Synthesis of MgAl2O4 Whiskers by an Oxidation-Reduction Reaction

Magnesium aluminate whiskers were synthesized by an oxidation—reduction reaction between MgO, C, and Al in a CO and CO₂ atmosphere. The oxygen partial pressure suitable for MgAl₂O₄ whisker growth ranged from 10^−12.1 to 10^−11.5 MPa. The average whisker diameter and length formed at 1500°C for 8 h were ∼3.1 μm and ∼4 mm, respectively. The whiskers grew in the [111] direction.     

Critical solution point and chain dimension of branched-polystyrene solutions

Summary Critical solution point and chain dimension were measured for branched polystyrene(BPS) in solution as a function of molecular weight(M) and compared with those for linear polystyrene(LPS). The critical concentration _c of BPS was quite different from that of LPS at a fixed M, but the same at a fixed overlap-concentration ^*, i.e., plots of _c vs. ^* fall on a single straight line for both BPS and LPS (gf_c ^*). Reduced critical temperature _c defined by gt_c=(–T_c)/ [T_c: critical temperature, : the -temperature] was related to _c as _{c c} ² for BPS, whereas _{c c} for LPS.     

Enhanced growth rates of nanodroplets in the free molecular regime: The role of long-range interactions

Recently, Pathak et al. (2013) Pathak, H., Mullick, K., Tanimura, S., and Wyslouzil, B. E. (2013). Nonisothermal Droplet Growth in the Free Molecular Regime. Aerosol Sci. Technol., 47:1310–1324.[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar] conducted a series of non-isothermal D₂O nanodroplet growth studies in the free molecular regime. They found that under highly non-equilibrium conditions, the condensation (q_c) and evaporation coefficients (q_e) can differ from each other and from the expected value of 1. Here, we confirm these observations by analyzing comparable experiments using n-propanol. We show that the best agreement with the non-isothermal Hertz–Knudsen growth law corresponds to setting (q_c, q_e) = (1, 0.6) or (q_c, q_e) = (1.3, 1). The approach of retarded evaporation yields values close to those observed by Pathak et al. for D₂O, but is difficult to justify theoretically. Enhancing the condensation coefficient is consistent with long-range attractive interactions between the vapor molecules and droplets in the nanometer size range.

© 2016 American Association for Aerosol Research     

Sintering behaviour of the diamond-super invar alloy system at high temperature and pressure

In the diamond-super invar alloy system, effect of the grain size of the starting diamond powder on the sintering behaviour was investigated at 5.8 G Pa and 1300 to 1500 ° C for 30 to 60 min. Abnormal grain growth was often observed in the sintered diamond using fine diamond powder, but a homogeneous sintered diamond was easily synthesized using 5 to 10m diamond. By the rigorous control of sintering conditions, a 3m grain size homogeneous sintered diamond was synthesized under conditions of 5.8 G Pa and 1350 ° C for 30 min. The Vickers hardness and thermal resistance of the fine grained sintered diamond was examined.     

Influence of aluminum precursors on structure and acidic properties of hollow silica–alumina composite spheres,and their activity for hydrolytic dehydrogenation of ammonia borane

In this study, we investigated the influence of aluminum precursors on structure and acidic properties of hollow silica–alumina composite spheres, as well as their activity for hydrolytic dehydrogenation of ammonia borane. Hollow silica–alumina composite spheres were prepared via the sol–gel method using polystyrene particles as templates. Activities of the hollow spheres prepared using various aluminum precursors for hydrolytic dehydrogenation of ammonia borane were compared. The molar ratios of evolved hydrogen to ammonia borane introduced were 1.0, 2.8, 1.5, and 3.0 in the presence of the hollow spheres prepared using aluminum ethoxide, aluminum isopropoxide, aluminum tributoxide, and aluminum-tri-sec-butoxide, respectively. Hollow spheres prepared using aluminum precursors with branched alkyl groups exhibit more hydrogen evolution than those prepared using aluminum precursors with normal alkyl groups. From the result of solid-state ²⁷Al nuclear magnetic resonance spectra and temperature-programmed desorption of ammonia, 4-coordinated aluminum species are related to Brønsted acid sites, and highly dispersed aluminum species increase the number of Brønsted acid sites.     

Formation mechanism of Ti2AlC under the self-propagating high-temperature synthesis (SHS) mode

Ti₂AlC was fabricated by the self-propagating high-temperature synthesis (SHS) technique from a compacted powder mixture consisting of Ti:Al:C = 2:1:1 (molar ratio) of mortar mixing, planetary mixing and various packing densities. A thermocouple was placed directly into the green compact body in order to monitor the combustion temperature during the SHS process. When the green compact with planetary mixing treatment and a packing density of 17% as well as 60% was used, propagation of the reaction exothermicity could occur, and the starting compact completely changed to Ti₂AlC. Formation mechanism of Ti₂AlC using a SHS technique was discussed. In addition, the melting point of the resultant sample was determined to be 1570 °C.     

High‐performance pMOSFETs with high Ge fraction strained SiGe‐heterostructure channel and ultrashallow source/drain formed by selective B‐doped SiGe CVD

The improvement of current drivability and short‐channel effect is very important for ultrasmall MOS device technology. SiGe‐channel pMOSFETs are one of the most promising devices because hole mobility in the SiGe layers is enhanced. In the previous work, it has been reported that Super Self‐aligned Shallow junction Electrode (S³E) MOSFETs formed by selective B‐doped SiGe CVD are effective for the suppression of short‐channel effect. In this paper, it is clarified that the (S³E) pMOSFETs with Si_0.65Ge_0.35 channel are realized not only with suppression of punch‐through due to the ultrashallow B‐diffused source/drain but also with enhancement of maximum linear transconductance due to the low parasitic resistance, compared to that with the Si channel fabricated by the same process conditions. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(3): 46–50, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20597     

Transient stability simulation of wind generator expressed by two‐mass model

Recently, wind power generation is increasing worldwide. In wind power stations, induction machines are mostly used as generators. Since induction generators have a stability problem similar to the transient stability of synchronous machines, it is important to analyze the transient stability of power systems including wind generators. Although there have been some reports analyzing the transient stability problem, wind turbine and wind generator are, in most cases, modeled as a one‐mass shaft system having total inertia constant. This paper presents simulation analyses of transient stability of power system including induction generator which is expressed by a two‐mass shaft model and analyzes an effect of shaft system modeling on the transient stability characteristics. Simulations are performed by PSCAD/EMTDC in this study. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 162(3): 27–37, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20394     

Sol–Gel Synthesis of Silica-Based Oxyfluoride Glass-Ceramic Thin Films: Incorporation of Eu3+ Activators into Crystallites

Transparent oxyfluoride glass-ceramic thin films were prepared using a sol–gel method starting from rare-earth trifluoroacetate/silicon alkoxide solutions. SiO₂–LaF₃ and SiO₂–LaOF glass-ceramics were formed by heating at temperatures of 300°–500°C and 600°–900°C, respectively. Eu³⁺ activators were successfully incorporated into oxyfluoride crystals, as evidenced by their luminescent properties, such as capability of a charge-transfer (O^2––Eu³⁺) excitation, suppression of a multiphonon relaxation, and occurrence of a cross-relaxation at low Eu³⁺ concentrations. As a result, the films exhibited strong red emission by ultraviolet excitation. The incorporation supposedly originated from decomposition of the (La,Eu)-trifluoroacetates in the silica-gel matrix.     

Fabrication and characterization of hardened bodies from Japanese volcanic ash using geopolymerization

Hardened bodies were fabricated from Japanese volcanic ash after mixing with an alkali solution, molding, and curing. The volcanic ash was composed of approximately 70% crystalline anorthite sodium [(Ca, Na) (Si, Al)₄O₈] phase and ≤30% amorphous silicate phase. First, a starting mixture was prepared by mixing the ground volcanic ash with a sodium hydroxide solution. The mixture was placed in a plastic mold using a glass rod, and then cured at 50 °C and 80% relative humidity for 3 days. The compressive strength of the resulting hardened body increased with increasing concentration of sodium hydroxide solution. When a 13.5 mol/L sodium hydroxide solution was used, the average compressive strength of the hardened body reached 80.1 MPa. The hardening mechanism for the volcanic ash during curing is discussed.