Chemistry Reference
In-Depth Information
Fig. 11.16
Kinetics of the
heterogeneous decomposition
of h/c H
2
O
2
on surfaces of
construction materials:
niobium, the data obtained by
calorimetry (
1
); nickel-based
alloy NP-2 (unoxidized) (
2
),
the data obtained by
calorimetry (
filled triangles
)
and volumetry (
unfilled
circles
); nickel-based alloy
NP-2 (oxidized) (
3
), the data
obtained by calorimetry
(
filled circles
) and volumetry
(
unfilled triangles
); stainless
steel H8N0T (
4
), the data
obtained by calorimetry
(
filled circles
) and volumetry
(
unfilled circles
);
aluminum-based alloys AD-1
(
5
) and A-000-93 (
6
), the data
obtained by volumetry
2.3
2.5
2.7
2.9
3.1
The good agreement observed between the experimental data obtained by the two
methods, in particular for the stainless steel and the oxidized and unoxidized nickel,
implies that the macrokinetic mechanisms of decomposition on the surfaces of these
metals were the same over a wide temperature range. The decomposition rate was
found to be highest for niobium and nickel (Fig. 11.16) and was independent of the
stirring rate (Fig. 11.17).
Thus one can conclude that the heterogeneous decomposition occurs in the ki-
netic region. The uniformity of the concentration is ensured by molecular diffusion
at lower temperatures and by active convection caused by the growth and detach-
ment of oxygen bubbles near the metal surface at higher temperatures.
Table 11.1
Kinetic constants for the heterogeneous decomposition of h/c H
2
O
2
on the surfaces of
construction materials
Material
Temperatures,
◦
C
Preexponential
factor
k
0S
,
cm s
−
1
Activation
energy
E
S
,kJmol
−
1
10
5
Stainless steel H18N10T
60-160
5
×
86.7
10
5
Aluminum-based alloy AD-1
110-160
1
.
3
×
87.5
1
.
0
×
10
5
Aluminum-based alloy
A-000-93
110-160
87.5
10
8
Niobium
40-90
9
×
83.3
10
7
Nickel-based alloy NP-2
(non-oxidized)
50-110
1
.
5
×
86.7
10
6
Nickel-based alloy NP-2
(oxidized)
70-140
2
.
0
×
86.7
