Microstructural evolution,mechanical and thermal properties of TiC-ZrC-Cr3C2 composites

Dense TiC-ZrC-Cr₃C₂ composites with various TiC content from 19.6 mol% to 78.4 mol% have been fabricated by hot-pressing sintering at 1950 °C using 2.0 mol% Cr₃C₂ as sintering aid. The effect of TiC content on the microstructure, mechanical and thermal properties of TiC-ZrC-Cr₃C₂ composites are investigated systematically. The single (Zr, Ti, Cr)C solid solution is obtained when TiC content is 19.6 mol%, while with increasing TiC content, the composites begin to consist of Zr-rich (Zr, Ti)C solid solution and Ti-rich (Ti, Zr, Cr)C solid solution phase. SEM and EDS analysis confirm that Cr element is not favorable to diffuse into ZrC lattice to form (Zr, Cr)C solid solution. Flexural strength and Vickers hardness increase gradually with increasing TiC content, but fracture toughness does not improve significantly. Fracture toughness are in the range of 3.34–4.01 MPa∙m^1/2 for all composites, and the optimum value reaches 4.01 MPa·m^1/2 with 49.0 mol% TiC. Experimental results of the thermal expansion coefficient reveal that the addition of TiC raises the thermal expansivity of TiC-ZrC-Cr₃C₂ composites. Noticeably, the thermal conductivities of TiC-ZrC-Cr₃C₂ composites show a decrement trend with increasing TiC content, not as theoretical predicting by the rule of mixtures. For instance, the thermal conductivity at 25 °C ranges from 18.0 W/m∙K for 8Z2T2C composite down to 10.6 W/m∙K for 2Z8T2C composite.     

Structure-design strategy of 0–3 type (Bi0.32Sr0.42Na0.20)TiO3/MgO composite to boost energy storage density,efficiency and charge-discharge performance

A novel 0–3 type (Bi_0.32Sr_0.42Na_0.20)TiO₃/MgO composite is investigated in this work, which possesses a high stored energy storage density w_s˜2.50 J/cm³, recoverable energy storage density W_R˜2.09 J/cm³ with high efficiency η˜84% under low electric field (20 kV/mm). The excellent performance is owning to the increase of breakdown strength (BDS) value and the intrinsic mechanism for enhanced BDS value by MgO incorporation is disclosed by numerical simulations (COMSOL). Moreover, the studied composite exhibits excellent charge-discharge performance, the current density (C_D) and power density (P_D) are 1671 A/cm² and 150 MW/cm³, respectively, which are much superior to that of other ceramics. Besides, most of the stored energy is discharged within ˜0.15 μs via charge-discharge tests. This work not only provides a novel technique to designing bismuth-based ceramic capacitors with simultaneously high W_d, η and excellent charge-discharge performance, but also deepens the understandings of the role for the metallic oxide in the composite.     

Damage assessment of composite materials by means of thermographic analyses

Composite materials are largely used for structural applications, thanks to their high strength-to-weight ratios. However, it is difficult to make accurate estimations on their mechanical behavior, as it is affected by several factors, involved both in the manufacturing process and in the experimental testing. In this study, GFRP laminates, with different stacking sequences, are tested under static loading conditions. During testing, thermal analyses are also performed by means of a thermal camera, obtaining an energetic parameter (i.e. the temperature) useful for the evaluation of damage. The thermographic method allows both qualitative and quantitative analyses to be performed in a relatively short time. Besides thermal analyses, damage is also assessed by means of static tests, interrupted at different load levels, and followed by stiffness reduction measurements and microscopic analyses, allowing for a comparison of the obtained results.     

两种萃取溶剂对塑料食品包装材料上 有机污染物检测效果的影响

目的 检测两种萃取溶剂对塑料食品包装材料上有机污染物检测效果的影响。方法 分别以正己烷和无水乙醇为萃取溶剂对塑料食品包装材料上污染物进行超声提取, 提取后用旋转蒸发浓缩, 最后采用气相色谱-质谱联机(GC-MS)分析方法以离子化方式对浓缩的污染物进行表征。结果 正己烷作为萃取溶剂能萃取出抗氧化剂2, 6-二叔丁基对甲酚、增塑剂邻苯二甲酸二丁酯、油墨生产中所用的溶剂正十六烷; 乙醇作为萃取溶剂能萃取出抗氧化剂2, 6-二叔丁基对甲酚、油墨生产中所用的溶剂正十六烷和正二十烷。结论 正己烷作为萃取溶剂的提取效果要比乙醇作为萃取溶剂提取效果好。     

Effects of mechanical activation on the sintering and dielectric properties of oxide-derived PZT

A single phase, nanocrystalline perovskite PZT powder has been successfully derived from a mixture of oxides via a mechanical activation route. Unlike in the conventional solid state reaction, the perovskite PZT phase was first triggered and then progressively formed without passing through the intermediate PT and PZ phases with increasing degree of mechanical activation. Similarly, the formation of a single phase PZT of perovskite structure can be completed in a partially activated mixture of oxide powders when heated at an elevated temperature, also without involving PT and PZ as transitional phases. Dense PZT (>95% theoretical density) with excellent dielectric properties was obtained when the mechanically activated powders are sintered at 1150°C. The relative density and dielectric properties of sintered PZT were improved when the formation of perovskite phase is completed by the mechanical activation.     

RGD功能化HA/PLLA多孔复合材料的制备和表征

通过碳二亚胺法将精氨酸-甘氨酸-天冬氨酸(RGD)接枝到羟基磷灰石(HA)颗粒表面,增强HA颗粒识别细胞的功能,然后将其均匀地分布于左旋聚乳酸(PLLA)中制备多孔复合材料,分别用XPS和SEM等对HA颗粒和多孔复合材料进行了表征。结果表明:RGD成功地接枝到了HA颗粒表面,多孔复合材料中RGD功能化的HA颗粒是纳米尺寸的,且分布均匀;RGD功能化HA/PLLA多孔复合材料的细胞粘附率从普通HA/PLLA多孔复合材料的37.21%提高到了69.11%。     

Investigation of carbon fiber reinforced polymer (CFRP) sheet with subsurface defects inspection using thermal-wave radar imaging (TWRI) based on the multi-transform technique

A combined theoretical and experimental approach is reported using thermal-wave radar imaging (TRWI) for carbon fiber reinforced polymer (CFRP) with subsurface defects inspection. The multi-transform technique (Fourier transform, FT; Hilbert transform, HT; and cross-correlation, CC) is applied to extract the characteristics of thermal-wave signal. Experimental results indicate that the multi-transform technique of thermal-wave signal is available for detecting the subsurface defect. For the shallow defect (defect depth ≤1 mm), the delay time image of CC exhibits high contrast, and the phase image of FT has high SNR at the right frequency component. For the deep defect (defect depth 2.0 mm), the phase images of HT have both high contrast and large SNR value.     

Integer transform based reversible watermarking incorporating block selection

We propose a new scheme based on integer Haar wavelet transform (IHWT), which utilizes block selection and difference expansion (DE) (or histogram shifting (HS)). IHWT has the characteristic that the average of a block remains unchanged before and after watermark embedding. Hence, this invariability can be used for determining whether a block is located in a smooth region or not. Specifically, for a block, its mean value and the neighborhood surrounding it are used for estimating the correlation between it and its neighborhood. In this way, only a reduced size location map is needed, and the block size can also be set to a small value. Since small blocks have stronger intra-block correlation than large ones, the embedding distortion caused by modifying small blocks is lower. Otherwise, if the difference between any two neighboring pixels in a block is large, then the distortion produced by directly expanding it is also high. To decrease the class of distortions, DE (or HS) is introduced into the proposed method.     

The CeO2–TiO2–ZrO2 sol–gel film: a counter-electrode for electrochromic devices

Thin films of CeO₂–TiO₂–ZrO₂ with 23 mol% of Ce, 45 mol% of Ti and 32 mol% of Zr were obtained by the sol–gel method. The precursor sol was prepared from a mixture of Ce(NH₄)₂ (NO₃)₆, Ti(OPrⁱ)₄ and Zr(OPrⁱ)₄ solubilized in isopropanol and then sonicated. Xerogels were characterized by Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA) and X-ray diffraction. The films were deposited by dip-coating technique on a glass plate coated with an indium tin oxide film (ITO) and thermally treated at 80 °C for 15 min. and heated at 450 °C for 15 min in an oxygen atmosphere. By means of the addition of a lithium salt (LiCF₃SO₃) to the precursor solution, films with different electrochemical performances were obtained. Their possible use as ion storage (counter-electrode) in electrochromic devices (ECD) was analyzed by spectroelectrochemical measurements using cyclic voltammetry and chronoamperometry coupled to spectrometric measurements.     

Synthesis of novel Cd2P2O7/Ag3PO4 photocatalyst with enhanced visible-light photocatalytic performance and the enhancement mechanism

Novel Cd₂P₂O₇/Ag₃PO₄ photocatalysts containing different mass fractions of Cd₂P₂O₇ were synthesized by a hydrothermal method. The photocatalysts were characterized by X-ray diffractometry, transmission electron microscopy, X-ray photoelectron spectroscopy, Electron spin resonance (ESR), Fourier transform infrared spectrometry, ultraviolet–visible absorption spectroscopy and photoluminescence spectroscopy. Photocatalytic activity was decided by the effective separation and low recombination rate of photogenerated electron-hole pairs. During the experiments, the Cd₂P₂O₇/Ag₃PO₄ composites possessed fierce electron- hole separation capacity. In particular, the 1 wt% Cd₂P₂O₇/Ag₃PO₄ catalyst displayed higher photocatalytic performance than pure Ag₃PO₄ under visible-light irradiation (λ>420 nm). The ESR spectrum showed the main active species during the methyl orange degradation were ·OH and ·O₂⁻.