MIL-DTL-23938B(AS)
where:
A = weight of crucible
B = weight of crucible plus residue
W = weight of sample
4.5.4 Silica content determination. The silica content shall be determined as follows:
a. Wet the residue from HCl insolubles with two drops of concentrated sulfuric acid. Add
about 15 mL of 48 percent hydrofluoric acid. Caution: Pour the acid directly from the
polyethylene bottle and do not measure it in a glass container. If the acid gets on the skin, wash
with water and soap to make sure that none of the material remains on the skin surfaces. This
acid can cause severe burns.
b. Place on a nichrome wire triangle or equivalent and place the triangle on a hot plate. The
triangle should be so adjusted that the bottom of the crucible is about 1-2 mm from the surface of
the hot plate. Heat until all of the acid is evaporated and heavy SO3 fumes are evolved.
c. Place on a burner and evaporate the last traces of SO3. Then, place in a muffle furnace at
1450 ±50 °F. Heat for 30 minutes.
d. Cool in a desiccator and weigh.
e. Calculate as follows:
B-A
percent SiO2 =
x 100
W
where: A = weight of crucible plus residue before HF treatment
B = weight of crucible plus residue after HF treatment
W = weight of sample
4.5.5 Total water solubles determination. The total water solubles shall be determined as
follows:
a. Transfer about 10 grams of the sample weighed to the nearest 0.1 mg to a 250 mL beaker
and add 100 mL distilled water. Bring to a boil and allow to boil for five minutes. Filter while
hot using a close grained paper and collect the filtrate in a clean, dry, 250 mL beaker which has
been previously weighed.
b. Wash the residue once using hot distilled water. Place the beaker with the filtrate on a hot
plate and evaporate to dryness. The sample may boil while evaporating but not so hard as to
allow loss by spattering, especially near the end of the evaporation. Allow to cool and weigh.
Calculate percent water soluble salts.
4.5.6 Sieve analysis.
6
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