1、Designation: D6492 99 (Reapproved 2011)Standard Practice forDetection of Hexavalent Chromium On Zinc and Zinc/Aluminum Alloy Coated Steel1This standard is issued under the fixed designation D6492; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、 of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice can be used to detect the presence ofhexavalent chromium on galvanized and zin
3、c/aluminum alloycoated steel surfaces. Hexavalent chromium-bearing treat-ments (passivates) can be applied to coated steels to preventstorage stain. While passivated 55 % aluminum-zinc alloycoated steel is commonly painted, passivated galvanized steelis not. Chrome passivation may interfere with the
4、 successfulpretreatment of galvanized steel, as well as contaminatecleaning and pretreatment baths on a coil coating line.1.2 The amount of hexavalent chromium that will cause theindicator to produce a discernible pink color is in the range of0.5 parts per million dissolved in the indicator solution
5、. It ispossible that a coated steel surface that produces a negativeresult does have chromium on the surface. If a material thatyields a negative result is suspected of having chromium on thesurface, instrumental methods should be used. Chrome depos-its of 1 mg/ft2can be easily missed by analytical
6、instrumentssuch as the scanning electron microscope with energy disper-sive x-ray analysis (EDXA) capability. Auger electron spec-troscopy (AES) or electron spectroscopy for chemical analysis(ESCA) can identify chemical species present in the levelsrequired for adequate detection. Stripping the meta
7、llic coatingand analyzing for chrome by atomic absorption or inductivelycoupled plasma can also give reliable results in detecting thepresence of chrome.1.3 This practice is designed to be a qualitative means ofscreening chrome passivated coils from those which are notchrome passivated.1.4 Some chro
8、mium-free passivates are being used com-mercially. Although these products will test negative forhexavalent chromium, they may interfere with cleaning andpretreating. Chromium bearing passivates that contain filmforming constituents such as acrylic resins are also beingcommercially applied. The reac
9、tion of these products to thespot test will vary. Abrading the surface with emery paper willimprove the likelihood of reliable detection. This technique isnot recommended for acrylic resin containing passivationtreatments.1.5 The values stated in SI units are to be regarded as thestandard. The value
10、s given in parentheses are for informationonly.1.6 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 practices and determine the applica-bility of regu
11、latory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D2092 Guide for Preparation of Zinc-Coated (Galvanized)Steel Surfaces for Painting3D5723 Practice for Determination of Chromium TreatmentWeight on Metal Substrates by X-Ray Fluorescence3. Apparatus3.1 The following materials
12、will be required to perform thestripping procedure:3.1.1 Dark colored or Brown Polyethylene Wash Bottle,(500 mL) or brown glass dropper bottle.3.1.2 Test Specimens, which may be cut panels or coil stock.4. Reagents4.1 The following chemical reagents are required to performthis procedure:4.1.1 1,5-Di
13、phenylcarbohydrazide.4.1.2 Acetone.4.1.3 Ethanol, 85 %.4.1.4 Phosphoric Acid.4.1.5 Distilled Water.1This practice is under the jurisdiction of ASTM Committee D01 on Paint andRelated Coatings, Materials, and Applications and is the direct responsibility ofSubcommittee D01.53 on Coil Coated Metal.Curr
14、ent edition approved Nov. 1, 2011. Published November 2011. Originallyapproved in 1999. Last previous edition approved in 2003 as D6492 99 (2003).DOI: 10.1520/D6492-99R11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Ann
15、ual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn. The last approved version of this historical standard is referencedon www.astm.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-
16、2959, United States.5. Preparation of Indicator Solution5.1 Combine 25 mL acetone with 25 mL ethanol in asuitable container. Add 0.5 g 1,5-diphenylcarbohydrazide andallow to dissolve completely. Vigorous agitation may berequired to effect complete dissolution. Slowly add 25 mL85 % phosphoric acid to
17、 25 mL distilled water. Add the dilutedphosphoric acid to the 1,5-diphenylcarbohydrazide solutionand mix well.5.2 The indicator solution has a shelf life of approximately6 h when exposed to light. Shelf life can be extended to severaldays if the solution is kept refrigerated. Discard the solution if
18、it becomes discolored.6. Procedure6.1 Remove oil and dirt from the metal surface to be tested.A thorough solvent wipe is generally sufficient. Apply severaldrops of the indicator to the material to be tested, or use a washbottle to apply a small amount of solution onto outer and innerwraps of a coil
19、. Samples of non-passivated material should betested side-by-side as controls. Any color change perceived inthe indicator on the material being tested should be comparedto the controls.7. Evaluation7.1 A pink color will develop if hexavalent chromium ispresent. The color can appear within 30 s for m
20、aterial with apassivation less than 1 week old. For material up to 1 monthold, the reaction time should be extended to 30 min. If thematerial is older than 1 month, the reaction time should beextended to 1 h. The color that is achieved and the timerequired for the color change to occur depends upon
21、age of themetal being tested, the amount of chromium on the surface, andthe age of the indicator. Heavier hexavalent chrome concen-trations will give a darker pink color.7.2 Even heavy chrome passivation (greater than 3 mg/ft2chrome) can yield a light pink color or no color change at all.The detecti
22、on of hexavalent chrome by this practice requireshexavalent chrome ions to be dissolved by the indicatorsolution. It is common for chrome passivation films to declinein hexavalent chrome content over time. The temperature andhumidity conditions under which the coils are stored willgreatly affect the
23、 residual hexavalent chrome concentration aswell as its solubility.8. Keywords8.1 diphenylcarbohydrazide; hexavalent chromium; passi-vate; passivation; steel; zinc; zinc/aluminumASTM International takes no position respecting the validity of any patent rights asserted in connection with any item men
24、tionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee
25、 and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meetin
26、g of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO
27、Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the ASTM website (www.astm.org/COPYRIGHT/).D6492 99 (2011)2
