Post-Midterm | MAT E 202 Questions With Complete Solutions

What is interdiffusion in an alloy? correct answer: In an alloy atoms tend to migrate from regions of high concentrations to regions of low concentrations. What is self-diffusion in a solid? correct answer: In an element solid atoms migrate. What are the conditions for diffusion of one atom from one lattice site to another? correct answer: 1. Must have an empty adjacent site. 2. Atom must have sufficient energy to break bonds with neighbor atoms and cause some lattice distortion during displacement. What are the properties of vacancy diffusion? correct answer: Atoms exchange with vacancies and applies to substitutional impurities in atoms. The rate depends on the number of vacancies, frequency of jumping, and activation energy to exchange. Vacancy diffusion is a thermally activated process and also depends on the number of vacancies present. What are the properties of interstitials diffusion? correct answer: The small interstitial atom jumps from one interstitial site to another. This applies to interstitial impurities and is more rapid than vacandy diffusion. What are some examples in which diffusion is faster or slower for? correct answer: Faster: 1. Open crystal structures 2. Lower melting temperature materials 3. Materials with secondary bonding 4. Smaller diffusing atoms 5. Cations 6. Lower density materials Slower: 1. Closed-packed structures 2. Higher melting temperature materials 3. Materials with covalent bonding 4. Large diffusing atoms