Synthesis and Magneto-mechanical Properties of Ce-TZP/La M-Type Hexaferrite Composite

An in situ composite composed of ceria-stabilized tetragonal zirconia polycrystals (Ce-TZP) and La{Co_0.5Fe_0.5(Fe_0.9Al_0.1)₁₁}O₁₉ was synthesized from a powder mixture of Ce-TZP, La(Fe_0.9Al_0.1)O₃, Fe₂O₃, Al₂O₃, and CoO. The dense Ce-TZP dispersed with platelike La{Co_0.5Fe_0.5(Fe_0.9Al_0.1)₁₁}O₁₉ crystals as a second phase were formed after sintering from 1250° to 1350°C. The saturation magnetization of the in situ composite Ce-TZP/La{Co_0.5Fe_0.5(Fe_0.9Al_0.1)₁₁}O₁₉ was proportional to the mass fraction of the hexaferrite second phase in Ce-TZP. The coercivity of the composite with a 20 mass% of second phase decreased from 9.14 to 2.52 kOe (from 728 to 201 kA/m) after the pulverization of the composite. The susceptibility (χ) increased by 15%–25% under uniaxial stress on the composite. The change of the susceptibility (Δχ/χ) value increased with decreasing the mass fraction of the second phase in the composite. The Δχ was found to increase linearly with applied stress and abruptly change on cracking, which is expected for the application in fracture sensing of the composite.     

Melt viscosity and flow birefringence of polycarbonate

Melt viscosity and flow birefringence of bisphenol A-type polycarbonate were measured and analyzed by the application of rubber-like photoelastic theory. The melt viscosity in the Newtonian flow region increased with the molecular weight to the power of 3.4. In polycarbonate, the shear stress of the Newtonian flow region was to 10⁶ dyn/cm², whereas in PMMA it was at most 3 = 10⁵ dyn/cm². The flow birefringence δn has a linear relation with shear stress S, that is δn = 5.7 × 10^?10 S. The principal polarization difference of flow unit α₁ – α₂ was 1.62 × 10^?23 cm³, which was obtained by the application of the rubber-like elastic theory. In PMMA, it was 3.9 = 10^?25 cm³; about 1/40 of that was polycarbonate. The anisotropy of polarizability of the flow unit of polycarbonate was also about 40 times larger than that of PMMA. So the anisotropy reflected the large flow birefringence of the polycarbonate.     

Interfacial tension of demixed polymer solutions near the critical temperature: polystyrene + methylcyclohexane

Interfacial tension between demixed solutions of polystyrene + methylcyclohexane has been measured near the critical temperature as a function of temperature using polystyrenes with molecular weights 9000 ～ 1.26 × 10⁶. The critical exponent for the interfacial tension was determined to be about 1.30 for the lower molecular weight systems. However, for higher molecular weights the exponent could not be obtained because the system departed from critical behaviour. Magnitudes of the interfacial tension were proportional to about N^?0.44, where N is the polymerization index. Experimental results were compared with the recently-proposed theories and found to be in qualitative agreement. The tricritical theory of polymer solutions was also compared with the experimental results.     

Surface Orientation and Wetting Phenomena in Si/α-Alumina System at 1723 K

Wetting phenomena and the effect of alumina surface orientation on the wettability in Si/α-Al₂O₃ system were studied by an improved sessile drop method using     ,     , C(0001) faces of single crystals and polycrystals at 1723 K in a reducing Ar–3% H₂ atmosphere. The contact angles show a vibration behavior for all the single crystals but to a less extent for the polycrystals. The extent of the vibration correlates not only with the reaction intensity but also with the stability of the Si droplet on the alumina surfaces. The interfacial reaction leads to the formation of a series of reaction rings, which is more serious at the single crystal surfaces. More importantly, the wettability is dependent on the alumina surface orientation, with the intrinsic contact angles being about 98±2°, 101±1°, 69±1°, and 98±2°, respectively, for the     ,     , C(0001) and polycrystal α-Al₂O₃ substrates. The much smaller contact angle for molten Si on the C(0001) surface is explained by the favorable reduction in the Si/α-Al₂O₃ interfacial free energy by the terminated and enriched aluminum atoms at the reconstructed     surface. The importance of the aluminum presence at the Si/α-Al₂O₃ interface to the wettability of this system was further demonstrated by a substantial improvement in the wettability of the     α-Al₂O₃ substrates by Si–Al alloys.     

A superconducting filter to separate an oxygen and argon mixture

Hot isostatic pressing in an oxygen atmosphere, known as O₂-HIP method, has been used successfully to synthesize oxide materials, as well as to produce porous materials. In this paper a porous superconducting oxide is synthesized by this method and its application as a gas filter is described. Porous superconductors can be used to separate a mixture of paramagnetic and diamagnetic gases, such as oxygen and argon. Separation occurs after a magnetic field is applied and is based on the Meissner effect. Experimental results showed that the oxygen content of an oxygen/argon mixture increased after passing through a filter with large pore size (about 10 m).     

Additional kernel observer: privilege escalation attack prevention mechanism focusing on system call privilege changes

International Journal of Information Security - Cyberattacks, especially attacks that exploit operating system vulnerabilities, have been increasing in recent years. In particular, if administrator...     

Phase evolution and <110>-orientation mechanism in RTGG-processed BaTiO3 ceramics with electrical properties

The <110>-oriented BaTiO₃ ceramics were fabricated using BaCO₃ matrix and H_1.08Ti_1.73O₄.nH₂O (HTO) template particles, and the mechanism of BaTiO₃ phase formation was investigated. The dielectric, ferroelectric, and piezoelectric properties were also investigated. The transformation of the HTO phase into the TiO₂ bronze or TiO₂ (B) phase was observed at 600°C, where the BaTiO₃ nucleation was accompanied by the formation of a Ba₂TiO₄ phase. The TiO₂ phase reacted with the Ba₂TiO₄ phase at 800°C to give a BaTiO₃ phase, whereas its reaction with the BaTiO₃ resulted in the formation of BaTi₂O₅ phase that got decomposed into BaTiO₃ and Ba₆Ti₁₇O₄₀ phase at sintering temperature ≥1300°C. Sintering with samples’ embedding in BaTiO₃ powders prevented the formation of the Ba₆Ti₁₇O₄₀ secondary phase. The crystallographic orientation along the <110> direction (F₁₁₀) was developed by the epitaxial grain growth mechanism. In addition to the contribution of the grain-size increment for enhancing the F₁₁₀, the preservation of the platelike structure was also found to have a significant impact. The ceramics prepared by the embedded sintering (grain size ≈12.4 µm and F₁₁₀ = 83%) exhibited the room-temperature dielectric constant of 1708 and piezoelectric strain constant of 445 pm/V, which are higher than those of the BaTiO₃ ceramics with randomly oriented grains.     

Influences of temperature and Sn-addition on microstructural evolution of Ag during FSW

ABSTRACT

The microstructural evolutions of pure Ag and Ag-0.75 wt-%Sn during rapid cooling friction stir welding (FSW) were examined. At the lower welding temperature of FSW conditions, the annealing twinning was highly suppressed and the microstructural evolution was dominated by the discontinuous dynamic recrystallisation (DDRX) via the high angle boundary (HAB) bulging. The fully recrystallised microstructure was remarkably finer than that formed through the frequent annealing twinning at the higher welding temperature. Moreover, the Sn-addition caused the HAB bulging due to the inhibition of dynamic recovery and decreased mobility of grain boundaries. With decreasing the ratio of the peak temperature to the recrystallisation temperature, the dominant grain refinement mechanism is implied to change from the annealing twinning to the DDRX.     

Microstructure development of steel during severe plastic deformation

The microstructure development during plastic deformation was reviewed for iron and steel which were subjected to cold rolling or mechanical milling (MM) treatment, and the change in strengthening mechanism caused by the severe plastic deformation (SPD) was also discussed in terms of ultra grain refinement behavior. The microstructure of cold-rolled iron is characterized by a typical dislocation cell structure, where the strength can be explained by dislocation strengthening. It was confirmed that the increase in dislocation density by cold working is limited at 10¹⁶m⁻², which means the maximum hardness obtained by dislocation strengthening is HV3.7 GPa. However, the iron is abnormally work-hardened over the maximum dislocation strengthening by SPD of MM because of the ultra grain refinement caused by the SPD. In addition, impurity of carbon plays an important role in such grain refinement: the carbon addition leads to the formation of nano-crystallized structure in iron.