ASTM B457-67(1998)

NOTICE: This standard has either been superceded and replaced by a new version or discontinued. NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information. Contact ASTM International (www.astm.org) for the latest information.
An American National Standard
Designation: B 457 – 67 (Reapproved 1998)
Standard Test Method for
Measurement of Impedance of Anodic Coatings on
Aluminum
This standard is issued under the fixed designation B 457; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope
A = area of cross section of conductor.
1.1 This test method describes the conditions and equipment
C 5 e~A/l!
for measuring the impedance of anodic coatings on aluminum.
(4)
Such measurements have been used to evaluate the quality of
where:
seal of an anodic coating. The test method does not prescribe
C = capacitance,
the procedure for producing the anodic coating, nor the
e = dielectric constant,
postanodizing treatment usually described as “sealing.”
A = area of opposing plates of capacitor, and
1.2 This test method is applicable to the rapid, nondestruc-
l = distance between plates.
tive testing of anodic coatings. The interpretation of results and
2.3 For measuring impedance of anodic coatings, the mate-
correlation of data with service experience and other tests are
rial constants are partly associated with the anodic coating and
not within the scope of this test method.
partly with the electrolyte employed in the test cell. For
simplification these constants are assumed not to vary. The
2. Nature of Test
variations in measured impedance then depend directly on
2.1 Impedance is an electrical characteristic described as the
geometric factors.
total opposition of all circuit elements to the flow of alternating
current. Inductive effects of anodic coatings are negligible and
3. Apparatus
the impedance is presumed to be made up of resistance and
3.1 Impedance Bridges—Commercially available a-c im-
capacitive reactance according to the following relationships:
pedance bridges with the following characteristics are satisfac-
2 2
Z 5 R 1 X (1) tory:
=
c
3.1.1 Range—1 μF (1000 nF) to 0.0001 μF (0.1 nF) full
and
scale with a dissipation factor of 0 to 2.
X 5 1/2 p fC (2)
c
3.1.2 Frequency—1000 Hz.
3.1.3 Accuracy—1 %.
where:
3.1.4 Voltage—Adjustable so as to be not greater than 0.5 V
Z = impedance,
as applied to the test specimen.
R = resistance,
3.2 Cell (Fig. 1) for containing the electrolyte during test. It
X = capacitive reactance,
c
f = frequency, and may be constructed from the following components:
C = capacitance. 3.2.1 Glass Tube, 9 mm (0.35 in.) in outside diameter by 9
2.2 Both resistance and capacitance are associated with a
cm (3.54 in.).
material constant and a geometric factor: 3.2.2 Rubber Gasket or Seal.
R 2 r l/A
~ !
(3)
The Alcoa Impedance Test for Anodic Coatings (AZTAC) evaluates a 0.129-cm
where:
2 (0.02-in. ) test area and expresses impedance in kilohms. Instructions are available
R = resistance,
from Alcoa Process Development Laboratories, P.O. Box 2970, Pittsburgh, PA
r = specific resistance,
15230.
l = length of conductor, and The Z-Scope, formerly manufactured by Twin City Testing Corp., Tonawanda,
NY was designed to measure the impedance of anodic coatings on aluminum.
2 2
AZTAC values (the impedance of a 0.129-cm (0.02-in. ) test area) can be read
directly in kilohms with this instrument.
Another test cell satisfactory for use with this method is the one used with the
This test method is under the jurisdiction of ASTM Committee B-8 on Metallic Kocour Electronic Thickness Tester Model 995 available from Kocour Co., 4800 S.
and Inorganic Coatings and is the direct responsibility of Subcommittee B08.07 on St. Louis Ave., Chicago, IL.
Chemical Conversion Coatings. Type A seal available from Kocour Co. or Twin City Testing Corp., 2440
Current edition approved Dec. 12, 1967. Published February 1968. Franklin Ave., St. Paul, MN, has been found satisfactory.
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NOTICE: This standard has either been superceded and replaced by a new version or discontinued. NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information. Contact ASTM International (www.astm.org) for the latest information.
B 457 – 67 (1998)
cannot be done or if the part has been subjected to an elevated
temperature drying treatment, the test area should be condi-
tioned as follows:
5.1.1 Wipe the test area with acetone, methylethylketone,
trichloroethylene, or similar solvent.
5.1.2 Immerse the test area in pure boiling water for 30 s.
5.1.3 Rinse in cold water.
5.1.4 Blot dry and test without further delay.
6. Procedure
6.1 Penetrate the anodic coating in a small area with a sharp
instrument and connect the lead from the low-impedance
terminal of the bridge to the exposed aluminum substrate.
6.2 Connect the other lead from the bridge to the counter
electrode of the test cell. Be certain the lead wires are not
twisted around each other. Turn on the bridge and allow it to
warm up.
6.3 Place the test cell on the area to be tested and apply
enough pressure, 490 to 1230 MPa (71 to 178 psi) to prevent
leakage of the electrolyte (the cell is spring-loaded to ensure
sufficient and constant pressure). Make certain the bottom of
FIG. 1 Diagram of Test Cell Construction
the gasket on the test cell is level with the test surface.
6.4 Fill the test cell at least half full with electrolyte and
3.2.3 Rubber Stopper—Any convenient size with a hole in
commence a 2-min soak period. The counter electrode should
center to accommodate the glass tube.
not contact the test specimen.
3.2.4 Platinum or Type 300 Stainless Steel Counter Elec-
6.5 Turn on and obtain a preliminary “balance” of the bridge
trode, 9 cm (3.54 in.) long by 0.75 to 1.0 mm (0.030 to 0.040
in accordance with the manufacturer’s instructions (not neces-
in.) diameter wire.
sary if a direct-reading instrument is used).
3.3 Wire Leads, two, insulated, app
...