The nickel dip : a radioisotope study of metallic deposits in porcelain enameling Page: 4 of 27
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NACA TN 3577
3
distribution of the deposit from the nickel dip. A companion paper
(ref. 4) is concerned with evaluation of the effect of the nickel dip on
adherence and presents a theory to explain the bonding mechanism, This
study is one phase of a broader investigation of the adherence of ceramic
coatings to metals being conducted at the National Bureau of Standards
under the sponsorship and with the financial assistance of the National
Advisory Committee for Aeronautics.
MATERIALS AND GENERAL PROCEDURE
The radioactive isotopes used in this study were procured from the
Oak Ridge National Laboratory, Oak Ridge, Tenn. Radioactive cobalt 60
was used in the form of oxide produced by pile irradiation of normal
cobalt oxide which was chemically pure. This isotope is the same as
that used in a previous study (refs. 1 and 2). The radioactive nickel
63 was produced by pile irradiation of highly purified cobalt-free
nickel. It was converted to nickel ammonium sulfate at the Oak Ridge
National Laboratory before shipment.
Each of these isotopes can be positively identified when present
in microgram quantities provided there is no other radioactive constit-
uent of the sample; and, if the geometry, backscattering, and self-
absorption factors are known, quantitative determinations can be made.
The radioassay is rapid, usually requiring but 1 minute to obtain results
of satisfactory accuracy, and leaves the specimen unaffected by the
determination. The usual chemical analysis for nickel deposits on steel
requires that an area of 0.01 square foot be stripped to provide the
sample. This area is covered by a circle approximately 1l inches in
diameter. With radioactive nickel at the concentrations used in this
study, accurate radioassays could be made on an area as small an 1/8 inch
in diameter. The ratio of areas is about 120:1.
The use of autoradiography, in which a photographic film is placed
in contact with the specimen and is sensitized by particles emitted from
the radioactive isotope, offers a still higher degree of resolution,
which under the most favorable conditions may distinguish between areas
0.001 inch or less in diameter and 0.001 inch apart. The area involved
in this case is only about 1/1,800,000 as much as that normally used for
chemical analysis. In studying the distribution of thin deposits, there-
fore, the use of radioactive isotopes has great advantages. The amount
of darkening produced on a photographic film that has been exposed in
contact with a specimen containing a radioactive isotope deposited on
its surface will bear a direct relationship to the amount of the radio-
active isotope on the specimen. Also, the variation in the amount of dark-
ening, or the distribution of light and dark areas, will give a good picture
of the distribution of the deposit. Spurious effects can be produced, how-
ever, by self-absorption and reflection of the radiations, particularly if
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Richmond, Joseph C.; Kirkpatrick, Harry B. & Harrison, William N. The nickel dip : a radioisotope study of metallic deposits in porcelain enameling, report, February 1956; (https://digital.library.unt.edu/ark:/67531/metadc57892/m1/4/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.