1、BRITISH STANDARD BS EN 24937:1991 ISO 4937:1986 Incorporating Amendment No.1 Steel and iron Determination of chromium content Potentiometric or visual titration method This European Standard EN24937:1990 has the status of a British StandardBSEN24937:1991 This British Standard was published under the
2、 authority ofthe Board of BSI and comes intoeffect on 31January1991 BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference ISM/18 Draft for comment 86/35722 DC ISBN 0 580 19303 9 Cooperating organizations The European Committee for Standardization, under wh
3、ose supervision this European Standard was prepared, comprises the national standards organizations of the following Western European countries. Austria Oesterreichisches Normungsinstitut Belgium Institut belge de normalisation Denmark Dansk Standardiseringsraad Finland Suomen Standardisoimisliito,
4、r.y. France Association franaise de normalisation Germany Deutsches Institut fr Normung e.V. Greece Hellenic Organization for Standardization Iceland Technological Institute of Iceland Ireland National Standards Authority of Ireland Italy Ente Nazionale Italiano di Unificazione Luxemburg Inspection
5、du Travail et des Mines Netherlands Nederlands Normalisatie-instituut Norway Norges Standardiseringsforbund Portugal Instituto Portugus da Qualidade Spain Asociacin Espaola de Normalizacin y Certificacin Sweden Standardiseringskommissionen i Sverige Switzerland Association suisse de normalisation Un
6、ited Kingdom British Standards Institution Amendments issued since publication Amd. No. Date of issue Comments 7082 July 1992 Indicated by a sideline in the marginBSEN24937:1991 BSI 10-1999 i Contents Page Cooperating organizations Inside front cover National foreword ii Brief history 2 Text of EN 2
7、4937 3 National appendix NA Inside back cover National appendix NB Inside back coverBSEN24937:1991 ii BSI 10-1999 National foreword This British Standard has been prepared under the direction of the Iron and Steel Standards Policy Committee. It is the English language version ofEN24937:1990 “Steel a
8、nd iron Determination of chromium content Potentiometric or visual titration method” published by the European Committee for Standardization (CEN). It supersedes BS6200-3.10.1:1985, which is withdrawn. EN24937:1990 is identical with ISO4937:1986 published by the International Organization for Standa
9、rdization (ISO). Other methods for the determination of chromium in ferrous materials have been published as BS6200-3.10.2 andBS6200-3.10.4. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct applica
10、tion. 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, theENtitle page, pages2to12, an inside back cover and a back cover. This standard has been updated (see cop
11、yright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN 24937 March 1990 UDC 669.1:543.257.1:546.76 Key words: Steels, cast iron, chemical analysis, determination of content, c
12、hromium, titration, potentiometric methods, macroscopic methods English version Steel and iron Determination of chromium content Potentiometric or visual method Aciers et fontes Dtermination de la teneur en chrome Mthode potentiomtrique ou visuelle Stahl und Eisen Bestimmung des Chromgehalts Potenti
13、ometrische oder visuelles Titrationsverfahren This European Standard was accepted by CEN on27November1989 and is identical to the ISO standard as referred to. CEN members are bound to comply with the requirements of the CEN/CENELEC Common Rules which stipulate the conditions for giving this European
14、 Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN Central Secretariat or to any CEN member. This European Standard exists in two official versions (English,
15、French). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to CEN Central Secretariat has the same status as the official versions. CEN members are the national standards organizations of Austria, Belgium, Denmark, Finland
16、, France, Germany, Greece, Iceland, Ireland, Italy, Luxemburg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and UnitedKingdom. CEN European Committee for Standardization Comit Europen de Normalisation Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, B-1050 Brussel
17、s CEN 1990 Copyright reserved to all CEN members Ref. No. EN 24937:1990EEN24937:1990 2 BSI 10-1999 Brief history On the proposal of the Technical Committee ECISS/TC20 “Methods of chemical analysis” the Coordinating Commission (COCOR) of the European Committee for Iron and Steel Standardization (ECIS
18、S) decided in November1988 to submit the InternationalStandard ISO 4937:1986, Steel and iron Determination of chromium content Potentiometric or visual titration method. to the Formal Vote. This European Standard was adopted by CEN on1989-11-27. According to the Common CEN/CENELEC Rules, being part
19、of the Internal Regulations of CEN, the following countries are bound to implement this European Standard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxemburg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and UnitedKingdom. Statement The text
20、of the InternationalStandard ISO4937, edition1,1986 was approved by CEN as a European Standard without any modification. Contents Page Brief history 2 1 Scope and field of application 3 2 References 3 3 Principle 3 4 Reagents 3 5 Apparatus 5 6 Sampling 5 7 Procedure 5 8 Expression of results 7 9 Tes
21、t report 8 Annex A Additional information on the international co-operative tests 9 Annex B Graphical representation of precisiondata 10 Figure 1 Potentiometric titration Logarithmic relationship between chromium content and repeatability (r) and reproducibility (R) 10 Figure 2 Visual titration Loga
22、rithmic relationship between chromium content and repeatability (r) and reproducibility (R) 11 Table 1 Potentiometric titration 8 Table 2 Visual titration 8 Table 3 Composition of test samples 9EN24937:1990 BSI 10-1999 3 1 Scope and field of application This International Standard specifies a method
23、 for the determination of chromium in steel and iron by potentiometric or visual titration. The method is applicable to chromium contents between0,25 and35%(m/m). If vanadium is present, the visual titration is applicable only to test portions containing less than3mg of vanadium. 2 References ISO 37
24、7, Wrought steel Selection and preparation of samples and test pieces. ISO 385-1, Laboratory glassware Burettes Part1: General requirements. ISO 648, Laboratory glassware One-mark pipettes. ISO 1042, Laboratory glassware One-mark volumetric flasks. ISO 5725, Precision of test methods Determination o
25、f repeatability and reproducibility by inter-laboratory tests. 3 Principle Dissolution of a test portion with appropriate acids. Oxidation of chromium in an acid medium to chromium(VI) by ammonium peroxydisulfate in the presence of silver sulfate. Reduction of manganese(VII) by hydrochloric acid. Re
26、duction of chromium(VI) by ammonium iron(II) sulfate standard solution. In the case of potentiometric detection, determination of the equivalence point by measurement of the potential variation when the ammonium iron(II) sulfate standard solution is being added. In the case of visual detection, titr
27、ation of the excess ammonium iron(II) sulfate by potassium permanganate standard solution which also acts as the indicator. 4 Reagents During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and only distilled water or water of equivalent purity, free from oxid
28、izing or reducing activity. 4.1 Urea 4.2 Perchloric acid, approximately1,67g/ml. 4.3 Hydrofluoric acid, approximately1,15g/ml. 4.4 Orthophosphoric acid, approximately 1,70g/ml. 4.5 Nitric acid, approximately1,40g/ml. 4.6 Hydrochloric acid, approximately1,19g/ml, diluted1+1. 4.7 Hydrochloric acid, ap
29、proximately1,19g/ml, diluted1+10. 4.8 Sulfuric acid, approximately1,84g/ml, diluted1+1. 4.9 Sulfuric acid, approximately1,84g/ml, diluted1+5. 4.10 Sulfuric acid, approximately1,84g/ml, diluted1+19. 4.11 Silver sulfate, 5g/l solution. 4.12 Ammonium peroxydisulfate (NH 4 ) 2 S 2 O 8 ,500g/l solution.
30、Prepare this solution immediately before use. 4.13 Manganese sulfate MnSO 4 H 2 O,4g/l solution. 4.14 Manganese sulfate MnSO 4 H 2 O, 100g/l solution. 4.15 Potassium permanganate, 5g/l solution. 4.16 Sodium nitrite, 3g/l solution. Prepare this solution immediately before use. 4.17 Sulfamic acid (NH
31、2 SO 3 H), 100g/l solution. This solution remains stable for one week only. 4.18 Potassium permanganate, standard solution. 4.18.1 Preparation of the solution Dissolve3,2g of potassium permanganate in1000ml of water. After storage in complete darkness for2weeks, filter through a thick fritted filter
32、 without washing. Keep the solution in a coloured glass bottle and avoid contact with organic matter. 4.18.2 Standardization of the solution Boil 250ml of sulfuric acid (4.10) in a600ml beaker for10min and allow to cool. Weigh, to the nearest0,0001g, 0,3000g of sodium oxalate (COONa) 2 previously dr
33、ied at105 C and cooled in a desiccator. Dissolve the salt in boiled sulfuric acid(4.10). Add39 to40ml of potassium permanganate solution (4.18.1) at a rate of25 to35ml/min, stirring gently. The violet colour of the permanganate will disappear in approximately45s. Heat to70 to75 C and complete the ti
34、tration. Towards the end, titrate very slowly and allow each drop to become colourless before adding the next. To determine the blank test, titrate250ml of sulfuric acid(4.10), as described above, concurrently.EN24937:1990 4 BSI 10-1999 The concentration (c 2 ) of the potassium permanganate standard
35、 solution, expressed as milligrams of chromium per millilitre, is given by the formula where 4.19 Ammonium iron(II) sulfate Fe(NH 4 ) 2 (SO 4 ) 2 6H 2 O, standard solution in sulfuric acid medium. 1ml of this solution corresponds to about2mg of chromium. 4.19.1 Preparation of the solution Dissolve 4
36、6g of ammonium iron(II) sulfate hexahydrate in about500ml of water, add110ml of sulfuric acid(4.8), cool, dilute to1000ml and mix. 4.19.2 Potentiometric standardization of the solution (to be carried out just before use) Take 30,0ml of the potassium dichromate standard reference solution (4.20), tra
37、nsfer to a600ml beaker, add45ml of sulfuric acid(4.9) and make up to about400ml with water. Titrate according to the conditions specified in7.3.3.1. The corresponding concentration (c 1 ) of ammonium iron(II) sulfate solution(4.19.1), expressed in milligrams of chromium per millilitre, is given by t
38、he formula where 4.19.3 Visual standardization of the solution (to be carried out just before use) Take 25,0ml of ammonium iron(II) sulfate solution(4.19.1) and add325ml of sulfuric acid(4.10). Titrate using the potassium permanganate standard solution(4.18) until a slight violet colour persists. To
39、 determine the blank test, titrate a mixture of25ml of water and325ml of sulfuric acid (4.10) using the potassium permanganate standard solution(4.18). The corresponding concentration (c 1 ) of the ammonium iron(II) sulfate standard solution(4.19), expressed in milligrams of chromium per millilitre,
40、 is given by the formula where 4.20 Potassium dichromate, standard reference solution. Weigh, to the nearest0,0001g, 4,9031g of potassium dichromate previously dried at150 C to constant mass and cooled in a desiccator. Dissolve in water, transfer quantitatively to a1000ml one-mark volumetric flask,
41、dilute to the mark and mix. 1ml of this standard reference solution contains1,733mg ofCr. V 1 is the volume, in millilitres, of potassium permanganate solution (4.18.1) used for titrating sodium oxalate; V 0 is the volume, in millilitres, of potassium permanganate solution(4.18.1) used for titrating
42、 the blank test of sulfuric acid(4.10); 6,700is the molar mass of sodium oxalate divided by20; 1,733is the mass, in milligrams, of chromium(VI) contained in1ml of the potassium dichromate standard reference solution(4.20); 300,0is the mass, in milligrams, of sodium oxalate weighed. V 2 is the volume
43、, in millilitres, of ammonium iron(II) sulfate solution (4.19.1) used for the standardization; 30,0is the volume, in millilitres, of the potassium dichromate standard reference solution (4.20) taken for the standardization; c 2 300,01,733 6,700V 1 V 0 () - = c 1 300,01,733 V 2 - = 1,733is the mass,
44、in milligrams, of chromium contained in1ml of the potassium dichromate standard reference solution(4.20). c 2 is the concentration of the potassium permanganate standard solution(4.18), expressed as milligrams of chromium per millilitre; V 3 is the volume, in millilitres, of the potassium permangana
45、te standard solution(4.18) used to oxidize25ml of ammonium iron(II) sulfate solution(4.19.1); V 0 is the volume, in millilitres, of the potassium permanganate standard solution(4.18) used for titrating the blank test of sulfuric acid(4.10); 25,0is the volume, in millilitres, of ammonium iron(II) sul
46、fate solution(4.19.1) used for the standardization. c 1 c 2 V 3 V 0 25,0 - =EN24937:1990 BSI 10-1999 5 5 Apparatus Ordinary laboratory apparatus (see the note) and 5.1 Potentiometric titration device, which permits a difference in potential to be measured with platinum-saturated calomel electrodes.
47、NOTEAll volumetric glassware shall be classA, in accordance with ISO385-1, ISO648 or ISO1042 as appropriate. 6 Sampling Carry out sampling in accordance with ISO377 or the appropriate national standards for iron. 7 Procedure WARNING: Perchloric acid vapour may cause explosions in the presence of amm
48、onia, nitrous fumes or organic material in general. 7.1 Test portion According to the presumed chromium content, weigh, to the nearest0,0001g, the following mass(m) of the test portion: a) for chromium contents between0,25 and2% (m/m), m approximately2g; b) for chromium contents between2 and10% (m/m
49、), m approximately1g; c) for chromium contents between10 and25% (m/m), m approximately0,5g; d) for chromium contents between25 and35% (m/m), m approximately0,25g. 7.2 Blank test Carry out a blank test in parallel with the determination, by the same procedure, using the same reagents, as in the determination, but omitting the test portion. 7.3 Determination 7.3.1 Prepa
