Effects of Atmospheric Composition on the Molecular Structure of Synthesized Silicon Oxycarbides

The dependence of silicon oxycarbides' chemical composition and molecular structure on their reaction conditions was tested by varying the atmosphere under which pyrolysis was performed. To obtain the silicon oxycarbides, densely cross‐linked silicone resin particles with an averaged diameter of 2 μm were pyrolyzed in various atmospheres of H₂, Ar, and CO₂, in the temperature range 700°C–1100°C. The residual mass of resin after pyrolysis was almost constant at 700°C, although their apparent colors varied distinctly. The sample obtained from the H₂ atmosphere was white, whereas that obtained from the CO₂ atmosphere was dark brown. Fourier‐transform infrared (FT‐IR) spectra of the residues suggested that the Si–O–Si network evolution was accelerated in the CO₂ atmosphere. Beyond 800°C, the chemical compositions of the compounds obtained from a H₂ atmosphere increasingly approached near‐stoichiometric SiO₂–xSiC composition with increasing the pyrolysis temperature. Compounds from a CO₂ atmosphere approached a composition of SiO₂–xC with no free SiC as the pyrolysis temperature increased. In the products from an Ar atmosphere, SiO₂–xSiC–yC compositions were typically obtained. The observed effects of the pyrolysis atmosphere on the resulting chemical compositions were analyzed in terms of thermodynamic calculations. Electron spin resonance (ESR) spectra revealed broad and intense signals from products obtained from either Ar or CO₂. Estimating from the signal intensity, the residual spin concentrations were in the range 10¹⁸–10¹⁹ g^?1. Meanwhile, the spectra from the samples obtained in H₂ showed weak and sharp signals with estimated spin concentrations ranging from 10¹⁶–10¹⁷ g^?1. This signal attenuation may have been due to the hydrogen capping of dangling bond formed during pyrolysis.     

Improving the gas recovery and separation efficiency of a hydrate-based gas separation

Efficient gas recovery and separation in a hydrate-based system was investigated for a model gaseous mixture of R22 and nitrogen. The formed hydrate settled in the recovery vessel; excess water was recycled and the hydrate was subsequently decomposed by releasing pressure from the vessel. The gas uptake rate of R22 gas from the vapor phase and the gas recovery rate from the hydrate were determined from hydrate formation and decomposition, respectively. The gas recovery rate of R22 gas gradually increased with time. On the contrary, the nitrogen gas recovery rate was a maximum in the initial stage of hydrate decomposition. A high separation factor (S.F.) was achieved by first separating the N₂-rich gas generated during initial hydrate decomposition. An efficient hydrate-based gas separation and recovery process is proposed.     

Wave venation in downward gas-liquid two-phase flow (part I,time-spatial behavior chart of interface and analysis of main wave-vein)

Time-series information on both the cross-sectional mean liquid holdup along a tube axis and the gas-liquid phase distribution along a tube diameter was obtained by means of supermultiple cross-sectional mean liquid holdup probes (S-CHOP) and semi-supermultiple point-electrode probes (SS-PEP) for vertical downward gas-liquid two-phase flow. Typical time-spatial behavior charts of interface and gas-liquid interfacial profiles are presented. Close inspection of these results reveals that a huge wave and a disturbance wave appear in downward two-phase flow as well as upward flow. It was clarified that the huge wave flow region covers a wide range of superficial gas velocities. Wave velocity, wave width and maximum liquid holdup of individual waves were examined by wave-vein analysis. Histograms of these flow parameters were also studied. It was found that there exist distinct differences in wave width between the huge wave and the disturbance wave. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res, 25(8): 499–510, 1996     

Characteristics of interfacial profiles in upward and downward gas-liquid two-phase plug flow

Gas-liquid interfacial profiles in plug flow for both upward and downward flows were obtained using semi-supermultiple point-electrode probes, comprising 67 sensing tips arranged on a tube diameter. Typical interfacial profiles are demonstrated for both flows. Close inspection of the profiles reveals that four zones exist in a pair of gas and liquid slugs for upward plug flow and a high slip velocity region in downward plug flow. The lengths of the swelling liquid front zone and the wake zone were determined. The length of the wake zone strongly depends on the relative velocity between the liquid film around the gas slug and the liquid phase in the liquid slug. Characteristic distributions of bubbles within liquid slugs were found, i.e., three types of radial distributions of void fraction, namely saddle-shaped, trapezoidal and bullet-shaped distributions, exist for upward flow. The two types for downward flow exclude the saddle-shaped distribution. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res, 25 (8): 568–579, 1996     

Interactive visualization of three-dimensional magnetic fields

In order to observe the physical values (magnetic flux density and eddy current) in 3D magnetic field analysis, an interactive and highly manipulative visualization system depicting stereo images is intalled in a graphics workstation with high functional graphic processors. The system has the following characteristics:

• 1 An interactive and highly manipulative menu window with many functions: it enables visualization of complex phenomena in a 3D field through observation of various combinations of physical values from various viewpoints.
• 2 Simultaneous display of both magnetic flux density and eddy current by using the appropriate use of two colour display methods for stream lines and distribution maps of density: this function facilitates observation of the mutual relations between two physical values in a 3D field.
• 3 Animations and stereo displays: since they give extremely distinct images, observers can easily understand even highly complex 3D phenomena.

In this paper, the calculation method of density vectors, their display methods, and interactive functions are described. Some examples are also illustrated.     

Monitoring cure viscosity of epoxy composite

Viscosity is an important process variable that should be monitored and controlled to ensure the consistent and reliable production of graphite-fiber-reinforced composite parts by the autoclave/vacuum bag process. Unfortunately, no technique is currently known for the direct measurement of viscosity in this process. However, d.c. conductivity and a.c. phase lag appear to correlate quite well with viscosity, and either electrical property may be followed in order to indirectly monitor viscosity. As the method of measuring d.c. conductivity is so inexpensive, simple, and almost free of electrical interference compared to the method of measuring a.c. phase lag, it appears to be the method of first choice for application in an autoclave environment.     

Cloning, sequencing and expression of an alpha-L-arabinofuranosidase from Aspergillus sojae

The arabinofuranosidase gene was cloned from the cDNA of Aspergillus sojae. It was found to contain an open reading frame composed of 984 base pairs (bp) and to encode 328 amino acid residues (aa). The cDNA sequence suggested that the mature enzyme is preceded by a 26-aa signal sequence and the molecular mass was predicted to be 32,749 Da. The A. sojae arabinofuranosidase consists of a single catalytic domain; it does not have a specific substrate-binding domain such as the xylan-binding domain reported in an arabinofuranosidase from Streptomyces lividans (Vincent, P. et al.: Biochem. J., 322, 845-852, 1997). The deduced amino acid sequence of the catalytic domain of the mature enzyme exhibits extensive identity with the catalytic domains of Streptomyces coelicolor (74%), Aspergillus niger (75%), S. lividans (74%), and Aspergillus tubingensis (75%), which are enzymes that belong to family 62 of the glycosyl hydrolases. The cloned AFdase gene was expressed in Escherichia coli BL21 (DE3) pLysS as a cellulose-binding domain tag fusion protein. The specific activity of the purified recombinant enzyme was 18.6 units/mg protein, which is one-fourth that of the enzyme purified from a solid-state culture of A. sojae.     

Porous Glass-Ceramics with a Skeleton of the Fast-Lithium-Conducting Crystal Li1+xTi2−xAlx(PO4)3

Porous glass-ceramics with a skeleton of the fast-lithium-conducting crystal Li_{1+ x} Ti_{2− x} Al _x (PO₄)₃ (where x = 0.3–0.5) were prepared by crystallization of glasses in the Li₂O─CaO─TiO₂─Al₂O₃–P₂O₅ system and subsequent acid leaching of the resulting dense glass-ceramics composed of the interlocking of Li_{1+ x} Ti_{2− x} Al _x (PO₄)₃ and β-Ca₃(PO₄)₂ phases. The median pore diameter and surface area of the resulting porous Li_{1+ x} Ti_{2− x} Al _x (PO₄)₃ glass-ceramics were approximately 0.2 μm and 50 m²/g, respectively. The electrical conductivity of the porous glass-ceramics after heating in LiNO₃ aqueous solution was 8 × 10⁻⁵ S/cm at 300 K or 2 × 10⁻² S/cm at 600 K.