When the number of constitutive atoms decreases to 10³∼10⁵, depending on the bonding mode and binding strength, the materials show different behavior from bulk ones as if they are new materials. These ultra-fine blocks are named “atom clusters” whose behavior is closely related to the many body effect of constitutive atoms.
Recently, an ultra-high voltage electron microscope “micro-laboratory” has been developed, in which the material behavior can be widely changed in-situ and the identification and characterization of materials in the atomic scale can be done. Various studies on the atom clusters have been carried out by this method.
In the present report, the anomalous behavior of these atom clusters is shown from the experimental results, and is discussed in terms of the formation of hybrid orbitals of valence electrons. Furthermore, the relationship between the so called “magic number” of micro-clusters and “magic size” of atom clusters is discussed.

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In order to clarify the problems involved in the measurement of the threshold stress for high-temperature deformation in a dispersion-strengthened alloy, using an Al-1.5 vol%Be alloy in which the strengthening mechanism has been identified, the threshold stress was measured by four different techniques: tensile test, stress relaxation test, creep test and stress abruptly loading test. The measured values were compared with the Orowan stress and the void-hardening stress calculated from the dispersion parameters. The yield stress obtained from the tensile test at room temperature was higher than the Orowan stress: the proportional limit was about 1.3 times and the 0.2% proof stress was about 3 times. For the stress relaxation test, no clear zero-creep stress was observed at high temperatures and the approximately determined zero-creep stress strongly depended on temperature, decreasing as temperature rose. The threshold stress obtained from the creep test agreed approximately with the void-hardening stress or the slightly higher Orowan stress than the void-hardening stress. The threshold stress at high temperatures, 623 and 673 K, obtained from the stress abruptly loading test decreased from the Orowan stress to the void-hardening stress with loading time.
From these results, the problems in the measurement of threshold stress are discussed and the stress abruptly loading technique is recommended.

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Growth behaviour of short and physical small cracks in a C-Mn steel heat treated to two microstructural conditions has been investigated experimentally on hour-glass shape specimens subjected to push-pull loading at room temperature and using the replica technique for crack length measurements. A crack growth equation which considers the microstructural effect on fatigue crack growth was used to explain the experimental behaviour obtained from constant amplitude tests. Long crack growth behaviour was studied using three point bend and cruciform specimens. The experimental data was analysed using fracture mechanics and presented in the form of a Paris law. The theoretical and empirical derivations were applied to predict the inspection intervals and fatigue life time of mine auxiliary ventilation fans.

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Differential Pulse Voltammetry was applied to measure the redox potential of the Cr⁶⁺/Cr³⁺ pair in alkali silicates. After it was carried out in the Na₂O–SiO₂ system, where Na₂O activity had been previously measured and the basicity was defined in such terms, it was extended to the xNa₂O(1−x)K₂O 2SiO₂ quasi-binary and M₂O 2SiO₂ (M=Li, Rb and Cs) systems. The redox significantly depends on the basicity and it seems promising that a basicity scale based on this redox potential may be applicable to alkali silicate melts in general.

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The heats of formation of six III-V compounds of GaP, InP, GaAs, InAs, GaSb and InSb were determined at 773 K from the heats of dissolution of these compounds and the components in a liquid tin solvent, using a Calvet-type twin solution calorimeter. The standard heats of formation at 298.15 K, ΔH_f,298.15°, are: GaP (P: red) −103.2±1.7 kJ/mol, InP (P: red) −70.2±4.4 kJ/mol, GaAs −87.7±0.5 kJ/mol, InAs −60.0±1.0 kJ/mol, GaSb −45.9±0.3 kJ/mol and InSb −34.1±0.6 kJ/mol. A relation was found between the heats of formation and the bond formation energy, and the overlap interaction in the cohesive energies of these compounds. ΔH_f,298.15° decreased linearly with increasing bond formation energy and overlap interaction energy per bond.

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Thermodynamic properties of NaO_0.5–CO₂–FeO_1.5 slag have been investigated for the application of sodium carbonate slag to the elimination of Fe from molten copper. The activities of NaO_0.5 and Na(CO₃)_0.5 were measured by the EMF method, using β″-alumina as a solid electrolyte for various partial pressures of CO₂ at 1423 to 1523 K. There is a stable solid compound NaFeO₂ in this system, and the solubility measurement of this compound into sodium carbonate melt at 1523 K revealed that the solubility is highly limited and controlled by the partial pressure of CO₂. The dissolution reaction seems to proceed according to the following reaction and Fe exists as FeO₃³⁻ anion in the sodium carbonate-based melt.
2Na(CO₃)_0.5(l)+NaFeO₂(s)=Na₃FeO₃(l)+CO₂(g).
The standard free energy change for the following reaction was determined as,
NaO_0.5(l)+FeO_1.5(s)=NaFeO₂(s)
ΔG°⁄J=−115000−10.33TlnT+98.32T(1283∼1423K)
by the EMF method. The activity of FeO_1.5 in the NaFeO₂(s)-saturated slag could be calculated by the above equilibrium relation from the activity of NaO_0.5. The activity of FeO_1.5 in the homogeneous liquid region of the slag was also evaluated by the distribution equilibrium measurements. The activity coefficient of FeO_1.5 in the homogeneous liquid region has a constant value for a constant CO₂ partial pressure, independent of the concentration.

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A model was proposed to simulate the growth rates of chemical-vapour deposited TiN films obtained in the previous study. In this model, flow and mass transfers are taken into account. The chemical reaction rate which expresses the effects of TiCl₄ and HCl partial pressures is used.
The calculated distributions of film growth rate almost agreed with the experimental results, and the effects of gas flow rate, deposition temperature and partial pressure of TiCl₄ on the growth rates of film were explained by the proposed model.
From a comparison between the calculated and experimental growth rates of the films, it was shown that the deposition occurred under the reaction controlled conditions at 1223 K, and that the effect of mass transfer resistance was larger at low partial pressures of TiCl₄ and at temperatures higher than 1273 K.

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The resistance of TiAl coupons to cyclic oxidation with temperature varying between room temperature and 1300 K in a flow of purified oxygen under atmospheric pressure has been significantly improved by preoxidation. The mass gain due to 20 cycle (400 h) oxidation was very small such as 5×10⁻³ kg m⁻² and correspondingly the scale formed by the preoxidation thickened very slightly during the cyclic oxidation. The preoxidation was performed by heating the specimens, buried in a chromia powder pack and encapsulated in a silica tube under a vacuum of 1.3×10⁻³ Pa, at 1200 K for 100 ks. Excellent oxidation resistance obtained is attributable to the formation of an alumina-rich scale, virtually alumina scale, by the preoxidation under a very low oxygen partial pressure. The preoxidation in mixtures of chromia and metallic chromium powders resulted in the formation of thin alumina scales. However, they are not protective. Local growth of rutile mounds during the cyclic oxidation indicated that the scales have mechanically weak points which provided sites for easy access of oxygen to the substrate.

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The Influence of beneficial additional elements (W, Mo, Nb and Si) on the oxidation behavior of a Ti-34.5 mass%Al alloy has been compared and their roles were studied. The relative effectiveness was in the order W, Mo, Nb, Si (the former, the better) at 1173 K. After the analyses of rate law and comparison in the Arrhenius plots of parabolic rate constants, it was clarified that the oxidation resistant temperature was increased by 100 and 200 K for the Mo (Nb) and W containing alloys respectively in comparison with the binary alloy for which the temperature was around 1000 K. The Mo, Nb and W containing alloys did not show any internal oxidation nor breakaway oxidation which was observed in the binary alloy. The reason for the non-occurrence of internal oxidation in these ternary alloys was verified by the result that those elements cause reduction of oxygen solubility in the TiAl alloys very significantly. Owing to this effect, the Al₂O₃ layer next to the outermost layer may be stabilized and the morphology of the Al₂O₃ in the inner layer may become more impermeable.

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Porosity formation in A206 aluminum plate castings was studied experimentally and theoretically. The experimental results indirectly confirm the roles of interdendritic liquid metal flow which causes a local pressure drop within the interdendritic liquid in accordance with the Darcy’s law. A solidification feeding efficiency index, denoted as G^0.4⁄V_s^1.6 (G is the thermal gradient and V_s is the solidus velocity), is employed to estimate the value of local pressure drop during solidification process and to predict the formation of porosity in A206 alloy castings. That the influence of the index is more prominent at a longer local solidification time than at a shorter local solidification time is also supported by the experiment. The experimental result indicates that an increase of G^0.4⁄V_s^1.6 and a decrease of solidification time reduce the amount of porosity content.

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The present work describes the magnetic properties of Nd_1−δ(Fe, Mo)₁₂N_x melt-spun ribbons which have lower Nd content than the stoichiometric composition. The crystallization temperatures of Nd(Fe, Mo)₁₂ phase with ThMn₁₂-type structure and α-Fe phase are at around 600 and 500°C, respectively. Nd_0.9Fe₁₁Mo_0.9N_x ribbon after heat treatment at 900°C for 30 min and subsequent nitriding at 550°C for 4 h exhibits coercivity of 240 kA m⁻¹. The V addition increases coercivity and the highest coercivity of 312 kA m⁻¹ can be obtained with the Nd_0.9(Fe_0.98V_0.02)₁₁Mo_0.9N_x ribbon annealed at 900°C for 30 min and nitrided at 550°C for 4 h. It can be concluded that Nd_1−δ(Fe, Mo)₁₂N_x melt-spun ribbons with lower Nd content than the stoichiometric composition show a relatively high coercivity.

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In the present work, the preparation of transparent yttria ceramics by vacuum hot pressing was investigated, using yttria powder whose mean diameter is 0.88 μm and whose purity is higher than 99.9%.
Transparent yttria ceramics were fabricated by vacuum hot pressing with small additions of LiF (about 1 mass%). Hot pressing temperature and pressure were kept at 1573 K and 44 MPa, respectively. The processed samples were observed to have transparencies up to 78% at the wavelength of 644 nm and over 80% in the range of 860 nm-6 μm.

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