MIL-DTL-53030D
4.5.4.2.2.1 Determination of zinc.
4.5.4.2.2.1.1 Reagents.
a. Buffer solution (pH 10): 350 ml concentrated NH4OH + 54g NH4C1 + H2O to give
1000 ml.
b. Eriochrome black T (0.5%): 0.25g Eriochrome black T + 2.2g hydroxylamine
hydrochloride/50 ml methanol solution.
c. Primary standard zinc oxide (0.200N): Accurately weigh 4.069g of oven-dried ZnO.
Dissolve it in 250 ml of the buffer solution and dilute to 500.0 ml.
d. 0.5N Disodium ethylenediaminetetra-acetate dihydrate (EDTA): 37.2g EDTA/liter
aqueous solution.
4.5.4.2.2.1.2 Procedure.
a. Accurately weigh 1.000 gram of pigment into a 250 ml glass-stoppered
Erlenmeyer flask.
b. Add 25 ml of buffer, stopper, and shake vigorously every few minutes over a period
of 30 minutes.
c. Filter through fine paper into a 400 ml beaker, washing well with water until 200 ml
of filtrate are collected.
d. Add 20.0 ml of the EDTA (an excess) to the filtrate.
e. Add 10 drops of Eriochrome black T.
f. Titrate with standard ZnO to a wine-red end point (Vs).
g. Run a blank by titrating 20.0 ml of the EDTA in 200 ml of an aqueous solution
containing 25 ml of the buffer (Vb).
4.5.4.2.2.1.3 Calculations.
Percent Zn = ((Vb Vs) x 0.2 x 3.269) / (Sample weight)
Percent zinc phosphate = ((Vb Vs) x 0.2 x 7.035) / (Sample weight)
Where: Vb = Milliliters of ZnO for blank and
Vs = Milliliters of ZnO for sample.
4.5.4.2.2.2 Determination of phosphate.
4.5.4.2.2.2.1 Reagents.
a.
Concentrated NH4OH
b.
Concentrated HNO3
c.
NH4NO3
d.
Ammonium molybdate - Johnson's formula: Mix 55g of (NH4)6MO7O24 · 4H2O
and 50g of NH4NO3 with 18 ml of concentrated NH4OH and 20 ml H2O. Stir.
Dilute to about 700 ml with H2O. Heat with occasional stirring until all salts have
dissolved. Dilute to 1000 ml. Let stand overnight. Filter through fine paper but do
not wash the residue.
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