TY - JOUR

T1 - Evolution of chemically induced cracks in alkali feldspar

T2 - thermodynamic analysis

AU - Abart, Rainer

AU - Petrishcheva, Elena

AU - Habler, Gerlinde

AU - Sutter, Christoph

AU - Fischer, Franz-Dieter

AU - Predan, Jozef

AU - Kegl, Marko

AU - Rammerstorfer, Franz G.

N1 - Publisher Copyright: © 2022, The Author(s).

PY - 2022/5/3

Y1 - 2022/5/3

N2 - A system of edge cracks was applied to polished (010) surfaces of K-rich gem-quality alkali feldspar by diffusion-mediated cation exchange between oriented feldspar plates and a Na-rich NaCl–KCl salt melt. The cation exchange produced a Na-rich layer at and beneath the specimen surface, and the associated strongly anisotropic lattice contraction lead to a tensile stress state at the specimen surface, which induced fracturing. Cation exchange along the newly formed crack flanks produced Na-enriched diffusion halos around the cracks, and the associated lattice contraction and tensile stress state caused continuous crack growth. The cracks nucleated with non-uniform spacing on the sample surface and quickly attained nearly uniform spacing below the surface by systematic turning along their early propagation paths. In places, conspicuous wavy cracks oscillating several times before attaining their final position between the neighboring cracks were produced. It is shown that the evolution of irregularly spaced towards regularly spaced cracks including the systematic turning and wavyness along the early propagation paths maximizes the rate of free energy dissipation in every evolutionary stage of the system. Maximization of the dissipation rate is suggested as a criterion for selection of the most probable evolution path for a system undergoing chemically induced diffusion mediated fracturing in an anisotropic homogeneous brittle material.

AB - A system of edge cracks was applied to polished (010) surfaces of K-rich gem-quality alkali feldspar by diffusion-mediated cation exchange between oriented feldspar plates and a Na-rich NaCl–KCl salt melt. The cation exchange produced a Na-rich layer at and beneath the specimen surface, and the associated strongly anisotropic lattice contraction lead to a tensile stress state at the specimen surface, which induced fracturing. Cation exchange along the newly formed crack flanks produced Na-enriched diffusion halos around the cracks, and the associated lattice contraction and tensile stress state caused continuous crack growth. The cracks nucleated with non-uniform spacing on the sample surface and quickly attained nearly uniform spacing below the surface by systematic turning along their early propagation paths. In places, conspicuous wavy cracks oscillating several times before attaining their final position between the neighboring cracks were produced. It is shown that the evolution of irregularly spaced towards regularly spaced cracks including the systematic turning and wavyness along the early propagation paths maximizes the rate of free energy dissipation in every evolutionary stage of the system. Maximization of the dissipation rate is suggested as a criterion for selection of the most probable evolution path for a system undergoing chemically induced diffusion mediated fracturing in an anisotropic homogeneous brittle material.

KW - Alkali feldspar

KW - Chemically induced fracturing

KW - Crack spacing

KW - Dissipation rate

KW - Thermodynamic Extremal Principle

KW - Wavy cracks

UR - http://www.scopus.com/inward/record.url?scp=85129609725&partnerID=8YFLogxK

U2 - 10.1007/s00269-022-01183-9

DO - 10.1007/s00269-022-01183-9

M3 - Article

AN - SCOPUS:85129609725

VL - 49.2022

JO - Physics and Chemistry of Minerals

JF - Physics and Chemistry of Minerals

SN - 0342-1791

IS - 14

M1 - 14

ER -