1、BRITISH STANDARD CONFIRMED AUGUST 1999 BS 1728-12: 1961 Incorporating Amendement No. 1 Method for the determination of Silicon in aluminium Part 2: Magnesium; Part 3: Zinc (mercuric potassium thiocyanate method); Part 4: Zinc (polarographic method); Part 5: Copper (absorptiometric method); Part 6: I
2、ron (volumetric: titanous chloride method); Part 7: Zinc (zinc oxide method); Part 8: Iron (absorptiometric 1:10-phenanthroline method); Part 9: Manganese (volumetric:arsenite/nitrite method); Part 10: Manganese (absorptiometric method); Part 11: Silicon (perchloric acid method). The preparation of
3、this series of methods has been authorized by the Non-ferrous Metals Industry Standards Committee as part of a general programme for the standardization of methods for the sampling and analysis of non-ferrous metals. These methods have been found to give reliable and reproducible results and, while
4、in some instances they may appear to be lengthy, it should be realized that they are put forward as “referee” methods to be used in cases of dispute. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correc
5、t 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 to 3 and a back cover. This standard has been updated (see copyright date) and may have h
6、ad amendments incorporated. This will be indicated in the amendment table on the inside front cover. 1) This description follows closely the method of L. Girolami, Aluminium Laboratories Ltd., Arvida, Canada, to whom the Institution wishes to acknowledge help received in compiling this standard meth
7、od.BS1728-12:1961 BSI 04-2000 1 Introduction a) Principle. Solution of the alloy is effected by sodium hydroxide solution followed by a nitric-hydrochloric acid mixture. Silicic acid is converted to yellow silicomolybdic acid; this isreduced to molybdenum blue by 1-amino-2-naphthol-4-sulphonic acid
8、at controlled pH, and the light absorption of the blue solution is measured photometrically. b) Range. The method is recommended for silicon contents between0.02 and0.3 per cent. For alloys containing bismuth, see Note1. c) Reproducibility. Experiments have been carried out independently by a number
9、 of analysts using the method recommended in this standard. The degree of reproducibility that can be expected is shown by the following results obtained. Seventy-seven results on samples with silicon contents ranging from0.024 to0.38 per cent gave a standard deviation of0.0044. Apparatus a) Wheneve
10、r possible, the use of glassware shall be avoided when dealing with alkaline solutions 2) . Where graduated glassware must be used it shall conform to Class A accuracy as defined in the appropriate British Standards. b) Special care must be taken to ensure that all apparatus is scrupulously clean. P
11、latinum vessels shall be cleaned by a preliminary fusion with sodium carbonate, followed by cleaning with hydrochloric acid. After rinsing in distilled water, the above treatments shall be repeated. Nickel vessels shall be cleaned first with hydrochloric acid then with nitric acid, finally with chro
12、mic acid cleaning solution, then rinsed with distilled water. All glassware shall be treated with chromic acid cleaning solution, then rinsed with distilled water. c) A spectrophotometer for measuring the optical density of the solution at a wavelength as near as possible to810m4. d) 4cm, 2cm or 1cm
13、 cells (Note 2), or, e) If a filter photometer is used, the filter combination should conform as closely as possible to the above wavelength. Using such an instrument, the following have been found suitable: Spekker absorptiometer. Ilford 608 spectrum filter. Tungsten lamp. Solutions required All re
14、agents shall be of analytical reagent quality and distilled water shall be used throughout. It may be necessary to use double distilled water in order to obtain consistently low blank values. Standard silicon stock solution (1 mlN 0.1mg of silicon). Calcine pure silica at1000 C for1hour and cool. Tr
15、ansfer0.2140g to a platinum vessel and add1.2g of sodium carbonate/potassium carbonate mixture (1+1). Fuse until a clear melt is obtained, cool, dissolve the melt in water, transfer to a polythene beaker, dilute and transfer to a1 litre graduated flask. Dilute to the mark and transfer the solution t
16、o a polythene 3)bottle. Standard silicon solution (1mlN 0.01mg of silicon). Transfer50.0ml of standard silicon stock solution (1mlN 0.1mg of silicon) to a500ml graduated flask and dilute to the mark. This solution should be prepared immediately before use. Nitric acid (8N). Dilute500ml of nitric aci
17、d (sp.gr.1.42) to1 litre. Standardize against10.600g of sodium carbonate (dried at150 C), using methyl red as indicator. The theoretical titration is25.0ml. If necessary adjust the strength of the solution to 8N ( 0.1), by adding water or nitric acid. Sodium hydroxide (8N). Dissolve160g of sodium hy
18、droxide in300ml of water, contained in a vessel, which is not attacked by sodium hydroxide, e.g.a stainless steel beaker. Cool, and transfer to a polythene bottle provided with a500ml graduation mark. Dilute to about500ml, mix and cool. Standardize this solution against the nitric acid(8N), using me
19、thyl red as indicator, and adjust the strength of the sodium hydroxide solution so that a10.0ml aliquot is equivalent to10.0 0.1ml of the nitric acid (8N). Hydrochloric acid (4N). Dilute400 or333ml respectively of hydrochloric acid (sp.gr.1.16 or1.18) to1 litre. Standardize against the sodium hydrox
20、ide solution (8N) using methyl red as indicator and if necessary adjust the strength of the acid so that20.0ml are equivalent to10.0 0.1ml of the sodium hydroxide solution (8N). 2) The use of a plastic burette or pipette is recommended. If glass pipettes are used, they shall be rinsed immediately af
21、ter use with dilute hydrochloric acid, then with distilled water. 3) It should be noted that the name “polythene” is equivalent to the name “polyethylene”.BS1728-12:1961 2 BSI 04-2000 Aluminium solution (0.2per cent w/v). Weigh1.00g of high purity (at least99.99 per cent) aluminium and transfer to a
22、100ml platinum or nickel vessel. Add40.0ml of sodium hydroxide solution (8N), cover and heat gently to complete solution of the metal. Cool and transfer to a400ml resistance-glass beaker containing68.0ml of nitric acid (8N) and16.0ml of hydrochloric acid (4N). Rinse the vessel and lid with hot water
23、. Mix well and warm until the solution becomes clear, then boil for1015 seconds. Cool, transfer to a500ml graduated flask and dilute to the mark. Ammonium molybdate (10 per cent w/v). Dissolve100g of ammonium molybdate (NH 4 ) 6 (Mo 7 O 24 .4H 2 O) in800ml of hot water, cool and dilute to1 litre. Tr
24、ansfer to a polythene bottle for storage. Filter immediately before use through a double fine textured filter paper 4) . Hydrogen peroxide (3per cent w/v). Dilute100ml of hydrogen peroxide (100vol) to1 litre. Reducing, solution. Dissolve7g of sodium sulphite (or the equivalent of the hydrated salt)
25、in about100ml of water, then add1.5g of1-amino-2-naphthol-4-sulphonic acid and allow to dissolve. Add this to a solution of90g of sodium metabisulphite in about800ml of water. Dilute the mixture to1 litre, mix, filter, and store in an amber-coloured bottle. Replace solution when discoloured. Sodium
26、nitrite solution (2per cent w/v). Dissolve2g of sodium nitrite in water and dilute to100ml. Sampling Recommended methods for obtaining a suitable sample for the analytical procedure given below are described in BS1499, “Sampling non-ferrous metals”. Procedure Transfer0.25g of the sample to a100ml pl
27、atinum or nickel vessel provided with a lid (Note3). Carry out simultaneously a blank determination on the reagents following the same procedure without the sample using the same quantities of reagents, except where specified. It is recommended to carry out duplicate blanks where the silicon content
28、 of the sample is low. Add10.0ml of sodium hydroxide solution (8N), cover the vessel and allow to stand until the reactionsubsides, then add3ml of hydrogen peroxide (3per cent). Move the lid slightly, to allow vapour to escape, then evaporate cautiously until the solution is of a syrupy consistency.
29、 Cool, add30ml of water and swirl gently to mix the contents. Boil gently until any solids adhering to the bottom of the vessel have become detached, remove from the source of heat, dilute to70ml, then warm for5 minutes. Cool and transfer the solution with thorough mixing to a250ml resistance-glass
30、beaker containing4.0ml of hydrochloric acid (4N) and17.0ml of nitric acid (8N), taking care that the alkaline solution does not come into direct contact with the glass of the beaker. Add the same volume of hydrochloric acid (4N) to the blank solution, but only13.5ml of nitric acid (8N). Rinse the me
31、tal vessel and the lid with hot water and mix the contents of the beaker thoroughly. Return a few ml of the acid solution to the metal vessel and add a few drops of sodium nitrite solution, just sufficient to dissolve any manganese hydroxide stains. Return the solution to the beaker and rinse the me
32、tal vessel again with hot water. Heat the solution almost to boiling and add a few drops of sodium nitrite solution, just sufficient to dissolve any manganese hydroxide, then boil gently for1015 seconds. Transfer the clear solution (Note4) to a250ml graduated flask. Cool and dilute to the mark. Tran
33、sfer a50.0ml aliquot to a100ml graduated flask, dilute to about80ml and mix. Adjust the temperature to20 1 C, add5.0ml of ammonium molybdate solution (10per cent), mix and allow to stand for5 minutes. Add7.5ml of nitric acid (8N), mix and add immediately5ml of reducing solution. Mix again, dilute to
34、 the mark, mix and allow to stand for10 minutes. Measure the optical density of the solution at20 1 C, using the conditions specified under “Apparatus” (Note2). Correct for the blank value or use the blank solution in the reference cell and calculate the silicon content of the alloy from the calibra
35、tion graph. 4) Whatman No.42 is suitable. The keeping qualities of this solution may be improved by the addition of2ml of ammonia solution (sp.gr.0.88) per litre. If the solution forms an appreciable quantity of white deposit it should be renewed.BS1728-12:1961 BSI 04-2000 3 Calibration To each of a
36、 series of100ml graduated flasks add25.0ml of aluminium solution (0.2per cent). In sequence, add0,1.0,2.0,3.0,4.0 and5.0ml of the standard silicon solution (1mlN 0.01mg of silicon) for the range00.06 per cent Si or0,5.0,10.0,15.0 and20.0ml for the range00.3 per cent Si. Dilute to about80ml and mix.
37、Adjust the temperature to20 1 C add5.0ml of ammonium molybdate solution (10 per cent), mix and stand for5 minutes. Continue then as described under “Procedure”. Measure the optical density of the solutions under the same conditions as for the samples, deduct the reading obtained on the solution cont
38、aining no added silicon (or place this solution in the reference cell) and prepare a calibration graph. NOTE 1The presence of bismuth alone, or in combination with lead and copper, may introduce a small error in this determination, e.g.0.5per cent of bismuth alone introduces a negative error equival
39、ent to about0.005 per cent at the0.2 per cent silicon level. For most practical purposes this interference can be ignored. NOTE 2It is desirable that the optical density of the sample solution should be within the range0.15 to0.85, although this range may be extended slightly in the preparation of t
40、he calibration graphs. NOTE 3Platinum vessels are recommended when silicon below0.1 per cent is to be determined. NOTE 4A turbidity at this stage may be due to the presence of titanium, or contamination from the vessel if nickel was used. In this case, filter the warm solution into the250ml graduated flask through a fine-textured paper 5) . Wash the paper with hot water. 5) Whatman No.42 is suitable.
