Effects of Particle Sizes on Sintering Behavior of 316L Stainless Steel Powder

In rapidly evolving powder injection molding technology, the wide prevalence of various microstructures demands the powders of smaller particle sizes. The effects of particle size on the sintering behavior are critical to not only shape retention of microstructure but also its mechanical properties. This study investigates the effects of three different particle sizes on the sintering behavior of the 316L stainless steel (STS316L) samples, prepared by powder injection molding, via the dilatometry experiments. For this purpose, the STS316L powders of three different mean particle sizes, i.e., 2.97, 4.16, and 8.04 μm, were produced for STS316L. The samples for the dilatometry test were prepared through powder-binder mixing, injection molding, and solvent and thermal debinding. Dilatometry experiments were carried out with the samples in a H₂ atmosphere at three different heating rates of 3, 6, and 10 K/min. The shrinkage data obtained by dilatometry experiments was collected and analyzed to help understand the densification and the sintering behaviors in terms of particles size and heating rate. The master sintering curve (MSC) model was used to quantify the effects of particle sizes. In addition, we investigated the microstructure evolutions in terms of particles sizes.     

Penetration behavior of water solution containing radioactive species into dried concrete/mortar and epoxy resin materials

Penetration behavior of radionuclides such as ¹³⁷Cs into dried concrete material, dried mortar material and epoxy paint for a few dozen days was observed using a solution containing fission products extracted from irradiated fuels to obtain fundamental information on the radionuclide penetration rate and depth. Hardly any radionuclides could penetrate into the epoxy paint. The radionuclide solution penetrated into concrete and mortar materials to a depth of a few millimeters for a few dozen days. The penetration behavior observed near the surface of concrete and mortar materials was similar to the diffusion of nuclides in media such as water-saturated concrete, bentonite and cement materials.     

Use of structure-controlled polymers as high performance powder dispersants in the silicone oil phase

A novel polymer dispersant with a tri-block structure was designed. The tri-block polymer was composed of polyglycerin (PGL) with two dimethylpolysiloxane chains (DMPS) at both ends of the molecular structure. The high dispersibility of the dispersant was confirmed in both a model silica system and a sunscreen formulation. The apparent silica particle size was employed as an index for the dispensability for the dispersants. The novel dispersant showed 5 times more effective than conventional one. The flow properties of a sunscreen formulation containing titanium dioxide with the novel dispersant was Newtonian, indicating that the dispersibility of the dispersant was excellent. On the other hand, the formulation with conventional dispersant showed shear-thinning flow due to aggregation of the powder. These results mean that such a tri-block copolymer would make it possible to develop consumer demanded sunscreens.     

Fluorescent SiC and its application to white light-emitting diodes

Fluorescent-SiC (f-SiC), which contains donor and acceptor impurities with optimum concentrations, has high conversion efficiency from NUV to visible light caused by donor-acceptor-pair (DAP) recombination. This material can be used as a substrate for a near UV light-emitting diode (LED) stack, and leads to monolithic white LED device with suitable spectral property for general lighting applications. In this paper, we describe basic technologies of the white LED, such as optical properties of f-SiC substrate, and epitaxial growth of NUV stack on the f-SiC substrate.     

Origin of enhanced cold crystallization rate for freeze‐dried poly(L‐lactide) from solutions

Poly(L ‐lactide) (PLLA) freeze‐dried from dilute 1,4‐dioxane solutions exhibited very porous structure composed of thin membranes of which the mean thickness was estimated to be 104–135 nm. Heating measurements of differential scanning calorimetry (DSC) showed that the freeze‐dried PLLA (FDPLLA) exhibits an exothermic peak of cold crystallization at 78–81°C, which is at least 20 K lower than that for a quenched amorphous bulk PLLA. In accord with this, the overall rate of isothermal cold crystallization was revealed to be greater for the FDPLLA than that for the bulk. The origin of such high crystallizability of FDPLLA is attributed to its large surface area where the chain mobility is greater than in the bulk PLLA. The exothermic peak in the DSC trace shifted to a further lower temperature when the FDPLLA is immersed in ligroin (nonsolvent), which also suggests a major role of the free surface in enhancing the cold crystallization rate. On the other hand, the density and the chain conformational feature of the FDPLLA were revealed to be identical to the bulk PLLA. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers.     

Heat and mass transfer coefficients of falling-film absorption process

This paper deals with the method to calculate heat and mass transfer coefficients of falling film absorption process over vertical tube or plate type surface employed in absorption refrigeration system. The conventional log mean temperature/concentration difference method is criticized for lack of physical rationality, and for incorrect results from the calculation. A new method based on a simplified model is proposed and demonstrated by numerical simulations and comparison analysis.     

Radiocarbon (14C) diurnal variations in fine particles at sites downwind from Tokyo, Japan in summer

The radiocarbon ((14)C) of total carbon (TC) in atmospheric fine particles was measured at 6 h or 12 h intervals at two sites, 50 and 100 km downwind from Tokyo, Japan (Kisai and Maebashi) in summer 2007. The percent modern carbon (pMC) showed clear diurnal variations with minimums in the daytime. The mean pMC values at Maebashi were 28 ± 7 in the daytime and 45 ± 16 at night (37 ± 15 for the overall period). Those at Kisai were 26 ± 9 in the daytime and 44 ± 8 at night (37 ± 12 for the overall period). This data indicates that fossil sources were major contributors to the daytime TC, while fossil and modern sources had comparable contributions to nighttime TC in the suburban areas. At both sites, the concentration of fossil carbon as well as O(3) and the estimated secondary organic carbon increased in the daytime. These results suggest that fossil sources around Tokyo contributed significantly to the high daytime concentration of secondary organic aerosols (SOA) at the two suburban sites. A comparison of pMC and the ratio of elemental carbon/TC from our particulate samples with those from three end-member sources corroborates the dominant role of fossil SOA in the daytime.     

Thermal stability of back side metallization multilayer for power device application

Metallization multilayers on the back side of a power device were focused in this study. Si wafers coated with high melting point metals were exposed at 300 °C for 300 h to investigate diffusion condition of the metallization layer. We developed and examined the thermal stability of die bonding material (Au paste) including sub–micrometer–sized Au particles. Auger electron spectroscopy was applied to observe the atomic composition of the multilayers in depth direction after the high temperature aging. Surface morphology was observed using optical microscope and scanning electron microscope. While atomic composition on Ti/Au changed drastically after the high temperature aging, other multilayers maintained their metallization composition. However, the surface morphology was slightly changed on Ti/Ru/Au, W/Au, and Ta/Au. Bond strength on the Ti/Pt/Au kept over 40 MPa with unified bonding layer after exposing at 300 °C for 1000 h.     

X-Ray Detected Magnetic Resonance at Sub-THz Frequencies Using a High Power Gyrotron Source

X-ray Detected Magnetic Resonance (XDMR) is a novel spectroscopy which makes use of X-ray Magnetic Circular Dichroism (XMCD) to probe the resonant precession of local magnetization components in a strong microwave pump field. In Sections?1 and 2, we briefly review the conceptual bases of XDMR and the potential interest of increasing the pumping frequency up to the THz frequency range. In Sections?3–5, we discuss the feasibility of such challenging experiments. Starting from a comparison of experiments carried out either in the transverse (TRD) or longitudinal (LOD) detection geometries, we show that XDMR measurements at sub-THz frequencies require a substantial increase in pumping power: this is where a gyrotron source looks most appropriate. It is the aim of this paper to discuss how to conduct such experiments, emphasis being laid on feasibility tests recently carried out at the ESRF using a refurbished version of Gyrotron FU-II built at the FIR-FU. In this context, we propose a new detection scheme of sub-THz XDMR spectra based on the concept of frequency-mixing in LOD geometry.     

Origin of defect-insensitive emission probability in In-containing (Al,In,Ga)N alloy semiconductors

Group-III-nitride semiconductors have shown enormous potential as light sources for full-colour displays, optical storage and solid-state lighting. Remarkably, InGaN blue- and green-light-emitting diodes (LEDs) emit brilliant light although the threading dislocation density generated due to lattice mismatch is six orders of magnitude higher than that in conventional LEDs. Here we explain why In-containing (Al,In,Ga)N bulk films exhibit a defect-insensitive emission probability. From the extremely short positron diffusion lengths (<4 nm) and short radiative lifetimes of excitonic emissions, we conclude that localizing valence states associated with atomic condensates of In-N preferentially capture holes, which have a positive charge similar to positrons. The holes form localized excitons to emit the light, although some of the excitons recombine at non-radiative centres. The enterprising use of atomically inhomogeneous crystals is proposed for future innovation in light emitters even when using defective crystals.