Piezoelectric and dielectric properties of low temperature sintering Pb(Mn1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)O3–Pb(Zr0.48Ti0.52)O3 ceramics with variation of sintering time

Pb(Mn_1/3Nb_2/3)O₃–Pb(Zn_1/3Nb_2/3)O₃–Pb(Zr_0.48Ti_0.52)O₃ (abbreviated as PMN–PZN–PZT) ceramics containing Li₂CO₃, Bi₂O₃ and CuO as sintering aids were fabricated using two-stage calcinations method in order to develop low temperature sintering ceramics for multilayer piezoelectric actuators. Their dielectric and piezoelectric properties were investigated according to the variation of sintering time. All the specimens sintered at 930°C for 60~150 min showed tetragonal phases without secondary phases. Electromechanical coupling factor (kp), dielectric constant (ε _r) and piezoelectric constant (d ₃₃) increased with the increase of the sintering time. The mechanical quality factor (Qm) exhibited maximum of 1,815 with the increase of sintering time for 120 min and then slightly decreased. At the sintering temperature of 930°C and the sintering time of 120 min, the optimal values such as the density of 7.69 g/cm³, kp of 0.516, ε _r of 1158, Qm of 1815, and d ₃₃ of 287 pC/N were found for multilayer piezoelectric actuators.     

Phase transformation and oxidation behavior of Pt-modified MCrAlY coatings

The effects of platinum (Pt) layer on phase transformation and oxidation behavior of MCrAlY (M = Co, Ni) coatings were investigated by isothermal and cyclic oxidation tests at temperature of 1100 °C. Pt layer of about 5 μm thickness was deposited on MAR M247-DS superalloy by an electroplating method, and then the MCrAlY layers were coated with air plasma spray (APS) and vacuum plasma spray (VPS) methods. APS process creates internal oxides and interface voids, whereas the VPS process shows fewer voids in the interface between the MCrAlY layer and the superalloy used as substrate. The oxides and voids formed in the APS process deteriorate the oxidation resistance, indicating that the oxides and voids are transferred to Al₂O₃ compounds during the oxidation tests. The Pt layer shows a strong affinity with Ni element and a weak affinity with Co and Cr elements, resulting in the formation of β-(Ni,Pt)Al phase. The Pt pre-coated layer forces down for the diffusion of soluble elements to get the reduced deplete zone in the superalloy. The VPS process enhances the oxidation resistance of the MCrAlY coating and shows better bonding strength, owing to the generation of homogenous microstructure in the coating and less processing defects.     

Synthesis of hollow and mesoporous polycaprolactone nanocapsules

New polycaprolactone (PCL) nanocapsules with a hollow core and mesoporous shell have been synthesized. The PCL nanocapsules have an average size of about 100 nm and a mesopores shell of about 20 nm. The size of the mesopores on the shell is about 4 nm. Fluorescent dye Rhodamin 6G was loaded into the nanocapsules to demonstrate the mesoporous structure of the capsules and their ability to load small molecules. The nanocapsules with such a structure can be used in many areas for various applications such as drug and gene delivery.     

Characterization of subtilin KU43 Produced by Bacillus subtilis KU43 isolated from traditional Korean fermented foods

An antimicrobial peptide produced by Bacillus subtilis KU25, KU43, and KU44 was isolated from traditional Korean fermented foods and characterized. It was named as subtilin KU25, KU43, and KU44. Subtilin KU25, KU43, and KU44 were sensitive against α-chymotrypsin, protease XIII, and various proteinase enzymes, respectively. B. subtilis KU43 was selected as the producer with the broadest antimicrobial spectrum. Subtilin KU43 was stable at a pH range of 3 to 9 for 4 h, and withstood exposure to temperatures of 50–90°C for 30 min. The mode of inhibition against Listeria monocytogenes ATCC 15313 involved a bactericidal effect by a reduction in the cell numbers and breakage of the indicator cell membranes. The molecular mass of subtilin KU43 was measured at approximately 3.5 kDa. These results demonstrate the development of novel strains from traditional Korean fermented foods, and illustrate the possibility that some of these strains might generate a natural preservative compound.     

Analysis of thermoelastic characteristics for vertical-cracked thermal barrier coatings through mathematical approaches

Thermoelastic characteristics of thermal barrier coatings (TBCs) with vertical cracks were analyzed through mathematical approaches to investigate the thermoelastic behaviors of TBCs in a service temperature. TriplexPro?-200 system was applied to prepare the relatively dense TBC using METECO 204NS powder. The microstructure of top coat in the TBC was just controlled to create vertical type cracks by reheating without powder feeding in same equipment and rapid cooling process. A couple of governing partial differential equations were derived based on the thermoelastic theory, and a finite volume model was developed to the governing equations to evaluate the thermoelastic characteristics, such as temperature distribution profile, displacement, and stress, inducing a thermal fatigue. For the specimen with two or more vertical type cracks, smaller displacement appears to longitudinal direction and larger displacement to radial direction as the number of crack increases. In the longitudinal stress distribution profiles to z-direction, the tensile stress at the interface between the bond coat and the substrate converts into the compressive stress when the specimen has vertical cracks more than two, while larger magnitude undulation develops for the specimen with smaller number of crack in the radial stress distribution profiles. The results obtained demonstrate that multiple vertical cracks enhance the thermal durability and extend the lifetime of TBCs.     

Approximate yield criterion for voided anisotropic ductile materials

As most fractures of ductile materials in metal forming processes occurred due to the results of evolution of internal damage — void nucleation, growth and coalescence. In this paper, an approximate yield criterion for voided (porous) anisotropic ductile materials is developed. The proposed approximate yield function is based on Gurson’s yield function in conjunction with the Hosford’s non-quadratic anisotropic yield criterion in order to consider the characteristic of anisotropic properties of matrix material. The associated flow rules are presented and the laws governing void growth with strain are derived. Using the proposed model void growth of an anisotropic sheet under biaxial tensile loading and its effect on sheet metal formability are investigated. The yield surface of voided anisotropic sheet and void growth with strain are predicted and compared with the experimental results.     

Interfacial Structure of Ordered Domains in Barium Lanthanum Magnesium Niobate

Microstructural studies on the interfacial boundaries of 1:1 and 1:2 ordered domains in (Ba_0.9La_0.1)(Mg_0.37Nb_0.63)O₃ were conducted using high-resolution transmission electron microscopy and X-ray diffractometry. Both 1:2 and 1:1 ordered domains coexisted in a fully ordered single grain. Each ordered domain occupied its own region, and the interfaces were atomically sharp and coherent. The wavelength of the superlattice modulation was ∼0.47 nm in the 1:1 ordered domain and ∼0.71 nm in the 1:2 ordered domain. The transition from the 1:2 ordered region to the 1:1 ordered region was clearly shown at the interface. These observations well support the structural models that have been previously presented.     

Fiberoptic intrinsic fluorescence for in-situ cure monitoring of amine cured epoxy and composites

The cure reactions of epoxy-diamine and its composites are monitored in-situ using the intrinsic fluorescence of the aromatic diamine, diaminodiphenyl sulfone (DDS). With a fiberoptic fluorimeter, in-situ cure monitoring was performed via a single fiber, distal-end probe, in neat epoxy as well as in commercial grade prepregs containing graphite fibers and DDS curing agent. The prepregs were investigated during multiply lamination in an oven. The fluorescence excitation spectra were obtained by emitting at 420 nm with a scan range of 320 to 400 nm, and the DDS peak position was determined as a function of cure time and temperature. The DDS spectra show a progressive red shift up to 24 nm when the primary amine is reacted with epoxide to become the secondary and the tertiary amines. The spectral shift of the DDS is also correlated with the extent of epoxide reaction determined by the Fourier transform infrared (FTIR) spectroscopy. Both data exhibit a linear relation, consistent with the behavior of the DDS peak shift, which increases linearly with the amine reaction. The excitation spectra also show a temperature dependency such that the amount of red shift increases with the measurement temperature in a manner that can be described by an exponential function. The temperature effects also depend on the state of cure in the sample. The temperature correction can be made by the application of an empirically developed equation. Thus, a direct comparison can be made among the on-line data obtained under varying conditions of cure, by reducing the spectral data to any reference temperature. This intrinsic fluorescence technique is much simpler than the previously reported extrinsic fluorophore technique, which requires the addition of an extrinsic fluorophore and an internal dye, and can be applied to any commercial prepregs containing DDS, thus making it a very powerful and widely applicable monitoring tool for composite processing.     

Xenon ion laser-induced fluorescence using a visible tunable diode laser near 680 nm

Laser-induced fluorescence (LIF) measurements have been performed for the first time in a low temperature (Te approximately 0.6 eV) Xe plasma using a tunable diode laser in the visible range of wavelengths. The transition in Xe II involved the (3P1)5d[3]7/2 metastable state and the excitation wavelength was found to be 680.570+/-0.001 nm (air). LIF measurements of I 2 in a room temperature iodine gas cell were used to monitor the wavelength of the laser during the measurements.