Impacts of layout,surface condition and alloying elements on diffusion welding of micro process devices

The formation of a monolithic part during diffusion bonding is accompanied by the diffusion of atoms across the bonding planes. At sufficient low roughness, it mainly depends on the temperature and dwell time. At the same time, the diffusion process competes against grain growth. By adjusting an appropriate level of bearing pressure, it is possible to control deformation taking into account additional parameters resulting from mechanical microstructures and the design and aspect ratio of the part. Furthermore, material properties, such as the content of alloying elements, the degree of cold work hardening and the grain size, have an impact on diffusion and deformation behavior. Also the surface condition of mating surfaces is important to diffusion kinetics and the quality of the joint. Especially passivation layers of corrosion‐resistant alloys, such as stainless steels and nickel‐based alloys, impair diffusion. In contrast to this, cold work hardening at low depth below the surface, e. g. by means of a blasting processes, may facilitate formation of a good bond and help to limit grain size. For oxide dispersion‐strengthened materials, additional impacts on diffusion bonding behavior applies.     

Investigations of geometrical structure and morphology of samples made of hard machinable materials after wire electrical discharge machining and vibro‐abrasive finishing

In this article the results concerned influence of processing conditions of the wire electrical discharge machining and vibro‐abrasive machining on the surface layer and morphology of samples made of hard machinable materials used in aircraft industry like: Titanium 5553 β, Inconel 617, Hastelloy X and Magnesium AZ31 have been presented. For this purpose the cubic and cylindrical samples made of hard machinable alloys have been prepared using optimal electric parameters of wire‐cut electrical discharge machining and finally they have been polished using circular vibratory finishing technology and different ceramic shaped stones.     

Origin of the temperature stability of dielectric constant in CaCu3Ti4O12

The temperature and dc bias stability of the dielectric constant and loss tangent of CaCu₃Ti₄O₁₂ samples sintered under different oxygen atmospheres are discussed. The results suggest that the metal-oxygen vacancy related defects not only provide the charge carriers for the conduction (defect doping) but also contribute to the huge permittivity in the way of defect dipoles repositioning under charge carrier hopping. The charge localization in a specific copper-oxygen vacancy defect complex is the reason of the huge and stable permittivity and low dielectric loss in the middle temperature range, 90 K-200 K (20 Hz), while the implementation of the large barrier layer height needs a contribution by the titanium oxygen vacancy related trap charges in the grain boundaries, which also lead to a second permittivity stable range in a higher temperature range 200 K–300 K.     

正电子湮没研究Al、Nb共掺CaCu3Ti4O12陶瓷高介电常数机理

关于CaCu₃Ti₄O₁₂陶瓷的高介电常数机理，目前广泛接受的是非本征的内阻挡层电容模型。该模型认为在多晶中元素变价、缺陷和非化学计量比等导致的半导化晶粒被绝缘晶界层，即内阻挡层所包围。其中内阻挡层的厚度对材料的介电性能影响较大，而扫描电子显微镜（SEM）测试表明样品晶界呈稀烂的果酱状，SEM难以测量晶界区域绝缘内阻挡层厚度。本文采用正电子湮没技术表征其厚度，通过对CaCu₃Ti₄O₁₂陶瓷共掺不同浓度的Al、Nb（CaCu₃Ti_4-xAl_0.5xNb_0.5xO₁₂，x=0.2%、0.5%、5.0%）改变其晶粒和晶界的微观结构，研究CaCu₃Ti₄O₁₂陶瓷高介电常数机理。正电子湮没结果显示，掺杂样品符合多普勒展宽谱S参数的变化趋势与平均寿命的变化趋势一致。x=0.5%掺杂样品的介电常数最高，其平均寿命、S参数和湮没长寿命成分均最小，阻挡层最薄。实验结果验证了描述CaCu₃Ti₄O₁₂陶瓷高介电常数机理的内阻挡层电容模型的预测。     

Stabilizing temperature-capacitance dependence of (Sr,Pb, Bi)TiO3-Bi4Ti3O12 solutions for energy storage

(1-x)Sr_0.7Pb_0.15Bi_0.1TiO₃-xBi₄Ti₃O₁₂ ((1-x)SPBT-xBIT, x = 0-0.125) bulk ceramics were developed and calcined via the solid-state method, aimed at the application of pulsed power capacitors. The phase structures, temperature stability, hysteresis loop, and discharge properties were systematically investigated. Considering both the temperature stability and dielectric properties, 0.925SPBT-0.075BIT bulk ceramics with a capacitance variation satisfying the X7R specification were developed for pulsed power capacitors. The energy storage density was 0.252 J/cm³, and the ceramics showed high temperature stability at 80 kV/cm. The discharge current waveforms of the 0.925SPBT-0.075BIT ceramics were recorded. A high discharge power density of approximately 1.01 × 10⁸ W/kg with an 8 Ω load resistor and short discharge period of 84 ns were achieved at 50 kV/cm. The good temperature stability properties and high power density show that the 0.925SPBT-0.075BIT ceramics are well suited for pulsed power capacitors with a wide temperature range.     

Heat propagation in thermally conductive polymers of PA6 and hexagonal boron nitride

Thermally conductive polymers offer new possibilities for the heat dissipation in electric and electronic components, for example, by a three‐dimensional shaping of the heat sinks. To face safety regulations, improved fire performance of those components is required. In contrast to unfilled polymers, those materials exhibit an entirely different thermal behavior. To investigate the flammability, a phosphorus flame retardant was incorporated into thermally conductive composites of polyamide 6 and hexagonal boron nitride. The flame retardant decreased the thermal conductivity only slightly. However, the burning behavior changed significantly, due to a different heat propagation, which was investigated using a thermographic camera. An optimum content of hexagonal boron nitride for a sufficient thermal conductivity and fire performance was found between 20 and 30 vol%. The improvement of the fire performance was due to a faster heat release out of the pyrolysis zone and an earlier decomposition of the flame retardant. For higher contents of hexagonal boron nitride, the heat was spread faster within the part, promoting an earlier ignition and increasing the decomposition rate of the flame retardant.     

Dielectric,ferroelectric, and piezoelectric properties of lead-free Ba0.95Ca0.05Ti1-xZrxO3 ceramics

Abstract

Ba_0.95Ca_0.05Ti_1-xZr_xO₃ (BCTZO) ceramics were prepared by a solid state reaction method. The samples were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and X-ray absorption near edge structure (XANES). The ceramics exhibit a pure perovskite structure. The average grain size gradually decreases with increasing Zr concentration. XANES results indicate that the intensities of pre-edge peaks dropped with increasing Zr concentration. The BCTZO ceramic of x?=?0.05 has the optimum electrical properties with the maximum dielectric constant (ε'_m), remanent polarization (2P_r), coercive electric field (2E_c) and piezoelectric charge constant (d₃₃) of 7,244, 12.54 (μC/cm²), 5.29 (kV/cm) and 288 (pC/N), respectively.     

Structural and Functional Characterization of the ABCC6 Transporter in Hepatic Cells: Role on PXE,Cancer Therapy and Drug Resistance

Pseudoxanthoma elasticum (PXE) is a complex autosomal recessive disease caused by mutations of ABCC6 transporter and characterized by ectopic mineralization of soft connective tissues. Compared to the other ABC transporters, very few studies are available to explain the structural components and working of a full ABCC6 transporter, which may provide some idea about its physiological role in humans. Some studies suggest that mutations of ABCC6 in the liver lead to a decrease in some circulating factor and indicate that PXE is a metabolic disease. It has been reported that ABCC6 mediates the efflux of ATP, which is hydrolyzed in PPi and AMP; in the extracellular milieu, PPi gives potent anti-mineralization effect, whereas AMP is hydrolyzed to Pi and adenosine which affects some cellular properties by modulating the purinergic pathway. Structural and functional studies have demonstrated that silencing or inhibition of ABCC6 with probenecid changed the expression of several genes and proteins such as NT5E and TNAP, as well as Lamin, and CDK1, which are involved in cell motility and cell cycle. Furthermore, a change in cytoskeleton rearrangement and decreased motility of HepG2 cells makes ABCC6 a potential target for anti-cancer therapy. Collectively, these findings suggested that ABCC6 transporter performs functions that modify both the external and internal compartments of the cells.     

Investigation on the mechanism of charge generation in organic heterojunctions: Analysis of I–V and C–V characteristics

The charge generation mechanism of organic heterojunction (OHJ) consisted of 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN) and different hole transporting materials (HTMs) are studied systematically by current-voltage (I–V) and capacitance-voltage measurements. The analysis of I–V characteristics of the devices based on OHJs at forward and reverse voltages by comparing the thickness of HTM layers finds that a forward and reverse symmetrical I–V curve is observed at thin HTM layers and the forward current becomes larger than the reverse current with the increase of HTM thickness, fully illustrating the effectiveness of OHJ charge generation. Moreover, the I–V characteristics at different temperatures indicate that the efficient charge generation is originated from electron tunneling rather than diffusion. And the C–V and capacitance-frequency (C–F)characteristics further illustrate the highly efficient charge generation ability of OHJs so that the charge density is as high as 4.5 × 10¹⁷ cm⁻³, guaranteeing the high conductivity of OHJs, which is very beneficial to developing highly efficient OLEDs using OHJs as charge injector and generator.     

Enhanced electrochemical performance of LiNi0.8Co0.1Mn0.1O2 via titanium and boron co-doping

Titanium and boron are simultaneously introduced into LiNi_0.8Co_0.1Mn_0.1O₂ to improve the structural stability and electrochemical performance of the material. X-ray diffraction studies reveal that Ti⁴⁺ ion replaces Li⁺ ion and reduces the cation mixing; B³⁺ ion enters the tetrahedron of the transition metal layers and enlarges the distance of the [LiO₆] layers. The co-doped sample has spherical secondary particles with elongated and enlarged primary particles, in which Ti and B elements distribute uniformly. Electrochemical studies reveal the co-doped sample has improved rate performance (183.1 mAh·g^-1 at 1 C and 155.5 mAh·g^-1 at 10 C) and cycle stability (capacity retention of 94.7% after 100 cycles at 1 C). EIS and CV disclose that Ti and B co-doping reduces charge transfer impedance and suppresses phase change of LiNi_0.8Co_0.1Mn_0.1O_2.