Mössbauer Spectroscopy Studies on Zn-Bearing Ferrite

Ion distribution in Zn-bearing ferrite Zn _x Fe_{3− x} O₄ was examined using Mössbauer spectra at room temperature. Ion distribution models I and II have been proposed for the samples prepared by a solid-state reaction and from an aqueous Zn(II)–Fe(II) hydroxides suspension, respectively.
(I) (II)     

Proposal and Design of a Slim Electronically Steerable Parasitic Array Radiator Antenna in the 2.4-GHz Band

We propose an electronically steerable parasitic array radiator antenna that is about 96% smaller than a conventional one. The antenna can shape a beam with a working gain of about 6 dBi without a matching circuit and steer the beam in steps of 45°. The reactance with which parasitic elements are loaded is designed to achieve vswr of <3 in the frequency band for IEEE802.11b by controlling the set of reactance values in three steps. Consequently, a pen-sized beam steerable antenna can be made for a 2.4-GHz-band wireless local area network. The antenna is unique in that the current excited on parasitic elements is stronger than that excited on the fed element when a beam is shaped.     

Effect of the amount of excess oxides on the densification of α-SiAlON fabricated via a reaction-bonding process

Y-α-SiAlONs with elongated grains were fabricated via a reaction-bonding process using starting compositions containing excess oxides in the form of Y₂O₃ and SiO₂. The density of post-sintered specimens reached a maximum value with compositions containing 2 mass% excess oxides, although conventionally sintered materials of this composition were not fully dense. However for compositions containing smaller amounts of excess oxides, the density of the specimen fabricated via a reaction-bonding process was lower than that via a conventional process. In these samples it is thought that liquid phase sintering was difficult to be achieve during the post-sintering process, since the amount of SiO₂ contained in the starting powder was lower and the Al₂O₃ in the starting composition was consumed for the production of β-SiAlON during nitridation. There was also a decrease in density of the reaction-bonded materials with further increases in the amounts of additional oxides. For these samples the compacts could not be densified uniformly, because of non-uniformity of the phase composition in the nitrided compacts. The dense reaction bonded α-SiAlON with elongated grains, fabricated from compositions with 2 mass% excess oxides exhibited both high fracture toughness and high hardness.     

A new type of fatigue striation on PMMA immersed in organic agents

Fatigue crack growth tests of PMMA were undertaken at 295 K in organic agents with relatively high viscosity. Regular wavy striations, the wave length and amplitude of which were dependent on the characteristics of the agent, appeared on the fracture surfaces at low values of the stress intensity factor ranges. This type of striation has not been reported elsewhere. The formation mechanism of these was analysed based on the two dimensional viscous-fluid flow through a narrow gap between the crack planes. The theoretical suggestion that the wave length of the striation tends to increase with increase in the surface tension of the liquid and a decrease in its viscosity was in good agreement with the experimental trend.     

Structural properties of carbon materials from the electrochemical reduction of fluorinated naphthalene pitch

Synthesis of carbon materials from fluorinated naphthalene pitch has been carried out by means of electrochemical reduction. Structural and morphological properties of synthesized carbons were investigated using X-ray photoelectron spectrum (XPS), Raman scattering spectrum, X-ray diffraction measurements and scanning and transmission electron microscopy (SEM and TEM). Furthermore, a change in the structure of synthesized carbons with an electron beam irradiation was examined. The synthesized carbon has a disordered structure composed of fragments of the sp² hexagonal network, and also has lots of micro-voids. A carbyne-like structure was found only a little with the reduction of fluorinated naphthalene pitch by Raman spectra. A lot of ribbon-like graphite nanocrystal was formed by irradiation of an electron beam at a high temperature to the defluorinated carbon. Bending of a long ribbon-like crystal of graphite was often observed. Formation mechanism of graphite nanocrystals was discussed.     

Thermal Shock Behavior of Isotropic and Anisotropic Porous Silicon Nitride

The thermal shock behavior of isotropic and anisotropic porous Si₃N₄ was evaluated using the water-quenching technique. The critical temperature difference for crack initiation was found to be strongly dependent on the ratio of fracture strength to elastic modulus. Because of a very high strain-to-failure, anisotropic porous Si₃N₄ showed no macroscopic cracks and was able to retain its strength even at a quenching-temperature difference of ∼1400°C.