Piezoelectric Multilayer Ceramic/Polymer Composite Transducer with 2–2 Connectivity

A multilayer piezoelectric ceramic/polymer composite with 2–2 connectivity was fabricated by thermoplastic green machining after co-extrusion. The multilayer ceramic body was composed of piezoelectrically active lead zirconate titanate (PZN)–lead zinc niobate (PZN)-lead zirconate titanate (PZT) layers and electrically conducting PZN–PZT/Ag layers. After co-extruding the thermoplastic body, which consisted of five piezoelectric layers interspersed with four conducting layers, it was computer numeric-controlled machined to create periodic channels within it. Following binder burnout and sintering, an 18 vol% array of 190 μm thin PZT slabs with a channel size of 880 μm was fabricated. The channels were filled with epoxy in order to fabricate a PZN–PZT/epoxy composite with 2–2 connectivity. The piezoelectric coefficient (effective d ₃₃) and hydrostatic figure of merit ( d _h× g _h) of the PZN–PZT/epoxy composite were 1200 pC/N and 20 130 × 10⁻¹⁵ m²/N, respectively. These excellent piezoelectric characteristics as well as the relatively simple fabrication procedure will contribute in widening the application range of the piezoelectric transducers.     

Dehydrogenation and hydrogenation characteristics of MgH2 with transition metal fluorides

The effect of transition metal fluorides on the dehydrogenation and hydrogenation of MgH₂ has been investigated. Many of the fluorides show a considerable catalytic effect on both the dehydrogenation temperature and hydrogenation kinetics of MgH₂. Among them, NbF₅ and TiF₃ most significantly enhance the hydrogenation kinetics of MgH₂. It is suggested that hydride phases formed by the reaction between MgH₂ and these transition metal fluorides during milling and/or hydrogenation play a key role in improving the hydrogenation kinetics of MgH₂.     

Grain-Size Effects on the High-Temperature Oxidation of Modified 304 Austenitic Stainless Steel

The high-temperature oxidation behavior of modified 304 austenitic stainless steels in a water vapor atmosphere was investigated. Samples were prepared by various thermo mechanical treatments to result in different grain sizes in the range 8–30 μm. Similar Σ3 grain boundary fraction was achieved to eliminate any grain-boundary characteristics effect. Samples were oxidized in an air furnace at 700 °C with 20 % water vapor atmosphere. On the fine-grained sample, a uniform Cr₂O₃ layer was formed, which increased the overall oxidation resistance. Whereas on the coarse-grained sample, an additional Fe₂O₃ layer formed on the Cr-rich oxide layer, which resulted in a relatively high oxidation rate. In the fine-grained sample, grain boundaries act as rapid diffusion paths for Cr and provided enough Cr to form Cr₂O₃ oxide on the entire sample surface.     

Mechanical characterization of nano-structured materials using nanoindentation

The principal strengths of the nanoindentation technique, which is used extensively to measure the mechanical properties of nano/micro materials, are easy sample preparation and simple experimental method. Hardness and Young's modulus are essential properties measured by nanoindentation; hardness corresponds to resistance to plastic deformation whereas Young's modulus is related to elastic deformation. Two key difficulties arise in association with nanoindentation on small volumes: measurement accuracy and material response. Here we discuss the indentation size effect (ISE) considering tip bluntness and variation in hardness of nano-multilayers with a bilayer period, representative research on measurement improvement, and material response at nanoscales.     

Numerical simulation of hydrogen desorption from high-density metal hydride hydrogen storage vessels

Metal hydride (MH) alloys are a promising type of material in hydrogen storage applications, allowing for low-pressure, high-density storage. However, while many studies are being performed on enhancing the hydrogen storage properties of such alloys, there has been little research on large-scale storage vessels which make use of the alloys. In particular, large-scale, high-density storage devices must make allowances for the temperature variations caused by the heat of reaction between hydrogen and MH alloys, which may impact the storage characteristics. In this study, we propose a numerical model for the design and evaluation of hydrogen storage devices using MH alloys. Hydrogen desorption reaction behavior for an alloy is observed in terms of temperature and reaction rate. This behavioral correlation is used as the basis for a comprehensive simulation model of the alloy system. Calculated results are found to be in good agreement with experimentally measured data, indicating that the model may be applied to multiple system geometries, scales, and alloy compositions.     

A novel electrolytic process using a Cu cathode for the production of Mg metal from MgO

Journal of Applied Electrochemistry - An environmentally friendly and effective molten salt electrolysis process using a copper (Cu) cathode was developed for producing magnesium (Mg) metal from...     

The direct nano-patterning of ZnO using nanoimprint lithography with ZnO-sol and thermal annealing

Nano-patterned ZnO layer was fabricated by ZnO-sol imprinting with a polymeric mold, followed by annealing. Instead of polymer based imprint resin, ZnO-sol was used as an imprint resin. During the imprinting process, the organic solvent in the ZnO-sol was absorbed into a polymeric mold and thus, ZnO-sol was converted to ZnO-gel. These patterns were subsequently annealed at 650 °C for 1 h in atmospheric ambient to form ZnO patterns. X-ray diffraction (XRD) and photoluminescence (PL) confirmed that ZnO-gel was completely converted into ZnO by annealing. Using this ZnO-sol imprinting method, ZnO nano-patterns, as small as 50 nm, were fabricated on Si and oxidized Si wafer substrates. The ZnO nano-patterns were characterized using scanning electron microscopy (SEM) and Transmission electron microscopy (TEM).     

Determination of tensile properties by instrumented indentation technique: Representative stress and strain approach

Tensile properties can be evaluated by defining representative stress and strain with the parameters obtained from instrumented indentation tests using a spherical indenter. The accuracy of this approach depends strongly on how the contact depth is analyzed and how the representative stress and strain are defined. The primary factors influencing the determination of contact depth, pile-up/sink-in and elastic deflection, were quantified by analyzing indentation morphology by finite element simulation; then plastic pile-up/sink-in behavior was formulated in terms of the strain-hardening exponent and the ratio of indentation depth to indenter radius. For the representative strain, the definition by tangent function was determined to be more appropriate for assessing tensile properties based on derived behaviors of the strain-hardening exponent. This approach was experimentally verified by comparing tensile properties of 10 metallic materials from uniaxial tensile tests and instrumented indentation tests.     

Instrumented indentation of a Pd-based bulk metallic glass: Constant loading-rate test vs constant strain-rate test

Most of the previous nanoindentation experiments on bulk metallic glasses (BMGs) were made under a constant ‘loading rate,’ although ‘strain rate’ is a more useful parameter than loading rate to analyze the inhomogeneous plasticity in the BMG according to the classic free-volume theory. Here, we explore the strain-rate dependency of plastic characteristics in a Pd-based BMG through nanoindentation tests under a variety of constant strain rates (0.01–0.25 s⁻¹). The results are compared with those from nanoindentations under various constant loading rates (0.05–5 mN/s) and discussed in terms of the influences of strain rate on the plastic flow characteristics in the BMG.     

Development of a 3 MJ/750 kVA SMES system

Research and development on superconducting magnetic energy storage (SMES) system have been carried out to realize efficient electric power management for several decades. Korea Electrotechnology Research Institute (KERI) has developed a 3 MJ/750 kVA SMES system to improve power quality in sensitive electric loads. It consists of an IGBT based power converter, NbTi mixed matrix Rutherford cable superconducting magnet and a cryostat with HTS current leads. A computer code was developed to find the parameters of the SMES magnet which used minimum amount of superconductors for the same energy storage capability, and the 3 MJ SMES magnet was designed based upon that. This paper describes the fabrication and experimental results of the 3 MJ/750 kVA SMES system.