Environmental Engineering Reference
In-Depth Information
atoms after total destruction of metal-containing molecules is 10% with respect to
argon atoms. We compare typical times of various processes which are responsi-
ble for evolution of this system. As a result of decomposition of metal-containing
molecules, metal atoms are formed and they are transformed into clusters accord-
ing to scheme (6.66). For simplicity, we assume the binding energies of each halo-
gen atom in the initial molecule
MX
k
and forming radicals to be identical and
equal to
X
. We take the following rates of decay of molecules and radicals in colli-
sions with buffer gas atoms:
ε
N
a
k
gas
exp
T
.
ε
X
ν
D
(6.92)
d
Here
N
a
is the number density of buffer gas atoms,
T
is a current temperature of
buffer gas atoms, and
k
gas
is the gas-kinetic rate constant for collisions of molecules
and radicals with atoms of a buffer gas, that is,
k
gas
v
T
is the
thermal velocity of argon atoms, and the gas kinetic cross section of collision is
σ
D
v
T
σ
gas
,where
10
15
cm
2
. We assume the rate
d
to be independent of the number of
halogen atoms
k
inthemoleculeorradicals.
Let us apply this scheme to metal-containing molecules MoF
6
,WF
6
,IrF
6
,and
WCl
6
at the temperature
T
D
3
ν
gas
in the center of a flow that is given by
N
m
/
N
sat
(
T
)
10 for MoF
6
and WF
6
,and
N
m
/
N
sat
(
T
)
1000 for IrF
6
and WCl
6
,where
N
m
is the total number density of metal atoms in metal-containing molecules,
N
sat
is
the number density of metal toms at the saturated vapor pressure for the indicated
temperature, and
T
ε
X
. Under the above assumption, the time for decompo-
Ta b l e 6 . 3
Parameters of some compounds of heat-resistant metals [41].
T
1
,10
3
K
T
2
,10
3
K
T
3
,10
3
K
Compound
Cluster existence
ε
X
ε
M
HfCl
4
(4.2)
6.0 (6.4)
(2.4)
3.0 (3.2)
3.15
C
HfF
4
(6.3)
6.0 (6.4)
(3.5)
3.0 (3.2)
3.15
-
ThCl
4
(4.7)
5.8 (6.2)
(2.6)
3.0 (3.1)
3.12
C
ThF
4
6.2 (6.5)
5.8 (6.2)
3.5 (3.6)
3.0 (3.1)
3.12
-
TiBr
4
3.0 (3.2)
4.4 (4.9)
1.7 (1.8)
2.2 (2.5)
2.28
C
TiCl
4
3.5 (3.8)
4.4 (4.9)
2.0 (2.1)
2.2 (2.5)
2.28
C
UCl
4
3.8 (4.1)
5.1 (5.5)
2.1 (2.3)
2.6 (2.8)
2.73
C
UF
4
5.7 (5.9)
5.1 (5.5)
3.2 (3.3)
2.6 (2.8)
2.73
-
ZrCl
4
4.3 (4.8)
5.9 (6.3)
2.4 (2.7)
3.0 (3.2)
3.08
C
ZrF
4
6.5 (6.9)
5.9 (6.3)
3.6 (3.9)
3.0 (3.2)
3.08
-
IrF
6
2.2 (2.5)
6.4 (6.9)
1.2 (1.4)
3.2 (3.5)
3.15
C
MoF
6
3.9 (4.2)
6.3 (6.8)
2.2 (2.4)
3.2 (3.4)
3.19
C
UCl
6
3.0 (3.3)
5.1 (5.5)
1.7 (1.8)
2.6 (2.8)
2.73
C
UF
6
4.7 (5.0)
5.1 (5.5)
2.6 (2.8)
2.6 (2.8)
2.73
-
WCl
6
(3.0)
8.4 (8.8)
(1.7)
4.2 (4.4)
4.04
C
WF
6
4.5 (4.9)
8.4 (8.8)
2.5 (2.7)
4.2 (4.4)
4.04
C
