Standard Test Method for Measurement of Impedance of Anodic Coatings on Aluminum

This test method describes the conditions and equipment for measuring the impedance of anodic coatings on aluminum. Such measurements have been used to evaluate the quality of seal of an anodic coating. The test method does not prescribe the procedure for producing the anodic coating, nor the postanodizing treatment usually described as "sealing." This test method is applicable to the rapid, nondestructive testing of anodic coatings. The interpretation of results and correlation of data with service experience and other tests are not within the scope of this test method. The impedance of anodic coatings is defined in terms of resistance and capacitive reactance. The apparatus to be used shall have the characteristics specified for the following: (1) impedance bridge range, frequency, accuracy, and voltage, (2) cell components such as glass tube, rubber gasket or seal, rubber stopper, and platinum or Type 300 stainless steel counter electrode, (3) wire leads, (4) support strand, (5) glass or stainless steel tank, and (6) container for cell standardization. The conditions for the test specimen and electrolyte, and the procedure of measurement, cell standardization, and temperature correction are detailed. The test cell construction and test set-up are illustrated.