GB/T 3653.1-2024Ferroboron - Determination of boron content - Alkalimetry method (English PDF)

0 Note on the printed English title

The English title on the cover of the document is printed as Ferroboron—Determination of boron content—Alkalimelry method, with the last word spelt Alkalimelry and with the word spacing lost in the digitised text. The spacing has been restored and the misspelling has been corrected to Alkalimetry; no other word of the printed title has been altered.

0b Warning

Persons using this document should have practical experience of work in a regular laboratory. The document does not point out all the possible safety problems; it is the responsibility of the user to adopt suitable safety and health measures and to ensure compliance with the conditions laid down in the relevant national regulations.

1 Scope

The document specifies a method for determining the boron content of ferroboron by alkalimetric titration.

It applies to the determination of boron in ferroboron over a mass fraction range of 3.00 % to 26.00 %.

2 Normative references

The content of the following documents constitutes indispensable provisions of this document through normative reference in the text. For dated references, only the version corresponding to that date applies; for undated references, the latest version, including all amendments, applies.

GB/T 4010 Ferroalloys—Sampling and preparation of samples for chemical analysis; GB/T 6379.1 Accuracy (trueness and precision) of measurement methods and results—Part 1: General principles and definitions; GB/T 6379.2 Accuracy (trueness and precision) of measurement methods and results—Part 2: Basic method for the determination of repeatability and reproducibility of a standard measurement method; GB/T 6682 Water for analytical laboratory use—Specification and test methods; GB/T 8170 Rules of rounding off for numerical values and expression and judgement of limiting values; GB/T 12806 Laboratory glassware—One-mark volumetric flasks; GB/T 12808 Laboratory glassware—One-mark pipettes.

3 Terms and definitions

The document lists no terms and definitions that require defining.

4 Principle

The test portion is decomposed by fusion with anhydrous sodium carbonate or with potassium sodium carbonate and sodium peroxide, leached with water, and the iron, manganese and nickel are separated by dry filtration. Part of the filtrate is taken, citric acid is added to mask aluminium, and the test solution is adjusted to pH 6.9 under the control of a pH meter; mannitol is then added and the solution is titrated with sodium hydroxide standard solution to pH 6.9, which is the end point.

5 Reagents and materials

Unless otherwise stated, only approved analytical grade or better reagents are used in the analysis, together with grade two or better distilled water complying with GB/T 6682 or water of equivalent purity.

The list comprises: anhydrous sodium carbonate, solid; potassium sodium carbonate, solid; sodium peroxide, solid; mannitol, solid; anhydrous ethanol, described in the document as solid; citric acid solution 20 g/L; hydrochloric acid 1+1; methyl red indicator 1 g/L; sodium hydroxide solution 100 g/L.

Boron standard solution: 11.4320 g of primary reference boric acid is weighed into a 500 mL beaker, 200 mL of water is added and, after dissolution, the solution is transferred to a 500 mL volumetric flask, diluted to the mark with water and mixed; 1 mL of this solution contains 0.0040 g of boron.

Sodium hydroxide standard solution, c(NaOH) = 0.1 mol/L. Preparation: 4 g of sodium hydroxide is weighed and dissolved in 250 mL of previously boiled water, shaken, poured into a polytetrafluoroethylene container, and left closed until the solution is clear; it is diluted to 1 L with previously boiled water and mixed, and the clear upper layer is taken with a plastic tube into another bottle and used after standardisation.

Standardisation: 5.00 mL of the boron standard solution is transferred to a 250 mL beaker, 100 mL of water and 10 mL of citric acid solution are added, the electrodes are inserted and connected to the pH meter, the magnetic stirrer is started, the solution is adjusted to pH 6.9 with the sodium hydroxide solution, 20 g of mannitol is added and the solution is titrated with the sodium hydroxide standard solution to pH 6.9, which is the end point. The titre T of the sodium hydroxide standard solution for boron, in g/mL, is calculated from equation (1); the equation as printed could not be reconstructed from the digitised text and is therefore not reproduced. Its symbols are V0, volume of boron standard solution taken for the titration, in mL; c, boron content of 1 mL of the boron standard solution, in g/mL; V1, volume of sodium hydroxide standard solution used in the titration, in mL.

6 Instruments and equipment

Unless specifically stated otherwise, ordinary laboratory instruments are used in the analysis; one-mark volumetric flasks and one-mark pipettes comply with GB/T 12806 and GB/T 12808 respectively.

The equipment comprises a pH meter with a smallest scale division of 0.01; an analytical balance with a readability of 0.1 mg; a magnetic stirrer with a plastic coated stirring bar and speed control; a glass electrode; and a calomel electrode.

7 Sampling and sample preparation

Sampling and sample preparation are carried out as specified in GB/T 4010; the whole of the test sample passes a 0.088 mm sieve.

8 Analytical procedure

Test portion: 0.50 g of sample is weighed to the nearest 0.0001 g.

Number of determinations: at least 2 independent determinations are carried out on the same sample.

Blank test: a blank test is carried out along with the test portion.

Determination, first step: the test portion is placed in a nickel or iron crucible containing 4 g of anhydrous sodium carbonate or 4 g of potassium sodium carbonate and heated in a furnace at 500 °C to 600 °C until the sample and the flux just turn red; it is then removed and cooled. 6 g of sodium peroxide is added, the crucible is placed at the mouth of the furnace and, once the sodium peroxide has become liquid, it is moved to the middle of the furnace at a furnace temperature of 800 °C to 850 °C, fused for 15 min to 20 min, removed and cooled.

Determination, second step: the crucible with the melt is placed in a 300 mL quartz beaker or a 500 mL polytetrafluoroethylene beaker containing 120 mL of water and leached with heating; the crucible is then removed and washed. If a little melt is found stuck to the bottom of the crucible, a few drops of hydrochloric acid 1+1 may be added and the residue dissolved with slight heating before the crucible is removed and washed. 2 mL of anhydrous ethanol is added, the solution is boiled for 3 min to 5 min, cooled, transferred to a 500 mL volumetric flask, diluted to the mark with water, mixed and left to stand for a moment.

Determination, third step: the solution is dry filtered through a double layer of rapid filter paper and 100.0 mL of the filtrate is transferred to a 300 mL quartz beaker; 10 mL of citric acid solution and 2 drops of methyl red indicator are added and the solution is neutralised with hydrochloric acid 1+1 until it turns red. The beaker is covered with a watch glass, the solution is heated and boiled for 10 min, cooled to room temperature, and made up with carbon dioxide free water to a volume of about 120 mL. The electrodes and the pH meter are connected and the stirrer is started. The solution is adjusted with the sodium hydroxide solution to about pH 6.0 and then with the sodium hydroxide standard solution to pH 6.90 plus or minus 0.02; 20 g of mannitol is added and, with continuous stirring, the solution is titrated with the sodium hydroxide standard solution to pH 6.90 plus or minus 0.02, which is the end point.

9 Calculation and expression of results

The boron content of the sample, expressed as a mass fraction in %, is calculated from equation (2). The equation as printed could not be reconstructed from the digitised text and is therefore not reproduced; its symbols are V2, volume of sodium hydroxide standard solution consumed in titrating the test solution, in mL; V3, volume of sodium hydroxide standard solution consumed by the blank run with the sample, in mL; T, titre of the sodium hydroxide standard solution for boron, in g/mL; m, mass of the test portion, in g; r, aliquot ratio of the test solution.

If the absolute value of the difference between two independent analytical results on the same sample is not greater than the repeatability limit r, the arithmetic mean is taken as the analytical result. If that absolute difference is greater than the repeatability limit r, further determinations are made and the result is established as specified in Annex A. The analytical result is rounded in accordance with GB/T 8170.

10 Precision

The collaborative precision trial was carried out in 2023 by 8 laboratories on samples at 7 different levels, each laboratory testing each level three times independently; the precision established by the statistical methods of GB/T 6379.1 and GB/T 6379.2 is given in Table 1 and the raw data of the trial in Annex B.

Table 1 has three columns, the determination range as a mass fraction in %, the repeatability limit r in % and the reproducibility limit R in %, with a single row covering the range 3.00 % to 26.00 %. In the digitised text the expressions given in the r and R cells run into one another and cannot be separated with certainty, so they are not reproduced here; a note to the table states that m in the expressions is the content of the element determined, as a mass fraction in %.

Under repeatability conditions, the absolute difference between two independent test results is not greater than the repeatability limit r, and the cases in which it is greater than r do not exceed 5 %. Under reproducibility conditions, the absolute difference between two independent test results is not greater than the reproducibility R, and the cases in which it is greater than the reproducibility limit R do not exceed 5 %.

11 Test report

The test report includes the sample identification, the name of the laboratory and the test date; the number of this document; the results and the form in which they are expressed; any abnormal phenomena noticed during the determination; and any characteristic noted during the determination, together with any operation not specified in this document that may have affected the results obtained on the sample or on the certified reference material.

A Annex A (normative) Flow chart of the acceptance procedure for test analysis results

The flow chart of the acceptance procedure for sample analysis results is given as Figure A.1, with a note stating that r is the repeatability limit. The content of the flow chart itself is graphical and is not reproduced in this description.

B Annex B (informative) Raw data of the precision trial

Table B.1 records the raw data of the precision trial for boron as mass fractions in %: the individual results of laboratories A to H, three per laboratory, at 7 levels. In the digitised text the laboratory letters run into the first value of each block, so the individual values are not reproduced here.

C Relationship to previous standards

The document replaces GB/T 3653.1-1988, Methods for chemical analysis of ferroboron—Determination of boron content by alkalimetric titration. Besides structural and editorial changes, the foreword lists the following technical changes: anhydrous sodium carbonate was added; the preparation of sodium hydroxide in previously boiled water was changed; an analytical balance was added; the number of determinations was added; the expression of results was added; the repeatability limit and the reproducibility limit replaced the permissible difference; and the content of the test report was added.

The standard was first published in 1988 and this is the first revision. It is Part 1 of GB/T 3653, a series of analytical methods for ferroboron planned in 7 parts covering, in order, boron by alkalimetric titration, carbon by the gas volumetric method, silicon by the perchloric acid dehydration gravimetric method, aluminium by EDTA titration, sulfur by chromatographic separation and barium sulfate gravimetry, phosphorus by the antimony phosphomolybdenum blue photometric method, and sulfur by infrared absorption.