1、BRITISH STANDARD BS 6200-3.19.1: 1985 ISO4941:1978 Sampling and analysis of iron, steel and other ferrous metals Part3: Methods of analysis Section 3.19 Determination of molybdenum Subsection 3.19.1 Steel and cast iron: photometric method UDC 669.1:543.42.062:546.77BS6200-3.19.1:1985 This British St
2、andard, having been prepared under the directionof the Iron and Steel Standards Committee, was published under the authority ofthe Board of BSI and comes intoeffect on 28 February1985 BSI 09-1999 The following BSI references relate to the work on this standard: Committee reference ISM/18 Draft for a
3、pproval84/39008 ISBN 0 580 14268 X National foreword This Subsection of BS6200 has been prepared under the direction of the Iron and Steel Standards Committee. It is identical with ISO4941:1978 “Steels and cast irons Determination of molybdenum content Photometric method” published by the Internatio
4、nal Organization for Standardization (ISO) and supersedes method1 for the determination of molybdenum in BSI Handbook No.19. Terminology and conventions. The text of the International Standard has been approved as suitable for publication as a British Standard without deviation. Some terminology and
5、 certain conventions are not identical with those used in British Standards; attention is drawn especially to the following. The comma has been 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 “Interna
6、tional Standard” appear, referring to this standard, they should be read as “British Standard”. Cross-reference. The Technical Committee has reviewed the provisions of ISO/R377, to which reference is made in clause6, and has decided that they are acceptable for use in conjunction with this standard.
7、 A related standard to ISO/R377 is BS1837 “Methods for the sampling of iron, steel, permanent magnet alloys and ferro-alloys”. Appropriate procedures from ISO/R377 will be incorporated in BS6200-2 “Methods of sampling and sample preparation”, which will be published in due course and which will supe
8、rsede BS1837. 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 obligations. Summary of pages This docum
9、ent 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 inside front cover. Amendments issue
10、d since publication Amd. No. Date of issue CommentsBS6200-3.19.1:1985 BSI 09-1999 i Contents Page National foreword Inside front cover 1 Scope and field of application 1 2 Reference 1 3 Principle 1 4 Reagents 1 5 Apparatus 2 6 Sampling 2 7 Procedure 2 8 Expression of results 4 9 Test report 4 Public
11、ations referred to Inside back coverii blankBS6200-3.19.1:1985 BSI 09-1999 1 1 Scope and field of application This International Standard specifies a photometric method for the determination of the molybdenum content of steels and cast irons. The method is applicable to steels and cast irons having
12、molybdenum contents between0,003 and9%(m/m). Vanadium and tungsten interfere with the measurement if, because of their contents, the V/Mo ratio is greater than16 or the W/Mo ratio is greater than8. NOTEGreater V/Mo or W/Mo ratios (up to300) may, however, be permitted, but in such cases it is necessa
13、ry to carry out the measurement very quickly after the extraction. 2 Reference ISO/R377, Selection and preparation of samples and test pieces for wrought steel. 3 Principle Dissolution of a test portion in an appropriate mixture of acids and decomposition of the carbides by oxidation. Quantitative f
14、ormation of a coloured compound of molybdenum, in the presence of thiocyanate, iron(II) and/or copper(II) ions and extraction of this compound using n-butyl acetate. Photometric measurement of the coloured compound at a wavelength of about470nm. NOTEWhen the conditions of the procedure are respected
15、, the coefficient of molecular absorption is18930 60. 4 Reagents During the analysis, use only reagents of recognized analytical grade and only distilled water or water of equivalent purity. 4.1 Iron, in flake or powder form, with a molybdenum content less than0,005% and free from tungsten and vanad
16、ium. 4.2 n-Butyl acetate 4.3 Nitric acid, about1,40g/ml, about14M solution. 4.4 Hydrochloric acid, about1,19g/ml, about12M solution. 4.5 Hydrochloric acid, about9M solution(3+1). 4.6 Hydrochloric acid, about6M solution(1+1). 4.7 Acid mixtureI To1volume of the nitric acid(4.3) add2volumes of the hydr
17、ochloric acid(4.4) and mix well. Prepare the solution immediately before use. 4.8 Acid mixture II Add150ml of phosphoric acid, about1,70g/ml, to300ml of water, and add this diluted acid to360ml of perchloric acid, about1,67g/ml. Dilute to1000ml with water and mix. NOTEIn the preparation of this acid
18、 mixture, the360ml of perchloric acid, about1,67g/ml, may be replaced by150ml of sulphuric acid, about1,84g/ml. 4.9 Ascorbic acid,100g/l solution. Prepare this solution at the moment of use. 4.10 Ammonium thiocyanate,320g/l solution. Store this solution away from light. 4.11 Copper(II), solution cor
19、responding to70mg of Cu(II)per litre in a hydrochloric medium about1,5M. Dissolve0,188g of copper(II)chloride dihydrate (CuCl 2 .2H 2 O) or0,275g of copper(II)sulphate pentahydrate (CuSO 4 .5H 2 O) in125ml of the hydrochloric acid(4.4). Make up the volume to1000ml with water and mix. 4.12 Tin(II) co
20、pper(II) chloride, solution in a hydrochloric medium about2M. Dissolve80g of tin(II) chloride in155ml of the hydrochloric acid(4.4). Add100ml of the copper(II) solution(4.11). Make up the volume to1000ml with water and mix. Prepare the solution immediately before use. 4.13 Iron, acidic solution corr
21、esponding to10g ofFeper litre. Dissolve10g of the iron(4.1) in500ml of the acid mixtureII(4.8) used for the determination; after cooling, make up the volume to1000ml with water and mix. 4.14 Molybdenum, standard solution corresponding to500mg of Mo per litre. Weigh, to the nearest0,001g,1,261g of so
22、dium molybdate dihydrate (Na 2 MoO 4 .2H 2 O) or0,920g of ammonium heptamolybdate tetrahydrate (NH 4 ) 6 Mo 7 O 24 .4H 2 O and dissolve in500ml of the hydrochloric acid(4.4). Transfer the solution quantitatively to a1000ml one-mark volumetric flask, dilute to the mark with water and mix. 4.15 Molybd
23、enum, standard solution corresponding to5mg of Mo per litre. Transfer10,0ml of the standard molybdenum solution(4.14) to a1000ml one-mark volumetric flask, add500ml of the hydrochloric acid(4.4), dilute to the mark with water and mix. 1ml of this solution contains5g of Mo.BS6200-3.19.1:1985 2 BSI 09
24、-1999 5 Apparatus Ordinary laboratory apparatus and 5.1 Gilson separating funnel (spherical separating funnel), capacity125ml. 5.2 Spectrophotometer or 5.3 Photometer, fitted with suitable filters, with a maximum transmission at470nm. 5.4 Cells, having an optical path length of0,5,1,0and2,0cm. 6 Sam
25、pling Sampling shall be carried out in accordance with ISO/R377 or appropriate national standards for other types of steel and for cast iron. 7 Procedure WARNING: Perchloric acid vapour may cause explosions in the presence of ammonia, nitrous fumes or organic material in general. NOTEMeasure all the
26、 reagents, without exception, using a pipette, preferably with one mark, in particular then-butyl acetate(4.2) the volume of which is used for the calculation of the concentration of molybdenum. 7.1 Test portion According to the presumed molybdenum content, weigh, to the nearest0,001g, the following
27、 masses(m) of sample, remaining within the tolerance of 10% of the specified mass: a) Mo contents less than0,125% : m about1g; b) Mo contents from0,125 to2,5% : m about0,25g, with the addition of0,75g of the iron(4.1); c) Mo contents greater than2,5% : m about0,3g, with the addition of1,7g of the ir
28、on(4.1). 7.2 Determination 7.2.1 Preparation of test solution Place the test portion(7.1) in a250ml conical flask and add30ml of acid mixture I(4.7). Heat gently until effervescence ceases. The tungsten present partially precipitates. Add50ml of acid mixtureII(4.8) in cases7.1 a) and7.1 b) or100ml o
29、f acid mixtureII(4.8) in case7.1 c). Heat to gentle boiling and continue heating until dense white fumes are given off. When acid mixtureII is made up of perchloric and phosphoric acids, heating shall be continued until the carbides have completely decomposed: the chromium, if present, is then oxidi
30、zed. When acid mixtureII is made up of sulphuric and phosphoric acids, heating shall be continued and the complete decomposition of the carbides achieved by the addition of nitric acid. NOTEThe precipitated tungsten dissolves because of the presence of phosphoric acid. Cool and transfer the solution
31、 quantitatively to a100ml one-mark volumetric flask in cases7.1 a) and7.1 b) or a200ml one-mark volumetric flask in case7.1 c). Dilute to the mark with water and mix. Solution A of volume V 2is thus obtained. If there is a residue or precipitate in solution A, filter a part of it through a dry filte
32、r, collecting the filtrate in a dry beaker after having discarded the first fraction. Transfer20,0ml of solution A to a50ml one-mark volumetric flask fitted with a ground stopper, add10ml of the hydrochloric acid(4.4), dilute to the mark with water and mix. Solution B is thus obtained. 7.2.2 Prepara
33、tion of the compensating solution Dissolve, in the appropriate volume of the acid mixtures, the same quantity of iron(4.1) as added to the test portion(0,0,75 or1,7g) and proceed as indicated in7.2.1 until a solution D is obtained, similar to the test solution B. NOTEThe compensating solution thus e
34、stablished permits the subtraction, during the measurement, of the absorption of the molybdenum caused by the iron (4.2) and all the reagents. 7.2.3 Formation and extraction of the coloured compound NOTEMeasure all the reagents, without exception, using a pipette, preferably with one mark, in partic
35、ular the n-butyl acetate(4.1) the volume of which is used for the calculation of the concentration of molybdenum. 7.2.3.1 Test solution Take an aliquot portion V oof solution B(7.2.1) equal to25,0ml if the molybdenum content is less than1%, or10,0ml if the molybdenum content is greater than or equal
36、 to1%, and transfer to a separating funnel(5.1). If10,0ml of solution B has been taken, add15ml of compensating solution D(7.2.2). In all cases, add in order: 5ml of the copper solution(4.11), 10ml of the hydrochloric acid(4.5), and 5ml of the ascorbic acid solution(4.9). Shake and wait for3min unti
37、l the colour of the solution decreases in intensity. Add a volume V 1of25,0ml of the n-butyl acetate(4.2) if the molybdenum content is less than or equal to0,5% or of50,0ml if it is greater, and mix by simple inversion.BS6200-3.19.1:1985 BSI 09-1999 3 Immediately add5ml of the ammonium thiocyanate s
38、olution(4.10) and shake gently for1min to extract the molybdenum compound into the organic layer. Allow to separate. When the layers are well separated, remove the aqueous layer and discard it. Add10ml of the tin(II) copper(II) chloride solution(4.12) to the separating funnel(5.1), shake for about1m
39、in, allow to separate, remove the aqueous layer and discard it. Collect the organic layer in a flask fitted with a ground stopper. The drops of water in suspension in the organic layer collect at the bottom of the flask and do not interfere with the measurement. 7.2.3.2 Compensating solution Take25,
40、0ml of compensating solution D(7.2.2) and proceed in accordance with7.2.3.1, beginning at “In all cases, add in order. . .”. 7.2.4 Photometric measurements Carry out the photometric measurements on the test solution(7.2.3.1), using the spectrophotometer(5.2) at a wavelength of about470nm or the phot
41、ometer fitted with suitable filters(5.3), after having adjusted the instrument to zero absorbance against the compensating solution(7.2.3.2). Generally, the following optical path lengths are used: for Mo contents less than0,025% :2cm; for Mo contents between0,025and4%.1cm; for Mo contents greater t
42、han4% :0,5cm. NOTEWhen the V/Mo ratio is greater than16 and/or the W/Mo ratio is greater than8, the measurements shall be carried out in a period not exceeding30min after the extraction. 7.3 Establishment of the calibration curve 7.3.1 Preparation of the reference solutions, related to photometric m
43、easurements carried out with cells having an optical path length of1cm Transfer successively to a series of six separating funnels(5.1), marked from0 to5, the volumes of reagents indicated in the following table: Shake each funnel and wait for3min until the colour of the solutions decreases in inten
44、sity. Add to each funnel25,0ml of the n-butyl acetate(4.2) and mix by simple inversion. Continue in accordance with7.2.3.1, beginning at “Immediately add5ml of the ammonium thiocyanate solution. . .”. Repeat this operation five times. 7.3.2 Photometric measurements Carry out the photometric measurem
45、ents on the reference solutions(7.3.1) in accordance with the indications given in7.2.4, after having adjusted the instrument(5.2 or5.3) to zero absorbance against the reference solution “0”. 7.3.3 Plotting of the calibration curve or calculation of the angular coefficient of the straight line From
46、the means of the measured values of the absorbances and the masses, in micrograms, of Mo contained in the reference solutions, the calibration curve may be plotted or its angular coefficient (a) calculated. Reagent Volumes, in millilitres, for reference number: 0 1 2 3 4 5 Iron solution(4.13) Copper
47、 solution(4.11) Standard molybdenum solution(4.15) Hydrochloric acid(4.6) Ascorbic acid solution(4.9) 10 5 0 25 5 10 5 5,0 20 5 10 5 10,0 15 5 10 5 15,0 10 5 10 5 20,0 5 5 10 5 25,0 0 5BS6200-3.19.1:1985 4 BSI 09-1999 8 Expression of results The molybdenum (Mo) content is given, as a percentage by m
48、ass, by the formula 9 Test report The test report shall include the following particulars: a) the method used by reference to this International Standard; b) the results, and the form in which they are expressed; c) any unusual features noted during the determination; d) any operation not specified
49、in this International Standard, or any optional operations which may have influenced the result. where D is the ratio of the absorbance of the test solution to that of its compensating solution; a is the absorbance of an n-butyl acetate solution containing14g of molybdenum complexed with thiocyanate per millilitre, measured with an optical path length of1cm(7.3.3); d is the optical path length, in centimetres, used for the measurement(7.2.4); V 1is the volume, in millilitres, of n-butyl acetate(4.2) used for the determination(7.2.3.1); V 0is the vol
