DIN ISO 1431-3-2011 Rubber vulcanized or thermoplastic - Resistance to ozone cracking - Part 3 Reference and alternative methods for determining the ozone concentration in laborato.pdf

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1、May 2011 Translation by DIN-Sprachendienst.English price group 13No part of this translation may be reproduced without prior permission ofDIN Deutsches Institut fr Normung e. V., Berlin. Beuth Verlag GmbH, 10772 Berlin, Germany,has the exclusive right of sale for German Standards (DIN-Normen).ICS 83

2、.060!$o+ b) the UV absorption method has been adopted as the reference technique; c) the description of an electrochemical method and a chemiluminescence method has been included. Previous editions DIN 53509-2: 1977-03, 1994-11 DIN ISO 1431-3:2011-05 3National Annex NA (informative) Bibliography DIN

3、 ISO 13964, Air quality Determination of ozone in ambient air Ultraviolet photometric method DIN ISO 1431-3:2011-05 4DIN ISO 1431-1, Rubber, vulcanized or thermoplastic Resistance to ozone cracking Part 1: Static and dynamic strain testing IntroductionA number of techniques exist for the analysis of

4、 gaseous ozone/air mixtures used for ozone crack testing ofrubbers. 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

5、 general yield the same results.Wet-chemical methods, which 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 suit

6、able for continuous operation or control and hence are less 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 thestoichiomet

7、ry of the reaction.Electrochemical methods are widely used 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,

8、have beenincreasingly used. Most important, this technique 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. Lik

9、e any measurement instrument, the accuracy of any particular 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-

10、standard apparatus.Although this part of ISO 1431 is concerned 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 t

11、ests conducted in North America3, the variation inozone resistance 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 highl

12、y toxic nature of ozone. Efforts should be made to minimize 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 a

13、n absolutemaximum concentration, whilst the maximum average concentration should be appreciably lower.Unless a totally enclosed system is being used, an exhaust vent to remove ozone-laden air is recommended.Rubber, vulcanized or thermoplastic Resistance to ozone cracking Part 3: Reference and altern

14、ative methods for determining the ozone concentration in laboratory test chambers DIN ISO 1431-3:2011-05 51 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

15、used as the means 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

16、reference in this 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 mo

17、st recent editions 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

18、to ozone cracking Part 1: Static strain test.ISO 1431-2:1994N1), Rubber, vulcanized or thermoplastic Resistance to ozone cracking Part 2: Dynamicstrain test.ISO 13964:1998, Air quality Determination of ozone in ambient air Ultraviolet photometric method.DIN ISO 1431-3:2011-05 6N1) National footnote:

19、 ISO 1431-2:1994 was withdrawn on 2004-09-08 and has not been replaced. 3 PrincipleAn ozone/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 agai

20、nstthe UV absorption method.4 ApparatusApparatus used for the determination of the ozone 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 m

21、ethod asspecified in clause 5.The apparatus used for the UV absorption method shall be in 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 ann

22、ex C (wet-chemicalmethods).5 CalibrationCalibration of the apparatus for determining the 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

23、with the manufacturers instructions, attention being paidin particular to initial setting 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 concentrat

24、ion G6aO3is expressed in parts of ozone by volume per hundred million parts of air byvolume (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 b

25、oth pressure andtemperature.For conversion purposes, the following equation is valid:DIN ISO 1431-3:2011-05 7G6aG6aOOmg/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 atmos

26、pheric pressure, is in hPa.At 1013 hPa and 273 K, 1 pphm = 1,01 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

27、 not continuous;d) the ozone concentration or range of concentrations measured, expressed in pphm or mg/m3or mPa partialpressure of O3, corrected if necessary by a calibration factor;e) the date of the test.DIN ISO 1431-3:2011-05 8Annex A(normative)The effect of ambient atmospheric pressure on ozone

28、 cracking of rubberThe rate of reaction 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 an

29、d Daltons law permit the partial pressure 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 s

30、tandard conditions of temperature (273 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

31、the number of moles of ozonevary in the 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 concentrat

32、ion in laboratory test chambers on a volume 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 mix

33、ture in an inverse ratio to the atmospheric pressure. The effect canalso be overcome by expressing the ozone concentration as the partial pressure of the ozone in ozonized air.DIN ISO 1431-3:2011-05 9Annex B(normative)Alternative instrumental methodsB.1 Electrochemical methodB.1.1 PrincipleOzonized

34、air is bubbled 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 ano

35、de to produce 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)

36、.The stoichiometry 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.Th

37、e cathode is in 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 a

38、nd is transported 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 s

39、hall 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 air is passed through the cell. This standard potential will depend on the an

40、ode material.DIN ISO 1431-3:2011-05 10B.1.3 ReagentsPrepare a buffered solution of potassium iodide as follows:Weigh out the following analytical-reagent quality chemicals and dissolve in 1 litre of chloride-free and sulfate-freedistilled water:Potassium iodide (KI) 1,50 gSodium monohydrogen phospha

41、te (Na2HPO4)1,50gPotassium dihydrogen phosphate (KH2PO4)1,40gThis should give a solution buffered at pH 6,5 to pH 6,8.B.1.4 Cell calibrationAssuming a gas flow rate of 150 cm3/min measured at STP and an ozone content of 100 pphm, the size of thecurrent is:100 10 150 2 96,500 1022,400 6021,55 A86Gb4G

42、b4Gb4Gb4 Gb4Gb4G3dG2dG6dThus, in the typical circuit shown in Figure B.2, the analyser can be calibrated directly by relating cell current toozone concentration.B.2 ChemiluminescenceIn chemiluminescence instruments, ozonized air is passed through a chamber where it comes into contact with astream of

43、 ethylene, and the two gases undergo a chemiluminescence reaction with the emission of photons at about430 nm. This emission of energy is measured by a photomultiplier and converted to an electrical output which isproportional to the ozone concentration.DIN ISO 1431-3:2011-05 11Key1Air/O32Air3 Catho

44、de4 Anode5 Solution6TowasteFigure B.1 AnalyserKey1 Micro-ammeter2 Stable d.c. source3CelFigure B.2 Simple analyser circuitDIN ISO 1431-3:2011-05 12Annex C(normative)Wet-chemical methodsC.1 General theoryC.1.1 The absorption of ozone in an buffered neutral aqueous KI solution yields free iodine by ox

45、idation:O3+2KI+H2OGae2KOH + O2+I2The addition of sodium thiosulfate solution to the KI solution prior to the absorption causes an immediate reactionbetween the free iodine and the thiosulfate:I2+2Na2S2O3GaeNa2S4O6+2NaIThus one O3is equivalent to 2Na2S2O3.C.1.2 Three alternative procedures are availa

46、ble, I, II and III, any of which may be used.C.1.2.1 Procedure I is the well established technique by which O3is absorbed in a buffered KI solution withexcess Na2S2O3, for a fixed length of time, followed by titration of the excess Na2S2O3in the usual way with astandardized I2solution to an electrom

47、etric end-point.C.1.2.2 Procedure II is a modification of procedure I and uses a recorder to monitor the voltage across theelectrodes of an electrometric end-point detection device. A smaller quantity (more dilute solution) of Na2S2O3isadded to the buffered KI solution and the absorption process is

48、continued until the Na2S2O3is totally consumed. Atthis point, the voltage abruptly rises. From the chart record the total elapsed time for the completion of the reactionis easily determined, and this is used to calculate the ozone concentration.C.1.2.3 Procedure III is a further variant using a cons

49、tant-current electrolysis apparatus in conjunction with theelectrometric end-point detector.C.2 Procedure IC.2.1 ReagentsC.2.1.1 Buffered potassium iodide solutionA solution of KI in a 0,1 mol/l phosphate buffer is used. This is prepared by dissolving in 1 litre of distilled water:17,8 g of crystalline disodium hydrogen phosphate dihydrate (Na2HPO4Gd72H2O) or the corresponding amount ofanother hydrate of disodium hydrogen phosphate;13,6 g of potassium dihydrogen phosphate (KH2PO4);30 g Gb1 2 g of potassium iodide (KI).This solution shall have