GB/T 14849.1-2020Methods for chemical analysis of silicon metal—Part 1: Determination of iron content (English PDF)

3.1 Method summary

Use hydrofluoric acid and nitric acid to dissolve the specimen. Add perchloric acid to evaporate till smoke appears to remove silicon and fluorine. Use hydrochloric acid to dissolve the residue. Use hydroxylamine hydrochloride to reduce Fe(III) to Fe(II). In pH3~pH5 sodium acetate buffer medium, Fe(II) ion and 1,10-phenanthroline form a red complex. At 510nm wavelength, measure the absorbance of the solution. Calculate the mass fraction of iron.

3.2 Reagents and materials

Unless otherwise specified, in the analysis, it shall only use the confirmed analytically-pure reagent AND distilled water or deionized water or equivalent-pure water.

3.2.1 Hydrofluoric acid (rho=1.14g/mL).

3.2.2 Perchloric acid (rho=1.67g/mL).

3.2.3 Nitric acid (1+1).

3.2.4 Hydrochloric acid (1+1).

3.2.5 Hydroxylamine hydrochloride solution (10g/L): Weigh 2.0g of hydroxylamine hydrochloride. Place in a 100mL beaker. Add a small amount of water and stir to dissolve completely. Use water to dilute to 200mL. Mix well.

3.2.6 1,10-phenanthroline solution (5g/L): Weigh 2.5g of 1,10-phenanthroline. Place in a 100mL beaker. Add 2mL of hydrochloric acid (3.2.4), 20mL of water. Stir and dissolve completely. Use water to dilute to 500mL. Mix well.

3.2.7 Acetic acid-sodium acetate buffer solution: Weigh 272g of sodium acetate trihydrate. Place in a 1L beaker. Add 500mL of water. Stir and dissolve completely. Filter in a 1000mL volumetric flask. Add 240mL of glacial acetic acid (rho=1.05g/mL). Use water to dilute to the scale. Mix well.

3.2.8 Mixed color developing solution: Mix hydroxylamine hydrochloride solution (3.2.5), 1,10-phenanthroline solution (3.2.6) and acetic acid-sodium acetate buffer solution (3.2.7) according to the volume of (1+1+2). Use within one week.

3.2.9 Iron standard stock solution: Weigh 0.2860g of ferric oxide that has been burned at 600°C for 1h and placed in a dryer to cool to room temperature (benchmark reagent, >=99.995%). Place in a beaker. Add 30mL of hydrochloric acid (3.2.4). Heat at a low temperature to dissolve. Cool to room temperature. Transfer to a 1000mL volumetric flask. Use water to dilute to the scale. Mix well. 1mL of this solution contains 200µg of iron.

3.2.10 Iron standard solution: Pipette 25.00mL of iron standard stock solution (3.2.9) into a 100mL volumetric flask. Use water to dilute to the scale. Mix well. 1mL of this solution contains 50µg of iron.

3.3 Instruments

3.3.1 Spectrophotometer.

3.3.2 Teflon beaker, 250mL.

3.5.5 Drawing of working curve

3.5.5.1 Pipette 0mL, 1.00mL, 2.00mL, 4.00mL, 6.00mL, 8.00mL, 10.00mL of iron standard solution (3.2.10). Respectively put them in a set of 100mL volumetric flasks. Add 2.5mL of hydrochloric acid (3.2.4). Use water to dilute to about 50mL. Add 5mL of mixed color developing solution (3.2.8). Use water to dilute to the scale. Mix well. Leave it for 15min.

3.5.5.2 Transfer part of the color developing solution (3.5.5.1) into the cuvette (3.3.4). Take reagent blank solution as reference. At a wavelength of 510nm, measure its absorbance. Use the mass of iron as the abscissa and absorbance as the ordinate to draw the working curve.

3.6 Processing of test data

Calculate the iron mass fraction wFe according to formula (1):

Where,

m1 - Iron mass of test material solution checked from the working curve, in micrograms (µg);

R1 - Dilution factor;

m0 - Mass of test material, in grams (g).

Two significant digits are reserved for test results. Numerical rounding shall be implemented in accordance with GB/T 8170.

3.7 Precision

4.5.2 Number of determinations

Do two tests in parallel.

4.5.3 Blank test

Conduct blank test with test material.

4.5.4 Determination

4.5.4.1 Place the test material (4.5.1) in a 250mL PTFE beaker (4.3.2) or platinum dish (4.3.3). Use a little water to moisten. Add 5mL of hydrofluoric acid (4.2.1) in portions. Decompose at room temperature for 3min. Add 10mL of nitric acid (4.2.3) in drops. Cover the lid. Heat at a low temperature to dissolve the sample until the sample is completely dissolved. Rinse the lid and wall. Add 5mL of perchloric acid (4.2.2). Continue heating till smoke appears. Steam to nearly dry. Remove. Add about 10mL of water. Heat to dissolve the salt. Cool to room temperature.

4.5.4.2 According to the mass fraction of iron in the test material, respectively process according to the following methods:

- When the mass fraction of iron is 0.050%~0.15%, transfer the test solution (4.5.4.1) into a 100mL volumetric flask. Add 10mL of hydrochloric acid (4.2.4). Use water to dilute to the scale. Mix well. The test solution volume (V) is 100mL.

- When the mass fraction of iron is >0.15%~0.25%, transfer the test solution (4.5.4.1) into a 200mL volumetric flask. Add 20mL of hydrochloric acid (4.2.4). Use water to dilute to the scale. Mix well. The test solution volume (V) is 200 mL.

- When the mass fraction of iron is >0.25%~0.75%, transfer the test solution (4.5.4.1) into a 500mL volumetric flask. Add 50mL of hydrochloric acid (4.2.4). Use water to dilute to the scale. Mix well. The test solution volume (V) is 500 mL.

4.5.4.3 Put test solution (4.5.4.2) at a wavelength of 248.3nm. Use Air-acetylene flame, and use test material blank solution to adjust zero. Measure the absorbance of iron. Find the iron mass concentration (rho) from the working curve.

4.5.5 Drawing of working curve

4.5.5.1 Pipette 0mL, 1.00mL, 2.00mL, 4.00mL, 6.00mL, 8.00mL, 10.00mL of iron standard solution (4.2.6). Respectively put them in a set of 100mL volumetric flasks. Add 10mL of hydrochloric acid (4.2.4). Use water to dilute to […]