GOST 12350-78

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  ГОСТ 12350-78

GOST 12350−78 (ST SEV 961−78) Steel alloyed and high alloy. Methods for determination of chromium (with Amendments No. 1, 2, 3)

GOST 12350−78
(ST CMEA 961−78)

Group B39

STATE STANDARD OF THE USSR

STEEL ALLOYED AND HIGH-ALLOYED

Methods for determination of chromium

Alloyed and high-alloyed steels.
Methods of chromium determination

AXTU 0809

Date of introduction 1980−01−01

Promulgated by the decree of the USSR State Committee for standards of 23 November 1978 N 3081

Proven in 1984 by decree of the state standard from 15.08.84 2877 N validity extended until 01.01.95*

_______________

* Expiration removed by the resolution of Gosstandart of the USSR No. 1211 from 05.07.91 (IUS N 10 1991). — Note the CODE.

REPLACE GOST 12350−66, in addition to General guidance

July REPRINT with Amendments 1, 2, approved in December 1980 and August 1984 (IUS 3−81; 11−84)

AMENDED N 3, approved by decree of Committee of standardization and Metrology of the USSR from 05.07.91 N 1211, introduced with effect from 01.03.92 and published in IMS No. 10, 1991

Change 3 N entered the law office of «Code» in the text ICS N 10, 1991


This standard sets the photometric method for the determination of chromium (in mass fractions of from 0.01 to 0.50%), titrimetric method for the determination of chromium (in mass fractions of from 0.20 to 35.0%).

The standard fully complies ST SEV 961−78.

(Changed edition, Rev. N 1).

1. GENERAL REQUIREMENTS

1.1. General requirements for methods of analysis GOST 28473−90.

(Changed edition, Rev. N 3).

2. THE PHOTOMETRIC METHOD FOR THE DETERMINATION OF CHROMIUM (0,01−0,50%)

2.1. The essence of the method

The method is based on the oxidation diphenylcarbazide chromium (VI) in sulfate environment before painted in red-violet color compound and measuring the optical density of the colored solution at a wavelength of 546 nm.

Iron, Nickel, manganese, and other elements that hinder the analysis, separated by deposition of carbonate of sodium.

2.2. Equipment and reagents

Photoelectrocolorimeter and spectrophotometer.

Hydrochloric acid by the GOST 3118−77 or GOST 14261−77.

Nitric acid GOST 4461−77 or GOST 11125−84.

Sulfuric acid GOST 4204−77 or GOST 14265−79 and diluted 1:1, 1:4.

Acetic acid GOST 61−75.

Potassium permanganate according to GOST 20490−75, 1% solution.

The anhydrous sodium carbonate according to GOST 83−79, 20% solution.

Diphenylcarbazide with 0.1% freshly prepared solution of 0.1 g diphenylcarbazide dissolved in 10 cmof acetic acid, poured 90 cmof water and stirred.

Potassium dichromate according to GOST 4220−75, the standard solutions A and B.

Preparation of the solution A. 0,2829 g svejeprigotovlennogo and dried at 170−180 °C to constant weight of potassium dichromate is dissolved in 200 cmof water. The solution was transferred to a volumetric flask with a capacity of 1 DM, made up to the mark with water and mix.

1 cmof the solution contains 0.0001 g of chromium.

Preparation of the solution B. 200 cmof the solution And placed in a volumetric flask with a capacity of 1 DM, made up to the mark with water and mix.

1 cmof the solution contains 0,00002 g of chromium.

(Changed edition, Rev. N 3

).

2.3. Analysis

The weight became 0.2 g when the mass fraction of chromium from 0.01 to 0.3% and 0.1 g for the mass concentration of chromium more than 0.3 to 0.5% is placed in a conical flask with a capacity of 100 cm, flow 10 cmof hydrochloric acid and heated moderately to dissolve. Then poured dropwise nitric acid until the termination of foaming solution and an excess of 2−3 cm. The solution was boiled to remove oxides of nitrogen, cooled, carefully poured 5 cmsulphuric acid 1:1 and evaporated to the appearance of its vapors. After cooling, pour 25−30 cmof water and heated to dissolve the salts. In the hot solution poured 2cmof potassium permanganate solution, boil until falling out of the precipitate of manganese dioxide and dilute with water to 40−50 cm. Then gently, in small portions with stirring, poured 30 cmof sodium carbonate solution. Solution and the precipitate are heated to coagulate the precipitate, cool, transferred to volumetric flask with a capacity of 250 cm, made up to the mark with water and mix.

The solution was filtered through two dry filter «white ribbon» in a flask, the first portions of the filtrate discarded.

Aliquot part of the solution was 50 cmwhen the mass fraction of chromium from 0.01 to 0.05%, or 10 cmwhen the mass fraction of chromium in excess of 0.05 to 0.5% was placed in a volumetric flask with a capacity of 100 cmand 3 cm pour thesulfuric acid 1:4. The solution was stirred, poured 5cmof the solution diphenylcarbazide, made up to the mark with water and mix. If the steel contains vanadium, solutions after the addition, the solution difenilcarbazida incubated for 15 min.

After 5 min measure the optical density of the solution on the spectrophotometer at 546 nm or photoelectrocolorimeter with a filter having maximum transmission in the wavelength range of 530−550 nm in a cuvette with the thickness of the absorbing layer is 50 mm, using as a comparison solution of water.

From the values of optical density of analyzed solutions is subtracted the value of the optical density of the solution in the reference experiment. The chromium content is determined according to the calibration schedule.

Construction of calibration curve.

In six volumetric flasks with a capacity of 250 cmpour consistently 2,0; 4,0; 6,0; 8,0; 10,0 and 12,0 cmstandard solution B, containing 0,04; 0,08; 0,12; 0,16; 0,20 and 0,24 mg chromium. The solution in each flask topped up to the mark with water and mix.

From each volumetric flask aliquote select the three parts of a solution of 25 cmand placed in a volumetric flask with a capacity of 100 cm. In each flask poured 3 cmof sulphuric acid 1:4, 5 cmof a 0.1% strength solution diphenylcarbazide, stirred, topped up to the mark with water and mixed again. After 5 min, the optical density of the solution measured on a spectrophotometer at 546 nm or photoelectrocolorimeter with a filter having maximum transmission in the wavelength range of 530−550 nm in a cuvette with the thickness of the absorbing layer is 50 mm.

For solution comparison in volumetric flask with a capacity of 100 cmpour 25−30 cmof water, 3 cmsulphuric acid 1:4 and 5 cmof a 0.1% strength solution diphenylcarbazide, stirring the solution after addition of each reagent. The solution was topped to the mark with water and mix.

The found values of optical density and corresponding mass building chromium calibration curve.

(Modified, edited by

I, ISM. N 1, 2, 3).

2.4. Processing of the results

2.4.1. Mass fraction of chromium in percent is calculated by the formula

where is the weight of steel, suitable aliquote part of the solution, mg;

is the mass of chromium was found in the calibration schedule, mg.

(Changed edition, Rev. N 2).

2.4.2. Norms of accuracy and norms control the accuracy of determining the mass fraction of chromium shown in the table.

(Changed edition, Rev. N 3).

3. TITRIMETRIC METHOD FOR THE DETERMINATION OF CHROMIUM (0,20−35,0%)

3.1. The essence of the method

Chromium (III) neccersarily oxidize ammonium to chromium (VI) in acidic medium in the presence of silver nitrate. Chromic acid is titrated with a solution of salt of iron (II) and set the end point by potentiometric or visual method of inverse titration. In the latter case, the excess iron (II) octarepeat solution of potassium permanganate.

Present in the solution of vanadium after oxidation potentiometric titrated with a solution of salt of iron (II) and taken into account when calculating the mass fraction of chromium.

(Changed edition, Rev. N 1).

3.2. Equipment and reagents

The setup for potentiometric titration:

a pair of electrodes: a platinum indicator electrode and a reference electrode — a calomel, silver chloride or tungsten;

magnetic stirrer;

the DC millivoltmeter or pH meter that clearly capture the potential jump at the end point during the titration with the selected pair of electrodes. If necessary, the instrument sequentially connecting a variable resistance that allows you to make measurements in the range of the instrument scale.

Hydrochloric acid by the GOST 3118−77 or GOST 14261−77.

Nitric acid GOST 4461−77 or GOST 11125−84.

Sulfuric acid GOST 4204−77 or GOST 14265−79 and diluted 1:1, 1:4, 1:20.

Orthophosphoric acid according to GOST 6552−80.

A mixture of acids: 720 cmwater gently with continuous stirring, pour 200 cmof sulfuric acid, cooled, poured 80 cmof phosphoric acid and stirred.

Hydrofluoric acid (hydrofluoric) according to GOST 10484−78.

Potassium preservatory according to GOST 7172−76.

Silver nitrate according to GOST 1277−75, 0,2% solution.

Neccersarily ammonium (ammonium persulfate) according to GOST 20478−75, 25% solution, freshly prepared.

Manganese sulfate according to GOST 435−77, a 0.5% solution.

Sodium chloride according to GOST 4233−77, 5% solution.

Urea according to GOST 6691−77, 10% solution, freshly prepared.

Potassium permanganate according to GOST 20490−75, 2% solution.

Sodium atomistically according to GOST 4197−74, solution 20 g/l, freshly prepared.

Sodium oxalate according to GOST 5839−77, recrystallized and dried at 105−110 °C to constant weight.

Potassium dichromate according to GOST 4220−75, recrystallized and dried at 180−200 °C to constant weight.

Double sulfate salt of oxide of iron and ammonium (salt Mora) according to GOST 4208−72, of 0.1 molar concentration of an equivalent mole/l, standard solution. 40 g of Mohr salt dissolved in 200 cmof sulfuric acid 1:20, solution transferred to a volumetric flask with a capacity of 1 DM, made up to the mark with sulphuric acid of 1:20 and mixed.

A 0.05 molar concentration of an equivalent mole/lstandard solution: 500 cmof 0.1 molar concentration of an equivalent mole/lof a standard solution of salt Mora is transferred to a volumetric flask with a capacity of 1 DM, made up to the mark with sulphuric acid of 1:20 and mixed.

Mass concentration of 0.1 molar concentration of an equivalent mole/DMsolution of salt Mora set for potassium dichromate, 0,1000-of 0.2000 g of potassium dichromate were placed in a glass with a capacity of 500 cm, is dissolved in 200 cmof water, poured 40 cmsulphuric acid 1:4 and stirred. In a glass of solution, immerse the electrodes, turn on the stirrer and quickly pour the solution of salt Mora to obtain a slightly yellow color. Then the salt solution Mora is added slowly drop by drop, recording the volume of solution in the burette and the readings after adding each drop of solution. The volume of solution in the burette, corresponding to the maximum change of the readings taken for the volume used for titration.

The mass concentration of salt solution Mora , expressed in grams of chromium, calculated by the formula

where  — weight of potassium dichromate, g;

0,3535 — the ratio of potassium dichromate to chromium;

- the volume of salt solution Mora, used for titration, sm.

Potassium permanganate in 0.1 molar equivalents concentration mol/DM, standard solution. To 31.6 g of potassium permanganate dissolved in water, the solution is transferred into a bottle made of dark glass with a capacity of 10 DM, add water to volume of 10 DM, mix and leave for 7−10 days. The supernatant solution is poured, using a glass siphon, not reaching to the bottom of the bottle for 10−15 mm, in another bottle of dark glass.

A 0.05 molar concentration of an equivalent mole/l, standard solution. 15.8 g of potassium permanganate dissolved in water and then do as in the preparation of a 0.1 molar concentration of an equivalent mole/lof a standard solution.

Establish the relationship between solutions of potassium permanganate and salt Mora. To do this in a conical flask with a capacity of 250 cmpoured from a burette 25 cmof salt solution Mora, 100−120 ml of sulfuric acid 1:20 and titrated with 0.1 molar concentration of an equivalent mole/DMsolution of potassium permanganate to the appearance of slightly pink color, stable for 1 min.

The relation between the solutions of potassium permanganate and salt Mora is calculated by the formula

where  — the volume of salt solution Mora, taken for titration, ml;

 — the volume of potassium permanganate solution consumed for titration, sm.

The mass concentration of potassium permanganate solution set oxalate sodium. In a conical flask with a capacity of 500 cmis placed 200 cmsulphuric acid 1:20, heated to 70−75 °C and added dropwise a solution of potassium permanganate until a stable pink color. The contents of the flask add of 0.2000 g of sodium oxalate and after dissolution of the sample titrated with stirring with a solution of potassium permanganate until stable for 1 min pink color. By the end of the titration, the solution temperature should not be below 60 °C.

Mass concentration of 0.1 molar concentration of an equivalent mole/DMsolution of potassium permanganate , expressed in grams of chromium, calculated by the formula expressed in grams of chromium, calculated by the formula

where 0.2 is the weight of sodium oxalate, g;

0,2588 — the conversion factor of sodium oxalate for chrome;

 — the volume of potassium permanganate solution consumed for titration, sm.

(Changed edition, Rev. N 2, 3).

3.3. Analysis

3.3.1. Preparation of the solution for titration

The weight of steel

placed in a conical flask or beaker with a capacity of 500−600 cm, 50−70 cm, pour themixture of sulphuric and phosphoric acids, is heated to a decomposition of the sample. Pour 3−5 cmof nitric acid and evaporate the solution until the appearance of sulphuric acid fumes.

If the steel is not soluble in the mixture of sulfuric and phosphoric acids, the sample was dissolved in 20−30 cmof hydrochloric acid, then add 3−5 cmof nitric acid and continue heating to remove the nitrogen oxides. The solution is poured 50−70 cmof a mixture of sulfuric and phosphoric acids (when the content in steel more than 5% of tungsten, poured another 5−10 cmof phosphoric acid) and evaporated until the sulphuric acid fumes.

The side of the Cup washed with water and the solution again evaporated to fumes of sulfuric acid. The contents of the flask cooled, poured 100 cmof water and heated to dissolve the salts.

In the analysis of steels containing a large amount of carbides, the insoluble residue is filtered on a filter «white ribbon» containing a small amount filtrowanie mass. The filtrate collected in a flask with a capacity of 500 cm. The filter cake was washed 5−6 times with hot water, collecting the wash liquid in the same flask.

The filter with precipitate was placed in a platinum crucible, dried and incinerated. The precipitate is calcined at 900−950 °C and cooled.

The residue in the crucible is moistened with 2−3 drops of water, add 2−3 drops of sulfuric acid and 3−4 ml of hydrofluoric acid. The contents of the crucible carefully evaporated to dryness and calcined at 550−600 °C. the Residue in the crucible is fused with a 2−3 g peacemaking potassium. The cooled crucible was placed in a beaker with a capacity of 300 cmand the smelt is leached when heated in 30−40 cmof water. The resulting solution was attached to the main filtrate.

In the analysis of the steels with a mass fraction of manganese, less than 0.1% to the solution are added 1 ml of 0.5% solution of sulfate of manganese.

The solution is diluted with water to 250 cm, pour 10−15 cmof 0.2% solution of nitrate of silver, 30−40 cm25% solution of ammonium naternicola and heated until the appearance of crimson color. Then the solution was heated to the complete destruction of excess ammonium naternicola, poured 10 cm of5% strength sodium chloride solution and gently boil until the disappearance of the crimson color. The solution was cooled to room temperature, stirred and titrated (see PP.3.3.2 and 3.3.3).

(Changed edition, Rev. N

1, 2).

3.3.2. Potentiometric titration

Into the beaker with the test solution are immersed the electrodes, turn on the stirrer, the solution was stirred and quickly poured a 0.1 molar concentration of an equivalent mole/DMsolution of salt Mora to obtain a slightly yellow color. Then the salt solution Mora is added slowly drop by drop, recording the volume of solution in the burette and the readings after adding each drop. The volume of solution in the burette, corresponding to the maximum change of the readings taken for the volume used for titration.

In the presence of vanadium initially octarepeat the total content of chromium and vanadium, and then added dropwise a 2% solution of potassium permanganate until the appearance of pink coloring, stable within 2 minutes, the Excess potassium permanganate restore 1−2 drops of 2% solution of sodium attestatio to the disappearance of the pink color, add 20 cmof a 10% solution of urea, 25 cmsulphuric acid 1:1 (the arrow of the millivoltmeter returns to its original position) and titrated with a solution of salt Mora, adding it drop by drop, as described above. The difference in the volume of solution in the burette between the first and second titration is taken for the volume used for titration of chromium.

When the mass fraction of chromium in the steel is less than 2% is used for the titration of a 0.05 molar concentration of an equivalent mole/DMsolution of salt Mora.

(Changed edition, Rev. N 1, 3).

3.3.3. Visual titration

In the flask with the test solution is poured from the burette with 0.1 molar concentration of an equivalent mole/DMsolution of salt Mora to the transition of color from yellow-orange to green, and an excess of 7−10 cm. Iron ions (II) octarepeat a 0.1 molar concentration of an equivalent mole/DMsolution of potassium permanganate until the appearance of pink coloring, stable within 2 min.

When the mass fraction of chromium in the steel is less than 2% is used for the titration of a 0.05 molar concentration of an equivalent mole/DMRostow of salt Mora and potassium permanganate.

3.4. Processing of the results

3.4.1. When potentiometric titration mass fraction of chromiumpercentage in the steels containing vanadium, calculated by the formula

where - the volume of salt solution Mora, used for titration of chromium, cm;

mass concentration of salt solution Mora, expressed in grams of chromium;

 — the weight of the portion,

Mass fraction of chromium percentage in steels containing vanadium, calculated by the formula

where  — the volume of salt solution Mora, used for titration of chromium and vanadium, cm;

 — the volume of salt solution Mora, used for titration of vanadium, cm;

mass concentration of salt solution Mora, expressed in grams of chromium;

 — the weight of the portion,

3.4.2. Norms of accuracy and norms control the accuracy of determining the mass fraction of chromium shown in the table

(Changed edition, Rev. N 3).