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1、 WORLDWIDE ENGINEERING STANDARDS Test Method Materials GMW3034 Absence of Hexavalent Chrome, Cr VI, in Coatings Copyright 2006 General Motors Corporation All Rights Reserved October 2006 Originating Department: North American Engineering Standards Page 1 of 2 1 Scope This test is used to prove the a
2、bsence of Cr VI in coatings. Note: Nothing in the specification supersedes applicable laws and regulations unless specific exemption has been obtained. Note: In the event of conflict between the English and domestic language, the English language shall take precedence. 2 References This test method
3、is derived from ISO 3613; 1980; section 3.3, and is equivalent to DIN 50993-1. Note: Only the latest approved standards are applicable unless otherwise specified. 2.1 External Standards/Specifications. DIN 50993 ISO 3613 2.2 GM Standards/Specifications. None 3 Test Equipment 3.1 Ordinary Laboratory
4、Apparatus. 3.2 Colorimeter or Spectrophotometer. With a colorimeter, use a filter having a mean transmission of 540 nm. A wavelength of 540 nm shall be set for the spectrophotometric measurement. Use an absorption cell with an optical path length of 1 cm in both cases. 4 Test Material 4.1 Test Sampl
5、e. Coating materials. 4.2 Reagents. Use only reagents of recognized analytical grade, and only distilled water or water of equivalent purity. 4.2.1 Sulfuric Acid, 4.5 M. Mix three (3) volumes of water with one (1) volume of concentrated sulfuric acid (1.84 g/mL). Note: When preparing sulfuric acid s
6、olution wear safety glasses. Take a vessel of heat resistant glass and fill it with three (3) volumes of water. Add one (1) volume of concentrated sulfuric acid slowly or in small portions, while stirring the water. Never pour water into concentrated sulfuric acid. 4.2.2 Diphenylcarbazide Solution.
7、Dissolve 0.5 g of diphenylcarbazide in 50 mL of acetone. Dilute slowly, while stirring, with 50 mL of water (rapid mixing may result in precipitation of diphenylcarbazide) For maximum stability store under refrigeration in an amber colored glass bottle. Note: Be aware that diphenylcarbazide is a can
8、cer producing material. When handling it, make sure that you do not breathe in the dust or get otherwise in contact with it. 4.2.3 Cr VI Standard Solution. Dissolve 0.113 g K2Cr2O7 in water and dilute it in a volumetric flask to 100 mL. Pipette 0.25 mL of this solution into a second 100 mL volumetri
9、c flask and dilute to the mark with water. The second solution contains 1 g Cr VI per mL (5 mL = 5 g Cr VI). 5 Test Method 5.1 Summary of Test Method. The test sample is leached with boiling water for 5 minutes. Hexavalent chrome compounds will react with diphenylcarbazide and form a red colored com
10、plex that can be observed visually, and, or detected colorimetrically or spectrophotometrically. 5.2 Test Sample Preparation. The test sample shall have a surface area of 50 5 cm. From small parts take the suitable number of samples. From larger parts, use only a 50 5 cm segment. 5.3 Test Procedure.
11、 5.3.1 Place the sample in a 100 mL beaker with volume graduation, or other suitable beaker with volume graduation. Add 50 mL water. Heat the water to boiling and keep it boiling for exactly 5 minutes. 5.3.2 Remove the test piece and cool the beaker and its contents to room temperature. Fill up with
12、 GMW3034 GM WORLDWIDE ENGINEERING STANDARDS Copyright 2006 General Motors Corporation All Rights Reserved Page 2 of 2 October 2006 water to 50 mL if some water evaporated. If the solution is milky or has a precipitate, filter through a paper filter into a dry beaker. Add 1.5 mL of dilute sulfuric ac
13、id solution (4.5 M) and 1 mL of diphenylcarbazide solution; then mix well. Evaluate the color against the comparison solution (see “Comparison Solution Preparation”). A red color indicates Cr VI. 5.3.3 If a clear evaluation against the comparison solution is not possible visually, the sample is pour
14、ed into an absorption cell and after a reaction time of 2 minutes, it is measured with a spectrophotometer against the comparison solution. 5.3.4 Colorimetric or spectrophotometric measurement is to be performed when water leaching produces a colored solution which interferes with the visual evaluat
15、ion. 5.3.5 Comparison Solution Preparation. 5.3.5.1 For comparison, dilute 5 mL of the Cr VI- standard solution (5 mL = 5 g Cr VI) to 50 mL with water. This solution is treated in the same way as the sample solution (5.3). 5.3.5.2 If according to this method, the coating is found to be Cr VI free, i
16、t still may be that a Cr VI containing prime coat is covered by a Cr VI free top coat. In this case, scrape the coating in thin layers with a suitable instrument and test against the test sample together with the coating particles. 6 Evaluation and Rating The coating is accepted to be free of Cr VI
17、(0.1 g/cm2) if the red color of the test sample solution is less than the comparative solution visually, or the absorption of the sample solution at 540 nm is less than the comparative solution absorption at 540 nm. 7 Report Not applicable. 8 Safety This method may involve hazardous materials, opera
18、tions, and equipment. This method does not propose to address all the safety problems associated with its use. It is the responsibility of the user of the method to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 9 Notes 9.1 G
19、lossary. Not applicable. 9.2 Acronyms, Abbreviations, and Symbols. Not applicable. 10 Coding System This test method shall be referenced in other documents, drawings, VTS, CTS, etc. as follows: Test per GMW3034 11 Release and Revisions 11.1 Release. This standard originated in March 1998. It was first approved by GM in October 1999. It was first published in October 1999. 11.2 Revisions. Rev Approval Date Description (Organization) A APR 2001 Editorial, Section 4.2.3 (GM) B SEP2006 Added information on DIN standard and adapted legal limit in section 6 (GM)