1、BRITISH STANDARD BS 6200-3.10.5: 1992 Sampling and analysis of iron, steel and other ferrous metals Part 3: Methods of analysis Section 3.10 Determination of chromium Subsection 3.10.5 Ferrochromium: volumetric methodBS 6200-3.10.5:1992 This British Standard, having been prepared under the direction
2、of the Iron and Steel Standards Policy Committee, waspublished under the authorityof the Standards Boardand comes into effect on 15 June 1992 BSI 09-1999 The following BSI references relate to the work on this standard: Committee reference ISM/18 Draft for comment 91/44338 DC ISBN 0 580 20793 5 Comm
3、ittees responsible 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
4、(Laboratory of the Government Chemist) Ferro Alloys and Metals Producers Association Ministry of Defence Amendments issued since publication Amd. No. Date CommentsBS6200-3.10.5:1992 BSI 09-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Principle 1 3 Reagents 1
5、 4 Apparatus 1 5 Sampling 1 6 Procedure 2 7 Calculation and expression of results 3 8 Test report 4 Table 1 Precision data 4 Publication(s) referred to Inside back coverBS 6200-3.10.5:1992 ii BSI 09-1999 Foreword This Subsection of BS6200 has been prepared under the direction of the Iron and Steel S
6、tandards Policy Committee and supersedes method3 for the determination of chromium in BSI Handbook No.19, to which it is technically equivalent. BS 6200 is a multipart British Standard, covering all aspects of the sampling and analysis of iron, steel and other ferrous metals. A list of contents, tog
7、ether 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 application. Compliance with a British Standard does not of itself confer immunity from legal obl
8、igations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to4, 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
9、 inside front cover.BS6200-3.10.5:1992 BSI 09-1999 1 1 Scope This Subsection of BS6200 describes a volumetric method for the determination of chromium in ferrochromium. The method is applicable to high and low carbon grades of ferrochromium, but is not recommended for high silicon grades containing
10、more than4% (m/m) of silicon. The method is not applicable to alloys containing vanadium unless the alternative titrant is used. NOTEThe titles of the publications referred to in this Subsection of BS6200 are listed on the inside back cover. 2 Principle The test portion is dissolved in sulfuric acid
11、 followed by phosphoric acid. After fuming, silica and insoluble carbides are removed and any insoluble chromium is recovered and returned to the solution. Iron is oxidized with nitric acid and chromium is oxidized to dichromate by ammonium peroxodisulfate in the presence of silver ions as catalyst.
12、 Residual peroxodisulfate is destroyed by boiling and permanganic acid is selectively reduced with dilute hydrochloric acid. Chromium is determined by titration with diammonium iron(II) sulfate. Potassium dichromate is used as back-titrant with sodium N-phenylsulfanilate as indicator, except in the
13、presence of vanadium when potassium permanganate is substituted. 3 Reagents During the analysis use only reagents of recognized analytical grade and only grade3 water as specified in BS3978. 3.1 Ammonium peroxodisulfate 3.2 Diammonium iron(II) sulfate, 80g/l solution. Dissolve 80g of diammonium iron
14、(II) sulfate, (NH 4 ) 2 SO 4 .FeSO 4 .6H 2 O, in a mixture of500ml of water and20ml of sulfuric acid, density =1.84g/ml, and cool. Transfer to a1l volumetric flask, dilute to the mark, and mix.1ml of this solution is equivalent to approximately3.5mg of chromium; the exact equivalence is determined a
15、t the time of use. 3.3 Hydrochloric acid, = 1.16 g/ml to 1.18g/ml, diluted1+3. 3.4 Hydrofluoric acid, 40 % (m/m). 3.5 Nitric acid, = 1.42 g/ml. 3.6 Orthophosphoric acid, = 1.75 g/ml, diluted1+1. 3.7 Potassium dichromate, standard solution. Dissolve4.9035g of potassium dichromate, K 2 Cr 2 O 7(previo
16、usly dried to constant weight at150 C) in approximately500ml of water. Cool, transfer to a1l volumetric flask, dilute to the mark and mix.1ml of this solution is equivalent to1.734mg of chromium. 3.8 Potassium hydrogen sulfate 3.9 Potassium permanganate, volumetric solution. Dissolve3.2g of potassiu
17、m permanganate, KMnO 4 , in approximately500ml of water and allow to stand in a closed vessel for24h. Filter through a well-washed synthetic ceramic fibre pad into a1l volumetric flask and wash with water. Add5ml of orthophosphoric acid, =1.75g/ml, dilute to the mark and mix.1ml of this solution is
18、equivalent to approximately1.734mg of chromium; the exact equivalence is determined at the time of use. 3.10 Potassium permanganate, 10g/l solution. Dissolve1g of potassium permanganate in80ml of water, dilute to100ml and mix. 3.11 Silver nitrate, 10 g/l solution. Dissolve10g of silver nitrate in wa
19、ter, dilute to1l and mix. 3.12 Sodium oxalate, minimum assay99.9%. 3.13 Sodium N-phenylsulfanilate, preoxidized, (sodium diphenylaminesulfonate). Use pellets containing the equivalent of1mg of preoxidized sodium N-phenylsulfanilate, or a suitable solution containing the same equivalent of preoxidize
20、d sodium N-phenylsulfanilate. 3.14 Sulfuric acid, diluted1+1. To400ml of water add cautiously with cooling and stirring,500ml of sulfuric acid, =1.84g/ml. Cool, dilute to1l and mix. 3.15 Sulfuric acid, diluted1+49. To400ml of water add cautiously with cooling and stirring,20ml of sulfuric acid, =1.8
21、4g/ml. Dilute to1l and mix. 4 Apparatus 4.1 Ordinary laboratory apparatus 4.2 Volumetric glassware, in accordance with class A of BS846, BS1583 or BS1792, as appropriate. 5 Sampling Carry out sampling in accordance with BS1837. NOTEBS 6200-2, which will supersede BS1837, is currently in preparation.
22、 On its publication, this Subsection will be amended to include sampling in accordance with BS6200-2.BS 6200-3.10.5:1992 2 BSI 09-1999 6 Procedure 6.1 Test portion Weigh, to the nearest 0.001g, a test portion of0.4g. 6.2 Determination 6.2.1 Preparation of the test solution Place the test portion in
23、a750ml conical flask, add25ml of sulfuric acid (3.14) and heat very gently, avoiding loss of volume, for20min or until solvent action ceases. NOTEIt is important to ensure that the whole test portion is covered by the acid and that no particles adhere to the wall of the flask during transfer of the
24、test portion or subsequent shaking of the flask during solution. Add 20 ml of orthophosphoric acid (3.6) and evaporate just to fuming. Cool, add40ml of cold water, heat to boiling, oxidize with nitric acid (3.5), boil for2min and dilute with hot water to100ml. Filter through a paper-pulp pad into a7
25、50ml conical flask, washing with cold sulfuric acid (3.15). Reserve the filtrate. Dry the pad by suction and transfer it and the insoluble residue, using small pieces of filter paper, to a platinum dish. Ignite gently at as low a temperature as possible until carbonaceous matter is removed and cool.
26、 Moisten the residue with a few drops of water, add two drops of sulfuric acid (3.14) and2ml of hydrofluoric acid (3.4). Evaporate to dryness, preferably under an infra-red lamp. Heat on a hot plate to complete the removal of sulfuric acid and finally at700 C to800 C for5min and cool. Fuse the resid
27、ue with 2g of potassium hydrogen sulfate (3.8), cool, dissolve the cold salts in a few millilitres of sulfuric acid (3.15) and return the solution to the main filtrate. Dilute to400ml with hot water and add a few glass beads. 6.2.2 Oxidation of chromium Add 1 ml of potassium permanganate solution(3.
28、10),25ml of silver nitrate solution (3.11) and6g of ammonium peroxodisulfate (3.1). Heat to boiling and boil for 10 min after the colour of permanganic acid develops. If the colour does not develop after boiling for5min, make0.5g additions of ammonium peroxodisulfate (3.1) to the hot solution until
29、the colour is obtained. Add 15 ml of hydrochloric acid (3.3) and boil for10min. If the permanganic acid colour is not discharged, make further5ml additions of the hydrochloric acid, boiling after each addition, until the colour disappears. Cool to room temperature. 6.2.3 Titration of chromium 6.2.3.
30、1 In the absence of vanadium Titrate with diammonium iron(II) sulfate solution(3.2) until an excess of at least2ml is present. Add one pellet of preoxidized sodium N-phenylsulfanilate (3.13) (equivalent to1mg of the indicator) and back-titrate with potassium dichromate solution (3.7) until one drop
31、produces a deep violet colour. Note the volume of diammonium iron(II) sulfate solution (3.2) V Feand of potassium dichromate solution (3.7) V Crused. 6.2.3.2 In the presence of vanadium Titrate with diammonium iron(II) sulfate solution(3.2) until an excess of at least2ml is present. Back-titrate wit
32、h potassium permanganate solution (3.9). In the presence of vanadium the end-point fades. Continue until the colour change persists for at least30s. Note the volume of diammonium iron(II) sulfate solution (3.2) V Feand of potassium permanganate solution (3.9) V Mnused. High chromium concentrations t
33、end to mask the colour change. Make duplicate tests and, after the titration of the first of these, discharge the end-point by the addition of a few drops of diammonium iron(II) sulfate solution (3.2). Compare the colour of this solution with that of the assay test during titration to facilitate det
34、ection of the colour change at the end-point. 6.3 Standardization of volumetric solutions 6.3.1 Potassium permanganate solution Heat 200 ml of sulfuric acid (3.15) in a500ml flask to75 C and add potassium permanganate solution(3.9) dropwise from a burette until a permanent pink colour is produced. T
35、ransfer to a dry500ml beaker containing0.268g of sodium oxalate (3.12), previously dried at105 C for1h. When dissolved, add5ml of potassium permanganate solution (3.9) and as soon as the pink colour is discharged continue the titration until a permanent pink colour again persists. (Approximately40ml
36、 will be required.) Note the volume V aof potassium permanganate solution added between the two end-points.BS6200-3.10.5:1992 BSI 09-1999 3 6.3.2 Diammonium iron(II) sulfate solution Transfer 25 ml of sulfuric acid (3.14) and20ml of orthophosphoric acid (3.6) to a750ml conical flask, and dilute to40
37、0ml. Add one pellet of sodium N-phenylsulfanilate (3.13), three drops of diammonium iron(II) sulfate solution (3.2) and potassium dichromate solution (3.7) until one drop produces a deep violet colour. Add exactly40ml of diammonium iron(II) sulfate solution (3.2) and titrate with potassium dichromat
38、e solution (3.7) until one drop again produces a deep violet colour. (Approximately80ml will be required.) Note the volume V bof potassium dichromate solution added between the two end-points. 7 Calculation and expression of results 7.1 Calculation of solution factors 7.1.1 Potassium permanganate so
39、lution factor Calculate the factor F Mnfor the potassium permanganate solution (3.9) from the equation: F Mn= 40/V a where 7.1.2 Diammonium iron(II) sulfate solution factor Calculate the factor F Fefor the diammonium iron(II) sulfate solution (3.2) from the equation: F Fe= V b /80 where 7.2 Calculat
40、ion of chromium content 7.2.1 Vanadium absent Calculate the chromium content Cr expressed as a percentage by mass, from the equation: where 7.2.2 Vanadium present Calculate the chromium content, Cr, expressed as a percentage by mass, from the equation: where 7.3 Precision A planned trial of this met
41、hod was carried out by eight to nine laboratories on each of five samples. The mean results for each laboratory given in the original report 1) , have been examined statistically to obtain values of between-laboratory agreement. In the absence of individual results it is not possible to calculate re
42、peatability r and reproducibility R, as defined in BS5497-1. From the reported results, for probability P =95%, the statistical limits (2.83s) for agreement between laboratory means have been calculated and are given inTable 1. The difference between the mean results of two laboratories found on ide
43、ntical test material will exceed the P=95% probability level, on average, not more than once in20cases in the normal and correct operation of the method. Table 1 shows that there is considerable variation in between-laboratory agreement; the average for the series is approximately0.30% (m/m) over a
44、range of chromium contents from62.5% (m/m) to71.3%(m/m). V a is the volume of potassium permanganate solution (3.9) used in6.3.1 (inml). V b is the volume of potassium dichromate solution (3.7) used in6.3.2 (inml). Cr 1.734 2V Fe F Fe V Cr () 10m - = V Fe is the volume of diammonium iron(II) sulfate
45、 solution (3.2) used in6.2.3.1 (in ml); F Fe is the factor of the diammonium iron(II) sulfate solution (3.2) found in7.1.2; V Cr is the volume of potassium dichromate solution (3.7) used in6.2.3.1 (in ml); m is the mass of the test portion in6.1 (in g). V Fe is the volume of diammonium iron(II) sulf
46、ate solution (3.2) used in6.2.3.2 (in ml); F Fe is the factor of the diammonium iron(II) sulfate solution (3.2) found in 7.1.2; V Mn is the volume of potassium permanganate solution (3.9) used in 6.2.3.2 (in ml); F Mn is the factor of potassium permanganate solution (3.9) found in 7.1.1; m is the ma
47、ss of the test portion in6.1 (in g). 1) Methods of Analysis Committee Journal of the Iron and Steel Institute 163,1949,307310. Cr 1.734 2V Fe F Fe V Mn F Mn () 10m - =BS 6200-3.10.5:1992 4 BSI 09-1999 Table 1 Precision data 8 Test report The test report shall include the following information: a) al
48、l information necessary for the identification of the sample, the laboratory and the date of analysis; b) the method used, by reference to this Subsection of BS6200; c) the results, and the form in which they are expressed; d) any unusual features noted during the determination; e) any operation not
49、 specified in this BritishStandard or any optional operation which may have influenced the results. Sample number Type Number of laboratories Chromium content C Si Mean value Between-laboratory agreement, 2.83s % (m/m) % (m/m) % (m/m) 1 6.0 3.6 9 62.47 0.308 2 0.08 1.1 9 67.24 0.180 3 5.02 1.7 8 68.79 0.439 4 0.08 0.13 8 69.46 0.165 5 0.95 1.20 8 71.32 0.434BS6200-3.10.5:1992 BSI 09-1999 Publication(s) referred
