Engineering Materials and Corrosion
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What is the main purpose of material selection in the mining industry?

  • To ensure maximum electrical conductivity
  • To mitigate corrosion and wear-related damages (correct)
  • To reduce operational costs entirely
  • To improve aesthetic appearance of equipment

    • Which of the following best describes alloys?

  • Single-element materials with poor conductivity
  • Materials that are always better than pure metals
  • Pure metals with low density
  • Substances formed by combining multiple elements with special properties (correct)

    • Which factor is NOT typically used to characterize metals?

  • Bright lustre
  • High density
  • Low thermal conductivity (correct)
  • Good ductility

    • What is corrosion primarily defined as?

    <p>A reaction with the environment that deteriorates material properties</p> Signup and view all the answers

    What role do engineers play in the context of corrosion and wear?

    <p>They mitigate corrosion and wear-related costs</p> Signup and view all the answers

    Which of the following is a component of tribology?

    <p>Wear mechanisms</p> Signup and view all the answers

    Which type of materials can undergo corrosion?

    <p>Metals, ceramics, and polymers</p> Signup and view all the answers

    How can the addition of elements to pure metals be summarized?

    <p>It improves the properties and applicability of the metal</p> Signup and view all the answers

    What is the primary role of the anode in an electrochemical cell during corrosion?

    <p>Oxidation of the metal</p> Signup and view all the answers

    Which of the following factors is NOT necessary for electrochemical corrosion to occur?

    <p>High temperature environment</p> Signup and view all the answers

    What product is typically generated when steel corrodes in hydrochloric acid?

    <p>Ferrous chloride</p> Signup and view all the answers

    What does a negative value of Gibbs free energy (∆G) indicate about a material's susceptibility to corrosion?

    <p>Increased susceptibility to corrosion</p> Signup and view all the answers

    During the corrosion of iron, which compound is formed and commonly known as red rust?

    <p>Ferric oxide</p> Signup and view all the answers

    Which requirement is essential for the electrical bridge necessary for electrochemical corrosion to be completed?

    <p>Direct contact between anode and cathode</p> Signup and view all the answers

    What is the significance of the interface between material and environment in the corrosion process?

    <p>It is where the reactions necessary for corrosion take place.</p> Signup and view all the answers

    Which ions are typically involved in the corrosion of steel when placed in an acidic medium?

    <p>Chloride ions</p> Signup and view all the answers

    What does a more negative Gibbs energy (∆G0) indicate about a metal's dissolution rate?

    <p>It may not absolutely indicate a high dissolution rate.</p> Signup and view all the answers

    Which of the following statements about corrosion reactions is true?

    <p>Corrosion reactions involve the concurrent generation and discharge of charged entities.</p> Signup and view all the answers

    What is indicated by a positive value of Gibbs energy (∆G0) for a corrosion reaction?

    <p>The corrosion reaction will never occur.</p> Signup and view all the answers

    In the context of metal corrosion, what do the terms 𝐢→ and 𝐢← represent?

    <p>Electric currents flowing to and from the metal surface.</p> Signup and view all the answers

    What does the exchange current density (𝐢𝑜) depend on according to the provided equations?

    <p>The ion activity and process-related constants.</p> Signup and view all the answers

    What characterizes the relationship between activation energy (∆G∗) and corrosion kinetics?

    <p>Activation energy is crucial for determining the rate of corrosion.</p> Signup and view all the answers

    What can be inferred about the metal's corrosion reaction when its ΔG = 0?

    <p>A dynamic equilibrium is established.</p> Signup and view all the answers

    Which equation relates the electric currents and Gibbs free energy for corrosion?

    <p>𝐢𝑜 = 𝐤 e^{−∆𝐆∗/(𝑅𝑇)}</p> Signup and view all the answers

    What is a primary reason for the high production of new steel according to the Corrosion Institute?

    <p>To replace rusted steel</p> Signup and view all the answers

    What is the main purpose of protective coatings in corrosion prevention?

    <p>To protect structural components from corrosion</p> Signup and view all the answers

    Which method controls corrosion by using a sacrificial metal?

    <p>Cathodic Protection</p> Signup and view all the answers

    What is anodic protection intended to achieve?

    <p>Create a protective layer by applying an anodic current</p> Signup and view all the answers

    Which of the following statements about cathodic protection is true?

    <p>It minimizes anodic dissolution by applying cathodic current.</p> Signup and view all the answers

    What is one disadvantage of corrosion mentioned?

    <p>It causes considerable inconvenience to human beings.</p> Signup and view all the answers

    What are the two methods to generate cathodic current?

    <p>Using sacrificial anodes or an external power source</p> Signup and view all the answers

    What is one of the financial impacts of corrosion as mentioned?

    <p>It leads to substantial financial waste.</p> Signup and view all the answers

    What happens to the anodic current density when corrosion starts on a metal?

    <p>It is greater than the cathodic current density.</p> Signup and view all the answers

    What does the term ∆G+ represent in the context of corrosion?

    <p>The free energy of activation for corrosion.</p> Signup and view all the answers

    Which type of corrosion is characterized by localized attack leading to the formation of small holes or pits?

    <p>Pitting corrosion</p> Signup and view all the answers

    What is a key factor associated with the corrosion rate of a metal?

    <p>The activation energy required for corrosion.</p> Signup and view all the answers

    How much was the economic cost of rust estimated to be in 2016?

    <p>$2.5 trillion</p> Signup and view all the answers

    Which type of corrosion occurs due to a difference in electrochemical potential between two dissimilar metals in contact?

    <p>Galvanic corrosion</p> Signup and view all the answers

    According to the information provided, what percentage of global damage cost can be saved by implementing corrosion prevention protocols?

    <p>15-35 percent</p> Signup and view all the answers

    What is the estimated physical cost of rust in South Africa in 2013?

    <p>R130 billion</p> Signup and view all the answers

    Study Notes

    Introduction

    • Corrosion is a chemical or electrochemical reaction between a material and its environment that deteriorates its properties
    • Corrosion can occur on metals, ceramics, or polymers
    • The environments can be aqueous, non-aqueous liquids, or gases

    Material Selection

    • Engineers play a key role in mitigating corrosion and wear-related costs in the mining industry
    • The selection of materials is one of the solutions to minimize corrosion and wear-related damages

    Engineering Materials

    • Engineering materials are solids useful for humankind
    • Many of these materials are found in combined forms as alloys, compounds, or mixtures
    • The application of pure elements is often limited

    Metals and Alloys

    • Metals are pure engineering materials that are bonded by metallic bonds
    • Pure metals have high density, high electrical and thermal conductivity, bright luster, good ductility, malleability, and opacity
    • The application of pure metals is limited due to their inherent properties
    • Alloys are created by adding one or more elements to a pure metal, improving the overall properties and increasing applicability

    Corrosion

    • Corrosion is a reaction of a material with its environment
    • This reaction can be chemical, electrochemical, physical, or a combination of these
    • The material that is vulnerable can be metals, ceramics, or polymers
    • The environment can be aqueous and non-aqueous liquids and gases

    Electrochemical Corrosion

    • The oxidation reaction occurs at the anode of an electrochemical cell
    • The reduction reaction occurs at the cathode
    • In the case of steel corroding in hydrochloric acid, it produces ferrous chloride and hydrogen gas

    Requirements for Electrochemical Corrosion of Metal

    • Metal oxidation must take place at the anode of an electrolytic cell
    • The reduction of some ions must occur at the cathode
    • There must be a potential applied between the anode and cathode
    • An electrolyte must be present to facilitate the movement of charges
    • An electrical bridge must be completed

    Thermodynamic Aspects of Corrosion

    • The susceptibility of a material to corrode is evaluated by the Gibbs free energy (∆G)
    • The more negative the value of ∆G, the higher the susceptibility for material to corrode
    • The Gibbs energy is only indicative of the tendency of the metal to corrode, not directly related to the corrosion rate

    Kinetics Effect of Metals Corrosion

    • Thermodynamics provides insight into the susceptibility of a system to corrode and requires an equilibrium condition with no net flow of current
    • Corrosion reactions cause current to flow, so the kinetics of corrosion reactions must be considered
    • The equilibrium between the anodic and cathodic reactions at an electrode is not static and the charged entities are generated and discharged concurrently at the conductive surface

    Forms of Corrosion

    • There are eight forms of corrosion:
      • Uniform corrosion (general corrosion)
      • Galvanic corrosion
      • Pitting corrosion
      • Crevice corrosion
      • Selective leaching corrosion (parting corrosion)
      • Inter-granular corrosion
      • Stress corrosion
      • Erosion-corrosion

    Economic Cost of Corrosion

    • Corrosion costs an estimated $2.5 trillion globally each year
    • Implementing corrosion prevention protocols could save an estimated $375-875 billion globally
    • South Africa alone saw around R130 billion in physical damage from corrosion in 2013
    • Mintek and the Corrosion Institute of South Africa (CorrISA) estimate that half of each ton of steel manufactured is to simply replace rusted steel

    Corrosion Impacts

    • Corrosion is expensive financially
    • Corrosion wastes natural resources
    • Corrosion causes inconvenience to human beings

    Corrosion Control

    • Coatings are the most widely applied products for corrosion prevention
    • Painting is used to protect metal substrates from atmospheric corrosivity
    • Cathodic protection (CP) is a corrosion controlling technique which makes the surface of the metal the cathode of an electrochemical process
      • This can be achieved by using connected sacrificial anodes to create a galvanic cell or by applying an external power current source
    • Anodic protection involves the formation of a protective layer on metals by applying an external anodic current

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    Description

    This quiz covers the fundamental concepts of corrosion and the selection of engineering materials to minimize its impact. It explores various materials, including metals and alloys, and their properties. Understanding these principles is crucial for engineers in the mining industry.

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