TY - JOUR
T1 - Compressibility and pressure-induced amorphization of guest-free melanophlogite
T2 - An in-situ synchrotron X-ray diffraction study
AU - Xu, Hongwu
AU - Zhang, Jianzhong
AU - Zhao, Yusheng
AU - Guthrie, George D.
AU - Hickmott, Donald D.
AU - Navrotsky, Alexandra
N1 - Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.
PY - 2007/1
Y1 - 2007/1
N2 - Melanophlogite, a clathrasil, possesses a framework of corner-linked silica tetrahedra forming framework cavities that can enclose small guest molecules. Synchrotron X-ray diffraction experiments of the guest-free melanophlogite have been conducted at pressures up to 12 GPa and temperatures up to 1473 K. Upon compression at room temperature, melanophlogite gradually lost its crystallinity and became completely X-ray amorphous at ∼8 GPa. The amorphization process was similar to those of denser silica polymorphs, but it reached completion at a much lower pressure (e.g., quartz becomes X-ray amorphous at ∼30 GPa). The decreased amorphization pressure of melanophlogite may be attributed to its lower framework density and the ease of bending of its Si-O-Si linkages, thereby accelerating the collapse of the structure under high pressure. Determination of cell volumes of melanophlogite prior to its amorphization yielded a room-temperature bulk modulus of 26.3 ± 1.7 GPa, which is consistent with the relatively large compressibilities reported for the structurally similar zeolites. When heated at ∼8 GPa, the amorphous phase started to crystallize at 873 K into coesite, the stable silica phase at these pressure and temperature conditions. Thus the occurrence of pressure-induced amorphization in melanophlogite appears to result from the kinetic hindrance to its transformation to the thermodynamically stable coesite.
AB - Melanophlogite, a clathrasil, possesses a framework of corner-linked silica tetrahedra forming framework cavities that can enclose small guest molecules. Synchrotron X-ray diffraction experiments of the guest-free melanophlogite have been conducted at pressures up to 12 GPa and temperatures up to 1473 K. Upon compression at room temperature, melanophlogite gradually lost its crystallinity and became completely X-ray amorphous at ∼8 GPa. The amorphization process was similar to those of denser silica polymorphs, but it reached completion at a much lower pressure (e.g., quartz becomes X-ray amorphous at ∼30 GPa). The decreased amorphization pressure of melanophlogite may be attributed to its lower framework density and the ease of bending of its Si-O-Si linkages, thereby accelerating the collapse of the structure under high pressure. Determination of cell volumes of melanophlogite prior to its amorphization yielded a room-temperature bulk modulus of 26.3 ± 1.7 GPa, which is consistent with the relatively large compressibilities reported for the structurally similar zeolites. When heated at ∼8 GPa, the amorphous phase started to crystallize at 873 K into coesite, the stable silica phase at these pressure and temperature conditions. Thus the occurrence of pressure-induced amorphization in melanophlogite appears to result from the kinetic hindrance to its transformation to the thermodynamically stable coesite.
KW - Clathrasil
KW - Compressibility
KW - Melanophlogite
KW - Pressure-induced amorphization
KW - Synchrotron X-ray diffraction
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U2 - 10.2138/am.2007.2195
DO - 10.2138/am.2007.2195
M3 - Article
AN - SCOPUS:33846454018
SN - 0003-004X
VL - 92
SP - 166
EP - 173
JO - American Mineralogist
JF - American Mineralogist
IS - 1
ER -