MIL-PRF-4556F
4.3.5.2
Determination of lead by X-ray emission spectroscopy analysis
(alternate method).
4.3.5.2.1 Test panel preparation. Using 100 grams of a known lead free primer
and topcoat, prepare standard aliquots containing 0.00, 0.03, 0.06, and 0.09
percent lead metal, based on total nonvolatile paint, by adding calculated amounts
of lead naphthenate of a known lead content. Thoroughly mix the aliquots to
incorporate the lead and draw down the standards and coatings to be tested on
duplicate black and white charts2 using a 0.0020 inch (0.004 inch gap clearance)
film applicator. Air dry for 48 hours under dust free conditions. Cut the
drawdowns into a suitable size and shape to fit the sample holder of the X-ray
fluorescence spectrometer.
4.3.5.2.2 X-ray analytical procedure. Lead content shall be determined using an
X-ray fluorescence spectrometer capable of determining lead content at a minimum
level of 0.03 percent by weight of the total nonvolatile paint. The parameters of
angle, crystal, pulse height selection, counting time, collimator, X-ray tube,
voltage and amperage, shall be established for a wave length dispersive
fluorescence spectrometer according to conventional X-ray analytical procedures.
The analytical line Pb L-Alpha or Pb L-Beta shall be used. To calibrate, place the
known standards in the X-ray unit and measure the count rates of lead, lead
background and the Compton scattered background from the X-ray tube. The ratio R,
of the net lead intensity and Compton scattered background is calculated as
follows:
Ipb - (Ipb background I + Ipb background II)
R=
2
_________________________________________________
Icompton line
Where I = gross intensity, and the background is taken on each side of the Pb
line. Establish a lead calibration curve using these results. Determine the lead
content of the test coatings using the above procedure and calibration curve.
When using an energy dispersive fluorescence spectrometer, it shall be set up in
accordance with the manufacturer's manual.
4.3.6
Chromium (hexavalent) content.
a.
Reagents:
(1) 25 percent aqueous KOH.
b.
Procedure:
(1) Add 5 ml of 25 percent
aqueous KOH to 1/2 gm of the extracted
pigment contained in a
15 ml centrifuge tube.
(2) Agitate by shaking the
tube for a few minutes then centrifuge.
(3) The supernatant liquid
should be colorless. A yellow color
indicates the presence
of chromate.
4.3.7 Viscosity. Mix four parts, by volume, of component A with one part, by
volume, of the appropriate component B for both primer and topcoat. Allow each
mixture to stand for thirty minutes in sealed containers and measure viscosity
according to ASTM D562. Evaluate for compliance with table I. Make sure that
components of the primer are not mixed with those of the topcoat.
4.3.8 Flash point. Mix samples as specified in 4.3.7 and determine flash points
according to ASTM D3278. Check for compliance with table I.
4.3.9 Drying time. Mix samples as specified in 4.3.7 and prepare drawdowns using
0.004 inch (0.008 inch gap clearance) film applicator on a glass panel and air dry
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