1、Reference numberISO 1431-3:2000(E)ISO 2000INTERNATIONALSTANDARDISO1431-3First edition2000-04-01Rubber, vulcanized or thermoplastic Resistance to ozone cracking Part 3:Reference and alternative methods fordetermining the ozone concentration inlaboratory test chambersCaoutchouc vulcanis ou thermoplast
2、ique Rsistance au craquelage parlozone Partie 3: Mthode de rfrence et autres mthodes pour la dterminationde la concentration dozone dans les enceintes dessai de laboratoireISO 1431-3:2000(E)PDF disclaimerThis PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this f
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5、e file is suitable for use by ISO member bodies. In theunlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below. ISO 2000All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any fo
6、rm or by any means, electronicor mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISOs member bodyin the country of the requester.ISO copyright officeCase postale 56 Gb7 CH-1211 Geneva 20Tel. + 41 22 749 01 11Fax + 41 22 734 10 7
7、9E-mail copyrightiso.chWeb www.iso.chPrinted in Switzerlandii ISO 2000 All rights reservedISO 1431-3:2000(E) ISO 2000 All rights reserved iiiContents PageForeword.ivIntroduction.v1 Scope12 Normative references13 Principle24 Apparatus .25 Calibration26 Procedure.27 Expression of results 28 Test repor
8、t3Annex A (normative) The effect of ambient atmospheric pressure on ozone cracking of rubber4Annex B (normative) Alternative instrumental methods.5Annex C (normative) Wet-chemical methods.8ISO 1431-3:2000(E)iv ISO 2000 All rights reservedForewordISO (the International Organization for Standardizatio
9、n) is a worldwide federation of national standards bodies (ISOmember bodies). The work of preparing International Standards is normally carried out through ISO technicalcommittees. Each member body interested in a subject for which a technical committee has been established hasthe right to be repres
10、ented on that committee. International organizations, governmental and non-governmental, inliaison with ISO, also take part in the work. ISO collaborates closely with the International ElectrotechnicalCommission (IEC) on all matters of electrotechnical standardization.International Standards are dra
11、fted 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 voting.Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.A
12、ttention is drawn to the possibility that some of the elements of this part of ISO 1431 may be the subject of patentrights. ISO shall not be held responsible for identifying any or all such patent rights.International Standard ISO 1431-3 was prepared by Technical Committee ISO/TC 45, Rubber and rubb
13、er products,Subcommittee SC 2, Physical and degradation tests.ISO 1431 consists of the following parts, under the general title Rubber, vulcanized or thermoplastic Resistanceto ozone cracking:Gbe Part 1: Static strain testGbe Part 2: Dynamic strain testGbe Part 3: Reference and alternative methods f
14、or determining the ozone concentration in laboratory test chambersAnnexes A, B and C form a normative part of this part of ISO 1431.ISO 1431-3:2000(E) ISO 2000 All rights reserved vIntroductionA number of techniques exist for the analysis of gaseous ozone/air mixtures used for ozone crack testing of
15、rubbers. These include wet-chemical procedures, electrochemical cells, UV absorption and chemiluminescencewith ethylene.In principle, the wet-chemical, electrochemical and UV absorption methods are all absolute, but in practice they donot in general yield the same results.Wet-chemical methods, which
16、 usually consist of the absorption of ozone in a potassium iodide solution and titrationof the iodine released with sodium thiosulfate, were traditionally used in the rubber industry and were specified innational standards. They are not suitable for continuous operation or control and hence are less
17、 desirable inpractice than instrumental methods. The results obtained have been shown to be sensitive to small variations in testprocedures and the concentration and purity of reagents, and there has been much controversy over thestoichiometry of the reaction.Electrochemical methods are widely used
18、in the rubber industry and found to be convenient in continuouslymonitoring and controlling ozone. Chemiluminescence methods have also been used.More recently, UV absorption analysers, which have the same monitoring and controlling ability, have beenincreasingly used. Most important, this technique
19、has been adopted by all major environmental agencies as thestandard and is regarded by them to be absolute.Consequently, this standard UV absorption method is adopted as the reference technique against which all othersmust be calibrated. Like any measurement instrument, the accuracy of any particula
20、r UV instrument is dependenton the calibration and maintenance of its components, and hence even UV analysers should be checked againstacknowledged standard instruments. Studies are being undertaken in several countries to propose a primary-standard apparatus.Although this part of ISO 1431 is concer
21、ned with ozone analysis, it also draws attention to the influence ofatmospheric pressure on the rate of cracking of rubber at constant ozone concentrations as normally expressed interms of parts by volume. As established by interlaboratory tests conducted in North America3, the variation inozone res
22、istance that can result between laboratories operating at significantly different atmospheric pressures canbe corrected by specifying ozone concentration in terms of the partial pressure of ozone (see annex C).Attention is drawn to the highly toxic nature of ozone. Efforts should be made to minimize
23、 the exposure of workersat all times. In the absence of more stringent or contrary national safety regulations, it is recommended that 10 partsof ozone per hundred million parts of air of the surrounding atmosphere by volume be regarded as an absolutemaximum concentration, whilst the maximum average
24、 concentration should be appreciably lower.Unless a totally enclosed system is being used, an exhaust vent to remove ozone-laden air is recommended.INTERNATIONAL STANDARD ISO 1431-3:2000(E) ISO 2000 All rights reserved 1Rubber, vulcanized or thermoplastic Resistance to ozonecracking Part 3:Reference
25、 and alternative methods for determining the ozoneconcentration in laboratory test chambers1 ScopeThis part of ISO 1431 describes three types of method for the determination of ozone concentration in laboratorytest chambers.Method A UV absorption: this is the reference method, and is used as the mea
26、ns of calibration for thealternative methods B and C.Method B Instrumental techniques:B1: electrochemicalB2: chemiluminescenceMethod C Wet-chemical techniques:Procedure IProcedure IIProcedure III2 Normative referencesThe following normative documents contain provisions which, through reference in th
27、is text, constitute provisions ofthis part of ISO 1431. For dated references, subsequent amendments to, or revisions of, any of these publicationsdo not apply. However, parties to agreements based on this part of ISO 1431 are encouraged to investigate thepossibility of applying the most recent editi
28、ons of the normative documents indicated below. For undatedreferences, the latest edition of the normative document referred to applies. Members of ISO and IEC maintainregisters of currently valid International Standards.ISO 1431-1:1989, Rubber, vulcanized or thermoplastic Resistance to ozone cracki
29、ng Part 1: Static strain test.ISO 1431-2:1994, Rubber, vulcanized or thermoplastic Resistance to ozone cracking Part 2: Dynamic straintest.ISO 13964:1998, Air quality Determination of ozone in ambient air Ultraviolet photometric method.ISO 1431-3:2000(E)2 ISO 2000 All rights reserved3 PrincipleAn oz
30、one/air mixture is sampled from an ozone exposure chamber and the ozone concentration is determined bythe UV absorption reference method or by alternative instrumental or chemical-analysis methods calibrated againstthe UV absorption method.4 ApparatusApparatus used for the determination of the ozone
31、 concentration shall be one of the following types:UV absorptionElectrochemicalChemiluminescenceWet-chemicalThe reference method is UV absorption, and all equipment shall be calibrated against the UV absorption method asspecified in clause 5.The apparatus used for the UV absorption method shall be i
32、n accordance with ISO 13964, except that it shall becapable of measuring ozone concentrations specified in ISO 1431-1 and -2.Descriptions of alternative methods are given in annex B (instrumental methods) and annex C (wet-chemicalmethods).5 CalibrationCalibration of the apparatus for determining the
33、 ozone concentration shall be in accordance with the proceduresgiven in ISO 13964.6 ProcedureThe UV method shall be carried out in accordance with ISO 13964.Other instrumental methods shall be used in accordance with the manufacturers instructions, attention being paidin particular to initial settin
34、g up, zero adjustment and maintaining and checking the instrument as mentioned inannex B.Wet-chemical methods shall be carried out in accordance with annex C.7 Expression of resultsGenerally, the ozone concentration G6aO3is expressed in parts of ozone by volume per hundred million parts of air byvol
35、ume (pphm).However, the ozone concentration may also be expressed in mg/m3or in mPa. The expression mg/m3indicates thenumber of ozone molecules in the volume which is available for ozone cracking and depends on both pressure andtemperature.For conversion purposes, the following equation is valid:ISO
36、 1431-3:2000(E) ISO 2000 All rights reserved 3G6aG6aOOmg/m 5,78 10 pphm3333G3dGb4Gb4Gb4G2dpTwhere p, the atmospheric pressure, is in hPa and T is in K.In terms of the partial pressure of ozone:ppOO33mPa pphmG3dG2d103G6awhere p, the atmospheric pressure, is in hPa.At 1013 hPa and 273 K, 1 pphm = 1,01
37、 mPa.8 Test reportThe test report shall contain the following information:a) a reference to this part of ISO 1431, i.e. ISO 1431-3;b) the method used, i.e. type of instrument or wet-chemical;c) the measurement interval if measurement was not continuous;d) the ozone concentration or range of concentr
38、ations measured, expressed in pphm or mg/m3or mPa partialpressure of O3, corrected if necessary by a calibration factor;e) the date of the test.ISO 1431-3:2000(E)4 ISO 2000 All rights reservedAnnex A(normative)The effect of ambient atmospheric pressure on ozone cracking of rubberThe rate of reaction
39、 of ozone with rubber, i.e. the cracking rate, is a function of the rate of collision of the ozonemolecules with the rubber surface and is therefore a function of the number of ozone molecules present, all otherfactors being constant.The perfect-gas equation and Daltons law permit the partial pressu
40、re of ozone pO3to be calculated as a function ofthe number of moles of ozone nO3in volume V of the ozone/air mixture, measured at temperature T:pnRTVOO33G3dwherepO3is in mPa;T is in K;V is in m3;R is the gas constant (R = 8,314 PaGd7m3Gd7mol1Gd7K1).NOTE Under standard conditions of temperature (273
41、K) and pressure (1 atm., 760 torr or 1013 hPa), 1 pphm = 1,01 mPa.It can be demonstrated that, for the same ozone content, by volume, of the ozonized air, measured at the sametemperature but at different atmospheric pressures, the partial pressure of ozone and the number of moles of ozonevary in the
42、 same ratio as the atmospheric pressure.The results of an interlaboratory test programme conducted in North America3prove the effect of ambientpressure on the cracking rate at a constant volumetric ozone content.Therefore, the expression of the ozone concentration in laboratory test chambers on a vo
43、lume per volume basis isinappropriate where differences in atmospheric pressure are likely to exist.The effect of these variations can be corrected for by working at a constant test chamber pressure or by varying thevolumetric ozone content of the ozone/air mixture in an inverse ratio to the atmosph
44、eric pressure. The effect canalso be overcome by expressing the ozone concentration as the partial pressure of the ozone in ozonized air.ISO 1431-3:2000(E) ISO 2000 All rights reserved 5Annex B(normative)Alternative instrumental methodsB.1 Electrochemical methodB.1.1 PrincipleOzonized air is bubbled
45、 at a fixed rate through a coulometric cell containing a buffered solution of potassium iodideand having a platinum cathode and a silver (preferred) or mercury anode.The ozone reacts with the potassium iodide to liberate free iodine which is ionized at the cathode and removed atthe anode to produce
46、silver or mercury iodide. Two units of charge are produced for each ozone molecule and theresultant current is proportional to the ozone concentration. The net emf of the cell is cancelled by an applied backemf and corrections made for ambient temperature and pressure (see reference 1).The stoichiom
47、etry is:O3+2KI+H2OGae2KOH + O2+I2At the cathode: I2+2eGae2IAt the anode: 2I2e+2HgGaeHg2I2By Faradays Law:O3Gae2IGae2eGae2 Gb4 96500 coulombsB.1.2 ApparatusThe analyser shall include a coulometric cell of the general type shown in Figure B.1. Standard models are availablecommercially.The cathode is i
48、n the form of a platinum basket through which the ozonized air is bubbled. The anode can take theform of one of the following, although (b) is the preferred type:a) a pool of mercury;b) a silver mesh spiral.The iodine liberated from the solution by the ozone is ionized at the cathode and is transpor
49、ted to the anode by theliquid circulation induced in the direction of the arrows by the bubbling action. At the anode, insoluble silver iodide ormercurous iodide is formed with the release of ionic charges which are exactly equivalent to the ozone introduced bythe air stream.The cell shall be connected to an analyser circuit of the general type shown in Figure B.2.A stabilized d.c. voltage source is provided as a means of opposing the standard potential which appears at the cellterminals when ozone-free a
