Growth thermally-activated

We have mentioned above the tendency of atoms to preserve their coordination in solid state processes. This suggests that the diffusionless transformation tries to preserve close-packed planes and close-packed directions in both the parent and the martensite structure. For the example of the Bain-transformation this then means that 111) -> 011). (J = martensite) and <111> -. Obviously, the main question in this context is how to conduct the transformation (= advancement of the p/P boundary) and ensure that on a macroscopic scale the growth (habit) plane is undistorted (invariant). In addition, once nucleation has occurred, the observed high transformation velocity (nearly sound velocity) has to be explained. Isothermal martensitic transformations may well need a long time before significant volume fractions of P are transformed into / . This does not contradict the high interface velocity, but merely stresses the sluggish nucleation kinetics. The interface velocity is essentially temperature-independent since no thermal activation is necessary. 

In general, the result that the platelets form very rapidly (at speeds of the order of the speed of sound) at relatively low temperatures, at rates that are not significantly temperature-dependent, indicates that the platelet growth is not thermally-activated and occurs only when a sufficiently high driving pressure is available. 

Actually this growth is caused by thermally activation of nodal quasiparticles. At higher temperatures the quasiparticle relaxation time drops down [29]. The peak in a temperature dependence of oab appears then as a result of an interplay between the temperature dependences of the relaxation rate and concentration of quasiparticles. 

The growth kinetics describes the nucleation processes on the atomic scale. Thermally activated processes as adsorption, desorption, and diffusion at the surface and in the volume, nucleation, and crystallization/ recrystallization determine the film structure and can be controlled by the substrate temperature and the growth rate. Using a diagram ln(J ) over 1/ T, R being the deposition rate and T the growth temperature, three different growth modes (epitaxial, polycrystalline, and amorphous) can be... 

Since diffusion is thermally activated, the growth rate in oxide film thickness during sliding as a function of temperature, similar to thermal oxidation under static conditions, follows an Arrhenius type of relationship... 

One can attempt to predict somewhat more quantitatively what should be observed for r by using Eqs. (19) and (20) of the craze growth model. We require the value of = (U/4a) (Mj,/ gVM) from Eq. (19) everything in this expression is known approximately except which we take to be thermally activated with an activation enthalpy corresponding to that for flow or diffusion of PS at temperatures well above... 

Diffusion is a thermally activated process, whereby a chemical or isotopic species moves down a chemical potential gradient (usually from high to low concentration), at a rate dependent on the diffusion coefficient, D. This applies to the progressive decrease of growth zoning in a mineral as a rock heats, and to diffusive fluxes into or out of the surface of a mineral as processes in the matrix alter the rim composition relative to the mineral interior. The diffusion coefficient is formally defined as the proportionality constant between flux rate (7) and concentration gradient (VC) ... 

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