1、Designation: B 368 97 (Reapproved 2003)e1Standard Test Method forCopper-Accelerated Acetic Acid-Salt Spray (Fog) Testing(CASS Test)1This standard is issued under the fixed designation B 368; the number immediately following the designation indicates the year oforiginal adoption or, in the case of re
2、vision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.e1NOTESections 8.1 and 10.1.
3、12 were editorially updated in July 2003.1. Scope1.1 This method prescribes the conditions required incopper-accelerated acetic acid-salt spray (CASS) testing forspecification purposes. The standard does not specify the typeof test specimen or exposure periods to be used for a specificproduct, nor t
4、he interpretation to be given to the results.1.2 This method is applicable to evaluating the corrosiveperformance of decorative copper/nickel/chromium or nickel/chromium coatings on steel, zinc alloys, aluminum alloys, andplastics designed for severe service. It is also applicable to thetesting of a
5、nodized aluminum. The suitability of this test andcorrelation of results with service experience should be deter-mined before it is specified for coating systems or materialsother than those mentioned in this paragraph.NOTE 1The following standards are not requirements. They arereferenced for inform
6、ation only: Practices B 537 and E 50, SpecificationsB 456 and B 604, and Test Method B 602.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practi
7、ces and determine the applica-bility of regulatory limitations prior to use. For more specificsafety precautionary information see 8.1.2. Referenced Documents2.1 ASTM Standards:B 117 Practice for Operating Salt Spray (Fog) Apparatus2B 162 Specification for Nickel Plate, Sheet, and Strip3B 456 Specif
8、ication for Electrodeposited Coatings of Cop-per Plus Nickel Plus Chromium and Nickel Plus Chro-mium4B 537 Practice for Rating of Electroplated Panels Subjectedto Atmospheric Exposure4B 602 Test Method for Attribute Sampling of Metallic andInorganic Coatings4B 604 Specification for Decorative Electr
9、oplated Coatingsof Copper Plus Nickel Plus Chromium on Plastics4D 1193 Specification for Reagent Water5E 50 Practices for Apparatus, Reagents, and Safety Consid-erations for Chemical Analysis of Metals, Ores, andRelated Materials63. Significance and Use3.1 The CASS test is widely employed and is use
10、ful forspecification acceptance, simulated service evaluation, manu-facturing control, and research and development. It was devel-oped specifically for use with decorative, electrodepositednickel/chromium and copper/nickel/chromium coatings. Use ofthe test has improved the quality of electroplated p
11、arts and ledto the development of new and superior electroplating pro-cesses.4. Apparatus4.1 The apparatus required for the CASS test consists of afog chamber, a salt-solution reservoir, a supply of compressedair, one or more atomizing nozzles, specimen supports, provi-sion for heating the chamber,
12、and necessary means of control.4.2 The size and detailed construction of the apparatus areoptional, provided the conditions meet the requirements of thismethod. The construction of the apparatus is described in theappendix of Test Method B 117. For the CASS test, however,1This method is under the ju
13、risdiction of ASTM Committee B08 on Metallic andInorganic Coatings and is the direct responsibility of Subcommittee B08.10 on TestMethods.Current edition approved May 10, 2003. Published July 2003. Originallyapproved in 1961. Last previous edition approved in 1997 as B 368 97.The CASS test was devel
14、oped by the initiative of the Research Board of theAmerican Electroplaters Society under AES Project 15.2Annual Book of ASTM Standards, Vol 03.02.3Annual Book of ASTM Standards, Vol 02.04.4Annual Book of ASTM Standards, Vol 02.05.5Annual Book of ASTM Standards, Vol 11.01.6Annual Book of ASTM Standar
15、ds, Vol 03.05.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.the requirements for air pressure and temperature are typically0.08 to 0.12 MPa and 60 to 65C, respectively. The actual airpressure will be that required to produce the pr
16、oper collectionrate (see 8.3.1).4.3 The apparatus shall be constructed so that drops ofsolution that accumulate on the ceiling or cover of the chamberdo not fall on the specimens being tested. Drops of solutionthat fall from the specimens shall not be returned to thesolution reservoir for respraying
17、.4.4 Materials of construction shall not affect the corrosive-ness of the fog, nor be themselves corroded by the fog.5. Test Solution5.1 Prepare the salt solution by dissolving 5 parts by weightof salt in 95 parts of water conforming to Specification D 1193,Type IV. The salt shall be sodium chloride
18、 (NaCl), ACS reagentgrade, or equivalent. The pH of this solution shall be between6.0 and 7.0. Impurities or contam-ination of either the salt orthe water, or both, should be suspected if the pH is outside ofthis range (Note 2).5.2 Add 0.25 g of reagent grade copper chloride (CuCl22H2O) to each litr
19、e of the salt solution; dissolve and mixthoroughly.5.3 The pH of the salt-copper solution shall be adjusted tothe range of 3.1 to 3.3, as measured on a sample of thecollected spray, by the addition of glacial acetic acid, ACSreagent grade, or equivalent (Note 3). The pH measurementshall be made elec
20、trometrically at 25C. Before the solution isatomized, it shall be free of suspended solids (Note 4).NOTE 2A solution having a specific gravity of 1.030 to 1.040, whenmeasured at a temperature of 25C, will meet the concentration require-ment. It is suggested that a daily check be made.NOTE 3The initi
21、al solution may be adjusted to a pH of 3.0 to 3.1, withthe exception that the pH of the collected fog will be within the specifiedlimits. Adjustment of the initial pH for makeup solution is based upon therequirements to maintain the required pH of the collected samples. If lessthan 1.3 or more than
22、1.6 mL of the glacial acetic acid are required per litreof sodium chloride and copper solution to attain the specified pH, somediscrepancy in the system may be suspected (the purity of the water orsalt, or both; the accuracy of the pH meter; the general cleanliness of thesystem; etc.).NOTE 4The fres
23、hly prepared salt solution may be filtered or decantedbefore it is placed in the reservoir, or the end of the tube leading from thesolution to the atomizer may be covered with a double layer of cheesecloth to prevent plugging of the nozzle.6. Air Supply6.1 The compressed air supply to the nozzle or
24、nozzles foratomizing the test solution shall be free of oil and dirt (Note 5).Pressure shall be adequate to provide a specified condensaterate. Pressure of 0.10 6 0.02 MPa has been found satisfactory(Note 6).NOTE 5The air supply can be freed of oil and dirt by passing itthrough a water scrubber or a
25、t least 60 cm of suitable cleaning material,such as sheeps wool, excelsior, slag wool, or activated alumina. Com-mercial filters for compressed air may be used.NOTE 6Atomizing nozzles may have a critical pressure, at which anabnormal increase in the corrosiveness of the salt fog occurs. If the criti
26、calpressure of a nozzle has not been determined with certainty, control offluctuation in the air pressure within 60.0007 MPa by installing a pressureregulator valve minimizes the possibility that the nozzle will be operatedat its critical pressure.7. Test Specimens7.1 The type and number of test spe
27、cimens to be used, aswell as the criteria for the evaluation of the test results, shall bedefined in the specifications covering the material or productbeing tested or shall be mutually agreed upon between thepurchaser and the supplier.8. Procedure8.1 Preparation of Test Specimens Clean metallic and
28、metallic coated specimens. Unless otherwise agreed upon,clean decorative copper/nickel/chromium or nickel/chromiumcoatings immediately before testing by wiping significantsurfaces with a cotton pad saturated with a slurry containing 10g of pure magnesium oxide powder (ACS reagent grade) in 100mL of
29、distilled water. Upon rinsing in warm running water, besure that the clean surface is free of water break. Anodizedaluminum parts may be cleaned with inhibited 1,1,1-trichloroethane or other suitable organic solvent (see Warning).Do not clean organic and other nonmetallic coated specimens.Other meth
30、ods of cleaning, such as the use of a nitric-acidsolution for the chemical cleaning or passivation of stainlesssteel specimens, are permissible when agreed upon betweenthe purchaser and the supplier. Take care that the specimensafter cleaning are not recontaminated by excessive or carelesshandling.
31、Protect the cut edges of plated, coated, or multilay-ered materials and areas containing identification marks or incontact with the racks or supports with a coating that is stableunder the conditions of the test, such as wax, stop-off lacquer,or pressure-sensitive tape. (Warning1,1,1-Trichloroethane
32、should be used in a well-ventilated area away from openflames.)8.2 Positioning of SpecimensPosition the specimens inthe CASS test chamber during the test so that the followingconditions are met:8.2.1 Support or suspend the specimens 15 6 2 from thevertical and preferably parallel to the principal di
33、rection ofhorizontal flow of fog through the chamber, based upon thedominant surface being tested. Support or suspend automobileparts, however, so as to expose all significant surfaces at thegeneral level of the condensate collectors. If the position on theautomobile is vertical, place the part in a
34、n incline position 15from vertical to allow surface wetting by the condensate. If theposition on the automobile is facing down, rotate the partapproximately 180 to test the significant surface. If there areseveral significant surfaces at different angles, expose eachsurface of one or more specimens.
35、8.2.2 Make sure the specimens do not come in contact witheach other or any other metallic material or any materialcapable of acting as a wick.8.2.3 Place each specimen so as to permit free settling of fogon all specimens.8.2.4 Make sure the salt solution from one specimen doesnot drip on any other s
36、pecimen.8.2.5 Place the specimens in the chamber just prior tobringing the test chamber to the required temperature andB 368 97 (2003)e12turning on the air, since storage in an idle chamber overnight,or for other significant length of time, can affect test results.NOTE 7Suitable materials for the co
37、nstruction or coating of racks andsupports are glass, rubber, plastic, or suitably coated wood. Bare metalshould not be used. Specimens are preferably supported from the bottomor the side. Slotted wooden strips are suitable for the support of flat panels.Suspension from glass hooks or waxed string m
38、ay be used as long as thespecified position of the specimens is obtained. If necessary, suchsuspension may be made by means of secondary support at the bottom ofthe specimens.8.3 Conditions in the Salt-Spray ChamberMaintain theexposure zone of the CASS test chamber at a temperature of496 1C during t
39、he exposure period (Note 8). After closing thetest chamber, bring the temperature to 49C before the fog isturned on. The test duration shall commence when the tem-perature is 49 6 1C and fog is present in the chamber. Heatthe air supply by passing fine bubbles through heated distilledor deionized wa
40、ter (see Specification D 1193, Type IV) so thatthe temperature of the air after expansion at the nozzle is 49 61C. Record the temperature within the exposure zone of theclosed cabinet (Note 9) twice a day at least 7 h apart (exceptSaturdays, Sundays, and holidays, when the salt-spray test isnot inte
41、rrupted for exposing, rearranging, or removing testspecimens or to check and replenish the solution in thereservoir).NOTE 8This can be best accomplished by preheating the chamber to49C before starting solution atomization.NOTE 9A suitable method to record the temperature is by a thermom-eter that ca
42、n be read from outside the closed cabinet. The recordedtemperature must be obtained with the salt-spray chamber closed to avoida false low reading, because of wet-bulb effect when the chamber is open.Automatic control of temperature in the chamber and a continuous recordof temperature are desirable.
43、8.3.1 Place at least two clean fog collectors within theexposure zone so that no drops of solution will be collectedfrom the test specimens or any other source. Position thecollectors in the proximity of the test specimens, one nearest toany nozzle and the other farthest from all nozzles. A preferre
44、darrangement is shown in Fig. 1. Make sure that the fog is suchthat for each 80 cm2of horizontal collecting area each collectorcollects from 1.0 to 2.0 mL/h of solution, based on a typical runof at least 22 h (Note 10). Maintain the sodium chlorideconcentration of the collected solution between 4.5
45、and 5.5mass % (Note 11 and Note 12). Dilution and evaporation ofcondensate should be avoided (Note 13).NOTE 10Suitable collecting devices are glass funnels with the stemsinserted through stoppers into graduated cylinders. Funnels with adiameter of 10 cm (area of about 80 cm2) and 50-mL cylinders are
46、preferred.NOTE 11A solution having a specific gravity of from 1.030 to 1.040,when measured at 25C, will meet the concentration requirement. Theconcentration may also be determined as follows: Dilute 5 mL of thecollected solution to 100 mL with distilled water and mix thoroughly;pipet a 10-mL aliquot
47、 into an evaporating dish or casserole; add 40 mL ofdistilled water and 1 mL of 1% potassium chromate (K2CrO4) (ACSreagent grade with less than 0.005% chloride) and titrate with 0.1 N silvernitrate (AgNO3) (ACS reagent grade) solution to the first appearance of apersistent red coloration. A test sol
48、ution that requires between 3.9 and 4.9mL of 0.1 N Ag NO3solution will meet the concentration requirements.NOTE 12It has not been found necessary to check copper concentra-tion of the collected solution.NOTE 13Factors that may contribute to dilution and evaporation ofcondensate and make it difficult
49、 to control the concentration are lowertemperature, inadequate cover insulation, and prolonged storage of testsolution at above room temperature.8.3.2 Direct or baffle the nozzle or nozzles so that none ofthe spray can impinge directly on the test specimens.8.4 Continuity of TestUnless otherwise specified in thespecification covering the material or product being tested, thetest shall be continuous for the duration of the entire testperiod. Continuous operation implies that the chamber beclosed and the spray operating continuously, except for theshort d
