GB/T 4698.10-2020Methods for chemical analysis of titanium sponge, titanium and titanium alloys - Part 10: Determination of chromium content - Ammonium ferrous sulfate titration and inductively coupled plasma atomic emission spectrometry (with vanadium) (English PDF)

2.1 Principle

The sample is dissolved in sulfuric acid, and in a sulfuric acid medium at room temperature, the vanadium is oxidized to a high price with potassium permanganate, and the standard drop of ferrous ammonium sulfate is used.

Titrate vanadium with a constant solution.

Under heating conditions, using silver nitrate as a catalyst, ammonium persulfate is used to simultaneously oxidize vanadium and chromium to high prices, and then use ferrous ammonium sulfate standard

The titration solution titrates vanadium and chromium.

The difference between the volume of the titrant consumed in the two titrations is the volume of the titrant required for the titration of chromium, from which the amount of chromium is obtained.

2.2 Reagents

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

2.2.1

Nitric acid (rho=1.42g/L).

2.2.2

Sulfuric acid (1 1).

2.2.3

Potassium permanganate solution (5g/L).

2.2.4

Urea solution (100g/L).

2.2.5

Sodium nitrite solution (10g/L).

2.2.6

Silver nitrate solution (10g/L).

2.2.7

Ammonium persulfate solution (250g/L), prepared immediately after use.

2.2.8

Sodium chloride solution (100g/L).

2.2.9 Chromium standard solution

weigh 2.8290g of potassium dichromate (reference reagent) dried at 105°C for 1h and cooled to room temperature in 500mL

In the beaker, add about 100mL of water to dissolve it, transfer to a 1000mL volumetric flask, dilute to the mark with water, and mix. This solution 1mL contains

1.0mg chromium.

2.2.10

Preparation of ferrous ammonium sulfate standard titration solution [c(Fe2)~0.025mol/L]. Weigh 10.0g ferrous ammonium sulfate [Fe(SO4)· (NH4)2SO4·6H2O] was placed in a 500mL beaker, and.200mL sulfuric acid (2.2.2) was added to dissolve it. Transfer into 1000mL capacity

In the bottle, dilute to the mark with water and mix well.

2.2.11

Calibration of ferrous ammonium sulfate standard titration solution. Pipette three 10.00mL chromium standard solutions (2.2.9) into three 500mL cones.

In the flask, add 25mL sulfuric acid (2.2.2), 2 drops of manganese sulfate solution (50g/L), and perform the other operations according to 2.4.4.5~2.4.4.7.parallel

The volume range of the standard titration solution (2.2.10) of ferrous ammonium sulfate consumed for calibration should be no more than 0.10mL, whichever is the average value. According to formula (1)

Calculate the actual concentration of the ferrous ammonium sulfate titration solution (2.2.10).

2.2.12 N-phenylanthranilic acid solution (2g/L). Weigh 0.2g of N-phenylanthranilic acid and dissolve in 100mL sodium carbonate solution.

Solution (2g/L).

2.3 Sample

Follow the published sampling standards for titanium sponge, titanium and titanium alloys.

2.4 Test procedure

2.4.1 Sample

Weigh the sample (2.3) according to Table 1, accurate to 0.0001g.

2.4.2 Parallel test

Do two tests in parallel and take the average value.

2.4.3 Blank test

Do a blank test with the sample.

2.4.4 Determination

2.4.4.1

Place the sample (2.4.1) in a 500mL conical flask, add 25mL sulfuric acid (2.2.2), heat to dissolve the sample, and add nitric acid dropwise (2.2.1) To the solution purple disappears, heat to remove nitrogen oxides, and cool.

2.4.4.2

Dilute with water to about 100mL, add potassium permanganate solution (2.2.3) dropwise until the solution is stable red, and leave it for 3min.

2.4.4.3

Add 10mL urea solution (2.2.4), add sodium nitrite solution (2.2.5) dropwise under shaking until the red color of the solution disappears, and place

2min.

2.4.4.4

Add 5 drops of N-phenylanthranilic acid solution (2.2.12) and titrate to solution with ferrous ammonium sulfate standard titration solution (2.2.10)

The end point is the change from pink to yellow-green.

2.4.4.5

Dilute the solution (2.4.4.4) with water to.200mL, add 5mL silver nitrate solution (2.2.6), 10mL ammonium persulfate solution (2.2.7), heat the solution until the red color of permanganic acid appears, and boil until big bubbles appear.

2.4.4.6

Remove, add 5mL sodium chloride solution (2.2.8), heat and boil until the solution red disappears, remove, cool to room temperature with running water.

2.4.4.7

Add 10mL sulfuric acid (2.2.2), 5 drops of N-phenylanthranilic acid solution (2.2.12), and use ferrous ammonium sulfate standard titration solution (2.2.10) Titration until the solution changes from pink to yellow-green is the end point.

2.5 Test data processing

2.6 Precision

2.6.1 Repeatability

The measured values of two independent test results obtained under repeatability conditions are within the average range given in Table 2.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%. Repeatability limit (r) adopts the line according to the data in Table 2

Obtained by sexual interpolation or extension method.

2.6.2 Reproducibility

The measured values of two independent test results obtained under reproducibility conditions are within the range of the average value given in Table 3.

The absolute difference does not exceed the reproducibility limit (R), and does not exceed 5% in the case of exceeding the reproducibility limit (R). Reproducibility limit (R) is adopted according to the data in Table 3

Obtained by linear interpolation or extension method.

3.1 Principle

Dissolve the sample with hydrochloric acid and hydrofluoric acid, and add titanium oxide nitrate dropwise. Use inductively coupled plasma atomic emission spectrometry to determine

Calculate the mass concentration of chromium by curve method, and express the measurement result by mass fraction.

3.2 Reagents

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

3.2.1

Hydrochloric acid (rho=1.18g/mL).

3.2.2

Hydrofluoric acid (rho=1.15g/mL).

3.2.3

Nitric acid (rho=1.42g/mL).

3.2.4 Chromium standard storage solution

weigh 2.8290g of potassium dichromate (reference reagent) dried at 105°C for 1h and cooled to room temperature in 500mL

In the beaker, add about 100mL of water to dissolve it, transfer to a 1000mL volumetric flask, dilute to the mark with water, and mix. This solution 1mL contains

1.0mg chromium.

3.2.5

Chromium standard solution A. Pipette 10.00mL chromium standard stock solution (3.2.4) into a 100mL volumetric flask, add 5mL hydrochloric acid (3.2.1), dilute to the mark with water, and mix well. This solution 1mL contains 100µg chromium.

3.2.6 Chromium standard solution B

Pipette 10.00mL chromium standard solution A (3.2.5) into a 100mL volumetric flask, add 5mL hydrochloric acid (3.2.1), dilute to the mark with water, and mix well. This solution 1mL contains 10µg chromium.

3.2.7

Titanium (wTi>=99.95%, wCr< 0.001%).

3.2.8

Argon (volume fraction >=99.99%).

3.3 Apparatus

3.3.1 Inductively coupled plasma atomic emission spectrometer

equipped with a hydrofluoric acid resistant sampling system, with a resolution of less than 0.006nm (at.200nm).

3.3.2

The recommended wavelength of the chromium element analysis line is 283.56nm.

3.4 Sample

Follow the published sampling standards for titanium sponge, titanium and titanium alloys.

3.5 Test procedure

3.5.1 Sample

Weigh 0.10g sample (3.4), accurate to 0.0001g.

3.5.2 Parallel test

Do two tests in parallel and take the average value.

3.5.3 Blank test

Do a blank test with the sample.

3.5.4 Preparation of test solution

3.5.4.1 Preparation of analysis test solution

Place the sample (3.5.1) in a polytetrafluoroethylene beaker, blow in a small amount of water, add 5 mL of hydrochloric acid (3.2.1), and add 1 mL of hydrofluoric acid (3.2.2), heat at low temperature until the sample is completely dissolved, then add 0.5mL nitric acid (3.2.3) dropwise until the solution is clear. Remove and cool to room temperature,

Transfer to a 100mL plastic volumetric flask, dilute to the mark with water, and mix.

For samples containing chromium >= 8%, it is necessary to separate them for determination. Pipette 10.00mL of the above test solution into a 100mL volumetric flask, add 2mL of salt

Acid (3.2.1), dilute to the mark with water, and mix well.

3.5.4.2 Preparation of standard series solutions

Curve 1 (the mass fraction of chromium is 0.010%~8.00%). Weigh 7 parts of titanium metal (3.2.7) equivalent to the titanium content of the sample (3.5.1)

In a series of 100mL PTFE beakers, dissolve the sample according to 3.5.4.1 along with the sample. After the solution is cooled, transfer 7 100mL plastic

Material in a volumetric flask. Add 0mL, 1.00mL chromium standard solution B (3.2.6), 1.00mL chromium standard solution A (3.2.5), 1.00mL,

2.00mL, 4.00mL, 8.00mL chromium standard stock solution (3.2.4), dilute to the mark with water, and mix.

Curve 2 (the mass fraction of chromium is 8.00%~15.00%). Weigh the metal titanium (3.2.7) with the titanium content of the sample (3.5.1) into one

In a 100mL polytetrafluoroethylene beaker, dissolve, cool and dilute with the sample according to 3.5.4.1.Divide 10.00mL test solution into 6

100mL plastic volumetric flask. Add 0mL, 3.00mL, 6.00mL, 9.00mL chromium standard solution A (3.2.5), 1.20mL,

1.60mL chromium standard stock solution (3.2.4), dilute to the mark with water, and mix.

3.6 Determination

Measure the working curve solution on the inductively coupled plasma emission spectrometer at the recommended wavelength, when the linear correlation coefficient of the working curve

When k>=0.999, measure the emission intensity of the test element in the analysis test solution (3.5.4.1) and the accompanying sample blank solution (3.5.3), from the working curve

Check the mass concentration of chromium.

3.7 Test data processing

The amount of chromium is calculated by the mass fraction wCr of chromium, calculated according to formula (3).

When the result is less than or equal to 0.10%, two significant digits are reserved; when the result is greater than 0.10%, it is reserved to two decimal places.

3.8 Precision

3.8.1 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 based on the data in Table 4.

Obtained by sexual interpolation or extension method.

3.8.2 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 based on the data in Table 5.

Obtained by sexual interpolation or extension method.