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1、1AS 1180.7FNovember 1972 STANDARDS ASSOCIATION OF AUSTRALIA Australian Standard Methods of Test for HOSE MADE FROM ELASTOMERIC MATERIALS METHOD 7F. RESISTANCE OF HOSE LINING AND COVER TO OZONE 1 SCOPE. This test is an artificial accelerated test which gives an indication of the resistance to crackin
2、g of the rubber components of hose to outdoor weathering by exposing them to ozone. Absence of certain factors in outdoor weather such as sunshineandrainfalllimitthecorrelation.Themethodisderivedfrom ASTM D1149Test for Ozone Cracking of Vulcanized Rubber. 2 PRINCIPLE. The rubber components of the ho
3、se are placed under tensile strain in a chamber containing an ozone-air atmosphere under such controlled conditions as concentration and temperature and subsequently are assessed for cracking. 3 APPARATUS. 3.1 Ozone Test Chamber. Requirements for an acceptable ozone test chamber are sufficient air-o
4、zone throughput rate, sufficient internal circulation, and sufficient internal volume. A secondary requirement is that of controlling the temperature within acceptable limits. An acceptable ozone test chamber can be custom-made in a particular laboratory, or one of the commercial manufactured chambe
5、rs. The ozone test chambers shall conform to the following requirements: (i)The test chamber shall be constructed of a material with minimal reaction to ozone. (ii) The volume of the chamber shall be at least 140 litres and capable of holding the apparatus for mounting the test specimens. (iii) The
6、air-ozone replacement rate or throughput rate must be of a magnitude such that no appreciable reduction in ozone concentration results from the introduction of test specimens. This minimum replacement rate will vary with the ozone concentration, temperature, number of test specimens introduced, and
7、their reaction with ozone. For many chambers operating under normal conditions (approximately 50 parts per 100 000 000), an air-ozone replacement rate of a three-fourths change per minute is an acceptable and adequate value. For thorough b Accessed by UNIVERSITY OF SOUTH AUSTRALIA on 23 Jan 2008 AS
8、1180.7FNovember 19722 and accurate work, especially under unusual conditions, the minimum or safe replacement rate should be determined. NOTE: Upward concentration adjustments can compensate for a reduction in ozone concentration when specimens are introduced. (iv) A means of providing adequate inte
9、rnal circulation shall be provided. The air- ozone velocity in the chamber shall be at least 600 mm/s. Where it is doubtful that such velocities exist, the installation of an ordinary 1700 rev/min electric motor and fan blade of approximately 150 mm diameter and 20 to 30 degrees pitch will produce s
10、uch air velocities. The motor itself shall not be in the chamber. An extension shaft shall be used with an appropriate seal. (v) A means of controlling the temperature of the chamber from ambient to 70C shall be provided. The temperature regulation should be capable of maintaining the test temperatu
11、re within 1C. (vi) It is often advantageous to have glass window or front door as part of the chamber. 3.2 Mounting for Test Specimens or Pieces. Mountings for test specimens or pieces shall be as shown in Figs 1 and 2. 3.3 Ozone Generator. A means for generating and controlling an ozone-air stream
12、shall be provided. The generating source shall be located outside the chamber and fed with filtered air drawn directly from the laboratory or from a compressed air supply. The air-ozone stream shall be introduced into the chamber in such a manner that stratification of ozone is prevented. NOTE: The
13、mercury vapour lamp is the most common source for generating ozone. With such a lamp the ozone concentration can be easily controlled by means of a variable transformer. This will transform the voltage fed to the primary of the transformer to that required by the mercury lamp. 3.4 Apparatus for Dete
14、rmining Ozone Concentration. 3.4.1 General. Apparatus for measuring the concentration of ozone in the test chamber shall be provided. A satisfactory method is absorption of the ozone in a buffered potassium iodide solution followed by titration of the released iodine with a standard solution of sodi
15、um thiosulphate. One of three alternative absorption devices shall be provided, two of which are spray-jet devices and the third a counter-current absorption column. The end point of the titration may be determined by the microammeter method or by the null indicator method described herein. The air
16、sample is drawn directly from the ozone chamber. Special precautions to draw air from various levels of the chamber are not necessary, since adequate circulation will be maintained if the preceding chamber specifications are met. Glass lines only should be used to convey the air-ozone stream to the
17、absorbing device. Plasticized plastics are to be avoided, except as short connecting pieces for joining glass tubing. Accessed by UNIVERSITY OF SOUTH AUSTRALIA on 23 Jan 2008 3AS 1180.7FNovember 1972 Fig. 1. MOUNTING FOR TEST SPECIMENSPLAN VIEW Fig. 2. MOUNTING FOR TEST SPECIMENSSIDE ELEVATION 3.4.2
18、 Absorption of ozone. (i)The spray-jet device is shown in Fig. 3. The glass tube, A, is approximately 90 mm in diameter and 100 mm long terminating at B in a short length capillary tubing with a base of 1.0 to 2.0 mm. Concentric within A is a smaller glass tube, C (Fig. 3 (a) is an enlarged view of
19、this part). The end of C is first carefully heated in a blowpipe flame until the bore is reduced in size so as just to admit a wire or drill 0.75 mm in diameter. At this thickened end two flats are ground off on a sheet of fine alumina abrasive paper as at D in Fig. 3 (b). When in position in tube A
20、, end D fits snugly against the hole in capillary B. A rubber tubing connection at E holds the two tubes in position. F is a trap about 50 mm in diameter and 100 mm long, and G is an enlargement in the exit tube about 38 mm Accessed by UNIVERSITY OF SOUTH AUSTRALIA on 23 Jan 2008 AS 1180.7FNovember
21、19724 in diameter, containing glass wool to trap spray passing F. F is connected to the side of tube A. H is a 1-litre three-neck Woulff bottle or round-bottom chemically resistant flask in which A and F are secured by standard-taper ground joints, A occupying the centre opening with B protruding ju
22、st below the neck and J reaching to within 13 mm of the bottom of the bottle. The third opening serves to introduce and remove the reagent. A is connected through plasticized polyvinyl chloride tubing and glass tubing to rotameter graduated from 0 to 1000 litres of air per hour. The entrance to the
23、rotameter is connected with glass tubing to the sampling tube, and the exit of F is connected to a vacuum line. When properly regulated and a vacuum applied at F, most of the reagent enters F, furnishing a head of reagent at B, where the entering air resolves it into a fine mist which fills the enti
24、re bottle. The absorption flask shall be mounted in a light-tight box to protect it from light during the time a run is being made. Fig. 3. OZONE ABSORBING DEVICE (SPRAY-JET) (ii) Modified spray-jet device. A modification of the spray-jet method is in current use on some commercial ozone chambers. T
25、his involves absorbing the ozone in a buffered potassium iodide solution which contains a measured amount of Accessed by UNIVERSITY OF SOUTH AUSTRALIA on 23 Jan 2008 5AS 1180.7FNovember 1972 standard sodium thiosulphate solution. The time for the sodium thiosulphate to be consumed by reaction with i
26、odine is measured. This has the advantage over the unmodified spray-jet method, in that no iodine is volatilized, and no empirical factor is therefore necessary to correct for this loss. To use this modified method, it is necessary to alter slightly the equipment shown in Fig. 3. A round-bottom flas
27、k with a bottom drain cock shall be used with four necks or outlets. Two of these are used as depicted in Fig. 3, to house the spray-jet and the upper reservoir return tube, and the other two contain a pair of platinum electrodes and a burette for adding sodium thiosulphate solution. The modified ap
28、paratus is shown in Fig. 4. Fig. 4. MODIFIED SPRAY-JET APPARATUS (iii) Counter-current absorption column. This device absorbs the ozone from the air-ozone stream by providing a large surface area for gas-liquid contact. A buffered solution of potassium iodide percolates down through the column, and
29、this counter-current flow (solution downair stream up) removes the ozone from the air-ozone stream. Fig. 5 is a diagram for the counter-current column. Such a Accessed by UNIVERSITY OF SOUTH AUSTRALIA on 23 Jan 2008 AS 1180.7FNovember 19726 column can be fabricated by a qualified glass blower. The c
30、olumn is filled with clean 3 mm glass helices. These must be packed down tightly for efficient operation. Glass beads, 6 mm may be used at the bottom of the column below the inlet to prevent fragments of the helices from entering the stopcock. None of the dimensions on the drawing are critical, but
31、the lower part of the column should be not less than 200 mm. It has been found unnecessary to shield this column Fig. 5. COUNTER-CURRENT OZONE ABSORPTION COLUMN Accessed by UNIVERSITY OF SOUTH AUSTRALIA on 23 Jan 2008 7AS 1180.7FNovember 1972 from artificial lighting. It is not recommended that it b
32、e used in direct outdoor light. The advantages of this column over the spray-jet device are (a) the mechanical operation is simpler since no tedious spray adjustments are required, (b) there is no volatilization of iodine since it is carried promptly into the collection flask, and (c) no pressure dr
33、op occurs in the analysis apparatus train. Such a pressure drop will cause faulty ozone concentration measurements if a small undetected leak develops. 3.5 Titration Apparatus. Two methods are described for the titration differing only in the means used to determine the end point. The solution and w
34、ashings from the ozone absorption device may be titrated in a 250 ml wide-mouth flask or a beaker of equal size. A microburette shall be used to deliver the titrant and the solution stirred with an air or magnetic stirrer. (i)Microammeter method. A microammeter of 0-20 range. A heavy duty dry cell o
35、f 11/2V. One 1000 ohm and one 30 000 ohm resistor. Two platinum electrodes approximately 2.5 mm in diameter and 25 mm in length, embedded in glass tubing. Connect the resistors in series across the 11/2V battery and apply the potential across the 1 000 ohm resistor to the electrodes. The microammete
36、r is connected in series, with proper consideration for polarity, with the electrodes in this secondary circuit. NOTE: It is possible to use a microammeter with a 0-50 range instead of 0-20, but with a loss of sensitivity. (ii) Null indicator method. A special null meter can be employed that utilize
37、s a one- transistor amplification stage and represents a ten-fold increase in end-point sensitivity. This null meter may be used with any ozone absorption device. The initial reading is taken for the buffered potassium iodide solution with a potential of 100 mV applied to the electrodes. This potent
38、ial shall be automatically applied by the circuitry in the null meter. 4 REAGENTS. 4.1 Reagents Used for Determination of Ozone Concentration. (i)Reagent grade chemicals and distilled water shall be used in all tests. (ii) Buffer solution. Prepare a 0.025M solution of anhydrous disodium hydrogen pho
39、sphate (Na2HPO4) and a 0.025M solution of anhydrous potassium dihydrogen phosphate (KH2PO4). To prepare the buffer solution having a pH of 6.7 to 7.1, add 1.5 vol. of 0.025M Na2HPO4solution to 1 vol. of 0.025M KH2PO4solution. Shake thoroughly. (iii) Potassium iodide (KI). (iv) Sodium thiosulphate so
40、lution (0.020N).Prepare a 0.020N sodium thiosulphate Accessed by UNIVERSITY OF SOUTH AUSTRALIA on 23 Jan 2008 AS 1180.7FNovember 19728 (Na2S2O3) solution. This may be standardized by using a standard 0.0200N potassium bromate (KBrO3) solution to oxidize an excess quantity of potassium iodide (KI) in
41、 acid solution. Titrate the liberated iodine immediately with the Na2S2O3solution. The titration equipment for the Microammeter Method (Clause 3.5(i) may be used to determine the end point in this titration. Store the prepared 0.020N Na2S2O3solution in a cool dark place. (v) Sodium thiosulphate solu
42、tion (0.0020N). Prepare 0.0020N Na2S2O3solution for use in the ozone analysis by diluting the 0.020N solution 10 to 1, using a 10-ml pipette and 100-ml volumetric flask. Redeterminations of the normality of the 0.020N N2S2O3solution should be carried out weekly. 4.2 Determination of Ozone Concentrat
43、ion. 4.2.1 Absorption of ozone. (i)With spray-jet absorber. Dissolve 15 g of KI in 75 ml of buffer solution. Add this to the absorber flask, adjust the jet to produce a fine mist, and turn on the vacuum. Adjust the flow rate to 250 to 310 litres per hour. Allow the absorption to continue for a speci
44、fied time. (ii) Modified spray-jet absorber. A sufficient quantity of buffer solution containing 15 g of potassium iodide is added so that a pool of solution fully immerses the electrodes. The air-ozone stream is drawn through the apparatus. (iii) Counter-current absorption column (see Fig. 5). Prep
45、are 150 ml of the buffer solution, containing 15 g of KI and use part of this to flood and wet the column. Drain the solution out of the column and return to the reservoir R. Keep stopcock 4 closed during this operation. NOTES: 1.Do not use any type of stopcock grease on the column. The efficient op
46、eration of the column depends upon good contact between the air stream and fully wetted glass helices. If grease is used, the helices will gradually become coated, and efficient air-liquid contact will be lost. Since the column does not cause a sharp pressure drop in the line or analysis train, leak
47、s can be easily prevented by water lubrication of the glass joints of caps I and II when the clamps are used. 2.Do not allow any solution or water to enter the inlet tube. If it does enter, dry the tube interior with a stream of compressed air before starting any test. Keeping stopcock 4 tightly clo
48、sed will prevent any water from entering the tube. Lubricate ground-glass joints I and II with water and fit both caps in place. Use clamp on joint I. Close stopcock 1 and open stopcock 2. Adjust stopcock 5 so that approximately 20 drops per minute (d.p.m.) of solution are flowing into the column fr
49、om R. Open stopcock 3, apply the vacuum, open stopcock 4, and start the clock. Adjust the flow rate to 310 litres per hour. A Accessed by UNIVERSITY OF SOUTH AUSTRALIA on 23 Jan 2008 9AS 1180.7FNovember 1972 slight readjustment of the solution flow rate may be necessary due to the vacuum. At least 20 d.p.m. should be used. Continue the run for at least 30 minutes. After the elapsed time, close stopcock 4, stop the clock, shut off the vacuum and close stopcock 3. Close stopcock 2, open stopcock 5, and allow the column to fill up above the helices. If sufficient solution is not