Preparation and properties of borosilicate glass-coated Cu powder for internal electrode of multilayer ceramic device

In this study, a process was proposed which allows a base metal electrode to be burnt-out in an oxidative atmosphere for fabrication of multilayer ceramic device. To protect Cu in an oxidative atmosphere, the Cu powder was coated with borosilicate glass via a sol-gel process. The oxidation resistance and shrinkage of the glass-coated Cu were investigated. When a 10% glass-coated Cu was heated up to 500°C under an oxidative atmosphere, the Cu could survive without formation of copper oxide. The oxidation of the Cu was observed when heating at temperatures above 700°C. This might be due to exposure of Cu to oxidative atmosphere related to softening behavior of glass. The glass-coated Cu exhibited a shrinkage behavior which follows the shrinkage behavior of glass in the low temperature range and the shrinkage of pure Cu in the high temperature range. To measure the electrical conductivity of the glass-coated Cu electrode, the Cu pastes were prepared and printed onto alumina substrate. The binder-burn-out process of the glass-coated Cu was carried out at 550°C under an air atmosphere, and was then sintered at 1000°C under a nitrogen atmosphere. The electrical conductivity of the Cu electrode measured was above 10⁴ /Ωcm which means that it can be used as the internal electrode of a multilayer device.     

Lead-free NKN-5LT piezoelectric materials for multilayer ceramic actuator

As a candidate for lead-free piezoelectric materials, Li₂O excess 0.95(Na_0.5K_0.5)NbO₃–0.05LiTaO₃ (NKN-5LT) ceramics were developed by conventional sintering process. Sintering temperature was lowered by adding Li₂O as a sintering aid. Abnormal grain growth in NKN-5LT ceramics was observed with varying Li₂O content. In the 1 mol% Li₂O excess NKN-5LT samples sintered at 1000°C for 4 h in air, electromechanical coupling factor and piezoelectric constant of NKN-5LT ceramics were found to reach the highest values of 0.37 and 250 pC/N, respectively. Lead-free piezoelectric ceramic, Li₂O excess NKN-5LT, multilayer ceramic actuators (MLCA) were fabricated. 10?×?10?×?1 mm³ size MLCAs were fabricated by conventional tape casting method. The displacement of Li₂O excess NKN-5LT MLCA with 3 mm thickness was ~1 μm at 150 V.     

Topological design sensitivity on the air bearing surface of head slider

In this study, a topological design sensitivity of the air bearing surface (ABS) is suggested by using an adjoint variable method. The discrete form of the generalized lubrication equation based on a control volume formulation is used as a compatible condition. A residual function of the slider is considered as an equality constraint function, which represents the slider in equilibrium. The slider thickness parameters at all grid cells are chosen as design variables since they are the topological parameters determining the ABS shape. Then, a complicated adjoint variable equation is formulated to directly handle the highly nonlinear and asymmetric coefficient matrix and vector in the discrete system equation of air-lubricated slider bearings. An alternating direction implicit (ADI) scheme is utilized for the numerical calculation. This is an efficient iterative solver to solve large-scale problem in special band storage. Then, a computer program is developed and applied to a slider model of a sophisticated shape. The simulation results of design sensitivity analysis (DSA) are directly compared with those of FDM at the randomly selected grid cells to show the effectiveness of the proposed approach. The overall distribution of DSA results are reported, clearly showing the region on the ABS where special attention should be given during the manufacturing process.     

Erosive Wear Mechanism of New SiC/SiC Composites by Solid Particles

A solid-particle erosive wear test by impinging silicon carbide (SiC) powders was carried out at room temperature over a range of median particle sizes of 425–600 μm, speed of 100 m/s and impact angle of 90° and assessed by wear measurements and scanning electron microscopy. Erosive wear behaviour was examined on newly fabricated nano-powder infiltration and transient eutectoid (NITE) SiC/SiC composites and two commercial composites by the chemical vapour infiltration (CVI) and NITE fabrication route. Microstructural observation was performed to examine the correlation between erosive wear behaviours and fabrication impurities. Conspicuous defects were observed in the prototype materials as the forms of porosity, fibre deformation, residual oxide, pyrolytic carbon (PyC) deformation, PyC cleavage, among others. Erosive wear behaviour was rather serious in the prototype of fabricated composites, which employ pre-SiC fibre and phenolic resin. Two dominant erosive wear mechanisms were observed: delamination of constituents, mainly caused by erosive crack propagation, and fragmentation and detachment of constituents, which usually resulted from erosive impact. A unit size of delamination was the most decisive factor affecting wear volume. The bonding strength of each constituent was mostly affected by various forms of porosities. Therefore, the fundamental cause and subsequent results must be carefully elucidated. The correlation of microstructural defect and wear behaviour was investigated with the aim of reducing dominant wear by improving fabrication conditions. The final product of the cost-effective composite had a 2.5-fold higher resistance than the commercial CVI composite. Consequently, by controlling fabrication impurities, we have been successful in developing and improving a new fabrication technique; consequently, the known defects are rarely observed in final product. A schematic wear model of erosive wear mechanisms is proposed for the newly fabricated SiC/SiC composites under particle erosion.     

Antioxidant activities of phlorotannins purified from Ecklonia cava on free radical scavenging using ESR and H2O2-mediated DNA damage

The potential antioxidant activities of three phlorotannins (phloroglucinol, eckol and dieckol) purified from Ecklonia cava collected in Jeju Island were investigated to evaluate their potential value as the natural products for foods or cosmetic application. In this study, antioxidant activities were measured by electron spin resonance spectrometry (ESR) technique for scavenging effects of free radicals such as 1,1-diphenyl-2-picrylhydrazyl (DPPH), alkyl, hydroxyl (HO^•) and superoxide anion radical (O₂ ^•−) and by comet assay for protecting effects against H₂O₂-mediated DNA damage. The results show that all the phlorotannins have the potential DPPH, alkyl, hydroxyl and superoxide radical scavenging activities. Especially, eckol samples scavenged around 93% of DPPH at 0.25, 0.5, 1 mg/mL of concentrations and were higher than the other phlorotannins, such as phloroglucinol and dieckol samples. Also, protecting effects of the phlorotannins against H₂O₂-mediated DNA damage increased with increased concentrations of the samples in the L5178 mouse T-cell lymphoma cell lines (L5178Y-R). In conclusion, these results suggest that the three phlorotannins purified from E. cava have the potential inhibitory effect on H₂O₂-mediated DNA damage and harmful free radicals and can be used as antioxidants in cosmetic, foods and drug industry.     

Relation between piezoelectric properties of ceramics and output power density of energy harvester

(1?x)Pb(Zr_0.47Ti_0.53)O₃–xPb[(Zn_0.4Ni_0.6)_1/3Nb_2/3]O₃ [(1?x)PZT–xP(ZN)N] ceramics with 0.26 ≤ x ≤ 0.31 were sintered at 1100 °C, and their energy harvesters were fabricated. All specimens exhibit a similar energy convergence efficiency. However, the transduction coefficient (d₃₃ × g₃₃) increased with x, reaching 21.5 × 10^?15 m²/N for the x = 0.31specimen; the figure-of-merit of the specimens shows a similar variation. The output energy density of the energy harvester also increased with x, and a high output energy density of 231 mW/cm³ was obtained for the harvester fabricated using the x = 0.31 specimen, indicating that the d₃₃ × g₃₃ value significantly affects the output energy density of the energy harvester.     

Kriging interpolation methods in geostatistics and DACE model

In recent study on design of experiments, the complicate metamodeling has been studied because defining exact model using computer simulation is expensive and time consuming. Thus, some designers often use approximate models, which express the relation between some inputs and outputs. In this paper, we review and compare the complicate metamodels, which are expressed by the interaction of various data through trying many physical experiments and running a computer simulation. The prediction model in this paper employs interpolation schemes known as ordinary kriging developed in the fields of spatial statistics and kriging in Design and Analysis of Computer Experiments (DACE) model. We will focus on describing the definitions, the prediction functions and the algorithms of two kriging methods, and assess the error measures of those by using some validation methods.     

Development of microbial genome-probing microarrays using digital multiple displacement amplification of uncultivated microbial single cells

A crucial problem in the use of previously developed genome-probing microarrays (GPM) has been the inability to use uncultivated bacterial genomes to take advantage of the high sensitivity and specificity of GPM in microbial detection and monitoring. We show here a method, digital multiple displacement amplification (MDA), to amplify and analyze various genomes obtained from single uncultivated bacterial cells. We used 15 genomes from key microbes involved in dichloromethane (DCM)-dechlorinating enrichment as microarray probes to uncover the bacterial population dynamics of samples without PCR amplification. Genomic DNA amplified from single cells originating from uncultured bacteria with 80.3-99.4% similarity to 16S rRNA genes of cultivated bacteria. The digital MDA-GPM method successfully monitored the dynamics of DCM-dechlorinating communities from different phases of enrichment status. Without a priori knowledge of microbial diversity, the digital MDA-GPM method could be designed to monitor most microbial populations in a given environmental sample.     

Analysis of yeast and archaeal population dynamics in kimchi using denaturing gradient gel electrophoresis

Kimchi is a traditional Korean food that is fermented from vegetables such as Chinese cabbage and radish. Many bacteria are involved in kimchi fermentation and lactic acid bacteria are known to perform significant roles. Although kimchi fermentation presents a range of environmental conditions that could support many different archaea and yeasts, their molecular diversity within this process has not been studied. Here, we use PCR-denaturing gradient gel electrophoresis (DGGE) targeting the 16S and 26S rRNA genes, to characterize bacterial, archaeal and yeast dynamics during various types of kimchi fermentation. The DGGE analysis of archaea expressed a change of DGGE banding patterns during kimchi fermentation, however, no significant change was observed in the yeast DGGE banding patterns during kimchi fermentation. No significant difference was indicated in the archaeal DGGE profile among different types of kimchi. In the case of yeasts, the clusters linked to the manufacturing corporation. Haloarchaea such as Halococcus spp., Natronococcus spp., Natrialba spp. and Haloterrigena spp., were detected as the predominant archaea and Lodderomyces spp., Trichosporon spp., Candida spp., Saccharomyces spp., Pichia spp., Sporisorium spp. and Kluyveromyces spp. were the most common yeasts.     

Comparison of the Crystallization Behavior of Silica Between Mg- and Al-Phosphate Used in Tension Coatings of Grain-Oriented Electrical Steel

Metals and Materials International - The effect of the phosphate component on the thermal stability of tension coatings was investigated with a focus on the crystallization behavior of amorphous...