This standard specifies a test method for testing the porosity or discontinuity of metal coatings. During the test, the coating tested does not react significantly with ferrocyanide and chloride ions, and is cathodic to the steel substrate. This method is particularly suitable for engineering chromium coatings. GB/T 17721-1999 Metallic coating porosity test Iron reagent test GB/T17721-1999 Standard download decompression password: www.bzxz.net
This standard specifies a test method for testing the porosity or discontinuity of metal coatings. During the test, the coating tested does not react significantly with ferrocyanide and chloride ions, and is cathodic to the steel substrate. This method is particularly suitable for engineering chromium coatings.

GB/T 17721 -- 1999
This standard adopts the international standard IS010309:1994 equivalent to the porosity test of gold flag covering layer
iron reagent test
This standard makes the following modifications and supplements to the international standard 5010309:1994:---In clause 4.2.1, "elasticizer 0P-10" is added to make it more convenient when the application of this standard is difficult. In clause 4.2.2, in order to facilitate the implementation of this standard, combined with the actual situation of the country and based on experimental verification, it is modified and supplemented. "The pH is adjusted to 6.0 ± 0.2 with hydrochloric acid solution (1-+9) or 5% (m/m) sodium hydroxide solution. The solution should be prepared as it is used." ---- The provisions on "test paper" are not clearly defined in the fourth inspection of ISO10309:1994. Considering that "test paper" is used in the test Because of its importance in testing, the provisions of *4. Test paper\ are supplemented in this standard. This standard was proposed by the State Bureau of Machinery Industry. This standard is under the jurisdiction of the National Technical Committee for Standardization of Metal and Non-metallic Coatings: The drafting unit of this standard is: Wuhan Institute of Material Protection. The drafters of this standard are Zhong Lichang, Zhu Sheng, and An Zhiling. GB/T17721—1999
ISO Foreword
ISO (International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of formulating international standards is generally carried out through ISO technical committees. If the member bodies are interested in the topics determined by a technical committee, they have the right to make representations to the committee: governmental and non-governmental international organizations in contact with ISO may also participate in this work. In all aspects of international electrotechnical standardization, ISO Closely cooperate with the International Electrotechnical Commission (IEC). The draft of the international standard developed by the technical committee is first sent to each member group for voting. According to ISO procedures, at least 75% of the member groups participating in the voting must approve it before it can be published as an international standard. International standard ISO10309 was developed by SC7 Corrosion Test Subcommittee of ISO/TC107 Metallic and other inorganic coatings technical committee:
1 Scope
National Standard of the People's Republic of China
Metallic coatings-Parosity tests
Iron reagent test
Metallic ceatings-ParositytestsFerroxyl test
GB;T17721—1999
cq1so10309:1994
This standard specifies a test method for testing the porosity or discontinuity of metallic coatings. During the test, the coating tested does not react significantly with ferrocyanide and chlorine, and is cathodic to the steel substrate: this method is particularly suitable for engineering chromium coatings. Note 1 During the 1Gmim test, the non-chemical solution will dissolve a layer of the coating material (see 5.2.3), so that sometimes the pores in the cathode layer are exposed again. Tests have shown that in actual use, such pores often reappear. 2 Referenced standards
The provisions contained in the following references constitute the provisions of this standard by reference in this standard. At the time of publication of this standard, the versions shown are valid. All standards will be revised. Parties using this standard should explore the possibility of using the latest version of the following standards: IS03696:1987 Specification and test methods for water used in analytical laboratories 3 Principle
At the bottom of the pore domain discontinuity of the metal covering layer, the matrix metal ions formed by the action of the corrosion cell migrate to the treated test paper close to the surface of the covering layer. When the test paper is exposed to the iron compound indicator solution, the matrix metal ions on the test paper are separated to form blue spots.
4 Reagents and Materials
4.1 Purity
The chemical reagents used in the test must be analytical grade reagents. The test water should be distilled water or deionized water with a conductivity not exceeding 20 μS/cm (see I503696).
4.2 Preparation of Reagent Solutions
4.2-1 Sodium Chloride Reagent
Dissolve 5 g of sodium chloride and 1 g of non-ionic wetting agent in 1 L of hot water (90°C). Then dissolve 50 g of gelatin or agar in the hot sodium chloride solution. The solution will produce a gel after cooling. It needs to be heated to 35°C to reliquefy it when used. Note 2: Various non-ionic wetting agents are available, such as emulsifier OP-1D. 4.2.2 Potassium Ferrocyanide Reagent
Dissolve 10 g of potassium ferrocyanide in 1 L of water and adjust the pH to 6.0 with hydrochloric acid solution (1+9) or 5% (m/m) sodium hydroxide solution. 0! 0. 2. The solution should be prepared as it is used.
4.3 Test paper
The test paper should have a certain strength when it is moistened and coagulated, such as filter paper. The test paper should not be contaminated before the test. Approved by the State Administration of Quality and Technical Supervision on April 8, 1999 and implemented on September 1, 1999
4.4 Optional instruments
GB/T 17721 --1999
Prepare a flat flexible plastic sheet (template) with square holes (size not less than 10 mm × 10 mm) to determine the area of ​​blue spots on the test paper.
5 Procedure
5-1 Sample pretreatment
Use appropriate organic solvents, such as 1.1.1-trichloroethane, to clean and degrease the surface of the sample to be tested. 5.2 Test paper treatment
5.2.1 Iron contamination test
The paper used to prepare the test paper must not be contaminated by iron. First, immerse the paper in sodium oxide solution, drain it, and then immerse it in potassium ferrocyanide solution. Compare the dried paper with the untreated paper. If blue spots appear or the appearance of the self-colored paper changes slightly, it proves that there is iron contamination. 5.2.2 Preparation
Cut the test paper of appropriate size (see 4.3), and immerse it in the sodium chloride gel solution (see 4.2.1). After the test paper is fully moistened, take out the test paper, wait for about 1 minute, and drip off the excess solution. bZxz.net
Note 3 Use a piece of test paper that can effectively de-moisten and drip off the excess liquid. Note 4: Directly dropping the oxidizing solution onto the surface of the test specimen will produce diffuse, rather than obvious, holes. Therefore, it is recommended to use test paper. 5.2.3 Application of test paper
Apply the soaked test paper to the clean surface of the tested coating. The test paper should be in full contact with the entire test surface, and no bubbles should be left, so that the sodium chloride solution can react with the exposed substrate metal. The test paper and the test surface should remain in contact for 10 minutes. If the test paper dries during the test, appropriate drops of sodium chloride solution should be added to moisten it, but the test paper should not be moved. Note 5: Test paper cut according to the shape of the test surface can be used for irregular surfaces or small surfaces. 5.2.4 Color development of test paper
Remove the test paper from the test surface and immediately immerse it in potassium ferrite solution (see 4.2.2) to make blue spots appear on the test paper corresponding to the pores or discontinuities in the coating.
5.3 Test paper inspection
Inspect the surface of the color-developed test paper to confirm whether the coating has pores or discontinuities. When the pores or discontinuities on the cover are exposed to the steel substrate, a visible blue spot will appear on the test paper. 5.4 Pore counting
Visually count the number of blue spots in the test area on the test paper. Note 6 For larger test areas, a plastic template (see 4.4) can be placed flat on the test paper. After the test paper develops color, it can be used to count the pores. 5.5 Repeat test
If it is necessary to repeat the test on the same area, the surface of the cover layer must be rinsed with hot distilled water (see 4.1) to remove the reaction products and residual liquid that may have been left on the surface of the cover layer during the previous test: the cleaned sample should be fully dried before testing. 6 Test results
The porosity rate is expressed as the average number of pores per unit area in the test area, that is, X pores/cm2. Or it can be expressed as the maximum number of pores/cm2 measured by the 10mm×10rnm counting template (see 4.4). Note 7 Due to the different specifications of different coatings, different products have different specifications and different thickness of coatings, this standard does not specify the qualified or unqualified judgment criteria.
7 Test report
The test report should include the following contents:
a) This standard number;
b) Test surface area;
|b) Reference to relevant coating or product specifications;
c) Test results.
GB/T17721—1999
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