GOST 22536.7-88

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  ГОСТ 22536.7-88

GOST 22536.7−88 carbon Steel and unalloyed cast iron. Methods for determination of chromium

GOST 22536.7−88

Group B09

STATE STANDARD OF THE USSR

CARBON STEEL AND UNALLOYED CAST IRON

Methods for determination of chromium

Carbon steel and unalloyed cast iron.
Methods for determination of chromium

AXTU 0809

Valid from 01.01.90
to 01.07.95*
______________________________
* Expiration removed
Protocol N 4−93 inter-state Council
for standardization, Metrology and certification.
(IUS N 4, 1994). — Note the CODE.

INFORMATION DATA

1. DEVELOPED AND INTRODUCED by the Ministry of ferrous metallurgy of the USSR

PERFORMERS

D. K. Nesterov, PhD. tech. Sciences; S. I. Rudyuk, PhD. tech. Sciences; S. V. Spirina, PhD. chem. Sciences (head of subject); V. F. Kovalenko, PhD. tech. science; N. N. Gritsenko, PhD. chem. Sciences; L. I. birch; O. M. Kirzhner

2. APPROVED AND put INTO EFFECT by decision of the USSR State Committee for standards from 25.08.88 N 3018

3. REPLACE GOST 22536.7−77

4. REFERENCE NORMATIVE AND TECHNICAL DOCUMENTS

This standard specifies the photometric (with a mass fraction of chromium from 0.01 to 0.50%), titrimetric (mass fraction of chromium with from 0.10 to 0.50%) and atomic absorption (at a mass fraction of chromium from 0.01 to 0.50%) methods for determination of chromium.

1. GENERAL REQUIREMENTS

1.1. General requirements for methods of analysis GOST 22536.0−87.

1.2. The error analysis result (at p = 0.95) does not exceed the limit shown in the table, when the conditions are met:

the difference between the two (three) parallel dimensions should not exceed (with a confidence probability =0,95) of the values () given in the table;

played in the standard sample, the value of the mass fraction of chromium should not differ from the certified more than acceptable (at a confidence level =0,85) the value given in the table.

If any of the above conditions, a second measurement of the mass fraction of chromium. If in repeated measurements the precision requirement of the results are not met, the results of the analysis recognize the incorrect measurements cease to identify and eliminate the causes of violation of the normal course of analysis.

The divergence of the two middle results of an analysis performed under different conditions (for example, when the control intralaboratory reproducibility) shall not exceed (at p = 0.95) of the values given in the table.

2. THE PHOTOMETRIC METHOD FOR THE DETERMINATION OF CHROMIUM

2.1. 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.

The influence of Fe (III) eliminate the addition of phosphoric acid. In the determination of chromium in steel and iron with a mass fraction of manganese over 1% in the determination of chromium less than 0.1% of iron, manganese and other elements that hinder the analysis, separated by deposition of carbonate of sodium.

2.2. Equipment and reagents

Photoelectrocolorimeter or spectrophotometer.

Sulfuric acid GOST 4204−77, diluted 1:4.

A mixture of acids: 150 cmsulphuric acid carefully poured into 700 cmof water, after cooling, poured 150 cmof phosphoric acid.

Acetic acid GOST 61−75.

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

Silver nitrate according to GOST 1277−75, a solution with a mass concentration of 2 g/DM; store in a container made of dark glass.

Rectified ethyl alcohol according to GOST 5962−67 or GOST 18300−87.

Ammonium neccersarily according to GOST 20478−75, a solution with a mass concentration of 200 g/DM.

1,5-Diphenylcarbazide according to GOST 5859−78, a solution with a mass concentration of 1 g/DM: 0.1 g dissolved in 10 cmof acetic acid, poured 50 cmof ethyl alcohol and made up to 100 cmwater.

Radio engineering carbonyl iron according to GOST 13610−79.

Sodium carbonate according to GOST 83−79, a solution with a mass concentration of 300 g/DM.

Potassium permanganate according to GOST 20490−75, a solution with a mass concentration of 10 g/DM.

Potassium dichromate according to GOST 4220−75.

Standard solutions of chromium.

Solution a: 0,2829 g dried at 140 °C to constant weight of potassium dichromate is dissolved in 250 cmof water in a volumetric flask with a capacity of 1 DM, made up to the mark with water and mix thoroughly.

1 cmof the solution contains 0.0001 g of chromium. Shelf life of solution 3 months.

Solution B: 50 cmsolution And placed in a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix.

1 cmof a solution of 0.00005 g contains chromium; (prepared immediately before use).

Solution: 10 cmof solution B is placed in a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix.

1 cmof the solution contains 0,0

00005 g of chromium.

2.3. Analysis

2.3.1. Without separation with sodium carbonate (at a mass fraction of chromium of from 0.1 to 0.5%).

2.3.1.1. The weight of steel or cast iron with a mass of 0.1 g was placed in a conical flask with a capacity of 100 cm, flow 20 cmof a mixture of acid, cover with watch glass and dissolve with a moderate heat. Then wash the glass over the bulb a small amount of water, poured drop by drop nitric acid until the termination of foaming solution, boil to remove oxides of nitrogen and cooled.

If there is a precipitate (graphite, silicic acid), the solution was filtered through a filter «white ribbon» and washed 5−6 times with hot water collecting the filtrate and washings. The filter with the sediment is discarded and the filtrate evaporated to a volume of 50−60 cm. To the cooled solution poured 5 cmof a solution of silver nitrate and 10 cmsolution naternicola ammonium and gradually heated until the appearance of pink coloring and boil until the destruction naternicola ammonium. The solution was then cooled, transferred to a volumetric flask with a capacity of 100 cm, top up to the mark with water and mix.

In a volumetric flask with a capacity of 100 cmis placed aliquot part of the solution was 10 cm, pour 2 cmof phosphoric acid (l:2), 15 cmwater and 5 cmof the solution diphenylcarbazide, made up to the mark with water, mix and immediately measure the optical density of colored solution with spectrophotometer at a wavelength of 546 nm or photoelectrocolorimeter with a filter having maximum transmission in the range of 530−550 nm. If the sample contains vanadium, the optical density is measured after 10−15 minutes Because of the low stability of the complex at the same time prepare 4−5 samples. For solution comparison in volumetric flask with a capacity of 100 cmis placed 20 cmwater 2 cmof the mixture of acids, 5 cmsolution diphenylcarbazide, made up to the mark with water and mix. From the values of optical density of analyzed solutions subtract the values of the optical density of the solution in the reference experiment.

The analysis results calculated by a calibration chart or by comparison with a standard sample similar in composition to the sample and carried through all the stages

analysis.

2.3.1.2. Construction of calibration curve

In six conical flasks with a capacity of 100 cmis placed 0.1 g of carbonyl iron. Five of them add the sequence 1, 2, 5, 10, 12 cmstandard solution B, which corresponds to 0,00005; 0,00010; 0,00025; 0,00050; 0,00060 g of chromium. The sixth linkage is used for the reference experiment. All the flasks were poured 20 cmof the mixture of acids and then do as given in claim 2.3.1.1.

On the found values of optical density and corresponding weight values of chromium build a calibration curve.

Allowed construction of calibration curve in the coordinates; the optical density — mass fraction of chromium.

2.3.1.3. Processing of the results

Mass fraction of chromium () in percent is calculated by the formula

,

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

 — the weight of the portion of the sample,

2.3.2. With the separation of sodium carbonate (at a mass fraction of chromium from 0.01 to 0.50%).

2.3.2.1. The weight of steel or cast iron with a mass of 0.2 g (with a mass fraction of chromium of 0.01 to 0.10%) or 0.1 g (for the mass concentration of chromium above 0.10 percent) were placed in a glass with a capacity of 200 cm, flow 20 cmof sulphuric acid (1:4), dissolved under moderate heating. Then poured dropwise nitric acid until the termination of foaming solution and an excess of 1−2 cm. The solution was boiled to remove oxides of nitrogen and evaporated to the appearance of sulphuric acid fumes. After cooling, the solution was poured 25−30 cmof water and heated to dissolve the salts. In the hot solution poured 2cmof potassium permanganate solution, boil to complete the precipitation of manganese and dvuoksid pour 15 cmof water. Then gently, in small portions, while stirring, poured 30 cmof sodium carbonate solution and kept warm on the stove for 20−30 min.

The solution with precipitate was cooled, transferred to a volumetric flask with a capacity of 100 cm, made up to the mark with water and mix. Part of the solution is filtered over a dry filter «white ribbon» in a dry flask, discarding first portion of filtrate.

Aliquot part of the solution was 50 cm(at a mass fraction of chromium of 0.01−0.03%), 20 cm(with mass fraction of chromium 0,03−0,10%) and 10 cm(when the mass fraction of chromium in excess of 0.10%) is placed in a volumetric flask with a capacity of 100 cm, pour 3 cmof sulphuric acid (1:4), the solution was cooled, poured 5cmof the solution diphenylcarbazide, stirred, topped up to the mark with water and mixed again.

After 5 min measure the optical density of the solution on the spectrophotometer at a wavelength of 546 nm or photoelectrocolorimeter with a filter having maximum transmission in the wavelength range of 530−550 nm. If the sample contains vanadium, the optical density is measured after 10−15 minutes simultaneously on 3−4 samples. A solution of comparison used 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 analysis results calculated by a calibration chart or by comparison with a standard sample similar in composition to the sample and carried through all the stages

analysis.

2.3.2.2. Construction of calibration curve

In seven volumetric flasks with a capacity of 100 cmflow consistently 1, 2, 4, 6, 8, 10, 12 cmstandard solution, which corresponds to 0,000005; 0,000010; 0,000020; 0,000030; 0,000040; 0,000050; 0,000060 g chrome. In each flask poured 3 cmof sulphuric acid (1:4), 5 cmsolution diphenylcarbazide, stirred, topped up to the mark with water and mixed again. After 5 min measure the optical density of the solution on the spectrophotometer at a wavelength of 546 nm or photoelectrocolorimeter with a filter having maximum transmission in the wavelength range of 530−550 nm.

For solution comparison in volumetric flask with a capacity of 100 cmpour 25−30 cmof water cm 3of sulfuric acid (1:4) and 5 cmdifenilcarbazida, 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 weight values of chromium build a calibration curve.

Allowed construction of calibration curve in the coordinates: the optical density is the mass fraction of chrome

.

2.4. Processing of the results

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

,

where

is the mass of chromium was found in the calibration schedule g;

-the weight of the portion of the sample corresponding to aliquote part of the solution,

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

3. TITRIMETRIC METHOD

3.1. The method is based on the oxidation of chromium (III) neccersarily ammonium to chromium (VI) in sulfate medium in the presence of silver nitrate. Chromic acid reduced solution of salt of iron (II) and set the end point of a potentiometric or visual titration. In the latter case, the excess Fe (II) octarepeat solution of potassium permanganate.

3.2. Equipment and reagents

The setup for potentiometric titration: two electrode — flat (platinum) and reference electrode (calomel, silver chloride or tungsten) magnetic or mechanical stirrer; millivoltmeter DC 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, which allows measurements in the range of the instrument scale.

Sulfuric acid GOST 4204−77 and diluted 5:95 and 1:1.

Orthophosphoric acid according to GOST 6552−80.

A mixture of acids: 160 cmsulphuric acid poured gently 760 cmof water, cooled and poured 80 cmof phosphoric acid.

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

Silver nitrate according to GOST 1277−75, a solution with a mass concentration of 2 g/DM; store in a container made of dark glass.

Ammonium neccersarily according to GOST 20478−75, a solution with a mass concentration of 100 g/DM, freshly prepared.

Sodium chloride according to GOST 4233−77, a solution with a mass concentration of 50 g/DM.

Sodium oxalate, anhydrous, according to GOST 5839−77.

Manganese (II) sulfate 5-water according to GOST 435−77, a solution with a mass concentration of 5 g/DM.

Urea according to GOST 6691−77; a freshly prepared solution with a mass concentration of 100 g/DM.

Sodium nitrate according to GOST 4197−74, a solution with a mass concentration of 20 g/DM.

Potassium dichromate according to GOST 4220−75.

Salt of protoxide of iron and ammonium double sulfate (salt Mora) according to GOST 4208−72, the solution with the mass concentration of the equivalent 0,02 mol/DM: 7,84 g of Mohr salt dissolved in 1 DMof sulphuric acid (5:95).

Mass concentration solution of salt Mora () is set according to the standard solution of chromium (VI) or the suspension of anhydrous potassium dichromate, dried at 150 °C to constant weight. A portion of potassium dichromate mass 0,1000 g dissolved in 150 DMwater in a volumetric flask with a capacity of 250 cm, and topped to the mark with water. Aliquot part 20 cmis placed in a beaker with a capacity of 400 cm, 20 cm pour thesulfuric acid 1:1.5 cmof phosphoric acid 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, accept for the volume used for titration.

Mass concentration solution of salt Mora (), expressed in grams of chromium per 1 cmof a solution, calculated by the formula

,

where  — weight of potassium dichromate, the corresponding aliquote part g;

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

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

Potassium permanganate according to GOST 20490−75, a standard solution with a mass concentration of the equivalent 0,02 mol/DM: 0,63 g of potassium permanganate dissolved in 1 DMof water, the solution transferred to a flask made of dark glass, closed glass stopper, mix thoroughly and leave for 7−10 days.

The solution is filtered through ignited asbestos or a funnel with a porous plate or poured gently siphon in a vessel made of dark glass. The solution was stored in this vessel, equipped with a siphon tube that is directly connected to the burette.

Mass concentration of solution () set of anhydrous sodium oxalate, dried to constant weight at 110 °C.

A portion of the sodium oxalate with a mass of 0.1 g was dissolved with heating in 50 cmof water is added 15 cmof sulphuric acid (1:1), heated to 70−80 °C and titrated with a solution of potassium permanganate until a stable pink color.

The mass concentration of a solution of potassium permanganate, expressed in grams of chromium per 1 cmof a solution, calculated by the formula

,

where 0,259 — the conversion factor of sodium oxalate for chrome;

 — weight of sodium oxalate, g;

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

Set the ratio () of the volume of the solution of salt Mora and potassium permanganate in a conical flask with a capacity of 500 cm, is poured from a burette 25 cmof salt solution Mora, add 250 cmof water, 60 cmof the mixture of acids and titrated solution of potassium permanganate until stable for 2−3 min slightly pink color.

The ratio is calculated by the formula

,

where is the volume of potassium permanganate solution consumed for titration of the salt solution Mora, cm;

 — the volume of salt solution Mora, taken for titration, sm.

The ratio set three times and take the average value.

3.3. Analysis

3.3.1. The weight of steel or cast iron with a mass of 2 g (for mass fraction of chromium of from 0.1 to 0.3%) and 1 g (in mass fraction of chromium from 0.3 to 0.5%) was placed in a conical flask or beaker with a capacity of 500−600 cmand dissolved in 60 cmof the mixture of acids. After complete dissolution are added dropwise nitric acid until the termination of foaming and boil until the destruction of carbides and removal of nitrogen oxides. In the analysis of cast iron graphite and partially precipitated silicic acid is filtered off and washed the filter with the sediment 5−6 times with hot water collecting the filtrate and washings in a flask or beaker with a capacity of 500−600 cm.

In the analysis of steel or cast iron with a mass fraction of manganese is less than 0.1% to the solution is added 1 cmof a solution of sulphate of manganese.

The solution is diluted with hot water to a volume of 200−250 cm, flow 10 cmof a solution of nitrate of silver, 20 cmsolution naternicola ammonia and heated to boiling. The emergence of the crimson coloration of the resulting manganese acid indicates the complete oxidation to hexavalent chromium. The solution was heated to destruction naternicola ammonium, poured 5cmof sodium chloride solution and continue boiling until the disappearance of the crimson and the appearance of the yellow color. If the solution to precipitate acquires a brown color, you need to add 1−2 cmof sodium chloride solution and continue boiling to obtain a pure yellow color. The solution was cooled in running water to room temperature, stirred and titrated (see PP.3.3.2 and 3.3.

3).

3.3.2. Visual titration

To the solution is added from a burette with continuous stirring a solution of salt Mora to the transition of color from yellow to green and an excess of 7−10 cm. An excess of salt solution Mora immediately octarepeat solution of potassium permanganate until a stable (within 2−3 min) pink color.

3.3.3. Potentiometric titration

Into the beaker with the test solution are immersed the electrodes, turn on the stirrer and pour the solution of salt Mora in the beginning quickly to obtain a slightly yellow color, then slowly dropwise to obtain a jump of the potential.

In the presence of vanadium initially octarepeat amount of chromium and vanadium, and then added dropwise a solution of potassium permanganate with a mass concentration of 20 g/DMbefore the appearance of a pink color, stable for 2 minutes, the Excess potassium permanganate restore 1−2 drops of a solution of sodium attestatio to the disappearance of the pink color, add 20 cmof a solution of urea, 25 cmof sulphuric acid (1:1) (the arrow of the millivoltmeter returns to its original position) and titrated with a solution of salt Mora, adding dropwise the above. The difference in the volume of solution in the burette between the first and second titration is taken for the volume consumed for titration of chromium.

3.4. Processing of the results

3.4.1. By visual titration mass fraction of chromium () in percent is calculated by the formula

,

where is the mass concentration of potassium permanganate, expressed in grams of chromium per 1 cmof solution;

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

 — the relationship between solutions of salt Mora and potassium permanganate;

 — the volume of potassium permanganate solution consumed for titration, cm;

 — the weight of the portion of the sample,

G.

3.4.2. When potentiometric titration mass fraction of chromium () in percent is calculated by the formula:

,

where is the mass concentration of salt solution Mora, expressed in g of chromium per 1 cmof solution;

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

 — the weight of the portion of the sample,

Mass fraction of chromium () in % in steel and cast iron, containing vanadium, calculated by the formula

,

where V is 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 Mora, expressed in grams of chromium;

 — the weight of the portion of the sample,

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

The method used in the dispute in the assessment of quality carbon steel and unalloyed cast iron.

4. ATOMIC ABSORPTION METHOD FOR THE DETERMINATION OF CHROMIUM

4.1. The essence of the method

The method is based on measuring the degree of absorption of resonance radiation by free atoms of chromium, formed as a result of spraying the test solution into the flame of air — acetylene or nitrous oxide — acetylene.

4.2. Equipment and reagents

Atomic absorption spectrophotometer fiery.

Lamp with hollow cathode for the determination of chromium.

Acetylene according to GOST 5457−75.

The nitrous oxide.

The compressor supplying compressed air, or compressed air.

Hydrochloric acid by the GOST 3118−77 or GOST 14261−77 diluted 1:1, and the solution with a mass concentration of 50 g/DM.

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

Potassium dichromate according to GOST 4220−75.

Metal chrome brand Х99А, Х99Б, H98,5, Х99А (H), Х99Б (H) X98,5 (H) according to GOST 5905−79.

Standard solutions of chromium.

Solution a: 2,8290 g dried at 140 °C to constant weight of potassium dichromate is dissolved in 250 cmof hydrochloric acid solution (50 g/DM) in a volumetric flask with a capacity of 1 DM, made up to the mark with hydrochloric acid and stirred. Solution a can be prepared from metallic chromium. 1 g of chromium metal was dissolved with heating in 20 cm. hydrochloric acid are carefully added dropwise 1−2 cmof nitric acid and boil to remove oxides of nitrogen. The solution was cooled, 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 0.001 g of chromium.

Solution B: 50 cmsolution And placed in a volumetric flask with a capacity of 1 DM, made up to the mark with water and mix. 1 cmof a solution of 0.00005 g contains chromium.

Ammonium chloride according to GOST 3773−72, a solution with a mass concentration of 50 g/DM.

Radio engineering carbonyl iron according to GOST 13610−79 and a solution with a mass concentration of 50 g/l: 50 grams of carbonyl iron is dissolved in 400 cmof hydrochloric acid (1:1), then added dropwise nitric acid until the end of foaming, is evaporated to wet salts, add 40−50 cmof hydrochloric acid and again evaporated to wet salts. This operation is repeated again. Of salt dissolved in 100 cmof hydrochloric acid (1:1), cooled, transferred to a volumetric flask with a capacity of 1 DM, adjusted to the mark with water, mix and filter the solution through a filter medium

density.

4.3. Preparation of the device

The preparation instrument to the analysis carried out in accordance with the attached instructions. Set the spectrophotometer at a resonance line 357,9 nm. After switching on the gas flow and ignition of the burner spray water into the flame and set the zero readings.

4.4. Analysis

4.4.1. The weight of steel or cast iron with a mass of 1 g (in mass fraction of chromium from 0.01 to 0.10%) or 0.5 g (at a mass fraction of chromium of from 0.1 to 0.2%), or 0.2 g (for a mass fraction of chromium of from 0.2 to 0.5%) were placed in a glass with a capacity of 100 cmand dissolved by heating in 15 cmof hydrochloric acid and 5 cmof nitric acid. The solution was evaporated to dryness, cooled, poured 5cmof hydrochloric acid of 30 cmof water and heated to dissolve the salts. The cooled solution was transferred to volumetric flask with a capacity of 100 cm, flow 10 cmof a solution of ammonium chloride, made up to the mark with water and mix. The solution is filtered through dry filter «white ribbon», discarding the first two portions of the filtrate.

To prepare the solution in the reference experiment in a volumetric flask with a capacity of 100 cmpour all reagents used in the analysis. Sprayed in the flame of the solution in the reference experiment, and then analyze the solutions in order of increasing mass fraction of chromium to obtain stable readings for each solution.

Prior to introduction into the flame each of the analyzed solution is sprayed water to wash the system and check the zero point.

From the average value of absorbance of each of the analyzed solutions, the average value is subtracted absorption in the reference experiment.

A lot of chrome find on a calibration curve

.

4.4.2. Construction of calibration curve

In seven volumetric flasks with a capacity of 100 cmplaced at 20 or 10 or 4 cmof solution carbonyl iron (depending on the sample of steel or cast iron), pour in six of them consecutively 1,0; 3,0; 5,0; 10,0; 15,0; 25,0 cmstandard solution B, which corresponds to 0,00005, 0,00015; 0,00025; 0,00050; 0,00075; 0,00125 g chrome pour 10 cmof a solution of ammonium chloride, made up to the mark with water and mix. Further analysis was carried out as given in claim 4.4.1. The seventh flask is used for the reference experiment.

On the found values of absorbance of solutions and their corresponding mass values of chromium build a calibration curve.

4.5. Processing of the results

4.5.1. Mass fraction of chromium () in percent is calculated by the formula

,

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

 — the weight of the portion of the sample,

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