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Densification of Large Pores: II, Driving Potentials and Kinetics
Author(s) -
Slamovich Elliott B.,
Lange Frederick F.
Publication year - 1993
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1993.tb03943.x
Subject(s) - materials science , grain size , diffusion , grain boundary diffusion coefficient , grain boundary , surface diffusion , effective diffusion coefficient , radius , crystallite , pore water pressure , kinetic energy , porosity , mineralogy , composite material , thermodynamics , chemistry , microstructure , metallurgy , geology , physics , medicine , computer security , geotechnical engineering , adsorption , radiology , quantum mechanics , computer science , magnetic resonance imaging
A kinetic analysis of densification is presented for the case of isolated, identical pores separated by dense, polyerystal‐line material where the grain size is a variable (smaller to larger, relative to the pore size). The analysis includes the influence of both grain growth and mass transport rates on the driving potential for mass transport to the pore. For the expected condition where the rate of grain growth is much greater than the rate of pore shrinkage, it is shown that the driving potential is relatively independent of pore surface curvature, and approaches (2γ s / R po ) sin (ψ e /2) during grain growth, where γ s is the surface energy per unit area of the material, ψ e is the dihedral angle, and R po is the initial pore radius. Using this driving potential, an expression is derived for the current densification rate. The proposed mechanism for mass transport is radial diffusion through a spherical polycrystalline unit cell containing a spherical pore, where diffusion is restricted to grain boundaries that intersect the pore. The expression includes the average separation distance between pores and the grain boundary area intersecting each pore. This expression is in qualitative agreement for data reported in Part I for a Zr(3Y)O 2 material where the grain size is always smaller than the pore size, and a Zr(8Y)O 2 material where the grain size is larger than the pore size.