ISO 12989-2-2004 Carbonaceous materials used in the production of aluminium - Baked anodes and sidewall blocks - Determination of the reactivity to air - Part 2.pdf

1、 Reference number ISO 12989-2:2004(E) ISO 2004INTERNATIONAL STANDARD ISO 12989-2 First edition 2004-05-15 Carbonaceous materials used in the production of aluminium Baked anodes and sidewall blocks Determination of the reactivity to air Part 2: Thermogravimetric method Produits carbons utiliss pour

2、la production de laluminium Anodes et blocs de faade cuits Dtermination de la ractivit lair Partie 2: Mthode thermogravimtrique ISO 12989-2:2004(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 no

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5、ember bodies. In the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below. ISO 2004 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or

6、 mechanical, including photocopying and microfilm, 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 22 749 09 47 E-mail copyrightiso.org Web w

7、ww.iso.org Published in Switzerland ii ISO 2004 All rights reservedISO 12989-2:2004(E) ISO 2004 All rights reserved iiiContents Page Foreword iv Introduction v 1 Scope 1 2 Terms and definitions. 1 3 Principle. 2 4 Apparatus. 2 5 Reagents 3 6 Sample 3 7 Calibration 4 8 Procedure. 5 9 Calculation of r

8、esults 6 9.1 Exposed surface area of the sample. 6 9.2 Total air reactivity . 6 9.3 Initial air reactivity. 6 9.4 Final air reactivity 7 9.5 Air dusting rate 7 10 Precision and bias 7 10.1 Precision 7 10.2 Repeatability 7 10.3 Reproducibility limits 9 10.4 Bias. 10 11 Test report 10 Bibliography . 1

9、3 ISO 12989-2:2004(E) iv ISO 2004 All rights reservedForeword 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. E

10、ach member 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 Internati

11、onal Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standa

12、rds adopted by the technical committees are circulated to the member bodies for voting. 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 document may be the subject

13、 of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 12989-2 was prepared by Technical Committee ISO/TC 47, Chemistry, Subcommittee SC 7, Aluminium oxide, cryolite, aluminium fluoride, sodium fluoride, carbonaceous products for the aluminium industr

14、y. ISO 12989 consists of the following parts, under the general title Carbonaceous materials used in the production of aluminium Baked anodes and sidewall blocks Determination of the reactivity to air: Part 1: Loss in mass method Part 2: Thermogravimetric method ISO 12989-2:2004(E) ISO 2004 All righ

15、ts reserved vIntroduction Comparison of air reactivities, or air reaction rates, and air dusting rates is useful in selecting raw materials for the manufacture of commercial electrodes for specific smelting technologies in the production of aluminium. Air reactivities are used to quantify the tenden

16、cy of a carbon artifact to react with air. Carbon consumed by this unwanted side reaction is unavailable for the primary reaction of reducing alumina to the metal. Air reactivities and the dusting rate are used by some companies to quantify the tendency of the coke aggregate or binder coke of a carb

17、on artifact to selectively react with air. Preferential attack of the binder coke or coke aggregate of a carbon artifact by air causes some carbon to fall off as dust, making the carbon unavailable for the primary reaction of reducing alumina and, more importantly, reducing the efficiency of the red

18、uction cell. Air reactivities are used for evaluating the effectiveness of beneficiation processes and for research purposes. Sampling guidelines are under development. This part of ISO 12989 is based on ASTM D 6559-00. INTERNATIONAL STANDARD ISO 12989-2:2004(E) ISO 2004 All rights reserved 1Carbona

19、ceous materials used in the production of aluminium Baked anodes and sidewall blocks Determination of the reactivity to air Part 2 Thermogravimetric method WARNING This part of ISO 12989 does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility

20、 of the user of this part of ISO 12989 to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 1 Scope This part of ISO 12989 allows the determination by thermogravimetric analysis (TGA) of air reactivities and dusting of shaped ca

21、rbon electrodes used in the aluminium-reduction industry. Many types of apparatus are available, with various thermal conditions, sample-size capabilities, materials of construction and procedures for determining the mass loss and subsequent rate of reaction. This test method standardizes the variab

22、les of sample dimensions, reaction times and temperatures, and provides a mathematical method to normalize the gas velocity over the exposed surfaces, such that results obtained on different types of apparatus are correlatable. 2 Terms and definitions For the purposes of this document, the following

23、 terms and definitions apply. 2.1 air dusting rate dnormalized rate at which carbon falls off the carbon artifact during the test NOTE The dusting rate is expressed in milligrams per square centimetre per hour. 2.2 final air reactivity frate of mass loss of the carbon artifact during the final 30 mi

24、n of exposure to air in the reaction chamber divided by the initial exposed surface area of a sample having the form of a right cylinder NOTE The final air reactivity is expressed in milligrams per square centimetre per hour. 2.3 initial air reactivity irate of mass loss of the carbon artifact durin

25、g the first 30 min of exposure to air in the reaction chamber divided by the initial exposed surface area of a sample having the form of a right cylinder NOTE The initial air reactivity is expressed in milligrams per square centimetre per hour. ISO 12989-2:2004(E) 2 ISO 2004 All rights reserved2.4 t

26、otal air reactivity Trate of mass loss of the carbon artifact (including dusting) during the total time that the sample is exposed to air (180 min) in the reaction chamber divided by the initial exposed surface area of a sample having the form of a right cylinder NOTE The total air reactivity is exp

27、ressed in milligrams per square centimetre per hour. 3 Principle The air dusting rate and the initial, final and total air reactivities are determined by passing air at a flow rate giving a standard velocity of reactant gas around cylindrically shaped carbon artifacts under nearly isothermal conditi

28、ons for a specified length of time. The air reactivities are determined by continuously monitoring the mass loss of the sample. The air dusting rate is determined by collecting and determining the mass of the carbon particles that fall off the sample during reaction. 4 Apparatus 4.1 Air reactivity a

29、pparatus, as simple as possible and commensurate with the aims of the test. The principal criterion is that the reaction rate be determined under isothermal conditions and be unaffected by physical and chemical properties inherent in the apparatus (such as gas diffusion patterns, gas temperature, ex

30、posed sample surface area, and so forth). A typical apparatus that has been found to be suitable is illustrated in Figure 1. 4.2 Furnace and controller, capable of maintaining the temperature constant to within 2 C in the 100-mm reaction zone in which the sample is centred. A typical apparatus (Figu

31、re 1) employs a three-zone heating element and associated controls to accomplish this, but other types of heaters such as tapered windings or long linear heaters are also suitable. The control thermocouple is a grounded type and shall be located within the reaction chamber near the surface of the te

32、st sample. This is to allow the furnace controller to compensate for the exothermic reactions that occur when the furnace is used for air reactivity testing. The control thermocouple shall be positioned 4 mm 1 mm from the side surface of the sample and within 5 mm vertically of the centre of the rea

33、ction chamber. The furnace shall be large enough to accommodate the reaction chamber. 4.3 Reaction chamber, consisting of a vertical tube constructed of a material capable of withstanding the temperature of the reaction and with a sufficiently large inside diameter to accomodate the sample and sampl

34、e suspension device while not affecting the gas flow past the sample. An inside diameter of 100 mm 25 mm is recommended. The reaction chamber shall be constructed with a removable dust collection cup at the bottom capable of capturing all the dust that falls off the sample during the test. The most

35、common materials of construction are quartz and Incone 1) . 4.4 Sample suspension device, capable of supporting the sample in the reaction chamber for the duration of the test and which should be reusable. The sample suspension device shall not change in mass during the test, shall not affect the fl

36、ow pattern of the gas past the sample, shall not limit the gas-accessible surface area of the test sample and shall not interfere with the production of dust by the sample. A typical sample suspension device is illustrated in Figure 2. 1) Inconel is an example of a suitable product available commerc

37、ially. This information is given for the convenience of users of this part of ISO 12989 and does not constitute an endorsement by ISO of this product. ISO 12989-2:2004(E) ISO 2004 All rights reserved 34.5 Gas preheat tube, extending into the first heating zone of the reaction chamber, to preheat the

38、 gas prior to entering the reaction chamber. The length and diameter of the tube may vary, as long as the gas leaving the tube is at the same temperature as the reaction chamber. The inlet gas shall leave the preheat tube downward to prevent channelling of the gas through the reaction chamber and to

39、 prevent plugging of the preheat tube with carbon dust. 4.6 Balance, capable of measuring the mass (approximately 200 g maximum) of the sample and sample suspension device to the nearest 0,01 g continuously throughout the duration of the test. 4.7 Gas flow meter, capable of measuring the flow rate o

40、f the gas entering the reaction chamber. All gas flow rates shall be maintained at the rate specified for the particular test apparatus. 4.8 Needle valve, to make fine adjustments to the gas flow rate. 4.9 Pressure-reducing valve, to reduce the pressure of the compressed gas to near atmospheric pres

41、sure before it enters the gas flow meter. 4.10 Thermocouple(s), (for example, three couples in the same sheath with probes located at the tip, and at 50 mm and 100 mm above the tip; or a packet of thermocouples with tips located at similar known distances) capable of being inserted into the reaction

42、 chamber to calibrate the furnace zone controllers. An optional thermocouple may be used to monitor reaction temperatures. Some users find continuous temperature measurement of the central part of the reaction chamber to be of value. 4.11 Callipers, or other suitable device, capable of measuring the

43、 sample diameter and height to within 0,01 mm to calculate the geometric surface area exposed to the test gas. 4.12 Optional equipment, including, but not limited to, automatic control devices, multi-channel line selectors and personal computers to automate data recording, processing, reporting and

44、storage. 5 Reagents Use only reagents of recognized analytical grade, unless otherwise specified. 5.1 Nitrogen, 99,95 %. 5.2 Air, containing less than 0,1 % by mass of moisture. 6 Sample 6.1 Prepare the sample by coring and then cutting or machining to a right cylinder, 50 mm 1,0 mm high and 50 mm 1

45、0 mm in diameter. Most sample suspension devices (4.4) require a hole of about 3 mm in diameter to be drilled vertically through the centre of the cylinder to accommodate a suspension wire. The sampling plans for anodes and cathode blocks given in ASTM D 6353 and D 6354 may be used if desired. The

46、finished sample shall be smooth and free of visible cracks and gouges. 6.2 Dry the finished sample in an oven at 105 C 5 C to constant mass. 6.3 Free the finished sample from loose carbon dust and impurities from the shaping process by blowing with dry air. ISO 12989-2:2004(E) 4 ISO 2004 All rights

47、reserved7 Calibration 7.1 The purpose of this procedure is to establish a relationship between the controller settings for the three- zone furnace and the actual temperature inside the reaction chamber in the region of the sample. The length of the calibrated zone shall be 100 mm. 7.2 Insert a multi

48、probe thermocouple (4.10) into the zone where the sample will be located. Align the middle probe of the multi-probe thermocouple with the sample position. 7.3 Connect the middle thermocouple (4.10) to the main controller, set at 525 C. 7.4 Connect the other two thermocouples to any temperature-indi

49、cating device. A recording temperature indicator is required to determine the actual temperature profile. 7.5 Allow 4 h for the furnace to reach equilibrium under nitrogen purge (at a rate of gas flow in accordance with 7.7). 7.6 Adjust the zone temperature controllers until all three temperature indicators are within 2 C of each other. 7.7 The gas flow rate for the reference analysis is based on 250 l/h 5 l/h (at ambient temperature) for a sample diameter of 50 mm in a reaction chambe