1、BRITISH STANDARD BS 6200-3.22.1: 1992 Sampling and analysis of iron, steel and other ferrous metals Part3: Methods of analysis Section3.22 Determination of nitrogen Subsection3.22.1 Steel: volumetric methodBS6200-3.22.1:1992 This British Standard, having been prepared under the directionof the Iron
2、and Steel Standards Policy Committee, waspublished under the authorityof the Standards Boardand comes into effect on 15 June1992 BSI09-1999 The following BSI references relate to the work on this standard: Committee reference ISM/18 Draft for comment91/46620DC ISBN 0 580 20797 8 Committees responsib
3、le for this British Standard The preparation of this British Standard was entrusted by the Iron and Steel Standards Policy Committee (ISM/-) to Technical Committee ISM/18, upon which the following bodies were represented: BCIRA British Steel Industry Department of Trade and Industry (Laboratory of t
4、he Government Chemist) Ferro Alloys and Metals Producers Association Ministry of Defence Amendments issued since publication Amd. No. Date CommentsBS6200-3.22.1:1992 BSI 09-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Principle 1 3 Reagents 1 4 Apparatus 2 5
5、 Sampling 2 6 Procedure 2 7 Calculation and expression of results 6 8 Test report 6 Figure 1 Steam distillation apparatus 3 Figure 2 Cation exchange column 4 Table 1 Precision data 7 Table 2 Predicted values of r and R 7 Publication(s) referred to Inside back coverBS6200-3.22.1:1992 ii BSI 09-1999 F
6、oreword This Subsection of BS6200 has been prepared under the direction of the Iron and Steel Standards Policy Committee and supersedes method1 for the determination of nitrogen in BSI Handbook No.19, to which it is technically equivalent. BS6200 is a multipart British Standard, covering all aspects
7、 of the sampling and analysis of iron, steel and other ferrous metals. A list of contents, together with general information, is given in Part1. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct app
8、lication. 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, pagesi andii, pages1 to8, an inside back cover and a back cover. This standard has been updated (see copyright date)
9、and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS6200-3.22.1:1992 BSI 09-1999 1 1 Scope This Subsection of BS6200 describes a volumetric method for the determination of nitrogen in steel. The method is applicable to nitrogen contents
10、 from0.005%(m/m) to0.25%(m/m) in all types of steel except those containing silicon nitride. NOTE 1Complete recovery of nitrogen cannot be obtained from steels containing silicon nitride. This nitride has been found only in samples of silicon steels manufactured without aluminium additions, and then
11、 only in sheet material. NOTE 2The titles of the publications referred to in this Subsection of BS6200 are listed on the inside back cover. 2 Principle After solution of the test portion in hydrochloric acid the “acid soluble” and “insoluble” nitrogen are separated by means of a centrifuge and the i
12、nsoluble residue is decomposed by fuming strongly with sulfuric acid. The “acid soluble” and “insoluble” nitrogen contents are recovered separately as ammonia by steam distillation over sodium hydroxide and the determinations are completed volumetrically by titration with hydrochloric acid. The tota
13、l nitrogen content is obtained from the sum of the two determinations. NOTEThe terms “soluble” and “insoluble” nitrogen refer to chemical reactivity under the solvent conditions specified in this method, and do not necessarily imply metallurgical states. 3 Reagents During the analysis use only reage
14、nts of recognized analytical grade which are known to give a very low nitrogen blank. Use only grade3 water as specified in BS3978 except where ammonia-free water is specifically stated. NOTEIf a solution requires filtration, wash the filter paper thoroughly with ammonia-free water before use. 3.1 A
15、mmonia-free water. Prepare ammonia-free water by passing distilled water through the cation exchange column(4.4). It is essential to wash the resin column with acid before use to convert it to the hydrogen form. This is conveniently performed by passing2l of hydrochloric acid(3.9) through the column
16、, then washing with water until freed from acid. 3.2 Barium chloride solution,100g/l. Dissolve10g of barium chloride, BaCl 2 .2H 2 O, in ammonia-free water(3.1), dilute to100ml with ammonia-free water and mix. 3.3 Boric acid solution,1g/l. Dissolve1g of boric acid in water, dilute to1l and mix. 3.4
17、Chromic-sulfuric acid. Dissolve2g of chromium(VI) oxide in50ml of water and add slowly and with constant stirring,100ml of sulfuric acid(3.16). 3.5 Diphenylamine reagent. To25ml of water, add cautiously with stirring,75ml of sulfuric acid(3.16). Then add0.1g of diphenylamine, stir until dissolved an
18、d cool. 3.6 Disodium tetraborate, standard solution,1ml equivalent to0.14mg nitrogen. Dissolve1.9072g of freshly recrystallized disodium tetraborate, Na 2 B 4 O 7 .10H 2 O, in200ml of water. Cool, transfer to a1l volumetric flask, dilute to the mark and mix. To prepare recrystallized disodium tetrab
19、orate, dissolve15g of the reagent in50ml of hot water. Cool. Filter the crystals under suction. Wash first with two10ml portions of cold water, then with two10ml portions of95% ethanol, and finally with two10ml portions of diethyl ether. Spread the crystals on a clock glass and as soon as the ether
20、has evaporated, transfer them to a weighing bottle and stopper tightly. 3.7 Hydrochloric acid, density =1.16g/ml to1.18g/ml. 3.8 Hydrochloric acid, redistilled. To300ml of ammonia-free water(3.1) add300ml of hydrochloric acid(3.7) and distil in an all-glass distillation apparatus(4.6). Reject the fi
21、rst100ml of distillate and collect the next400ml for use. 3.9 Hydrochloric acid, =1.16g/ml to1.18g/ml, diluted1+9. 3.10 Hydrochloric acid,0.01M, approximately. Transfer9.0ml of hydrochloric acid(3.7) by means of a burette to a1l volumetric flask, dilute to the mark and mix. Transfer100ml of this sol
22、ution to a second1l volumetric flask, dilute to the mark and mix. 3.11 Hydrofluoric acid,40%(m/m) approximately. 3.12 Hydrogen peroxide, approximately6g per100ml(20 volume). 3.13 Screened methyl red indicator. Dissolve0.125g of methyl red and0.083g of methylene blue in100ml of ethanol and mix. 3.14
23、Sodium hydroxide solution,400g/l. Dissolve400g of sodium hydroxide in ammonia-free water(3.1), dilute to1l with ammonia-free water(3.1) and mix. Prepare this solution in a polyethylene beaker with stirring and cooling. Store in a stoppered polyethylene bottle. 3.15 Sodium sulfate, anhydrous. 3.16 Su
24、lfuric acid, =1.84g/ml. Test individual bottles of sulfuric acid and select one with a nitrogen content in any form of less than0.5g/g. Nitrogen as ammonia will usually be the major source of contamination, and this may be detected by normal methods. Nitrate may also be present and may be detected b
25、y the following procedure.BS6200-3.22.1:1992 2 BSI 09-1999 Cautiously add6ml of the sulfuric acid to2ml of water and cool to60 C. Add one drop of hydrochloric acid(3.7) and one drop of diphenylamine reagent(3.5). No blue colour should develop. Less than0.1g/g can be detected by this test. 3.17 Sulfu
26、ric acid, diluted1+4. To400ml of ammonia-free water(3.1) add cautiously, with cooling and stirring,200ml of sulfuric acid(3.16). Cool, dilute to1l with ammonia-free water(3.1) and mix. 4 Apparatus 4.1 Ordinary laboratory apparatus 4.2 Volumetric apparatus, in accordance with classA of BS846, BS1583
27、or BS1792, as appropriate. 4.3 Steam distillation apparatus. The distillation unit illustrated in Figure 1 has been found to be suitable. NOTEApparatus assembled from units with standard tapered glass joints is NOT recommended. The joints may be attacked by the caustic solution and “freeze”. Flexibi
28、lity is required to allow for the considerable vibration when the correct very rapid boil is used. Flask E is attacked by the sodium hydroxide solution and double-thickness glass is recommended. 4.4 Cation exchange column, packed with a sulfonated polystyrene cation exchange resin. SeeFigure 2. 4.5
29、Centrifuge, electrically-driven, capable of attaining a measured speed of3000r/min and with centrifuge tubes of at least50ml capacity. 4.6 Distillation apparatus, for purification of hydrochloric acid(3.8). 4.7 Burette, of10ml capacity, with0.02ml graduations. NOTEA burette with double tap for conne
30、ction to the storage bottle for hydrochloric acid(3.10) is convenient. A piston burette with certified precision has also been found to be satisfactory. 5 Sampling Carry out sampling in accordance with BS1837. NOTEBS6200-2, which will supersede BS1837, is currently in course of preparation. On its p
31、ublication this Subsection will be amended to include sampling in accordance with BS6200-2. 6 Procedure 6.1 Laboratory environment Carry out nitrogen determinations in a laboratory reserved for the purpose. It is particularly important to exclude ammonium salts and ammonia fumes. Reserve the glasswa
32、re exclusively for this work. Clean the glassware with chromic-sulfuric acid solution(3.4) and wash thoroughly with ammonia-free water(3.1) before use. 6.2 Test portion Weigh, to the nearest0.001g, a test portion of3.5g. For nitrogen contents greater than0.04%(m/m) reduce the mass of the test portio
33、n proportionately. For nitrogen contents greater than0.03%(m/m), where separate values for “soluble” and insoluble nitrogen fractions are not required, weigh, to the nearest0.001g, a test portion of1.4g and follow the dissolution procedure described in6.6. 6.3 Blank test In parallel with the determi
34、nation and following the same procedure, carry out a blank test using the same quantities of all reagents. NOTEThe combined blank values should not exceed0.4ml of hydrochloric acid(3.10), to which the blank from the insoluble nitrogen determination should not contribute more than0.25ml. 6.4 Preparat
35、ion of the steam distillation apparatus(4.3) 6.4.1 The detailed instructions in6.4.2 refer to the electrically heated apparatus. If the steam generator is heated by gas, lower the temperature during the syphoning of the sodium hydroxide solution, isolate the generator from flask C by a clip at posit
36、ion3, and discharge the steam through funnelB. 6.4.2 Prepare the apparatus (seeFigure 1) for use as follows. Add3l of ammonia-free water(3.1) to flask A. Remove the weighted stopper J, add10ml of sodium hydroxide solution(3.14) to flask E through funnel D and rinse in with ammonia-free water(3.1). W
37、ith clips1 and2 open and stopper J removed, heat the water in flask A to boiling and allow steam to escape through funnel B. Close clip1 and allow steam to escape from the open drain tube of flask C for approximately1min. Transfer three drops of screened methyl red indicator(3.13) and10ml of boric a
38、cid solution(3.3) to the250ml conical beaker G. Add hydrochloric acid(3.10) dropwise to the change point of the indicator. Place beaker G under the condenser F and raise until the condenser tip is immersed in the neutralized boric acid solution. Close clip2, replace stopper J, and allow steam to pas
39、s through flask E into condenser F until approximately60ml of distillate has collected. This should take5min to6min. Lower the beaker until the condenser tip is uncovered, then collect a further10ml of distillate. Rinse down the condenser tip with water and titrate the distillate with hydrochloric a
40、cid(3.10).BS6200-3.22.1:1992 BSI 09-1999 3 NOTEThis apparatus may be heated electrically by means of a1500W immersion heater or alternatively by means of gas. Figure 1 Steam distillation apparatusBS6200-3.22.1:1992 4 BSI 09-1999 If the titration is greater than0.1ml, repeat the procedure. Collect a
41、second70ml of distillate and titrate. If the titration still exceeds0.1ml a source of contamination is indicated. Do not make determinations until the source has been ascertained and eliminated. Switch off the heat to the boiling flask A. When the solution in flask E has syphoned into trap C, open c
42、lip2 and discharge into the waste receiver H. NOTEAll linear dimensions are in millimetres. Figure 2 Cation exchange columnBS6200-3.22.1:1992 BSI 09-1999 5 6.5 Determination 6.5.1 Preparation of the test solution Place the test portion in a200ml conical flask and add30ml of hydrochloric acid(3.8). D
43、issolve steels which are resistant to hydrochloric acid in30ml of sulfuric acid(3.17). Cover and heat until solvent action appears to have ceased. Add2ml of hydrogen peroxide(3.12) and evaporate to20ml. If silica separates, add1ml of hydrofluoric acid(3.11). 6.5.2 Centrifuge separation of insoluble
44、nitrides Transfer the solution together with any insoluble residue to a centrifuge tube containing1ml of barium chloride solution(3.2), rinsing the flask with ammonia-free water(3.1). Add1ml of sulfuric acid(3.17), mix by shaking the tube gently, place in the centrifuge(4.5) and centrifuge at3000r/m
45、in until the supernatant liquid is clear. Without disturbing the residue, transfer the clear solution to another200ml conical flask and reserve. Wash the insoluble residue twice by centrifuging with20ml of ammonia-free water(3.1) and combine the washings with the reserved solution. NOTE 1Transfer of
46、 the supernatant liquid is facilitated by the use of a syphon tube and suction line fitted to a2-hole bung to fit the neck of the200ml flask. This solution contains ammonium salts equivalent to the nitrogen soluble in hydrochloric acid. Rinse the insoluble residue into the original conical flask wit
47、h ammonia-free water(3.1), add5ml of sulfuric acid(3.16),2g of sodium sulfate(3.15) and evaporate to fuming. NOTE 2For boron steels it may be necessary also to fume the soluble fraction to dissolve traces of fine suspended nitrides. Treat the solution by the procedure described in6.6. Continue fumin
48、g at a temperature of335 C for60min. If carbides are still present or in any case for boron steels, cool, rinse any undecomposed residue from the side of the flask with a rubber-tipped glass rod, evaporate again to fuming and continue for30min. Cool, add25ml of ammonia-free water(3.1) and boil for5m
49、in. This solution contains ammonia equivalent to the nitrides insoluble in hydrochloric acid. 6.6 Alternative dissolution procedure for1.4g test portion Place the test portion in a200ml conical flask. Add20ml of hydrochloric acid(3.8), cover and heat until solvent action ceases. Evaporate the solution until salts deposit. Cool, add10ml of sulfuric acid(3.16) and2g of sodium sulfate(3.15). Fume strongly at335 C for at least60min. If carbides are still present, or in any case for boron steels, cool, rinse the flask with ammonia-free water(3.1), remove a
