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Shock induced formation of MgAl 2 O 4 spinel from oxides
Author(s) -
Potter David K.,
Ahrens Thomas J.
Publication year - 1994
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/94gl00079
Subject(s) - spinel , corundum , periclase , materials science , grain boundary , mineralogy , quenching (fluorescence) , shock (circulatory) , phase boundary , scanning electron microscope , phase (matter) , grain boundary sliding , analytical chemistry (journal) , thermodynamics , microstructure , composite material , metallurgy , geology , chemistry , optics , medicine , physics , organic chemistry , chromatography , fluorescence
The physics of mineral grain sliding, which occurs upon dynamic compression of rocks, is investigated by shock loading single crystals of corundum (Al 2 O 3 ) and periclase (MgO) in contact obliquely in impact experiments. Energy dispersive X‐ray analysis and X‐ray diffraction studies of samples recovered from 26–36 GPa, 800 ns experiments indicated that under certain conditions a spinel phase of composition MgAl 2 O 4 and thickness ≤20 µm was produced at the interface between the two crystals. Although the computed shock (continuum) temperatures were below those necessary to melt the initial oxides, the spinel nonetheless appears to have formed as a result of localised melting, via grain boundary sliding friction, followed by rapid quenching. Scanning electron microscopy (SEM) revealed some evidence for such melting. Moreover, the timescale of the experiments is too short for solid state diffusion (during the shock state) to explain the observed spinel thickness, although defect enhanced solid state diffusion, subsequent to loading and unloading, remains a possibility. The results also reinforce other recent observations and theories of heterogeneous deformation in minerals.