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 (B)

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. (A)</p> Signup and view all the answers

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

<p>Vacancy (C)</p> Signup and view all the answers

All crystalline materials exist perfectly without any defects.

<p>False (B)</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 (B)</p> Signup and view all the answers

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

<p>False (B)</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 (B)</p> Signup and view all the answers

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

<p>True (A)</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% (D)</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 (B)</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. (A)</p> Signup and view all the answers

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

<p>False (B)</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 (B)</p> Signup and view all the answers

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

<p>6 (B)</p> Signup and view all the answers

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

<p>False (B)</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 (B)</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 (B)</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% (A)</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

Flashcards

Crystalline Defect

A deviation from the perfect, ordered arrangement of atoms in a crystal lattice, usually on the scale of an atomic diameter.

Why study imperfections?

Imperfections in solids significantly influence their properties, often in beneficial ways, allowing us to control and modify materials for specific applications.

Catalytic Converter

A device in an automobile's exhaust system that uses crystalline materials with defects to convert harmful pollutants into less harmful substances.

Atomic Defect

A type of crystalline imperfection confined to a few atoms, affecting their arrangement or bonding.

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Solid Solution

A mixture of two or more elements where the solute atoms are dispersed within the crystal lattice of the solvent (host) element.

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Substitutional Solid Solution

A type of solid solution where solute atoms replace solvent atoms in the crystal lattice.

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Interstitial Solid Solution

A type of solid solution where solute atoms occupy spaces between the atoms in the crystal lattice of the solvent.

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Dislocation

A linear defect in a crystalline material where the atomic arrangement is disrupted along a line, influencing how the material deforms.

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Point Defects

Defects affecting one or two atomic positions, causing imperfections in the crystal structure.

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Vacancy

An empty lattice site where an atom should be, but is missing.

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Interstitials

Atoms crammed into spaces between regularly spaced atoms in the crystal lattice.

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Substitutional

An atom of a different type replacing an atom in the crystal lattice.

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What affects the number of vacancies in a material?

The number of vacancies increases exponentially with temperature.

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Activation Energy

The energy needed to create a vacancy by forcing an atom out of its lattice site.

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Equilibrium Number of Vacancies

The number of vacancies in a material at a specific temperature.

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How does the number of vacancies influence material properties?

The number of vacancies influences a material's strength, electrical conductivity and diffusion rate.

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Self-Interstitial

An atom from the crystal lattice that occupies a normally empty interstitial site, causing significant distortion in the surrounding lattice due to its size.

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Impurity Atoms

Atoms of different elements present in a pure metal, even in highly refined materials. These atoms exist as point defects within the crystal structure.

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Alloy

A mixture of metals, where impurity atoms have been intentionally added to modify the properties of the base metal.

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New Second Phase

A type of alloy where the impurity atoms form a distinct, separate phase within the crystal structure.

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How do impurities affect metal properties?

Adding impurity atoms can significantly improve mechanical strength and corrosion resistance in metals. For example, alloying with copper enhances the strength of silver.

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What is the typical purity level of familiar metals?

Most common metals are not highly pure. They are typically alloys with intentional impurities to enhance their properties.

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How do the concentrations of impurities impact the formation of solid solutions or new phases?

Depending on the types, concentrations, and temperature, impurities can form either solid solutions or distinct new phases within the crystal structure of the base metal.

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Solvent

The element or compound present in the greatest amount in an alloy. It's the host material, often called the 'host atom'.

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Solute

A component present in a smaller amount within an alloy. It's the 'guest' element or compound.

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Substitutional Impurity

A type of impurity where solute atoms replace the host atoms in the crystal lattice.

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Interstitial Impurity

A type of impurity where solute atoms fit into the gaps between host atoms in the lattice.

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Hume-Rothery Rules

Four rules that describe how much a solute can dissolve in a solvent, affecting the formation of a solid solution.

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Atomic Size Factor

One of the Hume-Rothery Rules, stating that large differences in atomic radii (more than 15%) between solute and solvent hinder the formation of solid solutions.

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Crystal Structure

One of the Hume-Rothery Rules, requiring both solute and solvent to have the same crystal structure for successful solid solution formation.

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Interstitial Site

A location in a crystal lattice where an atom can be inserted between the host atoms, creating an interstitial solid solution.

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Coordination Number

The number of nearest neighbor atoms surrounding a specific atom in a crystal lattice.

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Octahedral Site

An interstitial site in a crystal lattice with a coordination number of 6, meaning 6 host atoms surround it.

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Tetrahedral Site

An interstitial site in a crystal lattice with a coordination number of 4, meaning 4 host atoms surround it.

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Weight Percent (wt%)

A way to express the composition of an alloy, representing the mass of a specific element relative to the total alloy mass.

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Atom Percent

A way to express the composition of an alloy, representing the number of moles of a specific element relative to the total moles of all elements.

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Edge Dislocation

A linear defect in a crystal lattice where an extra half-plane of atoms is inserted, creating a line of misalignment.

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Screw Dislocation

A linear defect in a crystal lattice that creates a helical distortion, like a spiral staircase.

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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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