GOST 3240.8-76

• gost-32408-76.pdf (194.49 KiB)
  ГОСТ 3240.8-76

GOST 3240.8−76 magnesium Alloys. Method for determination of silicon (with Change No. 1)

GOST 3240.8−76

Group B59

INTERSTATE STANDARD

MAGNESIUM ALLOYS

Method for determination of silicon

Magnesium alloys.
Method for determination of silicon

ISS 77.120.20
AXTU 1709

Date of introduction 1978−01−01

INFORMATION DATA

1. DEVELOPED AND INTRODUCED by the Ministry of aviation industry of the USSR

2. APPROVED AND promulgated by the Decree of the State Committee of standards of Ministerial Council of the USSR from 28.12.76 N 2889

3. REPLACE GOST 3240−56 in part of sec. IV

4. REFERENCE NORMATIVE AND TECHNICAL DOCUMENTS

5. Limitation of actions taken by Protocol No. 2−92 of the Interstate Council for standardization, Metrology and certification (ICS 2−93)

6. EDITION with Change No. 1, approved in June 1987 (IUS 11−87)


This standard sets the photometric method for the determination of silicon (with a mass fraction of silicon of from 0.003 to 0.6%).

The method is based on formation of colored complex compounds of silicon with ammonium molybdate at a pH of 1.35−1.50 is followed by reduction of the complex with ascorbic acid. Colored solution photometered at 680 nm.

1. GENERAL REQUIREMENTS

1.1. General requirements for method of analysis according to GOST 3240.0.

2. APPARATUS, REAGENTS AND SOLUTIONS

Spectrophotometer or photoelectrocolorimeter.

pH meter equipped with glass electrode

Bromine according to GOST 4109.

Bromine water, the solution saturated at 15−18 °C.

Sulfuric acid according to GOST 4204 and solutions with molar concentration (½ HSO)=1 mol/DM(1 M) and 10 mol/DM(10 M).

Sulfuric acid solution with molar concentration (½ HSO)=10 mol/DM(10 M) to 700 cmof water was added 280 cmsulfuric acid, cooled, poured into a volumetric flask with a capacity of 1 DM, dilute to the mark with water and mix.

Sulfuric acid solution with molar concentration (½ HSO)=1 mol/DM(1 M): 100 cm10 M solution of sulfuric acid diluted with water to 1 DM.

Boric acid according to GOST 9656, saturated at 20 °With a solution prepared as follows: 40 g of boric acid dissolved in hot water, dilute to about 900 cm, cooled, diluted to a volume of 1 DMand stirred.

Ammonium fluoride, 5% solution.

Ammonium molybdate according to GOST 3765, recrystallized; prepared as follows: 140 g ammonium molybdate dissolved in 1 DMof water. If necessary, before applying the filter. the pH of the solution should be around 7.

Magnesium purity of 99.99% according to GOST 804, the solution is prepared as follows: 10.0 g of magnesium was placed in a beaker with a capacity of 600 cm, add 200 cmof water and small portions of 140 cm1 M sulfuric acid solution. After dissolving, the solution was boiled for 5 min.

The solution was cooled, transferred with rinsing water in a volumetric flask with a capacity of 1 DM. The glass is rinsed, the solution was diluted to the mark with water and mix.

The anhydrous sodium carbonate according to GOST 83.

Anhydrous potassium carbonate according to GOST 4221.

Tartaric acid according to GOST 5817, 30% solution.

Desiccators with GOST 25336.

Ascorbic acid, 2% freshly prepared solution.

Silicon dioxide according to GOST 9428, fine, pre-calcined at 1000 °C to constant weight and cooled in a desiccator.

Standard solutions of silicon.

Solution A, prepared as follows: a platinum crucible weighed 0,2140 g of silicon dioxide, is added 2 g of a mixture of equal quantities of anhydrous sodium carbonate and anhydrous potassium carbonate. Platinum mixed well with a spatula and gently melt until a clear mass. The melt is cooled, dissolved in hot water and pour the solution into a plastic Cup. The crucible washed with water and the washings are attached to the main solution. The solution was then diluted with water to approximately 700 cm, cooled, poured into a volumetric flask with a capacity of 1 DM, dilute to the mark with water and mix.

1 cmof solution A contains 0.1 mg of silicon.

Solution B is prepared as follows: 50 cmsolution And taken in a volumetric flask with a capacity of 500 cm, made up to the mark with water and mix.

1 cmof a solution contains 0.01 mg of silicon.

For the preparation of solutions and for analysis use bidistillated water.

Solutions and reagents, with the exception of bromine water should be stored in plastic vessels.

(Changed edition, Rev. N 1).

3. ANALYSIS

3.1. A portion of the alloy take, depending on the mass fraction of silicon in accordance with the table.1.

Table 1

The sample is placed in a beaker with a capacity of 400 cm, add bromine water and then small portions while cooling add 10 M solution of sulfuric acid in the amounts indicated in the table.1. During dissolution of bromine water is necessary to pour so that the solution was always painted. Boiling the solution to remove the bromine, it is diluted with water to about 100 cmand poured into a plastic beaker with a capacity of 300 cm. Glass, which had a dissolution, washed with water and the washings are attached to the basic solution, then add 5 cmof a solution of ammonium fluoride, stirred with a plastic stick and leave it for 15−20 min at 60−70 °C. then add 50 cmof boric acid solution and mixed.

The solution was cooled to room temperature, poured into a volumetric flask with a capacity of 250 cm, made up to the mark with water and mix.

The solution is poured into a plastic glass and take two aliquote parts whose quantities are shown in table.1. One of alikvotnih parts is transferred to a beaker with a capacity of 100 cmand, if necessary, diluted to 50 cm.

To aliquote parts in a beaker, add 5 cmof ammonium molybdate and stirred, the pH of the solution was checked using pH meter (the pH value must be equal to 1,35−1,50). If necessary, the pH is adjusted by adding 1 M sulfuric acid solution from burette. After each addition the solution was stirred. Then bring the solution volume up to 65 cmand re-check the pH.

Aliquotes to the corresponding parts in a volumetric flask with a capacity of 100 cm, was added 1 n solution of sulfuric acid in the amount indicated in the preliminary experience with the pH control, diluted, if necessary, up to 60 cmand mix, then add 5 cmof ammonium molybdate solution, mix and leave for 10 mins then add 5 cmof a solution of tartaric acid 10 cm10 n sulfuric acid solution and 5 cmof ascorbic acid solution, dilute to the mark with water and mix.

After 10 minutes measure the optical density of the solution at 680 nm, using appropriate cuvettes.

In parallel spend control experience with the use of reagents, quantities which are listed in table.2.

Table 2

(Changed edition, Rev. N 1)

3.2. Construction of calibration curve

3.2.1. Construction of calibration curve for sample weighing 1 g

Eight plastic cups with a capacity of 250 cmeach injected with 100 cmof solution of magnesium sulfate containing 1 g of magnesium, then pour 0; 3,0; 5,0; 7,0 and 9,0 cmof solution B and 1.0; 3.0 and 5.0 cmof solution A, which corresponds to 0; 0,03; 0,05; 0,07; 0,09; 0,10; 0,30; 0,50 mg silicon.

Then in each Cup add 5 cmof a solution of ammonium fluoride, stirred with a plastic stick and leave it for 15−20 min at 60−70 °C, then add 50 cmof boric acid solution, stirred, cooled to room temperature and pour the solutions into a volumetric flasks with a capacity of 250 cm. Glasses rinsed, the rinse water is attached to the main solution, and then diluted to the mark with water, mixed and further analysis are as indicated in claim 3.1

.

3.2.2. Construction of calibration curve for sample weighing 0.5 g

Six plastic cups with a capacity of 250 cmeach injected with 50 cmof a solution of magnesium sulfate containing 0.5 g of magnesium, 25 cm10 M solution of sulfuric acid and 0; 2,5; 5,0; 10,0; 25,0 30,0 cm andstandard solution A, which corresponds to 0; 0,25; 0,50; 1,00; 2,50 and 3,00 mg of silicon.

The solutions were diluted to 100 cm, is introduced into each beaker at 5 cmof a solution of ammonium fluoride, stirred with a plastic stick and leave it for 15−20 min at 60−70 °C.

Then add 50 cmof boric acid, stirred and cooled to room temperature, pour the solutions into a volumetric flasks with a capacity of 250 cm, made up to the mark with water, mixed and further analysis are as indicated in claim 3.1.

On the found values of optical density of solutions to build calibration graphs.

4. PROCESSING OF THE RESULTS

4.1. Mass fraction of silicon () in percent is calculated by the formula

,

where is the mass of silicon was found in the calibration schedule g;

 — volume of initial solution, cm;

 — volume aliquote part of the solution, cm;

 — the weight of the portion of alloy,

(Changed edition, Rev. N 1).

4.2. Allowable absolute differences of the results of the parallel definitions should not exceed the values given in table.3

Table 3

5. CONTROL OF MEASUREMENT ACCURACY

To control the accuracy of measuring the mass fraction of silicon of from 0.003 to 0.6% using state standard samples of magnesium alloys, as well as industry standard samples and standard samples of the enterprise of magnesium alloys, issued in accordance with GOST 8.315. Accuracy control measurement is carried out in accordance with GOST 25086.

Allowed to control the accuracy of measuring the mass fraction of silicon by a method of additives.

Sec. 5. (Added, Rev. N 1).