Keiko Fujiwara

Hydration heats of zeolites for evaluation of heat exchangers

The enthalpy of hydration of purified clinoptilolite from Beli Plast, Bulgaria, and various cation-exchanged types such as Na-, K-, Ca- and Mg-clinoptilolite was determined by the adiabatic water-vapor absorption calorimeter. The hydration enthalpy becomes more exothermic in the sequence K, Na, Ca, Mg depending on hydration energy values of exchanged cations. Na-clinoptilolite would be an efficient heat exchanger in a wide temperature range of dehydration, 180–300°C, while Mg-clinoptilolite in higher temperatures, 300–350°C.

Computed tomography enteroclysis for recurrent severe gastrointestinal bleeding in a patient with vascular malformation of the small bowel

This is a case study of a 66-year-old woman who had a vascular malformation of the small bowel that was visualized on computed tomography enteroclysis (CTE). She presented with repeated tarry stool and severe anemia. Although the source of bleeding was not identified on upper and lower gastrointestinal endoscopy, active bleeding was revealed by capsule endoscopy in the deep jejunum. The cause of bleeding was not found on capsule endoscopy. CTE was requested as double-balloon endoscopy would have been difficult because of strong adhesion of the small intestine. A continual subtle vascular malformation of the jejunum, starting from the third jejunal branch end, was demonstrated on CTE with dynamic contrast enhancement. Because this vascular malformation was considered the cause of small intestinal bleeding, selective arterial coil embolization was performed. After embolization, the repeated tarry stool disappeared and the severe anemia dramatically improved. CTE may be a safe and useful method for determining the cause of small intestinal bleeding and for subsequent therapy.

Crystal structure of SrGeO3 in the high-pressure perovskite-type phase

The high-pressure phase of SrGeO3 synthesized at 6 GPa and 1223 K adopts the ideal cubic perovskite-type structure. The Ge—O bond is largely covalent, which influences the thermal vibration behavior of the O atom.

Single-crystal X-ray diffraction study of SrGeO3 high-pressure perovskite phase at 100 K

Single-crystal X-ray diffraction study of SrGeO3 perovskite (cubic; space group Pmɜm) synthesized at 6 GPa and 1223 K was conducted at a low temperature of 100 K. The residual electron density revealed the presence of the bonding electron at the center of the Ge–O bond, in accordance with our previous conclusion that the Ge–O bond is strongly covalent. From comparison with our previous structure-refinement result at 296 K, the mean square displacement (MSD) of the O atom in the direction of the Ge–O bond is suggested to exhibit no significant temperature dependence, in contrast to that in the direction perpendicular to the bond. Thus, the strong covalency of the Ge–O bond can have a large influence on the temperature dependence of thermal vibration of the O atom.

Hydrothermal synthesis and Er3+ ion exchange of sodium GTS-type titanosilicate

Powder samples of Na-GTS have been prepared using a hydrothermal method. Er3+- exchanged Na-GTS [Na4(1-x)Er(4/3)x Ti4Si3O16nH2O] with the compositions in the range of 0.28 ≤ x ≤ 0.64 was obtained by shaking the single-phase sample of Na-GTS in the ErC13 aqueous solutions (25 mL, 0.01~0.1 M) at 25 °C for 6 hours. The chemical analyses by atomic absorption spectrometry (AAS) show that the maximum allowance of Er3+ incorporated into Na-GTS is x = 0.64. TG-DTA measurements show that the incorporation of Er3+ slightly decreases the water contents and the dehydration temperatures. The powder X-ray diffraction (XRD) patterns indicate that the diffraction-peak intensities vary systematically with increasing the Er3+ composition (x). The simulation of XRD patterns suggests the cation-distribution model that Er3+ and Na+ ions preferentially occupy the 4e and 6g sites, respectively.

A new high-pressure strontium germanate, SrGe2O5

The Sr-Ge-O system has an earth-scientific importance as a potentially good low-pressure analog of the Ca-Si-O system, one of the major components in the constituent minerals of the Earths crust and mantle. However, it is one of the germanate systems that has not yet been fully examined in the phase relations and structural properties. The recent findings that the SrGeO3 high-pressure perovskite phase is the first Ge-based transparent electronic conductor make the Sr-Ge-O system interesting in the field of materials science. In the present study, we have revealed the existence of a new high-pressure strontium germanate, SrGe2O5. Single crystals of this compound crystallized as a co-existent phase with SrGeO3 perovskite single crystals in the sample recovered in the compression experiment of SrGeO3 pseudowollastonite conducted at 6 GPa and 1223 K. The crystal structure consists of germanium-oxygen framework layers stacked along [001], with Sr atoms located at the 12-coordinated cuboctahedral site; the layers are formed by the corner linkages between GeO6 octahedra and between GeO6 octahedra and GeO4 tetrahedra. The present SrGe2O5 is thus isostructural with the high-pressure phases of SrSi2O5 and BaGe2O5. Comparison of these three compounds leads to the conclusion that the structural responses of the GeO6 and GeO4 polyhedra to cation substitution at the Sr site are much less than that of the SrO12 cuboctahedron to cation substitution at the Ge sites. Such a difference in the structural response is closely related to the bonding nature.

Crystal structure of post-perovskite-type CaIrO3 reinvestigated: new insights into atomic thermal vibration behaviors

Single crystals of CaIrO3 were grown from a CaCl2 flux at atmospheric pressure and crystallized with the post-perovskite type of structure. The crystal structure is reinvestigated on the basis of single-crystal X-ray diffraction data measured using a high-power X-ray source, and the atomic thermal vibration behavior is discussed in terms of the coordination environments.