ISO 1232-1976 Aluminium oxide primarily used for the production of aluminium Determination of silica content Reduced molybdosilicate spectrophotometric method《主.pdf

1、INTERNATIONAL STANDARD INTERNATIONAL ORGANIZATION FOR STANDARDIZATION +EXUWHAPOHAR OPrAHM3AUMII n0 CTAHLIAPTA3ALWiH.ORGANISATION INTERNATIONALE DE NORMAUSATION Aluminium oxide primarily used for the production of aluminium - Determination of silica content - Reduced molybdosilicate spectrophotometri

2、c method Oxyde daluminium principalemen t utilise pour la production de Ialuminium - Dosage de la silice - Methode spectrophotometrique au molybdosilicate rtiduit First edition - 1976-09-15 31. i b ;, : ;, p; )” ,“?, j”t,lj : I 1 1. 1 j,pr”j(J, ,;, .y,ti” t qyr.;, i , UDC 661.862.22 : 546.284 : 543.

3、42 Ref. No. IS0 1232-1976 (E) I Descriptors : aluminium oxide, chemical analysis, determination of content, silicon dioxide, spectrophotometric analysis. , Price based on 5 pages Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduct

4、ion or networking permitted without license from IHS-,-,-FOREWORD IS0 (the International Organization for Standardization) is a worldwide federation of national standards institutes (IS0 Member Bodies). The work of developing International Standards is carried out through IS0 Technical Committees. E

5、very Member Body interested in a subject for which a Technical Committee has been set up has the right to be represented on that Committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. Draft International Standards adopted by the Te

6、chnical Committees are circulated to the Member Bodies for approval before their acceptance as International Standards by the IS0 Council. Prior to 1972, the results of the work of the Technical Committees were published as IS0 Recommendations; these documents are now in the process of being transfo

7、rmed into international Standards. As part of this process, Technical Committee ISO/TC 47 has reviewed IS0 Recommendation R 1232 and fount it technically suitable for transformation. International Standard IS0 1232 therefore replaces IS0 Recommendation R 1232-1970 to which it is technically identica

8、l. IS0 Recommendation R 1232 was approved by the Member Bodies of the following countries : Austria Belgium Canada Chile Czechoslovakia Egypt, Arab Rep. of France Germany Greece Hungary India Iran Israel Italy Netherlands Portugal Romania South Africa, Rep. of Spain Sweden Switzerland Turkey United

9、Kingdom U.S.S.R. No Member Body expressed disapproval of the Recommendation. No Member Body disapproved the transformation of ISO/R 1232 into an International Standard. 0 International Organization for Standardization, 1976 l Printed in Switzerland Copyright International Organization for Standardiz

10、ation Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS-,-,-INTERNATIONAL STANDARD IS0 1232-1976 (E) Aluminium oxide primarily used for the production of aluminium - Determination of silica content - Reduced molybdosilicate spectroph

11、otometric method 1 SCOPE AND FIELD OF APPLICATION This International Standard specifies a reduced molybdo- silicate spectrophotometric method for the determination of the silica content of aluminium oxide primarily used for the production of aluminium. The method is applicable to products having an

12、SiO, content between 0,005 and 0,025 % (m/m), provided that the content of (P,OB i- V205) does not exceed 0.02 % (m/m). 1 .I Special cases 1.1.1 SiO, content between 0,025 and 0,25 % (m/m) (P,O, -I- V205) content not exceeding 0,02 % (m/m). 1.1.2 (P205 i- V205) content exceeding 0,02 % (m/m) (under

13、study). 2 REFERENCES IS0 802, Aluminium oxide primarily used for the production of aluminium - Preparation and storage of test samples. IS0 804, Aluminium oxide primarily used for the production of aluminium - Preparation of solution for analysis - Method by alkaline fusion. IS0 2927, Aluminium oxid

14、e primarily used for the production of aluminium - Sampling. 3 PRINCIPLE Formation of the oxidized molybdosilicate (yellow) under well-defined conditions of acidity, concentration of reagents, temperature and time. Selective reduction of the complex in a highly acidic medium of sulphuric acid and in

15、 the presence of tartaric acid. Spectrophotometric measurement of the reduced coloured complex at a wavelength of about 815 nm. 4 REAGENTS During the analysis, use only reagents of analytical grade and only redistilled water. 4.1 Sodium carbonate, anhydrous. 4.2 Boric acid (HaBOa). 4.3 Nitric acid,

16、approximately 8 N solution. Dilute 540 ml of nitric acid solution, p approximately I,40 g/ml, about 68 % (m/m), with water to 1 000 ml. 4.4 Sodium molybdate, 195 g/l solution (approximately 0,8 N). Dissolve in a polytetrafluorethylene (PTFE) beaker 19,5 g of sodium molybdate dihydrate (Na,Mo04.2H,0)

17、 in hot water and, after cooling, dilute to 100 ml. Transfer the solution to a bottle made of silica-free material and, if necessary, filter before use. 4.5 Tartaric acid, 100 g/l solution. 4.6 Sulphuric acid, approximately 16 N solution. Add carefully 450 ml of sulphuric acid, p approximately I,84

18、g/ml, about 96 % (m/m), to about 500 ml of water. Cool, dilute to 1 000 ml and mix. 4.7 Reducing solution. Use one of the following two solutions : 4.7.1 4-Amino-3-hydroxy-I-naphthalene sulphonic acid, I,5 g/l solution. a) Dissolve 7 g of anhydrous sodium sulphite (Na$Od in 50 ml of water. Add I,5 g

19、 of 4-amino-3-hydroxy- I-naphthalene sulphonic acid (C,oHeN04S). b) Dissolve 90 g of anhydrous sodium metabisulphite (Na2S205) in 900 ml of water. Mix the two solutions a) and b), dilute to 1 000 ml and mix. Filter if necessary. Store in a cool place in an amber-coloured bottle made of silica-free m

20、aterial. 4.7.2 Ascorbic acid, 20 g/l solution. Prepare this solution just before use. Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS-,-,-ISO1232-1976 (E) 4.8 Silica, standar

21、d solution corresponding to 0,500 g of SiO, per iitre. 5.5 Spectrophotometer. Into a platinum crucible of suitable capacity, weigh, to the nearest 0,001 g, either - 0,500 g of SiO, obtained from pure silicic acid (H,Si03), ignited at 1 000 “C to constant mass, i.e. until the results of two consecuti

22、ve weighings do not differ by more than 0,001 g, after cooling each time in a desiccator, or NOTE - Glassware shall be carefully washed with hot chromic- sulphuric acid, taking all necessary precautions, thoroughly rinsed with water and finally with redistilled water. It should not be dried. Avoid t

23、he use of glass vessels for alkaline solutions. 6 PROCEDURE - 0,500 g of finely ground pure quartz, previously ignited at 1 000 OC for 1 h and cooled in a desiccator. 6.1 Preparation of the principal solution P Follow the procedure specified in 6.1, 6.2 and 6.3 of IS0 804. Add to the crucible 5 g of

24、 the sodium carbonate (4.1). Mix thoroughly, preferably with a platinum spatula, and fuse carefully. Add hot water to the crucible, heat gently to complete the dissolution and transfer the solution quantitatively into a beaker made of silica-free material. Cool, dilute to about 500 ml, transfer quan

25、titatively to a 1 000 ml one-mark volumetric flask, dilute to the mark and mix. Prepare this principal solution immediately before use. 6.2 Aliquot portion of principal solution (test portion) Transfer the solution immediately to a bottle made of silica-free material. Take two aliquot portions of th

26、e principal solution P (6.1) according to the directions given in table 1; transfer one aliquot portion to a beaker of suitable capacity and the other to a 100 ml one-mark volumetric flask, and add the volume of water stated. 1 ml of this standard solution contains 0,500 mg of SiO,. Principal 4.9 Si

27、lica, standard solution corresponding to 0,020 g of SiO, per litre. Transfer 40,O ml of the standard silica solution (4.8)to a 1 000 ml one-mark volumetric flask, dilute to the mark and mix. 1 ml of this standard solution contains 0,020 mg of SiO,. Prepare this solution just before use. 4.10 Silica,

28、 standard solution corresponding to 0,005 g of SiO, per litre. Transfer 50,O ml of the standard silica solution (4.9) to a 200 ml one-mark volumetric flask, dilute to the mark and mix. 1 ml of this standard solution contains 0,005 mg of SiO,. Prepare this solution just before use. 5 APPARATUS Ordina

29、ry laboratory apparatus and 5.1 Platinum dish, flat bottomed, of diameter approxi- mately 70 mm, and height approximately 35 mm, fitted with a platinum lid. 5.2 Electric furnace, capable of being controlled at 500 f 50 “c. 5.3 Electric furnace, capable of being controlled between 1 000 and 1 025 “C.

30、 5.4 pH meter. TABLE 1 Aliquot portion t0 be taken Water to be added 6.3 Preparation of the calibration graph 6.3.1 Preparation of the base solution Weigh into the platinum dish (5.1) 12 g of the sodium carbonate (4.1) and 4 g of the boric acid (4.2), and mix carefully, preferably with a platinum sp

31、atula. Cover the dish with its lid and place it in the electric furnace (5.2), controlled at 500 k 50 C, taking care to isolate the dish from the floor of the furnace. Maintain at 500 + 50 “C until the reaction subsides. NOTE - Avoid contact of the platinum vessel with refractory materials. To isola

32、te it from the floor of the furnace, use, for example, platinum supports. Transfer the dish to the electric furnace (5.31, controlled between 1 000 and 1 025 C, taking care to isolate it, as before, from the floor of the furnace. The time at this temperature shall not exceed 5 min. Remove the dish f

33、rom the furnace and allow it to cool in air. Add boiling water to the dish and heat gently to complete dissolution. After cooling slightly, transfer the contents of the dish to a PTFE beaker of suitable capacity, containing 35 ml of the nitric acid solution (4.3). Wash the dish and its lid carefully

34、 with hot water, add the washings to the PTFE beaker and 2 Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS-,-,-IS0 1232-1976(E) stir. Carefully wash the contents of the PTFE

35、beaker into a glass beaker. Simmer gently for a few minutes. Cool slightly and transfer the solution quantitatively to a 250 ml one- mark volumetric flask. After cooling, dilute to the mark and mix. 6.3.2 Preliminary test for the control and adjustment ofpH Transfer 25,0 ml of the base solution (6.3

36、.1) to a beaker of suitable capacity. Add to the beaker 10 ml of water, 15 ml of the standard silica solution (4.10), and 5 ml of the sodium molybdate solution (4.4); mix and check the pH value with the pH meter (5.4). This value should lie between 0,85 and 0,90. If it does not, adjust the pH by the

37、 slow addition, drop by drop, of the required volume of the nitric acid solution (4.3) from a graduated pipette or burette, mixing after each addition. Dilute, if necessary, so that the volume of the solution, after the addition of the nitric acid solution, is 65 ml and check the pH value again (bet

38、ween 0,85 and 0,90). Note the volume of the nitric acid solution (4.3) used for the pH adjustment and discard the solution. 6.3.3 Preparation of the standard calorimetric solutions for spectrophotometric measurement using a cell having an optical path length of 1 cm. Into each of a series of six 100

39、 ml one-mark volumetric flasks, transfer 25 ml of the base solution (6.3.1) and then add the volume of nitric acid solution (4.3) used for the adjustment of the pH in the preliminary test (6.3.2). Transfer respectively to the flasks the volumes of the standard silica solution (4.10) shown in table 2

40、. TABLE 2 Standard silica solution (4.10) Corresponding mass of SiOp ml f-w 0” 0 5,O 0,025 10.0 0,050 15.0 0.075 20,o 0,100 25,0 0,125 * Compensation solution. Dilute the solutions to about 60 ml. 6.3.4 Colour development Add to each flask 5 ml of the sodium molybdate solution (4.4), mix and leave t

41、o stand for 15 to 25 min maximum at 20 to 25 “C. Then add 5 ml of the tartaric solution (4.5), 11 ml of the sulphuric acid solution (4.6) and finally 2 ml of the reducing solution (4.7.1 or 4.7.2). Mix, dilute to the mark and mix again. 6.3.5 Spectrophotometric measurements After 10 min but not long

42、er than 40 min, make the spectro- photometric measurements by means of the spectrophoto- meter (5.5) at a wavelength of about 815 nm, after having adjusted the instrument to zero absorbance against the compensation solution. NOTE - Calibrate accurately the cells used for the measurements. 6.3.6 Plot

43、ting of the calibration graph Plot a graph having, for example, as abscissae the values, expressed in milligrams, of the masses of SiOz per 100 ml of standard calorimetric solution and, as ordinates, the corresponding values of absorbance. 6.4 Determination 6.4.1 Preliminary test for the control and

44、 adjustment ofpH To the aliquot portion of the principal solution contained in the beaker (see.6.2), add 5 ml of the sodium molybdate solution (4.4) and mix. Check the pH value using the pH meter (5.4), adjust it to a value between 0,85 and 0,90 as indicated in 6.3.2 and discard this solution. 6.4.2

45、 Colour development To the aliquot portion of the principal solution contained in the 100 ml one-mark volumetric flask (see 6.2). add the volume of the nitric acid solution (4.3) used for the adjustment of the pH in the preliminary test (6.4.1). dilute the solution to about 60 ml and mix. Proceed as

46、 specified in 6.3.4 for the colour development. 6.4.3 Spectrophotometric measurement Carry out spectrophotometric measurement following the procedure specified in 6.3.5, after having adjusted the instrument to zero absorbance against water. 6.5 Blank test 6.5.1 Preparation of the solution Prepare th

47、e blank test solution without addition of extra- pure aluminium oxide, following the procedure specified in 6.4.2 of IS0 804. 6.5.2 Colour development Carry out the development of the colour as specified in 6.4.2. 6.5.3 Spectrophotometric measurement Carry out the spectrophotometric measurement as s

48、pecified in 6.4.3. Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS-,-,-IS0 1232-1976 (El 7 EXPRESSION OF RESULTS By means of the calibration graph (see 6.3.6), determine the

49、silica contents corresponding to the values of the spectrophotometric measurements of the aliquot portion of the principal solution and of the blank test solution. The silica (SiOp) content, expressed as a percentage by mass, is given by the formula (mo -ml) xD x100= m0 -ml 1000x5 5 where m. is the mass, in milligrams, of silica (Si02) found in the aliquot portion of the principal solution P used for the determination; m, is the mass, in milligrams, of silica (SiO,) found in