Introduction to Corrosion & the types.pptx

It's about corrosion techniques

1. GENERAL IDEAS OF Group-04 Md Mosaddique Hossain (134) Sourove Pal (136) Most. Rowshanur Siddique Tua (137) Rakib Hasan Risad (139) Md. Zubaer Hasan Shoyan (141) Md. Abu Zobair Emu (143) Isteak Uddin Mohammed Tanim (147) Shariar Hossain Emon (152) Shafinur Rashid (164) Members

2. Corrosion? Corrosion, in its simplest form, can be defined as the gradual degradation of materials, often metals, due to chemical reactions with their environment. These reactions lead to the deterioration of the material's properties, ultimately compromising its structural integrity and functionality.

3. "Corrosion is a natural process, which converts refined metal to their more chemically stable form, such as oxide, hydroxide, or sulfide." - *Herbert H. Uhlig* "Corrosion is a complex and universal malaise which can be held in check (not cured) by our understanding." - * Niharranjan Mandal* "Corrosion may be defined as an attack on a material as a result of chemical, frequently electrochemical reaction with the surrounding medium." - * Ulick Richardson* In conclusion, corrosion stands as a formidable adversary in the realm of materials science and engineering. By understanding its mechanisms and employing preventive measures, we can mitigate its destructive effects and ensure the longevity and reliability of our structures and devices. As we continue our exploration of corrosion, let us heed the wisdom of these scientists and strive towards innovative solutions to combat this persistent challenge.

4. CONSEQUENCES OF CORROSION • More serious than the simple loss of a mass of metal • Need for expensive replacements may occur even though the amount of metal destroyed is quite small. The major harmful effects of corrosion can be summarized as follows: • Reduction of metal thickness leading to loss of mechanical strength and structural failure or breakdown • Hazards or injuries to people arising from structural failure or breakdown (e.g. bridges, cars, aircraft) • Loss of time in availability of profile-making industrial equipment

5. Classification of Corrosion Corrosion has been classified in many different ways. Mainly corrosion are categorized into two groups as follows: ★General or Uniform corrosion ★Localized corrosion One method divides corrosion into: ★High temperature corrosion ★Low temperature corrosion Another separates corrosion into: ★Chemical corrosion ★Electrochemical corrosion The preferred classification here is: ★Wet corrosion ★Dry corrosion

6. Corrosion Mechanism Wet Corrosion Mechanism Dry Corrosion Mechanism

7. Wet Corrosion Mechanism Metal comes in contact with a conducting liquid or when two dissimilar metals are immersed or dipped partly in a solution. Formation of a galvanic cell on the surface of metals Oxidation of anodic part takes place and it results in corrosion at anode, while reduction. takes place at cathode Anodic Reaction:

8. Corrosion Reactions in Different Medium: To produce a huge amount of electrons for the reduction of H+ rapid oxidation happens in anode which requires a large anodic area and small cathodic area.

9. In absence of Oxyg en In presence of Oxygen Adsorption of Oxygen in cathodic surface Larger cathodic area required because of the lower amount of dissolved oxygen

10. Dry Corrosion Mechanism Oxidation Corrosion: S ome metals directly react with oxygen in absence of moisture and forms metal oxides. This oxide layer protects the metal surface from further corrosion. Corrosion by other Gases: Corrosion is due to direct reaction of atmospheric gases like halogens, oxides of sulfur, nitrogen, hydrogen sulphide and fumes of chemicals with metals Liquid metal corrosion: Industrially happens in metallic pipes when molten metal passes through these. For example, liquid metal mercury dissolves most metals by forming amalgams, thereby corroding them.

11. The thermodynamics of corrosion focuses on understanding the energy changes associated with these chemical reactions. Here's an overview of the thermodynamics involved in corrosion: *Gibbs Free Energy (ΔG):* The driving force behind corrosion reactions is the change in Gibbs free energy. If the Gibbs free energy change (ΔG) for a corrosion reaction is negative, the reaction is thermodynamically favorable and spontaneous. A negative ΔG indicates that the products of the corrosion reaction are more stable than the reactants. *Redox Reactions:* Corrosion often involves oxidation-reduction (redox) reactions, where one substance loses electrons (oxidation) and another gains electrons (reduction). The thermodynamics of these redox reactions can be analyzed using concepts such as standard electrode potentials and Nernst equation. *Pourbaix Diagrams:* Pourbaix diagrams, also known as potential-pH diagrams, are used to predict the stability of different corrosion products under specific conditions of pH and potential. These diagrams provide valuable insights into the thermodynamically stable regions for metals and their corrosion products in aqueous environments.

12. 4. *Activation Energy:* While thermodynamics governs whether a corrosion reaction will occur spontaneously, kinetics also play a crucial role in determining the rate of corrosion. The activation energy barrier must be overcome for the corrosion reaction to proceed, and understanding this energy barrier is essential for predicting and controlling corrosion rates. 5. *Electrochemical Cells:* Corrosion can be viewed as an electrochemical process, where metal dissolution (anodic reaction) and reduction of oxidizing agents (cathodic reaction) occur simultaneously. The thermodynamics of electrochemical cells, including the calculation of cell potentials and equilibrium constants, can provide insights into corrosion mechanisms and behaviors. By applying thermodynamic principles to corrosion processes, scientists and engineers can better understand the factors influencing corrosion behavior, predict the corrosion susceptibility of materials in different environments, and develop strategies to mitigate corrosion damage. This understanding is crucial for designing corrosion-resistant materials, coatings, and corrosion protection systems in various industries, ranging from infrastructure and transportation to manufacturing and electronics.

13. Dissimilar electrode cell Concentration cell Fe Cu Anode: Fe Fe + 3e 3+ - Cathode: Cu + 2e 2+ Cu - Example Salt concentration cell Cathode: Cu (1M)+ 2e Cu 2+ - Metal pipe under soil Example Different concentration cell Anode: Cu (0.1M) + 2e Cu 2+ - Different temperature cell

14. Potential-pH Diagram Potential-pH diagrams are also called Pourbaix diagram after the name of their originator,Marcel Pourbaix (1963),a Belgian electrochemist and corrosion scientist.These diagrams represent the stability of a metal as a function of potential and pH. Potential-pH diagrams are used to predict the Passivity range of metals in contact with water based on the thermodynamic stability of the species in solution and the oxidized species that may form from the metal as a function of temperature and percentage composition of the metal.At a particular combination of pH and potential,a stable phase can be determined from the Pourbaix diagram.

15. Advantages and disadvantages of Potential-pH diagram Significances: Pourbaix approach is extremely useful for visualisation of materials’ behaviour in corrosion environments. This method can help in the analysis of complex environments with multiple ionic species present. The diagrams convinently summarise thermodynamics of the corrosion process and readily propose the remedy( cathodic /anodic protection options). Drawbacks: However,this method is limited to wet corrosion where varying pH is involved. The diagrams fail to account for localised nature of corrosion and provide only general prediction for uniform corrosion. It excludes corrosion by chloride ions. One of the most crucial drawbacks of this is that it shall not be used for evolution of the kinetics of the process .

16. The lines in the diagrams represent redox reactions that occur in neutral solutions (horizontal lines), acid-base reactions (vertical lines), and redox reactions that occur in acid or basic conditions (diagonal lines). Each lines indicate a equilibrium between two species. Introduction to Potential pH diagram iron in water

17. The diagram defines the following zones of the equilibrium states: ➤Below the line a-b-j ➤Area of a-b-n-c-d-e ➤Area of e-d-f-g-k ➤Area of h-f-g-m ➤Area of c-d-f-h- i ➤Area of n-c- i -p ➤Area of b-n-p-j

18. Fig. Pourbaix diagram E -pH, for aluminium Figures show the Pourbaix diagrams of aluminium It helps in understanding the corrosion behavior of aluminum in aqueous environments. In such a diagram, you would typically see regions indicating the stability of different aluminum oxidation states (such as Al(III)), along with regions where various aluminum hydroxide and oxide species are stable. Aluminum is known to undergo passivation in certain pH ranges, forming a protective oxide layer on its surface that inhibits further corrosion. However, in acidic or alkaline conditions, the corrosion rate can increase. Understanding the Pourbaix diagram helps in predicting the corrosion behavior of aluminum and selecting appropriate corrosion prevention strategies .

19. Fig. Pourbaix diagram, E -pH, for chromium A Pourbaix diagram, often referred to as a pH diagram, illustrates the stability regions of different chemical species in an electrochemical system as a function of pH and potential. In the case of chromium in water, the Pourbaix diagram would show the stable forms of chromium (e.g., Cr(III) as well as their oxidation states at various pH and potential conditions. This diagram is crucial for understanding the corrosion behavior of chromium in aqueous environments.

20. The Importance of Corrosion Studies Materials are Precious resources Engineering design is incomplete without knowledge of corrosion Applying knowledge of corrosion protection can minimize disasters Corrosion may contaminate stored food, dairy products, etc . Corrosion products cause pollution. Artificial implants for the human body. THANK YOU