Photoacoustic (PA) spectra on ZnO and CdO compound semiconductor sintered at 600°C for 24 h in glass tube were measured. CdO concentration was changed from 0% to 10% (0, 1, 3, 4, 5, 7 and 10% CdO) and CdO (99.9% purity) powder was also measured for comparison. The PA spectra were constructed from the PA signals of Zn_1-xCd_xO at the short wavelength region and those of CdO above 450 nm. Using the PA spectra below 450nm, the Cd contents dependence of the band gap of Zn_1-xCd_xO can be estimated. The band gap was modulated below 5% CdO samples and not changed above 5% CdO samples because the maximum CdO concentration might be between 5% and 7%.

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Copper is one of the most important alloying elements in sintered steel parts. However, reduction or removal of copper in the parts which are mainly used in automobiles is desirable for the promotion of recycling of steel from scrapped cars.
Calculation with a thermodynamic software and observation of slumping in shape of small compacts have indicated a low melting point near 1400K(1127°C)in the(lmass%Cr-0.7mass%Mn-0.3mass%Mo)steel-2.5mass%B-lmass%C powder mixture. The temperature is comparable to the melting point of copper or 1357K(1084°C). Thus, boron with carbon is a candidate replacement for copper at temperatures no higher than 1423K(1150°C)which can be easily reached in a conventional mesh belt furnace.
The addition of 2 mass% of the low-melting-point mixture or the combined addition of 0.05mass%B and lmass%C to the Cr-Mn-Mo steel has been proved to be effective in activating sintering. The addition has provided a reduction of sharp corners in the periphery of small pores, leading to a dimple fracture and an improvement in tensile strength of a basic Cr-Mn-Mo-lmass%C sintered steel by 15%.

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Diamond was deposited on a large-area substrate (SiAlON: 100×30×5mm, deposition surface: 100×30mm) by hot-filament CVD with using a straight 140mm-long TaC filament under H₂-3%CH₄ at 25 Torr for 130min, and the morphology, quality and thickness of the film were examined by SEM and Raman spectroscopy. No tension was applied to the filament during heating up to 2600°C for diamond deposition and no visible deformation of the filament after deposition was observed. The deposited film showed the clear facet and Raman peak of diamond all over the deposition surface. Uniformity of film thickness is good in the longitudinal direction of the filament but poor in the transverse direction. Deposition rates were about 4μm/h at the center nearest the filament and about 1μm/h at the edge farthest from the filament.

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Mechanical properities such as fracture toughness and bending strength were determined in zirconia-3 mol% yttria (PSZ) containing 0-5mass% alumina addition. They were sintered at various temperatures ranging 1673-1873K and various times ranging 1-8h. The mechanical properties of PSZ were improved by a small addition of alumina. This improvement is not related to the factors of density and grain size, but will be related to the formation of grain boundary phase, which is consisted of amorphous structure enriched alumina, silica, yttria and magnesia. The sintering of PSZ containing alumina occurs by liquid sintering mechanism.

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Surface relief associated with isothermal tetragonal-to-monoclinic phase transformation, i.e., martensitic transformation, in zirconia-3mol yttria (PSZ) with and without alumina addition, which occurred during aging at 130°and 200°C in air or vacuum environment was observed by an atomic force microscopy. The surface relief occurred from grain boundaries into grain interiors as the aging time increased and then spread succsessively into the surrounding grains with further aging. However, alumina particles and cubic phase paricles in PSZ containing alumina acted as obstacles for the advance of transformation, which would be the major reason for the improved mechanical properties of PSZ by the addition of alumina.

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The present paper describes a new evaluation for ejection behavior in iron powder compacting process and optimum die-wall lubrication conditions. In the new method, ejection force is broken down to static friction force and kinetic friction force, which make it possible to explain ejection behavior more clearly. The incremental rate of kinetic ejection force is more important for surface quality of compacts than the value of static ejection force. Among three lubricants used, zinc stearate showed the highest static ejection force but the lowest incremental rate of kinetic ejection force. It also showed an excellent surface quality of the compacts. Characteristic crystalline structure gave a low shear strength, which contributed to decrease the kinetic friction. In the die-wall lubrication method, the projected area rate of lubricant particles should be 90% or more, therefore, the multiple coating method which is repetition of short time shot is requested.

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Using (Ba, Sr, Ca)CO₃, nickel and Sc₂O₃ powders as starting materials, an electron emitter pellet for low temperature operating cathodes has been developed by hot isostatic pressing. During the exhaustion process of a cathode ray tube with the new pellet, carbonate (Ba, Sr, Ca)CO₃ was thermally decomposed into oxide (Ba, Sr, Ca)O and CO₂. In situ observation of the surface of the pellet during this thermal decomposition process and the examination of the microstructu-es of the pellets after decomposition revealed the condition for thermal decomposition; the highest maximum cathode current can be obtained at the heating rate of 3.2K/s. It was also found that when the carbonate was converted into the oxide at this heating rate, the carbonate confined in the pellet erupted, releasing CO₂, and an approximately 10μm thick flat emitting layer with pores was formed on the pellet surface. After the decomposition process, thermal aging by external heating, which is applied to the conventional oxide cathode, and current drawing aging by conduction heating, result in the superior emission property of the emitter pellet.

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Solid solutions of Ce_0.25Sr_1.75(Ni_1-yM_y)O_4-δ(M=Fe or Co, 0≤y≤0.3), having the tetragonal K₂NiF₄-type structure, were synthesized at 1100°C under flowing O₂. The a and c-axis lengths of Ce_0.25Sr_1.75(Ni_1-yM_y)O_4-δ(a=3.7999(1), c=12.3760(2)Å for Ce_0.25Sr_1.75NiO_3.75(y=0; CeSr₇Ni₄O₁₅)) increased with increasing y(a=3.8108(1), c=12.4268(4)Å for Ce_0.25Sr_1.75Ni_0.7Fe_0.3O_4-δ). Decrease of the a-axis length to 3.7975 (1)Å and increase of the c-axis length to 12.4302(2)Å were observed by the substitution of Co to the composition of Ce_0.25Sr_1.75Ni_0.7Co_0.3O_4-δ. Samples for characterization of the electrical properties were sintered at 1350°C and annealed at 1100°C under flowing O₂. The lowest electrical resistivity (1.7-3.1×10^-2Ωcm at 20-800°C) among the solid solutions was measured for Ce_0.25Sr_1.75(Ni_0.7Fe_0.3)O_4-δ. Seebeck coefficients of the solid solutions ranged from -22 to -38μVK^-1 around 450-500°C. The absolute values of the Seebeck coefficients decreased above or below this temperature.

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The outline of the history of mechanical alloying (MA) was presented. The researches on MA of metallic materials in 80's focused mainly on the formation of amorphous alloys. In 90's nanocrystallization by ball milling seemed the major interest. The amorphization by ball milling can be achieved either by mechanical alloying of the mixture of pure elements or by grinding of intermetallic compounds. The heavy rolling of TiNi plate revealed the formation of amorphous phase as shear bands. This suggests that deformation is purely responsible to the amorphization by ball milling. Nanocrystallization by ball milling examined by structural observation revealed a sudden change from work-hardened to nanocrystalline structure. This suggests that when deformation exceeds a certain critical condition, dislocation cell structure changes to grain boundary structure by the rearrengement of dislocations. Some of the previous and future applications of MA were discussed. ODS alloys, ultrafine particles, laminate rolling to produce TiNi thin plate and materials processing by means of mechanochemistry were intoduced.

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Mg-9%Al alloy was mechanically alloyed with addition of metal oxide (TiO₂ and ZrO₂) by using a planetary ball mill under an Ar gas atmosphere. After mechanical alloying, the powders were consolidated to the P/M material by vacuum hot pressing and hot extrusion. Solid state reaction during heating of the mechanically alloyed powders and P/M materials was studied by DSC, XRD and TEM. In both Mg-Al-TiO₂ and Mg-Al-ZrO₂ systems, the solid state reaction occurred during heating after mechanical alloying. TiO₂ and ZrO₂ were decomposed and formation of MgO occurred. In the Mg-Al-ZrO₂ system, however, the added ZrO₂ remAlned partially even after heating of the extruded material at 773K for 7.2ks. Consequently, obtained dispersion strengthened Mg materials showed high hardness and proof strength.

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The mechanochemical (MC) synthesis of La-modified lead zirconate titanate (PLZT) powder from the constituent oxides was conducted using a planetary ball milling. A single-phase perovskite PLZT powder was synthesized by dry-milling of the oxide mixture for a relatively short period (36ks at a rotational speed of 400r.p.m.). Dense PLZT bulk samples with fine-grained microstructures were obtained even from powders subjected to MC for a short time (3.6ks), at lower sintering temperature than the powders prepared by the conventional wet-mixing process. The present study suggests that the mechanochemical synthesis of PLZT consists of the following three stages: First, the pulverization, intimate mixing and granulation of the starting powders occur at the early stage. Secondly, the crystallites of the powders were increasingly disordered due to the impact of the milling balls. Finally, the reaction between PbO and TiO₂ was activated to produce PbTiO₃, and (Pb, La) (Zr, Ti)O₃ solid solutions were formed by the reaction between PbTiO₃ and the remaining oxides.

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Three polymorphs of titania, rutile, anatase and brookite have been known. In this work, brookite was synthesized from anatase by using a shaker ball-milling (NEV-MA8, Nissin-Giken Co., Ltd). Three experimental conditions, weak, medium and strong ball-millings, varied with changing shaking frequency and TiO₂ powder mass, were carried out. It has been concluded that the almost single phase of brookite type titania was obtained after 54ks and 72ks ballmilling under the condition of medium intensity. It has been also found that the brookite obtained in this study shows almost the same photocatalytic activity as anatase.

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Ti-xat%Nb-10at%Si (x=5-40) alloys were synthesized by mechanical alloying (MA) using a planetary ball mill with as starting materials of Ti, Nb and Si powders. The MA powders milled for 360ks were spherical particles of about 20μm in all the alloys studied. The characteristics of these MA powders were examined by XRD, DSC and TEM.
Ti-5at%Nb-10at%Si powder milled for 360ks consisted of fine α-Ti crystals. The MA powders containing 10at%Nb to 40at%Nb showed exothermic reaction in the DSC curves. In Ti-20at%Nb-10at%Si and Ti-10at%Nb-10at%Si, the exothermic reactions were observed at higher temperature than 800K. This exothermic reaction was the crystallization from amorphous phase in MA powder to α-Ti crystalline phase. In Ti-40at%Nb-10at%Si and Ti-30at%Nb-10at%Si, the exothermic reaction was observed at about 600K. This exothermic reaction was characterized as crystallization from amorphous phase to β-Ti crystalline. The Ti-10at%Nb-10at%Si MA powder was consolidated by the pulsed current sintering with a high pressure. The obtained bulk amorphous compact contained 18vol% pores.

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Nano-structured functional materials are expected to have superior properties to the coarse-grained, bulk materials. In the present paper, pure palladium is refined to nano-sized state to investigate the hydrogen absorption and desorption behavior. Using the bulk mechanical alloying, the palladium platelets can be successfully refined to nano-sized grains with the order of 10nm. In comparison of pressure composition isotherms between nano-sized and bulk palladium, the phase boundary of the Pd-H miscibility gap is significantly narrower for nano-Pd. While the hydrogen solubility at α (α+β) phase boundary is much increased, that at β/(α+β) phase boundary is drastically reduced by nano-structuring. This might be because of the broadening of the site energy distribution, induced by the intrinsic strains constraining the nano-grains. The broadening mechanism of site energy distribution has direct influence on the hydrogen absorption and desorption processes. The Curie temperature for hydrogen absorption and desorption is drastically reduced by 135K through the nanostructuring. The above precise discussion helps us to make nano-structured material design in the hydrogen storage alloys and compounds.

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Non-equilibration of Mg₂Ni by nickel enrichment was investigated by using the bulk mechanical alloying (BMA). Although little or no solubility of nickel in Mg₂Ni was present in the phase diagram of Mg-Ni system, BMA enables us to make solid-state synthesis of Mg_2-xNi for 0<x<0.5 with success. The synthesized Mg_2-xNi has a common crystalline, nano-sized structure of Mg₂Ni together with a small amount of amorphous phase. Through precise analysis of the measured pressure-composition isotherms for these Mg_2-xNi samples, it was found that two hydride phases should exist for Mg₂NiH₄. This formation of low-temperature phase Mg₂NiH₄ is common to hydride formation from the nano-structured Mg₂Ni. With nickel enrichment, the maximum storage capacity decreased irrespectively of the holding temperature. This might be because the hydrogen-site energy distribution is broadened by the intrinsic strains constraining the nano-grain of Mg₂Ni. This is just corresponding to the hydrogen ordering especially in low temperature. Effect of non-equilibration on the hydrogen absorption can be seen in the monotonic reduction of the transformation temperature from high-temperature to low-temperature phases of Mg₂NiH₄. The amorphous phase became never negligible in Mg_1.5Ni. Its hydrogen behavior was a little different from those for Mg₂Ni and Mg_1.75Ni, especially in low temperature.

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The synthesis of Ti₃SiC₂ powder by mechanical alloying (MA) from elemental Ti, Si and C powders and pressureless sintering of the synthesized Ti₃SiC₂ powder were conducted. A high energy vibratory mill was used for the MA, in which the process parameters, such as milling time and ball size, were varied to investigate the MA conditions for Ti₃SiC₂ formation from the elemental powders. The Ti₃SiC₂ phase was first formed during the MA process using large-sized balls, i.e. with a large energy, but subsequently transformed gradually to an amorphous phase. When using small-sized balls, no Ti₃SiC₂ was formed during the MA although amorphous phase were obtained similarly as a fine powder. The MA-derived amorphous powders could be pressulessly sintered to dense Ti₃SiC₂-based ceramics containing less than 30% TiC_x as a secondary phase. The density, microstructure and mechanical properties of the sintered compacts were investigated with an emphasis on the effect of MA time.

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Mechanical Alloying (MA) treatment is an effective technique in terms of ultra-grain-refining within powder particles and fabrication of alloy powders. In this study, a new powder metallurgy process using MA treatment was proposed for the fabrication of fine-grained high nitrogen stainless steels. Chromium nitride (Cr₂N) powder was mixed with Fe-Cr binary alloy powder to control its mean chemical composition to be Fe-23mass%Cr-1mass%N which is enough to stabilize austenitic structure at room temperature. The powder mixture was mechanically milled up to 360ks in an argon gas atmosphere to produce an alloyed powder (MA powder). MA powder was packed in a stainless steel tube in a vacuum and consolidated by hot rolling at 1073 K. The bulk material was finally heated to various temperatures (1173-1473K) and then quenched without holding at the temperature. The structure of bulk materials heated to the temperature below 1323K is of (bcc+Cr₂N) at room temperature, and the materials treated above 1373K has the structure of (fcc+Cr₂N). For instance, the materials treated at 1473K has fine austenitic structure of the grain size of 2.2μm due to finely dispersed Cr₂N particles in matrix and contains 0.86 mass% nitrogen in solid solution. The austenitic steel has very high yield strength of 1.1 GPa and enough elongation of 30%. Such a high strength is due to solid solution strengthening by nitrogen and grain refining strengthening of the matrix.

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FeAl-WC composite was proposed as a potentially novel hard metal. FeAl powder was synthesized in a planetary ball mill under an argon atmosphere. Powder mixtures consisting of FeAl and WC powders were dry blended in an automatic agitator. FeAl-0-65vol%WC composites were consolidated by pulse current sintering in a vacuum under the pressure application of 40MPa. Vickers hardness of the obtained composites increased with increasing WC content and 1075Hv was obtained for FeAl-50vol%WC composite. Transverse rupture strength of the composites was measured to be about 1.8 MPa up to 30vol%WC and abruptly decreased to 1.1 GPa for more than 50vol% WC. Oxidation test at 1173K exhibited weight gain of FeAl-50vol%WC was a one-seventh as much as that of Co-50vol%WC.

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