Katsuto Nakatsuka

Structure analysis of coprecipitated ZnFe2O4 by extended x‐ray‐absorption fine structure

Though the anomalous antiferromagnetism of zinc ferrite was a subject of intensive studies in the past, the unusually high magnetization of coprecipitated zinc ferrite at low temperatures has drawn renewed interest among researchers. The local structures of zinc ferrites around Fe and Zn atoms are measured using extended x-ray-absorption fine structure and the results are discussed in correlation with their magnetic properties. The structure around the Zn atom was found to differ between zinc ferrite produced by ceramic and coprecipitation techniques. The position of the second-nearest neighbor of the Zn atom for coprecipitated zinc ferrite was shorter than the one produced by the ceramic method. This suggests the possible occupation of the Zn atoms in the octahedral sites and the cause for the unusually high magnetization in coprecipitated zinc ferrite. Furthermore, the intensity of the peak is weak compared to the one produced by the ceramic method. This is thought to be due to the deformation induced by the occupation of zinc ions in the octahedral sites, causing a decrease in the structural periodicity,

The magnetic fluid for heat transfer applications

Abstract Real-time visual observation of boiling water-based and ionic magnetic fluids (MFs) and heat transfer characteristics in heat pipe using ionic MF stabilized by citrate ions (JC-1) as working liquid are reported. Irrespective of the presence or absence of magnetic field water-based MF degraded during boiling. However, the degradation of JC-1 was avoided by heating the fluid in magnetic field. Furthermore, the heat transfer capacity of JC-1 heat pipe under applied magnetic field was enhanced over the no field case.

Irregular distribution of metal ions in ferrites prepared by co-precipitation technique structure analysis of Mn–Zn ferrite using extended X-ray absorption fine structure

Abstract The tetrahedral/octahedral site occupancy of non-magnetic zinc ion, added to maximize the net magnetic moment of mixed ferrites has been found to depend on the method of preparation. In this paper, we qualitatively analyze the metal ion distribution in Mn–Zn ferrite particles prepared by co-precipitation and ceramic methods using extended X-ray absorption fine structure (EXAFS) technique. The results suggest that the differences observed in the magnetic properties of the samples prepared by different methods are not only due to the difference in particle size but also due to the difference in cation distribution. The difference in cation distributions between ferrites of similar composition prepared differently has been found to depend on the crystal field stability energies of the metal ion of interest and associated cations.

Ferrimagnetic ordering in nanostructured CdFe2O4 spinel

Nanostructured CdFe2O4 spinel powders with various grain sizes ranging from 60 to 4 nm were synthesized by ball milling the bulk material. The magnetization measurements at 1 and 9 T reveal a spin-glass-like surface structure and the material is found to have a large anisotropy. Mossbauer studies at 10 K in external magnetic fields of 6 and 8.5 T applied parallel to the direction of gamma rays could clearly show that CdFe2O4 behaves like a mixed spinel on reducing the grain size to nanometer level and exhibits ferrimagnetic ordering. Fe3+ spins at both A and B sites exhibit spin canting.

Heat transfer in temperature-sensitive magnetic fluids

Abstract The effect of thermomagnetic convection, which arises when a temperature-sensitive magnetic fluid is heated in a vessel under a nonuniform magnetic field, is studied by a model experiment. The heat transfer from a vessel wall into the fluid is promoted by the application of a magnetic field due to convection along the gradient of magnetic field.

Trends of magnetic fluid applications in Japan

Abstract Since the invention of magnetic fluid in the United States in 1965, the characteristics of the fluids have been progressively improved, and applications to various fields are growing. In this report the recent progress made in application devices of magnetic fluid will be reviewed focussing the techniques appraised as possessing, or promising the practical use in Japan.

Damper application of magnetic fluid for a vibration isolating table

Abstract An application of magnetic fluid to damp a loading table of a vibration isolator is attempted. A piston type damper with no solid contact between an inner and outer cylinder is designed by utilizing a levitation force for a nonmagnetic body in magnetic fluid. The performance of the isolator is evaluated through a series of experiments and it is concluded that the isolator cuts off the ground noise effectively with suppressing its resonant vibration.

Acoustic emission measurement of geothermal reservoir cracks in Takinoue (Kakkonda) field, Japan

Abstract Crack extension caused by a shut-down operation in production wells (build-up test) in Takinoue (Kakkonda) geothermal power plant, Iwate Prefecture, Japan, has been successfully measured by an acceleration-sensitive long-distance acoustic emission measurement technique. The distribution and activity of subsurface cracks in a geothermal reservoir can be determined by the combined procedure of the pressure build-up test and AE measurements. The feasibility and importance of the measurements are demonstrated by AE data and their interpretation.

Visual observation of the effect of magnetic field on moving air and vapor bubbles in a magnetic fluid

Abstract Theoretical prediction suggests that magnetic fluid (MF) as working liquid in heat pipe could enhance and control the heat transfer under the application of magnetic field. However, heat pipe experiments using ionic MF showed only marginal gain and demands investigation. As an initial step, visualization of air and vapor bubbles behavior under zero and applied magnetic field has been carried out using X-ray. The observations can be summarized as follows; applied magnetic field (a) reduces the size and deforms the shape of the bubble that secede from the heating surface or air supply tube, and (b) accelerates the movement of the bubble in the liquid.

Thermoluminescence as a new research tool for the evaluation of geothermal activity of the Kakkonda geothermal system, Northeast Japan

Abstract The thermoluminescence glow-curve of quartz in volcanic and pyroclastic rocks of the Miocene and Quaternary in the Kakkonda geothermal field was divided into L (low), M (medium) and H (high) peaks in order of increasing temperature. Thermoluminescence emission is independent of stratigraphic boundaries but it is closely related to surface geothermal manifestations. Thermally stimulated processes of thermoluminescence caused by natural annealing occurred in the Quaternary after the eruption of the Tamagawa Welded Tuffs; radiation storage processes then began, as a consequence of the temperature drop. Thermoluminescence behavior indicates natural temperature manifestations, together with the paleo-temperature history. The H peak was thermally stable compared to the L and M peaks, and the area within which the relative intensity of the H peak is less than 5% coincides with the surface zone where dominant fluid flow is convective. In addition, L and M peaks indicate that a relatively low-temperature fluid mixes with the hot upflow around the western margin of the ascending flow zone. Thermoluminescence characteristics reflect paleo-temperature history and are related to geothermal fluid flow. Thermoluminescence is an effective exploration technique for evaluating natural temperature manifestations and subterranean heat flow in geothermal systems.