Mechanism of production of ultra-fine silicon carbide powder by arc plasma irradiation of silicon bulk in methane-based atmospheres

The mechanism of production of ultra-fine SiC powder from a silicon bulk by arc plasma irradiation in either an Ar + CH₄ + H₂ or an Ar + CH₄ atmosphere was studied. Layer and island phases were newly formed in the silicon bulk upon irradiation, and it was revealed from scanning electron and Auger electron spectroscopy that these phases were composed of SiC. The intensity of the X-ray diffraction peaks due to the SiC phase increased with irradiation time almost in parallel to the carbon content involved in the silicon bulk. It is proposed that CH₄ is dissociated in the arc plasma and dissolved in the molten silicon bulk to produce the SiC phase, the sublimation of which is mostly responsible for the production of ultra-fine SiC powder.     

The simulated moving-bed reactor for production of bisphenol A

Bisphenol A was produced from acetone and phenol over an ion-exchange resin catalyst at 50–90°C. Phenol was used as solvent. The reaction proceeded under the excess phenol condition. The reaction rate was proportional to the acetone concentration in the initial period of the reaction. After the acetone conversion exceeded approximately 50%, the reaction rate became lower than expected by the first-order reaction rate. This was ascribed to water adsorption onto the resin. Batch adsorption and breakthrough experiments showed that water was adsorbed approximately seven times stronger than acetone and that bisphenol A was not adsorbed. Using the reaction rate equation for bisphenol A production, the adsorption isotherms and overall mass transfer coefficients of the components, the numerical simulation of the 3-zone-type simulated moving-bed reactor was carried out. High resin flow rate was required in order to remove water out of the reaction zone, and a high liquid flow rate was also required to desorb water from the resin in the recovery zone. As far as the flow rates were set appropriately, water was successfully removed to prevent the catalyst deactivation and the long-term stable production of BPA was allowed.     

Study of wind-toughness of metal arc welding with reference to multi-pass weld metal quality

The maximum cause to make mechanical toughness of a weld metal reduce in process management is known to be a mixture of nitrogen including in the atmosphere by breaking the shield condition. Mixture of the atmosphere is prevented by blowing the shielding gas such as carbon dioxide, argon, and this mixture to the arc and the molten pool in gas metal arc welding, but it is easily affected by wind. Therefore, it has been recommended conventionally that wind velocity should be controlled to less than 2.0 m/s. But it is thought that this recommendation value is unsuitable to produce multi-pass weld metal with high mechanical and porosity toughness properties because this was provided from examination results by only consideration of porosity toughness of single-pass weld metal but non-consideration mechanical toughness. In this paper, the shielding condition is evaluated not only chemical analysis and mechanical properties of multi-pass weld metal in some velocity wind environment but also visualizing varied shielding gas behaviour by the Schlieren method. As a result, it is necessary to control the wind velocity to less than 0.5 m/s to produce multi-pass weld metal with good properties. And the calculated velocity of shielding gas should be controlled to more than twice the wind velocity.     

Biological characteristics of the junctional epithelium

This review summarizes the biological properties of the junctional epithelium, focusing on its developmental aspects, wide intercellular spaces and desmosomes, dense granules, permeability barrier, phagocytotic activity, adhesive structures and nerve terminals. It also discusses the morphology and functions of long junctional epithelium and peri-implant epithelium. Junctional epithelium is derived from the reduced enamel epithelium during tooth development. Apoptosis occurs in the border between oral and reduced enamel epithelia during tooth eruption. Junctional epithelium expresses a cytokeratin-19 immunoreaction, suggesting that this protein is a consistent differentiation marker. Wide intercellular spaces, which contain neutrophils and nerve endings, are formed as there are fewer desmosomes than in the oral epithelium. Dense, membrane-bound granules in the epithelium might correspond with membrane-coating granules, as revealed by their shape, components and freeze-fracture images. Junctional epithelium with high permeability contains exogenously expressed alpha-defensins, while stratified epithelia contain endogenously expressed beta-defensins. The phagocytotic activity in this epithelium remains unclear. Integrin-alpha6beta4 and laminin-5 form a complex in the tooth surface internal basal lamina. Long junctional epithelium created experimentally attaches to the cementum surface by hemidesmosomes and basal lamina. The peri-implant epithelium differs in proliferation and in adhesive structure from the normal junctional epithelium. In conclusion, wide intercellular spaces and poorly developed desmosomes are closely correlated with a permeable nature. There is still uncertainty over the phagocytotic activity of the epithelium. Integrin-alpha6beta4 and laminin-5 form a significant complex in the internal basal lamina. Junctional epithelium receives a rich sensory nerve and has a high rate of cell turnover. Long junctional epithelium can be produced rapidly during wound healing, due to high proliferative activity. Peri-implant epithelium might be a poorly adhered and permeable epithelium.     

Modulated structure and magnetic properties of age-hardenable Fe-Mn-Al-C alloys

Microstructural changes in the age-hardenable Fe-(30 to 34) wt pct Mn-(8 to 11) wt pct Al-(0.9 to 1.0) wt pct C alloys during aging in the temperature range between 773 and 823 K have been investigated by means of transmission electron microscopy (TEM) and X-ray diffraction. The wavelength of the modulated structure was found to be nearly constant for short aging times and then to increase on further aging, whereas the compositional modulation amplitude was found to increase rapidly from the beginning of aging. The growth of a spinodally modulated structure along the orthogonal «100» directions results in a periodic arrangement of the κ-carbide precipitates, (Fe, Mn)₃AlC_x, in the austenite matrix. The increases in hardness and residual and saturation inductions in the early stage of aging were in accord with the increase in the amplitude.     

Development of dicing technique for thin semiconductor substrate using temporally shaped femtosecond laser

Recently, semiconductor substrates for integrated circuits (ICs) have been required to be as thin as 50 µm, because many electronic devices must be miniaturized and light in weight. Machining of such thin substrates with conventional dicing techniques is very difficult. Therefore, we have proposed processing them using femtosecond laser ablation. In this work, we investigate the influence of conditions of a double pulsed laser such as the delay time and fluence on the depth and diameter in order to develop a new dicing technique for very thin ICs. A double pulsed laser (λ = 780 nm, τ = 150 fs, f = 10 Hz, Δt = 0 to 100 ps, E₁ + E₂ = 100 µJ) was focused on the Si substrate with a plano‐convex lens having a nominal focal length of 100 mm. At a delay time of 10 ps, singularly shallow and flat‐bottomed holes were obtained. When the substrates were diced under these conditions, the bottom of the processing groove was flat and very smooth, whereas many microcracks starting from the bottom of the groove formed by the conventional method have been observed. From these results, we were able to identify femtosecond laser processing conditions that were applicable to dicing of thin Si substrates. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(3): 43–48, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20028     

Fault Diagnosis by Mathematical Programming

This paper presents the problem of fault diagnosis for logically represented continuous systems that can be formulated through nonlinear mathematical programming. This problem is transformed to an integer-programming problem and solved. Possible modifications and extensions of the problem are given. Although failure tables must be prepared in ordinary fault diagnosis, they are not necessary with this mathematical programming approach. By modifying constraints in the mathematical programming problem, difficulties such as multiple faults, correlated faults, modifications of test conditions and cycles in the system, which are encountered in the ordinary failure table approach, are made tractable.     

Effects of Mn content and texture on fatigue properties of as-cast and extruded AZ61 magnesium alloys

Fatigue behavior of as-cast and extruded AZ61 magnesium alloys in ambient air (20 °C–55%RH) was investigated. It was found that size and distribution of cast defect influenced tensile and fatigue performance of the as-cast alloy. Fatigue limit of the as-cast alloy was significantly low compared to the extruded alloy. The casting defects served as stress concentration sites for fatigue crack nucleation. Fatigue tests were also carried out on a high Mn content alloy. All of the specimens failed from an inclusion near the specimen surface. Fatigue limit of Mg alloy with high Mn content was lower compared to that of the low Mn content alloy. Further, investigation on the effect of texture on fatigue and fatigue crack growth behavior of the extruded AZ61 magnesium alloy plate was carried out. The results showed that fatigue strength in the longitudinal direction to the extruded direction was higher compared to those in the transverse and 45° directions. Significant effect of specimen orientation on fatigue crack growth behavior for both short and long cracks was found near the threshold region. However, regardless of specimen orientation, the da/dN–ΔK_eff curves for all three kinds of specimens were in a narrow band. It is suggested that the difference in the fatigue life among the specimen orientations will be mainly due to the difference in the crack closure behavior. A transition of fracture mechanism was found for a long crack. Slip fracture mechanism was dominant above the transition point, whereas below the transition point, slip fracture mechanism was associated with cleavage fracture.     

The observation of the nucleation and growth of electrolessly plated nickel deposited from different bath pH by TEM and QCM method

The important factors for fabricating thinner and more uniform films by electroless plating were discussed. Two kinds of Ni-P films were electrolessly plated from hypophosphite baths. The number density of the grains was low in the Ni-5.3 wt%P deposits which were plated from the pH 9 bath. As deposition proceeded, the grains grew and merged to form a continuous structure. In case of the Ni-12.6 wt%P deposits, which were plated from the pH 6 bath, the number density of the grains was more than twice that of the Ni-5.3 wt%P deposits. The grains formed a continuous structure, with nucleation governed by the initial deposition. Thus, the transition thickness, i.e., the thickness at which the deposits assumed a continuous structure, was lower in the case of pH 6. The difference was caused by the different autocatalytic activity of the deposits due to the difference in phosphorus content. It was found that the thinner and more uniform nickel films could be electrolessly plated under lower autocatalytic activity.