BS 6200-3 34 1-1987 Sampling and analysis of iron steel and other ferrous metals - Methods of analysis - Determination of vanadium - Steel and cast iron potentiometric titration me.pdf

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1、BRITISH STANDARD BS 6200-3.34.1: 1987 EN24947: 1991 ISO4947:1986 Incorporating Amendment No.1 Sampling and analysis of iron, steel and other ferrous metals Part3: Methods of analysis Section3.34 Determination of vanadium Subsection3.34.1 Steel and cast iron: potentiometric titration method The Europ

2、ean Standard EN24947:1991 has the status of a British Standard UDC669.13:669.14:620.1:546.881BS6200-3.34.1:1987 This British Standard, having been prepared under the directionof the Iron and SteelStandards Committee, waspublished under the authorityof the Board ofBSIandcomes into effect on 29 May198

3、7 BSI10-1999 The following BSI references relate to the work on this standard: Committee reference ISM/18 Draft for comment85/40193DC ISBN 0 580 15928 0 National foreword This Subsection of BS6200 has been prepared under the direction of the Iron and Steel Standards Committee. It is identical with I

4、SO4947:1986 “Steel and cast iron Determination of vanadium content Potentiometric titration method”, published by the International Organization for Standardization (ISO). In1991 the European Committee for Standardization (CEN) accepted ISO4947:1986 as European Standard EN24947:1991. Terminology and

5、 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 b

6、een 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

7、 reviewed the provisions of ISO377, to which reference is made in clause6, and has decided that they are acceptable for use in conjunction with this standard. A related British Standard to ISO377 is BS1837 “Methods for the sampling of iron, steel, permanent magnet alloys and ferro-alloys”. Appropria

8、te procedures from ISO377 will be incorporated in BS6200-2 “Methods of sampling and sample preparation”, which will be published in due course and which will supersede BS1837. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are re

9、sponsible 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, pagesi andii, theEN title page, pages2 to8, an inside back cover and a back cover. Thi

10、s 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 issue Comments 7081 February1992 Indicated by a sideline in the marginBS6200-3.34.1

11、:1987 BSI 10-1999 i Contents Page National foreword Inside front cover Foreword 2 Text of EN24947 3 Publications referred to Inside back coverii blankEUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN24947 March1991 UDC669.13:669.14:620.1:546.881 Descriptors: Steel, cast iron, chemicalanalysis, de

12、termination of content, vanadium, potentiometric methods English version Steel and cast iron Determination of vanadium content Potentiometric titration method (ISO4947:1986) Acier et fonte Dtermination de la teneur en vanadium Mthode de titration potentiomtrique (ISO4947:1986) Stahl- und Gusseisen B

13、estimmung des Vanadium-Gehaltes Potentiometrisches Titrierverfahren (ISO4947:1986) This European Standard was approved by CEN on1991-01-30. CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a natio

14、nal standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CEN member. This European Standard exists in three official versions (English, French, German). A version in any

15、 other language made by translation under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official versions. CEN members are the national standards organizations of Austria, Belgium, Denmark, Finland, France, Germany, Greece

16、, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. CEN European Committee for Standardization Comit Europen de Normalisation Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels CEN1991 Copyright res

17、erved to all CEN members Ref.No.EN24947:1991EEN24947:1991 BSI 10-1999 2 Foreword On the proposal of the Technical Committee ECISS/TC20 “Chemical Analysis” the Coordinating Commission (COCOR) of the European Committee for Iron and Steel Standardization (ECISS) decided in January1991 to submit the Int

18、ernationalStandard ISO4947:1986, Steel and cast iron Determination of vanadium content Potentiometric titration method, to Formal Vote. This European Standard was adopted by CEN on1991-01-30. According to the Common CEN/CENELEC Rules, being part of the Internal Regulations of CEN, the following coun

19、tries are bound to implement this European Standard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. Statement The text of the International Standard ISO4947:1986, edition1

20、, was approved by CEN as a European Standard without any modification. Contents Page Foreword 2 1 Scope and field of application 3 2 Reference 3 3 Principle 3 4 Reagents 3 5 Apparatus 4 6 Sampling 4 7 Procedure 4 8 Expression of results 5 9 Test report 5 Annex A Additional information on the interna

21、tional co-operative tests 6 Annex B Graphic presentation of precision data 7 Figure Relationship between vanadium content and repeatability r or reproducibility R 7 Table 1 5 Table 2 6EN24947:1991 BSI 10-1999 3 1 Scope and field of application This International Standard specifies a potentiometric t

22、itration method for the determination of vanadium in steel and cast iron. The method is applicable to vanadium contents between0,04 and2%(m/m). 2 Reference ISO377, Wrought steel Selection and preparation of samples and test pieces. 3 Principle Dissolution of a test portion with appropriate acids. Ad

23、dition of hydrofluoric acid to keep tungsten in solution. Oxidation of chromium and vanadium by potassium peroxydisulfate. Partial oxidation of chromium. While checking the potential of the solution, reduction of chromium(VI) and vanadium(V) by ammonium iron(II) sulfate; oxidation of vanadium by sli

24、ght excess of potassium permanganate; reduction of the excess permanganate by sodium nitrite, and reduction of the excess sodium nitrite by sulfamic acid. Potentiometric titration of vanadium by ammonium iron(II) sulfate standard solution. 4 Reagents During the analysis, unless otherwise stated, use

25、 only reagents of recognized analytical grade and only distilled water or water of equivalent purity, free from reducing or oxidizing activity. 4.1 Potassium peroxydisulfate (K 2 S 2 O 8 ). 4.2 Hydrochloric acid, about1,19g/ml. 4.3 Nitric acid, about1,40g/ml. 4.4 Hydrofluoric acid, about1,15g/ml. 4.

26、5 Sulfuric acid, about1,84g/ml, diluted1+4. 4.6 Sulfuric acid, about1,84g/ml, diluted1+50. 4.7 Orthophosphoric acid, about1,70g/ml. 4.8 Ammonium iron(II) sulfate Fe(NH 4 ) 2 (SO 4 ) 2 .6H 2 O, solution in sulfuric acid medium. Dissolve40g of ammonium iron(II) sulfate hexahydrate in approximately500m

27、l of water, add20ml of sulfuric acid, about1,84g/ml, cool, make up the volume to1000ml and mix. 4.9 Potassium permanganate,5g/l solution. 4.10 Sodium nitrite,3g/l solution. 4.11 Sulfamic acid (NH 2 SO 3 H),100g/l solution. This solution is stable for only one week. 4.12 Potassium dichromate, standar

28、d reference solution. Weigh, to the nearest0,001g, approximately1g of potassium dichromate (the highest purity grade) previously dried at150 C until a constant mass is obtained on cooling in the desiccator. Introduce the weighed mass into a250ml beaker, dissolve it in20ml of water and add160ml of su

29、lfuric acid(4.5). Transfer the solution quantitatively into a1000ml onemark volumetric flask, cool, dilute to the mark with water and mix. 4.13 Ammonium iron(II) sulfate Fe(NH 4 ) 2 (SO 4 ) 2 .6H 2 O, standard solution. 1ml of this solution corresponds to approximately1,275mg of vanadium. 4.13.1 Pre

30、paration of the solution Dissolve10g of ammonium iron(II) sulfate hexahydrate in approximately500ml of water, add25ml of sulfuric acid, about1,84g/ml, make up the volume to1000ml and mix. 4.13.2 Standardization of the solution (to be carried out just before use) Take25,0ml of the potassium dichromat

31、e standard reference solution(4.12) and titrate potentiometrically with the ammonium iron(II) sulfate solution(4.13.1). The corresponding concentration (c) of the ammonium iron(II) sulfate standard solution(4.13) is given by the formula: where c is the corresponding concentration of the ammonium iro

32、n(II) sulfate standard solution(4.13) expressed in milligrams of vanadium per millilitre; m 0 is the mass, in milligrams, of the weighed potassium dichromate; V is the volume, in millilitres, of the ammonium iron(II) sulfate standard solution(4.13) used for titration; 0,025is the ratio between the v

33、olume taken and the total volume of the potassium dichromate standard reference solution; 49,03is the relative molecular mass of potassium dichromate divided by6; 50,94is the relative atomic mass of vanadium. c 0,025m 0 49,03V -50,94 = m 0 V -0,026 =EN24947:1991 4 BSI 10-1999 5 Apparatus Ordinary la

34、boratory apparatus and 5.1 Potentiometric titration device which permits a difference in potential to be measured with platinum/saturated calomel electrodes. 6 Sampling Carry out sampling in accordance with ISO377 or appropriate national standards for cast iron. 7 Procedure 7.1 Test portion Accordin

35、g to the presumed vanadium content, weigh, to the nearest0,001g, the following mass of the test portion: a) for vanadium contents between0,04 and0,25%(m/m): approximately5g; b) for vanadium contents between0,25 and1%(m/m): approximately2g; c) for vanadium contents between1 and2%(m/m): approximately1

36、g. The quantity of vanadium in the test portion may vary between2 and20mg. 7.2 Blank test Carry out a blank test in parallel with the determination, by the same procedure and using the same quantities of all reagents. 7.3 Determination 7.3.1 Preparation of the test solution 7.3.1.1 Samples soluble i

37、n sulfuric acid Introduce the test portion(7.1) into a400ml beaker (seenotes1 and2) and add40ml of sulfuric acid(4.5) for a1g or2g test portion. For a5g test portion, add70ml of sulfuric acid(4.5). Cover the beaker with a watch-glass and heat gently until effervescence ceases. For samples with high

38、silicon contents, add5 to10 drops of hydrofluoric acid(4.4). Bring to the boil to ensure complete cessation of effervescence. If the test portion contains tungsten, add a sufficient quantity of hydrofluoric acid(4.4) to keep it in solution. In general5ml of hydrofluoric acid(4.4) will suffice for a1

39、g test portion,7ml for a2g test portion, and13ml for a5g test portion. Dilute the solution to between90 and100ml with water and proceed as in7.3.2. NOTE 1If hydrofluoric acid(4.4) is used, a fused silica beaker and a fused silica watch-glass shall be employed. NOTE 2The glassware used should not con

40、tain more than0,05%(m/m) of arsenic. If the glass contains barium, a barium sulfate precipitate may form; however, this will not adversely affect the determination. 7.3.1.2 Samples not readily soluble in sulfuric acid For test portions difficult to dissolve in the sulfuric acid medium the initial di

41、ssolution may be accomplished with a mixture of nitric acid(4.3) and hydrochloric acid(4.2). After dissolution, add the quantity of sulfuric acid(4.5) already indicated in7.3.1.1 and heat until white fumes are given off. Take up again with water, heating to dissolve the salts, then repeat the evapor

42、ation to white fumes to ensure that the nitric acid is completely eliminated. If the test portion contains tungsten, add a sufficient quantity of hydrofluoric acid(4.4) to keep it in solution. In general5ml of hydrofluoric acid(4.4) will suffice for a1g test portion,7ml for a2g test portion, and13ml

43、 for a5g test portion. Dilute the solution to between90 and100ml with water and proceed as in7.3.2. 7.3.2 Oxidation of chromium and vanadium Cool the solution(7.3.1) to approximately50 C. Add3g of potassium peroxydisulfate(4.1) per gram of test portion, heat slowly to boiling and boil for at least10

44、min. 7.3.3 Preparation of the solution for measurement 7.3.3.1 Control of the oxidation of chromium and vanadium Cool the solution(7.3.2) to room temperature. If it is necessary to remove graphite, filter the solution through a cellulose pulp lined coarse filter paper and wash with sulfuric acid(4.6

45、), adding several drops of hydrofluoric acid(4.4) to facilitate filtering. Make up the final volume of the solution to approximately150ml. Introduce the electrodes of the potentiometric device(5.1) into the beaker and agitate the solution, preferably with an electromagnetic stirrer. The potential sh

46、ould be above770mV. If the potential is lower, or if it falls regularly, remove the electrodes from the solution, and repeat the operations of7.3.2. Cool to room temperature and make up the volume to approximately150ml. Verify that the potential is above770mV. 7.3.3.2 Reduction of chromium and vanad

47、ium Introduce the electrodes into the beaker and reduce chromium(VI) and vanadium(V) by adding ammonium iron(II) sulfate solution(4.8) (seenote) to a slight excess (the potential drops to between500 and570mV), agitating continuously at a constant speed.EN24947:1991 BSI 10-1999 5 NOTEWhen the quantit

48、y of chromium is large (test portion of5g, or high chromium content) it is necessary to use a more concentrated ammonium iron(II) sulfate solution (e.g.400g/l) at the start, then finish with the solution4.8. 7.3.4 Oxidation of vanadium Cool the solution(7.3.3) to a temperature below15 C to avoid par

49、tial oxidation of the chromium. Wait2min. Then add, drop by drop, potassium permanganate solution(4.9) until the potential of the indicator electrode stabilizes between1100 and1160mV (seenote). The potential shall not exceed this range in order to avoid partial oxidation of the chromium. NOTEWhen the solution is not highly coloured, oxidation with the permanganate can be observed (light pink colouring, stable for2min). Wait2 to3min, during which time the potential shall neither