Chemistry Reference
In-Depth Information
Z content
C
Z
= 0.05 mas. % the value t
50
reaches 250 h. The authors of Refs.
[19, 20] explained this important from the theoretical and practical points of
view effect within the frameworks of the transport processes fractal concept
[21, 22].
For theoretical prediction of the value t
50
, characterizing stability to
cracking, two main assumptions were made [19]. Firstly, it has been sup-
posed, that samples fracture occurs then, when active medium in diffusion
process reaches their median plane. This assumption is based on the analysis
of cracking under stress process [17]. Then the theoretical value
5
t
is given
T
by the main equation of stationary diffusion [23]:
2
l
D
T
50
,
(8.5)
t =
6
dif
where
l
is one half of sample thickness.
D
dif
is active medium diffusivity in
HDPE.
The second assumption consists in the fact, that water molecules clusters
diffusion is considered without appreciation of detergent OP-7 molecular
size. In essence this means that in H
2
O molecules cluster the replacement
of one from these molecules by OP-7 molecule is supposed. Water mol-
ecules cluster formation at interaction with polymer is a well-known fact
[24, 25]. The estimations showed, that in this case cluster consisted of H
2
O
three molecules [25]. The water cluster schematic presentation according to
the data of Ref. [24] is adduced in Fig. 8.11. This scheme allows to calculate
the greatest cluster size
d
m
= 7.8 Ǻ with appreciation of the fact, that water
molecule diameter is equal to 3.08 Ǻ [24].
d
FIGURE 8.11
The model of adsorbed by polymers cluster [24].
is water molecule
H
2
O
diameter,
d
m
is water cluster rated diameter [20].
