GB/T 13747.2-2019Methods for chemical analysis of zirconium and zirconium alloys - Part 2: Determination of iron content - 1,10-phenanthroline spectrophotometry and inductively coupled plasma atomic emission spectrometry (English PDF)

2.1 Principle

The test portion is decomposed with sulfuric acid-ammonium sulfate, zirconium is complexed with citric acid, and Fe3+ is reduced to Fe2+ with hydroxylamine hydrochloride. At about pH 6, Fe2+ forms a red complex with 1,10-phenanthroline, whose absorbance is measured with a spectrophotometer at a wavelength of 510 nm.

2.2 Reagents

Unless otherwise stated, use only reagents of recognized analytical grade and grade 2 laboratory water.

2.2.1 Hydrochloric acid (1+1).

2.2.2 Ammonium sulfate.

2.2.3 Sulfuric acid (rho = 1.84 g/mL).

2.2.4 Hydroxylamine hydrochloride solution (100 g/L).

2.2.5 Citric acid solution (500 g/L).

2.2.6 Acetic acid-ammonium acetate buffer solution: dissolve 500 g of ammonium acetate in water, add 20 mL of glacial acetic acid, dilute to 1 000 mL with water and mix.

2.2.7 Ammonia solution (1+1).

2.2.8 1,10-phenanthroline solution (5 g/L): dissolve 0.5 g of 1,10-phenanthroline in 20 mL of absolute ethanol, dilute to 100 mL with water, mix and store in a brown bottle.

2.2.9 Iron standard stock solution: weigh 1.000 0 g of metallic iron (wFe >= 99.99%) into a 200 mL beaker, add 30 mL of hydrochloric acid (2.2.1) and heat gently until completely dissolved; cool, transfer to a 1 000 mL volumetric flask, dilute to the mark with water and mix. 1 mL of this solution contains 1 mg of iron.

2.2.10 Iron standard solution: pipette 10.00 mL of the iron standard stock solution (2.2.9) into a 100 mL volumetric flask, dilute to the mark with water and mix. 1 mL of this solution contains 100 µg of iron.

2.3 Apparatus

Spectrophotometer.

2.4 Sample

The sample shall be machined into chips not longer than 5 mm.

2.5 Procedure

2.5.1 Test portion

Weigh the sample (2.4) according to Table 1, to the nearest 0.000 1 g.

Table 1 - Mass of test portion: iron mass fraction 0.010% to 0.10%: test portion 1.00 g, total volume of test solution 100 mL, aliquot 20.00 mL; iron mass fraction >0.10% to 0.40%: test portion 0.50 g, total volume of test solution 100 mL, aliquot 10.00 mL.

2.5.2 Parallel determination

Carry out two determinations in parallel and take the mean value.

2.5.3 Blank test

Carry out a blank test together with the test portion. Where the iron mass fraction is not more than 0.1%, carry out two blank tests in parallel.

2.5.4 Determination

2.5.4.1 Place the test portion (2.5.1) in a 150 mL beaker, add 10 mL of sulfuric acid (2.2.3) and 5 g of ammonium sulfate (2.2.2), cover with a watch glass and decompose by heating on a high-temperature electric hotplate; continue heating until the separated sulfur has disappeared. Cool, transfer to a 100 mL volumetric flask, dilute to the mark with water and mix. Transfer an aliquot of the test solution, as given in Table 1, into a 100 mL volumetric flask.

2.5.4.2 Add 5 mL of citric acid solution (2.2.5) and 5 mL of hydroxylamine hydrochloride solution (2.2.4) and allow to stand for 10 min. Add a small piece of Congo red test paper and neutralize with ammonia solution (2.2.7) until the Congo red paper just turns from blue to purple.

2.5.4.3 Add 3 mL of acetic acid-ammonium acetate buffer solution (2.2.6) and 5 mL of 1,10-phenanthroline solution (2.2.8), heat in a water bath at 70 °C to 80 °C for 15 min, remove, cool to room temperature, dilute to the mark with water and mix.

2.5.4.4 Transfer part of the solution (2.5.4.3) into a 2 cm cell and, using the blank solution carried through with the test portion as reference, measure the absorbance with a spectrophotometer at a wavelength of 510 nm. Read the corresponding iron content from the calibration curve.

2.5.5 Preparation of the calibration curve

2.5.5.1 Pipette 0 mL, 0.20 mL, 0.50 mL, 1.00 mL, 1.50 mL, 2.00 mL and 2.50 mL of iron standard solution (2.2.10) into a series of 100 mL volumetric flasks, add to each a volume of blank test solution equal to the aliquot of test solution, and proceed as in 2.5.4.2 and 2.5.4.3.

2.5.5.2 Transfer part of each solution (2.5.5.1) into a 2 cm cell and, using the reagent blank solution as reference, measure the absorbance with a spectrophotometer at a wavelength of 510 nm. Plot the calibration curve with iron content as abscissa and absorbance as ordinate.

2.6 Calculation and expression of results

The iron content, expressed as the mass fraction of iron wFe, is calculated by formula (1):

wFe = (m1 × V0 × 10^-6) / (m0 × V1) × 100% ... (1)

where:

m1 - mass of iron read from the calibration curve, in micrograms (µg);

V0 - total volume of the test solution, in millilitres (mL);

m0 - mass of the test portion, in grams (g);

V1 - volume of the aliquot of test solution, in millilitres (mL).

The result is expressed to two significant figures.

2.7 Precision

2.7.1 Repeatability

The absolute difference between two independent test results obtained under repeatability conditions, within the range of mean values given in Table 2, shall not exceed the repeatability limit (r) in more than 5% of cases. The repeatability limit (r) is obtained from the data in Table 2 by linear interpolation or extrapolation.

Table 2 - Repeatability limits (Method 1): iron mass fraction 0.047%: r = 0.004%; 0.27%: r = 0.02%; 0.37%: r = 0.03%.

2.7.2 Reproducibility

The absolute difference between two independent test results obtained under reproducibility conditions, within the range of mean values given in Table 3, shall not exceed the reproducibility limit (R) in more than 5% of cases. The reproducibility limit (R) is obtained from the data in Table 3 by linear interpolation or extrapolation.

Table 3 - Reproducibility limits (Method 1): iron mass fraction 0.047%: R = 0.005%; 0.27%: R = 0.02%; 0.37%: R = 0.03%.

3.1 Principle

The test portion is dissolved with nitric acid and hydrofluoric acid. The determination is made by inductively coupled plasma atomic emission spectrometry; the mass concentration of iron is calculated by the calibration curve method and the result is expressed as a mass fraction.

3.2 Reagents

Unless otherwise stated, use only reagents of recognized analytical grade and grade 2 laboratory water.

3.2.1 Hydrofluoric acid (rho = 1.13 g/mL).

3.2.2 Nitric acid (1+1).

3.2.3 Iron standard stock solution: weigh 1.000 0 g of metallic iron (wFe >= 99.99%) into a 250 mL beaker, dissolve with 20 mL of nitric acid (3.2.2) and cool. Transfer to a 1 000 mL volumetric flask, dilute to the mark with water and mix. 1 mL of this solution contains 1 mg of iron.

3.2.4 Iron standard solution: pipette 10.00 mL of the iron standard stock solution (3.2.3) into a 100 mL volumetric flask, add 2 mL of nitric acid (3.2.2), dilute to the mark with water and mix. 1 mL of this solution contains 100 µg of iron.

3.2.5 Zirconium metal (wZr >= 99.9%, wFe <= 0.001%).

3.2.6 Argon (volume fraction >= 99.99%).

3.3 Apparatus

Inductively coupled plasma atomic emission spectrometer with a hydrofluoric acid-resistant sample introduction system and a resolution better than 0.006 nm (at 200 nm).

3.4 Sample

The sample shall be machined into chips not longer than 5 mm.

3.5 Procedure

3.5.1 Test portion

Weigh 0.20 g of the sample (3.4), to the nearest 0.000 1 g.

3.5.2 Parallel determination

Carry out two determinations in parallel and take the mean value.

3.5.3 Blank test

Weigh 0.200 g of zirconium metal (3.2.5) and carry out a blank test together with the test portion.

3.5.4 Preparation of the test solution

Place the test portion (3.5.1) in a 150 mL polytetrafluoroethylene beaker, add 10 mL to 15 mL of water and 2 mL of hydrofluoric acid (3.2.1) to dissolve. When the reaction has ceased, add 2 mL of nitric acid (3.2.2) until the sample is completely dissolved, cool, transfer to a 100 mL plastic volumetric flask, dilute to the mark with water and mix.

3.5.5 Preparation of the calibration solutions

Weigh 0.200 g portions of pure zirconium (3.2.5) into a series of 150 mL polytetrafluoroethylene beakers and dissolve them as in 3.5.4. After cooling, transfer each into a 100 mL plastic volumetric flask, add respectively 0 mL, 0.20 mL, 0.50 mL, 2.00 mL, 5.00 mL and 10.00 mL of iron standard solution (3.2.4), dilute to the mark with water and mix.

3.5.6 Determination

3.5.6.1 Recommended analytical line wavelength: 238.20 nm.

3.5.6.2 On the inductively coupled plasma atomic emission spectrometer, at the selected analytical wavelength, measure the calibration solutions (3.5.5). When the linear correlation coefficient of the calibration curve k >= 0.999, measure the emission intensity of iron in the test solution (3.5.4) and in the blank solution (3.5.3), and read the mass concentration of the element from the calibration curve.

3.6 Calculation and expression of results

The iron content, expressed as the mass fraction of iron wFe, is calculated by formula (2):

wFe = ((rho1 - rho0) × V2 × 10^-6) / m × 100% ... (2)

where:

rho1 - mass concentration of iron in the test solution, in micrograms per millilitre (µg/mL);

rho0 - mass concentration of iron in the blank solution, in micrograms per millilitre (µg/mL);

V2 - volume of the test solution, in millilitres (mL);

m - mass of the test portion, in grams (g).

The result is expressed to two significant figures.

3.7 Precision

3.7.1 Repeatability

The absolute difference between two independent determination results obtained under repeatability conditions, within the range of mean values given in Table 4, shall not exceed the repeatability limit (r) in more than 5% of cases. The repeatability limit (r) is obtained from the data in Table 4 by linear interpolation or extrapolation.

Table 4 - Repeatability limits (Method 2): iron mass fraction 0.047%: r = 0.003%; 0.27%: r = 0.02%; 0.37%: r = 0.03%.

3.7.2 Reproducibility

The absolute difference between two independent determination results obtained under reproducibility conditions, within the range of mean values given in Table 5, shall not exceed the reproducibility limit (R) in more than 5% of cases. The reproducibility limit (R) is obtained from the data in Table 5 by linear interpolation or extrapolation.

Table 5 - Reproducibility limits (Method 2): iron mass fraction 0.047%: R = 0.006%; 0.27%: R = 0.02%; 0.37%: R = 0.03%.