BS-6200-3.22.2-1985 ISO-4945-1977.pdf

BRITISH STANDARD BS 6200-3.22.2: 1985 ISO 4945:1977 (Including ISO 4945:1977(E)/ Erratum) Sampling and analysis of iron, steel and other ferrous metals Part 3: Methods of analysis Section 3.22 Determination of nitrogen Subsection 3.22.2 Steel: spectrophotometric method ISO title: Steel Determination of nitrogen content Spectrophotometric method UDC 669.1:543.42.062:546.17 Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 14:58:08 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6200-3.22.2:1985 This British Standard, having been prepared under the direction of the Iron and Steel Standards Committee, was published under the authority of the Board of BSI and comes into effect on 28 February 1985 © BSI 09-1999 The following BSI references relate to the work on this standard: Committee reference ISM/18 Draft for approval 84/39008 ISBN 0 580 14269 8 National foreword This Subsection of BS 6200 has been prepared under the direction of the Iron and Steel Standards Committee. It is identical with ISO 4945:1977 “Steel Determination of nitrogen content Spectrophotometric method” published by the International Organization for Standardization (ISO) and also incorporates the Erratum to ISO 4945 which was published in 1979. Terminology and conventions. The text of the International Standard has been approved as suitable for publication as a British Standard without deviation. Some terminology and certain conventions are not identical with those used in British Standards; attention is drawn especially to the following. The comma has been used as a decimal marker. In British Standards it is current practice to use a full point on the baseline as the decimal marker. Wherever the words “International Standard” appear, referring to this standard, they should be read as “British Standard”. Cross-reference. The Technical Committee has reviewed the provisions of ISO/R 377, to which reference is made in clause 7, and has decided that they are acceptable for use in conjunction with this standard. A related standard to ISO/R 377 is BS 1837 “Methods for the sampling of iron, steel, permanent magnet alloys and ferro-alloys”. Appropriate procedures from ISO/R 377 will be incorporated in BS 6200-2 “Methods of sampling and sample preparation”, which will be published in due course and which will supersede BS 1837. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No.Date of issueComments Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 14:58:08 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6200-3.22.2:1985 © BSI 09-1999i Contents Page National forewordInside front cover 1Scope1 2Field of application1 3Reference1 4Principle1 5Reagents1 6Apparatus2 7Sampling2 8Procedure2 9Expression of results4 10Test report4 Figure 1 Semi-micro distillation apparatus5 Figure 2 Apparatus for distillation under a current of steam6 Publication referred toInside back cover Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 14:58:08 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ii blank Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 14:58:08 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6200-3.22.2:1985 © BSI 09-19991 1 Scope This International Standard specifies a spectrophotometric method for the determination of the nitrogen content of non-alloy and low-alloy steels. This method allows the determination only of the nitrogen content which can be converted to an ammonium salt. 2 Field of application The method is applicable to non-alloy and low-alloy steels containing between 0,002 % and 0,050 % (m/m) of nitrogen and less than 0,6 % (m/m) of silicon. 3 Reference ISO/R 377, Selection and preparation of samples and test pieces for wrought steel. 4 Principle Dissolution of a test portion in dilute sulphuric acid. After concentration, progressive increasing of the temperature to above 300 °C. Separation of ammonia from the ammonium salt formed, by displacement and distillation in a boiling sodium hydroxide medium and collecting in an acid medium. At ambient temperature, formation of a blue-coloured complex between the ammonium ions and phenol in the presence of sodium hypochlorite and sodium pentacyanonitrosylferrate(II) (sodium nitroprusside). Spectrophotometric measurement of the complex at a wavelength of about 640 nm. 5 Reagents During the analysis, use only reagents of recognized analytical grade. 5.1 Distilled or de-ionized water, free from nitrogen compounds, purified by a second passage through ion-exchange resins. 5.2 Potassium sulphate, anhydrous (K2SO4). 5.3 Sulphuric acid, Ô approximately 1,84 g/ml, about 96 % (m/m) solution, free from nitrogen compounds. 5.4 Sulphuric acid, Ô approximately 1,21 g/ml, about 29 % (m/m) solution. Add in small portions, whilst cooling, 200 ml of sulphuric acid (5.3) to about 700 ml of water (5.1), make up the volume to 1 000 ml with water (5.1) and mix. 5.5 Sodium hydroxide, approximately 12 N solution. Dissolve, with caution, 480 g of sodium hydroxide pellets in 700 ml of water (5.1) contained in a polytetrafluoroethylene beaker. Heat the solution to boiling and boil for 10 min. Cool, make up the volume to 1 000 ml with water (5.1) and mix. Store in a suitable plastics container. 5.6 Sulphuric acid, approximately 1 N solution. Add 30 ml of sulphuric acid (5.3) to about 700 ml of water (5.1); after cooling make up the volume to 1 000 ml with water (5.1) and mix. 5.7 Sulphuric acid, approximately 0,04 N solution. Dilute 40 ml of sulphuric acid solution (5.6) to 1 000 ml with water (5.1) and mix. 5.8 Sodium hydroxide, approximately 0,2 N solution. Dilute 30 ml of a 250 g/l solution of sodium hydroxide with water (5.1), make up the volume to 1 000 ml with water (5.1) and mix. 5.9 Sodium phenate solution. Add, whilst agitating and cooling, 5 g of phenol to a mixture of 10 ml of a 250 g/l solution of sodium hydroxide and 80 ml of water (5.1). Make up the volume to 100 ml with water (5.1) and mix. Prepare this solution at the time of use. 5.10 Disodium hydrogen phosphate, 0,1 M solution. Dissolve 36 g of disodium hydrogen phosphate dodecahydrate (Na2HPO4.12H2O) in water (5.1), make up the volume to 1 000 ml with water (5.1) and mix. 5.11 Disodium pentacyanonitrosylferrate(II), 0,25 g/l solution. Dissolve 10 g of disodium pentacyanonitrosylferrate(II) dihydrate (sodium nitroprusside) Na2Fe (CN)5NO.2H2O in water (5.1), make up the volume to 1 000 ml with water (5.1) and mix. At the moment of use, dilute 25 ml of this solution to 1 000 ml with water (5.1). 5.12 Sodium hypochlorite, approximately 0,1 N solution (approximately 0,3 % (m/m) of active chlorine). Store this solution at a temperature less than 10 °C. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 14:58:08 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6200-3.22.2:1985 2 © BSI 09-1999 5.13 Nitrogen, standard solution corresponding to 0,100 0 g of nitrogen (N) per litre. Weigh, to the nearest 0,1 mg, 0,471 6 g of dry ammonium sulphate, dissolve in water (5.1) and transfer the solution quantitatively to a 1 000 ml one-mark volumetric flask. Dilute to the mark and mix. 1 ml of this standard solution contains 100 Èg of nitrogen (N). 5.14 Nitrogen, standard solution corresponding to 0,002 0 g of nitrogen (N) per litre. Transfer 20,0 ml of the standard nitrogen solution (5.13) to a 1 000 ml one-mark volumetric flask, dilute to the mark with water (5.1) and mix. 1 ml of this standard solution contains 2 Èg of nitrogen (N). Prepare this standard solution at the time of use. 5.15 Methyl red, 0,1 g/l solution. Dissolve 0,1 g of methyl red in water (5.1), make up the volume to 1 000 ml with water (5.1) and mix. 6 Apparatus Ordinary laboratory apparatus and 6.1 Semi-micro apparatus for distillation without additional steam (see Figure 1) or 6.2 Apparatus for distillation under a current of steam (see Figure 2). 6.3 Spectrophotometer NOTEAll glassware shall be cleaned prior to use in hot sulphuric-chromic acid prepared from pure ingredients and water (5.1). 7 Sampling Sampling shall be carried out in accordance with ISO/R 377. For wrought steels not complying with ISO/R 377, the appropriate national standard shall be used. 8 Procedure NOTECarry out operations in a well-ventilated room away from all work on nitrogenous products. 8.1 Test portion Weigh, to the nearest 0,001 g, masses of 1 g and 2 g respectively of the test sample, to be treated concurrently. 8.2 Blank test The procedure specified in 8.3 and 8.4 eliminates the incidence of the value of the blank test when the same reagents are used with the two test portions indicated in 8.1. 8.3 Determination 8.3.1 Preparation of the test solution In a 150 ml Kjeldahl flask covered with a watch-glass, dissolve the test portion (8.1) with 30 ml of sulphuric acid solution (5.4). Allow to digest, taking care that the temperature of the liquid does not exceed 90 °C, until the release of hydrogen has definitely ceased. When the release of hydrogen has ceased, remove the watch-glass and heat until white sulphuric fumes begin to appear. Then add 5 ml of sulphuric acid (5.3) and 1 g of potassium sulphate (5.2). Heat for 2 h at a temperature above 300 °C, in such a way that the mixture remains liquid. Cool, add 10 ml of water (5.1) and heat to dissolve the majority of the sulphates. 8.3.2 Distillation The distillation may be carried out with or without additional steam. NOTEThe flasks used in distillation are attacked by the sodium hydroxide solution; change them frequently. 8.3.2.1 DISTILLATION WITHOUT ADDITIONAL STEAM Use the apparatus shown in Figure 1 (6.1). To collect the distillate, transfer 5 ml of sulphuric acid solution (5.6) to a 100 ml volumetric flask with a ground neck and having a mark at 85 ml. Introduce the tapered tube extension of the condenser into the flask in such a manner that it is immersed in the sulphuric acid solution (5.6). Pass the test solution (8.3.1) quantitatively into the distillation flask, rinsing with 60 ml of water (5.1), add 50 ml of sodium hydroxide solution (5.5) and rinse the neck of the flask with 30 ml of water (5.1). The final volume of the solution should be approximately 160 to 165 ml. Moisten the ground neck and connect the flask to the condenser immediately after the addition of the sodium hydroxide solution (5.5). Now begin the distillation. Distil about 80 ml in 25 min. When the distillation is ended, rinse the immersed tube with water (5.1), collecting the washings in the volumetric flask; make up to volume with water (5.1) and mix. Solutions S1 for the 1 g test portion and S2 for the 2 g test portion are obtained. Repeat the same operation (8.3.2.1) for each sample to be analysed, taking care, after each distillation, to rinse the flask with plenty of water, then distilled water and finally the water (5.1). Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 14:58:08 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6200-3.22.2:1985 © BSI 09-19993 NOTETo regulate the boiling during the distillation in the apparatus shown in Figure 1, it is as well to add some pieces of porous ceramic. These pieces are previously treated as a test sample and collected up after distillation. They are then washed with sulphuric acid solution (5.6) until neutral, then with water (5.1) and finally dried. 8.3.2.2 DISTILLATION UNDER A CURRENT OF STEAM Use the apparatus shown in Figure 2 (6.2). To collect the distillate, transfer 5 ml of sulphuric acid (5.7) to a beaker of suitable capacity, introduce the tapered tube extension of the condenser into this beaker which has a mark at 85 ml, in such a manner that it is immersed in the 5 ml of sulphuric acid solution (5.7). Pass the test solution (8.3.1) quantitatively into the distillation flask with the aid of the funnel. Rinse the Kjeldahl flask with 60 ml of water (5.1), add through the funnel 50 ml of sodium hydroxide solution (5.5) and rinse the funnel with 30 ml of water (5.1). The volume of the solution should then be about 160 to 165 ml. The steam generator should be preheated to allow the distillation to commence immediately the sodium hydroxide is introduced. Distil about 80 ml in 25 min. When the distillation is ended, rinse the immersed tube with water (5.1), collecting the washings in the beaker. Transfer the solution quantitatively to a 100 ml one-mark volumetric flask, make up to volume with water (5.1) and mix. Solutions S1 for the 1 g test portion and S2 for the 2 g test portion are obtained. Interrupt the heating of the steam generator and allow to cool; the liquid in the flask syphons into the empty flask. Repeat the same operation for each sample to be analysed. 8.3.3 Development of the colour According to the presumed nitrogen content, take the following aliquots of solutions S1 and S2: 10,0 ml for nitrogen contents between 0,020 and 0,050 % (m/m) 25,0 ml for nitrogen contents between 0,010 and 0,020 % (m/m) 50,0 ml for nitrogen contents between 0,002 and 0,010 % (m/m) and transfer them respectively into two 100 ml volumetric flasks. Make up to 50 ml with water (5.1) those volumes less than 50 ml. Add 1 drop of methyl red solution (5.15) and neutralize exactly with sodium hydroxide solution (5.8). Add with a pipette and in the following order: 5,0 ml of sodium phenate solution (5.9) 5,0 ml of disodium hydrogen phosphate solution (5.10) 10,0 ml of sodium pentacyanonitrosylferrate(II) solution (5.11) 5,0 ml of sodium hypochlorite solution (5.12). Make up the volume to 100 ml with water (5.1) and agitate the flasks in an identical manner by alternately turning them upside down (at least ten times). Allow the colour to develop in the dark for 1 h at ambient temperature. NOTEThe aliquots indicated are such that in relation to the nitrogen contents, the quantity of nitrogen in the 100 ml flask used for the spectrophotometric measurement is always between 10 and 50 Èg for S1 and 20 and 100 Èg for S2: thus, the difference is between 10 and 50 Èg. 8.3.4 Spectrophotometric measurement Homogenize the coloured solutions S1 and S2 and measure the absorbance of solution S2 in a 1 cm cell, using the spectrophotometer (6.3) at a wavelength corresponding to the maximum absorption a maximum which is situated at about 640 nm after having adjusted the apparatus to zero absorbance in relation to solution S1. 8.4 Plotting of the calibration curve 8.4.1 Preparation of the standard solutions, related to the spectrophotometric measurement carried out in a 1