Sintering mechanism of low-temperature co-fired alumina featuring superior thermal conductivity

Densely sintered alumina is produced with a 5 wt% addition of a CuO-TiO₂-Nb₂O₅-Ag₂O sintering aid under a firing temperature of only 835°C with a prolonged holding time of 96 hours. The sintered material exhibits a thermal conductivity of 20 W/mK, which is significantly greater than that of conventional low-temperature co-fired ceramic (LTCC) materials (~2-7 W/mK). Additionally, suitable dielectric characteristics are observed, such as a relative dielectric constant ε_r of 11.3, quality factor–resonant frequency product Q × f of 4700 GHz, and temperature coefficient of resonant frequency τ_f of −87 ppm/K. The low-temperature densification is revealed to occur mainly in the solid state, before liquid phase formation. Lattice constant measurements, transmission electron microscopy, and energy dispersive spectroscopy reveal an increase in unit cell volume upon densification and the incorporation of Cu²⁺ and Ti⁴⁺ ions into the alumina lattice, which promotes densification. The diffusion speeds of Cu²⁺ and Ti⁴⁺ ions are indirectly affected by Nb and Ag atoms by lowering the additive melting temperature. Therefore, sintering additives with low melting points and elements that incorporate into the lattice of the base material are effective for low-temperature sintering of aluminum-based oxides.     

Absolute Stereochemistry of TXIB,a Bioactive Plasticizer That Inhibits Oviposition of the Peach Fruit Moth,Carposina sasakii (Lepidoptera: Carposinidae)

Journal of Chemical Ecology - TXIB (2,2,4-trimethyl-1,3-pentanediol diisobutyrate), a common plasticizer, inhibits the peach fruit moth, Carposina sasakii from ovipositing on young apple fruits....     

Dynamics of phase-separated fluids under external fields

Phase separation in external fields has attracted much attention recently. The reason is twofold. Since kinetics of phase separation and morphology of growing domains can be controlled by external fields, it is of technological importance. The other is that existence of mesoscale domains causes curious dynamical properties in fields, which provides us with a fundamental statistical dynamic problem. One example is a phase separation of binary fluids under shear flow. Phase-separated domains are deformed under the field, which causes burst, fusion, and reconnection of domains so that extra energy dissipation occurs in these processes. Because of this large deformation of domains, the system exhibits quite unusual rheological behavior. The kinetics of phase separation of binary fluids is also influenced by an external electric field when the new phases have different dielectric constants. Deformation and interaction of domains in an electric field are investigated by means of an interfacial approach.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Melt‐electrospun fibers obtained from polypropylene/poly(ethylene‐co‐vinyl alcohol)/polypropylene three‐layer films

Production of polypropylene (PP) nanofibers below 1 μm in average diameter is difficult with conventional melt‐spinning. A nozzle‐free melt‐type electrospinning (M‐ESP) system with a line‐like CO₂ laser beam melting device were used to produce PP nanofibers. To achieve the purpose, core [poly(ethylene‐co‐vinyl alcohol) (EVOH)]–clad (PP) nanofibers (average diameter, 0.88 μm) were fabricated from PP/EVOH/PP three‐layer films using the M‐ESP. The core–clad structure was formed by a wrapping phenomenon caused by the difference in the melt flow rates (MFRs) of PP and EVOH melts. Hollow PP nanofibers were obtained from the core–clad nanofibers by extraction of EVOH. Nanofiber diameter and hollow wall thickness could be altered by changing the MFR of the PP melt. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46393.     

Four-leg independent mechanism for MEMS microrobot

In this paper, the development of a quadruped micro-electro mechanical system (MEMS) microrobot with a four-leg independent mechanism is described. As the actuator mechanism inside small robot bodies is difficult to realize, many microrobots use external field forces such as magnetism and vibration. In this paper, artificial muscle wires that are family of shape memory alloy are used for the force of the actuator. The artificial muscle wire shows the large displacement by passing the electrical current through the material itself. The double four-link mechanism is adopted for the leg system. The link mechanism transforms the linear motion of the artificial muscle wire to the foot step-like pedaling motion. The location of the backward swing motion is lower than that of forward swing motion. This motion generates the locomotion force. As a result, the total length of the constructed quadruped MEMS microrobot was 6 mm. The microrobot could perform similar gait pattern changes as the quadruped animal.     

Preparation, structure, and electrical conductivity of vanadium fluoridegraphite intercalation compound

Graphite intercalation compounds (GIC) of vanadium fluoride have been prepared in a fluorine atmosphere. The GICs prepared from highly oriented pyrolytic graphite (HOPG) were stage 1–8 compounds with composition, C_8.4–79.5VF_5.8–6.0. The apparent size of intercalated VF₆⁻(d_i) decreased from 5.33 Å to 4.15 Å along the c axis with increasing x in C_xVF₆. Various intercalated structures of VF₆⁻ between the carbon layers have been proposed for this change in d_i values. The compounds with small d_i around 4.2 Å show high stability in the air, which is due to the nestling of the VF₆⁻ anion between the carbon layers. Electron diffraction measurements have indicated that a well-nestled stage 2 GIC has high regularity in orientation of intercalated VF₆⁻ anions, which make two large unit cells of the hexagonal system ( ) with the different vectors by ±14° from that of graphite lattice. The ¹⁹F-NMR spectra and X-ray diffraction data in the low temperature region suggest a reversible phase transition. The highest electrical conductivity was 1.97 × 10⁵Scm⁻¹, which is 12 times that of pristine HOPG.     

The phospholipids of rabbit type II alveolar epithelial cells: Comparison with lung lavage,lung tissue,alveolar macrophages,and a human alveolar tumor cell line

The phospholipid composition of type II alveolar epithelial cells from the rabbit was compared with that of alveolar macrophages, lung lavage and lung tissue. In addition, the phospholipid composition of a human alveolar tumor cell line, which is morphologically similar to type II cells, was examined. Phosphatidylcholine accounted for 48% of the total phospholipid in the type II cells, 41% in the tumor cells, and 30% in the macrophages. Phosphatidylcholine was 51% disaturated in the type II cells, 54% in lung lavage, 39% in whole lung, 29% in lavaged lung and macrophages, and 16% in the tumor cells. Palmitic acid was the major fatty acid in phosphatidylcholine from all samples with the exception of the tumor cells in which almost half of the fatty acids were accounted for by oleic acid. The phospholipids of the type II cells were more similar to those of lung lavage, and thus surfactant, than to lung tissue and macrophages. This is consistent with their supposed role in surfactant production. The tumor cells, although morphologically similar to type II cells, were quite different with respect to phospholipid composition.     

Carbonation reaction of (Ca,Mg)O protective layer on plasma display panel

We have been applying a low discharge voltage (Ca, Mg)O protective layer to plasma display panels to reduce their power consumption. However, (Ca, Mg)O is highly reactive with CO₂, and the resulting carbonate formation during high‐temperature panel sealing in air impairs the low discharge voltage characteristic. We investigated the mechanism of the carbonation reaction that occurs on a (Ca, Mg)O surface during annealing in air at 450°C and found that the CO₂ diffuses through the formed CaCO₃ layer and that a (Ca, Mg)O + CO₂ → CaCO₃ + MgO reaction then occurs. This carbonation reaction evidently stops when the growing MgO finally forms a layer at all boundaries between the CaCO₃ and (Ca, Mg)O regions.     

Ca2+-ATPase Molecules as a Calcium-Sensitive Membrane-Endoskeleton of Sarcoplasmic Reticulum

The Ca²⁺-transport ATPase of sarcoplasmic reticulum (SR) is an integral, transmembrane protein. It sequesters cytoplasmic calcium ions released from SR during muscle contraction, and causes muscle relaxation. Based on negative staining and transmission electron microscopy of SR vesicles isolated from rabbit skeletal muscle, we propose that the ATPase molecules might also be a calcium-sensitive membrane-endoskeleton. Under conditions when the ATPase molecules scarcely transport Ca²⁺, i.e., in the presence of ATP and ≤ 0.9 nM Ca²⁺, some of the ATPase particles on the SR vesicle surface gathered to form tetramers. The tetramers crystallized into a cylindrical helical array in some vesicles and probably resulted in the elongated protrusion that extended from some round SRs. As the Ca²⁺ concentration increased to 0.2 µM, i.e., under conditions when the transporter molecules fully carry out their activities, the ATPase crystal arrays disappeared, but the SR protrusions remained. In the absence of ATP, almost all of the SR vesicles were round and no crystal arrays were evident, independent of the calcium concentration. This suggests that ATP induced crystallization at low Ca²⁺ concentrations. From the observed morphological changes, the role of the proposed ATPase membrane-endoskeleton is discussed in the context of calcium regulation during muscle contraction.