Relation Between Roughness of Interface and Adherence of Porcelain Enamel to Steel Page: 4 of 31
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NACA TN 2934
Each frit, with the appropriate metallic-oxide addition, was batched,
smelted, and prepared as an enamel slip according to standard procedures.
Table III lists the metallic oxides added to the base frit batch to pro-
duce the various frits.
The oxides indicated in table III were chosen for several reasons.
Cobalt, nickel, and manganese oxides are commonly used as adherence-
promotion oxides in commercial ground coats, although manganese oxide
is of no value when used alone and of questionable value when used in
combination with the other two oxides. Antimony and molybdenum oxides
have been reported in the literature (refs. 4 and 5) to promote adherence
to some extent. The other oxides were included because of the position
of the metal in the electromotive-force series of the elementsl in rela-
tion to iron and cobalt. In this series Cr+++ is above Fe++ (which is
considered the active iron ion at the enamel-metal interface); Cd++ is
between Fe++ and Co++; and As+ and Cu++ are considerably below Cot++
Twenty-gage enameling-iron blanks, 4 by 4 inches, were sheared to
size, marked for identification, and punched to provide hanging holes.
The metal blanks were prepared for enameling (a) by sandblasting, (b) by
pickling, using standard procedures not including the nickel dip, or
(c) by grinding and polishing. Photomicrographs of typical uncoated metal
blanks are shown in figure 2 to indicate the degree of surface roughening
produced by these various treatments.
The enamels were applied by dipping, and each slip was adjusted to
give a fired enamel coating 5 1 mils thick. Specimens of all enamels
were fired at 1,5750 F for 4 minutes, except that a temperature of
1,5500 F was used in that part of the study in which adherence was varied
by changing the firing time.
1The electromotive-force series of the elements listed in standard
textbooks was prepared from measurements of the potential developed between
the element and an aqueous solution of the ion involved in which the ion
was at unit activity (approximately one normal for most ions). Under these
conditions the ions used in this study fall in the following order: Mn++,
Cr+, Fe+y, Cdr", Co++, Ni+p, Mo+, Sb+++, As*, and Cu++. It is known
that molten glass acts as an electrolyte and that electrode potentials are
developed in it, but the measurement of such potentials involves serious
experimental difficulties. While the magnitude of the potentials may be
considerably different, it is to be expected that the order of the elements
will be about the same whether the electromotive force is developed in
water or a glass, provided there are no complicating, side reactions in the
glass.3
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Richmond, J. C.; Moore, D. G.; Kirkpatrick, H. B. & Harrison, W. N. Relation Between Roughness of Interface and Adherence of Porcelain Enamel to Steel, report, April 1953; (https://digital.library.unt.edu/ark:/67531/metadc56644/m1/4/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.