Sulfuric acid iron oxide corrosion

Corrosion resistance of nickel allovs is superior to that of cast irons but less than that of pure nickel. There is uttle attack from neutral or alkaline solutions. Oxidizing acids such as nitric are highly detrimental. Cold, concentrated sulfuric acid can be handled. 

Sulfur dioxide emissions may affect building stone and ferrous and nonferrous metals. Sulfurous acid, formed from the reaction of sulfur dioxide with moisture, accelerates the corrosion of iron, steel, and zinc. Sulfur oxides react with copper to produce the green patina of copper sulfate on the surface of the copper. Acids in the form of gases, aerosols, or precipitation may chemically erode building materials such as marble, limestone, and dolomite. Of particular concern is the chemical erosion of historical monuments and works of art. Sulfurous and sulfuric acids formed from sulfur dioxide and sulfur trioxide when they react with moisture may also damage paper and leather. 

The composition of this alloy (54% nickel, 15% molybdenum, 15% chromium, 5% tungsten and 5% iron) is less susceptible to intergranular corrosion at welds. The presence of chromium in this alloy gives it better resistance to oxidizing conditions than the nickel/molybdenum alloy, particularly for durability in wet chlorine and concentrated hypochlorite solutions, and has many applications in chlorination processes. In cases in which hydrochloric and sulfuric acid solutions contain oxidizing agents such as ferric and cupric ions, it is better to use the nickel/molybdenum/ chromium alloy than the nickel/molybdenum alloy. 

Figure 4-422. Corrosion characteristics of iron and 18% Cr stainless steel in diiute sulfuric acid and as a function of soiution oxidizing power (corrosion potential). (From Ref. [187].)...

Zinc and zinc-coated products corrode rapidly in moisture present in the atmosphere. The corrosion process and its mechanism were studied in different media, nitrate [283], perchlorate [259], chloride ions [284], and in simulated acid rain [285]. This process was also investigated in alkaline solutions with various iron oxides or iron hydroxides [286] and in sulfuric acid with oxygen and Fe(III) ions [287]. In the solution with benzothia-zole (BTAH) [287], the protective layer of BTAH that formed on the electrode surface inhibited the Zn corrosion. 

The important point to note is that these bacteria require oxygen and a source of reduced sulfur. The end product is sulfuric acid. The problem of septic sewage systems in hot climates starts with growth of anaerobic SRB in the sewage, producing H2S. This gas migrates to the air space at the top of the line, where it is oxidized into sulfuric acid in the water droplets at the crown of the pipe by Thiobacillus. The corrosion problem is due to the combination of the bacterial action that results in dissolution of the alkaline mortar by the acid, followed by corrosion of the ductile iron. (Stott)5... 

In the atmosphere, sulfur oxides can combine with water and oxygen to form sulfurous and sulfuric acids. The deposition of these acids causes corrosion or decomposition of materials such as limestone, marble, iron, and steel. The deterioration of building facades and monuments is one result of this worldwide problem. Flushing of the sulfur oxides from the air by precipitation (acid rain) can lead to acidification of lakes and sods, weakening or killing plants and animals. 

In sulfuric acid production, acid brick lining of membrane coated mild steel tanks and reaction vessels is considered the most durable and versatile construction material for the sulfuric acid plant. Such linings wiil reduce the steel shell temperature and prevent erosion of the normally protective iron sulfate film that forms in stagnant, concentrated (oxidizing) sulfuric acid. Dilute (red uC ing) sulfuric acid solutions are very corrosive to carbon steel, which must be protected by impermeable (e.g., elastomeric) membranes and acid brick lining systems. Such acid brick linings often employ membranes comprising a thin film of Teflon or Kynar sandwiched between layers of asphalt mastic. 

Recently Perusich and Alkire [105] have proposed a mathematical model to determine the reaction and transport between liquid microjets and a reactive solid surface. Conditions were established under which oxide depassivation and repassivation occurs as a function of ultrasonic intensity, surface film thickness, and fluid microjet surface coverage. The model was based on the concept that cavitation induces sufficient momentum and mass transfer rates (water hammer pressures as described earlier) at a surface to create oxide film stresses leading to depassivation. The model was used to evaluate experimental data on the corrosion behavior of iron in sulfuric acid [106,107], Focused ultrasound was used to investigate processes that influence depassivation and repassivation phenomena on pure and cast iron in 2N H2S04 at two ultrasound frequencies and at power intensities of up to 7.8 kW/cm2. 

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