Coupon specimens of 30Nb-40Al-xCr-yMo-zSi (mol%), with x+y+z=30, were oxidised in air at 1573, 1673 and 1773 K for 72 ks. The original specimens and oxidation products were characterised by X-ray diffractometry, scanning electron microscopy and electron probe microanalysis. All the specimens consist of several phases with complex structures. The major phases of the specimens are AlNbCr, Nb₅Si₃, NbAl₃ and Mo₃Al, and their minor phases are Cr₂Al, Cr₅Al₈, NbCr₂ and Nb₂Al. The amount of AlNbCr decreases and that of Nb₅Si₃ increases as the Si content increases. At 1573 and 1673 K all the specimens, except 30Nb-40Al-15Cr-15Si oxidised at 1673 K, form protective scales with inner α-Al₂O₃ layers very sound and adherent to the substrates. At 1773 K 30Nb-40Al-7.5Cr-7.5Mo-15S and 30Nb-40Al-10Cr-5Mo-15Si show excellent oxidation resistance with scales consisting mainly of α-Al₂O₃. The other specimens form poorly protective scales or oxidation zones without scales. In general, the oxidation resistance increases with an increase in the Si content for the Mo-containing alloys. This is attributable to the formation of protective scales containing SiO₂ and mullite in the initial oxidation stages. However, an adverse relationship was found for those without Mo. This is explained in terms of the strength of the specimen. This view is supported by the fact that the specimens without Mo were elongated and deformed. These shape changes would have introduced mechanical failure in the scales.

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  In order to improve the oxidation resistance of WSi₂ at 873-1573 K, boron added WSi₂ was fabricated by a spark plasma sintering method and the oxidation tests were carried out in air. The fabricated boron added WSi₂ consisted of WSi₂, Si and W₂B₅. The addition of boron into WSi₂ led to the formation of a protective borosilicate scale, resulted in improvement of the oxidation resistance. Requisite concentration of boron for the formation of a protective borosilicate scale decreased as temperature is raised. Consequently, the addition of 2 or 3 mass% boron was the most effective for improvement of oxidation resistance of WSi₂ in the temperature range of 873-1573 K. Such effect of boron on high-temperature oxidation of WSi₂ was also discussed.

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  TiAl-based alloys (Ti-48Al-2Cr-2Nb, Ti-48Al -2Cr-2Fe, Ti-48Al-2Cr-2W and Ti-48Al-2Cr-1W-1Ta in mol%) were oxidized isothermally at 1123 K for 360 ks in a flow of O₂, O₂-H₂O, H₂O, O₂-CO₂, CO₂, O₂-N₂ or N₂ and the influence of H₂O, CO₂ and N₂ in the oxidizing atmosphere on the oxidation behavior has been studied. The oxidation of Nb, W or Ta containing alloys in O₂ results in the formation of continuous Al₂O₃ layers in the scales and thus in superior oxidation resistance. On the other hand, the alloy with Fe shows large mass gains due to oxidation without forming a continuous Al₂O₃ layer. The presence of H₂O in the atmosphere accelerates the oxidation of all the alloys, and this influence is prominent for the Fe-containing alloy. Since H₂O affects more significantly TiO₂ than Al₂O₃, the observed influence of H₂O is attributable to the anisotropic and enhanced growth of TiO₂. While the oxidation behavior of the alloy with Fe is affected by the presence of CO₂, the other alloys are not susceptible to it. Although N₂ is less influential than H₂O and CO₂, the alloys with Nb, W or Ta show larger mass gains in O₂-N₂ than in O₂. The influence of CO₂ or N₂ is attributable to the formation of carbides or nitrides respectively in the scales that impede the continuity of the protective Al₂O₃ layers. The influence of these gas species is smaller for the alloys forming protective Al₂O₃ layers in the scales and vice versa.

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  The effects of coatings on the deformation and oxidation behavior of Ti-50Al alloy were investigated at 1173 K in air at a constant loading of 30 MPa. The coating was formed by a two-step Cr/Al diffusion treatment and consisted of an outermost TiAl₂ layer, an outer Al-rich γ layer, an intermediate γ, Laves and β mixed layer, and a Cr diffusion zone. Tensile tests were also carried out with sole Cr or Al coated TiAl and uncoated TiAl at 1173 K for comparison purposes. The oxide scales formed on the uncoated TiAl and the sole Cr coated specimens were a mixture of TiO₂ and Al₂O₃, which displayed extensive exfoliation. Both the two-step Cr/Al coated TiAl and the sole Al coated specimens formed a protective Al₂O₃ layer and little oxide exfoliation was observed here. Significant cracks were observed in the sole Al coated TiAl, while no cracks were observed in the sole Cr coated TiAl; the two-step Cr/Al coated TiAl showed a number of cracks in the coatings. Low creep rates in the two-step Cr/Al coated TiAl could be due to the Laves phase with a hexagonal C14 structure in the intermediate, γ, β and Laves phase mixture, and the high creep rates of the sole Cr coated TiAl may originate in the major β phase component with a B2 structure in the γ, β, and Laves phase mixture.

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  The oxidation behavior of Pt+Hf-modified γ-Ni+γ′-Ni₃Al alloys containing up to 20 at%Pt and either 15 or 20 at%Al was studied by oxidizing the alloys in air at 1150°C under both isothermal and thermal cycling conditions. It was found that the co-addition of Pt and Hf was extremely beneficial to oxidation resistance, to the extent that Ni-20Al-20Pt-0.4Hf and Ni-20Al-10Pt-0.4Hf alloys (all compositions are in at%) oxidized at significantly slower rates than that of a Ni-50Al-15Pt β-NiAl alloy. A Ni-20Al-5Pt-0.3Hf alloy also showed relatively good oxidation resistance, with the oxidation rate being almost the same as that obtained for Ni-50Al-15Pt alloy. Over a period of up to 500 one-hour oxidation cycles, no oxide spallation from the modified γ+γ′ alloys was observed. From cross-sectional SEM examination coupled with X-ray diffraction analyses, it was found that a compact and planar exclusive scale layer of α-Al₂O₃ formed on the Ni-20Al-20Pt-0.4Hf alloy. By contrast, Ni-20Al-10Pt-0.4Hf and Ni-20Al-5Pt-0.3Hf alloys formed a very thin outer layer of NiAl₂O₄ and a planar inner layer of α-Al₂O₃. The thickness of this inner Al₂O₃ layer increased with increasing oxidation time relative to that of the NiAl₂O₄ layer, suggesting that the latter primarily formed during the initial stages of scale formation. Both NiO and NiAl₂O₄ were found in the outer scales formed on the Ni-20Al-0.3Hf and Ni-15Al-0~10Pt-Hf alloys, with the thickness of these oxide layers decreasing with increasing Pt content in the alloys. Further, it was found that the extent of internal HfO₂ formation decreased significantly with increasing in Pt content, to the extent that no HfO₂ was found in the oxidized Ni-20Al-20Pt-0.4Hf alloy. Inferences for the observed beneficial effects of Pt promoting protective Al₂O₃ formation and decreasing the tendency for Hf to oxidize in γ+γ′ alloys will be presented.

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  The formation of a Ni aluminide coating layer containing Zr on a Ni substrate was attempted by the electrodeposition of Zr and Al. The cyclic oxidation resistance of the Ni covered with the coating was then evaluated. Zr and Al were deposited by molten salt electrolysis. For the sample treated with the Al deposition, a layer consisting of Ni₂Al₃ was uniformly formed. On the other hand, for the sample treated with the Zr deposition, followed by the Al deposition, a layer consisting of Ni₂Al₃ and a Ni aluminide layer containing Zr on the Ni₂Al₃ layer were formed. Furthermore, when the Zr electrodeposition conditions were changed, the concentration of Zr in the Ni aluminide layer containing Zr, formed on the surface, changed. The cyclic oxidation test showed that for the sample with the Al deposition, the mass reduction due to scale exfoliation took place, whereas for the sample treated with a small deposit of Zr, followed by Al deposition, no mass reduction was observed. For this sample, after the cyclic oxidation test, a scale consisting of α-Al₂O₃ adhering to the substrate was formed. Consequently, it was found that the cyclic oxidation resistance of the Ni was improved by a small of Zr, followed by Al deposition.

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  In order to improve the high-temperature durability of the plasma sprayed thermal barrier coating (TBC) systems, high-temperature oxidation test was conducted under the isothermal condition at 1100°C for 100 h for several kinds of TBC systems in connection with their coating characteristics such as the coating microstructures and interfacial natures depending on the coating process conditions. Specimens with different coating characteristics were prepared by controlling the coating parameters such as the top-coat spraying conditions and the reheat-treatment (RHT) conditions after spraying. Especially, the RHT was applied to the TBC specimen with different temperature, heating rate, holding time at maximum temperature and so on in inert argon (Ar) gas atmosphere.
   High-temperature oxidation behavior was found to differ depending strongly on the RHT conditions. The RHT at lower temperature could not inhibit the heterogeneous development of thermally grown oxides (TGO) layer and the wart-like oxides at the top-coat/bond-coat interface. On the contrary, the RHT with either the slow rate heating or the long time holding at the maximum temperature was found to be effective for an improvement of the oxidation resistance, since such a RHT process is able to develop dominantly the continuous α-Al₂O₃ layer at the interface so as to reduce sufficiently the growth rate of TGO to maintain the suitable environmental barrier function during high-temperature oxidation.
  The influence of the RHT conditions on the high-temperature oxidation property was discussed in connection with both the morphology of bond-coat powders and the surface morphology of bond-coat sprayed.

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  Acoustic emission and Raman spectroscopy were applied to measure in situ oxide spallation during cooling. The AE signal was detected during a temperature decrease due to fracture of a Cr₂O₃ scale formed on a 25%Cr-20%Ni steel oxidized at 1173 K for 10.8 ks. Measured AE energy drastically increased at a temperature decrease of about 500 K where Raman spectroscopy showed relaxation of a stress generated in the scale. Based on the data obtained from both measurements, Youngs modulus of the Cr₂O₃ scale has been calculated to be 248 GPa at 973 K and 342 GPa at 773 K. In addition, the fracture energy required to produce decohesion at Cr₂O₃/metal interface has been estimated to be 4.1 Jm^-2 from the equation of strain energy proposed by Evans.

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  Degradation of component materials such as gas or steam turbines under high temperature environments has been one of severe problems due to not only high temperature corrosion or oxidation but also erosion caused by the impact of metallic oxide particle formed in upstream systems. It is important to know mechanical properties and adhesion of oxide films formed on metal surfaces at high temperatures, in order to estimate degradation rates and to select high resistant materials against high temperature erosion-corrosion. We have tried to examine these properties of oxide films formed on carbon steel, and to establish degradation models of the oxide films. The phenomenon of high temperature erosion-corrosion caused by solid particle impact was also discussed.

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  High-temperature oxidation of a pure iron, Fe-2Cr alloy, Fe-10Cr alloys and an Fe-10Cr-0.08C steel was examined in both air and steam at 923 K. In case of pure iron, the thickness of the oxide scale formed in steam at 923 K for 360 ks was comparable to that of the scale formed in air. On the other hand, in case of the Fe-Cr binary alloys and the ternary martensitic steel, the oxide scale was much thicker in steam than in air. The amount of hydrogen dissolved into the pure iron and the steels during exposure to the high-temperature steam was measured with thermal desorption spectroscopy (TDS). It was found that the amount of the dissolved hydrogen in the oxide scale was much larger in both the binary alloys and the ternary ferritic steel than in pure iron, and then it leads to the more accelerated oxidation rate of the binary alloys and the ternary steel in the steam. Furthermore, the martensite structure of the ternary steel exhibited an excellent oxidation resistance in air compared to the ferrite phase in the same steel. This is probably because the martensite phase has a lot of plane defects such as block boundaries for the fast diffusion path of Cr element.

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  In order to improve the durability of high efficiency waste-to-energy boilers, it is essential to develop and apply high temperature corrosion-resistant materials having a long corrosion life time in the severe corrosive conditions of waste combustion gas. Two types of high Cr-high Si-Fe-Ni alloy seamless tubes, i.e. MAC-N (26Cr-3.5Si-11Fe-Ni base) and MAC-F (23Cr-3.8Si-38Ni-Fe base) respectively, which contain no expensive molybdenum and have better corrosion resistance than the conventional alloys under mixed corrosion reactions of oxidation, chlorination and sulfidation, have developed. The optimum composition range of two alloys were determined by confirming the effect of the alloying elements on the corrosion resistance, high-temperature mechanical properties and workability in the laboratory and field tests.
   Furthermore, the seamless tubes were mounted on the actual superheaters of the 773 K/9.8 MPa high efficiency waste-to-energy boiler to examine the durability of both tubes for approximately four years. As a result, it was confirmed that the MAC-N and MAC-F alloys have better corrosion resistance than the conventional Alloy 625. In addition, it has become clear that corrosion resistance of both alloys is displayed through the formation of silicon oxide and chromium oxide (III) rich protective scale caused by the combined effect of the principal elements, silicon, chromium, iron and nickel. The corrosion rate increases under severe thermal cycle condition, such as soot blowing, as the results of deterioration of protective oxidation scale.

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  The surface structure of a metallic mirror fabricated in the late Edo period has been investigated. A Sn layer of 100 nm thickness on the mirror surface is observed by cross-sectional Transmission electron microscopy (TEM). Hg is detected in the Sn layer by EDX analysis. This means that the surface Sn layer of the mirror was fabricated using an Hg-amalgam technique. By AES measurement, an Sn-Cu alloy at the interface between the Sn layer and the Cu base metal is detected. The Sn surface has been oxidized. The oxide layer consists of SnO₂, SnO•SnO₂, SnO and Sn in order of increasing distance from the surface.

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  Test methods were studied for determining whether permeable pores exist in high Cr-Fe alloy plasma spray coatings applied to the inner surface NAS battery Al containers. Al containers were first filled with a NaOH solution. If permeable pores were to exist in the sprayed coating, the NaOH solution would reach the container wall through these pores, react with the Al, and generate H₂ gas. When the Al in a container came into contact with the 0.25-6 mol•L^-1 NaOH solution, the Al dissolved and H₂ gas bubbles were immediately generated. However, the 75 mass%Cr-Fe alloy plasma spray coating itself does not react with the NaOH solution and does not generate H₂ gas. When Al containers with 75 mass%Cr-Fe alloy plasma spray coating of different porosities were tested, results showed that the higher the porosity of the coating, the greater the amount of H₂ gas produced. Thus the presence of permeable pores could be easily detected. When Al containers have 75 mass%Cr-Fe alloy plasma spray coating applied under optimal spray conditions for mass production, the sprayed coatings were relatively dense. Therefore, when the NaOH solution was put into the container, H₂ gas was not immediately found. H₂ gas began to generate four minutes after the NaOH solution was added. It was confirmed that the amount of H₂ gas generated is proportionate to the existence of permeable pores in the sprayed coating and the size of the pores.

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  Changes in microstructures of α₂/γ lamellar boundaries was studied on fully lamellar Ti-38Al-xM (at%, x=0, 3, M=Zr, Nb) alloys over a wide range of average lamellar thickness from 290 to 20 nm. The lamellar structure was formed by isothermal aging and lamellar thickness was controlled by changing aging temperature. The addition of Nb or Zr alters the lattice mismatch between α₂ and γ phases. At lamellar boundaries the mismatch is accommodated by elastic deformation and/or by introducing misfit dislocations. The elastic deformation totally accommodates the lattice mismatch (coherent boundary) when γ lamellae are thin enough. Misfit dislocations are introduced to accommodate partly the mismatch when γ lamellar thickness exceeds a critical value λ_c. Density of the misfit dislocations saturates to an upper limit d_s in thick lamellar structures. The critical value of λ_c decreases and the saturation level d_s increases with increasing lattice mismatch. Zr increases and Nb decreases the lattice mismatch.

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  The catalytic activities of propylene oxidation on different aluminum silicates with the mayenite structure [Ca₁₂Al_14-xSi_xO_33+0.5x (x=0, 4)] formed at 500, 800 and 1000°C were investigated. The aluminum silicates were prepared by the hydrothermal and solid-state reaction of the stoichiometric mixture of calcium oxide, alumina sol and silica. The XRD results of the aluminum silicates obtained by the solid-state reaction showed that the peak intensities of the mayenite phases became larger as the calcination temperature increased. The aluminum silicates included two kinds of active oxygen species (O₂^2-, O₂^-) related to Raman sifts around 887 and 1092 cm^-1, respectively. As a result, the aluminum silicates exhibited the oxidation activities based on the easily reducible active oxygen species. Notably, the Ca₁₂Al₁₀Si₄O₃₅ calcined at 1000°C without the hydrothermal treatment showed the highest activity of all catalysts, indicating that the crystal structures play an important role in determining the catalytic activity.

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  A high magnetic field is a useful tool to control crystal alignment of non-magnetic materials such as metals, ceramics and polymers. However, uni-axial alignment of hexagonal crystals with a magnetic susceptibility of χ_c<χ_a, cannot be achieved under a static magnetic field, because the c-axis can be in arbitrary direction in the plane perpendicular to the direction of the magnetic field. For a uni-axial alignment of these materials, an application of the rotating magnetic field during a slip casting (process) has been proposed.
   In this study, both theoretical analysis and model experiment have been carried out for elucidation of crystal alignment phenomena under rotating magnetic field and for quantitative clarification of optimum operating parameters such as magnetic field strength and viscosity of the medium surrounding the crystals. It has been found that the alignment time was shortened by decreasing the magnetic field strength and/or increasing the viscosity of the surrounding medium. This relation is opposite in the case of crystal alignment under the static magnetic field. The result of the model experiment well agrees with that obtained by the theoretical analysis.

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  The purpose of this study is to compare the biocompatibility of commercial purity Ti, Ti-6Al-4V and Ti-6Al-7Nb alloy specimens with and without surface treatment in mouse abdominal connective tissue in vivo. Each metal was implanted into specific abdominal subdermal tissue site of female mouse. After 4 weeks, the implants were removed and abdominal tissues were fixed, dehydrated and embedded in glycol methacrylate resin. And the tissues were histologically prepared for microscopical evaluation. It was characterized by the presence of connective tissue with fibrous capsule surrounding the implant. The fibrous tissue surrounding the implant was studied to determine the biocompatibility of implanted metals. The average thickness of the fibrous capsule formed around the implant was much thinner for the hydrogen peroxide added hydrochloric acid solution-treated specimen than for the others. The results of this evaluation indicate that modification of the surface properties of titanium and titanium alloy implants changes the biological properties in the abdominal connective tissue. In conclusion, these observations suggest that the proper surface treatment performed in the study is effective for the improvement of biocompatibility.

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  Structure and tensile properties of a high-purity Al-Si hypo-eutectic alloy, which was H-Alloy of 99.98 mass% purity, have been investigated comparing with a conventional one which was L-Alloy of 99.89 mass% purity. Although the base structure in both of the alloys was composed of proeutectic α-phase and eutectic structure, the eutectic structure of H-Alloy was finer than that of L-Alloy. Coarse crystals of plate-like silicon were observed in L-Alloy, while was not observed in H-Alloy. Based on the results of Brinell Hardness Test on the solidification structure, it was found that there was little difference of the hardness between the both alloys. Tensile tests were also performed in an atmosphere at room temperature. The elongation of H-Alloy was twice as large as that of L-Alloy, though the tensile strength of L-Alloy and H-Alloy were almost the same. Al-Fe-Si system compounds were observed at the interface between α-phase and eutectic silicon in L-Alloy.

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  Si₂N₂O was focused to high temperature materials by its high oxidation resistance and thermal shock, sintered by Si₃N₄ and SiO₂. However, it was unclear that the lipophilic of Si₃N₄ ceramics was influence by added SiO₂. In this study, Si₃N₄ ceramics were sintered with added SiO₂ or Fe₃O₄, and the mechanical and lipophilic properties of these ceramics were investigated. Si₂N₂O was formed by sintering Si₃N₄ with added SiO₂. The hardness, bending strength, fracture toughness, and wear volume of the sintering material decreased with Si₂N₂O formation. The lipophilic property was improved by adding the appropriate amount of SiO₂. The lipophilic property of the Si₃N₄/Si₂N₂O composite was higher than that of monolithic Si₂N₂O. The fracture toughness rises a little though hardness and bending strength decrease when Fe₃O₄ is added to Si₃N₄. The lipophilic property of the Si₃N₄ ceramic improved with added Fe₃O₄.

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  Experimental and theoretical studies on the initial leaching rate of a spherical pellet of ZnO introduced in H₂SO₄ and H₂SO₄-ZnSO₄ solution have been conducted to discuss the characteristics of liquid-phase mass transfer for ZnO-H₂SO₄ solution systems in an agitated vessel.
   The results obtained are as follows:
   1) For the ZnO-H₂SO₄ systems, the leaching rate is proportional to the 0.6th power of the stirring rate. The leaching rate increases with the concentration of H₂SO₄ and H⁺.
   2) For the ZnO-H₂SO₄-ZnSO₄ systems, the leaching rate increases with the concentration of ZnSO₄. At a high concentration of H⁺, the rate is independent of the concentration of H⁺.
   3) The leaching process for these systems is controlled by the liquid-phase mass transfer rate.
   4) For the ZnO-H₂SO₄ and ZnO-H₂SO₄-ZnSO₄ systems, the rates calculated by a mass-transfer model based on a film theory that takes into account diffusion and electrical migration are in good agreement with the experimental values at a low concentration of H⁺. However, the calculated values are not consistent with the experimental values at high concentration. This disagreement might be caused by the effect of chemical reaction at the ZnO surface.

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  The number of ancient iron mirrors excavated in China is far smaller than those of ancient bronze mirrors. Fortunately, we were honored to have a chance to analyze some of the rare ancient iron mirrors excavated in China. Un-corroded parts were subjected to a structural observation under an optical microscope and a chemical composition analysis with EPMA (Electron Probe Micro Analyzer). Based on the results, the production techniques of the ancient iron mirrors were discussed. The results were as follows. 1. The iron mirror produced during the later Han Period showed a mixture of ferrite and pearlite particles. The possibility that the iron mirror was made by forging small pieces of pig iron, which process accompanied decarburization, can be inferred. Traces of silicon and phosphorous were found as impurities in the uncorroded alloy. 2. The iron mirror excavated from the tomb of the Sui period showed the structure of single-phase ferrite. It is inferred to be made by forging wrought iron which had been decarburized enough. Traces of silicon, phosphorous and sulfur were found as impurities in the uncorroded alloy.

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