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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 d aluminium principalemen t utilise pour la production de I aluminium - Dosage de la silice - Me thode spectrophotome trique 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
3、 : 543.42 Ref. No. IS0 1232-1976 (E) I Descriptors : aluminium oxide, chemical analysis, determination of content, silicon dioxide, spectrophotometric analysis. , Price based on 5 pages FOREWORD IS0 (the International Organization for Standardization) is a worldwide federation of national standards
4、institutes (IS0 Member Bodies). The work of developing International Standards is carried out through IS0 Technical Committees. Every 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, go
5、vernmental and non-governmental, in liaison with ISO, also take part in the work. Draft International Standards adopted by the Technical 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 th
6、e work of the Technical Committees were published as IS0 Recommendations; these documents are now in the process of being transformed 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 tran
7、sformation. International Standard IS0 1232 therefore replaces IS0 Recommendation R 1232-1970 to which it is technically identical. 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
8、Greece Hungary India Iran Israel Italy Netherlands Portugal Romania South Africa, Rep. of Spain Sweden Switzerland Turkey United 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
9、International Organization for Standardization, 1976 l Printed in Switzerland -,-,- INTERNATIONAL STANDARD IS0 1232-1976 (E) Aluminium oxide primarily used for the production of aluminium - Determination of silica content - Reduced molybdosilicate spectrophotometric method 1 SCOPE AND FIELD OF APPLI
10、CATION 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 SiO, content between 0,005 and 0,025 % (m/m
11、), 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 study). 2 REFERENCES IS0 802, Aluminium oxi
12、de 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 oxide primarily used for the production of alum
13、inium - 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 the presence of tartaric acid. Spectrophot
14、ometric 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, approximately 8 N solution. Dilute 540 ml o
15、f 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) in hot water and, after cooling, dilute to
16、 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 g/ml, about 96 % (m/m), to about 500 ml of
17、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 of 4-amino-3-hydroxy- I-naphthalene sulpho
18、nic 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 material. 4.7.2 Ascorbic acid, 20 g/l soluti
19、on. Prepare this solution just before use. -,-,- ISO1232-1976 (E) 4.8 Silica, standard 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
20、,Si03), ignited at 1 000 “C to constant mass, i.e. until the results of two consecutive 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
21、rinsed with water and finally with redistilled water. It should not be dried. Avoid the 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 Foll
22、ow the procedure specified in 6.1, 6.2 and 6.3 of IS0 804. Add to the crucible 5 g of 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 in
23、to a beaker made of silica-free material. Cool, dilute to about 500 ml, transfer quantitatively 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
24、immediately to a bottle made of silica-free material. Take two aliquot portions of the 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 wat
25、er stated. 1 ml of this standard solution contains 0,500 mg of SiO,. Principal 4.9 Silica, 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 s
26、olution contains 0,020 mg of SiO,. Prepare this solution just before use. 4.10 Silica, 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 solutio
27、n contains 0,005 mg of SiO,. Prepare this solution just before use. 5 APPARATUS Ordinary 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
28、f 50 “c. 5.3 Electric furnace, capable of being controlled between 1 000 and 1 025 “C. 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 (
29、4.1) and 4 g of the boric acid (4.2), and mix carefully, preferably with a platinum spatula. 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 sub
30、sides. NOTE - Avoid contact of the platinum vessel with refractory materials. To isolate 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
31、of the furnace. The time at this temperature shall not exceed 5 min. Remove the dish from 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, c
32、ontaining 35 ml of the nitric acid solution (4.3). Wash the dish and its lid carefully with hot water, add the washings to the PTFE beaker and 2 -,-,- IS0 1232-1976(E) stir. Carefully wash the contents of the PTFE beaker into a glass beaker. Simmer gently for a few minutes. Cool slightly and transfe
33、r 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 (6.3.1) to a beaker of suitable capacity. Add to the beaker 10 ml of water, 15 ml of the s
34、tandard 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 slow addition, drop by drop, of the required volume of the nitric acid solution (4.3)
35、 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 (between 0,85 and 0,90). Note the volume of the nitric acid solution (4.3) used for the pH
36、 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 ml one-mark volumetric flasks, transfer 25 ml of the base solution (6.3.1) and then a
37、dd 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. TABLE 2 Standard silica solution (4.10) Corresponding mass of SiOp ml f-w 0” 0 5,O 0
38、,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 to stand for 15 to 25 min maximum at 20 to 25 “C. Then add 5 ml of the tartaric solutio
39、n (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 longer than 40 min, make the spectro- photometric measurements by means of the spectrophot
40、o- 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 Plotting of the calibration graph Plot a graph having, for example, as abscissae the value
41、s, 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 adjustment ofpH To the aliquot portion of the principal solution contained in the bea
42、ker (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 Colour development To the aliquot portion of the principal solution contained in the
43、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 specified in 6.3.4 for the colour development. 6.4.3 Spectrophotometric measurement C
44、arry 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 the blank test solution without addition of extra- pure aluminium oxide, following the p
45、rocedure 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 specified in 6.4.3. IS0 1232-1976 (El 7 EXPRESSION OF RESULTS By means of the calibrati
46、on graph (see 6.3.6), determine the 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 x1
47、00= 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 the corresponding aliquot portion of the blank test solution; D is the ratio of the
48、volume of the principal solution P to the volume of the aliquot portion used for the deter- mination; in the method specified, this ratio is equal to 10; 5 is the mass, in grams, of the test portion used for the preparation of the principal solution P. 8 SPECIAL CASE - SiO, CONTENT BETWEEN 0,025 AND
49、 0.25 % (m/m) 8.1 Principle See clause 3. NOTE - To effect the colour reaction in the same environmental conditions and in the presence of the same quantities of reagents as used for the preparation of the calibration curve, an addition is made to the aliquot portion of the principal solution P - which should always be less than 50 ml - the amount of the blank test solution required to bring the volume to 50,O ml. 8.2 Reagents See clause 4. 8.3 Appara