Experimental
Commercially supplied AISI 316 stainless steel plate (thickness: 0.2mm) with chemical composition of C: 0.05 mass%, Si: 0.63%, Mn: 0.90%, P: 0.032%, S: 0.002%, Cr: 18.05%, Ni: 8.10%, Fe: balanced was used as material in the corrosion tests. In the case of the pitting corrosion test, the plate was cut to be 200 mm x 20 mm square shape. The central area of 10 mm x 10 mm was used as the test area and the remaining area was sealed with solidified liquid silicon gum (Fig. 1).
The series of NaCl solutions were prepared with different Cl- concentrations (table 1).
The concentrations of NaCl solutions for corrosion tests| No |
Mass of NaCl, mg/l |
Cl- content, mg/l |
| 1 |
|
150 |
| 2 |
|
200 |
| 3 |
|
250 |
| 4 |
|
300 |
| 5 | | 350 |
| 6 |
|
5000 |
| 7 | | 10000 |
| 8 | | 50000 |
| 9 | | 100000 |
All corrosion tests were carried out in a corrosion cell connected to a potentiostat and an ultrasound unit (100 W, 28 kHz) (Fig.1). The mean intensity of US on the specimen surface was about 3 £ 103 W/m2. The specimen was immersed in NaCl aqueous solution in the corrosion cell and the temperature was kept at 20 and 50 °C. A platinum plate was used as the counter electrode and a saturated silver chloride electrode (S.S.C.E.) was used as the reference electrode.