operation specified in Annex A. The analysis results are revised according to GB/T 8170. The analysis result keeps two decimal places. […]