ASTM B767-88(2021)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: B767 − 88 (Reapproved 2021)
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 B767; 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 ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.1 This guide outlines a general method for determining
mendations issued by the World Trade Organization Technical
the mass per unit area of electrodeposited, electroless,
Barriers to Trade (TBT) Committee.
mechanically-deposited, vacuum-deposited, anodicoxide, and
chemical conversion coatings by gravimetric and other chemi-
2. Referenced Documents
cal analysis procedures.
2.1 ASTM Standards:
1.2 This guide determines the average mass per unit area
A90/A90M Test Method for Weight [Mass] of Coating on
over a measured area.
Iron and Steel Articles with Zinc or Zinc-Alloy Coatings
1.3 The stripping methods cited are described in specifica- A309 Test Method for Weight and Composition of Coating
tions or in the open literature or have been used routinely by at onTerne Sheet by theTriple-SpotTest (Withdrawn 2015)
least one laboratory. A428/A428M Test Method for Weight [Mass] of Coating on
Aluminum-Coated Iron or Steel Articles
1.4 The procedures outlined can be used for many coating-
B137 Test Method for Measurement of Coating Mass Per
substrate combinations.They cannot be used where the coating
Unit Area on Anodically Coated Aluminum
cannot be separated from the substrate by chemical or physical
B449 Specification for Chromates on Aluminum
means as would be the case if white brass were plated with
2.2 British Standards Institution Documents:
yellow brass.
BS 729 Hot Dip Galvanized Coatings on Iron and Steel
1.5 In principle, these procedures can be used to measure
Articles, Specification for
very thin coatings or to measure coatings over small areas, but
BS 1706 Electroplated Coatings of Cadmium and Zinc on
not thin coatings over small areas. The limits depend on the
Iron and Steel, Specification for
required accuracy. For example, 2.5 mg⁄cm of coating might
BS 1872 Electroplated Coatings of Tin, Specification for
2 2
require 2.5 mg of coating covering 1 cm , but 0.1 mg⁄cm of
BS 3189 Phosphate Treatment of Iron and Steel, Specifica-
coating would require 25 cm to obtain 2.5 mg of coating.
tion for
1.6 The values stated in SI units are to be regarded as BS 3382 Electroplated Coatings on Threaded Components,
standard. No other units of measurement are included in this Specification for
standard. BS 3597 Electroplated Coatings of 65/35 Tin-Nickel Alloy,
Specification for
1.7 This standard does not purport to address all of the
2.3 Government Standards:
safety concerns, if any, associated with its use. It is the
2.3.1DOD Standard:
responsibility of the user of this standard to establish appro-
DOD-P-16232F Phosphate Coatings, Heavy, Manganese or
priate safety, health, and environmental practices and deter-
Zinc Base (for Ferrous Metals)
mine the applicability of regulatory limitations prior to use.
1.8 This international standard was developed in accor-
dance with internationally recognized principles on standard-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
1 3
This guide is under the jurisdiction of ASTM Committee B08 on Metallic and The last approved version of this historical standard is referenced on
Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on Test www.astm.org.
Methods. Available from British Standards Institute (BSI), 389 Chiswick High Rd.,
Current edition approved Oct. 1, 2021. Published November 2021. Originally London W4 4AL, U.K.
approvedin1987.Lastpreviouseditionapprovedin2016asB767 – 88(2016).DOI: Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,
10.1520/B0767-88R21. Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B767 − 88 (2021)
2.3.2Federal Standards: 5. Apparatus
FED-STD151b Metals;TestMethods:Test513.1forWeight
5.1 In addition to normal chemical laboratory equipment for
of Coating on Hot DipTin Plate and ElectrolyticTin Plate
handling small amounts of corrosive and toxic chemicals, an
RR-T-51D Tableware and Flatware—Silverplated
accurate ruler or vernier caliper and a good balance are
2.3.3Military Standard:
required. See Sections 7 and 8.
MIL-M-45202C Magnesium Alloys, Anodic Treatment of
6. Specimen Preparation
2.4 ISO Standards:
6.1 Size—Thespecimenmustbelargeenoughtopermitarea
ISO 2081 Metallic Coatings—Electroplated Coatings of
and mass measurement of adequate accuracy. (See Section 7
Zinc on Iron or Steel
and 8.2.)
ISO 2082 Metallic Coatings—Electroplated Coatings on
Cadmium on Iron or Steel
6.2 Shape—The shape of the test specimen must be such
ISO 2093 Metallic Coatings—Electrodeposited Coatings of
that the surface area can be easily measured. A rectangular or
Tin, Annex B
circular test specimen is usually suitable.
ISO 2106 Anodizing of Aluminum and its Alloys—
6.3 EdgeCondition—If the area to be measured is small and
Determination of Mass Per UnitArea (Surface Density) of
needs to be known accurately, the edges must be dressed to
Anodic Oxide Coatings—Gravimetric Method
remove smeared coating, to remove loose burrs, and to provide
ISO 3892 Conversion Coatings on Metallic Materials—
well-defined and (for rectangles) straight edges.This should be
Determination of Coating Mass Per Unit Area—
considered for areas less than 100 mm . One method of
Gravimetric Methods
dressing the edges of a rectangular specimen is to clamp the
ISO 4522/1 Metallic Coatings—Test Methods for Electrode-
specimen between two plastic or metal blocks with the edge of
posited Silver and Silver Alloy Coatings—Part 1: Deter-
the specimen flush with the edges of the blocks and then to
mination of Coating Thickness
grind and polish the edges metallographically.
ISO 4524/1 Metallic Coatings—Test Methods for Electrode-
6.4 Heat Treatment—If the substrate is to be dissolved
posited Gold and Gold Alloy Coatings—Part 1: Determi-
leaving the coating intact, it is desirable to first heat-treat the
nation of Coating Thickness
test specimen so that the coating will not curl up tightly or fall
apart. Some gold deposits of 1.5 mg⁄cm will fall apart when
3. Summary of Guide
theirsubstratesaredissolved,butafterheattreatmentat120 °C
3.1 The mass of a coating over a measured area is deter-
for 3 h will support themselves. If the thickness of a coating
mined by the following:
(instead of its mass per unit area) is being determined, one
3.1.1 Weighingthetestspecimenbeforeandafterdissolving
should not use a heat treatment that might change the density
the coating in a reagent that does not attack the substrate.
of the coating material.
3.1.2 Weighing the coating after dissolving the substrate in
7. Measurement of Coated Area:
a reagent that does not attack the coating, or
7.1 Measurement Method—The accuracy of the area mea-
3.1.3 Dissolving both the coating and the substrate and
surement must be better than the desired accuracy of the mass
quantitatively analyzing the resulting solution.
perunitareameasurement.Hencethemethodofmeasuringthe
3.2 The mass per unit area is calculated from the mass and
area will depend on the desired accuracy and the specimen
area measurements, the thickness from the mass, area, and
size.
density of the coating materials.
7.2 Equipment—The area can be measured with a
planimeter, but it is usually determined by linear measure-
4. Significance and Use
ments. Often a micrometer or vernier caliper is used. For large
4.1 The thickness of a coating is critical to its performance
areas, however, a ruler may do. For maximum accuracy, a
and is specified in many specifications calling for coatings.
measuring microscope is used.
4.2 These procedures are used for acceptance testing and
7.3 Number of Measurements—Because circular or rectan-
appear in a few specifications.
gular specimens will not be perfectly circular or rectangular, it
is desirable to measure each dimension in three places. For a
4.3 Coating thickness instruments are often calibrated with
rectangle, one would measure the length of each edge and the
thickness standards that are based on mass and area measure-
length and width through the center and obtain an average for
ments.
each dimension.
4.4 The average thickness of a coating on the measured area
NOTE 1—In the case of a cylinder one would normally measure the
can be calculated from its mass per unit area only if the density
diameterandlength.Inonespecificationforgalvanizedwire(fencing),the
of the coating material is known.
length of the wire specimen is not measured, but in effect is calculated
from the mass (which is measured anyway), the radius, and the density of
the steel substrate. (l=m⁄πr D)
AvailablefromU.S.GovernmentPrintingOfficeSuperintendentofDocuments,
8. Gravimetric Determination of Mass of Coating:
732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401.
8.1 Specimen Size—The accuracy of the mass measurement
Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036. must be better than the desired accuracy of the mass per unit
B767 − 88 (2021)
area measurement. Hence, the test specimen must be large for the same length of time as it was during the stripping
enough that the coating can be weighed with the desired process. Any loss of mass enables one to make a judgment of
accuracy. a possible error due to any dissolution of the coating with the
substrate during the stripping process.
8.2 Equipment—A balance is required, but the required
sensitivity of the balance depends on the size of the test
NOTE 2—The test procedure given at the end of 9.1.1 and 9.1.2 should
be conducted to evaluate a gravimetric method the first time it is used.
specimen, the coating thickness (coating mass), and the re-
quired accuracy of the measurement. A balance that weighs to
9.2 Determination of Mass of Coating by Chemical
0.01 g is sometimes satisfactory, though a good analytical
Analysis—This method is by nature very general. Both the
balanceweighingto0.0001 gismoreversatile.Amicrobalance
coating and substrate are dissolved in a suitable reagent and
is required for small specimens of thin coatings, but it is
then the resulting solution is analyzed for the coating material.
limited to small samples.
For each coating-substrate-reagent combination, there are sev-
eral analytical methods. For possible analytical methods see
9. Procedure
Volumes 03.05 and 03.06 of the Annual Book of ASTM
Standards.
9.1 The mass of coating may be determined: (1) by weigh-
ing the test specimen before and after dissolving the coating
10. Calculation
(see AnnexA1) and taking the difference, or (2) by dissolving
10.1 Calculate the mass per unit area as follows:
thesubstrate(seeAnnexA1)andweighingthecoatingdirectly.
Mass per unit area 5 m/A mg/cm (1)
9.1.1 By Difference—The test specimen is first cleaned of ~ !
any foreign material and finally rinsed with alcohol, blown dry
where:
with clean air, and weighed. The specimen is immersed in the
m = mass of coating (mg), and
appropriate reagent (see Annex A1) to dissolve the coating,
A = area covered by coating (cm )
rinsed with water, rinsed with alcohol, blown dry with clean
10.2 Calculate the thickness as follows:
air, and weighed again. The loss of mass is the mass of the
coating. To determine if there was any dissolution of the
Thickness 5 10 3M/D µm (2)
~ !
substrate, repeat the process with the stripped substrate making
where:
sure that it is in the reagent just as long as before. Any loss of
M = mass per unit area (mg/cm ), and
mass enables one to make a judgment of a possible error due
D = density (g/cm ).
to any dissolution of the substrate with the coating during the
NOTE 3—The density of a coating metal is usually not the same as the
stripping process.
handbook value or the theoretical value. For example, the density of
9.1.2 By Direct Weighing—The substrate is dissolved in the
electrodeposited gold is generally less than 19.3 g⁄cm and sometimes as
appropriate reagent (see AnnexA1). The coating is rinsed with
low or lower than 17 g⁄cm . The densities of some electrodeposited
water, rinsed with alcohol, blown dry with clean air, and
metals are given by W. H. Safranek.
weighed. To determine if there was any dissolution of the
coating, submit the isolated coating to the same stripping
Printed in The Properties of Electrodeposited Metals and Alloys, Second
process making sure that the coating is in the stripping reagent Edition, American Electroplaters’ and Surface Finishers Society, 1986.
ANNEX
(Mandatory Information)
A1. REAGENTS FOR SELECTIVE DISSOLUTION OF METAL LAYERS
NOTEA1.1—The specific issues of standards are cited in this table and
Often the dissolution is not significant, but the possibility
included in the literature as references because they contain the informa-
should be tested for as suggested in 9.1.1, and 9.1.2.
tion from which this table is based.
A1.2
A1.1
Dissolution is carried out at room temperature unless other-
With many of the reagents given in TableA1.1, there may be wise indicated. All test pieces are rinsed and dried (see 9.1.1
some dissolution of the layer other than the one being stripped. and 9.1.2) before weighing.
B767 − 88 (2021)
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 i
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