Combustion synthesis of α-Si3N4 assisted by molten salt additives

Combustion synthesis (CS) of silicon nitride (Si₃N₄), assisted by molten salt additives under high N₂ pressure, is reported. The effect of salt additives (NaCl, MgCl₂, and MgCl₂?6H₂O) on the reaction temperature and the final α-Si₃N₄ content is studied. The maximum reaction temperature (T_max) decreased with an increase in the amount of the salt additives. NaCl is found to be the most suitable as it results in 57.8% α-Si₃N₄ at 30 mass% concentration. MgCl₂ is strongly hygroscopic, and MgCl₂?6H₂O decomposes at very low temperature. Therefore, they absorb heat at low temperatures, which makes it difficult to reach the ignition temperature, thereby hindering the reaction propagation. Si₃N₄ is necessary as a diluent for creating pores in the raw materials to allow effective penetration and contact of N₂ gas with the Si particles.     

Harmonic-structured copper: performance and proof of fabrication concept based on severe plastic deformation of powders

Pure copper (Cu) having bimodal ‘harmonic structure’ (HS) was fabricated by a technique based on severe plastic deformation of powders, which involved tailored mechanical milling and spark plasma sintering. The harmonic-structured Cu demonstrates a unique combination of high strength and large elongation superior to its homogeneous as well as bimodal heterogeneous counterparts. Specific features of harmonic structure, i.e. continuous network of ultra-fine grained (UFG) regions encompassing coarse-grained areas, lead to the extension of uniform elongation. The optimum combination of properties in pure Cu is found to be in the harmonic-structured material having 40 % UFG fraction.     

Formation and properties of nitrogen‐rich phases in austenitic stainless steel by plasma‐based ion implantation

Surface modification of austenitic stainless steel by plasma‐based ion implantation at elevated temperatures below 450°C has been studied experimentally. The nitrogen depth profile at room temperature was similar to that obtained by TRIM code simulation, but the depth of nitrogen penetration increases with target temperature and reaches a few micrometers at a treatment condition of 450°C and an implantation time of 2 h. High‐dose nitrogen implantation exceeding 10¹⁸ cm^?2 at temperatures above 350°C results in the formation of expanded austenite phase (supersaturated f.c.c. phase) with little CrN precipitation, leading to remarkable enhancement of surface hardness without loss of corrosion resistance. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(4): 9–16, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10340     

Improvement of microwave power from a virtual cathode oscillator and its repetitive operation using a metal mesh anode

A virtual cathode oscillator with a stainless‐steel mesh anode of various transparencies and wire diameters was studied experimentally for the enhancement of microwave power and its repetitive operations. The maximum microwave power observed was about 20 MW at 12 GHz for a diode voltage of 250 kV and an electron beam current of 39 kA using an anode mesh with wire diameter of 0.22 mm and a transparency of 67%. The microwave emission was enhanced by decreasing the mean angle of beam scattering when a mesh of smaller wire diameters was used in the anode. The increased transparency of the fine mesh also contributed to the enhancement of the microwave emission. Use of the mesh anode afforded the operation in several repetitive shots. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(2): 1–10, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10259     

Influence of sulfuric-acid-bath pretreatment and soaked in sulfuric acid on surface morphology and photocatalytic activity of titania coatings

Science China Technological Sciences - Titania (TiO2) photocatalyst coatings have been fabricated by the low-cost approach of sulfuric-acid-bath pretreatment (SAP) followed soaked in sulfuric acid...     

Structural Analysis of Crystalline R(+)-α-Lipoic Acid-α-cyclodextrin Complex Based on Microscopic and Spectroscopic Studies

R(+)-α-lipoic acid (RALA) is a naturally-occurring substance, and its protein-bound form plays significant role in the energy metabolism in the mitochondria. RALA is vulnerable to a variety of physical stimuli, including heat and UV light, which prompted us to study the stability of its complexes with cyclodextrins (CDs). In this study, we have prepared and purified a crystalline RALA-αCD complex and evaluated its properties in the solid state. The results of ¹H NMR and PXRD analyses indicated that the crystalline RALA-αCD complex is a channel type complex with a molar ratio of 2:3 (RALA:α-CD). Attenuated total reflection/Fourier transform infrared analysis of the complex showed the shift of the C=O stretching vibration of RALA due to the formation of the RALA-αCD complex. Raman spectroscopic analysis revealed the significant weakness of the S–S and C–S stretching vibrations of RALA in the RALA-αCD complex implying that the dithiolane ring of RALA is almost enclosed in glucose ring of α-CD. Extent of this effect was dependent on the direction of the excitation laser to the hexagonal morphology of the crystal. Solid-state NMR analysis allowed for the chemical shift of the C=O peak to be precisely determined. These results suggested that RALA was positioned in the α-CD cavity with its 1,2-dithiolane ring orientated perpendicular to the plane of the α-CD ring.     

Palladium on Carbon‐Catalyzed Aqueous Transformation of Primary Alcohols to Carboxylic Acids Based on Dehydrogenation under Mildly Reduced Pressure

The catalytic dehydrogenation of alcohols to carbonyl products is a green sustainable oxidation with no production of waste except for hydrogen, which can be an energy source. Additionally, a reusable heterogeneous catalyst is valuable from the viewpoint of process chemistry and water is a green solvent. We have accomplished the palladium on carbon (Pd/C)‐catalyzed dehydrogenation of primary alcohols to carboxylic acids in water under a mildly reduced pressure (800 hPa). The reduced pressure can be easily controlled by the vacuum controller of the rotary evaporator to remove the excess of generated hydrogen, which causes the reduction (reverse reaction) of aldehydes to alcohols (starting materials) and other undesirable side reactions. The present method is applicable to the reaction of various aliphatic and benzylic alcohols to the corresponding carboxylic acids, and the Pd/C could be reused at least 5 times.

     

Direct space vector PWM strategy for matrix converters with reduced number of switching transitions

This paper proposes a novel “Direct Space Vector PWM (Direct SVPWM)” strategy based on the direct AC/AC conversion approach for three‐phase to three‐phase matrix converters. This method allows the sinusoidal input and output waveforms as a major premise, and gives top priority to the improvement of output control performance in motor drive applications, such as providing maximum riding comfort in elevators, etc. Output voltage harmonics, switching losses, and common‐mode voltages can be reduced across the entire voltage region. In addition, the switching count can be reduced even further by fully utilizing the output current detection value. Direct space vectors are first defined, and the method of selecting space vectors is described. Next, the PWM duty calculation technique is explained. Finally, the validity of the proposed method is demonstrated by comparison with the conventional virtual indirect method based on experimental and analytical results. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 172(3): 52–63, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20953