Enhancement of electrical stability of anisotropic conductive film (ACF) interconnections with viscosity-controlled and high Tg ACFs in fine-pitch chip-on-glass applications

This paper describes how anisotropic conductive film (ACF) properties including viscosity affect the electrical stability of ACF interconnections for fine pitch chip-on-glass (COG) applications. In this study, new ACFs for COG applications were designed by combining a high viscosity ACF layer and a low viscosity NCF layer to prevent the electrical shortage between bumps. As expected, the viscosity-controlled ACF showed better electrical insulation stability than a conventional ACF in fine pitch COG assemblies. According to the results of thermo-mechanical analysis (TMA) and dynamic-mechanical analysis (DMA), the viscosity-controlled ACF showed the improved thermo-mechanical properties such as lower coefficient of thermal expansion (CTE), higher storage modulus (E′) at higher temperature region, and higher glass transition temperature (T_g) than the conventional ACF. Furthermore, hot air reliability test and pressure cooker test (PCT) results showed that the viscosity-controlled ACF with higher T_g had better hot air test and PCT reliabilities than the conventional ACF.     

Performance characteristic of a tubular carbon-based fuel cell short stack coupled with a dry carbon gasifier

A carbon gasified carbon-based fuel cell (CFC) short stack was fabricated and investigated for generating effective carbon fuel cell reactions. Anode-supported tubular CFC cells with a 45 cm² active electrode area were used to manufacture the CFC short stack, which was coupled with a dry gasifier induced by a reverse Boudouard reaction. Activated carbon (BET area 1800 m²/g) powder was mixed with K₂CO₃ powder (5 wt.%) and used to fill a dry gasifier as a solid carbon fuel, and pure CO₂ gas was supplied to the gasifier. The CO fuel generated by the reverse Boudouard reaction in the dry gasifier increased the performance of the CFC short stack. The tubular CFC short stack showed a maximum power of 29.4 W at 800 °C. It was operated under a range of operating conditions by changing the operating temperature, flow rate of the pure CO₂ and the thermal cycle operation. The results indicate that the fabricated tubular CFC is a promising power generation system candidate for many practical applications, such as residential power generation (RPG) and stationary power systems.     

Power source research at USC: Development of advanced electrocatalysts for polymer electrolyte membrane fuel cells

This paper provides an overview on the development of advanced fuel cell cathode catalysts at University of South Carolina (USC) with the emphasis on the stability of non-precious metal and Pt alloy catalysts. Nitrogen-modified carbon composite (NMCC) catalysts were developed for the oxygen reduction reaction (ORR) through the pyrolysis of cobalt (iron)-nitrogen chelate followed by the treatment combination of pyrolysis, acid leaching, and re-pyrolysis. A promising stability was observed for 1050 h fuel cell operation under current density of 200 mA cm⁻² as evidenced by a potential decay rate as low as 40 μV h⁻¹. The performance degradation mechanism of the NMCC-based fuel cell is discussed. Pt and PtPd hybrid catalysts are developed that use a NMCC, which is itself active for the ORR, instead of a conventional carbon black support. The stability test at 1 A cm⁻² indicated that the Pt/NMCC hybrid catalyst (new Pt-Co/C) is more stable than the conventional Pt-Co/C without the Co leaching out. The PEM fuel cell accelerated stress test (AST) for supports and catalysts demonstrated that their stability changes in the order: Pt₃Pd₁/NMCC hybrid catalyst > Pt/NMCC hybrid catalyst > conventional Pt/C catalyst. Moreover, the hybrid catalysts exhibit higher mass activity than the Pt/C catalysts.     

The effect of fission products on the rate of U3O8 formation in SIMFUEL oxidized in air at 250°C

The effect of fission products on the rate of U₃O₈ formation was investigated by oxidizing UO₂-based SIMFUEL (simulated high burnup nuclear fuel) and unirradiated UO₂ fuel specimens in air at 250°C for different times (1–317 days). The progress of oxidation was monitored by X-ray diffraction, revealing that the rate of U₃O₈ formation declines with increasing burnup. An expression was derived to describe quantitatively the time for U₃O₈ powder formation as a function of simulated burnup. These findings were supported by additional isochronal oxidation experiments conducted between 200 and 300°C.     

Power module stray inductance extraction: Theoretical and experimental analysis

We propose a stray inductance extraction method on power modules of the few-kilovolts/several-hundred-amperes class using only low voltages and low currents. The method incorporates a double-pulse generator, a level shifter, a switching device, and a load inductor. The conventional approach generally requires a high voltage of more than half the power module's rated voltage and a high current of around half the rated current. In contrast, the proposed method requires a low voltage and low current environment regardless of the power module's rated voltage because the module is measured in a turn-off state. Both theoretical and experimental results are provided. A physical circuit board was fabricated, and the method was applied to three commercial power modules with EconoDUAL3 cases. The obtained stray inductance values differed from the manufacturer-provided values by less than 1.65 nH, thus demonstrating the method's accuracy. The greatest advantage of the proposed approach is that high voltages or high currents are not required.     

The influence of seepage forces on ground reaction curve of circular opening

When a tunnel is excavated underneath a groundwater table, groundwater flows into the tunnel and consequently, seepage forces act on the cross-section of the tunnel. Such seepage forces significantly affect the ground reaction curve, which is defined by the relationship between the internal pressure and displacement of the tunnel wall. From a practical point of view, a simplified analytical solution of the ground reaction curve accounting for the seepage forces with steady-state flow was developed in this study based on ground reaction curve theories from earlier studies. The simplified analytical solution derived in this study was validated by numerical analysis. The changes in the ground reaction curve according to various ground and groundwater table conditions were investigated. Finally, the simplified analytical solution of the ground reaction curve developed in this study can be used for approximate design of circular openings such as tunnels excavated underneath a groundwater table with seepage forces.     

Efficient recovery of CO2 from flue gas by clathrate hydrate formation in porous silica gels

Thermodynamic measurements and NMR spectroscopic analysis were used to show that it is possible to recover CO2 from flue gas by forming a mixed hydrate that removes CO2 preferentially from CO2/N2 gas mixtures using water dispersed in the pores of silica gel. Kinetic studies with 1H NMR microimaging showed that the dispersed water in the silica gel pore system reacts readily with the gas, thus obviating the need for a stirred reactor and excess water. Hydrate phase equilibria for the ternary CO2-N2-water system in silica gel pores were measured, which show that the three-phase hydrate-water-rich liquid-vapor equilibrium curves were shifted to higher pressures at a specific temperature when the concentration of CO2 in the vapor phase decreased. 13C cross-polarization NMR spectral analysis and direct measurement of the CO2 content in the hydrate phase suggested that the mixed hydrate is structure I at gas compositions of more than 10 mol % CO2, and that the CO2 molecules occupy mainly the more abundant 5(12)6(2) cages. This makes it possible to achieve concentrations of more than 96 mol % CO2 gas in the product after three cycles of hydrate formation and dissociation. 1H NMR microimaging showed that hydrate yields of better than 85%, based on the amount of water, could be obtained in 1 h when a steady state was reached, although approximately 90% of this yield was achieved after approximately 20 min of reaction time.     

Performance studies of solid oxide fuel cell cathodes in the presence of bare and cobalt coated E-brite alloy interconnects

The electrochemical performances of La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) electrodes were studied by half-cell measurements in the absence of chromia-forming alloy, in the presence of bare and Co coated E-brite alloy interconnects, respectively. The surface and cross-section properties of the bare and Co coated E-brite alloys, and LSCF electrodes were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, and electron probe microanalysis (EPMA). The results showed a rapid degradation in LSCF performance when the bare E-brite alloy was used as interconnect. The growth of chromia scale on the E-brite alloy and the increase of Cr content throughout the LSCF electrode were observed. The uniform and dense Co coating process was developed to coat the E-brite alloy by using both electroless and electrodeposition methods. It was demonstrated that the Co layer effectively mitigates the Cr migration, leading to improved electrochemical stability of LSCF electrodes.     

Dietary supplementation of red ginseng, Chinese lizard’s tail, and Korean raspberry extracts alleviate oxidative stresses in aged rats

To investigate antioxidant efficacy of medicinal plants known to possess anti-aging properties, the herb preparations were fed to 10-month-old rats. The herb preparations included ethanol extracts of red ginseng (Panax ginseng C.A. Mayer), Chinese lizard’s tail (Saururus chinensis Hort.ex Loud), and Korean raspberry (fruits of Rubus coreanus Miquel). Plasma protein carbonyls, malondialdehyde, 8-iso-prostaglandinF2α, lymphocyte DNA damage, α-tocopherol concentration, and ferric reducing ability were measured as oxidative stress markers. The aged rats showed higher levels of malondialdehyde, 8-isoprostaglandinF2α, and protein carbonyl and lower level of α-tocopherol compared to young rats. Malondialdehyde and protein carbonyl levels were decreased in the aged rats fed diets supplemented with any of the herbal preparations. 8-Iso-prostaglandinF2α was lower in rats fed the 0.5 or 1.0% Chinese lizard’s tail- or 1% Korean raspberry extract-supplemented diet. The 1:1:1 mixture of herbal preparations decreased the level of 8-iso-prostaglandinF2α. Rats fed 1.0% Chinese lizard’s tail or Korean raspberry diets showed increased α-tocopherol level. These results indicated that the level of oxidative stress is increased in the aged animals and herbal preparations are effective in the alleviation of age-related oxidation.     

Crack identification method for tapered cantilever pipe-type beam using natural frequencies

A method to detect location and size of a crack in tapered cantilever pipe-type beam using changes in natural frequencies is presented. The boundary conditions of cantilever beam are applied to a general solution for vibrating tapered beam. Then, an equivalent bending stiffness for cracked beam is used to obtain the natural frequencies. Numerical simulations are carried out to construct a set of training patterns of a neural network, and committee of neural networks is employed to identify the crack. Crack identifications are carried out for the 16 damage cases numerically and for the 3 damage cases experimentally. The identified crack locations and sizes agree reasonably well with the exact values.