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"Cs-tetra-ferri-annite; high-pressure and high-temperature behavior of a potential nuclear waste disposal phase

1999; Mineralogical Society of America; Volume: 84; Issue: 3 Linguagem: Inglês

10.2138/am-1999-0315

1945-3027

Paola Comodi, Pier Francesco Zanazzi, Zdeněk Weiss, Milan Rieder, M. Drábek,

Advanced Condensed Matter Physics

Structure deformations induced by pressure and temperature in synthetic ''Cs-tetra-ferriannite'' 1M [Cs 1.78 (Fe 2ϩ 5.93 Fe 3ϩ 0.07 )(Si 6.15 Fe 3ϩ 1.80 Al 0.05 )O 20 (OH) 4 ], space group C2/m, were analyzed to investigate the capability of the mica structure to store the radiogenic isotopes 135 Cs and 137 Cs. ''Cs-tetra-ferri-annite'' is not a mineral name, but for the sake of brevity is used here to designate a synthetic analog of the mineral tetra-ferri-annite.The bulk modulus and its pressure derivative determined by fitting the unit-cell volumes between 0 and 47 kbar to a third-order Birch-Murnaghan equation of state are K 0 ϭ 257(8) kbar and K 0 Ј ϭ 21(1), respectively.Between 23 ЊC and 582 ЊC, the a and b lattice parameters remain essentially unchanged, but the thermal expansion coefficient of the c axis is ␣ c ϭ 3.12(9) ϫ 10 Ϫ5 ЊC Ϫ1 .High pressure (P) and high temperature (T) produce limited internal strain in the structure.The tetrahedral rotation angle, ␣, is very small and does not change significantly throughout the P and T range investigated.Above 450 ЊC in air, ''Cs-tetraferri-annite'' underwent an oxidation of octahedral iron in the M2cis site, balanced by the loss of H and shown by a decrease of the unit-cell volume.Independent isobaric data on thermal expansion and isothermal compressibility data define the ''geometric'' equation of state for ''Cs-tetra-ferri-annite'': V/V 0 ϭ 1 ϩ 3.0(1) 10 Ϫ5 T Ϫ 2.68(9) 10 Ϫ3 P ϩ 2.0(2) ϫ 10 Ϫ5 P 2 where T is in degrees Celsius, P is in kilobars.The ␣/␤ ratio of about 12 bar/ЊC indicate that the cell volume of ''Cs-tetra-ferri-annite'' remains unchanged under geothermal gradients of ϳ23 ЊC/km.On the whole, the data confirm that the structure of ''Cs-tetra-ferri-annite'' may be a suitable candidate for the storage of large ions, such as Cs in the interlayer and should be considered as a potential Synroc component.