GB/T 223.6-2025Iron, steel and alloy - Determination of boron content - Neutralization titrimetric method and spectrophotometric method (English PDF)

4.1 Principle

Dissolve the specimen in hydrochloric acid. Hydroxide is oxidized by peroxide. Iron, chromium, nickel, and other elements are separated by a strong base. Use p-nitrophenol as an indicator to adjust the solution to acidity. Boil the solution to remove carbon dioxide. The pH of the solution is readjusted to 7.In the presence of mannitol, use phenolphthalein as an indicator to titrate with a standard sodium hydroxide solution.

When the tungsten content in 1 g of specimen is greater than 15 mg or the molybdenum content is greater than 15 mg, it shall interfere with the determination.

4.2 Reagents

Unless otherwise specified, only reagents confirmed to be analytically pure and Grade

II water as specified in GB/T 6682 shall be used in the analysis.

0.01081 - The mass of boron, equivalent to 1.00 mL of sodium hydroxide standard titration solution [c(NaOH) = 1.000 mol/L], in grams (g).

4.6 Precision

The precision of this method was tested in 1993 by eight laboratories determining the boron content at four levels. Each laboratory repeated the test three times for each boron content level. The repeatability limit r and reproducibility limit R were calculated based on the test results. The precision is shown in Table 1.The raw data are shown in Table

C.1 of Annex C.

The repeatability limit (r) and reproducibility limit (R) are obtained according to the equations given in Table 1.

Under repeatability conditions, the absolute difference between two independent test results shall not exceed the repeatability limit (r), and the cases that exceed the repeatability limit (r) shall not exceed 5%.

Under reproducibility conditions, the absolute difference between two independent test results shall not exceed the reproducibility limit (R), and the cases that exceed the reproducibility limit (R) shall not exceed 5%.

5.1 Principle

After the test material is dissolved in acid, boron compounds are decomposed using phosphoric acid and sulfuric acid. Boron reacts with methanol to form methyl borate, which is then separated from other elements by distillation. In the presence of oxalic acid, boron forms a red complex with curcumin. Measure the absorbance at a wavelength of 545 nm.

5.2 Reagents

Unless otherwise specified, only reagents confirmed to be guaranteed reagents and

Grade II water as specified in GB/T 6682 shall be used in the analysis.

5.2.1 Methanol. analytically pure.

5.2.2 Acetone. analytically pure.

5.2.3 Hydrogen peroxide. rho is approximately 1.10 g/mL.

5.2.4 Sulfuric acid. rho is approximately 1.84 g/mL.

5.2.5 Sulfuric acid, 1+6.Mix 1 portion of sulfuric acid (5.2.4) with 6 portions of water.

5.2.6 Phosphoric acid. rho is approximately 1.69 g/mL, MOS grade.

5.2.7 Nitric acid. rho is approximately 1.42 g/mL.

5.2.8 Hydrochloric acid. rho is approximately 1.19 g/mL.

5.2.9 Hydrochloric acid, 1+4.

Mix 1 portion of hydrochloric acid (5.2.8) and 4 portions of water.

5.2.10 Sulfur-phosphoric acid mixture, 3+5+2.

Mix 3 portions of sulfuric acid (5.2.4), 5 portions of phosphoric acid (5.2.6), and 2 portions of water.

5.2.11 Calcium hydroxide suspension.

Weigh 3.7 g of calcium hydroxide and add water to a volume of 500 mL. Store in a plastic bottle. Mix well before use.

5.2.12 Oxalic acid solution, 100 g/L.

5.2.13 Curcumin-ethanol solution, 0.5 g/L.

Weigh 0.05 g of curcumin. Dissolve it in 100 mL of anhydrous ethanol. Filter the solution through rapid filter paper. Store it in a plastic bottle.

5.2.14 Phenol-glacial acetic acid solution, 350 g/L.

Weigh 70 g of phenol. Dissolve it in 200 mL of glacial acetic acid. Store in a plastic bottle.

5.2.15 Boron standard solution, 50 µg/mL.

Weigh 0.2859 g of boric acid (mass fraction not less than 99.9%) into a 100 mL beaker.

Dissolve in water. Transfer to a 1000 mL volumetric flask. Dilute to the mark with water.

Mix well. Store in a plastic bottle.

5.2.16 Boron standard solution, 5 µg/mL.

Transfer 50.00 mL of boron standard solution (5.2.15) to a 500 mL volumetric flask.

Dilute to the mark with water. Mix well. Store in a plastic bottle.

Where,

V1 - Volume of test solution taken, in milliliters (mL);

V - Total volume of test solution, in milliliters (mL);

m1 - Boron content obtained from the working curve, in micrograms (µg);

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

5.7 Precision

The precision of this method was determined in 2007 by a joint test conducted by seven laboratories, selecting six total boron levels. Each laboratory performed four determinations for each total boron level according to GB/T 6379.1.The raw data (measured values) reported by each laboratory are shown in C.2.The raw data are statistically analyzed according to GB/T 6379.2.The precision is shown in Table 3.

The repeatability limit (r) and reproducibility limit (R) are obtained according to the equations given in Table 3.

Under repeatability conditions, the absolute difference between two independent test results shall not exceed the repeatability limit (r), and the cases that exceed the repeatability limit (r) shall not exceed 5%.

Under reproducibility conditions, the absolute difference between two independent test results shall not exceed the reproducibility limit (R), and the cases that exceed the reproducibility limit (R) shall not exceed 5%.

6.1 Principle

The sample is dissolved in hydrochloric acid and nitric acid. Boron compounds (such as nitrides) are decomposed with phosphoric acid and sulfuric acid at 290°C. In an acetate-acetate buffer medium, boric acid reacts with curcumin to form a colored compound. Photometric measurements are performed at a wavelength of 543 nm.

6.2 Reagents

Unless otherwise specified, reagents that are approved analytically pure and with very low boron content, and Grade 2 water as specified in ISO 3696, shall be used during the analysis.

6.2.1 Pure iron

It contains no boron or has a known residual boron content.

6.2.2 Sodium hypophosphite monohydrate (NaH2PO2 · H2O).

6.2.3 Hydrochloric acid. rho is approximately 1.19 g/mL.

6.2.4 Nitric acid. rho is approximately 1.40 g/mL.

6.2.5 Sulfuric acid. rho is approximately 1.84 g/mL.

6.2.6 Phosphoric acid. rho is approximately 1.71 g/mL.

6.2.7 Acetic acid.

It contains no acetaldehyde, with a pH of approximately 1.05 g/mL. To test whether the acetic acid contains acetaldehyde, add 20 mL of acetic acid (pH is approximately 1.05 g/mL) and 1 mL of potassium permanganate solution (1 g/L) to a 50 mL beaker. If it does not contain acetaldehyde, the solution shall retain the purple color of potassium permanganate; otherwise, it shall turn brown after 15 min.

6.2.8 Acetic acid-sulfuric acid mixture.

Cool with water. While stirring, slowly pour sulfuric acid (6.2.5) into an equal volume of acetic acid (6.2.7).

6.2.9 Acetic acid-ammonium acetate buffer solution.

Dissolve 225 g of ammonium acetate in 400 mL of water. Add 300 mL of acetic acid (6.2.7). Filter the solution into a 1000 mL polypropylene volumetric flask. Dilute to the mark with water. Mix well.

6.2.10 Sodium fluoride solution, 40 g/L.

Weigh 4 g of sodium fluoride and dissolve it in water. Dilute with water to 100 mL.

Store in a polypropylene bottle.

6.2.11 Boron standard solution, 100 µg/mL.

Weigh 0.2859 g of boric acid (mass fraction not less than 99.9%) into a 100 mL beaker.

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