Week 7 L1. Diffusion in Solids 2022

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ENSC 3002  
Material Science
May 21, 2023
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Week 7 Lecture 1. Diffusion in solids ENSC3002 Materials and Manufacturing Basic Syllables: ¾ Diffusion and diffusion mechanisms ¾ Steady state diffusion - Fick's 1 st Law ¾ Non-steady state diffusion - Fick's 2 nd Law Recommended Readings: Callister & Rethwisch, Materials Science and Engineering - an Introduction, 8 th edition: Chapter 5 Declaration: Figures and diagrams are adapted from Callister & Rethwisch , unless otherwise stated
As shown, an automobile transmission system consists of many steel gears. To improve the wear resistance of these gears, they are case hardened. In case hardening , the outer surface layer of a component is selectively hardened by a high temperature heat treatment (i.e. carburization ) during which carbon atoms from the surrounding atmosphere diffused into the surface of the steel component. The increase in the carbon content increases the surface hardness, thus improve the wear resistance of the gear. Diffusion of Carbon Atoms in Steel Automobile Transmissions Case Hardened Steel Gear Diffusion Phenomenon 2
Examples of diffusion: Heat treatment of metals to improve/enhance properties relies on the diffusion of atoms to either homogenize the composition, change the microstructure, or to form/to dissolve second phases; Semiconductors devices and batteries rely on the diffusion of electrons and ions to conduct electrical charges; Gas purification and production often rely on diffusion of gas molecules through solid filters or membranes. For example, purification of hydrogen gas by Pd alloy membrane (see http://www.hy9.com/purifier-technology) ... Diffusion Phenomenon Diffusion is a phenomenon of mass transport by the motion of particles (often on microscopic level ), such as atoms, molecules, ions and even clusters of them. It is a common phenomenon occurring in many systems and states, including gases , liquids and solids . 3
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