GB/T 14849.3-2020Methods for chemical analysis of silicon metal—Part 3: Determination of calcium content (English PDF)

3.1 Method summary

Use hydrofluoric acid and nitric acid to dissolve test material. Perchloric acid smokes to remove silicon and fluorine. Use nitric acid to dissolve the residue.

Use lanthanum salt to suppress aluminum interference. At a wavelength of 422.7nm of flame atomic absorption spectrometer, use air-acetylene flame to measure the absorbance of calcium. Calculate the mass fraction of calcium.

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 Perchloric acid (rho=1.67g/L).

3.2.7 Calcium standard solution

Pipette 25.00mL of calcium standard stock solution (3.2.6) in a 250mL volumetric flask. Use water to dilute to the scale. Mix well. 1mL of this solution contains 50µg of calcium.

3.3 Instruments

3.3.2 Platinum dish, 100mL.

3.3.3 Teflon beaker, 250mL.

3.3.1 Atomic absorption spectrometer, attached with calcium hollow cathode lamp

Under the best working conditions of the instrument, any atomic absorption spectrometer that can achieve the following indicators can be used.

3.4 Specimen

The specimen shall be able to pass through a 0.149mm standard sieve. Use magnet to remove iron.

3.5 Test steps

3.5.1 Test material

Weigh 0.50g of specimen (3.4), to the nearest of 0.0001g.

3.5.2 Number of determinations

Do two tests in parallel.

3.5.3 Blank test

Conduct blank test with test material (3.5.1).

3.5.4 Determination

3.6 Processing of test data

Calculate the mass fraction of calcium wCa according to formula (1).

3.7 Precision

3.7.1 Repeatability

Obtain the measured value of two independent test results under repeatability conditions. Within the average range given in Table 2, the absolute difference between the two test results does not exceed the repeatability limit (r).

4.1 Method summary

Use hydrofluoric acid and nitric acid to decompose the test material. Perchloric acid smokes to remove silicon and fluorine. Use hydrochloric acid to dissolve the residue. Use triethanolamine, 1,10-phenanthroline, and acetylacetone to mask interference elements. At pH10~pH10.5, calcium and chlorophosphonazo I form a colored complex. Take the faded solution of EGTA-Pb as a reference.

4.2 Reagents and material

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.

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

4.2.2 Nitric acid (1+1).

4.2.3 Perchloric acid (1+1).

4.2.4 Hydrochloric acid (1+1).

4.2.5 Triethanolamine (1+3), stored in polyethylene bottles.

4.2.11 Calcium standard stock solution

Weigh 2.4970g of calcium carbonate that has been dried at 105°C and cooled to room temperature in a dryer (reference reagent, >=99.95%). Place in a beaker. Add about 200mL of water. Then add hydrochloric acid (4.2.4) dropwise to completely dissolve.

4.3 Instruments

4.4 Specimen

The specimen shall be able to pass a 0.149mm standard sieve. Use magnet to remove iron.

4.5 Test steps

4.5.1 Test material

Weigh 1.0g of specimen (4.4), to the nearest of 0.0001g.

4.5.5 Drawing of working curve

4.5.5.1 Pipette 0mL, 0.50mL, 1.00mL, 2.00mL, 3.00mL, 4.00mL, 5.00mL, 6.00mL of calcium standard solution (4.2.12) to respectively place in a set of 50mL volumetric flasks. The following shall be carried out according to 4.5.4.4~4.5.4.5.