Advanced Materials Research Vols. 26-28

Abstract: The encapsulated induction melting was attempted to prepare the Sn-filled CoSb3 skutterudites and their electronic transport properties were investigated. Single phase δ-CoSb3 was successfully obtained by the subsequent isothermal heat treatment at 823K for 6 days in vacuum. The Sn-filled CoSb3 showed p-type conductivity at 300K to 700K at it is a highly degenerate semiconductor. Lattice contribution was dominant to thermal conductivity and it was considerably reduced by Sn filling in the CoSb3 skutterudite.

Abstract: In this study, porous concrete is applied to the stone column, which is a structural foundation in soft ground. The porous concrete reinforces the upper portion of the stone column and forms a composite foundation to restrain bulging collapse. To function as a foundation material properly in soft ground, concrete must be permeable to expel subsurface ground water outside and have sufficient compressive strength to reduce settlement, which is a critical factor for the foundation design. From laboratory experiments, the compressive strength increases and the permeability decreases as the amount of cement increases. To evaluate the settlement, full-scale tests and finite element analyses using porous concrete were performed. As a result, it was confirmed that the use of a stone column reinforced by porous concrete was very effective in reducing the settlement of the foundation in soft ground.

Abstract: A new cermet film Nb-NbN, deposited on the stainless steel substrate by direct reactive magnetron sputtering, was reported as solar selective absorptive coating. Some fundamental studies on microstructure and optical properties of the Nb-NbN cermet films were carried out by XRD, EDX, SEM and spectrophotometer. A solar absorptivity of 0.94 and a normal emissivity of 0.16 at room temperature were achieved for the coating. Thermal stability was investigated at 350°C and 500°C and it was observed that the absorptivity was changed in a range from 0.92 to 0.94 and the surface emissivity varied firstly from 0.16 to 0.14 and then increasing to 0.19 when the temperature was increased from room temperature to 350°C and up to 500°C.

Abstract: The present study is aiming at investigating the possibility of producing a magnesium foam from machined chips. To produce highly porous magnesium foam, precursor producing process was investigated by hot extrusion and compressive torsion processing (CTP). The CTP could realize well-consolidated precursors and homogeneous distribution of a blowing agent. The precursor made of machined chips satisfactorily expanded, and the porosity were comparatively high by optimizing processing parameters of the CTP.

Abstract: In this paper, a new attempt of transfer heat foaming was examined on the precursor method to fabricate long scale aluminum foams. In this new method, the induction coil heater was moved along the longitudinal direction of a rod precursor to foam a part of the precursor continuously. Long scale aluminum precursor was successfully foamed by the transfer heat foaming in which heating coil was moved along the precursor to control the temperature of heated part constantly.

Abstract: A Mo-free high-Cr cast iron with superior impact-wear resistance was tried to develop for mill balls by alloy design and subsequent heat treatment. The Cr/C ratio was varied up to 7.7 in order to minimize and eventually eliminate Mo addition, still ensuring hardenability. For the proper balance between abrasion resistance and toughness, the combined effects of each heat treatment parameters on the mechanical properties were systematically investigated using Taguchi method and response surface method (RSM), well recognized as powerful tools of the designs of experiments (DOE). It was found that hardness and impact energy were mainly affected by tempering and destabilization conditions, respectively. It is noted that high impact energy of 5.2 J/cm2 was obtained without deteriorating hardness (54 HRc) during the verification experiments under the heat treatment condition optimized by the DOE analyses.

Abstract: The paper outlined here uses self-propagating high-temperature synthesis (SHS) or combustion synthesis that employs more efficient and effective high reaction and cooling rates to produce high quality, reproducible nitride fuels. The fundamental SHS processing parameters was determined to produce Mn-Si-C-N ceramic compounds in which Mn is a surrogate for Am. Because manganese nitride has a relatively low heat of formation the reaction can not be self-sustaining when Si was blended with Mn in the Si:Mn=0.25:1 ratio. The purity of MnSiN2 increases with an increase of the Mn content in Mn-Si-N system. Pure MnSiN2 can be synthesized when Si was blended with Mn in the Si:Mn = 0.5:1 ratio. Volume expansion and porosity decreases, so density, strength and hardness increase as increasing the Mn content in Mn-Si-N system. The powders and sintered cake of MnSiN2-Si3N4 or MnSiN2-Si3N4-SiC was produced by combustion synthesis. The sintered cake of MnSiN2-Si3N4-SiC is attacked by atmospheric moisture to fall to a powder.

Abstract: Uranium powder, which can be obtained by the atomization process, was used to fabricate UAl2 by using powder metallurgy technology. Uranium powder and Al powder were blended, extruded, and annealed into a UAl2 rod in a mold. Sound UAl2 rods were fabricated by the powder metallurgical process. The relative density of the UAl2 pellet formed by an annealing was at about 94%. The density increased with higher constraints on the mold and a smaller particle size of the uranium powder. A coarse uranium powder of about 80 μm in average diameter represented the remaining un-reacted uranium phase. On the other hand, a fine uranium powder of about 50 μm in average diameter could achieve a pure UAl2 phase without a uranium phase. The analysis by an X-ray diffraction pattern confirmed that the annealed specimens had interacted to form a UAl2 phase. Conclusively, the sintered UAl2 pellet is expected to be useful in developing advanced fuels.

Abstract: Cerium dioxide (CeO2) is a well-studied oxide because of its technological applications, such as a major component in the catalysts, stable capacitors and so on. CeO2 with a cubic fluorite structure is also expected as the material for simulating behaviors of uranium dioxide under energetic particle irradiation, which leads high burn-up structure attributable to pressure increase in fuel cladding tubes. In this work, the stability of crystal structure and surface morphology change in CeO2 will be clarified. Polycrystalline samples were irradiated with 300 keV Xe+, 18 MeV I5+, 350 keV O+ and 12 MeV O3+ ions at temperatures from 370 to 1000 K. Microstructural evolutions was investigated with Scanning electron microscopy, Raman Spectroscopy and X-ray diffractometry. Irradiation effects at high temperature were observed as surface etching and resulting bubble formation, however blistering was not detected. Raman spectra and diffraction data indicates diffusion of oxygen vacancies is sufficient at 900 K and above.

Abstract: Density Functional Theory method within Generalized Gradient Approximation has been performed to obtain the static lattice parameters, oxygen positional parameter, bond length and bond angle and electronic properties of ideal Dy2Sn2O7 pyrochlore. The results are in excellent agreement with available experimental measurements. DOS of this compound was presented and analyzed. We also notice the presence of the hybridization between oxygen and both Sn and Dy metal.