Explore chapters and articles related to this topic
Open-Circuit Metal Dissolution Processes
Published in Madhav Datta, Electrodissolution Processes, 2020
A summary of thermodynamic data in the form of potential-pH diagrams, devised by Pourbaix, is popularly known as the Pourbaix diagram [10]. The diagrams are generally constructed using equilibrium constants, solubility data, and a form of the Nernst equation which includes a pH term. These diagrams provide useful information about the ability to predict the occurrence of corrosion, the nature of possible corrosion products, and predicting the influence of environmental changes on the corrosion reaction. However, since these diagrams do not provide any information about the kinetics of reactions, these diagrams cannot be used to assess the extent of corrosion damage.
Introduction to different electrochemical corrosion monitoring techniques
Published in Stefan Ritter, Anders Molander, Corrosion monitoring in nuclear systems: research and applications, 2017
Rik-Wouter Bosch, Walter F. Bogaerts
For the interpretation of the corrosion potential value, a Pourbaix or E–pH diagram [23] is one of the most powerful tools. In a Pourbaix diagram, the thermodynamic stability of a metal in water is given as a function of pH and potential. It allows one to determine the region where the metal is susceptible to corrosion (active region), where there is no corrosion at all (immunity region), and where the metal is covered by a protective oxide layer (passive region). It should be mentioned, however, that even though Pourbaix diagrams are very helpful, they do not give any information on the kinetics of reactions. For instance, the corrosion rate in the passive range not only depends on the thermodynamic stability of metal oxides, but moreover on the protective nature of the passive film. Also, the effect of more complex chemistries in the surroundings, e.g. aggressive or inhibitive ions, is not considered in these diagrams.
Metallic Biomaterials
Published in Joyce Y. Wong, Joseph D. Bronzino, Biomaterials, 2007
The Pourbaix diagram is a plot of regions of corrosion, passivity, and immunity as they depend on electrode potential and pH [Pourbaix, 1974]. The Pourbaix diagrams are derived from the Nernst equation and from the solubility of the degradation products and the equilibrium constants of the reaction. For the sake of definition, the corrosion region is set arbitrarily at a concentration of greater than 10–6 g atom/l (molar) or more of metal in the solution at equilibrium. This corresponds to about 0.06 mg/l for metals such as iron and copper, and 0.03 mg/l for aluminum. Immunity is defined as equilibrium between metal and its ions at less than 10–6M. In the region of immunity, the corrosion is energetically impossible. Immunity is also referred to as cathodic protection. In the passivation domain, the stable solid constituent is an oxide, hydroxide, hydride, or a salt of the metal. Passivity is defined as equilibrium between a metal and its reaction products (oxides, hydroxides, etc.) at a concentration of 10–6M or less. This situation is useful if reaction products are adherent. In the biomaterials setting, passivity may or may not be adequate; disruption of a passive layer may cause an increase in corrosion. The equilibrium state may not occur if reaction products are removed by the tissue fluid. Materials differ in their propensity to re-establish a passive layer which has been damaged. This layer of material may protect the underlying metal if it is firmly adherent and nonporous; in that case further corrosion is prevented. Passivation can also result from a concentration polarization due to a buildup of ions near the electrodes. This is not likely to occur in the body since the ions are continually replenished. Cathodic depolarization reactions can aid in the passivation of a metal by virtue of an energy barrier which hinders the kinetics. Equation 1.5 and Equation 1.6 are examples.
In situ quantitative topographic measurement and corrosion behaviour of low carbon steel in chloride solutions
Published in Corrosion Engineering, Science and Technology, 2023
Ebenezer O. Fanijo, Joseph G. Thomas, Yizheng Zhu, Wenjun Cai, Alexander S. Brand
The SMI surface topography map during the initiation and propagation of each corroded surface is shown in Figures 9 and 10, respectively. The cross-sectional plots, before corrosion activity on the as-polished surface, during the initiation and propagation of reaction are presented in Figure 11. For the sample without chlorides (Figure 9(a)), the early-age corrosion morphology showed localised shallow pits, ranging between 10 and 30 nm in depth, that nucleated after 1100 s. The localised pits can be attributed to a gradual breakdown in the oxidation film [41]. According to the Pourbaix diagram, carbon steel exposed to a pH 5 solution is not expected to experience passivation behaviour [72,73]. Nevertheless, an oxidation film forms following the exposure of the steel to air, and this film is assumed to be composed of an iron oxide (Fe2O3) compound with a thickness of ≤ 20 nm [74,75]. Hence, the time barrier for the localised pit to initiate is owing to the gradual breakdown of this oxide layer. This oxide breakdown is also evidenced by the steady roughening observed on the surface map, with the increase in the RMS value to 34.35 nm, (i.e. ∼50% greater than the as-polished surface). Likewise, the cross-sectional profile (Figure 11(a)) during corrosion initiation also confirmed the increase in surface height retreat from the uncorroded sample surface.
Experimental assessment of cement hydration and leaching characteristics for waste-to-energy bottom ash mixed with concrete
Published in Journal of the Air & Waste Management Association, 2021
Jinwoo An, Boo Hyun Nam, Byoung Hooi Cho, Jongwan Eun
Based on the results of the SPLP test, the optimum addition of BA to capture metal elements in the cement matrix could be between 10-30% of BA (see Figure 7). Most of the copper or copper compounds will be physically encapsulated in the cement matrix. Metallic copper could be oxidized through the combustion process. Based on Pourbaix diagram for copper, most of copper oxides remain in oxidized form with the high pH condition. Thus, copper may not react with other hydrates in a cement matrix. In other words, most of copper oxides physically embedded in hardened concrete. However, there is still the possibility that a small amount of copper ions (Cu2+) from copper oxide may react with cement components. During cement hydration which can cause a pH over 12, high concentrations of chloride and sulfate can result in
Durability of reinforced concrete bridges in marine environments
Published in Structure and Infrastructure Engineering, 2020
Rob E. Melchers, Igor A. Chaves
In brief, for corrosion to be possible, it is necessary to satisfy the thermodynamic conditions for the chemical reactions involved. In electrochemistry these are summarised in the Pourbaix diagram (Jones, 1996). It shows that without an applied potential (such as often is applied in electrochemical tests), corrosion of ferrous iron in pure water can occur only for pH < about 9 (Chitty et al., 2005; Jones, 1996; Pourbaix, 1970). The addition of chlorides to the solution can initiate pitting corrosion at (much) higher pH values, the incipient pH increasing with chloride concentration (Pourbaix, 1970). These conditions are well-established. However, they only indicate whether corrosion can occur, not how fast it will progress. The latter is important for infrastructure applications.