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ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678

MATERIALS TRANSACTIONS Vol. 46 (2005), No. 1

  • Composite Materials based on Light Elements for Hydrogen Storage

    Takayuki Ichikawa, Nobuko Hanada, Shigehito Isobe, Haiyan Leng, Hironobu Fujii

    pp. 1-14

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    DOI:10.2320/matertrans.46.1

    Abstract

    In this paper, we review our recent experimental results on hydrogen storage properties of light elements Li, C and Mg based nano-composite materials. The results are summarized as follows: In the Li-N-H system, such as the ball milled 1:1 mixture of Li amide and Li hydride containing a small amount of TiCl3 (1 mol%), a large amount of hydrogen (∼6 mass%) is absorbed and desorbed in the temperature range from 150 to 250°C with good reversibility and high reaction rate. Furthermore, in the ball milled mixture of 3Mg(NH2)2 and 8LiH, ∼7 mass% of hydrogen is reversibly stored in the temperature from 140 to 220°C, indicating one of the suitable hydrogen storage materials. In graphite containing a small amount of nanometer sized Fe (∼2 at.%), a large amount of hydrogen (∼7 mass%) is chemisorbed by ball milling for 80 h under less than 1 MPa of H2-gas pressure. However, the chemisorbed hydrogen capacity decreases with increase in the milling pressure for the 80 h ball milled graphite (down to ∼4.1 mass% at 6 MPa), while the physisorbed hydrogen capacity in graphite increases with increase in the milling pressure, reaching up to 0.5∼1.0 mass% at 6 MPa. Unfortunately, the desorption temperature of chemisorbed hydrogen is higher than 300°C. Therefore, some break-through is necessary for the development of carbon-based materials as one of the hydrogen storage systems. On the other hand, some nano-composite Mg catalyzed by Ni nano-particle or Nb oxide reveals superior reversible hydrogen storage properties: ∼6.5 mass% of hydrogen is reversibly stored in the temperature range from 150 to 250°C. Especially, the Nb metals uniformly dispersed in nanometer scale on the surface of MgH2, which was produced by reduction of Nb2O5, is the best catalyst we have studied so far. Thus, it seems that some Mg nano-composites catalyzed by nano-particles of d-electron transition metals is acceptable for practical applications.

  • Dependence of Dendritic Side-branches on Parameters in Phase-Field Simulations

    Zhu Changsheng, Liu Baicheng, Jing Tao, Feng Wenfang

    pp. 15-19

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    DOI:10.2320/matertrans.46.15

    Abstract

    The influence of phase-field parameters on dendritic side-branches is studied by using a phase-field model coupled with thermal noise. The result of calculation indicates that, the thermal diffusion layer collected around the dendrite tends to become thinner with the undercooling increasing, which is favorable to the growth of the side-branches and the dendrite takes on the morphology of developed side-branches; The less coupling coefficient λ is, the quicker the dendrite tip velocity converges on the Green function calculation, the more developed the side-branches are; The anisotropy coefficient ε influences the steady state of the dendrite tip, the largeris, the greater the dendrite tip velocity is, the more developed the side-branches are and the smaller the DAS is; The magnitude of thermal noise Fu has an obvious effect upon temperature field, when appropriate value is assigned to Fu, the noise can promote the emergence of side-branches, but it does not influence the tip operating state.

  • Liquidus Surfaces and Isothermal Section at 1073 K in the CaO-Fe2O3-(0–50 mol%)B2O3 Pseudo-Ternary System

    Hiroshi Sato

    pp. 20-25

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    DOI:10.2320/matertrans.46.20

    Abstract

    The liquidus surfaces and the isothermal section at 1073 K of the pseudo-ternary CaO-Fe2O3-B2O3 system were determined in a composition range of less than 50 mol% B2O3 using the thermal analysis and X-ray diffraction. The liquidus surface which is in equilibrium with Fe3O4 spreads over a wide composition range and that in equilibrium with Fe2O3 extends long and narrow toward CaO·B2O3 and then toward B2O3 apex. Temperature of the liquidus surface in equilibrium with Fe3O4 remains above 1473 K in the composition range of less than 20 mol% B2O3 but decreases when the B2O3 content exceeds 40 mol%. The liquidus surface in equilibrium with 2CaO·Fe2O3 extends widely and its slope is steep in the region of less than 10 mol% B2O3 but gentle when the B2O3 content exceeds 15 mol%. Pseudo-ternary CaO-Fe2O3-B2O3 compounds were not found in the composition range investigated.

  • Effect of Phosphorus on Sulfide Precipitation in Strip Casting Low Carbon Steel

    Zhongzhu Liu, Yoshinao Kobayashi, Kotobu Nagai

    pp. 26-33

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    DOI:10.2320/matertrans.46.26

    Abstract

    The effect of phosphorus addition on sulfide precipitation for strip casting low carbon steel containing copper was investigated and discussed with respect to the morphology, size, and composition of sulfide. Both experimental results and mathematical calculation showed that the addition of phosphorus retards the sulfide precipitation at high temperature, promotes the supersaturation of sulfur, and produces more copper bearings and smaller sulfides at low temperature. Phosphorus also promotes sulfide precipitation in α-Fe instead of in γ-Fe, so that small spherical copper sulfides form at a high cooling rate instead of plate-like shaped copper sulfides.

  • In-situ Observations of Fracture Processes in 0.6 μm and 9.5 μm SiCP/6061Al Composites

    Lihe Qian, Hiroyuki Toda, Shigeki Morita, Toshiro Kobayashi, Zhong-guang Wang

    pp. 34-41

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    DOI:10.2320/matertrans.46.34

    Abstract

    In-situ SEM observations of fracture processes in two 6061Al alloy composites reinforced with coarse and fine SiC particles, respectively, were carried out to clarify their fracture mechanisms. It was found that in the coarse particle reinforced composite, voids were formed in the matrix around SiC particles ahead of the main crack tip, then coalesced with each other, and finally connected with the main crack tip, causing propagation of the main crack. However, in the fine particle reinforced composite, multiple micro-cracks were formed at the boundaries between SiC particle clusters and surrounding matrix or within the clusters, then connected with each other, and finally joined with the main crack tip, leading to crack branching and growth of the main crack. Crack branching, multiple cracking and crack deflection were proposed to contribute to the enhanced fracture toughness in the fine particle reinforced composite compared with the coarse particle reinforced composite.

  • Microstructure and Mechanical Properties of Sn-8.55Zn-1Ag-XAl Solder Alloys

    Shou-Chang Cheng, Kwang-Lung Lin

    pp. 42-47

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    DOI:10.2320/matertrans.46.42

    Abstract

    The microstructure and mechanical properties of as cast lead-free solders including eutectic Sn-9Zn, Sn-8.55Zn-1Ag and Sn-8.55Zn-1Ag-XAl (X=0.01∼0.45 mass%) alloys were investigated. Microstructures of the Sn-Zn-Ag-XAl alloys consist of AgZn3 compound, Zn-rich phase, Al-rich segregation and hypoeutectic phase. The addition of Al dramatically improves the 0.2% offset yield stress, Vickers hardness, ultimate tensile stress (UTS) and total tensile strain of the Sn-8.55Zn-1Ag-XAl alloys. The increase in the Al content of the Sn-8.55Zn-1Ag-XAl alloy from 0.01 to 0.45 mass% increases the average yield stress from 49.9 to 54.0 MPa (∼47.6 MPa for eutectic Sn-9Zn) and the Vickers hardness from 17.0 to 18.3 Hv (∼16.8 Hv for eutectic Sn-9Zn). The average values of UTS of the Sn-8.55Zn-1Ag-XAl alloys with X=0.01, 0.1, 0.25 and 0.45 mass% Al are 55, 58, 55 and 60 MPa, respectively, while those of the tensile strain are 47%, 52%, 58% and 45%, respectively (52 MPa and 50% for the eutectic Sn-9Zn alloy). Fracture mechanisms of the Sn-8.55Zn-1Ag-XAl alloys are correlated with the Zn-rich phase and Al segregation.

  • Tungsten-Based Metallic Glasses with High Crystallization Temperature, High Modulus and High Hardness

    Madoka Ohtsuki, Kyoko Nagata, Ryuji Tamura, Shin Takeuchi

    pp. 48-53

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    DOI:10.2320/matertrans.46.48

    Abstract

    Ternary and quaternary tungsten-based alloys were melt-spun to produce metallic glasses having high crystallization temperature and high hardness. Alloy compositions were selected based on eutectic compositions of tungsten-based binary alloys; they are W46Ru37B17, W54Rh26B20, W56Ir23B21, etc. In most of the alloys, ductile metallic glasses were produced. DSC measurements showed that most of the metallic glasses undergo a two-step crystallization with the onset temperature of the first crystallization being as high as 1049∼1298 K. Vickers hardness values at room temperature are 13∼17 GPa. The ratio of the hardness Hv to Young’s modulus E satisfies the general rule for metallic glasses, i.e. HV⁄E\\fallingdotseq0.06. High temperature hardness measurements for W46Ru37B17 and W45Re23Ru15B17 metallic glasses showed that the Vickers hardness values are higher than 10 GPa up to 900 K.

  • μ Phase in a Nickel Base Directionally Solidified Alloy

    K. Zhao, Y. H. Ma, L. H. Lou, Z. Q. Hu

    pp. 54-58

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    DOI:10.2320/matertrans.46.54

    Abstract

    Scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD) were employed to study the μ phase in a directionally solidified experimental nickel base alloy. It was observed that the μ phase distribute at interdendritic area and precipitate mainly from the γ′ phase in this experimental alloy. Orientation relationship between the γ′ and the μ phase was found as (111)γ′||(0001)μ and ⟨\\bar110⟩γ′||⟨11\\bar20⟩μ. Detrimental effect of the μ phase on oxidation resistance of the alloys was also found.

  • Chemical Equilibria in a Mixed Solution of Nickel and Cobalt Chloride

    Man-Seung Lee, Young-Joo Oh

    pp. 59-63

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    DOI:10.2320/matertrans.46.59

    Abstract

    Ionic equilibria in the mixed solution of nickel and cobalt chloride were analyzed by considering the complex formation reactions, the mass and charge balance equations. The activity coefficients of solutes and water activity were calculated by using Bromley equation. Cobalt ion has a strong tendency to form various complexes with chloride ion, such as CoCl3− and CoCl42−, while NiCl+ was the only complex formed between nickel and chloride ion. Distribution of nickel and cobalt species with the compositions and pH values of the solution was obtained from the analysis of ionic equilibria in the mixed chloride solutions. The predicted pH values for NiCl2-CoCl2-HCl-NaOH-H2O system agreed well with those measured at 298 K up to ionic strength of 9.53 mol/kg.

  • Solvent Extraction of Sm from Chloride Solution with PC88A and Saponified PC88A

    Man-Seung Lee, Gwang-Seop Lee, Jin-Young Lee, Sung-Don Kim, Joon-Soo Kim

    pp. 64-68

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    DOI:10.2320/matertrans.46.64

    Abstract

    In this study, solvent extraction experiments of Sm from a chloride solution with PC88A and with partially saponified PC88A were performed. The extraction reaction of Sm with PC88A was identified from the experimental data using a graphical method. A chemical model was then developed to predict the distribution coefficients of Sm for its extraction with the saponified PC88A. In the experimental ranges conducted in this study, the equilibrium constants for the solvent extraction of Sm with PC88A and with the saponified PC88A were estimated through an analysis of the ionic equilibria.

  • Hydrogen Dissolution into 10% Chromium Ferritic Steels during High-Temperature Steam Oxidation

    Masaaki Nakai, Kensuke Nagai, Yoshinori Murata, Masahiko Morinaga, Shigeaki Matsuda, Motohiro Kanno

    pp. 69-73

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    DOI:10.2320/matertrans.46.69

    Abstract

    The amount of hydrogen dissolved into Fe-10Cr-0.08C-0∼0.03S (mass%) steels during the steam oxidation at 923 K was measured by thermal desorption spectroscopy (TDS). The amount of dissolved hydrogen was found to be dependent largely on the steam oxidation resistance of the steels. In other words, it was much smaller in the sulfur-doped steels with good oxidation resistance than in the sulfur-free steels with poor oxidation resistance. Thus, we suggest that the hydrogen dissolution is one of the most important factors to understand the steam oxidation resistance of the steels.

  • Phase Relations and Distribution of Some Minor Elements in Cu-Fe-Sb System Saturated with Carbon at 1473 K

    Leandro Voisin, Hector M. Henao, Kimio Itagaki

    pp. 74-79

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    DOI:10.2320/matertrans.46.74

    Abstract

    As a fundamental study to develop a new process for eliminating detrimental elements and for recovering valuable ones from secondary Cu-Fe base alloys with a considerably high content of antimony, both the phase relations in a miscibility gap of the Cu-Fe-Sb system saturated with carbon and the distribution of some minor elements such as silver, platinum, cobalt, nickel and sulfur between two phases in the miscibility gap were investigated at 1473 K by a quenching method. The phase separation into copper-rich and iron-rich phases occurred when the Cu-Fe-Sb system was saturated with carbon. The antimony content in the copper-rich phase was very large compared with that in the iron-rich phase, and carbon was mostly distributed in the iron-rich phase. Cobalt and nickel were distributed preferentially in the iron-rich phase and platinum and sulfur were distributed almost evenly in both phases, while silver mostly in the copper-rich phase. The experimental results for the phase separation and the distribution of the minor elements were discussed on the basis of activity coefficients in the copper-rich and iron-rich phases and were compared with the results for the Cu-Fe-As system saturated with carbon. By utilizing this phase separation, recovery of valuable silver and copper into the copper-rich phase and elimination of less valuable iron into the iron-rich phase are feasible for treating the secondary Cu-Fe-Sb base alloys.

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  • Corrosion Resistance of Fe-16%Cr-30%Mo-(C,B,P) Amorphous Coatings Sprayed by HVOF and APS Processes

    Fumitaka Otsubo, Katsuhiko Kishitake

    pp. 80-83

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    DOI:10.2320/matertrans.46.80

    Abstract

    Two kinds of Fe-16%Cr-30%Mo-(C,B,P) alloy powders having high ability to form an amorphous phase were thermal sprayed onto mild steel substrate using HVOF and APS processes. Perfectly amorphous coating was formed not only by the HVOF process but also by the APS process. The passive current densities of the amorphous coatings sprayed by the HVOF and APS processes were close each other and significantly low compared with that of SUS316L coating in 1 mol·L−1 HCl solution. The coatings of perfectly amorphous phase were little corroded after immersion tests in 1 mol·L−1 HCl solution for one week, though the coatings composed of the mixture of amorphous and crystalline phases corroded markedly.

  • The Friction and Wear Properties of PTFE Composite-Thermal Spray Metallic Binary Coatings

    Meigin Shi, Fujimasa Miyazawa, Shogo Tobe, T. A. Stolarski

    pp. 84-87

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    DOI:10.2320/matertrans.46.84

    Abstract

    Cu-Al alloy and Mo coatings were deposited on a low carbon steel substrate using an atmospheric plasma spray machine. Pure PTFE and PTFE metal powder composites were deposited on the metallic coatings. Studied and compared are PTFE-metal coatings and PTFE composites- metal coatings filled with different metal powders with the proportion of 10% (mass). Mass loss and coefficient of friction were measured under dry reciprocating sliding tests. The worn surfaces of samples were observed by microscopy. The influence of additives on the wear resistance was assessed.

  • Multi-Layered Potts Model Simulation of Morphological Changes of the Neck during Sintering in Cu-Ni System

    Takeshi Yamashita, Tomoki Uehara, Ryuzo Watanabe

    pp. 88-93

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    DOI:10.2320/matertrans.46.88

    Abstract

    A mathematical model is developed in this study to simulate the morphological change of the sintering neck by neck growth and the Kirkendall void formation in the Cu-Ni interdiffusion system. The fluxes of materials and vacancy are analyzed for estimating excessive-deficient vacancy regions. The Multi-Layered Potts Model (MLP Model) is used as the mathematical model. The MLP Model is an improved model of the traditional Potts Model which can treat multiple materials transportation mechanisms such as interdiffusion system. The Potts Model uses a two dimensional (2-d) array to describe a 2-d microstructure, on the contrary, the MLP Model uses a three dimensional (3-d) array which stacks several 2-d arrays. The MLP Model of present study could treat an interdiffusion and an intrinsic diffusion coefficient as a function of the local alloy component. The morphological change and analyzed materials and vacancy fluxes of the simulation results are compared with the experimental results, then good agreements is observed.

  • Effect of Low-Frequency Electromagnetic Vibration on Cast-ability, Microstructure and Segregation of Large-Scale DC Ingots of a High-Alloyed Al

    Dong Jie, Cui Jianzhong, Zeng Xiaoqing, Ding Wenjiang

    pp. 94-99

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    DOI:10.2320/matertrans.46.94

    Abstract

    Low-Frequency Electromagnetic Vibrating Casting (LFEVC) was developed to cast large-scale highly alloyed Al-Zn-Mg-Cu-Zr ingots for super-high strength and toughness. Compared with conventional Direct Chilling Casting (DC), LFEVC can significantly improve surface quality, decrease hot-tearing tendency, generate finer, more uniform and equiaxed microstructures, and greatly suppress macro segregation and grain boundary segregation with increasing alternate and direct current ampere turns. In the range of alternate and direct current ampere turns employed in the experiments, the optimum condition is that the alternate current ampere turns is 9,000 At and the direct current ampere turns is 14,300 At.

  • Structural, Electrical and Optical Characterization of SrIrO3 Thin Films Prepared by Laser-Ablation

    Yuxue Liu, Hiroshi Masumoto, Takashi Goto

    pp. 100-104

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    DOI:10.2320/matertrans.46.100

    Abstract

    SrIrO3 thin films were prepared by laser ablating a monoclinic SrIrO3 target at the substrate temperature of 973 K with oxygen pressure ranging from 4 to 67 Pa. The glancing angle incidence X-ray diffraction (GIXRD) and micro-X-ray photoelectron spectroscopy (XPS) results suggested that SrIrO3 thin films were obtained. The resistivities and transmittance of SrIrO3 thin films at room temperature were in the range from 0.93 to 4.8×10−5 Ωm and from 0.20 to 0.30 in the wavelength range of 600–800 nm, respectively. The electrical property of SrIrO3 thin films changed from semiconductive to metallic with increasing the ablation oxygen pressure.

  • Effect of Cryomilling on Particle Size and Microstrain in a WC-Co Alloy

    Seung-Hwan Back, Gwan-Hyoung Lee, Shinhoo Kang

    pp. 105-110

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    DOI:10.2320/matertrans.46.105

    Abstract

    The effects of temperature and milling time on the crystalline size and microstrain in WC and WC-Co powders were investigated in a cryomilling process. Within the limit of the analytical methods and TEM, the crystalline size of WC was estimated to be in the range of 50∼70 nm after 10 h of cryomilling. The presence of Co in the WC-Co system significantly reduced the level of strain in the WC particles in this low-temperature processing. A thermal cycle employed in cryomilling process was also found to be useful in various aspects. Various fitting methods were compared and the results are discussed in relation to processing parameters.

  • Assessment of Thermo-Mechanical Fatigue Behaviors of Cast Al-Si Alloys by Experiments and Multi-Step Numerical Simulation

    Hiroyuki Toda, Jun Katano, Toshiro Kobayashi, Toshikazu Akahori, Mitsuo Niinomi

    pp. 111-117

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    DOI:10.2320/matertrans.46.111

    Abstract

    Out-of-phase type thermo-mechanical fatigue tests have been performed for Al-Si cast alloys with the temperature range of 323–523 K and the applied mechanical strain range of 0.5–1.5%. Thermo-mechanical fatigue lives and stress-strain hysteresis loops are investigated by the experiments. In general, the thermo-mechanical fatigue is affected by various factors such as thermal expansion/contraction, elasto-plastic/creep deformation, softening by overaging, dynamic recovery, damaging and cracking. Multi-step finite element simulation techniques have provided an effective way of assessing the local damaging behavior of silicon particles, along with extracting the contribution from creep. Although the size and shape of the silicon particles in the material with a higher solidification rate are similar to those of a slowly cooled material, it exhibits superior thermo-mechanical fatigue property together with a smaller secondary dendrite arm spacing (SDAS, hereinafter). Since the difference in the stress-strain hysteresis loops between the two materials has vanished when the softening by overaging is almost finished, the observed difference in the thermo-mechanical properties is attributed to age-hardenability rather than the SDAS. The effects of damaging at the silicon particles to this difference are also suggested. In fact, damaged silicon particles have been observed extensively from an early stage of the thermo-mechanical loading, then forming fatigue cracks by the linkage of the damages. It has been clarified by the simulation that interfacial debonding is likely to occur rather than particle cracking in the materials used. The simulation provides valuable insights into the understanding of the spatial distribution of damage in the eutectic region. The simulation has also enabled to assess the contribution of the creep deformation, indicating that medium to high cycle fatigues are significantly affected by it.

  • Damping Properties of Ductile Cu-Al-Mn-Based Shape Memory Alloys

    Naoki Koeda, Toshihiro Omori, Yuji Sutou, Hidekazu Suzuki, Masami Wakita, Ryosuke Kainuma, Kiyohito Ishida

    pp. 118-122

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    DOI:10.2320/matertrans.46.118

    Abstract

    The damping property tanφ of Cu-Al-Mn-based alloys, where tanφ is nearly equal to internal friction Q−1, was investigated using a Dynamic Mechanical Spectrometer (DMS). It was found that the dependences of frequency and strain amplitude on tanφ are significantly different between the parent + martensite two-phase and the martensite single-phase states, i.e., tanφ is mainly influenced by frequency in the two-phase state and by strain amplitude in the martensite state. It was also found that the relative grain size d⁄D is a function of the damping capacity, where d and D are the grain diameter and the diameter of the wire, respectively, and that tanφ increases with increasing d⁄D. The maximum values of tanφ=0.54 and tanφ=0.07 were obtained in the two-phase state and in the martensite state, respectively, in the specimen of d⁄D≈1.

  • Microstructure of Explosively Compacted Nd-Fe-B Magnets

    Qi Ao, Wei Liu, Jiansheng Wu

    pp. 123-125

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    DOI:10.2320/matertrans.46.123

    Abstract

    The microstructure of explosively compacted Nd-Fe-B alloys has been investigated by means of transmission electron microscopy and X-ray diffraction. It is shown that there are three kinds of phases, i.e. the matrix phase Nd2Fe14B, O-rich phases and Nd-rich phases in explosively compacted Nd-Fe-B magnets. The matrix Nd2Fe14B phase is tetragonal, with lattice parameters of a=0.88 nm and c=1.22 nm. The O-rich phase was present at the two-grain boundary and three-grain junctions, with the fcc structure, and the lattice parameter is a=0.559 nm. The O-rich phase belongs to the compound Nd-Fe-O, and the contents of O, Nd and Fe are 45–60 at%, 20–40 at% and 10–21 at%, respectively. It is also shown that a large number of block-shaped Nd-rich phases are in a two-grain boundary or three-grain junctions or Nd2Fe14B phase, with the hcp structure and the lattice parameters of a=0.395 nm and c=0.628 nm. The Nd-rich phases belong to compound Nd-O, and the contents of Nd and O are 80–85 at% and 10–15 at%, respectively. Also a few dislocations in the boundary phase have been observed.

  • High Responsiveness Induced by Palladium Deposition on Thin Film Actuator of LaNi5 Hydrogen Storage Alloy

    Yoshitake Nishi, Haru-Hisa Uchida, Takamitsu Honjo

    pp. 126-129

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    DOI:10.2320/matertrans.46.126

    Abstract

    The unimorph actuator of the LaNi5 thin film deposited on polyimide substrates can be expected as a sensor and/or a controller of hydrogen gas flux in various hydrogen-related devices, since controlling the hydrogen concentration in the film by pressure change drives this actuator reversibility. In this study, the effect of the palladium deposition was investigated on the mechanical response of this thin film actuator. It was shown that the initiating time (incubation period) for the actuation to be measured after hydrogen gas exposure was reduced from 100 to 1 s by the palladium deposition. This significantly improvement of the mechanical response was attributed to the change in the rate determining steps: the dissociation of hydrogen gas molecules on the sample surface for the sample without palladium deposition, and hydrogen diffusion in the LaNi5 film for the palladium deposited sample. It was also suggested that the high permeability of hydrogen in palladium film at room temperature resulted in the high responsiveness.

  • Effect of Internal Structure on Thermal Properties of Alumina/Aluminum Composites Fabricated by Gelate-Freezing and Partial-Sintering Process, Respectively

    Masayuki Nakata, Katsuaki Suganuma

    pp. 130-135

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    DOI:10.2320/matertrans.46.130

    Abstract

    The purpose of the present work was to clarify the effects of parameters of porous ceramics on the characteristics of composites fabricated by high-pressure infiltration. Alumina with different porosity (15–70 vol%) and pore morphology was successfully fabricated by gelate-freezing and the partial-sintering, respectively. Alumina/aluminum composites were made by squeeze casting, the aluminum into the alumina sintered bodies. By evaluating the coefficient of thermal expansion (CTE) and thermal conductivity of the composites, it became obvious that variation in the structure and fraction of porous alumina sintered bodies influenced CTE, but not thermal conductivity.

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  • Difference between Cr and Ni K-edge XANES Spectra of Rust Layers Formed on Fe-Based Binary Alloys Exposed to Cl-Rich Environment

    Hiroyuki Konishi, Masato Yamashita, Hitoshi Uchida, Jun’ichiro Mizuki

    pp. 136-139

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    DOI:10.2320/matertrans.46.136

    Abstract

    The rust layer formed on weathering steel possesses a strong protective ability against corrosives in an atmosphere. This ability is related to the structure of the rust layer. The difference in the protective ability of a rust layer in a Cl-rich environment between conventional weathering steel containing Cr and advanced weathering steel containing Ni is believed to be caused by the differences in local structural and chemical properties between alloying elements, Cr and Ni, in the rust layer. In order to examine the effect of these alloying elements on the structure of the rust layer formed on steel in a Cl-rich environment, we have performed Cr and Ni K-edge X-ray absorption near-edge structure (XANES) measurements for the rust layer of Fe-Cr and Fe-Ni binary alloys exposed to a Cl-rich atmosphere using synchrotron radiation. The results of the Cr K-edge XANES measurements for the rust layer of Fe-Cr binary alloys show that the atomic geometry around Cr depends on the concentration of Cr. Therefore, it is expected that the local structure around Cr in the rust layer is unstable. On the other hand, from the results of the Ni K-edge XANES measurements for the rust layer of Fe-Ni binary alloys, Ni is considered to be positioned at a specific site in the crystal structure of a constituent of the rust layer, such as akaganéite or magnetite. As a consequence, Ni negligibly interacts with Cl− ions in the rust layer.
  • © 2005 The Japan Institute of Metals and Materials

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