1、 CEN: Page T EN 24933 : 199B 4.1 Ursa 6 kppamrns 23.1.3 Steel4 cmsaioing to- T.3.51l.2 Irr the presewceal: vanadium NmE- Apply the visual titratiQn Bestimmung des Chromgehalts; potentiometrisches oder visuelles Verfahren (IS0 4937 : 1986) European Standard EN 24 937 : 1990 has the status of a DIN St
2、andard. A comma is used as the decimal marker. National foreword This standard has been prepared by ECISSTTC 20. The responsible German body involved in the preparation of this standard was the NormenausschuB Eisen undStahl (Steel and Iron Standards Committee). Standards referred to See References.
3、EN comprises 10 pages. EUROPEAN STANDARD NORME EUROPENNE EUROP dtermination de la teneur en chrome; mthode potentio- metrique ou visuelle (IS0 4937 : 1986) Stahl und Eisen; Bestimmung des Chromgehalts; potentiometrisches oder visuelles Verfahren (IS0 4937 : 1986) This European Standard was approved
4、by CEN on 1989-11-27 and is identical to the IS0 Standard as referred to. CEN members are bound to comply with the CENKENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliogra
5、phical 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 other language made by translation under the responsibility of a C
6、EN 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 bodies of Austria, Belgium; Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spai
7、n, Sweden, Switzerland and United Kingdom. CEN European Committee for Standardization Comit Europen de Normalisation Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, 8-1050 Brussds 8 1989. Copyright reserved to all CEN members. Ref. No. EN 24 937 : 1990 E Page 2 EN 24 937 : 19
8、90 Foreword On the proposal of Technical Committee TC 20, the Coordinating Commission (COCOR) of the European Committee for Iron and Steel Standardization (ECISS) decided in November 1988 to submit International Standard IS0 4937 : 1986 Steel and iron - Determination of chromium content - Potentiome
9、tric or visual titration method to Formal Vote. This European Standard was approved by CEN on 1989-1 1-27. In accordance with the GENKENELEC Internal Regulations, the following countries are bound to implement this European Standard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Icela
10、nd, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. Endorsement notice The text of International Standard IS0 4937 : 1986 was approved by CEN as a European Standard without any modification. Page 3 EN 24 937 : 1990 1 Scope and field of applic
11、ation This International Standard specifks a method for the deter- mination of chromium in steel and iron by potentiometric M visual titration. The method is applicable to chromium contents between O,= and 35 % irn/mi. If vanadium is present, the viswl titration is applicable only to test portions c
12、ontaining less than 3 mg of vanadium. 2 References IS0 3n, Wrought stee/ - Sdection and prepamtion of samples and test pieces. is0 =/i, Laboratorygiassware - Burettes - Part I: General requirements. IS0 648, Laboratory glassware - Onemaark pipettes. Is0 1042, L86omtory g Vo is the volume, in millili
13、tres, of potassium permanganate solution (4.18.1) used for titrating the blank test of sulfuric acid (4.10): 6,700 is the molar mass of sodium oxalate divided by 20; 1.733 is the macs, in milligrams, of chromium(Vl) con- tained in 1 ml of the potassium dichromate standard reference solution (4.201 ;
14、 300.0 is the mass, in milligrams, of sodium oxalate weighed. 4.19 Ammonium iron(ll) sulfate Fe(NH,)z(S0,)Z6Hz01, standard solution in sulfuric acid medium. 1 ml of this solution corresponds to about 2 mg of chromium. 4.19.1 Preparation of the solution Dissolve 46 g of ammonium iron(ll1 sulfate hexa
15、hydrate in about 500 ml of water, add 110 rnl of sulfuric acid (4.8), cool, dilute to 1 O00 ml and mix. 4.19.2 Potentiometric standardization of the solution (to be carried out just before use) Take 30,O ml of the potassium dichromate standard reference solution (4.20), transfer to a 600 ml beaker,
16、add 45ml of sulfuric acid (4.9) and make UD to about 400 ml with water. Titrate according to the conditions specified in 7.3.3.1. The corresponding concentration (c,) of ammonium iron(ll) sulfate solution 14.19.1 ), expressed in milligrams of chromium per millilitre, is given by the formula where V2
17、 is the volume, in millilitres, of ammonium iron(l1) sulfate solution (4.19.1) used for the standardization; 30,O is the volume, in millilitres. of the potassium dichromate standard reference solution (4.20) taken for the standardization ; 1,733 is the mass, in milligrams, of chromium contained in 1
18、 ml of the potassium dichromate standard reference solu- tion (4.20). 4.19.3 Visual standardization of the solution (to be carried out just before use) Take25,O ml of ammonium iron(ll) sulfate solution (4.19.1) and add 325 ml of sulfuric acid (4.10). Titrate using the potassium permanganate standard
19、 solution (4.181 until a slight violet col- our Desists. To determine the blank test, titrate a mixture of 25 ml of water and 325 ml of sulfuric acid (4.10) using the potassium per- manganate standard solution (4.78). The corresponding concentration (c,) of the ammonium iron(ll) sulfate standard sol
20、ution (4.191, expressed in milligrams of chromium per millilitre, is given by the formula v3 - vo c1 = cz x - 25,O where c2 is the concentration of the potassium permanganate standard solution (4.18). expressed as milligrams of chromium per millilitre; V3 is the volume. in millilitres, of the potass
21、ium per- manganate standard solution (4.18) used to oxidize 25 ml of ammonium iron(ll) sulfate solution (4.19.1); Vo is the volume, in millilitres, of the potassium per- manganate standard solution (4.18) used for titrating the blank test of sulfuric acid (4.10); 25.0 is the vdume, in millilitres, o
22、f ammonium iron(ll) sulfate solution (4.19.11 used for the standardization. Page 5 EN 24 937 : 1990 4-20 Potassium dichromate. standard reference soiution. Weigh, to the nearest 0,oOOl g, 4,9031 g of pomssium dichromate previously dried at 150 OC to constacit mass and cooled in a desiccator. Dissolv
23、e in water, transfer quantitatively to a 1 o00 ml one- mark volumetric flask, dilute to the mark and mix. 1 ml of this standard reference solution contans 1,733 mg of Cr. 5 Apparatus Ordinary laboratory apparatus see the notei and 5.1 Potentiometric titration device, which permits a df- ference in p
24、otential to be measured with plathum-saturared calomel electrodes. NOTE - Ail volumetric glassware shall be class A, in accordance with IS0 385/1. IS0 648 or IS0 1042 as appropriate. 6 sampling Carry out sampling in accordance with IS0 377 or the appropriate national standards for iron. 7 Procedure
25、WARNING : Perchloric aci vapour may cause explosions in the presence of ammonia, nitrous fumes or organic material in general. 7.1 Test portion According to the presumed chromium content, weigh, to the nearest 0,O 1 g, the following mass (rn) of the test mon: a) for chromium contents between 0,25 an
26、d 2 % (rn/m), rn approximately 2 g ; b) for chromium contents between 2 and 10 % (m/rn), m approximately 1 g; ci for chromium contents between 10 and 25 56 (m/rn), m approximately 0,5 g; d) for chromium contents between 25 and 35 % (m/m), m approximately O,5 g. 7.2 Blank test Carry out a blank test
27、in parallel with the determination, by the same procedure, using the same reagents, as in the determim- tion, but omining the test portion. 7.3 Determination 7.3.1 Preparation of the test solution 7.3.1.1 Unalloyed steel and iron Pbce the test portion (7.1) in a 600 ml beaker, add 60 ml of sulfuric
28、acid (4.9) and 10 ml of orthophosphoric acid (4.41, and heat to dissolve, then oxidize with 15 ml of nitric acid (4.5). Heat until dense white fumes are given off, cool and then add 100 ml of water. To accelerate the discdutiori of a test portion which has a high silicon content, a few drops of hydr
29、ofkioric acid (4.3) may be added see note 1). 7.3.1.2 Chromium and/or nickel alloyed steel and Kon Place the test pottion (7.1) in a 600 rnl beaker, add 25 mi of hydrochloric acid (4.6) and heat to discdve, then oxidize with 15 ml of nitric acid (4.5). If dissolution proves to be particuiariy ditfic
30、ult, add 1 to 2 ml of hydrofluoric acid (4.31. Then add n) rnl of sulfuric acid (4.8) and 10 ml of orthophosphoric acid (4.41, and heat until dense white fumes appear. After cooling, add a further 15 rnl of nitric acid (4.5) to the fum- ing solution, if necessary making further additions, until the
31、carbides have completely decomposed. Continue fuming to remove completely oxides of nitrogen then cool and add 100 ml of water (see note 1). . 7.3.1.3 Steel containing tungsten Place the test portion (7.1) in a 600 ml beaker, add 25 ml of hydrochloric acid (4.6) then 20 ml of suifunc acid (4.8) and
32、10ml of orthophosphoric acid (4.4) and heat until efferves- cence has ceased. If dissolution proves to be particularly dif- ficult add 1 to2 ml of hydrofluoric acid (4.3). Oxidize with 15 ml of nitric acid (4.5) then heat until dense white fumes appear. After cooling, add a further 15 ml of nitric a
33、cid (4.5) to the fum ing solution, if necessary making further additions, until the carbides have completely decomposed. Continue fuming to remove completely oxides of nitrogen then cool and add 100 ml of water (see note II. 7.3.1.4 High alloyed steel and iron, or steel and iron with high silicon co
34、ntent Place the test portion (7.11 in a 750 ml conical W, and add 20 ml of hydrochloric acid (4.61, 10 ml of nitric acid (4.5) and 1 ml of hydrofluoric acid (4.3). When effervescence has ceased, add 30 ml of perchloric acid (4.2). Heat until white fumes are given off, cover with a watch- glass and c
35、ontinue to heat until the alloy has completely dissolved (the white fumes being retained in the flask). Allow to cool. Add 30 ml of water, boil for 5 min. and allow to cool (see note 1). Transfer quantitatively into a 600 ml beaker and add 20 rnl of sulfuric acid (4.81, 10 ml of orthophosphoric acid
36、 (4.4) and 70 ml of water. Page 6 EN 24 937 : 1990 7.3.2 Oxidation of chromium and preparation for titration If necessaty, to remove graphite, filter the test solution through a cellulose-pulp-lined filter and wash with sutfurk acid (4.10). Dilute to about 350 ml with warm water, and add 20 ml of si
37、lver sulfate solution (4.1 1) and 10 ml of ammonium peroxydisulfate soiution 14.12). Cover the beaker with a watch-glass and boil for 10 min (see note 2). Then, break down the permanganic acid by adding to the sdu- tion, after it has been brought to the boil, firstly 15 ml of hydrochloric acid (4.7)
38、, then, after about 3 min, if necessary a further amount of hydrochloric acid (4.71, drop by drop, until the violet colour disappears (see note 3). Boil for 10 min until the odour from the chlorine compounds formed disappears (see note 4). Cool rapidly to room temperature. NOTES 1 The dissolution pr
39、ocedures (7.3.1) may be incomplete for particular sampies (for example samples with high contents of chromium and carbon). In such cases a fusion of the residue is required. and the result of this fusion shall be added to the test solution. 2 The Violet colour of the permanganic acid will be obsewed
40、. If the test pottion contains only a very small amount of manganese, add about 5 ml of manganese sulfate solution (4.131. so that the per- manganic acid is visible. 3 The addition of hydrochloric acid (4.7) must be made after com- plete oxidation, visible by the violet colour-formation of the per-
41、manganic acid. 4 In the case of a visual titration (7.3.3.21, after the decomposition of the permanganic acid and after boiling for 10 min, it is necescary to add 4 mi of manganese sulfate solution (4.141, then boil for a further 3 min. 7.3.3 Titration 7.3.3.1 Potentiometric titration 7.3.3.1.1 In t
42、he absence of vanadium Place the electrodes of the potentiometric device (5.1 1 into the beaker containing the solution (7.3.2) to be titrated. Agitate, preferably with an electromagnetic stirrer, and add from a burette the ammonium iron(ll) sulfate standard solution (4.19) until a potential drop oc
43、curs (see the note). Titrate slowly around this point. Let V4 be this volume in millilitres. With the platinum-saturated calomel dectrcdes the potential drop is of the order of 300 mV and the equivalence point occurs between 700 and 900 mi. NOTE - With chromium contents in solution less than 40 mg,
44、use a a) ml burette, and with chromium contents in solution more than 40 mg, use a 50 mi burette. . 7.3.3.1.2 In the presence of vanadium Titrate as indicated in 7.3.3.1.1. In this case the vanadium k measured dong with the chromium. Let V, be this volume in millilitres. The vanadium titrated with t
45、he chromium is oxidized by potassium permanganate solution (4.15). To oxidize the vanadium alone, measure the oxidation potential with the platinum-saturated calomel electrodes while potassium per- manganate solution (4.15) is being added. Add potassium per- manganate solution (4.151 drop by drop un
46、til a potential of 1 o00 to 1 160 mV is obtained. Maintain this potential for 2 min, after which, either - eliminate the excess potassium permanganate by the addition of about 10 ml of sodium nitrite solution (4.16); about a minute later add 3 g of urea (4.1): wait for the potential to become stabil
47、ized at around 800 mV, agitate and titrate as indicated in 7.3.3.1.1; or - eliminate the excess potassium permanganate by the addition, drop by drop, of sodium nitrite solution (4.16) until the potential stabilizes at around 77OmV; add 5mi of sulfamic acid solution (4.17) (potential 780 mV); then ad
48、d 30 ml of orthophosphoric acid (4.41, agitate and titrate as in- dicated in 7.3.3.1.1. Let V, be this volume in millilitres. 7.3.3.2 Visual titration (see the note). Whilst stirring, add from a burette accurately known amounts of the ammonium iron(ll) sulfate standard solution (4.19) until the colo
49、ur of the solution changes from orangeyellow to bluish-green. Add 5 mi of the ammonium iron(ll) sulfate stan- dar solution (4.191 in excess and continue to stir for 5 s. Let V7 be this volume in millilitres. Titrate immediately the excess ammonium iron(ll) sulfate with the potassium permanganate standard solution (4.18). Take as the end point of titration, the beginning of the slight permanent darkening of the pale green colour, which is very clear and well- defined to an experienced operator. Let Va be this volume in millilitres.
