ASTM B767-88(1994)
(Guide)Standard Guide for Determining Mass Per Unit Area of Electrodeposited and Related Coatings by Gravimetric and Other Chemical Analysis Procedures
Standard Guide for Determining Mass Per Unit Area of Electrodeposited and Related Coatings by Gravimetric and Other Chemical Analysis Procedures
SCOPE
1.1 This guide outlines a general method for determining the mass per unit area of electrodeposited, electroless, mechanically-deposited, vacuum-deposited, anodicoxide, and chemical conversion coatings by gravimetric and other chemical analysis procedures.
1.2 This guide determines the average mass per unit area over a measured area.
1.3 The stripping methods cited are described in specifications or in the open literature or have been used routinely by at least one laboratory.
1.4 The procedures outlined can be used for many coating-substrate combinations. They cannot be used where the coating cannot be separated from the substrate by chemical or physical means as would be the case if white brass were plated with yellow brass.
1.5 In principle, these procedures can be used to measure very thin coatings or to measure coatings over small areas, but not thin coatings over small areas. The limits depend on the required accuracy. For example, 2.5 mg/cm of coating might require 2.5 mg of coating covering 1 cm , but 0.1 mg/cm of coating would require 25 cm to obtain 2.5 mg of coating.
1.6 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety problems 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.
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Designation: B 767 – 88 (Reapproved 1994)
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Guide for
Determining Mass Per Unit Area of Electrodeposited and
Related Coatings by Gravimetric and Other Chemical
Analysis Procedures
This standard is issued under the fixed designation B 767; 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 B 137 Test Method for Measurement of Coating Mass Per
Unit Area on Anodically Coated Aluminum
1.1 This guide outlines a general method for determining
B 449 Practice for Chromate Treatments on Aluminum
the mass per unit area of electrodeposited, electroless,
2.2 British Standards Institution Documents:
mechanically-deposited, vacuum-deposited, anodicoxide, and
BS 729 Hot Dip Galvanized Coatings on Iron and Steel
chemical conversion coatings by gravimetric and other chemi-
Articles, Specification for:
cal analysis procedures.
BS 1706 Electroplated Coatings of Cadmium and Zinc on
1.2 This guide determines the average mass per unit area
Iron and Steel, Specification for:
over a measured area.
BS 1872 Electroplated Coatings of Tin, Specification for:
1.3 The stripping methods cited are described in specifica-
BS 3189 Phosphate Treatment of Iron and Steel, Specifica-
tions or in the open literature or have been used routinely by at
tion for:
least one laboratory.
BS 3382 Electroplated Coatings on Threaded Components,
1.4 The procedures outlined can be used for many coating-
Specification for:
substrate combinations. They cannot be used where the coating
BS 3597 Electroplated Coatings of 65/35 Tin-Nickel Alloy,
cannot be separated from the substrate by chemical or physical
Specification for:
means as would be the case if white brass were plated with
2.3 Government Standards:
yellow brass.
2.3.1 DOD Standard:
1.5 In principle, these procedures can be used to measure
DOD-P-16232F Phosphate Coatings, Heavy, Manganese or
very thin coatings or to measure coatings over small areas, but
Zinc Base (for Ferrous Metals)
not thin coatings over small areas. The limits depend on the
2.3.2 Federal Standards:
required accuracy. For example, 2.5 mg/cm of coating might
2 2
FED-STD 151b Metals; Test Methods: Test 513.1 for
require 2.5 mg of coating covering 1 cm , but 0.1 mg/cm of
Weight of Coating on Hot Dip Tin Plate and Electrolytic
coating would require 25 cm to obtain 2.5 mg of coating.
Tin Plate
1.6 This standard does not purport to address all of the
RR-T-51D Tableware and Flatware—Silverplated
safety concerns, if any, associated with its use. It is the
2.3.3 Military Standard:
responsibility of the user of this standard to establish appro-
MIL-M-45202C Magnesium Alloys, Anodic Treatment of
priate safety and health practices and determine the applica-
2.4 ISO Standards:
bility of regulatory limitations prior to use.
ISO 2081 Metallic Coatings—Electroplated Coatings of
2. Referenced Documents Zinc on Iron or Steel
ISO 2082 Metallic Coatings—Electroplated Coatings on
2.1 ASTM Standards:
Cadmium on Iron or Steel
A 90/A 90 M Test Method for Weight (Mass) of Coating on
ISO 2093 Metallic Coatings—Electrodeposited Coatings of
Iron and Steel Articles with Zinc or Zinc-Alloy Coatings
Tin, Annex B
A 309 Test Method for Weight and Composition of Coating
ISO 2106 Anodizing of Aluminum and its Alloys—
on Terne Sheet by the Triple-Spot Test
Determination of Mass Per Unit Area (Surface Density) of
A 428 Test Method for Weight (Mass) of Coating on
Aluminum-Coated Iron or Steel Articles
Annual Book of ASTM Standards, Vol 02.05.
Available from British Standards Institution, Linford Wood, Milton Keynes
This guide is under the jurisdiction of ASTM Committee B-8 on Metallic and MK14 6L3, England.
Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on Available from Standardization Documents Order Desk, Bldg. 4 Section D, 700
General Test Methods. Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.
Current edition approved Aug. 26, 1988. Published April 1989. Originally Available from U.S. Government Printing Office, Washington, DC 20402.
published as B 767 – 87. Last previous edition B 767 – 87. Available from American National Standards Institute, 11 W. 42nd St., 13th
Annual Book of ASTM Standards, Vol 01.06. Floor, New York, NY 10036.
B 767
Anodic Oxide Coatings—Gravimetric Method test specimen so that the coating will not curl up tightly or fall
ISO 3892 Conversion Coatings on Metallic Materials— apart. Some gold deposits of 1.5 mg/cm will fall apart when
Determination of Coating Mass Per Unit Area— their substrates are dissolved, but after heat treatment at 120°C
Gravimetric Methods for 3 h will support themselves. If the thickness of a coating
ISO 4522/1 Metallic Coatings—Test Methods for Elec- (instead of its mass per unit area) is being determined, one
trodeposited Silver and Silver Alloy Coatings—Part 1: should not use a heat treatment that might change the density
Determination of Coating Thickness of the coating material.
ISO 4524/1 Metallic Coatings—Test Methods for Elec-
7. Measurement of Coated Area:
trodeposited Gold and Gold Alloy Coatings—Part 1:
Determination of Coating Thickness 7.1 Measurement Method—The accuracy of the area mea-
surement must be better than the desired accuracy of the mass
3. Summary of Guide
per unit area measurement. Hence the method of measuring the
3.1 The mass of a coating over a measured area is deter-
area will depend on the desired accuracy and the specimen
mined by the following:
size.
3.1.1 Weighing the test specimen before and after dissolving
7.2 Equipment—The area can be measured with a planime-
the coating in a reagent that does not attack the substrate.
ter, but it is usually determined by linear measurements. Often
3.1.2 Weighing the coating after dissolving the substrate in
a micrometer or vernier caliper is used. For large areas,
a reagent that does not attack the coating, or
however, a ruler may do. For maximum accuracy, a measuring
3.1.3 Dissolving both the coating and the substrate and
microscope is used.
quantitatively analyzing the resulting solution.
7.3 Number of Measurements—Because circular or rectan-
3.2 The mass per unit area is calculated from the mass and
gular specimens will not be perfectly circular or rectangular, it
area measurements, the thickness from the mass, area, and
is desirable to measure each dimension in three places. For a
density of the coating materials.
rectangle, one would measure the length of each edge and the
length and width through the center and obtain an average for
4. Significance and Use
each dimension.
4.1 The thickness of a coating is critical to its performance
and is specified in many specifications calling for coatings. NOTE 1—In the case of a cylinder one would normally measure the
diameter and length. In one specification for galvanized wire (fencing), the
4.2 These procedures are used for acceptance testing and
length of the wire specimen is not measured, but in effect is calculated
appear in a few specifications.
from the mass (which is measured anyway), the radius, and the density of
4.3 Coating thickness instruments are often calibrated with
the steel substrate. (l 5 m/pr D)
thickness standards that are based on mass and area measure-
ments.
8. Gravimetric Determination of Mass of Coating:
4.4 The average thickness of a coating on the measured area
8.1 Specimen Size—The accuracy of the mass measurement
can be calculated from its mass per unit area only if the density
must be better than the desired accuracy of the mass per unit
of the coating material is known.
area measurement. Hence, the test specimen must be large
enough that the coating can be weighed with the desired
5. Apparatus
accuracy.
5.1 In addition to normal chemical laboratory equipment for
8.2 Equipment—A balance is required, but the required
handling small amounts of corrosive and toxic chemicals, an
sensitivity of the balance depends on the size of the test
accurate ruler or vernier caliper and a good balance are
specimen, the coating thickness (coating mass), and the re-
required. See sections 7 and 8.
quired accuracy of the measurement. A balance that weighs to
6. Specimen Preparation
0.01 g is sometimes satisfactory, though a good analytical
6.1 Size—The specimen must be large enough to permit balance weighing to 0.0001 g is more versatile. A microbalance
area and mass measurement of adequate accuracy. (Section 7 is required for small specimens of thin coatings, but it is
limited to small samples.
and 8.2.)
6.2 Shape—The shape of the test specimen must be such
9. Procedure
that the surface area can be easily measured. A rectangular or
circular test specimen is usually suitable. 9.1 The mass of coating may be determined (1) by weighing
the test specimen before and after dissolving the coating (see
6.3 Edge Condition—If the area to be measured is small and
needs to be known accurately, the edges must be dressed to Annex) and taking the difference or (2) by dissolving the
remove smeared coating, to remove loose burrs, and to provide substrate (see Annex) and weighing the coating directly.
well-defined and (for rectangles) straight edges. This should be 9.1.1 By Difference—The test specimen is first cleaned of
considered for areas less than 100 mm . One method of any foreign material and finally rinsed with alcohol, blown dry
dressing the edges of a rectangular specimen is to clamp the with clean air, and weighed. The specimen is immersed in the
specimen between two plastic or metal blocks with the edge of appropriate reagent (see Annex) to dissolve the coating, rinsed
the specimen flush with the edges of the blocks and then to with water, rinsed with alcohol, blown dry with clean air, and
grind and polish the edges metallographically. weighed again. The loss of mass is the mass of the coating. To
6.4 Heat Treatment—If the substrate is to be dissolved determine if there was any dissolution of the substrate, repeat
leaving the coating intact, it is desirable to first heat-treat the the process with the stripped substrate making sure that it is in
B 767
the reagent just as long as before. Any loss of mass enables one 10. Calculation
to make a judgment of a possible error due to any dissolution
10.1 Calculate the mass per unit area as follows:
of the substrate with the coating during the stripping process.
Mass per unit area 5 m/A ~mg/cm ! (1)
9.1.2 By Direct Weighing—The substrate is dissolved in the
appropriate reagent (see Annex). The coating is rinsed with
where:
water, rinsed with alcohol, blown dry with clean air, and
m 5 mass of coating (mg), and
weighed. To determine if there was any dissolution of the 2
A 5 area covered by coating (cm )
coating, submit the isolated coating to the same stripping
10.2 Calculate the thickness as follows:
process making sure that the coating is in the stripping reagent
Thickness 5 10 3 M/D ~μm! (2)
for the same length of time as it was during the stripping
process. Any loss of mass enables one to make a judgment of
where:
a possible error due to any dissolution of the coating with the 2
M 5 mass per unit area (mg/cm ), and
substrate during the stripping process.
D 5 density (g/cm ).
NOTE 2—The test procedure given at the end of 6.1.1 and 6.1.2 should
NOTE 3—The density of a coating metal is usually not the same as the
be conducted to evaluate a gravimetric method the first time it is used.
handbook value or the theoretical value. For example, the density of
9.2 Determination of Mass of Coating by Chemical electrodeposited gold is generally less than 19.3 g/cm and sometimes as
low or lower than 17 g/cm . The densities of some electrodeposited metals
Analysis—This method is by nature very general. Both the
are given by W. H. Safranek.
coating and substrate are dissolved in a suitable reagent and
then the resulting solution is analyzed for the coating material.
For each coating-substrate-reagent combination, there are sev-
eral analytical methods. For possible analytical methods see
Printed in The Properties of Electrodeposited Metals and Alloys, Second
vols 03.05 and 03.06 of the Annual Book of ASTM Standards. Edition, American Electroplaters’ and Surface Finishers Society, 1986.
ANNEX
(Mandatory Information)
A1. REAGENTS FOR SELECTIVE DISSOLUTION OF METAL LAYERS
NOTE A1.1—The specific issues of standards are cited in this table and
possibility should be tested for as suggested in 9.1.1, and 9.1.2.
included in the literature as references because they contain the informa-
tion from which this table is based.
A1.2 Dissolution is carried out at room temperature unless
otherwise indicated. All test pieces are rinsed and dried (see
A1.1 With many of the reagents given in Table A1.1, there
9.1.1 and 9.1.2) before weighing.
may be some dissolution of the layer other than the one being
stripped. Often the dissolution is not significant, but the
TABLE A1.1 Reagents
Coating Substrate Reagents Remarks—Sources
aluminum steel (1) 20 parts by mass Immerse a few min (avoid longer time) at about 90°C. While rinsing, scrub
NaOH, 80 parts with a sponge to remove loose material. Drain off water, immerse3sin
water concentrated HCl at room temperature, scrub again in running water, and
(2) concentrated HCl (sp gr 1.19) repeat entire process until there is no visible reaction in the HCl. Two or
three cycles are required normally. A more detailed description is given in
the 1981 issue of Test Method A 428.
aluminum steel (1) 200 g SbCl in 1L concentrated HCl Mix equal volume of (1) and (2), immerse until evolution of hydrogen stops,
about 1–4 min.
(2) 100 g SnCl H O in 1L concentrated Keep below 38°C, rinse and scrub with soft cloth.
2.2 2
HCl plus a few granules of tin This test procedure appears in Ref (1) and in the 1981 issue of Test
A
Method A 428.
anodized aluminum aluminum 35 mL 85 % phosphoric acid plus 20 g/L Immerse 5 min at 100°C, rinse, dry, weigh. Repeat cycle until weight is
CrO constant.
This procedure appears in the 1945 issue of Method B 137 and the 1982
issue of ISO Standard 2106.
anodized magnesium magnesium 300 g/L CrO Immerse at room temperature, rinse, dry, weigh, and repeat until weight
(HAE) loss is less than 3.9 mg/dm . Keep piece of commercially pure aluminum in
solution but not in contact with magnesium.
This procedure appears in Military Standard MIL-M-45202C.
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