Rate‐Determining Species in Diffusion‐Controlled Processes in Al₂O₃

Abstract

model proposed here suggests that the grain size should be an , < overestimate if the surface is assumed to be basically flat and contoured only by grain boundary grooves. An equilibrium surface, such as might be formed by polishing and thermal etching of a material in which the surface energy is isotropic, is shown in Fig. 2. The amplitude of the modulations in the surface contour is:

Early-Stage Oxidation Behavior of Pt-Modified γ′-Ni3Al-Based Alloys with and without Hf Addition

“…2, in which f lat and f gb , D lat and D gb are fraction of intragranular and grain boundary areas, and the diffusion coefficients in the Al 2 O 3 lattice and grain boundary, respectively. For the a-Al 2 O 3 and the oxidation temperature studied, D lat is known to be very low compared to D gb [17], therefore it is reasonable to assume that only the f gb D gb term in Eq. 2 needs to be considered in assessing the rate of scale growth.…”

Effect of Seeding and Water Vapor on the Nucleation and Growth of α‐Al2O3 from γ‐Al2O3

“…Defect concentration and therefore diffusion in alumina are controlled by aliovalent impurity contents as low as 10 ppm due to the low concentration of intrinsic defects. 46,48 This dependence of diffusion on low impurity concentrations is one cause of the variations in diffusion data between different investigations. 46,48 Another complication in determining a rate-limiting species is that most of the available diffusion data are for ␣-Al 2 O 3 rather than the transition aluminas.…”

Gabbro‐eclogite reaction rate and its geophysical significance

“…(Since in ideal solutions the binary diffusion fluxes are, at thermodynamic equilibrium, linear combinations of end member self-diffusion fluxes, for the present purpose we have not differentiated between binary and self-diffusion data.) The question of whether cation diffusion in a polycrystalline aggregate can be controlled (and presumably occur more rapidly) by surface diffusion processes has been examined by Paladino and Coble [1963] and Mistler and Coble [1971]. They conclude that cation-diffusion is usually independent of grain boundaries in ionic compounds although they point out that some exceptions do occur.…”