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Questions and Answers
Which type of defect is characterized by a missing atom from the lattice structure?
Which type of defect is characterized by a missing atom from the lattice structure?
What is the primary feature of a screw dislocation?
What is the primary feature of a screw dislocation?
Which of the following is classified as a planar defect?
Which of the following is classified as a planar defect?
Self-interstitials in metals increase distortions in which part of the material?
Self-interstitials in metals increase distortions in which part of the material?
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What type of defect is described as an atom occupying a space outside its normal lattice position?
What type of defect is described as an atom occupying a space outside its normal lattice position?
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What defines a bulk or volume defect?
What defines a bulk or volume defect?
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Which process combines mechanical deformation with thermal treatment?
Which process combines mechanical deformation with thermal treatment?
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How does the energy of self-interstitial formation compare to vacancies?
How does the energy of self-interstitial formation compare to vacancies?
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What is the result of adding carbon to iron?
What is the result of adding carbon to iron?
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Which defect involves a cation vacancy and an anion vacancy?
Which defect involves a cation vacancy and an anion vacancy?
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Which statement about electroneutrality is true?
Which statement about electroneutrality is true?
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What defines a stoichiometric compound?
What defines a stoichiometric compound?
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What occurs during n-type doping in semiconductors?
What occurs during n-type doping in semiconductors?
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Which pairing describes the Frenkel defect?
Which pairing describes the Frenkel defect?
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Why do defects in ceramics not occur alone?
Why do defects in ceramics not occur alone?
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Which component is added to silicon to create p-type semiconductors?
Which component is added to silicon to create p-type semiconductors?
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What point defect is created when a Ca2+ ion substitutes for an Na+ ion in NaCl?
What point defect is created when a Ca2+ ion substitutes for an Na+ ion in NaCl?
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What is the maximum atomic size difference generally allowed for solubility in solid solutions?
What is the maximum atomic size difference generally allowed for solubility in solid solutions?
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When creating an interstitial solid solution, what must be true about the solute's atomic radius relative to the solvent?
When creating an interstitial solid solution, what must be true about the solute's atomic radius relative to the solvent?
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Which of the following statements best describes a solid solution?
Which of the following statements best describes a solid solution?
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What is the role of electronegativity in solid solutions?
What is the role of electronegativity in solid solutions?
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Which of the following is an example of an alloy?
Which of the following is an example of an alloy?
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What occurs when solute atoms are added beyond a certain limit in an alloy?
What occurs when solute atoms are added beyond a certain limit in an alloy?
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Which factor is NOT critical for high solubility in a solid solution?
Which factor is NOT critical for high solubility in a solid solution?
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What is a characteristic of surface atoms compared to bulk atoms?
What is a characteristic of surface atoms compared to bulk atoms?
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What defines a low-angle grain boundary?
What defines a low-angle grain boundary?
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How do twin boundaries differ from regular grain boundaries?
How do twin boundaries differ from regular grain boundaries?
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Which type of grain boundary consists of arrays of screw dislocations?
Which type of grain boundary consists of arrays of screw dislocations?
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What is the outcome of heating shape-memory alloys?
What is the outcome of heating shape-memory alloys?
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What does weight percent (wt %) represent in a composition?
What does weight percent (wt %) represent in a composition?
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How is atom percent (at %) calculated?
How is atom percent (at %) calculated?
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What is the role of the Burgers vector in dislocations?
What is the role of the Burgers vector in dislocations?
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What is the defining characteristic of edge dislocations?
What is the defining characteristic of edge dislocations?
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What distinguishes a screw dislocation from an edge dislocation?
What distinguishes a screw dislocation from an edge dislocation?
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What describes mixed dislocations?
What describes mixed dislocations?
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What does a dislocation core refer to?
What does a dislocation core refer to?
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Partial dislocations are characterized by what feature?
Partial dislocations are characterized by what feature?
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Study Notes
Impurities in Solids
- Impurities are atoms different from the host atoms
- May be intentional or unintentional
- All real solids are impure
- Very pure metals are ~99.9999% pure
- Typically one impurity per 106 atoms
Examples of Impurities
- Carbon added to iron creates steel, which is stronger than pure iron
- Boron or phosphorus added to silicon changes its electrical properties (doping)
Point Defects
- Vacancies - a lattice position that is vacant because the atom is missing
- Interstitials - an atom that occupies a place outside the normal lattice position
- May be the same type of atom as the others (self-interstitial) or an impurity atom (interstitial atom)
Types of Point Defects
- Vacancy
- Self-interstitial
- Interstitial impurity
- Substitutional impurities
Properties of Self-Interstitials
- Produce large distortions in the surrounding lattice
- The energy of self-interstitial formation is about 3 times larger than the energy of vacancy formation
- Equilibrium concentration of self-interstitials is very low (less than one self-interstitial per cm3 at room temperature)
0D Point Defects
- Atoms missing or in irregular places in the lattice
- Include vacancies, interstitials, and impurities
1D Linear Defects/Dislocations
- Groups of atoms in irregular positions
- Include edge dislocations and screw dislocations
2D Planar Defects
- Interfaces between the homogeneous regions of the material
- Include external surfaces, grain boundaries (tilt and twist)
3D Bulk/Volume Defects
- Extended defects (pores, cracks)
- Atomic vibrations
Solid Solutions
- Made of a host (solvent or matrix) that dissolves a minor component (solute)
- Solubility is the ability to dissolve
- Solvent: in an alloy, the element or compound present in greater amount
- Solute: element or compound present in lesser amount
- Solid solution: homogeneous, crystal structure is maintained, contains randomly dispersed impurities (substitutional or interstitial)
- Second phase: as solute atoms are added, new compounds/structures are formed, or solute forms local precipitates
Alloys
- Deliberate mixtures of metals
- Example: Sterling silver is a 92.5% silver, 7.5% copper alloy. It is stronger than pure silver
- Other examples include gold alloys (yellow, red, rose, white, etc., each with a different composition of metals)
Factors for High Substitutional Solid Solubility
- Atomic size factor: the solute and solvent atomic radii should be within ~15% of each other
- Crystal structures of solute and solvent should be the same
- Electronegativities of solute and solvent should be comparable
- Generally, solubility increases if solute has a higher valence than solvent
Factors for High Interstitial Solid Solubility
- For FCC, BCC, HCP structures, the voids (interstices) between the host atoms are relatively small
- The atomic radius of the solute should be significantly less than the solvent
- Usually the max solute concentration is ≤10% (Example: 2% for C-Fe)
Composition/Concentration
- Composition can be expressed as weight percent (wt%) or atom percent (at%)
- Weight percent is useful for making solutions
- Atom percent is useful for understanding the material at the atomic level
Composition/Concentration Examples
- Calculating weight percent involves comparing the weight of the particular element to the total weight of the alloy.
- Calculation of atomic percent involves comparing the number of moles (or atoms) of a particular element to the total number of moles (or atoms) in the alloy.
Linear Defects
- The interatomic bonds are significantly distorted near the dislocation line (dislocation core)
- Dislocations create small elastic deformations in the lattice
Burgers Vector
- Describes the size and direction of the main lattice distortion caused by a dislocation
Edge Dislocations
- Burgers vector perpendicular to the dislocation line
Screw Dislocations
- Burgers vector parallel to the dislocation line
Mixed/Partial Dislocations
- Dislocations are often split into partial dislocations, with cores spread over a larger area, adding to the complexity of real defect structures
Planar/Interfacial Defects
- External Surfaces: surface atoms have unsatisfied atomic bonds, higher energy than bulk. Areas tend to minimize (e.g., liquid drop). Solids can reconstruct to satisfy atomic bonds.
- Grain Boundaries: Polycrystalline materials are composed of many small crystals (grains) with different crystallographic orientations. Mismatch exists in the regions where grains meet, called grain boundaries.
Grain Boundaries - Tilt and Twist
- Tilt boundary: an array of aligned edge dislocations
- Twist boundary: the boundary region consisting of arrays of screw dislocations
Grain Boundaries - Twin Boundaries
- Low-energy twin boundaries with mirrored atomic positions across the boundary
- Produced by deformation of materials. Allows shape memory metals to recover their original shape when heated to high temperatures.
Bulk/Volume Defects
- Pores: greatly affect optical, thermal, and mechanical properties
- Cracks: greatly affect mechanical properties
- Foreign inclusions: greatly affect electrical, mechanical, and optical properties
Atomic Vibrations
- Heat causes atoms to vibrate
- Vibration amplitude increases with temperature
- Melting occurs when vibrations are sufficient to rupture bonds
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Description
Test your understanding of impurities in solids, including types of point defects and their properties. This quiz covers the effects of intentional and unintentional impurities on materials' strength and electrical properties. Explore how these concepts apply to real-world examples like steel and silicon.
