1、BRITISH STANDARD BS4993-3: 1974 Incorporating Amendment No.1 Methods of test for Aluminium fluoride for industrial use Part3: Determination of silica content UDC661.862.361:546.623161:543.42:546.28431BS4993-3:1974 This British Standard, having been approved by the ChemicalsIndustry StandardsCommitte
2、e, waspublished under the authorityof the Executive Boardon 28 February1974 BSI10-1999 The following BSI references relate to the work on this standard: Committee reference CIC/24 Drafts for comment/approval71/53613 and73/50651 ISBN 0 580 07999 6 Co-operating organizations The Chemicals Industry Sta
3、ndards Committee, under whose supervision this British Standard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations: British Steel Industry Chemical Industries Association* Department of Health and Social Security Department
4、 of Trade and Industry Fertilizer Manufacturers Association Limited Ministry of Agriculture, Fisheries and Food National Sulphuric Acid Association Royal Institute of Public Health and Hygiene Soap and Detergent Industry Association Amendments issued since publication Amd. No. Date of issue Comments
5、 2028 June1976 Indicated by a sideline in the marginBS4993-3:1974 BSI 10-1999 i Contents Page Co-operating organizations Inside front cover Foreword ii 1 Scope 1 2 Field of application 1 3 Principle 1 4 Reagents 1 5 Apparatus 2 6 Procedure 2 7 Calculation 4 Publications referred to Inside back cover
6、BS4993-3:1974 ii BSI 10-1999 Foreword This British Standard has been prepared under the authority of the Chemicals Industry Standards Committee in order to provide methods for the analysis of aluminium fluoride. For some years the UnitedKingdom has participated in the work of preparing methods of te
7、st applicable to aluminium fluoride for industrial use, organized by Sub-Committee7 “Alumina and related compounds” of Technical Committee47 “Chemistry” of the International Organization for Standardization (ISO). As international agreement is reached on the methods, it is proposed to publish them a
8、s parts of this British Standard. This part is based on the International Standard ISO2369, “Aluminium fluoride for industrial use Determination of silica content Spectrophotometric method using the reduced silicomolybdic complex”, modified to take into account the comments made by the UnitedKingdom
9、 during its development. This standard prescribes methods of test only, and should not be used or quoted as a Specification defining limits of purity. Reference to the standard should be in a form of words indicating that the methods of test used conform to BS4993. A British Standard does not purpor
10、t 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 document comprises a front cover, an inside front cov
11、er, 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.BS4993-3:1974 BSI 10-1999 1 1 Scope This Part of BS4993 specifies
12、 a spectrophotometric method for the determination of the silica content of aluminium fluoride for industrial use. NOTEThe titles of the British Standards referred to in this standard are listed on the inside back cover. 2 Field of application The method can be applied to the determination of the si
13、lica content of aluminium fluoride for industrial use, provided that the P 2 O 5content does not exceed0.02%. A method for the determination of silica when P 2 O 5contents greater than0.02% are present is in course of preparation. 3 Principle A test portion is fused under alkaline conditions with a
14、mixture of sodium carbonate and boric acid. The fused mass is dissolved in excess nitric acid so that the pH of the final solution is between0.3 and0.5. The (yellow) oxidized molybdophosphoric complex is formed, from a suitable aliquot portion, under clearly defined conditions of acidity, concentrat
15、ion of reagents, temperature and time. The complex is selectively reduced in a high acidity sulphuric acid medium and in the presence of tartaric acid. The reduced complex is measured spectrophotometrically at a wavelength of815nm. 4 Reagents The reagents used shall be of recognized analytical reage
16、nt quality. Redistilled water shall be used throughout. 4.1 Sodium carbonate, anhydrous. 4.2 Boric acid, (H 3 BO 3 ). 4.3 Nitric acid, approximately8Nsolution. Dilute540ml of nitric acid solution, 1.40g/ml,68%(m/m) approximately, with water to1000ml. 4.4 Sodium molybdate,195g/l(0.8M approximately) s
17、olution. Dissolve, in a plastics beaker (PTFE 1) , for example),19.5g of sodium molybdate dihydrate (Na 2MoO 4 .2H 2 O) in hot water and, after cooling, dilute to100ml. Transfer the solution to a plastics 2)bottle and, if necessary, filter before use. 4.5 Tartaric acid,100g/l solution. Dissolve10g o
18、f tartaric acid in water and dilute to100ml. 4.6 Sulphuric acid, approximately16N solution. Carefully add450ml of sulphuric acid, 1.84g/ml, approximately96%(m/m) solution, to about500ml of water. Cool and dilute to1000ml. 4.7 Reducing solution. Either of the following solutions may be used. 4.7.1 1-
19、Amino-2-naphthol-4-sulphonic acid,1.5g/l solution. a) Dissolve7g of anhydrous sodium sulphite in50ml of water. Add1.5g of 1-amino-2-naphthol-4-sulphonic acid. b) Dissolve90g of sodium metabisulphite (Na 2 S 2 O 5 ) in900ml of water. Mix the two solutions a) and b) and dilute to1000ml. Filter if nece
20、ssary. Store in an amber-coloured bottle, in a cool place. 4.7.2 Ascorbic acid,20g/l solution. Dissolve2g of ascorbic acid in water and dilute to100ml. Use a freshly prepared solution. 4.8 Standard silica solution, corresponding to a content of0.500g of silica (SiO 2 ) per litre. Into a platinum cru
21、cible, weigh to the nearest1mg, either 500mg of SiO 2obtained from pure silicic acid (H 2 SiO 3 ), heated to constant mass at1000 C and cooled in a desiccator, or 500mg of finely ground pure quartz, previously heated at1 000 C for1h and cooled in a desiccator. Add5g of the sodium carbonate(4.1) to t
22、he crucible. Mix thoroughly, preferably with a platinum spatula, and fuse carefully until a clear transparent melt is obtained. Cool. Add hot water to the crucible, heat gently to complete the dissolution and transfer the solution quantitatively into a PTFE beaker. Cool, dilute to about500ml and tra
23、nsfer quantitatively to a1000ml one-mark volumetric flask (BS1792), dilute to the mark and mix. Transfer immediately to a plastics 3)bottle. 1ml of this standard solution contains0.500mg of SiO 2 . 1) Polytetrafluorethylene. 2) For example PTFE, polypropylene or polyethylene may be used. 3) For exam
24、ple PTFE, polypropylene or polyethylene may be used.BS4993-3:1974 2 BSI 10-1999 4.9 Standard silica solution, corresponding to a content of0.020g of silica (SiO 2 ) per litre. Place40.0ml of the standard silica solution(4.8) in a1000ml one-mark volumetric flask (BS1792), dilute to the mark and mix.
25、1ml of this standard solution contains204g of SiO 2 . Prepare this solution just before use. 4.10 Standard silica solution, corresponding to a content of0.005g of silica (SiO 2 ) per litre. Place50.0ml of the standard silica solution(4.9) in a200ml one-mark volumetric flask (BS1792), dilute to the m
26、ark and mix. 1ml of this standard solution contains54g of SiO 2 . Prepare this solution just before use. 5 Apparatus Ordinary laboratory apparatus and the following are required. 5.1 Platinum dish, flat-bottomed, diameter approximately70mm, height approximately35mm, fitted with a platinum lid. 5.2 E
27、lectric furnace, capable of being controlled at550 25 C. 5.3 Electric furnace, capable of being controlled at750 25 C. 5.4 pH meter, provided with a glass electrode. Essential requirements are given in BS2586, and in BS3145 or BS3422. 5.5 Spectrophotometer NOTEGlassware should be carefully washed wi
28、th chromic-sulphuric acid mixture, thoroughly rinsed with water and finally with redistilled water. Do not dry. Avoid the use of glass vessels for alkaline solutions. 6 Procedure 6.1 Test portion Weigh, to the nearest0.001g, exactly1g of the dried test sample. 4) 6.2 Preparation of the calibration c
29、urve 6.2.1 Preparation of the base solution. Weigh24 g of the sodium carbonate(4.1) and8g of the boric acid(4.2) into the platinum dish(5.1). Mix thoroughly, preferably with a platinum spatula. Cover the dish with its lid and place it in the electric furnace(5.2), controlled at550 25 C, taking care
30、to isolate the dish from the floor of the furnace, using a support which avoids the risk of contamination (platinum support for preference). Maintain at550 25 C until the reaction subsides. Transfer the dish to the electric furnace(5.3), controlled at750 25 C, isolating it, as before, from the furna
31、ce floor, and allow to remain for a maximum of5min. Remove the dish from the furnace and allow to cool in the atmosphere. Add boiling water to the dish and heat gently until the contents are completely dissolved. After cooling slightly, transfer the contents of the dish to a plastics beaker (PTFE fo
32、r example) of suitable capacity, containing40 ml of the nitric acid(4.3). Carefully wash the dish and lid with36 ml of the nitric acid, and then with hot water, collecting the washings in the beaker. Heat gently for a few minutes at a temperature near to the boiling point. Allow to cool slightly and
33、 transfer to a200ml one-mark volumetric flask (BS1792). After cooling dilute to the mark and mix. 6.2.2 Preliminary test for the control and adjustment of pH. Transfer20.0 ml of the base solution(6.2.1) to a beaker of suitable capacity. Add to the beaker15ml of water,15ml of the standard silica solu
34、tion(4.10),5ml of the sodium molybdate solution(4.4), mix and check the pH value with the pH meter(5.4). This value should be between0.85 and0.90 but, if not, adjust the pH by slowly adding, drop by drop, the nitric acid solution(4.3) by means of a graduated pipette or burette, mixing after each dro
35、p. Dilute, if necessary, so that the final volume of the solution, after the introduction of the nitric acid solution, is65ml and check again the pH value (between0.85 and0.90). Note the volume of the nitric acid(4.3) used to correct the pH and discard the solution. 6.2.3 Preparation of the standard
36、 matching solutions for spectrophotometric measurements using a1cm cell. Into each of a series of six100ml one-mark volumetric flasks, place20ml of the base solution(6.2.1) and then add the quantity of the nitric acid(4.3) used to correct the pH in the preliminary test(6.2.2). 4) Methods for the pre
37、paration and storage of test samples of aluminium fluoride are in course of preparation and will be published as a part of this standard.BS4993-3:1974 BSI 10-1999 3 Add to each flask the volumes of the standard silica solution(4.10) shown in the following table. Dilute the solutions to approximately
38、60ml. 6.2.4 Colour development. To each flask add5ml of the sodium molybdate solution(4.4), mix and allow to stand for between15 min and25min at20 C to25 C. Then add5ml of the tartaric acid solution(4.5),11ml of the sulphuric acid(4.6) and finally2ml of the reducing solution(4.7.1 or4.7.2). Dilute t
39、o the mark and mix. 6.2.5 Spectrophotometric measurements. After10min, but not longer than40min, carry out the spectrophotometric measurements by means of the spectrophotometer(5.5) at a wavelength of about815nm, after having adjusted the instrument to zero absorbance against the compensation soluti
40、on. 6.2.6 Preparation of the calibration chart. Prepare a calibration chart having, for example, the silica contents, in milligrams of SiO 2per100ml of standard matching solutions, as abscissae and the corresponding values of absorbance as ordinates. 6.3 Determination 6.3.1 Preparation of the test s
41、olution 6.3.1.1 Fusion of the test portion. Weigh12g of the sodium carbonate(4.1) and4g of the boric acid(4.2) into the platinum dish(5.1). Mix carefully. Add the test portion(6.1) and mix the whole quantity thoroughly, preferably with a platinum spatula. Cover the dish with its lid and place it in
42、the electric furnace(5.2), controlled at550 25 C, taking care to isolate the dish from the furnace floor, using a support which avoids the risk of contamination (platinum support for preference). Maintain at550 25 C until the reaction subsides (the time required being approximately30min). Transfer t
43、he dish to the electric furnace(5.3), controlled at750 25 C, isolating it, as before, from the furnace floor. The dish should stay in this furnace for30min and the operator shall ensure that the temperature of750 25 C is maintained for at least20min. 6.3.1.2 Dissolving the fused mass. Remove the dis
44、h from the furnace and allow to cool in the atmosphere. Add boiling water to the dish, heating moderately until the contents are completely dissolved. After cooling slightly, transfer the contents of the dish to a plastics beaker (PTFE, for example), of a suitable capacity, containing20ml of the nit
45、ric acid(4.3). Dissolve the residue mainly iron (III) oxide still adhering to the walls of the dish in18ml of the nitric acid(4.3) and carefully wash the dish and lid with hot water, transferring the whole mixture to the plastics beaker. Heat for a few minutes at a temperature near to the boiling po
46、int until completely dissolved. Allow to cool slightly. When the solution is tepid, transfer it to a250ml one-mark volumetric flask (BS1792). Cool, dilute to the mark and mix. Transfer the solution immediately to a plastics 5)container. 6.3.2 Colour reaction 6.3.2.1 Taking of aliquot portions. Take
47、two50.0ml aliquot portions of the test solution(6.3.1) and place one in a beaker of suitable capacity and the other in a100ml one-mark volumetric flask (BS1792). 6.3.2.2 Preliminary test for the control and adjustment of pH. Add5ml of the sodium molybdate solution(4.4) to the aliquot portion of the
48、test solution in the beaker, and mix. Check the pH value using the pH meter(5.4), adjust to a value of between0.85 and0.90 as indicated in6.2.2, noting the volume of the nitric acid(4.3) used, and discard this solution. 6.3.2.3 Colour development. To the aliquot portion of the test solution in the10
49、0ml one-mark volumetric flask, add the quantity of the nitric acid(4.3) used to correct the pH in the preliminary test(6.3.2.2) and mix. Then proceed with the colour development as indicated in6.2.4. 6.3.2.4 Spectrophotometric measurement. Carry out the spectrophotometric measurement by the procedure described in6.2.5, after having adjusted the instrument to zero absorbance against water. Volume of standard silica solution(4.10) Corresponding mass of SiO 2 ml 0 a 5.0 10.0 15.0 20.0 25.0 4g 0 25 50 75 100 125 a Compensation solution 5) For exampl
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