1、4B117-19TABLE 1 Maximum Allowable Limits for Impurity Levels inbefore it is placed in the reservoir,or the end of the tube leading from theSodium Chloridesolution to the atomizer may be covered with a double layer of cheeseclothNorE 1-A measurable limit for anti-caking agents is not being definedto
2、prevent plugging of the nozzle.as a result of how salt is manufactured.During salt manufacturing.it isNorE 6-The pH can be adjusted by additions of dilute ACS reagentcommon practice to create salt slurry from the raw salt mined.Agrade hydrochloric acid or sodium hydroxide solutions.crystallization p
3、rocess then captures the pure salt from this slurry.Somenaturally occurring anti-caking agents can be formed in this process and9.Air Supplyare not removed from the resultant product.Avoid salt products where9.1 The compressed air supply to the Air Saturator Towerextra anti-caking agents are added.A
4、dditionally,when doing an elementalshall be free of grease,oil,and dirt before use by passinganalysis of salt,there can be trace elements present that are either astand-alone element or part of an anti-caking agent.It is not economicallythrough well-maintained filters(Note 7).This air should befeasi
5、ble to know where such elements came from due to the long list ofmaintained at a sufficient pressure at the base of the Airpossible anti-caking agents for which there would have to be testing.Saturator Tower to meet the suggested pressures of Table 2 atTherefore,a salt product that meets the impurit
6、y.halide,and copper limitsthe top of the Air Saturator Tower.with no anti-caking agents added will be acceptable.The salt supplier canprovide an analysis of the salt with a statement indicating that anti-cakingNorE 7-The air supply may be freed from oil and dirt by passing itagents were not added to
7、 the product.through a suitable oil/water extractor(that is commercially available)toImpurity DescriptionAllowable Amountstop any oil from reaching the Air Saturator Tower.Many oil/waterTotal Impurities0.3%extractors have an expiration indicator,proper preventive maintenanceHalides(Bromide,Fluoride
8、and lodide)excluding Chloridee0.19%intervals should take these into account.Copper0.3 ppm9.2 The compressed air supply to the atomizer nozzle orAnti-caking AgentsNone Addednozzles shall be conditioned by introducing it into the bottomA A common formula used to calculate the amount of salt required b
9、y mass toachieve a 5%salt solution of a known mass of water is:of a tower filled with water.A common method of introducingthe air is through an air dispersion device(X1.4.1).The level0.053 x Mass of Water=Mass of NaCl requiredof the water must be maintained automatically to ensureThe mass of water i
10、s 1 g per 1 mL.To calculate the mass of salt required inadequate humidification.It is common practice to maintain thegrams to mix 1 L of a 5%salt solution,multiply 0.053 g by 1000 g(35.27 oz,themass of 1 Lof water).This formula yields a result of 53g(1.87 oz)of NaCl requiredtemperature in this tower
11、 between 46 C and 49 C(114 F andfor each litre of water to achieve a 5%salt solution by mass.121 F)to offset the cooling effect of expansion to atmosphericThe 0.053 multiplier for the sodium chloride used above is derived by thepressure during the atomization process.Table 2 shows thefollowing:1000
12、g(mass of a full litre of water)divided by 0.95temperature,at different pressures,that are commonly used to(water is only 95%of the total mixture by mass)yields 1053 goffset the cooling effect of expansion to atmospheric pressure.This 1053 g is the total mass of the mixture of 1 L of watewith a 5%so
13、diumchloride concentration.1053 g minus the original weight of the litre of water.9.3 Careful attention should be given to the relationship of1000 g.yields 53 g for the weight of the sodium chloride.53 g of total sodiumtower temperature to pressure since this relationship can havechloridedivided by
14、the original 1000 g of water yields a 0.053multiplier for thesodium chlonde.a direct impact to maintaining proper collection rates(Note 8).As an example:to mix the equivalent of 200 L(52.83 gal)of 5%sodium chlondeIt is preferable to saturate the air at temperatures well above thesolution,mix 10.6 kg
15、(23.37 Ib)of sodium chloride into 200 L(52.83 gal)of waterchamber temperature as insurance of a wet fog as listed in200 L of water weighs 200 000 g.200 000 g of water x 0.053(sodium chloridemultiplier)10 600 g of sodium chloride,or 10.6 kg.Table 2.In order to ensure that the proper salt concentratio
16、was achieved whenmixingthe solution,it is recommended that the solution be checked with either a salimeterNore 8-If the tower is run outside of these suggested temperature andhydrometer or specific gravity hydrometer.When using a salimeter hydrometer,thepressure ranges to achieve proper collection r
17、ates as described in 10.2 ofeasurement should be between 4%and 6%at 25 C(77F).this practice,other means of verifying the proper corrosion rate in thetthe purity of the salt used is%then the limits for halides can be ignored.chamber should be investigated,such as the use of control specimensThis is d
18、ue to the fact that the halides cannot be 20.1%with a salt purity of(panels of known performance in the test conducted).It is preferred that99.9%.If the salt used is of lower purity,then test for halides.control panels be provided that bracket the expected test specimenperformance.The controls allow
19、 for the normalization of test conditionsduring repeated running of the test and will also allow comparisons of test(/When the pH of a salt solution is adjusted at room temperature,andresults from different repeats of the same test.(Refer to Appendix X3.atomized at 35C(95F).the pH of the collected s
20、olution will be higherEvaluation of Corrosive Conditions,for mass loss procedures).than the original solution due to the loss of carbon dioxide at the highertemperature.When the pH of the salt solution is adjusted at room10.Conditions in the Salt Spray Chambertemperature,it is therefore necessary to
21、 adjust it below 6.5 so the collected10.1 Temperature-The exposure zone of the salt spraysolution after atomizing at 35C(95F)will meet the pH limits of 6.5 tochamber shall be maintained at 35C+2 C(95 F+3 F)7.2.Take about a 50 mL sample of the salt solution as prepared at roomtemperature.boil gently
22、for 30 s.cool,and determine the pH.When theEach set point and its tolerance represents an operationalpH of the salt solution is adjusted to 6.5 to 7.2 by this procedure,the pHcontrol point for equilibrium conditions at a single location inof the atomized and collected solution at 35 C(95 F)will come
23、 withinthis range.(2)Heating the salt solution to boiling and cooling to 35 C(95 F)andTABLE 2 Suggested Temperature and Pressure Guidelinemaintaining it at 35 C(95 F)for approximately 48 h before adjusting thefor the Top of the Air Saturator Tower for the Operation of a TestpH produces a solution th
24、e pH of which does not materially change whenat35C(95F)atomized at 35 C(95 F).(3)Heating the water from which the salt solution is prepared to 35 CAir Pressure,kPaTemperature.C Air Pressure,psi Temperature.F114(95 F)or above,to expel carbon dioxide,and adjusting the pH of the salt964714117solution w
25、ithin the limits of 6.5 to 7.2 produces a solution the pH of which1104816119does not materially change when atomized at 35C(95 F).1244918121Nore 5-The freshly prepared salt solution may be filtered or decanted4B17-19the cabinet which may not necessarily represent the uniformityappropriate method can
26、 be chosen by the user.of conditions throughout the cabinet.The temperature withinNore 11-Suitable collecting devices are glass or plastic funnels withthe exposure zone of the closed cabinet shall be recorded(Notethe stems inserted through stoppers into graduated cylinders,or crystal-lizing dishes.F
27、unnels and dishes with a diameter of 10 cm(3.94 in.)have9)at least once daily(except on Saturdays,Sundays,andan area of about 80 cm2(12.4 in.2).holidays when the salt spray test is not interrupted forNorE 12-The specific gravity of salt solution will change withexposing,rearranging,or removing test
28、specimens or to checktemperature.Table 3 shows salt concentration and density versus tempera-and replenish the solution in the reservoir)tureand can be used to determine if the sample measured is withinspecification.The sample to be measured may be a composite sample fromNorE 9-A suitable method to
29、record the temperature is by a continu-multiple fog-collecting devices within a single cabinet,if necessary,toous recording device or by a thermometer which can be read from outsideobtain sufficient solution volume for measurement.the closed cabinet.The recorded temperature must be obtained with the
30、Table 3 shows the salt concentration and salt density of 4%5%andsalt spray chamber closed to avoid a false low reading because of wet-bulb6%salt solution between 20C and 40C.A measurement that fallseffect when the chamber is open.within the range between 4 and 6%is acceptable.It is important to unde
31、rstand the equipment being used to measure10.2 Atomization and Quantiry of Fog-Place at least twospecific gravity.One common practice for specific gravity measurement isclean fog collectors per atomizer tower within the exposurethe use of a hydrometer.If used,careful attention to the hydrometer type
32、zone so that no drops of solution will be collected from the testis important as most are manufactured and calibrated for measurements atspecimens or any other source.Position the collectors in the15.6 C(60 F).Since salt density is temperature dependent,an offset willproximity of the test specimens,
33、one nearest to any nozzle andbe necessary to make an accurate measurement at other temperatures.Contact the hydrometer manufacturer to find the proper offset for thethe other farthest from all nozzles.A typical arrangement ishydrometer being used.shown in Fig.1.The fog shall be such that for eachNor
34、E 13-Salt solutions from 2 to 6%will give the same results,80 cm(12.4 in.)of horizontal collecting area,there will bethough for uniformity the limits are set at 4 to 6%collected from 1.0 mL to 2.0 mL of solution per hour based on10.3 The nozzle or nozzles shall be so directed or baffledan average ru
35、n of at least 16 h(Note 11).The sodium chloridethat none of the spray can impinge directly on the testconcentration of the collected solution shall be 5%1specimens.mass(Notes 11-13).The pH of the collected solution shallbe 6.5 to 7.2.The pH measurement shall be made as described11.Continuity of Expo
36、surein 8.2(Note 4).Both sodium chloride concentration andvolume of condensate collected(measured in mL)shall be11.1 Unless otherwise specified in the specifications cover-ing the material or product being tested,the test shall berecorded once daily(except on weekends,or holidays when thecontinuous f
37、or the duration of the entire test period.Continu-salt spray test is not interrupted for exposing,rearranging,orremoving test specimens or to check and replenish the solutionous operation implies that the chamber be closed and the sprayin the reservoir.The maximum interval between these dataoperatin
38、g continuously except for the short daily interruptionscollection measurements shall not exceed 96 h).NorE 10-Common methods of measuring sodium chloride concentra3Thermodynamic Properties of the NaCl H20 system Il.Thermodynamiction are specific gravity hydrometer,salimeter hydrometer,refractometer,
39、Properties of NaCl(ag),NaCl.2H20(cr).and Phase Equilibria,Journal of Phrysicsand titration.This list is not all inclusive of every method,and anand Chemistry Reference Data.Vol.21.No.4.1992.Collectorsmin 10 cmMin.of 10 cmMin.of 20 cmWAtomizeTowerMin.of 20 cmFog ChamberNorE 1-This figure shows a typical fog collector arrangement for a single atomizer tower cabinet.The same fog collector arrangement is alsoapplicable for multiple atomizer tower and horizontal(Ttype)atomizer tower cabinet constructions as well.FIG.1 Arrangement of Fog Collectors
