Improving the Corrosion Behavior of Ductile Cast Iron in Sulphuric Acid by Heat Treatment

Figure 
8c
). It is known that for the same metal, under similar conditions, the value of i
a
(at a given potential) may be taken 
to be proportional with the rate of corrosion. 
Figure 9
shows log i
a
(at E= 700 mV) plotted against the reciprocal of 
the absolute temperature (1/T) for the specimen No. 0 as an example and the results are shown to be linear for all 
specimens which can be expressed by Arrhenius equation: 
log i
a
= A-(E* / 2.303 RT)
(2)
Where E* represents the apparent activation energy, the values were determined from the slopes of the straight lines. 
Table 1
includes the value of the apparent activation energy for each specimen. 

---

Ibrahim MAM, et al.
Der Chemica Sinica, 2017, 8(6):513-523
Pelagia Research Library
519
Figure 8:
Potentiodynamic polarization curves for the six specimens in 0.5 M H
2
SO
4
, scan rate 100 mVs
-1
at 40
º
C (a), at 60
º
C (b), 
and at 70
º
C (c).

---

Ibrahim MAM, et al.
Der Chemica Sinica, 2017, 8(6):513-523
Pelagia Research Library
520
Figure 9: 
Dependence of log i
p
on (1/T), (
o
K)
-1
for specimen No. 0 in 0.5 M H
2
SO
4
solution at scan rate of 100 mVs
-1
and at E=700 mV.
Cyclic polarization 
To throw more light on the effect of heat treatment on the electrochemical response of DCI, cyclic polarization 
measurements were performed [26] as shown in 
Figure 10 (a-c)
. It
 
illustrates cyclic polarization of specimen No. 0 in 
1.0 M H
2
SO
4
at 30
º
C and at scan rate of 100 mVs
-1
. The cyclic polarization started from -1500 mV and was reversed at 
various anodic potential limits. Inspections of these results show that if the anodic potential is reversed at the ascending 
branch of the active dissolution region (