ASTM B767-88(2016)

Standard Guide for Determining Mass Per Unit Area of Electrodeposited and Related Coatings by Gravimetric and Other Chemical Analysis Procedures

SIGNIFICANCE AND USE
4.1 The thickness of a coating is critical to its performance and is specified in many specifications calling for coatings.  
4.2 These procedures are used for acceptance testing and appear in a few specifications.  
4.3 Coating thickness instruments are often calibrated with thickness standards that are based on mass and area measurements.  
4.4 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

• Status: Historical
• Publication Date: 31-Oct-2016
• ICS: 25.220.40 - Metallic coatings
• Technical Committee: B08 - Metallic and Inorganic Coatings
• Drafting Committee: B08.10 - Test Methods

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: B767 − 88 (Reapproved 2016)
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-
onTerne Sheet by theTriple-SpotTest (Withdrawn 2015)
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
BS 1872 Electroplated Coatings of Tin, Specification for
means as would be the case if white brass were plated with
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
Zinc Base (for Ferrous Metals)
standard. No other units of measurement are included in this
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
responsibility of the user of this standard to establish appro-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
priate safety and health practices and determine the applica-
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
bility of regulatory limitations prior to use.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
The last approved version of this historical standard is referenced on
www.astm.org.
1 4
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, 2016. Published November 2016. Originally Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098.
approved in 1987. Last previous edition approved in 2010 as B767 – 88 (2010). AvailablefromU.S.GovernmentPrintingOfficeSuperintendentofDocuments,
DOI: 10.1520/B0767-88R16. 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 (2016)
RR-T-51D Tableware and Flatware—Silverplated 6. Specimen Preparation
2.3.3Military Standard:
6.1 Size—Thespecimenmustbelargeenoughtopermitarea
MIL-M-45202C Magnesium Alloys, Anodic Treatment of
and mass measurement of adequate accuracy. (See Section 7
2.4 ISO Standards:
and 8.2.)
ISO 2081 Metallic Coatings—Electroplated Coatings of
6.2 Shape—The shape of the test specimen must be such
Zinc on Iron or Steel
that the surface area can be easily measured. A rectangular or
ISO 2082 Metallic Coatings—Electroplated Coatings on
circular test specimen is usually suitable.
Cadmium on Iron or Steel
6.3 EdgeCondition—If the area to be measured is small and
ISO 2093 Metallic Coatings—Electrodeposited Coatings of
needs to be known accurately, the edges must be dressed to
Tin, Annex B
remove smeared coating, to remove loose burrs, and to provide
ISO 2106 Anodizing of Aluminum and its Alloys—
well-defined and (for rectangles) straight edges.This should be
Determination of Mass Per UnitArea (Surface Density) of
considered for areas less than 100 mm . One method of
Anodic Oxide Coatings—Gravimetric Method
dressing the edges of a rectangular specimen is to clamp the
ISO 3892 Conversion Coatings on Metallic Materials—
specimen between two plastic or metal blocks with the edge of
Determination of Coating Mass Per Unit Area—
the specimen flush with the edges of the blocks and then to
Gravimetric Methods
grind and polish the edges metallographically.
ISO 4522/1 Metallic Coatings—Test Methods for Electrode-
posited Silver and Silver Alloy Coatings—Part 1: Deter-
6.4 Heat Treatment—If the substrate is to be dissolved
mination of Coating Thickness
leaving the coating intact, it is desirable to first heat-treat the
ISO 4524/1 Metallic Coatings—Test Methods for Electrode-
test specimen so that the coating will not curl up tightly or fall
posited Gold and Gold Alloy Coatings—Part 1: Determi-
apart. Some gold deposits of 1.5 mg/cm will fall apart when
nation of Coating Thickness
their substrates are dissolved, but after heat treatment at 120°C
for 3 h will support themselves. If the thickness of a coating
3. Summary of Guide
(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
7. Measurement of Coated Area:
the coating in a reagent that does not attack the substrate.
7.1 Measurement Method—The accuracy of the area mea-
3.1.2 Weighing the coating after dissolving the substrate in
surement must be better than the desired accuracy of the mass
a reagent that does not attack the coating, or
perunitareameasurement.Hencethemethodofmeasuringthe
3.1.3 Dissolving both the coating and the substrate and
area will depend on the desired accuracy and the specimen
quantitatively analyzing the resulting solution.
size.
3.2 The mass per unit area is calculated from the mass and
7.2 Equipment—The area can be measured with a
area measurements, the thickness from the mass, area, and
planimeter, but it is usually determined by linear measure-
density of the coating materials.
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
measuring microscope is used.
4.1 The thickness of a coating is critical to its performance
and is specified in many specifications calling for coatings.
7.3 Number of Measurements—Because circular or rectan-
gular specimens will not be perfectly circular or rectangular, it
4.2 These procedures are used for acceptance testing and
is desirable to measure each dimension in three places. For a
appear in a few specifications.
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.
NOTE 1—In the case of a cylinder one would normally measure the
4.4 The average thickness of a coating on the measured area
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
from the mass (which is measured anyway), the radius, and the density of
of the coating material is known.
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 (2016)
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 8
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 (2016)
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 %
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: B767 − 88(Reapproved 2010) B767 − 88 (Reapproved 2016)
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
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
2 2 2
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 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.
2. Referenced Documents
2.1 ASTM Standards:
A90/A90M Test Method for Weight [Mass] of Coating on Iron and Steel Articles with Zinc or Zinc-Alloy Coatings
A309 Test Method for Weight and Composition of Coating on Terne Sheet by the Triple-Spot Test (Withdrawn 2015)
A428/A428M Test Method for Weight [Mass] of Coating on Aluminum-Coated Iron or Steel Articles
B137 Test Method for Measurement of Coating Mass Per Unit Area on Anodically Coated Aluminum
B449 Specification for Chromates on Aluminum
2.2 British Standards Institution Documents:
BS 729 Hot Dip Galvanized Coatings on Iron and Steel Articles, Specification for
BS 1706 Electroplated Coatings of Cadmium and Zinc on Iron and Steel, Specification for
BS 1872 Electroplated Coatings of Tin, Specification for
BS 3189 Phosphate Treatment of Iron and Steel, Specification for
BS 3382 Electroplated Coatings on Threaded Components, Specification for
BS 3597 Electroplated Coatings of 65/35 Tin-Nickel Alloy, Specification for
This guide is under the jurisdiction of ASTM Committee B08 on Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on Test
Methods.
Current edition approved Nov. 1, 2010Nov. 1, 2016. Published November 2010 November 2016. Originally approved in 1987. Last previous edition approved in 20062010
as B767 – 88 (2006).(2010). DOI: 10.1520/B0767-88R10.10.1520/B0767-88R16.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Available from British Standards Institute (BSI), 389 Chiswick High Rd., London W4 4AL, U.K.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B767 − 88 (2016)
2.3 Government Standards:
2.3.1 DOD Standard:
DOD-P-16232F Phosphate Coatings, Heavy, Manganese or Zinc Base (for Ferrous Metals)
2.3.2 Federal Standards:
FED-STD 151b Metals; Test Methods: Test 513.1 for Weight of Coating on Hot Dip Tin Plate and Electrolytic Tin Plate
RR-T-51D Tableware and Flatware—Silverplated
2.3.3 Military Standard:
MIL-M-45202C Magnesium Alloys, Anodic Treatment of
2.4 ISO Standards:
ISO 2081 Metallic Coatings—Electroplated Coatings of Zinc on Iron or Steel
ISO 2082 Metallic Coatings—Electroplated Coatings on Cadmium on Iron or Steel
ISO 2093 Metallic Coatings—Electrodeposited Coatings of Tin, Annex B
ISO 2106 Anodizing of Aluminum and its Alloys—Determination of Mass Per Unit Area (Surface Density) of Anodic Oxide
Coatings—Gravimetric Method
ISO 3892 Conversion Coatings on Metallic Materials—Determination of Coating Mass Per Unit Area—Gravimetric Methods
ISO 4522/1 Metallic Coatings—Test Methods for Electrodeposited Silver and Silver Alloy Coatings—Part 1: Determination of
Coating Thickness
ISO 4524/1 Metallic Coatings—Test Methods for Electrodeposited Gold and Gold Alloy Coatings—Part 1: Determination of
Coating Thickness
3. Summary of Guide
3.1 The mass of a coating over a measured area is determined by the following:
3.1.1 Weighing the test specimen before and after dissolving the coating in a reagent that does not attack the substrate.
3.1.2 Weighing the coating after dissolving the substrate in a reagent that does not attack the coating, or
3.1.3 Dissolving both the coating and the substrate and quantitatively analyzing the resulting solution.
3.2 The mass per unit area is calculated from the mass and area measurements, the thickness from the mass, area, and density
of the coating materials.
4. Significance and Use
4.1 The thickness of a coating is critical to its performance and is specified in many specifications calling for coatings.
4.2 These procedures are used for acceptance testing and appear in a few specifications.
4.3 Coating thickness instruments are often calibrated with thickness standards that are based on mass and area measurements.
4.4 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.
5. Apparatus
5.1 In addition to normal chemical laboratory equipment for handling small amounts of corrosive and toxic chemicals, an
accurate ruler or vernier caliper and a good balance are required. See Sections 7 and 8.
6. Specimen Preparation
6.1 Size—The specimen must be large enough to permit area and mass measurement of adequate accuracy. (See Section 7 and
8.2.)
6.2 Shape—The shape of the test specimen must be such that the surface area can be easily measured. A rectangular or circular
test specimen is usually suitable.
6.3 Edge Condition—If the area to be measured is small and needs to be known accurately, the edges must be dressed to remove
smeared coating, to remove loose burrs, and to provide well-defined and (for rectangles) straight edges. This should be considered
for areas less than 100 mm . One method of dressing the edges of a rectangular specimen is to clamp the specimen between two
plastic or metal blocks with the edge of the specimen flush with the edges of the blocks and then to grind and polish the edges
metallographically.
6.4 Heat Treatment—If the substrate is to be dissolved leaving the coating intact, it is desirable to first heat-treat the 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 their
Available from Standardization Documents Order Desk, DODSSP, Bldg. 4, Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098.
Available from U.S. Government Printing Office Superintendent of Documents, 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036.
B767 − 88 (2016)
substrates are dissolved, but after heat treatment at 120°C for 3 h will support themselves. If the thickness of a coating (instead
of its mass per unit area) is being determined, one should not use a heat treatment that might change the density of the coating
material.
7. Measurement of Coated Area:
7.1 Measurement Method—The accuracy of the area measurement must be better than the desired accuracy of the mass per unit
area measurement. Hence the method of measuring the area will depend on the desired accuracy and the specimen size.
7.2 Equipment—The area can be measured with a planimeter, but it is usually determined by linear measurements. Often a
micrometer or vernier caliper is used. For large areas, however, a ruler may do. For maximum accuracy, a measuring microscope
is used.
7.3 Number of Measurements—Because circular or rectangular specimens will not be perfectly circular or rectangular, it is
desirable to measure each dimension in three places. For a rectangle, one would measure the length of each edge and the length
and width through the center and obtain an average for each dimension.
NOTE 1—In the case of a cylinder one would normally measure the diameter and length. In one specification for galvanized wire (fencing), the 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)
8. Gravimetric Determination of Mass of Coating:
8.1 Specimen Size—The accuracy of the mass measurement must be better than the desired accuracy of the mass per unit area
measurement. Hence, the test specimen must be large enough that the coating can be weighed with the desired accuracy.
8.2 Equipment—A balance is required, but the required sensitivity of the balance depends on the size of the test specimen, the
coating thickness (coating mass), and the required accuracy of the measurement. A balance that weighs to 0.01 g is sometimes
satisfactory, though a good analytical balance weighing to 0.0001 g is more versatile. A microbalance is required for small
specimens of thin coatings, but it is limited to small samples.
9. Procedure
9.1 The mass of coating may be determined: (1) by weighing the test specimen before and after dissolving the coating (see
Annex A1) and taking the difference, or (2) by dissolving the substrate (see Annex A1) and weighing the coating directly.
9.1.1 By Difference—The test specimen is first cleaned of any foreign material and finally rinsed with alcohol, blown dry with
clean air, and weighed. The specimen is immersed in the appropriate reagent (see Annex A1) to dissolve the coating, rinsed with
water, rinsed with alcohol, blown dry with clean air, and weighed again. The loss of mass is the mass of the coating. To determine
if there was any dissolution of the substrate, repeat the process with the stripped substrate making sure that it is in the reagent just
as long as before. Any loss of mass enables one to make a judgment of a possible error due to any dissolution of the substrate with
the coating during the stripping process.
9.1.2 By Direct Weighing—The substrate is dissolved in the appropriate reagent (see Annex A1). The coating is rinsed with
water, rinsed with alcohol, blown dry with clean air, and weighed. To determine if there was any dissolution of the coating, submit
the isolated coating to the same stripping process making sure that the coating is in the stripping reagent for the same length of
time as it was during the stripping process. Any loss of mass enables one to make a judgment of a possible error due to any
dissolution of the coating with the substrate during the stripping process.
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.
9.2 Determination of Mass of Coating by Chemical Analysis—This method is by nature very general. Both the 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 several analytical methods. For possible analytical methods see Volumes 03.05
and 03.06 of the Annual Book of ASTM Standards.
10. Calculation
10.1 Calculate the mass per unit area as follows:
Mass per unit area 5 m/A mg/cm (1)
~ !
where:
m = mass of coating (mg), and
A = area covered by coating (cm )
10.2 Calculate the thickness as follows:
Thickness 5 10 3M/D µm (2)
~ !
B767 − 88 (2016)
where:
M = mass per unit area (mg/cm ), and
D = density (g/cm ).
NOTE 3—The density of a coating metal is usually not the same as the handbook value or the theoretical value. For example, the density of
3 3
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 are
given by W. H. Safranek.
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 included in the literature as references because they contain the information from
which this table is based.
A1.1
With many of the reagents given in Table A1.1, there may be some dissolution of the layer other than the one being stripped.
Often the dissolution is not significant, but the possibility should be tested for as suggested in 9.1.1, and 9.1.2.
A1.2
Dissolution is carried out at room temperature unless otherwise indicated. All test pieces are rinsed and dried (see 9.1.1 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, immerse 3 s in
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.
(2) 100 g SnCl H O in 1L concentrated K
...