The effect of sulfur dioxide on iron, copper and brass

Introduction

Sulfur dioxide (SO₂ )is a pollutant gas that is often present in urban and industrial areas. Its effect on atmospheric corrosion has been known for many decades and yet it is still the subject of many research investigations ([13], [16] Dehri et al. , 1994, 1999; [29] Nunez et al. , 2005; [26] Mendoza et al. , 2004; [19] El-Mahdy and Kim, 2004; [22] Kilinççeker et al. , 2002; [14] Dehri and Erbil, 2000). The atmosphere, which is already corrosive to metals, becomes more corrosive and the corrosion rate of metals increases when the service environment contains SO₂ . Sulfurous gases are produced by the combustion of fuels in urban areas and, additionally, the oxides of nitrogen, ammonia and similar gases form electrolyte solutions that are highly corrosive. Many researchers believe that SO₂ gas is adsorbed onto moist metal surface, then changed to SO₃ and finally it is oxidized to H₂ SO₄ ([16] Dehri et al. , 1999; [23] Kilinççeker et al. , 1999; [32] Soon et al. , 2007). The H₂ SO₄ thus formed, is absorbed in the oxide film and enhances corrosion activity. The SO₂ cycle in the atmosphere is as shown below ([13] Dehri et al. , 1994; [29] Nunez et al. , 2005; [26] Mendoza et al. , 2004; [19] El-Mahdy and Kim, 2004): Equation 1 [Figure omitted. See Article Image.] Equation 2 [Figure omitted. See Article Image.] Equation 3 [Figure omitted. See Article Image.] Here, SO₂ · H₂ O represents the physically dissolved SO₂ . In the presence of oxygen, these reactions lead to the formation of SO₄^2- ion: Equation 4 [Figure omitted. See Article Image.] There are various views in literature concerning the mechanism of the effect of SO₂ on the atmospheric corrosion of iron, copper and brass. Some of these are given below ([13] Dehri et al. , 1994; [29] Nunez et al. , 2005; [26] Mendoza et al. , 2004; [25] Kilinççeker and Galip, 2008; [24] Kilinççeker, 2008; [6] Babic and Metikos-Hukovic, 1993): Equation 5 [Figure omitted. See Article Image.] Equation 6 [Figure omitted. See Article Image.] The sulfate ion formed in equation (4) is changed to sulfuric acid...