preview

Migration of Atoms: Basics of Diffusion Essay

Good Essays

B1.1 Introduction
In a sample having non-uniform composition of certain kind of atoms, a concentration gradient is set in, which leads to migration of atoms from region of their higher concentration to the region of lower concentration. This phenomenon is referred to as Diffusion and continues till atomic distribution becomes homogeneous throughout.
The diffusion process plays an important role in the field of metallurgy and fabrication of extrinsic semiconductors. The technology of controlled diffusion plays a sensitive role in accomplishment of desired devices. The metals, in their pure form, are soft and do not possess large tensile strength. Their properties can be modified by the process of alloying in a controlled manner. The …show more content…

For example diffusion of copper in copper (b) Inter-diffusion in which the solute atoms are different from the solvent atoms as in the case steel where solvent is iron whereas solute atoms are those of carbon and many other elements.
The phenomenon of diffusion of solute atoms into the solvent environment may occur through the following mechanisms:
(a) Vacancy mechanism where the solute atoms lie in the vacancy and moves to other available vacancy. Atoms can move from one site to another if there are vacancies and the atom has sufficient energy to overcome a local activation energy barrier. The activation energy for diffusion is the sum of energy required to form a vacancy and further cause its motion.
(b) Interstitial Mechanism is applicable in case of small atoms like hydrogen, helium, carbon, nitrogen diffuse through the interstitial spaces in a crystal. The activation energy for diffusion is the energy required for these atoms to squeeze through the small voids between the host lattice atoms.

B1.3 Macroscopic Model of Diffusion
B1.3.1 Steady State Diffusion: Fick’s I Law
The process of diffusion is time dependent which implies that one needs to study the quantity of solute material that gets transported in solvent is a function of time. This time dependent mass transfer is often represented by a quantity called diffusion flux (J) which is defined as the solute mass transferred in unit time through a unit cross-sectional area placed perpendicular to the

Get Access