مکانیزم های نفوذ در جامدات

مکانیزم های نفوذ در جامدات

اسلاید 1: Correlation in Solid-State Diffusion

اسلاید 2: Random walk of a atom on a latticeEinstein(alsoEinstein‐Smoluchowski) relation:relates the mean square displacement to the diffusion coefficient D and time t1

اسلاید 3: The tracer correlation factorThe tracer correlation factor can be expressed in terms of the cosine of the angle between the ‘first’ jump and allsubsequent jumps of a given atom (the tracer).f is the tracer correlation factor0 ≤ f ≤ 12

اسلاید 4: Example of the convergenceof the cosine between the firsttracer A jump and the m’th tracer A jumpThe tracer correlation factor3

اسلاید 5: Tracer correlation factors depend on:• the type of lattice.• the diffusion mechanism.• the type of diffusing atom in the matrix.• the degree of local order of the atomic components.4

اسلاید 6: interstitial mechanism – for small solutesAt low concentrations all jump directionsare equally probable → no correlation f = 1 means no correlationSmall solutes suchas H, C, N, and O inbcc and fcc metalsare dissolved inoctahedral and/ortetrahedral sites.They diffuse viadirect interstitialjumps5