1、BRITISH STANDARD BS 6721-10: 1989 ISO 6437:1984 Sampling and analysis of copper and copper alloys Part 10: Method for determination of chromium in copper alloys: titrimetric method ISO title: Copper alloys Determination of chromium content Titrimetric method UDC 669.3:546.76:543.24:620.1BS6721-10:19
2、89 This British Standard, having been prepared under the directionof the Non-ferrous Metals Standards Committee, waspublished under the authorityof the Board of BSIandcomes into effect on 28February1989 BSI 12-1999 The following BSI references relate to the work on this standard: Committee reference
3、 NFM/34 Draft (ref. 86/38276) announced inBSI News, January 1988 ISBN 0 580 17123 X Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Non-ferrous Metals Standards Committee (NFM/-) to Technical Committee NFM/34 upon which the following bod
4、ies were represented: British Non-ferrous Metals Federation Copper Development Association London Metal Exchange Non-ferrous Metal Stockists Society of British Aerospace Companies Limited Coopted members The following bodies were also represented in the drafting of the standard, through subcommittee
5、s and panels: BNF Metals Technology Centre British Bronze and Brass Ingot Manufacturers Association Copper Smelters and Refiners Association Ministry of Defence National Brassfoundry Association Coopted members Amendments issued since publication Amd. No. Date of issue CommentsBS6721-10:1989 BSI 12-
6、1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope and field of application 1 2 Principle 1 3 Reagents 1 4 Apparatus 2 5 Procedure 2 6 Expression of results 2 7 Test report 2BS6721-10:1989 ii BSI 12-1999 National foreword This Part of BS6721 has been prepared
7、 under the direction of the Non-ferrous Metals Standards Committee. BS6721 is a multi-part standard and describes methods of sampling and analysis for copper and copper alloys. It is intended that Parts1 to3 of BS6721 will describe methods of sampling copper and copper alloys in various forms. The r
8、emaining Parts will give methods for the determination of individual elements in copper and copper alloys. This Part of BS6721 is identical with ISO6437:1984 “Copper alloys Determination of chromium content Titrimetric method”, published by the International Organization for Standardization (ISO). T
9、erminology and 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. T
10、he 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 “International Standard” appear, referring to this standard, they should be read as “Part of BS6721”. In British Standards it is curre
11、nt practice to use the symbol “L” for litre (and in its submultiples) rather than “l” and to use the spelling “sulphur”, etc., instead of sulfur, etc. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their corre
12、ct 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, pages i and ii, pages1 and 2, an inside back cover and a back cover. This standard has been updated (see copyri
13、ght date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS6721-10:1989 BSI 12-1999 1 WARNING Throughout this International Standard, normal precautions regarding the use of perchloric acid in laboratory work shall be observed. 1 Sco
14、pe and field of application This International Standard specifies a titrimetric method for the determination of the total chromium content of copper-chromium alloys listed in International Standards. The method is applicable to products having chromium contents between0,10 and2,0% (m/m). 2 Principle
15、 Dissolution of a test portion followed by oxidation of the bulk of chromium by perchloric acid in the presence of orthophosphoric acid to avoid loss of chromium. Oxidation of residual chromium(III) by potassium permanganate. Reduction of chromium(VI) by iron(II) solution, and determination of the e
16、quivalence point either using an indicator or by measuring the change in potential as a function of the volume of titrant used. 3 Reagents During the analysis, use only reagents of recognized analytical grade, and only distilled water or water of equivalent purity. 3.1 Hydrochloric acid, 1,19 g/ml.
17、3.2 Nitric acid, 1,40 g/ml. 3.3 Hydrofluoric acid, 1,13 g/ml. 3.4 Perchloric acid, 1,61 g/ml. 3.5 Sulfuric acid, 1,83 g/ml. 3.6 Hydrochloric acid, solution,1+20. Dilute5,0ml of the hydrochloric acid (3.1) with100ml of water. 3.7 Orthophosphoric acid, solution,1+2. Dilute100ml of orthophosphoric acid
18、, 1,70 g/ml, with 200ml of water. 3.8 Potassium permanganate, 2,5g/l solution. Dissolve2,5g of potassium permanganate in water and dilute to1000 ml. 3.9 Diphenylamine, 2g/l in sulfuric acid. Dissolve0,2g of diphenylamine in100ml of sulfuric acid (3.5). 3.10 Potassium dichromate, standard solution co
19、rresponding to1,733g of Cr per litre. Weigh, to the nearest0,0001g, 4,9033g of potassium dichromate (K 2 Cr 2 O 7 ). Place in a beaker of suitable capacity and dissolve in reductant-free water. Transfer quantitatively to a1000ml one-mark volumetric flask, dilute to the mark with reductant-free water
20、 and mix. 1ml of this standard solution contains1,733mg ofCr. 3.11 Iron(II) ammonium sulfate, 46g/l solution in1mol/l sulfuric acid solution. 3.11.1 Preparation of the solution Dilute54ml of the sulfuric acid (3.5) to1litre with water. Dissolve46g of iron(II) ammonium sulfate hexahydrate Fe (NH 4 )
21、2 (SO 4 ) 2 6H 2 O) in a small amount of this solution, then dilute to1000 ml with the same sulfuric acid solution. 1ml of this solution is equivalent to approximately2mg ofCr. 3.11.2 Standardization of the solution 3.11.2.1 Volumetric standardization with an indicator Transfer20ml of the potassium
22、dichromate solution (3.10) to a400ml beaker. Add25ml of the orthophosphoric acid solution (3.7) and150ml of water. Add0,1ml of the diphenylamine solution(3.9) and titrate with the iron(II) ammonium sulfate solution (3.11) rapidly at first until the purple colour appears, then slowly until the colour
23、 disappears. The titre of the iron(II) ammonium sulfate solution, expressed as milligrams of chromium per millilitre of solution, is given by the formula where V 1 is the volume, in millilitres, of the potassium dichromate solution (3.10) used; V 2 is the volume, in millilitres, of the iron(II) ammo
24、nium sulfate solution (3.11.1) used in the titration. 3.11.2.2 Potentiometric standardization Transfer30ml of the potassium dichromate solution (3.10) to a600ml beaker containing15ml of the sulfuric acid (3.5), 25ml of the orthophosphoric acid solution (3.7), and about330ml of water. Titrate using t
25、he procedure specified in5.4.2. The titre of the iron(II) ammonium sulfate solution, expressed as milligrams of chromium per millilitre of solution, is given by the formula in3.11.2.1. Daily standardization of the iron(II) ammonium sulphate solution is required.BS6721-10:1989 2 BSI 12-1999 4 Apparat
26、us Ordinary laboratory apparatus, and 4.1 Beakers, capacity600ml, tall form. 4.2 Potentiometric titration apparatus 5 Procedure 5.1 Test portion Weigh, to the nearest0,001g, about2g of the test sample. 1) 5.2 Dissolution of test portion Transfer the test portion (5.1) to a600ml tall-form beaker (4.1
27、). Add20ml of the hydrochloric acid(3.1), 10ml of the nitric acid (3.2), and1ml of the hydrofluoric acid (3.3). When effervescence ceases, add10ml of the orthophosphoric acid solution (3.7) and30ml of the perchloric acid (3.4). Bring to the boil and evaporate until thick white perchloric fumes appea
28、r. Maintain until the test portion is totally dissolved. Reduce the heat and boil gently for5min. Cool. Add30ml of water and boil for5min. Cool. 5.3 Oxidation of residual chromium(III) Add 150ml of water to the solution (5.2), bring to the boil and add5ml of the potassium permanganate solution (3.8)
29、. Boil for3min., then add10ml of the hydrochloric acid solution (3.6) and boil for15min. Allow to cool. 5.4 Determination 5.4.1 Volumetric titration with indicator To the test solution (5.3), add25ml of the orthophosphoric acid solution (3.7) and0,1ml of the diphenylamine solution (3.9). Titrate rap
30、idly with the iron(II) ammonium sulfate solution (3.11) until a dark ultra-marine blue colour appears, then slowly until the clear blue-green end-point is reached. 5.4.2 Potentiometric titration Transfer the test solution (5.3) to a600ml tall-form beaker (4.1). Add20ml of the sulfuric acid (3.5) and
31、25ml of the orthophosphoric acid solution (3.7). Dilute to about400ml with water. Allow to cool, if necessary. Place the electrodes in the solution, and, while stirring, titrate with the iron(II) ammonium sulfate solution (3.11) until the potentiometric change occurs. Titrate slowly near the end-poi
32、nt. Using a platinum-saturated calomel electrode, the change in potential is of the order of200mV, and lies between900 and700mV. 5.5 Check test Verify the validity of the application of the method using a standard material or a synthetic sample containing a known amount of chromium and of compositio
33、n similar to the material to be analysed, and carrying out the procedure as specified in5.1 to5.4. 6 Expression of results The chromium content, expressed as a percentage by mass, is given by the formula where V is the volume, in millilitres, of the iron(II) ammonium sulfate solution (3.11) used in
34、the determination (5.4); c Cr is the titre of the iron(II) solution (3.11), expressed as milligrams of chromium per millilitre of solution, calculated in3.11.2; m is the mass, in grams, of the test portion. 7 Test report The test report shall include the following particulars: a) an identification o
35、f the sample; b) the reference of the method used; c) the results and the method of expression used; d) any unusual features noted during the determination; e) any operation not included in this International Standard or regarded as optional. 1) An International Standard dealing with the sampling of
36、 copper alloys is in preparation. Vc Cr 10 m -blankBS 6721-10: 1989 ISO 6437:1984 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body responsible for preparing BritishStandards. It presents the UK view on standards in Europe and at the interna
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