ASTM B767-88(2001)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:B767–88(Reapproved 2001)
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 Aluminum-Coated Iron or Steel Articles
B 137 Test Method for Measurement of Coating Mass Per
1.1 This guide outlines a general method for determining
Unit Area on Anodically Coated Aluminum
the mass per unit area of electrodeposited, electroless,
B 449 Specification for Chromates on Aluminum
mechanically-deposited, vacuum-deposited, anodicoxide, and
2.2 British Standards Institution Documents:
chemical conversion coatings by gravimetric and other chemi-
BS 729 Hot Dip Galvanized Coatings on Iron and Steel
cal analysis procedures.
Articles, Specification for:
1.2 This guide determines the average mass per unit area
BS 1706 Electroplated Coatings of Cadmium and Zinc on
over a measured area.
Iron and Steel, Specification for:
1.3 The stripping methods cited are described in specifica-
BS 1872 Electroplated Coatings of Tin, Specification for:
tions or in the open literature or have been used routinely by at
BS 3189 Phosphate Treatment of Iron and Steel, Specifica-
least one laboratory.
tion for:
1.4 The procedures outlined can be used for many coating-
BS 3382 Electroplated Coatings on Threaded Components,
substrate combinations.They cannot be used where the coating
Specification for:
cannot be separated from the substrate by chemical or physical
BS 3597 Electroplated Coatings of 65/35 Tin-Nickel Alloy,
means as would be the case if white brass were plated with
Specification for:
yellow brass.
2.3 Government Standards:
1.5 In principle, these procedures can be used to measure
2.3.1 DOD Standard:
very thin coatings or to measure coatings over small areas, but
DOD-P-16232F Phosphate Coatings, Heavy, Manganese or
not thin coatings over small areas. The limits depend on the
Zinc Base (for Ferrous Metals)
required accuracy. For example, 2.5 mg/cm of coating might
2 2
2.3.2 Federal Standards:
require 2.5 mg of coating covering 1 cm , but 0.1 mg/cm of
FED-STD 151b Metals; Test Methods: Test 513.1 for
coating would require 25 cm to obtain 2.5 mg of coating.
Weight of Coating on Hot Dip Tin Plate and Electrolytic
1.6 This standard does not purport to address all of the
Tin 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-
2.3.3 Military Standard:
priate safety and health practices and determine the applica-
MIL-M-45202C Magnesium Alloys, Anodic Treatment of
bility of regulatory limitations prior to use.
2.4 ISO Standards:
2. Referenced Documents ISO 2081 Metallic Coatings—Electroplated Coatings of
Zinc on Iron or Steel
2.1 ASTM Standards:
ISO 2082 Metallic Coatings—Electroplated Coatings on
A 90/A 90 M Test Method for Weight (Mass) of Coating on
Cadmium on Iron or Steel
Iron and Steel Articles with Zinc or Zinc-Alloy Coatings
ISO 2093 Metallic Coatings—Electrodeposited Coatings of
A 309 Test Method for Weight and Composition of Coating
Tin, Annex B
on Terne Sheet by the Triple-Spot Test
A 428 Test Method for Weight (Mass) of Coating on
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 B08 on Metallic and MK14 6L3, England.
Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 on AvailablefromStandardizationDocumentsOrderDesk,Bldg.4SectionD,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.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B767
ISO 2106 Anodizing of Aluminum and its Alloys— the specimen flush with the edges of the blocks and then to
Determination of Mass Per UnitArea (Surface Density) of grind and polish the edges metallographically.
Anodic Oxide Coatings—Gravimetric Method 6.4 Heat Treatment—If the substrate is to be dissolved
ISO 3892 Conversion Coatings on Metallic Materials— leaving the coating intact, it is desirable to first heat-treat the
Determination of Coating Mass Per Unit Area— test specimen so that the coating will not curl up tightly or fall
Gravimetric Methods apart. Some gold deposits of 1.5 mg/cm will fall apart when
ISO 4522/1 Metallic Coatings—Test Methods for Elec- their substrates are dissolved, but after heat treatment at 120°C
trodeposited Silver and Silver Alloy Coatings—Part 1: for 3 h will support themselves. If the thickness of a coating
Determination of Coating Thickness (instead of its mass per unit area) is being determined, one
ISO 4524/1 Metallic Coatings—Test Methods for Elec- should not use a heat treatment that might change the density
trodeposited Gold and Gold Alloy Coatings—Part 1: of the coating material.
Determination of Coating Thickness
7. Measurement of Coated Area:
3. Summary of Guide
7.1 Measurement Method—The accuracy of the area mea-
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.
4.2 These procedures are used for acceptance testing and NOTE 1—In the case of a cylinder one would normally measure the
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.
4.4 The average thickness of a coating on the measured area
8. Gravimetric Determination of Mass of Coating:
can be calculated from its mass per unit area only if the density
8.1 Specimen Size—The accuracy of the mass measurement
of the coating material is known.
must be better than the desired accuracy of the mass per unit
area measurement. Hence, the test specimen must be large
5. Apparatus
enough that the coating can be weighed with the desired
5.1 In addition to normal chemical laboratory equipment for
accuracy.
handling small amounts of corrosive and toxic chemicals, an
8.2 Equipment—A balance is required, but the required
accurate ruler or vernier caliper and a good balance are
sensitivity of the balance depends on the size of the test
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
area and mass measurement of adequate accuracy. (Section 7 is required for small specimens of thin coatings, but it is
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 Themassofcoatingmaybedetermined(1)byweighing
6.3 EdgeCondition—Iftheareatobemeasuredissmalland the test specimen before and after dissolving the coating (see
needs to be known accurately, the edges must be dressed to Annex A1) and taking the difference or (2) by dissolving the
remove smeared coating, to remove loose burrs, and to provide substrate (see Annex A1) 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 A1) to dissolve the coating,
B767
rinsed with water, rinsed with alcohol, blown dry with clean eral analytical methods. For possible analytical methods see
air, and weighed again. The loss of mass is the mass of the vols 03.05 and 03.06 of the Annual Book of ASTM Standards.
coating. To determine if there was any dissolution of the
10. Calculation
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 enables one to make a judgment of a possible error due 2
Mass per unit area 5 m/A ~mg/cm ! (1)
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
appropriate reagent (see Annex A1. The coating is rinsed with
A = area covered by coating (cm )
water, rinsed with alcohol, blown dry with clean air, and
10.2 Calculate the thickness as follows:
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
for the same length of time as it was during the stripping
where:
process. Any loss of mass enables one to make a judgment of 2
M = mass per unit area (mg/cm ), and
a possible error due to any dissolution of the coating with the
D = density (g/cm ).
substrate during the stripping process.
NOTE 3—The density of a coating metal is usually not the same as the
NOTE 2—The test procedure given at the end of 9.1.1 and 9.1.2 should handbook value or the theoretical value. For example, the density of
be conducted to evaluate a gravimetric method the first time it is used. electrodeposited gold is generally less than 19.3 g/cm and sometimes as
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. 8
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 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.
B767
Coating Substrate Reagents Remarks—Sources
This procedure appears in Military Standard MIL-M-45202C.
brass steel 500 g/L
...