Akio Fujimura

Preferred orientation of phyllosilicate [001] in matrix of Murchison meteorite and possible mechanisms of generating the oriented texture in chondrites

Abstract Preferred orientation of the dominant phyllosilicate phase (serpentine) in the matrix of the Murchison meteorite (C2) was determined by X-ray pole figure goniometry. The basal plane (001) of the phyllosilicate shows a clear preferred orientation of an axial concentration type. The preferred orientation is very weak in comparison with the orientations of known terrestrial tectonites, and it resembles the weakest case observed in the loosely consolidated clayey sediments from the deep ocean bottom. However, gentle sedimentation of platy phyllosilicate grains on a flat surface under a weak gravity field does not generate a sufficient preferred orientation. It is suggested that the preferred orientation in the matrix of Murchison was generated by uniaxial compaction, and the magnitude of strain to give rise to the observed degree of preferred orientation is evaluated as −9%. There are two possible explanations of the deformation: dynamic compression caused by impact, and static compaction in a parent body. Though the latter case appears to be appropriate in the present case, it is not straightforward, however, to conclude that the suggested deformation is caused by burial compaction along gravity under lithostatic stress in a small primitive parent body.

Pressure and temperature dependence of cation distribution in Mg-Mn olivine

Synthetic (Mg0.51, Mn0.49)2SiO4 olivine samples are heat-treated at three different pressures; 0, 8 and 12 GPa, all at the same temperature (∼500° C). X-ray structure analyses on these single crystals are made in order to see the pressure effect on cation distribution. The intersite distribution coefficient of Mg and Mn in M1 and M2 sites, KD = (Mn/Mg)M1/(Mn/Mg)M2, of these samples are 0.192 (0 GPa), 0.246 (8 GPa) and 0.281 (12 GPa), indicating cationic disordering with pressure. The small differences of cell dimensions between these samples are determined by powder X-ray diffraction. Cell dimensions b and c decrease, whereas a increases with pressure of equilibration. Cell volume decreases with pressure as a result of a large contraction of the b cell dimension. The effect of pressure on the free energy of the cation exchange reaction is evaluated by the observed relation between the cell volume and the site occupancy numbers. The magnitude of the pressure effect on cation distribution is only a fifth of that predicted from the observed change in volume combined with thermodynamic theory. This phenomenon is attributed to nonideality in this solid solution, and nonideal parameters are required to describe cation distribution determined in the present and previous experiments. We use a five-parameter equation to specify the cationic equilibrium on the basic of thermodynamic theory. It includes one energy parameter of ideal mixing, two parameters for nonideal effects, one volume parameter, and one thermal parameter originated from the lattice vibrational energy. The present data combined with some of the existing data are used to determine the five parameters, and the cation distribution in Mg-Mn olivine is described as a function of temperature, pressure, and composition. The basic framework of describing the cationic behavior in olivine-type mineral is worked out, although the result is preliminary: each of the determined parameters is not accurate enough to enable us to make a reliable prediction.

Generation of Large Volume Hydrostatic Pressure to 8 GPa for Ultrasonic Studies

A new solid-liquid hybrid device has been developed wherein a liquid pressure of 8 GPa can be generated with 150 mm3 in an MA8 high-pressure apparatus. This system was demonstrated by measurements of the velocity of elastic waves in fused quartz; the longitudinal wave had a velocity minimum and an attenuation maximum at 3 GPa.

Crosslinking of Piezoelectric Polymers by Ionizing Radiation

The effects of ionizing radiation on piezoelectric films of poly(vinylidene fluoride) were examined. Heat shrinkage of the films is reduced by the irradiation. After annealing at 153°C, the length of an unirradiated film is less than 80% of the initial length, whereas that of a film irradiated to a dose of 100 kGy is 93% of the initial length. Heat stability of the piezoelectric property of the films is also increased by the irradiation. The improvement in the stability arises from the crosslinking of poly(vinylidene fluoride).