Formation of Exclusive Al2O3 Scale on Nb and Nb-Rich Alloys by Two-Step Oxygen–Aluminum Diffusion Process

External Al₂O₃ scale formation behavior by a diffusion aluminizing process on Nb and Nb–X (X?=?Mo, Re, and Ta) alloys with different oxygen solubilities was investigated. The oxygen content in Nb and Nb–X alloys was controlled by oxygen diffusion treatment at 1,100?°C using Nb/NbO mixture. Nb–aluminide, NbAl₃ and Nb₂Al, layers were developed on the low-oxygen Nb substrate by an aluminum diffusion treatment using Al/Al₂O₃/NH₄Cl mixture at 1,100?°C; whereas an adhesive Al₂O₃ scale developed on the Nb substrate with higher oxygen content. The alloy oxygen content decreased by an addition of Ta, Mo and Re, in this order, and the decrease in alloy oxygen content resulted in the transition of Al₂O₃ formation from external scale to internal precipitates. This transition was not observed when low Al activity powder mixture, Ni50Al/Al₂O₃/NH₄Cl, was used for Al diffusion process, and only external Al₂O₃ scale was developed on all samples. In the present study, the effects of oxygen solubility limit, oxygen content, and the activity of Al in diffusion process on the formation of Al₂O₃ scale will be discussed.     

Genotoxicity of nano/microparticles in in vitro micronuclei, in vivo comet and mutation assay systems

Background

Recently, manufactured nano/microparticles such as fullerenes (C₆₀), carbon black (CB) and ceramic fiber are being widely used because of their desirable properties in industrial, medical and cosmetic fields. However, there are few data on these particles in mammalian mutagenesis and carcinogenesis. To examine genotoxic effects by C₆₀, CB and kaolin, an in vitro micronuclei (MN) test was conducted with human lung cancer cell line, A549 cells. In addition, DNA damage and mutations were analyzed by in vivo assay systems using male C57BL/6J or gpt delta transgenic mice which were intratracheally instilled with single or multiple doses of 0.2 mg per animal of particles.

Results

In in vitro genotoxic analysis, increased MN frequencies were observed in A549 cells treated with C₆₀, CB and kaolin in a dose-dependent manner. These three nano/microparticles also induced DNA damage in the lungs of C57BL/6J mice measured by comet assay. Moreover, single or multiple instillations of C₆₀ and kaolin, increased either or both of gpt and Spi^- mutant frequencies in the lungs of gpt delta transgenic mice. Mutation spectra analysis showed transversions were predominant, and more than 60% of the base substitutions occurred at G:C base pairs in the gpt genes. The G:C to C:G transversion was commonly increased by these particle instillations.

Conclusion

Manufactured nano/microparticles, CB, C₆₀ and kaolin, were shown to be genotoxic in in vitro and in vivo assay systems.     

Rigid plastic constitutive theory for porous materials including void evolution and mixed hardening effects

A new rigid plastic constitutive model was constructed in the previous research for porous ductile materials based on modified Gurson’s yield function. However, in that model, attention was focused on the effect of isotropic hardening on plastic deformation and damage processes of porous materials. In this paper, that model is further extended to a more general model in which both the isotropic and the kinematic hardening mechanisms of porous materials are incorporated. The characteristics and self-consistency of the extended model are briefly discussed.     

Formation mechanism for hexagonal-structured self-assemblies of nanocrystalline titania templated by cetyltrimethylammonium bromide

Hexagonal-structured self-assemblies of nanocrystalline (anatase) titania templated by cetyltrimethylammonium bromide (C(16)H(33)N(CH(3))(3)Br; CTAB) (Hex-ncTiO(2)/CTAB Nanoskeleton) were formed after mixing of aqueous solutions containing CTAB spherical micelles and titanium oxysulfate acid hydrate (TiOSO(4).xH(2)SO(4).xH(2)O) as a titania precursor in the absence of any other additives. Formation mechanism of the Hex-ncTiO(2)/CTAB Nanoskeleton was examined in terms of the reaction temperature, titania precursor/CTAB mixing ratio, surfactant type, electrostatic interaction, micelle formation and molecular component. We found that crystal growth of crystalline (anatase) titania (polymorphic crystallization) was promoted with higher temperature and lower titania precursor content in aqueous solutions. In addition, we revealed that the crystalline (anatase) titania was formed in polycation, poly(allylamine hydrochloride ([CH(2)CH(CH(2)NH(2))HCl](n); PAH), and formamide (HCONH(2)) solutions. On the other hand, no titania formation was observed in anionic systems such as sodium dodecyl sulfate (CH(3)(CH(2))(11)OSO(3)Na; SDS) and poly(sodium 4-styrenesulfonate ([C(8)H(7)SO(3)Na](n); PSSS). This indicates that hydrolysis reaction of the titania precursor is initiated by not only cations but also nitrogen atoms in molecules and polymers. Hexagonally structure was formed in only cationic surfactant micellar solutions but not in polycation solutions and formamide.     

Hydrodechlorination of para-substituted chlorobenzenes over a ruthenium/carbon catalyst

The hydrodechlorination (HDC) of chlorobenzene (abbreviated as CLB) and seven types of para-substituted chlorobenzenes (para-amino, -methoxy, -methyl, -chloro, -trifluoromethyl, -acetyl and -cyano: abbreviated as CLAN, CLAS, CLTN, DCLB, CLTF, CLAP and CLBN, respectively) were performed over 5%-ruthenium/carbon (Ru/C) under a hydrogen pressure of 0.5–1.5 MPa at 523 K.In the HDC of these model compounds, except for CLAP and CLBN, reductive cleavage between the carbon and chlorine atoms took place and dechlorinated compounds were produced preferentially. In the reaction of CLAP and CLBN, on the other hand, hydrogenation and/or hydrogenolysis of the substituent coincided with the HDC and a wide variety of products was observed accompanying the HDC product.For the chlorobenzenes of the simple HDC, the HDC reaction rate constants decreased in the orders of CLAN  CLB ≈ CLTN ≈ CLAS and CLB > DCLB  CLTF, respectively.In the reaction of the chlorobenzenes of the electron-donating substituent, the reaction constant (ln k/k₀) has no relevance to the Hammett substituent constant (). In the case of the chlorobenzenes possessing the electron-withdrawing substituent, on the other hand, it was indicated that the electron-withdrawing substituent suppressed the HDC reactivity of chlorobenzenes, although no proportional relationship was observed between the reaction rate constant and the Hammett substituent constant.To explore the factors affecting the HDC reactivity, quantum calculation according to the DFT method (B3LYP/LANL2DZ) was applied to the “chlorobenzenes-Ru₁₀” complex. As a result of the calculation, chlorobenzenes were adsorbed through a chlorine atom on the edge atom of the Ru₁₀ cluster. The magnitude of the adsorption energy, moreover, decreased in the order of CLAN > CLAS ≈ CLB ≈ CLTN and CLB > DCLB > CLTF, respectively. These orders of adsorption energy are similar to that of the HDC reaction rate constant. It was concluded that adsorption energy is a useful parameter for the reactivity index of the HDC.     

Effect of Polymer Dispersant Structure on Electrosteric Interaction and Dense Alumina Suspension Behavior

The present paper reports on research on the effect of molecular structure of polymer dispersants on the relationship between the electrosteric interaction of dispersants on solid surfaces and the viscosity of suspensions. Ammonium polyacrylate with different hydrophilic to hydrophobic ratios ( m:n ) was prepared and added to dense Al₂O₃ suspensions (40 vol%). The steric interactions and adsorbed structures of dispersants on Al₂O₃ powders were examined under an atomic force microscope (AFM). An optimum hydrophilic to hydrophobic group ratio, which was obtained from the maximum repulsive force and the minimum viscosity of suspension, was determined at m :n = 3:7. The changing mechanism of the adsorbed structure and the steric interaction of dispersants and the suspension viscosity by the hydrophilic to hydrophobic molecular ratio were discussed by comparing the experimental force curve and DLVO theory.     

Evaluation of hydrogen absorption properties of Ti–0.2 mass% Pd alloy in fluoride solutions

The hydrogen absorption properties of Ti–0.2 mass% Pd (Ti–0.2Pd) alloy in 2.0% and 0.2% acidulated phosphate fluoride (APF) and neutral 2.0% NaF solutions (25 °C) has been evaluated by hydrogen thermal desorption analysis. During the early stage of immersion (120 h) in the 2.0% APF solution, the amount of absorbed hydrogen was lower than 500 mass ppm. A thermal desorption of hydrogen primary appearing with a peak at 500–600 °C and a broad desorption ranging from 100 to 400 °C were observed. In the 0.2% APF solution, the amount of absorbed hydrogen saturated at 100–200 mass ppm; the thermal desorption of hydrogen appeared with a single peak at 550 °C. In the 2.0% NaF solution, hydrogen absorption was negligible even after 1000 h of immersion, although corrosion pits were observed. The results of the present study suggest that the hydrogen absorption of Ti–0.2Pd alloy, as compared with commercial pure titanium, is suppressed in fluoride solutions.     

Precision die-casting of optical MU/SC conversion sleeve

The performance of MU/SC conversion sleeve produced by bulk metallic glass (Zr₅₅Al₁₀Ni₅Cu₃₀) was examined. A precision die-casting method was applied to improve size accuracy. The size accuracy of the conversion sleeve produced by the precision die-casting method was ±1 μm, and optical insertion loss (Li) was less than 0.3 dB for a standard value. The wear resistance of metallic glass is improved by surface oxidation treatment in air at 673 K. The MU/SC conversion sleeve produced from bulk metallic glass has superior characteristics for optical parts.     

Effect of heating process on the formation of nanoparticles of elastin model polypeptide, (GVGVP)251, by gamma-ray crosslinking

Nanoparticles were prepared by the thermosensitive aggregation of the elastin model polypeptide, (GVGVP)₂₅₁, and gamma-ray crosslinking. Three different heating processes, “slow heating,” “fast heating,” and “heat shock,” were used for the aggregation of the peptide, followed by gamma-ray crosslinking. Only the “heat shock” process successfully yielded stable nanoparticles with diameters of less than ca. 150 nm and a narrow size distribution. Circular dichroism (CD) spectrometry showed that this polypeptide formed a type-II β-turn structure when the temperature was increased to above the cloudy point in the case of the “heat shock” process; suggesting that this structure might contribute to stable nanoparticle formation by gamma-rays. CD spectrometry also suggested that this structure would be affected during the formation of stable crosslinked particles.     

Preparation of 1 1 1-textured BaTiO3 ceramics by templated grain growth method using novel template particles

Dense BaTiO₃ ceramics with 1 1 1-texture were prepared by the TGG process. Platelike BaTiO₃ particles with their 1 1 1 direction perpendicular to the plate face were prepared by the reaction of platelike Ba₆Ti₁₇O₄₀ particles with BaCO₃ particles in molten NaCl. A green compact was composed of the aligned, platelike BaTiO₃ template particles dispersed in the matrix of small, equiaxed BaTiO₃ particles. Sintering caused densification and also the growth of template particles at the expense of matrix particles, resulting in texture development. Densification prior to grain growth was found to be necessary to obtain highly textured ceramics, and the effect of pre-sintering conditions on texture development was examined.