Hidekazu Todoroki

Rapid measurement scheme for texture in cubic metallic materials using time‐of‐flight neutron diffraction at iMATERIA

A rapid texture measurement system has been developed on the time-of-flight neutron diffractometer iMATERIA (beamline BL20, MLF/J-PARC, Japan). Quantitative Rietveld texture analysis with a neutron beam exposure of several minutes without sample rotation was investigated using a duplex stainless steel, and the minimum number of diffraction spectra required for the analysis was determined experimentally. The rapid measurement scheme employs 132 spectra, and by this scheme the quantitative determination of volume fractions of texture components in ferrite and austenite cubic phases in a duplex stainless steel can be made in a short time. This quantitative and rapid measurement scheme is based on the salient features of iMATERIA as a powder diffractometer, i.e. a fairly high resolution in d spacing and numerous detectors covering a wide range of scattering angle.

Penetration Depth of Microwave into the Mixture of Goethite with Graphite Estimated by Permittivity and Conductivity

A study has been conducted to understand the penetration behavior of microwave into the mixture of goethite with carbon (C) aiming at providing an appropriate guidance to dehydrate the substances with hydroxides occasionally contained in industrial sludge. At first, it was observed that microwave could not sufficiently penetrate into the specimen with C/goethite molar ratios greater than 2, giving incomplete dehydration. To understand the penetration behavior of microwave, permittivity and conductivity were measured. Permittivity measurements were successfully made below 9 vol pct C. For carbon content greater than 8.56 vol pct C, the conductivity of the mixture abruptly increased by four orders of magnitude because of the occurrence of the conductivity percolation. Above 13.7 vol pct C close to an inflection point approximating 10 vol pct C, the mixture became sufficiently conductive. Transition from dielectric to conductive behavior occurred between 8.56 and 13.7 vol pct C. The Generalized Effective Medium approximation could satisfactorily express the variation of the conductivity values in the whole range of vol pct C measured. The penetration depth of microwave was determined by the above two measurements. It was found that penetration depth decreased with the increasing vol pct of C contained in the mixture specimen. Finally, guidance could be provided as for the blend ratio of C to treated material along with the size of a briquette or a pellet referring to the obtained relation between penetration depth and vol pct of C. Furthermore, it was proved that the numerical simulation was quite helpful to predict how microwave behaves in the mixture under given conditions.

Estimation of microwave penetration distance and complex permittivity of graphite by measurement of permittivity and direct current conductivity of graphite powder mixtures

Microwave penetration distance into powder mixtures of FeO(OH)/graphite (C) and tri-calciumphosphate/C was studied by changing the fraction of graphite powder and the degree of the compression. They are combined into a parameter of carbon volume fraction [Pct. Vc]. Experimentally, it was shown that the penetration distance decreased at high [Pct. Vc]. Measurement of permittivity became impossible at certain [Pct. Vc], which is related with the abrupt increase in DC conductivity (occurrence of percolation). In this study, dependence of DC conductivity of the mixture on [Pct. Vc] was expressed using generalized effective medium approximation. And then, average permittivity of the mixture below percolation threshold was measured and analyzed using a mixing rule based on effective medium approximation. In this procedure, permittivity of carbon was estimated to fit the data of the measured average permittivity. Transition from the dielectric to the conductive nature of the powder mixture influences the penetration distance; however, it was shown that the predicted penetration distances by equations using conductivity (σ) or complex permittivity (e) of the mixtures are consistent with each other, namely, their extrapolations are continuous across the transition region of the percolation threshold.