Synthesis of BaCu(B2O5) Ceramics and their Effect on the Sintering Temperature and Microwave Dielectric Properties of Ba(Zn1/3Nb2/3)O3 Ceramics

BaCu(B₂O₅) ceramics were synthesized and their microwave dielectric properties were investigated. BaCu(B₂O₅) phase was formed at 700°C and melted above 850°C. The BaCu(B₂O₅) ceramic sintered at 810°C had a dielectric constant (ɛ_r) of 7.4, a quality factor ( Q × f ) of 50 000 GHz and a temperature coefficient of resonance frequency (τ_f) of −32 ppm/°C. As the BaCu(B₂O₅) ceramic had a low melting temperature and good microwave dielectric properties, it can be used as a low-temperature sintering aid for microwave dielectric materials for low temperature co-fired ceramic application. When BaCu(B₂O₅) was added to the Ba(Zn_1/3Nb_2/3)O₃ (BZN) ceramic, BZN ceramics were well sintered even at 850°C. BaCu(B₂O₅) existed as a liquid phase during the sintering and assisted the densification of the BZN ceramic. Good microwave dielectric properties of Q × f =16 000 GHz, ɛ_r=35, and τ_f=22.1 ppm/°C were obtained for the BZN+6.0 mol% BaCu(B₂O₅) ceramic sintered at 875°C for 2 h.     

Effect of Bi2O3 Addition on the Sintering Temperature and Microwave Dielectric Properties of Zn2SiO4 Ceramics

Bi₂O₃ was added to a nominal composition of Zn_1.8SiO_3.8 (ZS) ceramics to decrease their sintering temperature. When the Bi₂O₃ content was <8.0 mol%, a porous microstructure with Bi₄(SiO₄)₃ and SiO₂ second phases was developed in the specimen sintered at 885°C. However, when the Bi₂O₃ content exceeded 8.0 mol%, a liquid phase, which formed during sintering at temperatures below 900°C, assisted the densification of the ZS ceramics. Good microwave dielectric properties of Q × f =12,600 GHz, ɛ_r=7.6, and τ_f=−22 ppm/°C were obtained from the specimen with 8.0 mol% Bi₂O₃ sintered at 885°C for 2 h.     

Short carbon nanotubes produced by cryogenic crushing

A cryogenic crushing method to produce short carbon nanotubes (CNTs) is described. Crushing CNTs at liquid nitrogen temperature allows them to be shortened and make them appreciably soluble in a solvent without any dispersant. Typical lengths of less than 500 nm were obtained from 30 min crushing. The CNTs were characterized using atomic force microscopy, thermogravimetric, and Raman analyses.     

Electrical Characteristics and Thermal Stability of Pt/HfO 2 /Si Metal-Insulatror-Semiconductror Capacitors

The HfO 2 thin films for use in gate dielectric applications were deposited at 300 onto p-type Si (100) substratee using Hf[OC(CH 3 ) 3 ] 4 as the precursor in the absence of oxygen by plasma-enhanced chemical vapor deposition. The HfO 2 films deposited in the absence of O 2 show excellent electrical properties such as low capacitance equivalent thickness (CET), good thermal stability and low charge trapping. The as-deposited films have an interfacial layer of approximately 1 nm in thickness, resulting in a decrease in the thickness of the interfacial layer by about 50% compared to films deposited in the presence of oxygen. The leakage current density of HfO 2 films was approximately 3 orders of magnitude lower than an electrically comparable SiO 2 at the same CET. The improvement of electrical properties can be attributed to the decrease in the SiO 2 interfacial layer. The thickness of the interfacial layer can be contolled by the deposition in the absence of oxygen after evacuation of the reaction chamber by means of an ultra-high vacuum.     

Optimal design of an extrusion process for a hinge bracket

This study considers process design in forming a hinge bracket. A thin hinge bracket is typically produced by bending a sheet panel or welding a hollow bar into a sheet panel. However, the hinge bracket made by bending or welding does not have sufficient durability in severe operating conditions because of the stress concentration in the bended region or the low corrosion resistance of the welded region. Therefore, this study uses forming to produce the hinge bracket part of a foldable container and to ensure durability in difficult operating conditions. An extrusion process for a T-shaped hinge bracket is studied using finite element analysis. Preliminary analysis shows that a very high forging load is required to form the bracket by forging. Therefore, extrusion is considered as a candidate process. Producing the part through the extrusion process enables many brackets to be made in a single extrusion and through successive cutting of the extruded part, thereby reducing the manufacturing cost. The design focuses on reducing the extrusion load and on ensuring shape accuracy. An initial billet is designed to reduce the extrusion load and to obtain a geometrically accurate part. The extruded part is bent frequently because of uneven material flow. Thus, extrusion die geometries are designed to obtain straight parts.

     

Performance of a flying cross bar to incapacitate a long-rod penetrator based on a finite element model

Performance of a flying cross bar, instead of the flying plate, to incapacitate the long-rod penetrator, has been evaluated numerically based on a finite element model. The length to diameter ratio, L/D, of the penetrator was 30 and the velocity was 2.0 km/s. The length of the cross bar was fixed to 0.5L and the velocity of the bar was determined from its mass and given kinetic energy. The bar was assumed to impact the mid point of the penetrator at 45° of obliquity. The efficiency of flying cross bar is maximum when the diameter of the bar is in the range between 1D and 4D depending on the energy of the bar and the distance to witness block. The protection capability of the bar has been discussed in terms of the shape and lateral displacement of the disturbed penetrator by the flying cross bar.     

Effect of B2O3 and CuO on the sintering temperature and microwave dielectric properties of the BaTi4O9 ceramics

The effect of B₂O₃ and CuO on the sintering temperature and microwave dielectric properties of BaTi₄O₉ ceramics was investigated. The BaTi₄O₉ ceramics were able to be sintered at 975^∘C when B₂O₃ was added. This decrease in the sintering temperature of the BaTi₄O₉ ceramics upon the addition of B₂O₃ is attributed to the formation of BaB₂O₄ second phase whose melting temperature is around 900^∘C. The B₂O₃ added BaTi₄O₉ ceramics alone were not sintered below 975^∘C, but were sintered at 875^∘C when CuO was added. The formation of BaCu(B₂O₅) second phase could be responsible for the decrease in the sintering temperature of the CuO and B₂O₃ added BaTi₄O₉ ceramics. The BaTi₄O₉ ceramics containing 2.0 mol% B₂O₃ and 5.0 mol% CuO sintered at 900^∘C for 2 h have good microwave dielectric properties of ε_r = 36.3, Q× f = 30,500 GHz and τ_f = 28.1 ppm/^∘C     

Comparison of plasticity models for tantalum and a modification of the PTW model for wide ranges of strain,strain rate,and temperature

Four well-known constitutive models for plastic deformation of materials, i.e., Johnson–Cook (JC), Zerilli–Armstrong (ZA), Voyiadjis and Abed (VA), and Preston–Tonks–Wallace (PTW), have been compared with reference to existing deformation data of tantalum in wide ranges of strain, strain rate, and temperature. All of these models reasonably describe the flow stress and the strain-hardening behavior only in the certain ranges of strain, strain rate, and temperature for which the models were developed. The PTW model with appropriate parameters most effectively describes the effects of strain rate and temperature in a wider range, except for strain hardening. The strain-hardening term of PTW was thus modified in the current work and the modified PTW demonstrated very good prediction for the constitutive behavior of tantalum in wide ranges of strain, strain rate, and temperature.     

Functionalized carbon nanotube-poly(arylene sulfone) composite membranes for direct methanol fuel cells with enhanced performance

A new type of composite membrane, consisting of functionalized carbon nanotubes (CNTs) and sulfonated poly(arylene sulfone) (sPAS), is prepared for direct methanol fuel cell (DMFC) applications. The CNTs modified with sulfonic acid or PtRu nanopaticles are dispersed within the sPAS matrix by a solution casting method to afford SO₃CNT-sPAS or PtRu/CNT-sPAS composite membranes, respectively. Characterization of the composite membranes reveals that the functionalized CNTs are homogeneously distributed within the sPAS matrix and the composite membranes contain smaller ion clusters than the neat sPAS. The composite membranes exhibit enhanced mechanical properties in terms of tensile strength, strain and toughness, which leads to improvements in ion conductivity and methanol permeability compared with the neat sPAS membrane. In DMFC performance tests, the use of a PtRu/CNT-sPAS membrane yields high power density compared with the neat sPAS membrane, which demonstrates that the improved properties of the composite membranes induce an increase in power density. The strategy for CNT-sPAS composite membranes presented in this work can potentially be extended to other CNT-polymer composite systems.