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Questions and Answers
What is the primary mode of plastic deformation in metals and alloys?
What is the primary mode of plastic deformation in metals and alloys?
Which of the following is NOT a way to increase strength by impeding dislocation motion?
Which of the following is NOT a way to increase strength by impeding dislocation motion?
What is the term for mass transport by atomic motion in solids?
What is the term for mass transport by atomic motion in solids?
What mechanism allows smaller atoms to diffuse between larger atoms in a solid?
What mechanism allows smaller atoms to diffuse between larger atoms in a solid?
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In an alloy, atoms will migrate from regions of:
In an alloy, atoms will migrate from regions of:
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What is required for an atom to undergo self-diffusion?
What is required for an atom to undergo self-diffusion?
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In Fick's first law, which term represents the concentration gradient?
In Fick's first law, which term represents the concentration gradient?
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What units are used for the diffusion coefficient in steady-state diffusion?
What units are used for the diffusion coefficient in steady-state diffusion?
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What determines the jump frequency in interstitial diffusion?
What determines the jump frequency in interstitial diffusion?
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What does Ji represent in the context of diffusion?
What does Ji represent in the context of diffusion?
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What is interstitial diffusion primarily characterized by?
What is interstitial diffusion primarily characterized by?
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Which equation describes the net flux of atoms during diffusion?
Which equation describes the net flux of atoms during diffusion?
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What is the relationship between temperature and diffusion coefficient?
What is the relationship between temperature and diffusion coefficient?
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What is the primary result of case hardening in steel?
What is the primary result of case hardening in steel?
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What does the term 'activation energy' refer to in the context of diffusion?
What does the term 'activation energy' refer to in the context of diffusion?
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How long does it take for breakthrough diffusion in the given example?
How long does it take for breakthrough diffusion in the given example?
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In which environment does the unexpected diffusion of oxygen occur in Alloy 600?
In which environment does the unexpected diffusion of oxygen occur in Alloy 600?
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What is the primary mechanism of vacancy diffusion?
What is the primary mechanism of vacancy diffusion?
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In dilute binary alloys, the rate of solute diffusion is most directly related to which factor?
In dilute binary alloys, the rate of solute diffusion is most directly related to which factor?
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What increases the equilibrium vacancy concentration in a dilute binary alloy?
What increases the equilibrium vacancy concentration in a dilute binary alloy?
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What characterizes the diffusion distance of an atom after n jumps?
What characterizes the diffusion distance of an atom after n jumps?
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Which type of diffusion is generally more rapid?
Which type of diffusion is generally more rapid?
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What is the formula to calculate the diffusion distance r in terms of time t?
What is the formula to calculate the diffusion distance r in terms of time t?
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What component is often absorbed through the skin in chemical protective clothing scenarios?
What component is often absorbed through the skin in chemical protective clothing scenarios?
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The breakthrough time for gloves indicates what?
The breakthrough time for gloves indicates what?
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What is the diffusion coefficient of methylene chloride in butyl rubber at room temperature?
What is the diffusion coefficient of methylene chloride in butyl rubber at room temperature?
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What influences the energy barrier for the jump of a solute atom?
What influences the energy barrier for the jump of a solute atom?
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Study Notes
Diffusion in Solids
- Diffusion is the mass transport of atoms by atomic motion.
- Diffusion occurs in gases and liquids due to random (Brownian) motion.
- Diffusion in solids occurs through vacancy diffusion or interstitial diffusion.
- Vacancy diffusion occurs when atoms exchange positions with vacancies.
- Interstitial diffusion occurs when smaller atoms move between larger host atoms.
- Interstitial diffusion is more rapid than vacancy diffusion.
Diffusion Mechanisms
- Interdiffusion: In an alloy, atoms migrate from areas of high concentration to areas of low concentration.
- Self-diffusion: In an elemental solid, atoms also migrate.
- Vacancy diffusion: Atoms exchange positions with vacancies, applicable to self-diffusion and diffusion of substitutional impurity atoms.
- Interstitial diffusion: Smaller atoms move between atoms.
Factors Influencing Diffusion
- Vacancy concentration: Higher vacancy concentration leads to faster diffusion.
- Activation energy: Higher activation energy means greater energy barrier for atom jumps, leading to slower diffusion.
- Jump frequency: Higher jump frequency means faster diffusion.
Fick's First Law
- Describes steady-state diffusion.
- The net flux (Ji) is proportional to the concentration gradient (dCi/dx).
- Diffusion coefficient (Di) is a material property that quantifies the rate of diffusion.
Diffusion Distance
- Diffusion of an atom or vacancy occurs by random walk.
- The distance traveled after n jumps is n1/2 jumps from the initial position.
- Diffusion distance is proportional to the square root of time (r = √(6Dt)).
Applications of Diffusion
- Case hardening: Carbon is diffused into the surface of iron to increase hardness.
- Unexpected diffusion: Oxygen diffusion along grain boundaries in Alloy 600 at high temperatures can cause embrittlement.
Thermal Activation of Diffusion
- Diffusion is thermally activated, meaning it requires energy to overcome the activation energy (Q).
- Diffusion coefficient increases exponentially with temperature.
Importance of Diffusion
- Essential for understanding material processing, such as heat treatments and microstructural development.
- Plays a significant role in material properties like strength, hardness, and corrosion resistance.
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Description
Test your understanding of diffusion mechanisms in solids, including interstitial and vacancy diffusion. Explore factors that influence diffusion and the differences between interdiffusion and self-diffusion. This quiz is essential for students of materials science and solid-state physics.
