Micromeritics GEOPYC 1365 Operator's Manual page 73

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NVELOPE
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EPRODUCIBILITY
Achieving high reproducibility in any analytical measurement often requires performing tests in an
identical manner using a single instrument, fixed instrument parameters, and the same quantity of
test material. This is particularly true with the GeoPyc technique because it is very sensitive to
procedural variations and deviations in test parameters. Reproducibility of results of approximately
±1.0% can be expected when parameters are controlled to the fullest extent possible. A description
of these parameters and the criteria that must be observed to achieve this level are described below.
Envelope density is calculated from specimen mass and envelope volume, that is, volume including
both open and closed pores. This volume is measured using Dry Flo, which is confined in a
cylindrical sample chamber having one of five diameters from 12.7 mm (0.5 in.) to 50.8 mm (2.0 in.).
The volume of the specimen is determined by subtracting the volume of consolidated Dry Flo (blank
run) in a sample chamber from the volume of the same consolidated Dry Flo in the same chamber
with the specimen included (test run). The medium bed is agitated through rotation and vibration,
and the consolidation force is gradually increased to the same set value in both phases of a test.
1. The first criterion for a GeoPyc analysis is that the Dry Flo consolidate identically in the blank
and test runs. Repeated testing of the medium alone has shown that, almost without excep-
tion, it actually consolidates with a reproducibility of ±0.34% or better in all size sample cham-
bers for bed depths of one-half to twice the chamber diameter. Somewhat better
reproducibility of ±0.25% is typically achieved when the bed depth is restricted to approx-
imately the chamber diameter. In any event, between one-third and one-quarter of the min-
imal overall error of ±1.0% is due to the nonideal behavior of Dry Flo.
Guideline 1. Start an analysis with a Dry Flo bed depth a little less than the chamber
diameter.
2. Sample quantity plays the most significant role in reproducibility. Obviously, the specimen
extracted from a larger quantity of material must be of sufficient quantity to be representative
of the whole. The quantity of sample determines the minimum sample chamber size required
for analysis. A chamber should be selected in which the sample constitutes a minimum of 20%
of the total sample plus Dry Flo volume when consolidated. A larger percentage of sample is
preferable; however, keep in mind that the sample must always be surrounded sufficiently by
Dry Flo.
Every envelope density result is derived from the difference in two volumes, the consolidated
Dry Flo and the consolidated Dry Flo with sample. That difference should be as large as
possible simply for mathematical significance.
GeoPyc 1365 Operator Manual
136-42800-01 (Rev -) — Dec 2016
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ENSITY
C Envelope Density
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