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The nature of these solid compounds is relatively unknown, though. So investigations were
started to identify the main constituents and to devise methods to prevent their precipitation.
Results and Discussion
Generally, all samples of the precipitates were taken in air directly after disassembly of
evaporators or filters. They were introduced into an argon filled glove box where they were
washed with n-hexane and dried to remove all silane and soluble organic residues. The
precipitates found in the filters consisted of brown moisture sensitive powders. In pipes and
tubing these powders were compacted and had to be milled before washing and subsequent
analysis.
Elemental analysis of the solid precipitates by inductively coupled plasma atomic emission
spectroscopy (ICP-AES) showed that the main constituents with mass fractions > 10 % are
chlorine, carbon and aluminum. Iron and silicon were identified as secondary constituents with
mass fractions from 1 - 5 %. The actual percentages were found to be varying slightly from
sample to sample depending on the origin, but chlorine is always the element with the highest
mass fraction, followed by carbon and aluminum. A typical result of the elemental analysis of
a press cake sample is shown in figure 2.
Element
Mass
Fraction
[%]
Element
Mass
Fraction
[%]
Cl
37.70
P
0.32
C
27.00
Zr
0.10
Al
10.00
Ti
0.03
Fe
4.80
S
0.03
H
3.50
Na
0.03
Cu
3.20
Ca
0.02
Si
3.00
K
0.01
Sn
1.20
Mn
0.01
Zn
0.72
B
0.01
Figure 2:
Results of ICP-AES elemental analysis of solid precipitates from filters,
percent by weight
The solids were further characterized by scanning electron microscopy (SEM) in combination
with energy dispersive x-ray (EDX) analysis. The SEM images show very homogeneous
samples with particle sizes from 1 to 20
m (Figure 3). The EDX spectra are in very good
agreement with the ICP-AES results.
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