GOST 6689.14-92

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  ГОСТ 6689.14-92

GOST 6689.14−92 Nickel, alloys Nickel and copper-Nickel. Methods for determination of chromium

GOST 6689.14−92

Group B59

STATE STANDARD OF THE USSR

NICKEL, ALLOYS NICKEL AND COPPER-NICKEL

Methods for determination of chromium

Nickel, nickel and copper-nickel alloys. Methods for the determination of chromium

AXTU 1709

Date of introduction 1993−01−01

INFORMATION DATA

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

DEVELOPERS

V. N. Fedorov, Y. M. Leybov, Boris Krasnov, A. N. Bulanova, L. V. Morea, A. I. Vorobyov

2. APPROVED AND promulgated by the Decree of Committee of standardization and Metrology of the USSR from 18.02.92 N 167

3. REPLACE GOST 6689.14−80

4. REFERENCE NORMATIVE AND TECHNICAL DOCUMENTS

This standard specifies the titrimetric and atomic absorption methods for the determination of chromium (in mass fraction of chromium of from 8 to 11%) in Nickel alloys according to GOST 492*.
________________
* On the territory of the Russian Federation GOST 492−2006. — Note the manufacturer’s database.

1. GENERAL REQUIREMENTS

General requirements for methods of analysis GOST 25086 with the addition of sec. 1 GOST 6689.1.

2. TITRIMETRIC METHOD FOR THE DETERMINATION OF CHROMIUM

2.1. The essence of the method

The method is based on the oxidation of chromium (III) to chromium (IV) neccersarily ammonium in sulfate medium in the presence of silver nitrate as a catalyst, the recovery of chromium (IV) standard solution of salt Mora and the determination of the excess iron (II) potentiometric titration with potassium dichromate solution or by titration with solution of potassium permanganate with a visual indication of the titration end.

2.2. Apparatus, reagents and solutions

Potentiometer LPM-60M, pH 340 or any device of the same class.

The platinum electrode ETPL-OGM.

The reference electrode mercury sulfate.

Nitric acid according to GOST 4461.

Hydrochloric acid according to GOST 3118.

The mixture of acids to dissolve: to mix one part nitric acid with three parts hydrochloric acid.

Sulfuric acid according to GOST 4204, diluted 1:1 and 1:9.

Oxalic acid according to GOST 22180, a solution of 10 g/DM.

Silver nitrate according to GOST 1277, a solution of 5 g/DM.

Sodium oxalate according to GOST 5839.

Sodium chloride according to GOST 4233, a solution of 50 g/DM.

Ammonium neccersarily according to GOST 20478, a solution of 250 g/DM.

Salt of protoxide of iron and ammonium double sulfate (salt Mora) according to GOST 4208, 0.1 mol/DMsolution: 39,2 g of Mohr salt dissolved in a small volume of sulphuric acid (1:9), transfer the solution into a measuring flask with volume capacity of 1000 cm, made up to the mark with the same acid.

Potassium dichromate according to GOST 4220, 0,02 mol/DMsolution: prepare fiksanala or 4,9037 g of potassium dichromate dried at 140 °C, dissolved in water, the solution is transferred into a measuring flask with volume capacity of 1000 cmand topped to the mark with water.

1 cmof the solution contains 0,001734 g of chromium.

Potassium permanganate according to GOST 20490, 0,02 mol/DMsolution: prepare fiksanala or 3.2 g of potassium permanganate dissolved in a beaker with a capacity of 500 cm250 cmboiled and cooled water, allowed to settle and decanted by decantation in the flask with a capacity of 1000 cm. In a glass, added again with 250 cmof water, mix well, allow the grout to settle and again decanted into the same flask. The solution in the flask topped up to the mark with water, transferred to a flask made of dark glass and leave for 7−10 days in the dark

.

2.2.1. The installation of the mass concentration of the solution of potassium permanganate.

0.1 g of sodium oxalate, dried at 100−105 °C, placed in a conical flask with a capacity of 250 cm, 100 cm, addhot water, 10 cmof sulphuric acid (1:1) and titrated with a solution of potassium permanganate with constant stirring, until the appearance of slightly pink colour.

Correction factor () for the solution of potassium permanganate is calculated by the formula

,

where  — weight of sodium oxalate, g;

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

0,0067002 — theoretical mass of sodium oxalate, corresponding to 1 cmof 0.02 mol/DMsolution of potassium permanganate,

Mass concentration of solution () of potassium permanganate was calculated according to the formula

,

where  — correction factor;

0,001734 theoretical mass concentration of 0.02 mol/DMsolution of potassium permanganate for the chrome.

2.3. Analysis

A sample of alloy weighing 0.5 g were placed in a glass with a capacity of 300 cm, add 20−25 cmof a mixture of acid, cover with watch glass, glass or plastic plate and dissolved by heating. Glass or the plate and the wall of the beaker rinse with water, add 30 cmof sulphuric acid and evaporated until a white smoke of sulfuric acid. The residue is cooled, rinse the walls of the beaker and evaporated again until a white smoke of sulfuric acid. The residue is cooled, add 200 cmof water, dissolved by heating, the solution was transferred to a conical flask with a capacity of 500 cm, rinse the glass with water and diluted to 300 cm. Add 10 cmof a solution of silver nitrate, 10 cmsolution naternicola ammonium and boil until the destruction of excess ammonium naternicola (to complete the termination of allocation of bubbles of oxygen). If the alloy contains manganese, the add 5 cmof sodium chloride solution and again boil until clarification of the solution. Add three or four drops of a solution of oxalic acid. To the cooled solution is added from burette a solution of salt Mora to switch green to blue and 10 cmexcess.

The excess of salt Mora titrated with potassium permanganate solution until the appearance of pale purple staining.

In potentiometric titrations the oxidation of chromium and all further operations are carried out in the glass. The excess of salt Mora potentiometric titrated with a solution of potassium dichromate to the jump in the potential.

In both cases, the titrated solution add exactly the same amount of salt Mora and again titrated solution of potassium permanganate or potassium dichromate, as described in

up.

2.4. Processing of the results

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

,

where is the volume of permanganate solution or potassium dichromate, that is consumed in the last titration of the added solution of salt Mora, cm;

 — the volume of permanganate solution or potassium dichromate, that is consumed in the first titration of the excess of salt Mora, cm;

 — mass concentration of the permanganate solution or potassium dichromate for chromium, g;

 — the mass of alloy,

2.4.2. Discrepancies in the results of three parallel measurements and the results of the two tests should not exceed 0.12 percent and 0.17 percent, respectively.

2.4.3. Control of accuracy of analysis results is carried out by additives or by comparison of the results obtained by atomic absorption method in accordance with GOST 25086.

2.4.4. Titrimetric method is applied in case of disagreement in assessing the quality of Nickel alloys.

3. ATOMIC ABSORPTION METHOD FOR THE DETERMINATION OF CHROMIUM

3.1. The essence of the method

The method is based on measuring the absorption of light by atoms of chromium formed during the introduction of the analyzed solution in the flame acetylene-air.

3.2. Apparatus, reagents and solutions

Atomic absorption spectrometer with a radiation source for chromium.

Nitric acid according to GOST 4461, diluted 1:1.

Hydrochloric acid according to GOST 3118, diluted 1:1.

Hydrofluoric acid according to GOST 10484.

Sulfuric acid according to GOST 4204, diluted 1:1 and 1:4.

Chrome metal according to GOST 5905*.
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* On the territory of the Russian Federation GOST 5905−2004. — Note the manufacturer’s database.

Chrome sulfate according to GOST 4472.

Chromium standard solution: 0.1 g of chromium is dissolved by heating in 10 cmof hydrochloric acid (1:1) or 0.48 g of chromium sulfate was dissolved with heating in 10 cmof sulphuric acid (1:4).

The solution was transferred to a volumetric flask with a capacity of 1 DMand topped to the mark with water.

1 cmof the solution contains 0.0001 g of chromium.

3.3. Analysis

3.3.1. A sample of alloy weighing 0.1 g was placed in a platinum Cup and dissolved by heating in 10 cmof nitric acid (1:1) and 2 cmhydrofluoric acid. Then add 10 cmsulphuric acid (1:1) and evaporated until a white smoke of sulfuric acid. Cup cooled and the residue is dissolved in 50 cmof water when heated. The solution was transferred to a volumetric flask with a capacity of 100 cmand top up with water to the mark. Aliquot part of the sample solution of 10 cm,transferred to a volumetric flask with a capacity of 100 cmand top up with water to the mark.

Measure the atomic absorption of chromium in the flame acetylene-air at a wavelength 357,9 nm parallel to the calibration solutions

.

3.3.2. Construction of calibration curve

Four volumetric flasks with a capacity of 100 cmare placed 8,0; 9,0; 10,0 and 11,0 cmstandard solution chromium, which corresponds to 0,8; 0,9; 1,0 and 1,1 mg of chromium, and topped to the mark with water. Measure the atomic absorption of chromium, as stated in claim 3.3.1. According to the obtained results build a calibration curve.

3.4. Processing of the results

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

,

where is the concentration of chromium was found in the calibration schedule, g/cm;

 — the volume of the sample solution, cm;

 — weight of sample, g;

 — the dilution factor.

3.4.2. The discrepancy between the results of three parallel measurements (rate of convergence) and the results of the two tests (index of reproducibility) shall not exceed the values of permissible differences given in claim 2.4.2.

3.4.3. Control of accuracy of analysis results is carried out by additives or by comparing the results obtained with titrimetric method, in accordance with GOST 25086.