In caustic, universal austenitic stainless steels can only be used below 100oC in concentrations below 50%. Nickel and its corrosion resistant alloys exhibit excellent resistance to caustic alkali corrosion, and the corrosion resistance of the alloy increases as the nickel content increases. Practice has proved that pure nickel 200 alloy and 201 alloy have excellent corrosion resistance in boiling caustic medium of all concentrations, and even in the molten state corrosion resistance is also excellent. When used at temperatures above 315oC, a low carbon nickel 201 alloy is used to prevent the ink from causing brittleness of the material. In addition, when the alkaline solution is doped with chlorates, chlorides, and sulfides, the corrosion rate will increase, while pure nickel will not resist corrosion at higher concentrations of oxygen-containing NH4OH. Corrosion-resistant alloys containing chromium have desirable corrosion resistance in alkaline solutions that are detrimental to the corrosion resistance of pure nickel. In the high concentration of hot alkali, C-22 alloy and 59 alloy with high molybdenum content do not possess suitable corrosion resistance. Corrosion data in alkali are shown in the table.
| Corrosion of Ni200 and Inconel 600 in Boiling KOH | |||||
| Grade | time/d | corrosion average rate/ mm﹒a⁻¹ | |||
| KCI saturated 30% KOH,0.05% KCIO₃ | KCI saturated 47% KOH,0.078% KCIO₃ | ||||
| liquid phase | gaseous phase | liquid phase | gaseous phase | ||
| Ni200 | 26 | 0.005 | 0.003 | 0.003 | 0.008 |
| 600 | 26 | 0.003 | 0.003 | 0.01 | 0.003 |
| Corrosion of Ni200 and Inconel 600 in Boiling KOH | |||||
| Grade | time/d | corrosion average rate/ mm﹒a⁻¹ | |||
| KCI saturated 30% KOH,0.05% KCIO₃ | KCI saturated 47% KOH,0.078% KCIO₃ | ||||
| liquid phase | gaseous phase | liquid phase | gaseous phase | ||
| Ni200 | 26 | 0.005 | 0.003 | 0.003 | 0.008 |
| 600 | 26 | 0.003 | 0.003 | 0.01 | 0.003 |
| Corrosion of Ni200 and Inconel 600 in Boiling KOH | |||||
| Grade | time/d | corrosion average rate/ mm﹒a⁻¹ | |||
| KCI saturated 30% KOH,0.05% KCIO₃ | KCI saturated 47% KOH,0.078% KCIO₃ | ||||
| liquid phase | gaseous phase | liquid phase | gaseous phase | ||
| Ni200 | 26 | 0.005 | 0.003 | 0.003 | 0.008 |
| 600 | 26 | 0.003 | 0.003 | 0.01 | 0.003 |
| Effect of Sulfide on Corrosion Resistance of Ni200 in NaOH | |||
| medium condition | temperature ºC | time/h | corrosion average rate/ mm﹒a⁻¹ |
| 75%NaOH | 121 | 20 | 0.025 |
| 75%NaOH | 204 | 48 | 0.02 |
| 50%~75%NaOH,0.009%S(H₂S) | 108±5 | 19~22 | 0.04 |
| 75% Chemical Pure NaOH | 108±5 | 19~22 | 0.015 |
| 75% Chemical Pure NaOH，0.75% sulfide | 108±5 | 19~22 | 0.58 |
| 75% Chemical Pure NaOH,0.75% sodium sulfite | 108±5 | 19~22 | 0.13 |
| 75% Chemical Pure NaOH,0.75% sodium thiosulfate | 108±5 | 19~22 | 0.2 |
| 75% Chemical Pure NaOH,0.75% sodium sulfuric acid | 108±5 | 19~22 | 0.015 |
Post time: Apr-19-2018