Effect of green compact structure on the sintering of alumina

The effect of particle agglomeration on sintering has been studied by slipcasting suspensions with pH values ranging from 2 to 11. The rate of densification has been found to depend on the degree of agglomeration. Complete dispersion of alumina primary particles has not been attained through adjustment of pH of suspensions, and agglomerates also remained in the best-dispersed suspension. Elimination of the agglomerates by sedimentation lowered the densification temperature of slip-cast compacts. The grain size-density curve is a function of temperature. High-density and small-grained sintered bodies were obtained by low-temperature long-time firing.     

Measurement of internal stresses in coatings using time resolved fluorescence

This paper describes a new nondestructive technique for detecting internal stresses in coatings using time resolved fluorescence. The measurement principle is based upon an experimental result that the decay time of fluorescence from poly(3-octylthiophene), P3OT, dispersed in uniaxially-stretched polymer films decreases with increasing tensile stress acting on the films. Internal stresses in the clear coat and in the base coat of a multilayer structure, which was composed of electrodeposited coat, surface coat, base coat, and clear coat, were estimated from the decay time of fluorescence from P3OT in both coats. The order of internal stresses in the clear coat and base coat of the multilayer system was 1 MPa. When the coatings were piled up, the internal stress decreased as the distance from a metal substrate was increased. It was found that moisture and temperature influenced internal stresses in the clear coat rather than in the base coat. Internal stress in the clear coat, which was one layer coated on a metal substrate, was measured by the traditional bimetallic method or by the time resolved fluorescence technique. Comparing both methods, it was concluded that the time resolved fluorescence technique gave reliable values for internal stresses in coatings.     

Numerical computation for clustering of carbon particles with various sizes under both natural and magnetizing convections

The behavior of carbon particles from 0.01 to diameters in natural convection flow field of air was numerically studied including the effect of the magnetic field and the Brownian motion. One thousand carbon particles were released randomly in a vertical cylindrical enclosure whose height is equal to its radius. The enclosure was heated from below and cooled from above to produce the bulk flow of the natural convection of air in the atmospheric condition. A coil with electric current was set coaxially at the enclosure bottom to produce a magnetic field. Sample computations are carried out for the enclosure of 3 cm high and maximum magnetic field is 2.8 T or less. The results show that the natural convection of air is enhanced by the magnetic field. With the increase in the magnetic strength, more particles go along the fluid streak lines. With the increase in the particle size, more particles get together at the vortex center and cluster.     

WATER MIST FLOW IN A SUPERCONDUCTING MAGNET INCLINED AT VARIOUS ANGLES

Water mist (diamagnetic) flow in a superconducting magnet of 10 T at various angles is studied experimentally and numerically. Water mist is produced by ultrasonic atomizers and fed into a cylindrical Plexiglas pipe (inner diameter, 90 mm) placed in a bore space of an inclined superconducting magnet. The water mist is found to stop at some locations in the magnet at inclined angles ψ ≤ π/6. At ψ ≥ π/4, the amount of mist flowing out of the other opening of the pipe increases with an increase in inclined angle. In the computation of this phenomenon, water mist is simulated with 1000 water droplets of 3 μm diameter. Brownian motion is considered and the Langevin equation is solved. The numerical results show that at ψ ≤ π/6, most of the water droplets accumulate above the magnetic coil. However, at ψ ≥ π/4, with an increase in inclined angle, the number of water droplets passing through the magnetic coil increases.     

Thermal behavior of hydrostatically extruded polycarbonate and high-impact polystyrene

Effects of hydrostatic extrusion on the thermal properties of polycarbonate (PC) and of high-impact polystyrene (HIPS) were studied using differential scanning calorimeter (DSC) measurements. A glass transition temperature (T_g) and a peak temperature were determined from the DSC curves for both PC and HIPS extrudates. The T_g values of the PC extrudates, with a percentage reduction in area, R, from 40 to 50%, change appreciably from the value for the as–received PC. The results of the hydrostatic extrusion of the PC billets suggest that a two stage deformation process of molecular chains may be involved. Shear-banding is observed for HIPS extrudates with R = 30 to 60%; this fact indicates that a sub-glass transition (β-transition) occurs at temperatures below T_g. It is suggested that the molecular chains of the HIPS extrudate with R = 70% are oriented in the direction of hydrostatic extrusion. The deformation mechanism of molecular chains caused by the hydrostatic extrusion is discussed.     

Thermal shock resistance of flat plastic integrated circuit packages

Flat packages (FPs) were formed from epoxy molding compounds with various physical properties using a transfer molding machine. The compounds were prepared by changing kinds and amounts of additives and addition methods. The thermal shock test was carried out by the following procedures. The plastic package was soaked alternately in liquid nitrogen (?196°) and in liquid solder (200°) in the cycle of 140s. The median life to crack initiation was defined to be the cycles when half of the specimens exhibited crack initiation. According to linear fracture mechanics, the following expression was obtained relating the median life N, thermal stress σ_t, and strength σ_b; N = C/σ·(σ_b/σ_t)^m. We found the linear relation between logarithm of Nσ and logarithm of σ_b/σ_t for various packages, and estimated the values of C and m as 5 × 10⁴ MPa² and 5.5, respectively. The value of m was the same as that obtained for a dual-in-line package.     

New type of tin support for hydroprocessing catalyst

TiN supported molybdenum sulfide catalysts showed much higher activity for cleavage of C-C bonds than oxide supported molybdenum sulfide catalysts, indicating the possibility of a new generation of supports for hydroprocessing catalysts.     

Effect of MgO Addition on the Bondability and Interfacial Reaction between Dielectric and Glass-Ceramics for the Fabrication of Multi-Component Ceramic Substrates

Bondability and interfacial reaction between dielectric and insulator layers have been examined to obtain a basic understanding of bonding mechanisms. Lead-containing complex perovskite was used as a dielectric material. Two kinds of glass-ceramics were used as insulator material; lead borosilicate glass containing Al_2O3 (insulator A) and the same containing Al₂O₃ and M_gO (insulator B). Dielectric and insulator layers did not bond when insulator A was used. When insulator B was used, however, strong bonding was achieved between the two layers by firing the powder compacts at temperatures between 800° and 1000°C. Addition of M_gO to lead borosilicate glass increased the thermal expansion coefficient to that of the dielectric and enhanced the formation of reaction layers, resulting in good bonding. Two reaction layers were identified. The main reaction products were enstatite and bredigite for one layer contacting the dielectric, and enstatite and a compound with the same diffraction pattern as that of faujasite for the other layers contacting insulator B.     

On-chip fabrication of magnetic alginate hydrogel microfibers by multilayered pneumatic microvalves

Alginate hydrogel has widespread applications in tissue engineering, cancer therapy, wound management and drug/cell/growth factor delivery due to its biocompatibility, hydrated environment and desirable viscoelastic properties. However, the lack of controllability is still an obstacle for utilizing it in the fabrication of 3D tissue constructs and accurate targeting in mass delivery. Here, we proposed a new method for achieving magnetic alginate hydrogel microfibers by dispersing magnetic nanoparticles in alginate solution and solidifying the magnetic alginate into hydrogel fiber inside microfluidic devices. The microfluidic devices have multilayered pneumatic microvalves with hemicylindrical channels to fully stop the fluids. In the experiments, the magnetic nanoparticles and the alginate solution were mixed and formed a uniform suspension. No aggregation of magnetic nanoparticles was found, which is crucial for flow control inside microfluidic devices. By regulating the flow rates of different solutions with the microvalves inside the microfluidic device, magnetic hydrogel fibers and nonmagnetic hydrogel fibers were fabricated with controlled sizes. The proposed method for fabricating magnetic hydrogel fiber holds great potential for engineering 3D tissue constructs with complex architectures and active drug release.     

Copolymerization of phenylacetylene with various acetylenes by W- and Mo-based catalysts

In the copolymerization of phenylacetylene with various acetylenes catalysed by WCl₆·Ph₄Sn, the relative reactivity of monomer decreased with increasing steric effect of monomer, e.g. HC  Cn-Bu, HC  Cn-Hex > HC  CPh, HC  Cs-Bu > HC  Ct-Bu, MeCCPh, CICCPh. While 1-chloro-2-phenylacetylene (a disubstituted acetylene) showed high reactivity in the homopolymerization by Mobased catalysts, the reactivity was remarkably depressed in the presence of phenylacetylene as comonomer. Based on these results, the relative reactivity of the acetylenic monomers in copolymerization was explained in terms of competitive coordination of monomers to the propagating end.