ASTM B767-88(2006)
(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 cm 2 to obtain 2.5 mg of coating.
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.
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Designation:B767–88(Reapproved 2006)
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 A309 Test Method for Weight and Composition of Coating
on Terne Sheet by the Triple-Spot Test
1.1 This guide outlines a general method for determining
A428/A428M TestMethodforWeight[Mass]ofCoatingon
the mass per unit area of electrodeposited, electroless,
Aluminum-Coated Iron or Steel Articles
mechanically-deposited, vacuum-deposited, anodicoxide, and
B137 Test Method for Measurement of Coating Mass Per
chemical conversion coatings by gravimetric and other chemi-
Unit Area on Anodically Coated Aluminum
cal analysis procedures.
B449 Specification for Chromates on Aluminum
1.2 This guide determines the average mass per unit area
2.2 British Standards Institution Documents:
over a measured area.
BS 729 Hot Dip Galvanized Coatings on Iron and Steel
1.3 The stripping methods cited are described in specifica-
Articles, Specification for
tions or in the open literature or have been used routinely by at
BS 1706 Electroplated Coatings of Cadmium and Zinc on
least one laboratory.
Iron and Steel, Specification for
1.4 The procedures outlined can be used for many coating-
BS 1872 Electroplated Coatings of Tin, Specification for
substrate combinations.They cannot be used where the coating
BS 3189 Phosphate Treatment of Iron and Steel, Specifica-
cannot be separated from the substrate by chemical or physical
tion for
means as would be the case if white brass were plated with
BS 3382 Electroplated Coatings on Threaded Components,
yellow brass.
Specification for
1.5 In principle, these procedures can be used to measure
BS 3597 Electroplated Coatings of 65/35 Tin-Nickel Alloy,
very thin coatings or to measure coatings over small areas, but
Specification for
not thin coatings over small areas. The limits depend on the
2.3 Government Standards:
required accuracy. For example, 2.5 mg/cm of coating might
2 2
2.3.1 DOD Standard:
require 2.5 mg of coating covering 1 cm , but 0.1 mg/cm of
DOD-P-16232F Phosphate Coatings, Heavy, Manganese or
coating would require 25 cm to obtain 2.5 mg of coating.
Zinc Base (for Ferrous Metals)
1.6 This standard does not purport to address all of the
2.3.2 Federal Standards:
safety concerns, if any, associated with its use. It is the
FED-STD 151b Metals; Test Methods: Test 513.1 for
responsibility of the user of this standard to establish appro-
Weight of Coating on Hot Dip Tin Plate and Electrolytic
priate safety and health practices and determine the applica-
Tin Plate
bility of regulatory limitations prior to use.
RR-T-51D Tableware and Flatware—Silverplated
2. Referenced Documents 2.3.3 Military Standard:
MIL-M-45202C Magnesium Alloys, Anodic Treatment of
2.1 ASTM Standards:
2.4 ISO Standards:
A90/A90M Test Method for Weight [Mass] of Coating on
ISO 2081 Metallic Coatings—Electroplated Coatings of
Iron and Steel Articles with Zinc or Zinc-Alloy Coatings
Zinc on Iron or Steel
ISO 2082 Metallic Coatings—Electroplated Coatings on
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. Available from British Standards Institute (BSI), 389 Chiswick High Rd.,
Current edition approved April 1, 2006. Published April 2006. Originally London W4 4AL, U.K.
approved in 1987. Last previous edition approved in 2001 as B767 – 88 (2001). Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,
DOI: 10.1520/B0767-88R06. Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098.
2 5
For referenced ASTM standards, visit the ASTM website, www.astm.org, or AvailablefromU.S.GovernmentPrintingOfficeSuperintendentofDocuments,
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401.
Standards volume information, refer to the standard’s Document Summary page on Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
the ASTM website. 4th Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B767–88 (2006)
Cadmium on Iron or Steel dressing the edges of a rectangular specimen is to clamp the
ISO 2093 Metallic Coatings—Electrodeposited Coatings of specimen between two plastic or metal blocks with the edge of
Tin, Annex B the specimen flush with the edges of the blocks and then to
ISO 2106 Anodizing of Aluminum and its Alloys— grind and polish the edges metallographically.
Determination of Mass Per UnitArea (Surface Density) of 6.4 Heat Treatment—If the substrate is to be dissolved
Anodic Oxide Coatings—Gravimetric Method leaving the coating intact, it is desirable to first heat-treat the
ISO 3892 Conversion Coatings on Metallic Materials— test specimen so that the coating will not curl up tightly or fall
Determination of Coating Mass Per Unit Area— apart. Some gold deposits of 1.5 mg/cm will fall apart when
Gravimetric Methods their substrates are dissolved, but after heat treatment at 120°C
ISO 4522/1 Metallic Coatings—Test Methods for Elec- for 3 h will support themselves. If the thickness of a coating
trodeposited Silver and Silver Alloy Coatings—Part 1: (instead of its mass per unit area) is being determined, one
Determination of Coating Thickness should not use a heat treatment that might change the density
ISO 4524/1 Metallic Coatings—Test Methods for Elec- of the coating material.
trodeposited Gold and Gold Alloy Coatings—Part 1:
7. Measurement of Coated Area:
Determination of Coating Thickness
7.1 Measurement Method—The accuracy of the area mea-
3. Summary of Guide
surement must be better than the desired accuracy of the mass
3.1 The mass of a coating over a measured area is deter-
perunitareameasurement.Hencethemethodofmeasuringthe
mined by the following:
area will depend on the desired accuracy and the specimen
3.1.1 Weighingthetestspecimenbeforeandafterdissolving size.
the coating in a reagent that does not attack the substrate.
7.2 Equipment—The area can be measured with a planime-
3.1.2 Weighing the coating after dissolving the substrate in ter, but it is usually determined by linear measurements. Often
a reagent that does not attack the coating, or
a micrometer or vernier caliper is used. For large areas,
3.1.3 Dissolving both the coating and the substrate and however, a ruler may do. For maximum accuracy, a measuring
quantitatively analyzing the resulting solution.
microscope is used.
3.2 The mass per unit area is calculated from the mass and 7.3 Number of Measurements—Because circular or rectan-
area measurements, the thickness from the mass, area, and
gular specimens will not be perfectly circular or rectangular, it
density of the coating materials. is desirable to measure each dimension in three places. For a
rectangle, one would measure the length of each edge and the
4. Significance and Use
length and width through the center and obtain an average for
4.1 The thickness of a coating is critical to its performance
each dimension.
and is specified in many specifications calling for coatings.
NOTE 1—In the case of a cylinder one would normally measure the
4.2 These procedures are used for acceptance testing and
diameterandlength.Inonespecificationforgalvanizedwire(fencing),the
appear in a few specifications.
length of the wire specimen is not measured, but in effect is calculated
4.3 Coating thickness instruments are often calibrated with
from the mass (which is measured anyway), the radius, and the density of
thickness standards that are based on mass and area measure- the steel substrate. (l=m/pr D)
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
5. Apparatus
enough that the coating can be weighed with the desired
accuracy.
5.1 In addition to normal chemical laboratory equipment for
handling small amounts of corrosive and toxic chemicals, an 8.2 Equipment—A balance is required, but the required
sensitivity of the balance depends on the size of the test
accurate ruler or vernier caliper and a good balance are
required. See Sections 7 and 8. specimen, the coating thickness (coating mass), and the re-
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 balanceweighingto0.0001gismoreversatile.Amicrobalance
areaandmassmeasurementofadequateaccuracy.(SeeSection is required for small specimens of thin coatings, but it is
7 and 8.2.) limited to small samples.
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 weigh-
6.3 EdgeCondition—Iftheareatobemeasuredissmalland ing the test specimen before and after dissolving the coating
needs to be known accurately, the edges must be dressed to (see Annex A1) and taking the difference, or (2) by dissolving
remove smeared coating, to remove loose burrs, and to provide thesubstrate(seeAnnexA1)andweighingthecoatingdirectly.
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
B767–88 (2006)
with clean air, and weighed. The specimen is immersed in the eral analytical methods. For possible analytical methods see
appropriate reagent (see Annex A1) to dissolve the coating, Volumes 03.05 and 03.06 of the Annual Book of ASTM
rinsed with water, rinsed with alcohol, blown dry with clean Standards.
air, and weighed again. The loss of mass is the mass of the
10. Calculation
coating. To determine if there was any dissolution of the
substrate, repeat the process with the stripped substrate making
10.1 Calculate the mass per unit area as follows:
sure that it is in the reagent just as long as before. Any loss of
Mass per unit area 5 m/A ~mg/cm ! (1)
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. where:
9.1.2 By Direct Weighing—The substrate is dissolved in the m = mass of coating (mg), and
A = area covered by coating (cm )
appropriate reagent (seeAnnexA1). The coating is rinsed with
10.2 Calculate the thickness as follows:
water, rinsed with alcohol, blown dry with clean air, and
weighed. To determine if there was any dissolution of the
Thickness 5 10 3 M/D ~µm! (2)
coating, submit the isolated coating to the same stripping
process making sure that the coating is in the stripping reagent
where:
for the same length of time as it was during the stripping
M = mass per unit area (mg/cm ), and
process. Any loss of mass enables one to make a judgment of
D = density (g/cm ).
a possible error due to any dissolution of the coating with the
substrate during the stripping process.
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
NOTE 2—The test procedure given at the end of 9.1.1 and 9.1.2 should 3
electrodeposited gold is generally less than 19.3 g/cm and sometimes as
be conducted to evaluate a gravimetric method the first time it is used. 3
loworlowerthan17g/cm .Thedensitiesofsomeelectrodepositedmetals
9.2 Determination of Mass of Coating by Chemical are given by W. H. Safranek.
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. 7
Printed in The Properties of Electrodeposited Metals and Alloys, Second
For each coating-substrate-reagent combination, there are sev- 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 TableA1.1, 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 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 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 constant.
This procedure appears in the 1945 issue of Test Method B137 and the
1982 issue of ISO Standard 2106.
B767–88 (2006)
Coating Substrate Reagents Remarks—Sources
anodized magnesium magnesium 300 g/L CrO Immerse at ro
...
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