1、Reference number ISO 12980:2000(E) ISO 2000 INTERNATIONAL STANDARD ISO 12980 First edition 2000-04-01 Carbonaceous materials used in the production of aluminium Green coke and calcined coke for electrodes Analysis using an X-ray fluorescence method Produits carbons utiliss pour la production de lalu
2、minium Coke calcin et coke cru pour lectrodes Analyse par fluorescence aux rayons XISO 12980:2000(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embe
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6、lm, without permission in writing from either ISO at the address below or ISOs member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 734 10 79 E-mail copyrightiso.ch Web www.iso.ch Printed in Switzerland ii ISO 2000 All
7、 rights reservedISO 12980:2000(E) ISO 2000 All rights reserved iii Contents Page Foreword.iv Introduction.v 1 Scope 1 2 Normative reference 1 3 Principle1 4 Apparatus and materials.2 5 Sampling and test specimen preparation .2 6 Procedure .3 7 Expression of results 8 8 Precision.8 9 Test report 9ISO
8、 12980:2000(E) iv ISO 2000 All rights reserved Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each me
9、mber body interested in a subject for which a technical committee has been established 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. ISO collaborates closely with the International E
10、lectrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3. Draft International Standards adopted by the technical committees are circulated to the member bodies for vot
11、ing. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of patent rights. ISO shall not be held responsible for identifying
12、any or all such patent rights. International Standard ISO 12980 was prepared by Technical Committee ISO/TC 47, Chemistry, Subcommittee SC 7, Aluminium oxide, cryolite, aluminium fluoride, sodium fluoride, carbonaceous products for the aluminium industry.ISO 12980:2000(E) ISO 2000 All rights reserved
13、 v Introduction The determination of the elemental impurities is important for reasons of metal quality and anode consumption. This International Standard refers only to petroleum coke although the principles described are valid for pitch, anthracite, graphite or electrode materials. As the sample p
14、reparation and/or the mass fraction ranges for these other materials are quite different it is intended that specific standard methods will be published for each material.INTERNATIONAL STANDARD ISO 12980:2000(E) ISO 2000 All rights reserved 1 Carbonaceous materials used in the production of aluminiu
15、m Green coke and calcined coke for electrodes Analysis using an X-ray fluorescence method 1 Scope This International Standard specifies an X-ray fluorescence method for the determination of elemental impurities in green and calcined petroleum cokes used for the manufacture of anodes. These anodes ar
16、e used in the production of aluminium. 2 Normative reference The following normative document contains provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these this publicatio
17、ns do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent edition of the normative document indicated below. For undated references, the latest edition of the normative document referred to applies.
18、Members of ISO and IEC maintain registers of currently valid International Standards. ISO 6375, Carbonaceous materials for the production of aluminium Coke for electrodes Sampling. 3P r i n c i p l e A pressed tablet of pulverized coke and organic binder is irradiated by X-rays from a target thin wi
19、ndow X-ray tube. The X-ray tubes can be chromium, rhodium or scandium depending on which elements are to be determined. Irradiation of the test specimen causes ejection and rearrangement of orbital electrons resulting in the emission of secondary radiation with a characteristic wavelength for each e
20、lement. This secondary radiation is reflected, onto the detector system, by a crystal, which is set at a specific angle to the secondary radiation. Only specific radiation which obeys Braggs law reaches the detector system. n =2 d sin (1) where n is the order of the diffraction; is the X-ray wavelen
21、gth; d is the interplanar distance in the crystal; sin is the angle setting of the crystal. The intensities of the specific secondary radiation are calculated into mass fractions according to given calibration curves.ISO 12980:2000(E) 2 ISO 2000 All rights reserved 4 Apparatus and materials 4.1 X-ra
22、y fluorescence spectrometer, equipped with the following crystals: LiF 200 (lithium fluoride, reflecting plane 200), PE (pentaerythiol), PX1 (synthetic W-Si), Ge, TIAP (thallium acid phthalate) and LSM (layered synthetic microstructure). For instruments equipped with a side window X-ray tube, a scan
23、dium tube is advantageous for light elements. For instruments equipped with an end window X-ray tube, a rhodium tube offers optimum sensitivity. 4.2 Swinging-disc mill, with tungsten-carbide grinding devices. 4.3 Organic binder, suitable for pressed-tablet preparation. The binder shall not contain a
24、ny of the elements to be analysed. Suitable binders are Hoechst wachs G or stearic acid. 4.4 Tablet press, capable of providing a 20-tonne load. 4.5 Appropriate sample holders, for example aluminium dishes or brass rings with the dimensions as shown in Figure 1. 4.6 Detector gas, consisting of 90 %
25、argon and 10 % methane. 4.7 Calibration standards, commercially available and certified covering the range of mass fraction given in clause 6.5. 4.8 Reference samples (RS), commercially available and certified with appropriate mass fractions for all elements. (See 6.4.2) Dimensions in millimetres Fi
26、gure 1 Dimensions of sample holder 5 Sampling and test specimen preparation 5.1 Sampling Sampling shall be in accordance with the requirements of ISO 6375. 5.2 Test specimen preparation Crush the sample into sufficiently small particles so as to pass it through a 4 mm sieve. Dry to constant mass at
27、120 C. Mill the sample of crushed material into sufficiently small particles so as to pass it through a 63 ms i e v e . Mix approximately 30 g of this sieved material with approximately 5 g of binder and remill for 20 s. Crush any remaining lumps with a spatula. If too many lumps are formed in this
28、mixture, repeat the above procedure with a smaller quantity of binder, for example 4 g. When a smaller quantity of binder is used, test it to see if the calibration sample and other samples give pressed tablets strong enough to withstand the procedure. Repeat the above procedure until a suitable qua
29、ntity of binder has been added to provide an acceptable mixture for pressing a tablet.ISO 12980:2000(E) ISO 2000 All rights reserved 3 Place the material into the selected sample holder. NOTE Aluminium dishes are preferred, but brass rings may also be used. Place the filled sample holder in the pres
30、s and press at 20 t for 20 s. For the best results, the test specimen should be at least 4 mm thick. 6 Procedure 6.1 Measurement conditions The measurement conditions are apparatus-dependent but the indications in Table 1 can serve as guidelines. Normally no line overlapping will be experienced if t
31、hese conditions are used for the measurement of petroleum coke. Table 1 Typical measurement conditions for the different elements Element line Na K Al K Si K S K Ca K V K Fe K Ni K Crystal LSM a or PX1 PE or PX1 PE or PX1 PE or Ge LiF 200 LiF 200 LiF 200 LiF 200 Counter F b FFFFFFF Exposure, total t
32、ime, s 100 20 20 10 10 20 30 20 Collimator coarse coarse coarse medium fine fine fine fine kV 40 40 40 40 40 40 60 60 mA 60 60 60 60 60 60 40 40 Angle 28 PE: 145,1 PX1: 19,5 PE: 109,2 PX1: 16,6 PE: 75,8 PX1: 110,9 113,1 76,9 57,5 48,7 Offset angle c 2 1 1 1 F = flow counter a Layered synthetic micro
33、structure with 2d value around 5 nm. b A1 mo r2 m flow counter window is required. c Background measurement angles ( offset angles). 6.2 Intensities and background corrections The net peak intensity I, expressed as the number of counts per second, of the element of interest is calculated as the diff
34、erence between the measured peak intensity of the element and the background intensity at the peak angle in accordance with equations (4) and (5). See Figure 2. I = I p I b (2) where I p is the count rate, expressed as the number of counts per second, at the element position (2 ); I b is the backgro
35、und count rate, expressed as the number of counts per second, at the element position (2 );ISO 12980:2000(E) 4 ISO 2000 All rights reserved and I = I p C 1 I b1 C 2 I b2 (3) where I b1 is count rate, expressed as the number of counts per second, at the negative ( offset angle of the background posit
36、ion; I b2 is count rate, expressed as the number of counts per second, at the positive ( offset angle of the background position; C d dd 1 2 12 C d dd 2 1 12 where d 2 is the difference between the positive ( offset angle of the background position and 2 ; d 1 is the difference negative ( offset ang
37、le of the background position and 2 ; to give the net count rate I. Figure 2 Intensities and background correctionsISO 12980:2000(E) ISO 2000 All rights reserved 5 6.3 Counting time The minimum counting time is the time necessary to achieve a net counting error (2 % ) net which is less than the desi
38、red precision for the measurement. Assume that the part of the counting error in the repeatability ( 4 ) of this method is about 50 %. Choose a reference material having an element mass fraction in the middle of the range given in 6.5.1. Measure the counting rate. Calculate the minimum counting time
39、 for each element by using equation (4). t = 100 2 1 % pb F H G G I K J J II 2 (4) Where t is the total counting time for the peaks and background; I p is measured peak intensity, expressed as the number of counts per second; I b is the background intensity, expressed as the number of counts per sec
40、ond; 2 % is the relative targeted precision, expressed as a percentage, at the 95 % probability level. For Na, take 2 % as the relative targeted precision for 2 % . For other elements, take 1 % for 2 % . This equation requires that the distribution of the counting time at peak and background follow
41、the equation below: t t I I p b p b = (5) where t p is the counting time for the peak; t b is the counting time for the background. NOTE Additional checks such as monitor samples are recommended, and will depend on the age and state of the equipment. A description is given in 6.4.1. 6.4 Drift detect
42、ion by use of a monitor sample 6.4.1 Drift detection Any drift in the net count rate can be detected by using a monitor standard during the calibration procedure and during the measurement of unknown samples. Calculate the drift factor f d for each element by the ratio f I I d = 1 n (6) where I 1 is
43、 the intensity of monitor standard during the calibration procedure; I n is the intensity of monitor standard when unknown samples are measured.ISO 12980:2000(E) 6 ISO 2000 All rights reserved If the drift factor does not lie within the repeatability range (see 7.1) this indicates that a major chang
44、e, or problem has occurred in the X-ray equipment. Check the X-ray equipment, rectify as necessary and recalibrate. 6.4.2 Selection and preparation of monitor standards A monitor standard can be prepared as described below or, alternatively, use a reference sample (RS), with appropriate mass fractio
45、ns for all elements. Monitor standards can be prepared in copper dishes, with dimensions according to the actual sample holder as sh ow ni nFi g u re1. Select appropriate components for the monitor sample, weigh them into the desired proportions, mix them carefully and fuse them at 1 200 C in a (Pt
46、+ 5 % Au)-crucible (a typical recipe is given in Table 2). Allow to cool, crush the melt and melt again. Repeat this procedure once more, then finely grind the melt in the swinging-disc mill. Place the powder in a thin layer in the copper dish and heat on a gas burner until the enamel softens and ad
47、heres to the copper. Repeat this procedure until a layer of 0,5 mm in the copper dish is created. A typical recipe for monitor standards is shown in Table 2. A suitable amount is 5 g. Table 2 Typical monitor recipe S V Ni Na Ca Al Fe Si Li 2 B 4 O 7 90 % K 2 SO 4 8% V 2 O 5 0,3 % NiO 0,3 % Na 2 CO 3
48、 0,2 % CaO 0,2 % Al 2 O 3 0,2 % Fe 2 O 3 0,3 % SiO 2 0,3 % It is preferable that the monitor standard gives somewhat higher intensities than the test samples. The best results are obtained when the mass fractions of the different elements are chosen in such a way that the monitor intensities are 10
49、times to 20 times the mean intensities measured on the calibration standards. Take the monitor sample, as described above, or the appropriate reference sample that is to be used as a monitor, and prepare according to 5.2. After calibration, in order to determine its nominal mass fraction, test the homogeneity of the monitor standard. If the actual value of the monitor RS lies outside the repeatability range
