Tetsuo Yoshio

Preparation of Co-N films by rf-sputtering

Co-N films in the wide compositional range can be prepared by reactive sputtering. Co-N sputtered films consist of one or two phases, such as CoN, Co2N, Co3N, Co4N and α-Co. Co4N phase with a cubic unit cell is observed, and its lattice constant isa = 0.3586 nm. The preferred orientation is observed on the Co-N films, CoN (200) plane, Co4N (1 1 1) plane and α-Co (002) plane parallel to the film surface, respectively. Saturation magnetization σs of Co-N sputtered film decreases from 160 to 1.7 e.m.u. g−1 with increasing content of N from 0 to 21.7 at%, and coercive forceIHc is the range of 43 to 5000e at room temperature.

Oxidation kinetics of hexagonal boron nitride powder

The isothermal oxidation of hexagonal boron nitride powders was carried out at 900–1050°C in dry oxygen and air. The oxidation kinetics were found to obey linear rate law and were described by the surface chemical reaction-controlled shrinking cylindrical model. The apparent activation energies were found to be 298 and 330 kJ mol−1in dry oxygen and air, respectively. The oxygen partial pressure dependence of the oxidation rate constant at 1000 °C is well represented by a Langmuir-type equation. Microscopic examination of the oxidized sample after removal of the oxide scale with water suggested that the rate of attack by oxygen was determined by an anisotropy due to the crystallographic direction, similar to oxidation in graphite. The volatilization of B2O3 was observed only in dry oxygen and obeyed a linear rate law, and was found not to affect the oxidation reaction.

Characterization of alkoxy-derived iron silicate

Abstract Amorphous iron silicates, x Fe 2 O 3 · (1 − x ) SiO 2 (0.1 ⩽ x ⩽ 0.4), were prepared by calcining alkoxy-derived gels obtained by the hydrolysis of metal alkoxide mixtures. Structural studies based on X-ray diffratometry. Mossbauer effect and infrared spectroscopy indicated that the materials were indeed amorphous up to 500°C in the composition range x ⩽ 0.3 and that the structure is formed by SiOFe bonds. Crystallization took place on calcining the samples with the composition x ⩽ 0.3 above 600°C. Fayalite deposited at 600°C and hematite and α-cristobalite deposited above 700°C. In the case of the composition x = 0.4 the product was amorphous up to 300°C and only hematite was detected above 400°C.

Preparation of Co-C films by radio-frequency sputtering

Determination des conditions de preparation des couches Co-C. Caracterisation de ces couches par diffraction de rayons X, microscopie electronique a balayage, et analyse chimique

Corrosion Behaviour of Structural Ceramics in Supercritical Water

The corrosion behavior of Si3N4, SiC, mullite, alumina and sapphire was investigated in supercritical water at 450 °C and 45MPa for 2 to 50h. Corrosion resistance for the ceramics was as follows in the order; Si3N4 < SiC < mullite < alumina < sapphire. Pitting corrosion with formation of amorphous layer and intergranular corrosion due to dissolution of additives were observed in PLS-Si3N4 and PLS-SiC, respectively. The corrosion behavior of mullite was characterized by dissolution of SiO2 and formation of boehmite residue layer. High purity alumina ceramics showed the highest corrosion resistance in the ceramics. Intergranular corrosion proceeded in the alumina ceramics and its corrosion rate was strongly dependent on the impurity content.

Preparation of Zr-B films by r.f. sputtering

Fe-N films over a wide compositional range have been prepared by the reactive sputtering method. Fe-N sputtered films were composed of a single or two phases such asζ-Fe2N,e-Fe3.02N,γ′-Fe3.82N,γ′-Fe4N andα-Fe; however, an unknown phase was observed at a higher nitrogen pressure. A remarkable preferred orientation of thee-Fe3.02N (110) plane parallel to the film surface was observed. The Curie temperature of the sputtered γ′-Fe3.82N sample was 490° C, which was almost the same as that ofγ′-Fe4N prepared by metal nitriding. The saturation magnetization,σs, of the sputtered Fe-N samples decreased from 151.8 to 42.4 e.m.u.g−1 with increasing nitrogen content from 7.94 to 24.87 at%, and its coercive force,1Hc was found to lie in the range 150 to 600 Oe in the powder form at room temperature.

Crystallization of amorphous BaOFe2O3 prepared by the method without melting

Abstract Formation of the amorphous barium ferrites, BaFe2O4 and BaFe12O19, by the methods of hydrolysis of metal alkoxides and rf-sputtering were studied. Alkoxy-derived barium ferrites crystallized into particles with size between 0.1 and 1 μm. From amorphous ferrite films were obtained the crystals having preferred orientations with (001) plane for BaFe2O4 and (110) for BaFe12O19 parallel to the film surface when the film thickness was less than 1 μm. BaFe12O19 of preferred orientation with (001) plane was also obtained from double layered film composed of BaFe2O4 with preferred orientation of (001) plane as a precursor and α-Fe2O3 as the second layer.

Crystallization of the amorphous BaFe2O4 film prepared by rf-sputtering

Abstract Amorphous BaFe 2 O 4 film was deposited on both the slide-glass and silica-glass substrates by applying the rf-sputtering technique. On heating the film above 500°c, the high-temperature modification of BaFe 2 O 4 crystallized on the slide-glass substrate on one hand, and the low-temperature form crystallized on the silica-glass substrate on the other hand. A remarkable preferred orientation with (001) of BaFe 2 O 4 parallel to the surface of the substrates was observed in a thin film with thickness less than 1 μm.

Properties of Va metal-B films prepared by r.f.-sputtering

Nb100−xBx alloy films were prepared by the r.f.-sputtering method in the chemical composition range of 30 ≦x ≦ 76. Nb100−xBx (30 ≦x ≦ 54) films consisted of the amorphous state, and NbB2 crystal phase was observed on Nb100−xBx (67 ≦x ≦ 76) films. A remarkable preferred orientation with the (001) plane of NbB2 in parallel to the film surface was observed on Nb33B67 film. d.c. electrical conductivity of Nb100−xBx (30 ≦x ≦ 76) films decreased with increasing content of boron in the range from 7.3×103 to 7.6 ×102Ω−1cm−1. Micro-Vickers hardness of Nb100−xBx (30 ≦x ≦ 76) films exhibited the values of 1070 to 2060 kg mm2.

Effect of grain morphology in pressureless-sintered Si3N4z.sbnd;Y2O3/Al2O3 on leaching behavior under hydrothermal conditions

The purpose of this work is to study the effect of grain morphology in sintered Si3N4 on the leaching behavior under hydrothermal conditions. The pressureless-sintered Si3N4-Y2O3/Al2O3 specimens were produced using two kinds of commercial grade Si3N4 powders, i.e., prepared by the imide-decomposition method (specimen-A) and the silicon-nitridation method (specimen-B). Differences in microstructures were observed for sintered specimens from these Si3N4 starting powders, i.e., specimen-A resulted in a finer microstructure than specimen-B. Leaching test was carried out using an autoclave under the hydrothermal conditions at 300°C and 8.6MPa for 1-10 days. The two specimens showed the similar trend of weight loss in leaching test, but larger weight loss was measured in specimen-B in the whole leaching time. A parabolic plot of weight loss suggested that the leaching mechanism consisted of two stages. SEM observation revealed that the both leached layers consisted of porous layer at the first stage and flakes on it at the second stage. The porous layer for specimen-A was finer than that for specimen-B and the traces of machining grooves was still visible on both porous layers. The results of this experiment showed that the leaching weight loss of sintered Si3N4 under hydrothermal conditions and the microstructures of the leached layer depended remarkably on the microstructural grain morphology of the sintered body generated by the starting powders and also on its mechanical history by grinding.