Abstract
The corrosion of Copper in various Ar-O2-SO2 atmospheres was investigated at 500∼1000°C. In 80%Ar atmospheres, the parabolic rate law was followed, not depending on the ratio O2 to SO2. In 40%Ar atmospheres, generally the reaction kinetics was complex and varied in accordance with the O2 to SO2 ratio and the temperature. Furthermore, the weight-gain vs temperature curves showed a maximum at about 700°C in any given atmosheres. This was considered to be due to the eutectic liquid phase between CuO and CuO·CuSO4.
At 500°C, the scale consisted of an outer CuSO4 layer and an inner Cu2O layer, at 600∼800°C generally it was CuSO4/CuO·CuSO4/CuO/Cu2O/Cu2O-Cu2S/Cu from surface to bulk; and above 900°C it consisted of an outer CuO layer and an inner Cu2O layer.
In all experimental conditions, the maximum weight-gain after corrosion for 2 h was found in a 5%O2-95%SO2 atmosphere at 700∼800°C. In this case, CuO·CuSO4 was produced easily, but CuSO4 was not much produced because of the paucity of oxygen in atmosphere. This CuO·CuSO4 reacts with CuO and makes an eutectic liquid. So the rate of corrosion was very fast in this case.
We found a duplex structure of Cu2O-Cu2S at the nearest part of the scale to the bulk metal formed in a 95%O2-5%SO2 atmosphere at 700°C. This indicates that not a little sulfur diffused from surface to bulk. This result may support the experimental result of Birks et al.
