RU1783393C - Method of quality detecting of boron in pyrolythic boron nitride - Google Patents

Abstract

SUMMARY OF THE INVENTION: Boric acid formed after decomposition of boron nitride quantitatively binds with a color reagent Azomethine H to a stable complex having a maximum absorption at a wavelength of 415 nm. 3 tab

Description

The invention relates to analytical and inorganic chemistry, in particular, it is useful for determining the percentage of boron in inorganic compounds, for example, boron nitride.

A method is known for determining boron in organoboron compounds using the azomethine H reagent. However, organic boron compounds are readily converted to a water-soluble state, in contrast to boron-containing inorganic compounds such as boron nitride.

Closest to the invention is the D-mannitol method for determining boron, in which a weighed portion of boron nitride (100-200 mg) is kept in a platinum crucible at 800 ° C with a mixture of alkali metal carbonates for 2 hours. A mixture of sodium and potassium carbonates is poured into the crucible, then a weighed portion of boron nitride is placed and again filled with the same mixture so that the total amount of the mixture is (5 ± 0.5) g. Then nitric acid is added

potassium in an amount of 0.05-0.1 g. Fusion is carried out in an oven. After cooling, the melt is dissolved in a glass in 10 ml of water, 2 drops of indicator methyl red and 20 ml of hydrochloric acid solution are added thereto. The solution was then quantitatively transferred to a volumetric flask and adjusted to the mark with distilled water. From a volumetric flask take 2 samples of 50 ml in a conical flask. The selected boron nitride solution is boiled for 10 minutes to remove carbon dioxide, cooled and neutralized with a saturated solution of barium hydroxide. The amount of boron in boron nitride is determined by titration of the resulting boric acid with barium hydroxide of a certain concentration. Five parallel determinations are made to determine the titer of barium hydroxide solution. The end of the titration is determined using the added reagent D-mannitol

Under the same conditions, a control sample is titrated.

cl

WITH

-h

00 SO SO SO

The amount of boron (% B) in boron nitride is calculated by the formula

K (Vi-V2V0.001082-4-100 L bm

where Vi.Va is the volume of 0.05 mol / l of barium hydroxide solution, which went to the titration of the test and control samples according to CTBeYmo, ml;

K is the correction factor to the titer of barium hydroxide solution;

fh is the mass of a sample of boron nitride;

4 - conversion factor for sampling (50 ml from 200 ml);

0.001082 - the amount of boron, corresponding to 1 ml of 0.05 mol / l of barium hydroxide solution,

The arithmetic average of two parallel definitions is taken as the result of the analysis. The absolute value of the total error of the analysis result is 0.6%.

The disadvantages of this method include: the need to take more samples of boron nitride (100-200 mg) for analysis; use for fusion of three reagents. The decomposition time of boron nitride is 2 hours; during the analysis it is necessary to prepare solutions of a strictly defined concentration with further verification of their titer; during the analysis, the test solution of boron nitride is boiled. The method is labor intensive and has a large number of sequentially performed operations; the titration process itself is visual.

The aim of the invention is to increase the accuracy of determining the amount of boron in boron nitride and simplify the analysis process. This goal is achieved by the fact that after fusing a sample of boron nitride with a reagent, cooling, quantitative transfer of melt, sampling for analysis, boric acid formed after decomposition of boron nitride is quantitatively bound into a stable yellow colored complex with a color reagent azomethine N, and the optical density at a wavelength of 415 nm and the boron content is determined by calculation. The color reagent azomethine H is the condensation product of salicylic aldehyde and al-acid. Its chemical name: 4- (2-hydroxybenzylidene amine) -5-hydroxy-naphthalene-2 6-lisulfonic acid.

S03H.

-HE

S03h

The absorption spectrum of a solution of a complex of azomethine H with boric acid has a distinct maximum at a wavelength of 415 nm. The method is carried out as follows.

A portion of boron nitride (3-8 mg) is fused in a hermetically sealed nickel potassium hydroxide reactor (8-10 granules) at a temperature of 850 ° C for 30 minutes. Plav

then transferred quantitatively to a volumetric flask. For analysis, 2 samples of the test boron nitride solution were taken from a volumetric flask. The following solutions are used in the analysis process: buffer solution (pH 5.0-5.3); a solution of the color-agent Azomethine is a standard solution of boric acid with a boron content of 100 μgV / ml.

To a sample of the test boron nitride solution to be studied, a solution of azomethine H, a buffer solution was added and adjusted to the mark with distilled water. A standard solution is prepared for analysis in the same way: a sample is taken into a volumetric flask

a boric acid solution with a known boron content, a buffer solution and a solution of azomethine H are added. The solutions prepared for analysis are placed in a dark place for 2 hours, after which the solutions

spectrophotometric at a wavelength of 415 nm. The optical density of the test and standard solutions was measured relative to a blank test.

The percentage of boron in boron nitride is calculated by the formula

o / oB DncaLVcI V.j (1)

DCT Wissle GL

Ossl, DCT — optical density of the test and standard solutions, respectively;

WISSSL, VCT aliquots of the test and standard solutions, respectively, ml;

V- dilution of the initial solution of boron nitride;

m - sample of boron nitride, mg. Standard and test solutions are prepared in such a way that the boron concentration in the photometric solution does not exceed 1 μgV / ml, since the region of boron concentration, where a linear dependence of the optical density of the solution on the concentration is observed, is 0.1-1.0 μg V / ml

5 The addition of a special buffer solution is due to the fact that the formation of a complex of boric acid with azomethine H and the development of a stable color of the complex occurs under strictly defined conditions, namely, if the pH of the solution is 5.0-5.3.

The reaction of the formation of a complex of a borate ion with a reagent azomethine H is reversible; therefore, it is necessary to add a precisely measured amount of the color reagent azomethine H of a strictly defined concentration to the analyzed boron nitride solution. 02-0.06 g / ml. In addition, the color intensity of the complex depends on the pH of the analyzed solution of boron nitride and is stable if the pH of the solution is 5.0-5.3; this pH value is maintained with a specially selected composition buffer solution. The results of the analysis are given in table.1.2.

Samples of pyrolytic boron nitride obtained by chemical vapor deposition on a graphite substrate were used for analysis.

Example 1. A portion of 3.810 mg boron nitride was fused with potassium hydroxide (0.5 g) for 30 minutes at 850 ° C in a hermetically sealed nickel reactor. The melt is cooled and quantitatively transferred to a conical flask by washing the reactor with water. 10 ml was withdrawn from the flask and transferred to a 100 ml volumetric flask. 10 ml of azomethine H solution and 10 ml of buffer solution are added thereto; adjusted to the mark with distilled water. Thus, two test solutions are prepared.

Preparation of a standard solution. 10 ml of boric acid solution with known boron content (10 μg V / ml) was taken into a 100 ml volumetric flask, 10 ml of azomethine H solution and buffer solution were added: adjusted to the mark with distilled water

Preparation of blank solution. 10 ml of azomethine H solution was taken into a 100 ml volumetric flask, a buffer solution was added and the mark was distilled with distilled water.

All prepared solutions are placed for 2 hours in a dark place, after which the solutions are spectrophotometric. Optical

the density of the solutions was measured on a Specord M 40 spectrophotometer (production of GDR).

The percentage of boron in the investigated sample of boron nitride, calculated according to the formula (1), is

% AT

0.3648-10ml-168.43 0.3700-3.81-10ml

43.59%.

where is oisl. 0.3648;

East 0.3700;

VCT WISSL. 10 ml;

t 3.81;

V 168.43.

PRI me R 2. Similar analysis operations were performed with a weight of boron nitride equal to 4,299 mg:

% AT

0.4210-10-193.09 0.4341-10-4.299

 43.56%

5

0

5

 0

5

where Oisl 0.4210;

Ost.-0.4341;

VCT WISSSL 10 ml;

V 193.09;

m 4.299 mg.

In the table. 3 presents the results of a comparative analysis of boron nitride samples according to the known method and invention.

Claims (1)

The claims A method for quantitative determination of boron in pyrolytic boron nitride, comprising fusing a sample of boron nmtride with a reagent, cooling, quantitative transfer of melt, sampling for analysis, obtaining a test solution, adding a color reagent, and determining boron content by calculation, which is different. that, in order to increase the accuracy of determining the amount of boron and simplify the analysis process, a solution of the color reagent azomethine H at a concentration of 0.02-0.06 g / ml and a buffer solution of pH 5.0-5.5 are added and the absorbance is measured solution at a wavelength of 415 nm. fifty Table 1 table 2 Table 3