GB/T 20975.5-2020Methods for chemical analysis of aluminium and aluminium alloys—Part 5: Determination of silicon content (English PDF)

4.1 Method summary

The sample is dissolved with sodium hydroxide and hydrogen peroxide, acidified with nitric acid and hydrochloric acid, and molybdate and silicon are used to form silicomolybdenum heteropolyacid (pH value is about 0.9), increase the acidity with sulfuric acid, reduce with 1-amino-2-naphthol-4-sulfonic acid or ascorbic acid to reduce the silicomolybdenum heteropoly acid to silicomolybdenum blue.

The absorbance is measured at the wavelength of 650.0nm~810.0nm with the photometer to determine the silicon content.

4.2 Reagents

Unless otherwise stated, only reagents and laboratory secondary water confirmed to be analytically pure are used in the analysis.

4.2.1 Hydrogen peroxide (rho=1.10g/mL).

4.2.2 Nitric acid (about 8mol/L). Pipette 540mL of nitric acid (rho=1.42g/mL) into a beaker containing about 200mL of water, shake well, and cool. However, transfer it to a 1000mL volumetric flask, dilute to the mark with water, and mix.

4.2.3 Sodium hydroxide (about 8mol/L). Weigh 320g of sodium hydroxide into a beaker, add about 400mL of water, shake well, cool, and transfer In a 1000mL polyethylene volumetric flask, dilute to the mark with water and mix well.

4.2.4 Hydrochloric acid (about 4.4mol/L). Pipette 352mL of hydrochloric acid (rho=1.19g/mL) into a beaker containing about 200mL of water, shake well, and cool. However, transfer it to a 1000mL volumetric flask, dilute to the mark with water, and mix.

4.2.5 Nitric acid (1 1).

4.2.6 Ammonia (1 1).

4.2.7 Sulfuric acid (1 2).

4.2.8 Tartaric acid solution (200g/L).

4.2.9 Reduction solution.

---1-Amino-2-naphthol-4-sulfonic acid solution (1.5g/L). Weigh 7g of anhydrous sodium sulfite, 1.5g 1-amino-2-naphthol-4-sulfonic acid in In a 250mL beaker, add 100mL of water and stir until completely dissolved; in addition, weigh 90g of sodium metadisulfite in 1000mL In the cup, add 600mL of water to slightly heat to dissolve. Mix these two solutions and filter them in a 1000mL volumetric flask with medium-speed quantitative filter paper Dilute to the mark with water and mix well. Transfer to a brown bottle. The validity period is 1 month.

---Ascorbic acid solution (20g/L), ready when used.

4.2.10 Ammonium molybdate solution (100g/L). Dissolve 50g of ammonium molybdate [(NH4)6Mo7O24·4H2O] in 250mL of water and add 30mL sodium hydroxide (4.2.3) mix well and cool. Dilute with water to 350mL, add sodium hydroxide (4.2.3) dropwise to adjust the solution under constant stirring To about pH 7.2 (check with acidity meter); filter in a 500mL volumetric flask, wash with water and dilute to the mark, and mix. Stored in polyethylene In the bottle.

4.2.11 Sodium sulfite solution (100g/L).

4.2.12 Silicon standard storage solution. Use a certified standard solution to prepare. Or weigh 0.2140g silica (wSiO2>=99.99%), Place in a platinum crucible, add 1g of anhydrous sodium carbonate, and mix well. Heat at 1000°C until it melts completely, cool, dissolve in water, transfer to 1000mL volume Dilute to the mark with water in a measuring bottle and store in a polyethylene bottle. 1mL of this solution contains 0.1mg of silicon.

4.2.13 Silicon standard solution A. Pipette 50.00mL silicon standard stock solution (4.2.12) into a 250mL volumetric flask, dilute to the mark with water, Mix well. Store in a polyethylene bottle. 1mL of this solution contains 0.02mg of silicon.

4.2.14 Silicon standard solution B. Pipette 20.00mL silicon standard stock solution (4.2.12) into a 500mL volumetric flask and dilute to the mark with water. Mix well. Store in a polyethylene bottle. 1mL of this solution contains 0.004mg of silicon.

4.2.15 p-nitrophenol solution (5g/L).

4.3 Apparatus

4.3.1 Spectrophotometer.

4.3.2 Acidity meter.

4.4 Sample

Process the sample into chips with a thickness of not more than 1mm.

4.5 Analysis steps

4.5.1 Sample

Weigh the sample (4.4) of the corresponding mass m0 according to Table 1, accurate to 0.0001g.

4.5.2 Parallel test

Do two tests in parallel and take the average value.

4.5.3 Blank test

Do a blank test with the sample (4.5.1).

4.5.4 Determination

4.5.4.1 Place the weighed sample (4.5.1) in a 250mL polytetrafluoroethylene (or silver) beaker, add 10mL sodium hydroxide (4.2.3), cover Place the watch glass and slowly heat (do not boil) until the sample is completely dissolved. Add 2mL hydrogen peroxide (4.2.1), heat to evaporate to a paste, and cool.

Rinse the watch glass and the wall of the beaker with about 30 mL of warm water. Heat slowly (do not boil) until the salt is dissolved. Dilute with warm water to 70mL~ 80mL, heat at low temperature for 15min~20min (do not boil), and cool.

4.5.4.2 Using a polyethylene rod while stirring, transfer the sample solution (4.5.4.1) into 400 mL of mixed acid and 50 mL of warm water in advance according to Table 1. In the PTFE beaker, wash the watch and the wall of the beaker with warm water (if manganese hydroxide precipitates and adheres to the wall (or watch) of the cup, add a small amount Dissolve it with hydrochloric acid (4.2.4) and a few drops of sodium sulfite solution (4.2.11), wash it into a beaker with warm water]. Dilute the sample solution to approximately 180mL, heated to near boiling, continue to add a few drops of sodium sulfite solution (4.2.11) to completely dissolve the manganese hydroxide. Boil slowly for 10s~15s, cool down. Transfer to 250mL volumetric flask V0, dilute to the mark with water, and mix.

Note: When the titanium or silver content is high, the sample solution is turbid, filter it in a 250mL volumetric flask with slow quantitative filter paper, and wash the filter paper with hot water.

4.5.4.3 When the silicon mass fraction is 0.0010%~0.020%, the pipetting volume (V1) is 50.00mL sample solution (4.5.4.2). In a 100mL volumetric flask; when the silicon mass fraction is >0.020%~15.00%, pipette the corresponding volume (V1) of the sample solution according to Table 1. (4.5.4.2) In a 100mL volumetric flask, dilute with water to about 50mL, add 1 drop of p-nitrophenol solution (4.2.15), and mix with ammonia (4.2.6) The solution was adjusted to bright yellow, then adjusted to colorless with nitric acid (4.2.5), and an excess of 2mL.

4.5.4.4 In a 100mL volumetric flask, add 5mL of ammonium molybdate solution (4.2.10), shake well, and place at 20°C~30°C for 15min. plus Add 5mL tartaric acid solution (4.2.8), 10mL sulfuric acid (4.2.7), 5mL reduction solution (4.2.9), and shake well. Dilute to the mark with water, mix uniform. Leave it for 10 minutes.

4.5.4.5 Transfer the sample solution (4.5.4.4) and the blank test solution (4.5.3) into the absorption cell respectively, and use water as the reference to perform the wave in the spectrophotometer. Measure the absorbance at 650.0nm~810.0nm (measured within 30min), and subtract the absorbance of the sample solution (4.5.4.4) For the absorbance of the blank test solution (4.5.3), the corresponding silicon mass m1 is found from the working curve.

4.5.5 Drawing of working curve

4.5.5.1 Preparation of substrate solution

In a 400mL plastic beaker, add 40mL sodium hydroxide (4.2.3), add.200mL water, use 110mL nitric acid (4.2.2) and 40mL hydrochloric acid (4.2.4) acidified and cooled. Transfer to a 500mL polyethylene volumetric flask, dilute to the mark with water, and mix.

4.5.5.2 Preparation of standard solution

According to the silicon mass fraction, the preparation of the working curve series standard solution is divided into 2 types.

a) When the silicon mass fraction is 0.0010%~0.020%. pipette 0mL, 0.50mL, 2.50mL, 5.00mL, 7.50mL, 10.00mL silicon standard solution B (4.2.14) in a set of 100mL volumetric flasks, respectively add 25mL base solution (4.5.5.1), dilute with water to about 50mL, and proceed according to 4.5.4.4 below;

b) When the silicon mass fraction is >0.020%~15.00%. pipette 0mL, 0.50mL, 2.50mL, 5.00mL, 7.50mL, 10.00mL silicon standard solution A (4.2.13) in a set of 100mL volumetric flasks, dilute with water to about 50mL, add a drop of paranitrile Base phenol solution (4.2.15), use ammonia (4.2.6) to adjust the solution to bright yellow, and then use nitric acid (4.2.5) to adjust to colorless and excessive 2mL. Then proceed according to 4.5.4.4.

4.5.5.3 Measurement

Move part of the series of standard solutions (4.5.5.2) into the absorption cell, take the reagent blank solution (without the silicon standard solution) as the reference, and At the wavelength of the photometer at 650.0nm~810.0nm, measure the absorbance (measured within 30min), and take the silicon mass as the abscissa to absorb The luminosity is the ordinate, and the working curve is drawn.

4.6 Test data processing

The silicon content is calculated as the silicon mass fraction wSi, calculated according to formula (1).

When the silicon mass fraction is less than 1.00%, the calculation result retains two significant digits; when the silicon mass fraction is >=1.00%, the calculation result is expressed as small Count the last two digits. The rounding of values shall be implemented in 3.2 and 3.3 of GB/T 8170-2008.

4.7 Precision

4.7.1 Repeatability

The measured values of two independent test results obtained under repeatability conditions, within the average range given below, these two test results The absolute difference does not exceed the repeatability limit r, and the case of exceeding the repeatability limit r does not exceed 5%. The repeatability limit r is within the linear range according to the data in Table 2. Obtained by interpolation or extension method.

4.7.2 Reproducibility

The measured values of two independent test results obtained under reproducibility conditions, within the average range given below, the two test results The absolute difference is not greater than the reproducibility limit R, and the case of exceeding the reproducibility limit R does not exceed 5%. Reproducibility limit R According to the data in Table 3, the linear internal Obtained by interpolation or extension method.

5.1 Method summary

The sample is dissolved with sodium hydroxide, acidified with perchloric acid and dehydrated. Filter, dry, burn and weigh the silica. Volatilize with hydrofluoric acid Silicon, dry, burn, weigh the residue. Determine the silicon content based on the difference between the two.

5.2 Reagents

Unless otherwise specified, only reagents and laboratory grade 3 water confirmed to be analytically pure and above are used in the analysis.

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

5.2.2 Nitric acid (rho=1.42g/mL).

5.2.3 Hydrofluoric acid (rho=1.19g/mL).

5.2.4 Hydrochloric acid (5 95).

5.2.5 Sulfuric acid (1 1).

5.2.6 Hydrogen peroxide (1 1).

5.2.7 Perchloric acid (1 2).

5.2.8 Sodium hydroxide solution (320g/L). Weigh 320g of sodium hydroxide and dissolve it in water, after cooling, transfer to 1000mL polyethylene capacity In the bottle, dilute to the mark with water and shake well.

5.3 Apparatus

High temperature furnace.

5.4 Sample

Process the sample into chips with a thickness of not more than 1mm.

5.5 Analysis steps

5.5.1 Sample

Weigh the sample (5.4) according to Table 4, accurate to 0.0001g, which is the mass (m2) of the sample.

5.5.2 Parallel test

Do two tests in parallel and take the average value.

5.5.3 Blank test

Do a blank test with the sample.

5.5.4 Determination

5.5.4.1 Place the sample (5.5.1) in a 250mL polytetrafluoroethylene (or silver) beaker, add 30mL sodium hydroxide solution (5.2.8) and cover it Watch the glass, slowly heat, when the sample is completely dissolved, add 2mL~4mL hydrogen peroxide (5.2.6) dropwise, wash the watch glass and the cup wall with as little water as possible, Evaporate to a paste (to prevent splashing) and cool.

5.5.4.2 Add 100mL hot water and rinse the wall of the cup, boil until the salt is dissolved, and cool. Transfer the sample solution into 5mL nitric acid (5.2.2) In a 500mL beaker with 60mL perchloric acid (5.2.1) and 30mL water, wash the beaker and the tableware with hot water, and use a total of about 10mL high Chloric acid (5.2.7) washes the particles adhering to the wall of the cup and the watch in stages, then washes them with hot water and merges them into the main liquid. Place the beaker on the hot plate Heat and evaporate until a large amount of perchloric acid smoke comes out, and when the solution starts to precipitate out of salt (about 15min to 20min when perchloric acid smokes), remove the but. Add water to the beaker to about 200mL, continue heating to completely dissolve the salts, stir carefully with a glass rod, if manganese dioxide is precipitated, Add a few drops of hydrogen peroxide (5.2.6) to dissolve.

5.5.4.3 Filter the sample solution (5.5.4.2) with medium-speed quantitative filter paper in a 400mL beaker while stirring, and wash with hot hydrochloric acid (5.2.4) The beaker and filter paper are washed 5 to 6 times with boiling water until the filtrate is neutral (pH approx. 7), and the filter paper is removed for use. The collected filtrate and wash The washing liquid is heated and evaporated until a large amount of perchloric acid smoke is emitted, and the smoke continues to emit for 15-20 minutes, and then cool. Dilute the sample solution volume to approximately 200mL, heat to dissolve, filter with another medium-speed quantitative filter paper, wash the beaker and filter paper with hot hydrochloric acid (5.2.4) 5 to 6 times, and then boil Wash with water until the filtrate is neutral (pH approx. 7).

5.5.4.4 Place the two filter papers together with the precipitate in a platinum crucible of constant weight, and completely ash at 500°C to 600°C (do not burn the filter paper).

Burn in a high-temperature furnace at 1000 °C for 1h, take it out and place in a desiccator, cool to room temperature, weigh m3, and blank test mass m5.

5.5.4.5 Add 1mL~2mL sulfuric acid (5.2.5), 3mL~5mL hydrofluoric acid (5.2.3) to the dried precipitate, and place it on the electric hot plate The top is evaporated to dryness, burned in a high temperature furnace at 1000 °C to constant weight, cooled to room temperature, weighed m4, blank test mass m6.

5.6 Test data processing

The silicon content is calculated as the mass fraction of silicon wSi, calculated according to formula (2).

m2 --- The mass of the sample, in grams (g).

The calculation result is expressed to two decimal places. The rounding of values shall be implemented in 3.2 and 3.3 of GB/T 8170-2008.

5.7 Precision

5.7.1 Repeatability

The measured values of two independent test results obtained under repeatability conditions are within the average range given in Table 4, and the two test results The absolute difference does not exceed the repeatability limit r, and the repeatability limit r does not exceed 5%. The repeatability limit r is within the linear range according to the data in Table 5. Obtained by interpolation or extension method.

5.7.2 Reproducibility

The measured values of two independent test results obtained under reproducibility conditions are within the range of the average value given in Table 5. The absolute difference does not exceed the reproducibility limit R, and the reproducibility limit R does not exceed 5%. The reproducibility limit R is linear according to the data in Table 6. Obtained by interpolation or extension.