GB 12305.4-1990 Test methods for metal coatings - Gold and gold alloy electroplated coatings - Part 4: Test for gold content GB12305.4-1990 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Metallic coatingsbZxz.net
Test methods for gold and gold alloy electroplated coatings
Part 4: Determination of gold content
Metailic coatings : Test methods electrodeposited goldand gold alloy coatings Part 4: Detemination of gold contentG12305.4—90
This standard is equivalent to the international standard IS0) 4524/1—1985 "Test methods for metal coatings: gold and gold-containing electroplated coatings Part 4: Determination of gold content".
1 Subject content and scope of application
This standard specifies the method for determining the gold content in gold and gold alloy coatings. This standard is applicable to the determination of gold content in gold and gold alloy electroplated coatings for engineering, installation and protection. 2 Reference Standards
GB12305.1 Metallic Coatings Test Methods for Gold and Gold Alloy Coatings Part I Measurement of Coating Thickness 3 Overview
The gold content of some gold alloy coatings is less than 90%. When the coating is separated from the base metal with nitric acid, some alloy elements may dissolve in the nitric acid solution, resulting in a higher measurement result. In this case, the gold coating should be peeled off from the base by mechanical methods. In order to obtain accurate measurement results, it is necessary to improve the weighing accuracy and require a larger sample. If necessary, a particularly thick electroplated sample should be prepared, but there is no necessary restriction on the area of ​​the work to be measured. The sample can be one or more small parts obtained from a plating tank, or a large electroplated area (including sides and edges) cut from a large workpiece. If the supplier and the buyer agree that the gold content should be greater than 99%, then the two parties should sign a special agreement to ensure the purity of the gold: this agreement should include spectral analysis of trace impurities with particularly thick coatings, or control of the gold plating solution to ensure that the contamination of metal impurities does not exceed the regulations. When the gold content is less than 99%, the determination methods 4 and 5 of this standard should be used. Other methods, such as the electron probe method, can also be used. Remove one or more test pieces from the sample by appropriate methods. If necessary, one or more complete workpieces can be cut into appropriate sizes. Mechanical methods should be used as much as possible to remove the base metal on the sample. Place the sample in a small beaker and add a certain amount of dilute nitric acid (1 volume of concentrated nitric acid plus 3 volumes of distilled water) at a temperature of about 20°C to completely dissolve the base metal and the bottom layer. However, in the case of alloy plating, the acid will dissolve some gold elements. It should be particularly noted that when the base metal contains tin, the tetravalent tin hydroxide adheres tightly to the gold plating. In order to prevent the formation of tetravalent hydroxide, 2% (V/V) hydrochloric acid or 5% (V/V) fluoroboric acid can be added to the dilute nitric acid and the solution can be poured out. The remaining gold plating is washed several times with distilled water and dried at about 100°C. 4 Fire assay method
can be determined using a 5Ⅱ gold plating. In order to obtain a higher accuracy, a larger amount of gold plating should be used for the determination as much as possible. 4.1 Procedure
Approved by the State Administration of Technical Supervision on April 6, 1990
Implementation on January 1, 1991
GB12305.4-90
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Use an analytical balance to weigh the gold plating accurately to 0.01 mg, and wrap the sample with a certain amount of pure steel and a small piece of pure copper in a piece of lead foil (analytical pure). The mass of silver is equivalent to 2-2.5 times the mass of the gold sample, the mass of copper is about 0.1 times the mass of the gold sample, and the mass of the lead foil is about 30 times the mass of the sample, but it cannot be less than 1g. Put the wrapped sample in a muffle furnace at 1100-1150℃, burn for 30min, open the furnace door, continue burning for 1h, flatten the small ball, anneal at about 700℃ for about 1min, press into thin strips and anneal again, immerse the thin strips in nitric acid with p=1.2g/mL (about 25%), and then immerse in nitric acid with p=1.3g/mL (about 45%). Both concentrations of nitric acid should be heated to boiling and kept in a fusant state, heat treat at about 700℃ for 5min, weigh the gold obtained, accurate to 0.01mg, take one or more standard samples with gold content and alloy element content close to the sample to be tested, and do parallel tests with the sample to be tested. 4.2 Calculation
The gold content w in the coating is expressed as mass percentage, which can be calculated by the following formula: 100m
In the formula, m. The mass of the coating weighed, mg: m—the mass of the sample obtained by this test method, ing. 5 Spectrophotometry and atomic absorption spectrometry
Use the chemical method specified in GB12305. to wash and dry the coating and weigh it, and then dissolve the sample in hot aqua regia for determination. 6 Test report
The test report should at least include the following contents: and. The relevant contents of this standard, including the terms of the specific test method used; the test results and the expression form of the test results, b.
Abnormal phenomena observed during the test; c.
d. Any operations not included in this part of this standard and its referenced standards; other relevant information required by the purchaser.
Additional remarks:
This standard was proposed by the Ministry of Machinery and Electronics Industry of the People's Republic of China: This standard is under the jurisdiction of the National Technical Committee for Standardization of Metallic and Non-metallic Coatings. This standard was drafted by the Technology Research Institute of the Ministry of Machinery and Electronics Industry. The main drafters of this standard are Han Shuhui and Zhao Shuying.
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