Presentation Information
[MIS19-05]Diffusion in Bicontinuous Structures: From the Perspective of Grain Growth and Creep
*Shenghao Jiang1, Takehiko Hiraga1 (1.ERI, UTokyo)
Keywords:
bicontinuous structure,diffusion,heterophase boundary,homophase boundary
Atomic diffusion is a fundamental mass transport process governing the dynamics of the Earth’s interior. Diffusion creep, a macroscopic deformation mechanism driven by atomic diffusion along stress gradients, represents an important deformation mechanism in mantle convection. Since diffusion creep is sensitive to grain size, grain growth, a spontaneous process that reduces total interfacial energy, is commonly regarded as a kinetically coupled process that regulates mantle rheology.
Earth materials are often approximated as two-phase systems as a first-order approximation, where the microstructure is typically interpreted as a dispersed minor phase embedded within a major phase (i.e., a matrix). In such systems, homophase boundaries of the matrix phase play the dominant role, and the growth of the minor phase is commonly described as Ostwald ripening. This process requires atomic diffusion of the minor phase along lattice or homophase boundaries of the major phase. Okamoto and Hiraga (2020) demonstrated that, under these conditions, creep and grain growth proceed through the same diffusion mechanism. However, this microstructural geometry does not apply to all two-phase systems. When the volume fraction of the minor phase exceeds ~36%, the secondary phase also becomes fully connected, forming a bicontinuous structure. In such cases, the distinction between minor/dispersed and major/matrix phases breaks down, and connected heterophase boundaries become dominant. Nevertheless, the detailed diffusion behavior in bicontinuous structures, particularly with respect to diffusion paths, diffusing species, and rate-limiting steps, remains poorly constrained.
In this study, we developed theoretical models describing grain growth and creep in bicontinuous structures and conducted corresponding experiments. Both theoretical models and experimental observations consistently demonstrate that, when diffusion is restricted to interfaces, grain growth in bicontinuous structures is governed solely by heterophase boundary, whereas creep requires the combined contribution of both homophase and heterophase boundaries, with the overall creep rate controlled by the slowest diffusion path.
Earth materials are often approximated as two-phase systems as a first-order approximation, where the microstructure is typically interpreted as a dispersed minor phase embedded within a major phase (i.e., a matrix). In such systems, homophase boundaries of the matrix phase play the dominant role, and the growth of the minor phase is commonly described as Ostwald ripening. This process requires atomic diffusion of the minor phase along lattice or homophase boundaries of the major phase. Okamoto and Hiraga (2020) demonstrated that, under these conditions, creep and grain growth proceed through the same diffusion mechanism. However, this microstructural geometry does not apply to all two-phase systems. When the volume fraction of the minor phase exceeds ~36%, the secondary phase also becomes fully connected, forming a bicontinuous structure. In such cases, the distinction between minor/dispersed and major/matrix phases breaks down, and connected heterophase boundaries become dominant. Nevertheless, the detailed diffusion behavior in bicontinuous structures, particularly with respect to diffusion paths, diffusing species, and rate-limiting steps, remains poorly constrained.
In this study, we developed theoretical models describing grain growth and creep in bicontinuous structures and conducted corresponding experiments. Both theoretical models and experimental observations consistently demonstrate that, when diffusion is restricted to interfaces, grain growth in bicontinuous structures is governed solely by heterophase boundary, whereas creep requires the combined contribution of both homophase and heterophase boundaries, with the overall creep rate controlled by the slowest diffusion path.