MIL-DTL-3301D
4.4.1 Values. Unless otherwise specified, the values specified in Section 3 apply to the average of the
results obtained from duplicate determinations for each particular test.
4.4.2 Heat resistance.
4.4.2.1 Preparation of test panels. Solvent-cleaned, mechanically-polished plain carbon steel panels, 6
by 4 inches, by approximately 1/8 inch thick shall be used. Coat the panels by dipping them into the
molten compound which shall be maintained at 150 to 160 ºC (302 to 320 ºF). Leave the top 1 inch of the
panel uncoated. The film thickness should be approximately 1/16 inch on each side of the panel. Suspend
the panel with the uncoated portion up and allow to cool to room temperature. Trim the excess compound
from the bottom edge of the panel with a hot sharp knife.
4.4.2.2 Procedure. Suspend a panel, prepared as described in 4.4.2.1, in a bath of reagent-grade glycerin
at 109 ± l ºC (228 ± 2 ºF) for 1 hour so that the uncoated end of the panel is uppermost and one half of
coated portion is submerged. Remove the panel and cool by immersion in cold water. Examine the film
for sag or flow. A slight surface displacement at the glycerin line is permissible.
4.4.3 Acid resistance. Place a panel, prepared as described in 4.4.2.1, on a flat horizontal surface. Place
on the coating at different places drops of the following solutions:
Saturated picric acid
Sulfuric acid, sp. gr. 1.30
Nitric acid, sp. gr. 1.22
Hydrochloric acid, sp. gr. 1.09
Allow the acids to remain in contact with the coating for 6 hours while the temperature is maintained at
approximately 21 ºC (70 ºF), covering the drops with small watch glasses in order to prevent evaporation.
Remove the acids by washing with cold water and dry the film at room temperature for 1 hour. Examine
the areas previously in contact with the acids and note if the compound is resistant to each of
these acids as indicated by absence of disintegration, browning, or dulling of the coating. Do not consider
a slight bloom around the area of a spot exposed to acid as an indication of failure to resist the acid.
Remove the coating with benzene and examine the metal. Note if the coating has resisted the action of
each acid as indicated by the absence of any corrosion of the metal.
4.4.4 Water resistance. Suspend a panel, prepared as described in 4.4.2.1 in a beaker of cold distilled
water for 18 hours so that the uncoated end of the panel is uppermost and one half of the coated portion is
submerged. Examine the panel for blistering, whitening, softening, or other visible defects.
4.4.5 Flexibility. A strip of No. 30 gage cold rolled steel sheet, 2 by 8 inches, shall be cleaned by washing
with benzene and thoroughly dried. It shall be coated on one side to a thickness of 1/16 inch by flowing
on the molten compound and then cooled at room temperature for a period of 48 hours. With the coating
on the outside, bend the test panel rapidly 180 degrees over a mandrel 1 inch in diameter. No cracking of
any kind shall be visible after the bending test.
4.4.6 Acidity or alkalinity. Dissolve 5 gm sample of the compound in 10 ml. of toluene which is neutral
to phenolphthalein. Shake the solution with 100 ml. of distilled water in a 250 ml. separator funnel for at
least 5 minutes. Filter and titrate with N /100 H2S04 or N /100 NaOH as necessary using phenolphthalein
as indicator. A blank shall be run on an equal volume of the water used. Calculate the acidity or
alkalinity of the sample as follows:
Acidity as sulfuric acid, percent by weight =
4.9 (C-B) N
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