ASTM B767-88(2010)
(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
SIGNIFICANCE AND USE
The thickness of a coating is critical to its performance and is specified in many specifications calling for coatings.
These procedures are used for acceptance testing and appear in a few specifications.
Coating thickness instruments are often calibrated with thickness standards that are based on mass and area measurements.
The average thickness of a coating on the measured area can be calculated from its mass per unit area only if the density of the coating material is known.
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/cm2 of coating might require 2.5 mg of coating covering 1 cm2, but 0.1 mg/cm2 of coating would require 25 cm2 to obtain 2.5 mg of coating.
1.6 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.7 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
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: B767 − 88(Reapproved2010)
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 2. Referenced Documents
2.1 ASTM Standards:
1.1 This guide outlines a general method for determining
A90/A90M Test Method for Weight [Mass] of Coating on
the mass per unit area of electrodeposited, electroless,
Iron and Steel Articles with Zinc or Zinc-Alloy Coatings
mechanically-deposited, vacuum-deposited, anodicoxide, and
A309 Test Method for Weight and Composition of Coating
chemical conversion coatings by gravimetric and other chemi-
on Terne Sheet by the Triple-Spot Test
cal analysis procedures.
A428/A428M Test Method for Weight [Mass] of Coating on
1.2 This guide determines the average mass per unit area
Aluminum-Coated Iron or Steel Articles
over a measured area.
B137 Test Method for Measurement of Coating Mass Per
Unit Area on Anodically Coated Aluminum
1.3 The stripping methods cited are described in specifica-
B449 Specification for Chromates on Aluminum
tions or in the open literature or have been used routinely by at
2.2 British Standards Institution Documents:
least one laboratory.
BS 729 Hot Dip Galvanized Coatings on Iron and Steel
1.4 The procedures outlined can be used for many coating-
Articles, Specification for
substrate combinations.They cannot be used where the coating
BS 1706 Electroplated Coatings of Cadmium and Zinc on
cannot be separated from the substrate by chemical or physical
Iron and Steel, Specification for
means as would be the case if white brass were plated with BS 1872 Electroplated Coatings of Tin, Specification for
yellow brass.
BS 3189 Phosphate Treatment of Iron and Steel, Specifica-
tion for
1.5 In principle, these procedures can be used to measure
BS 3382 Electroplated Coatings on Threaded Components,
very thin coatings or to measure coatings over small areas, but
Specification for
not thin coatings over small areas. The limits depend on the
BS 3597 Electroplated Coatings of 65/35 Tin-Nickel Alloy,
required accuracy. For example, 2.5 mg/cm of coating might
Specification for
2 2
require 2.5 mg of coating covering 1 cm , but 0.1 mg/cm of
2.3 Government Standards:
coating would require 25 cm to obtain 2.5 mg of coating.
2.3.1DOD Standard:
DOD-P-16232F Phosphate Coatings, Heavy, Manganese or
1.6 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this Zinc Base (for Ferrous Metals)
2.3.2Federal Standards:
standard.
FED-STD151b Metals;TestMethods:Test513.1forWeight
1.7 This standard does not purport to address all of the
of Coating on Hot DipTin Plate and ElectrolyticTin Plate
safety concerns, if any, associated with its use. It is the
RR-T-51D Tableware and Flatware—Silverplated
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
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 Available from British Standards Institute (BSI), 389 Chiswick High Rd.,
Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on Test London W4 4AL, U.K.
Methods. Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,
Current edition approved Nov. 1, 2010. Published November 2010. Originally Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098.
approved in 1987. Last previous edition approved in 2006 as B767 – 88 (2006). AvailablefromU.S.GovernmentPrintingOfficeSuperintendentofDocuments,
DOI: 10.1520/B0767-88R10. 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B767 − 88(2010)
2.3.3Military Standard: 6. Specimen Preparation
MIL-M-45202C Magnesium Alloys, Anodic Treatment of
6.1 Size—Thespecimenmustbelargeenoughtopermitarea
2.4 ISO Standards: and mass measurement of adequate accuracy. (See Section 7
ISO 2081 Metallic Coatings—Electroplated Coatings of
and 8.2.)
Zinc on Iron or Steel
6.2 Shape—The shape of the test specimen must be such
ISO 2082 Metallic Coatings—Electroplated Coatings on
that the surface area can be easily measured. A rectangular or
Cadmium on Iron or Steel
circular test specimen is usually suitable.
ISO 2093 Metallic Coatings—Electrodeposited Coatings of
6.3 EdgeCondition—If the area to be measured is small and
Tin, Annex B
needs to be known accurately, the edges must be dressed to
ISO 2106 Anodizing of Aluminum and its Alloys—
remove smeared coating, to remove loose burrs, and to provide
Determination of Mass Per UnitArea (Surface Density) of
well-defined and (for rectangles) straight edges.This should be
Anodic Oxide Coatings—Gravimetric Method
considered for areas less than 100 mm . One method of
ISO 3892 Conversion Coatings on Metallic Materials—
dressing the edges of a rectangular specimen is to clamp the
Determination of Coating Mass Per Unit Area—
specimen between two plastic or metal blocks with the edge of
Gravimetric Methods
the specimen flush with the edges of the blocks and then to
ISO 4522/1 Metallic Coatings—Test Methods for Electrode-
grind and polish the edges metallographically.
posited Silver and Silver Alloy Coatings—Part 1: Deter-
mination of Coating Thickness
6.4 Heat Treatment—If the substrate is to be dissolved
ISO 4524/1 Metallic Coatings—Test Methods for Electrode-
leaving the coating intact, it is desirable to first heat-treat the
posited Gold and Gold Alloy Coatings—Part 1: Determi-
test specimen so that the coating will not curl up tightly or fall
nation of Coating Thickness
apart. Some gold deposits of 1.5 mg/cm will fall apart when
their substrates are dissolved, but after heat treatment at 120°C
3. Summary of Guide
for 3 h will support themselves. If the thickness of a coating
(instead of its mass per unit area) is being determined, one
3.1 The mass of a coating over a measured area is deter-
should not use a heat treatment that might change the density
mined by the following:
of the coating material.
3.1.1 Weighingthetestspecimenbeforeandafterdissolving
the coating in a reagent that does not attack the substrate.
7. Measurement of Coated Area:
3.1.2 Weighing the coating after dissolving the substrate in
7.1 Measurement Method—The accuracy of the area mea-
a reagent that does not attack the coating, or
surement must be better than the desired accuracy of the mass
3.1.3 Dissolving both the coating and the substrate and
perunitareameasurement.Hencethemethodofmeasuringthe
quantitatively analyzing the resulting solution.
area will depend on the desired accuracy and the specimen
3.2 The mass per unit area is calculated from the mass and
size.
area measurements, the thickness from the mass, area, and
7.2 Equipment—The area can be measured with a
density of the coating materials.
planimeter, but it is usually determined by linear measure-
ments. Often a micrometer or vernier caliper is used. For large
4. Significance and Use
areas, however, a ruler may do. For maximum accuracy, a
4.1 The thickness of a coating is critical to its performance
measuring microscope is used.
and is specified in many specifications calling for coatings.
7.3 Number of Measurements—Because circular or rectan-
4.2 These procedures are used for acceptance testing and
gular specimens will not be perfectly circular or rectangular, it
appear in a few specifications.
is desirable to measure each dimension in three places. For a
rectangle, one would measure the length of each edge and the
4.3 Coating thickness instruments are often calibrated with
length and width through the center and obtain an average for
thickness standards that are based on mass and area measure-
each dimension.
ments.
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
diameterandlength.Inonespecificationforgalvanizedwire(fencing),the
can be calculated from its mass per unit area only if the density
length of the wire specimen is not measured, but in effect is calculated
of the coating material is known.
from the mass (which is measured anyway), the radius, and the density of
the steel substrate. (l=m⁄πr D)
5. Apparatus
8. Gravimetric Determination of Mass of Coating:
5.1 In addition to normal chemical laboratory equipment for
8.1 Specimen Size—The accuracy of the mass measurement
handling small amounts of corrosive and toxic chemicals, an
must be better than the desired accuracy of the mass per unit
accurate ruler or vernier caliper and a good balance are
area measurement. Hence, the test specimen must be large
required. See Sections 7 and 8.
enough that the coating can be weighed with the desired
accuracy.
8.2 Equipment—A balance is required, but the required
Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036. sensitivity of the balance depends on the size of the test
B767 − 88(2010)
specimen, the coating thickness (coating mass), and the re- a possible error due to any dissolution of the coating with the
quired accuracy of the measurement. A balance that weighs to substrate during the stripping process.
0.01 g is sometimes satisfactory, though a good analytical
NOTE 2—The test procedure given at the end of 9.1.1 and 9.1.2 should
balanceweighingto0.0001gismoreversatile.Amicrobalance
be conducted to evaluate a gravimetric method the first time it is used.
is required for small specimens of thin coatings, but it is
9.2 Determination of Mass of Coating by Chemical
limited to small samples.
Analysis—This method is by nature very general. Both the
coating and substrate are dissolved in a suitable reagent and
9. Procedure
then the resulting solution is analyzed for the coating material.
For each coating-substrate-reagent combination, there are sev-
9.1 The mass of coating may be determined: (1) by weigh-
eral analytical methods. For possible analytical methods see
ing the test specimen before and after dissolving the coating
Volumes 03.05 and 03.06 of the Annual Book of ASTM
(see AnnexA1) and taking the difference, or (2) by dissolving
Standards.
thesubstrate(seeAnnexA1)andweighingthecoatingdirectly.
9.1.1 By Difference—The test specimen is first cleaned of 10. Calculation
any foreign material and finally rinsed with alcohol, blown dry
10.1 Calculate the mass per unit area as follows:
with clean air, and weighed. The specimen is immersed in the
Mass per unit area 5 m/A ~mg/cm ! (1)
appropriate reagent (see Annex A1) to dissolve the coating,
rinsed with water, rinsed with alcohol, blown dry with clean where:
air, and weighed again. The loss of mass is the mass of the
m = mass of coating (mg), and
coating. To determine if there was any dissolution of the
A = area covered by coating (cm )
substrate, repeat the process with the stripped substrate making
10.2 Calculate the thickness as follows:
sure that it is in the reagent just as long as before. Any loss of
Thickness 5 10 3M/D µm (2)
~ !
mass enables one to make a judgment of a possible error due
to any dissolution of the substrate with the coating during the
where:
stripping process.
M = mass per unit area (mg/cm ), and
9.1.2 By Direct Weighing—The substrate is dissolved in the D = density (g/cm ).
NOTE 3—The density of a coating metal is usually not the same as the
appropriate reagent (see AnnexA1). The coating is rinsed with
handbook value or the theoretical value. For example, the density of
water, rinsed with alcohol, blown dry with clean air, and
electrodeposited gold is generally less than 19.3 g/cm and sometimes as
weighed. To determine if there was any dissolution of the
loworlowerthan17g/cm .Thedensitiesofsomeelectrodepositedmetals
coating, submit the isolated coating to the same stripping
are given by W. H. Safranek.
process making sure that the coating is in the stripping reagent
for the same length of time as it was during the stripping 7
Printed in The Properties of Electrodeposited Metals and Alloys, Second
process. Any loss of mass enables one to make a judgment of 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.
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 A428/A428M.
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.
B767 − 88(2010)
TABLE A1.1 Continued
Coating Substrate Reagents Remarks—Sources
(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 A428/A428M.
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 cons
...
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