Material Defects and Vacancies Quiz
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Questions and Answers

What type of defect is a vacancy classified as?

  • Bulk defect
  • Planar defect
  • Linear defect
  • Point defect (correct)

    • All crystalline solids are free of vacancies.

    False

    What is the relationship between temperature and the number of vacancies in a material?

    The number of vacancies increases exponentially with temperature.

    The energy required for the formation of a vacancy is measured in _____ per atom.

    <p>eV</p> Signup and view all the answers

    Match the following types of defects with their descriptions:

    <p>Point defect = Vacancy, Interstitial or Substitutional atoms Linear defect = Dislocations Planar defect = Grain boundaries Bulk defect = Pores and inclusions</p> Signup and view all the answers

    Which of the following statements about vacancies is true?

    <p>Vacancies are necessary for the stability of crystalline solids.</p> Signup and view all the answers

    Which of the following is an example of a point defect?

    <p>Vacancy</p> Signup and view all the answers

    All crystalline materials exist perfectly without any defects.

    <p>False</p> Signup and view all the answers

    Vacancies increase the _____ of the crystal.

    <p>entropy</p> Signup and view all the answers

    What is the primary purpose of a catalytic converter in an automobile?

    <p>To reduce pollutant emissions.</p> Signup and view all the answers

    What is the activation energy for vacancy formation in copper?

    <p>0.9 eV/atom</p> Signup and view all the answers

    A _______ defect is characterized by an irregularity in the atomic lattice structure at a point level.

    <p>point</p> Signup and view all the answers

    Match the types of defects with their classifications:

    <p>Vacancy = Point Defect Edge Dislocation = Linear Defect Interstitial Impurity = Point Defect Screw Dislocation = Linear Defect</p> Signup and view all the answers

    Which type of defect refers to the regular arrangement of atoms being interrupted by additional atoms in interstitial positions?

    <p>Interstitial impurity</p> Signup and view all the answers

    The presence of imperfections in solids only has negative effects on material properties.

    <p>False</p> Signup and view all the answers

    Name one type of linear defect mentioned in the lecture.

    <p>Edge dislocation or screw dislocation.</p> Signup and view all the answers

    What is a self-interstitial in a crystal structure?

    <p>An atom crowded into an interstitial site</p> Signup and view all the answers

    Impurity atoms can make a metal stronger and more resistant to corrosion.

    <p>True</p> Signup and view all the answers

    What is the composition of sterling silver?

    <p>92.5% silver and 7.5% copper</p> Signup and view all the answers

    The density of the material is given as __________ g/cm³.

    <p>8.4</p> Signup and view all the answers

    What is the typical purity level for most familiar metals?

    <p>Usually less than 99.9999%</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Self-Interstitial = An atom occupying an interstitial site Impurity Atom = An atom foreign to the main substance Alloy = A mixture of metals or a metal and another element Solid Solution = A homogeneous mixture of two or more substances</p> Signup and view all the answers

    Self-interstitial atoms exist in high concentrations compared to vacancies.

    <p>False</p> Signup and view all the answers

    What major benefit do impurity atoms provide when added to metals?

    <p>Improved mechanical strength</p> Signup and view all the answers

    Which of the following statements correctly describes the solute in an alloy?

    <p>The solute is the element or compound present in a minor concentration.</p> Signup and view all the answers

    In a solid solution, the crystal structure is altered when solute atoms are added.

    <p>False</p> Signup and view all the answers

    What are the two types of impurity point defects found in solid solutions?

    <p>Substitutional and interstitial</p> Signup and view all the answers

    The atomic size factor indicates that solute atoms may only be accommodated when the difference in atomic radii is less than ___%.

    <p>15</p> Signup and view all the answers

    According to the Hume–Rothery rules, which factor does NOT influence the degree of solute dissolution?

    <p>Melting point</p> Signup and view all the answers

    What is the coordination number of an octahedral site in a BCC crystal structure?

    <p>6</p> Signup and view all the answers

    Tetrahedral sites in both FCC and BCC crystal structures have a coordination number of 6.

    <p>False</p> Signup and view all the answers

    Match each element with its electro-negativity:

    <p>Copper = 1.9 Nickel = 1.8 Silver = 1.5 Zinc = 1.6</p> Signup and view all the answers

    How is weight percent defined in the context of alloy composition?

    <p>The weight of a particular element relative to the total alloy weight.</p> Signup and view all the answers

    Which two elements form a complete substitutional solid solution at all proportions?

    <p>Copper and Nickel</p> Signup and view all the answers

    A metal is more likely to dissolve another metal of lower valency than one of higher valency.

    <p>False</p> Signup and view all the answers

    A dislocation in a material leads to ___ deformation.

    <p>plastic</p> Signup and view all the answers

    Which of the following describes an edge dislocation?

    <p>A linear defect centered around an extra half-plane of atoms</p> Signup and view all the answers

    What is the atomic weight (Aw) of aluminum?

    <p>26.98 g/mol</p> Signup and view all the answers

    If an alloy consists of 97 wt.% aluminum and 3 wt.% copper, what is the approximate atom percent of copper assuming Aw of Cu is 63.55 g/mol?

    <p>5.0%</p> Signup and view all the answers

    Match the type of dislocation with its description:

    <p>Edge dislocation = A defect that creates a half-plane of atoms Screw dislocation = A defect causing spiral arrangements in atoms</p> Signup and view all the answers

    Study Notes

    Lecture 7: Imperfections in Solids

    • Materials are not perfectly ordered at the atomic level
    • Imperfections, or defects, exist in all crystalline solids
    • These defects significantly impact material properties

    Introduction

    • Imperfections are categorized based on geometry or dimensionality
    • Point defects: involve single or two atomic position changes (vacancy, interstitial, substitutional)
    • Linear defects: one-dimensional imperfections (dislocations)
    • Planar defects: two-dimensional imperfections (grain boundaries)
    • Volume defects: three-dimensional imperfections (pores/inclusions)

    Point Defects

    • Vacancy: missing atom from regular lattice site
    • Self-interstitial: host atom is inserted into an interstitial site (extra atom)
    • Impurities: foreign atoms in the crystal lattice structure
    • Substitutional: replace host atoms
    • Interstitial: occupy interstitial sites
    • Frenkel defects: a host atom leaves its regular site and occupies an interstitial site.
    • Schottky defects: atom pairs leave the crystal
    • The presence of vacancies increases the entropy (randomness) of the crystal
    • The equilibrium number of vacancies increases exponentially with temperature

    Specification of Composition

    • Alloy composition can be expressed as weight percent or atom percent
    • Weight percent: the weight of a component divided by the total alloy weight multiplied by 100
    • Atom percent: the number of moles of a component divided by the total number of moles in the alloy multiplied by 100

    Linear Defects

    • Dislocations: line imperfections or misalignment in the crystal structure
    • Edge dislocations: extra half-plane of atoms introduced
    • Screw dislocations: formed from a shear stress.

    Microscopic Examination

    • Dislocations can be observed using electron microscopy techniques.
    • Different techniques have varying resolution limits for observing smaller features

    Impurities in Solids

    • Pure metals are rare, all have some impurity atoms
    • Impurity atoms can significantly affect material properties
    • Solid solutions: impurity atoms can dissolve into the host metal structure
      • Substitutional: impurity replaces host atom
      • Interstitial: impurity occupies interstitial sites
    • Alloying: intentionally introducing impurities to modify material properties
    • Hume-Rothery rules explain the factors influencing solid solubility

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    MATSCI 201 Lecture 7 Imperfections in Solids PDF Fall 2024

    Description

    Test your knowledge about defects in crystalline solids, focusing on vacancies and other point defects. This quiz covers the relationship between temperature and vacancy formation, as well as the role of defects in the atomic lattice structure. Prepare to match types of defects with their classifications and understand their impact on materials.

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