Corrosion-product formation

Many factors influence acid corrosion. Metallurgy, temperature, water turbulence, surface geometry, dissolved oxygen concentration, metal-ion concentration, surface fouling, corrosion-product formation, chemical treatment, and, of course, the kind of acid (oxidizing or nonoxidizing, strong or weak) may markedly alter corrosion. 

Formulation of Corrosion Model. The corrosion products formed on galvanized steel consist of insoluble compounds (Zn(0H)2, ZnC03, etc.) and soluble compounds (ZnS04, Zn(N03)2, etc.). First, the time evolution of the insoluble component will be addressed. The corrosion will be expressed in terms of change in surface thickness due to corrosion product formation. 

Uniform Corrosion with Corrosion Product Formation... 

An example of corrosion product formation is the rusting of iron as illustrated in Fig. 1.3. When the pH is greater than approximately 4, and under aerated conditions, a layer of black Fe304, and possibly Fe(OH)2, forms in contact with the iron substrate. In the presence of the dissolved oxygen, an outer layer of red Fe203 or FeOOH forms. The adherence... 

Importance of Solid Corrosion-Product Formation Corrosion Acceleration Versus Passivation... 

M. Jonsson, D. Persson, D. Thierry, Corrosion product formation during NaCl induced atmospheric corrosion of magnesium alloy AZ91D, Corros. Sci. 49 (2007) 1540—1558. 

Figure 4.27. PWR corrosion product formation, transport and deposition mechanisms (Rodliffe et al., 1987 by courtesy of IAEA)...

Electrochemical techniques exhibit the unique possibility to overcome these problems, as they provide direct access to the corrosion rate and do not need indirect measurement of the time dependence of certain corrosion products formation. The corrosion of iron in air is indeed not given by reaction (7-1), but by the sum of two electrochemical reactions... 

Corrosion reactions can occur by a simple dissolution mechanism, whereby the containment material dissolves in the melt without any impurity effects. Material dissolved in a hot zone may be redeposited in a colder area, possibly compounding the corrosion problem by additional plugging and blockages where deposition has taken place. Dissolution damage may be of a localized nature, for example, by selective dealloying. The second corrosion mechanism is one of reactions involving interstitial (or impurity) elements such as carbon or oxygen in the melt or containment material. Two further subforms are corrosion product formation and elemental transfer. In the former the liquid metal is directly involved in corrosion product formation. In the latter the liquid metal does not react directly with the containment alloy rather, interstitial elements are transferred to, from, or across the liquid. 

In the present study the characterization of the effect of specimen geometry and the effect of exposure under thermal cycling conditions on the oxide scale failure mechanisms were the main objectives. Kinetics of corrosion product formation as well as changes in the chemical composition of both spalled oxide scale segments and internal corrosion products were determined to evaluate the material s resistance to high-temperature corrosion attack. 

Corrosion product formation on a rectanguiar-shaped CMSX-4 specimen after 76 thermai cycies (1 h hot dweii at 7 = 1100°C/0.25 h coid dweii at 40°C). 

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