1、BRITISH STANDARD BS 6200-3.17.1: 1992 Sampling and analysis of iron, steel and other ferrous metals Part 3: Methods of analysis Section 3.17 Determination of magnesium Subsection 3.17.1 Cast iron: volumetric methodBS6200-3.17.1:1992 This British Standard, having been prepared under the directionof t
2、he Iron and Steel Standards Policy Committee, waspublished under the authorityof the Standards Boardand comes into effect on 15June1992 BSI 08-1999 The following BSI references relate to the work on this standard: Committee reference ISM/18 Draft for comment91/44339 DC ISBN 0 580 20794 3 Committees
3、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 (Labora
4、tory of the Government Chemist) Ferro Alloys and Metals Producers Association Ministry of Defence Amendments issued since publication Amd. No. Date CommentsBS6200-3.17.1:1992 BSI 08-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Principle 1 3 Reagents 1 4 Appa
5、ratus 1 5 Sampling 1 6 Procedure 1 7 Calculation and expression of results 3 8 Test report 3 Table 1 Precision data 3 Publication(s) referred to Inside back coverBS6200-3.17.1:1992 ii BSI 08-1999 Foreword This Subsection of BS6200 has been prepared under the direction of the Iron and Steel Standards
6、 Policy Committee and supersedes method1 for the determination of magnesium in BSI Handbook No.19, to which it is technically equivalent. BS6200 is a multipart British Standard, covering all aspects of the sampling and analysis of iron, steel and other ferrous metals. A list of contents, together wi
7、th 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 obligations
8、. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 4, 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 insi
9、de front cover.BS6200-3.17.1:1992 BSI 08-1999 1 1 Scope This Subsection of BS6200 describes a volumetric method for the determination of magnesium in cast iron. The method is applicable to the range of magnesium contents normally found in nodular graphite cast iron containing up to2% (m/m) nickel. A
10、 very small number of nodular irons may also contain calcium, e.g.those treated with ferrosilicon magnesium containing calcium fluoride. In such cases the magnesium result will be inclusive of any residual calcium in the iron. NOTEThe titles of the publications referred to in this Subsection of BS62
11、00 are listed on the inside back cover. 2 Principle The test portion is dissolved in acid and interfering elements removed by solvent extraction. Magnesium is determined by titration with ethylenediaminetetra-acetic acid disodium salt. 3 Reagents During the analysis use only reagents of recognized a
12、nalytical grade and only grade3 water as specified in BS3978. WARNING. Perchloric acid vapour may cause explosions in the presence of nitrous fumes or organic material in general. 3.1 Ammonia-ammonium chloride buffer solution. Dissolve67.5g of ammonium chloride in250ml ofwater and570ml of ammonia so
13、lution, density = 0.91g/ml. Dissolve0.931g of ethylenediaminetetra-acetic acid disodium salt (EDTA Na 2 ) and0.616g of magnesium sulfate (3.9), both weighed to within0.001g, in50ml of water. Mix the two solutions, dilute to1l and mix. 3.2 Chloroform 3.3 Cupferron solution, 50g/l. Dissolve5g of cupfe
14、rron (N-nitroso-N-phenylhydroxylamine, ammonium salt) in water, dilute to100ml and mix. The solid reagent and its solution deteriorate in storage. Prepare this solution from fresh reagent immediately before use. 3.4 Ethylenediaminetetra-acetic acid disodium salt solution (EDTA Na 2 ) 1ml = 0.25mg ma
15、gnesium. Dissolve3.722g of EDTA Na 2in water, transfer to a1l volumetric flask, dilute to the mark and mix. 3.5 Hydrochloric acid, = 1.16g/ml to1.18g/ml. 3.6 Hydrochloric acid, = 1.16g/ml to1.18g/ml, diluted1+4. 3.7 Isobutyl acetate. Use only isobutyl acetate for the extraction. Grades of butyl acet
16、ate which contain appreciable amounts of n-butyl acetate cause unsatisfactory extractions. 3.8 Magnesium, standard solution, 0.25mg magnesium per millilitre. Dissolve0.25g, weighed to the nearest0.001g, of high purity magnesium in20ml of hydrochloric acid (3.6), cool, transfer to a1l volumetric flas
17、k, dilute to the mark and mix. 3.9 Magnesium sulfate, MgSO 4 .7H 2 O. 3.10 Nitric acid, = 1.42g/ml. 3.11 Perchloric acid, = 1.54g/ml. 3.12 Sodium acetate, 500g/l solution. Dissolve500g of sodium acetate, CH 3 COONa.3H 2 O, in water, dilute to1l and mix. 3.13 Sodium diethyldithiocarbamate, 200g/l sol
18、ution. Dissolve20g of sodium diethyldithiocarbamate in water, dilute to100ml and mix. 3.14 Solochrome black indicator, 1g/l solution. Dissolve0.1g of Solochrome black (also known as Eriochrome black T; CI14645) in a mixture of30ml of triethanolamine (3.15) and70ml of water. 3.15 Triethanolamine 4 Ap
19、paratus 4.1 Ordinary laboratory apparatus 4.2 Volumetric glassware, in accordance with classA of BS846, BS1583 or BS1792, as appropriate. 5 Sampling Carry out sampling in accordance with BS1837. NOTEBS6200-2, which will supersede BS1837, is currently in preparation. On its publication this Subsectio
20、n will be amended to include sampling in accordance with BS6200-2. 6 Procedure 6.1 Test portion Weigh, to the nearest0.001g, a test portion of5g. 6.2 Blank test In parallel with the determination and following the same procedure, carry out a blank test using the same quantities of all reagents. 6.3
21、Preparation of the test solution Place the test portion in a400ml squat beaker. Add,cautiously, a mixture of50ml of hydrochloric acid (3.5) and15ml of nitric acid (3.10), adding the pre-mixed acids in small portions (approximately10ml at a time), waiting until the vigorous reaction subsides before a
22、dding the next portion and covering the beaker after each addition. Do not apply heat.BS6200-3.17.1:1992 2 BSI 08-1999 NOTEWith some samples very gentle heat may be applied to initiate solution but the beaker should not be allowed to remain over the source of heat once solution has commenced. Cast i
23、ron samples dissolve readily and apparent drillings remaining5min after the final addition of acid are usually pseudomorphs of graphite and silica. A gentle effervescence is not evidence that the sample is still dissolving; it is more likely to be due to the oxidation of hydrochloric acid by nitric
24、acid. Heating during or after solution leads to loss of hydrochloric acid and decreased efficiency of the isobutyl acetate extraction. 6.4 Removal of iron by solvent extraction When the sample is dissolved, cool and filter through a glass filter or a dry glass wool pad into a dry250ml conical separa
25、ting funnel. NOTE 1A Whatman glass filter GF/A is suitable. NOTE 2The funnel may be rinsed out with hydrochloric acid(3.5) as an alternative to drying. Wash the beaker and the filter with hydrochloric acid (3.5) from a polyethylene wash bottle fitted with a safety trap and adjust the volume to appro
26、ximately90ml with hydrochloric acid (3.5). Add 150ml of isobutyl acetate (3.7) and shake vigorously for30s. Allow the two layers to separate and run the lower (aqueous) layer into a400 ml squat beaker. Allow the separating funnel to stand for2min, then run the small amount of acid which has drained
27、down into the same beaker, allowing the interface to travel to the bottom of the stopcock bore. NOTE 3A small amount of scum may be present at the interface and this may be allowed to enter the aqueous layer without serious entrainment of iron. Traces of iron re-introduced at this stage will be remo
28、ved later. Rinse the stem of the separating funnel with water into the beaker. Discard the upper (isobutyl acetate) layer. 6.5 Removal of interfering elements Evaporate the solution to approximately40ml, add5ml of nitric acid (3.10) and10ml of perchloric acid (3.11), then evaporate to fumes of the p
29、erchloric acid. Continue fuming for3min with the beaker covered. Cool slightly, add25ml of water and heat to boiling, then cool again slightly. Filter through a paper-pulp pad into a250ml conical separating funnel, washing the beaker and pad six times with a total volume of approximately50ml of cold
30、 water and adding the washings to the funnel. Cool and add25ml of sodium acetate solution (3.12). Add10ml of cupferron solution (3.3), then30ml of chloroform (3.2) and shake vigorously for30s. Allow the two phases to separate, then run off and reject the lower (chloroform) layer. WARNING. Chloroform
31、 solutions of heavy metal cupferrates are unstable and may explode on standing. Dispose of these solutions immediately. To the aqueous layer remaining in the funnel add40ml of sodium diethyldithiocarbamate solution (3.13) and mix well. Add50ml of chloroform (3.2) and shake vigorously for30s. Allow t
32、he phases to separate, rinse the stopper and neck of the funnel with chloroform (3.2) and run off and reject the lower (chloroform) layer. Add a further10ml of chloroform (3.2) to the funnel and1ml to2ml of sodium diethyldithiocarbamate solution (3.13). If a coloured precipitate is obtained, shake t
33、o extract this into the chloroform layer and make further1ml to2ml additions of sodium diethyldithiocarbamate solution (3.13), shaking and extracting with10ml portions of chloroform (3.2) between additions, until the precipitate formed is white. Reject the lower (chloroform) layer and shake the aque
34、ous layer with further10ml portions of chloroform (3.2) until the chloroform layer remains colourless. Before running off the last10ml portion of chloroform add two to three drops of cupferron solution (3.3). If a coloured precipitate is obtained add further cupferron solution until either no precip
35、itate or a white precipitate is formed. Shake to extract any precipitate into the chloroform and, if necessary, shake the aqueous layer with further 10 ml portions of chloroform (3.2) until the chloroform layer is again colourless. NOTE. Usually10ml of cupferron solution (3.3), 40ml of sodium diethy
36、lthiocarbamate solution (3.13) and a total of100ml of chloroform (3.2) are sufficient for all the extractions. 6.6 Titration of magnesium Transfer the aqueous layer via the top of the separating funnel to a400ml beaker, add15ml of ammonia-ammonium chloride buffer solution (3.1) and10 drops of Soloch
37、rome black indicator (3.14). Titrate with EDTA Na 2solution (3.4) until the colour of the solution changes from pink through purple to a pure blue end-point which does not change on further addition of EDTA Na 2solution. Note the volume, V t , of EDTA Na 2solution used for the titration of the test
38、portion. Titrate the blank solution following exactly the same procedure and note the volume, V b , of EDTA Na 2solution used. 6.7 Standardization of the EDTA Na 2solution(3.4) Transfer10.0ml of magnesium solution (3.8) to a400ml squat beaker, add approximately100ml of water, 15ml of ammonia-ammoniu
39、m chloride buffer solution (3.1) and10 drops of Solochrome black indicator (3.14). Titrate the magnesium solution with EDTA Na 2solution as described in6.6. Note the volume, V f , of EDTA Na 2solution used.BS6200-3.17.1:1992 BSI 08-1999 3 7 Calculation and expression of results 7.1 Calculation Calcu
40、late F, the magnesium equivalent in milligrams per millilitre of the EDTA Na 2solution(3.4) from the equation: F = 2.5/V f where Calculate the magnesium content Mg, expressed as a percentage by mass, from the equation: where 7.2 Precision A planned trial of this method was carried out by10 analysts
41、each from a different laboratory; three tests were carried out by each analyst on each of three standard samples (samples1 to3) of nodular cast iron specially prepared to ensure optimum homogeneity. To assess the reproducibility on samples normally encountered, similar trials were also carried out o
42、n a further three nodular irons sampled either by drilling or from a rotary sampling machine (samples4 to6). From the results obtained, the95% confidence limits (2s) have been calculated in accordance with BS 5497-1 and are given inTable 1. The difference between two single results found on identica
43、l material by one analyst using the same apparatus within a short time interval will exceed the repeatability r, on average, not more than once in20 cases in the normal and correct operation of the method. The difference between two single and independent results found by two operators working in di
44、fferent laboratories on identical test material will exceed the reproducibility R, on average, not more than once in20 cases in the normal and correct operation of the method. The correlations from regression analyses of repeatability r and reproducibility R with magnesium concentration have too low
45、 a probability to justify predictions of precision. 8 Test report The test report shall include the following information: a) all 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
46、 results, and the form in which they are expressed; d) any unusual features noted during the determination; e) any operation not specified in this British Standard or any optional operation which may have influenced the results. Table 1 Precision data V f is the volume of EDTA Na 2solution used in6.
47、7 (in ml). V t is the volume of EDTA Na 2used in the titration of the test portion (in ml); V b is the volume of EDTA Na 2used in the blank titration (in ml); m is the mass of the test portion (see6.1) (ing). Mg F V t V b ()0.025 m - = Sample number Sampling method (see note) Magnesium Repeatability
48、 r Reproduciblity R % (m/m) 1 2 3 a a a 0.015 0.046 0.098 0.0031 0.0020 0.0026 0.0037 0.0047 0.0065 4 4 a b 0.035 0.035 0.0051 0.0048 0.0059 0.0068 5 a 0.056 0.0031 0.0126 6 6 a b 0.128 0.128 0.0113 0.0110 0.0187 0.0146 NOTESampled by: a) drilling b) rotary sampling machine See A rotary sampling mac
49、hine for the sampling of cast iron. BCIRA J. of Res. and Dev. 7, April 1959, 644650 (methodrecommended in BSI Handbook No.19, Section 1, subsection A.1.f.)4 blankBS6200-3.17.1:1992 BSI 08-1999 Publication(s) referred to BS 846, Specification for burettes. BS 1583, Specification for one-mark pipettes. BS 1792, Specification for one-mark volumetric flasks. BS 1837, Methods for the sampling of iron, steel, permanent magnet alloys and ferro-alloys. BS 3978, Specification for water for laboratory use. BS 5
