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High Pressure Behavior of 7:4 Mullite and Boron‐Substituted Mullite: Compressibility and Mechanisms of Amorphization
Author(s) -
Kalita Patricia E.,
Cornelius Andrew,
Lipinska Kristina,
Sinogeikin Stanislav,
Fischer Reinhard X.,
Lührs Hanna,
Schneider Hartmut
Publication year - 2014
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/jace.13027
Subject(s) - mullite , materials science , compressibility , thermal expansion , equation of state , powder diffraction , diamond anvil cell , bulk modulus , mineralogy , aluminosilicate , rietveld refinement , compression (physics) , thermodynamics , composite material , crystallography , chemistry , crystal structure , high pressure , ceramic , physics , biochemistry , catalysis
The high‐pressure elastic properties behavior, phase stability, and mechanisms of amorphization of the alumino‐silicate 7:4 mullite and a corresponding mullite doped with boron were investigated in situ by powder synchrotron X‐ray diffraction with a diamond anvil cell in quasi‐hydrostatic conditions. The samples of 7 Al 2 O 3 :4 SiO 2 ( Al 4.66 Si 1.33 O 9.67 ), referred to as 7:4 mullite and an alumino‐silicate mullite with 3.5(4) mol% B 2 O 3 , referred to as B‐mullite, were compressed, in small pressure steps, up to 27.8 and 28.9 GPa, respectively, and then decompressed back to ambient pressure. All along the compression path both samples' patterns are indexable with a mullite structure. Compression data are smooth up to a threshold pressure, from which point the diffraction peaks appeared to broaden, and the refined unit cell parameters deviate significantly down from the compressional trend. Above ~23 GPa the diffraction patterns are not indexable anymore, suggesting amorphization. Rietveld structural refinements allow for a description of the pressure‐induced main deformation mechanisms and structural trends. Pressure‐induced mechanisms of amorphization are also discussed. A third‐order Birch Murnaghan equation of state is fitted to the pressure‐volume data to obtain experimental bulk moduli, as well as axial compressibilities for 7:4 mullite and B‐mullite. Finally the volume compression in response to the applied pressure, combined with thermal expansion coefficients, allows a P–T–V equation‐of‐state for B‐mullite to be proposed.