ASTM B457-67(2013)

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

ABSTRACT
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.
SCOPE
1.1 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.”  
1.2 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.  
1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.  
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 30-Apr-2013
• ICS: 25.220.20 - Surface treatment
• Technical Committee: B08 - Metallic and Inorganic Coatings
• Drafting Committee: B08.07 - Conversion Coatings

Relations

• Replaces: ASTM B457-67(2008)e1 - Standard Test Method for Measurement of Impedance of Anodic Coatings on Aluminum
• Effective Date: 01-May-2013
• Referred By: ASTM B580-79(2019) - Standard Specification for Anodic Oxide Coatings on Aluminum
• Effective Date: 01-May-2013

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: B457 − 67 (Reapproved 2013)
Standard Test Method for
Measurement of Impedance of Anodic Coatings on
1
Aluminum
This standard is issued under the fixed designation B457; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope where:
Z = impedance,
1.1 Thistestmethoddescribestheconditionsandequipment
R = resistance,
for measuring the impedance of anodic coatings on aluminum.
X = capacitive reactance,
c
Such measurements have been used to evaluate the quality of
f = frequency, and
seal of an anodic coating. The test method does not prescribe
C = capacitance.
the procedure for producing the anodic coating, nor the
2.2 Both resistance and capacitance are associated with a
postanodizing treatment usually described as “sealing.”
material constant and a geometric factor:
1.2 This test method is applicable to the rapid, nondestruc-
R 2 r ~l/A! (3)
tive testing of anodic coatings.The interpretation of results and
correlation of data with service experience and other tests are
where:
not within the scope of this test method.
R = resistance,
1.3 The values stated in SI units are to be regarded as the
r = specific resistance,
standard. The values given in parentheses are for information
l = length of conductor, and
only. A = area of cross section of conductor.
1.4 This standard does not purport to address all of the C 5 e~A/l! (4)
safety concerns, if any, associated with its use. It is the
where:
responsibility of the user of this standard to establish appro-
C = capacitance,
priate safety and health practices and determine the applica-
e = dielectric constant,
bility of regulatory limitations prior to use.
A = area of opposing plates of capacitor, and
l = distance between plates.
2. Nature of Test
2.3 For measuring impedance of anodic coatings, the mate-
2.1 Impedanceisanelectricalcharacteristicdescribedasthe
rial constants are partly associated with the anodic coating and
total opposition of all circuit elements to the flow of alternating
partly with the electrolyte employed in the test cell. For
current. Inductive effects of anodic coatings are negligible and
simplification these constants are assumed not to vary. The
the impedance is presumed to be made up of resistance and
variations in measured impedance then depend directly on
capacitive reactance according to the following relationships:
2
geometric factors.
2 2
Z 5 =R 1X (1)
c
3. Apparatus
and
3.1 Impedance Bridges—Commercially available a-c im-
X 51/2πfC (2)
c
pedance bridges with the following characteristics are satisfac-
3
tory:
3.1.1 Range—1 µF (1000 nF) to 0.0001 µF (0.1 nF) full
scale with a dissipation factor of 0 to 2.
2
The Alcoa Impedance Test for Anodic Coatings (AZTAC) evaluates a 0.129-
2 2
cm (0.02-in. ) test area and expresses impedance in kilohms. Instructions are
1
This test method is under the jurisdiction ofASTM Committee B08 on Metallic availablefromAlcoaProcessDevelopmentLaboratories,P.O.Box2970,Pittsburgh,
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.07 on PA 15230.
3
Conversion Coatings. The Z-Scope, formerly manufactured by Twin City Testing Corp., Tonawanda,
Current edition approved May 1, 2013. Published May 2013. Originally NY was designed to measure the impedance of anodic coatings on aluminum.
ε1 2 2
approved in 1967. Last previous edition approved in 2008 as B457 – 67 (2008) . AZTAC values (the impedance of a 0.129-cm (0.02-in. ) test area) can be read
DOI: 10.1520/B0457-67R13. directly in kilohms with this instrument.
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B457 − 67 (2013)
3.4 Support Strand, complete with a utility clamp to hold
the electrolytic test cell.
3.5 Glass or Stainless Steel Tank containing pure boiling
water is required for conditioning the test specimen.
3.6 Container for Cell Standardization—A 150 to 500-mL
2 6
Type 300 stainless steel beaker or standard 1-in. test cell may
be used.
4. Electrolyte
1
4.1 The electrolyte shall be a 3 ⁄2 % solution of sodium
chloride prepared by dissolving 36 g of the salt in 1 L of
distilled or deionized water.
5. Test Specimen
5.1 The area to be tested should be sufficiently large to
accommodate the test cell, sufficiently flat to prevent leakage
of the solution from the probe, and free from mechanical
defects such as scratches. After an anodic coating has been
sealed, moisture is lost from the coating thus producing an
increase in impedance. The rate at which moisture is lost
FIG. 1 Diagram of Test
...