磁力可控电磁超声换能器设计及特性

电磁超声换能器一般采用具有超强磁力的稀土永磁制作,在实际检测中由于磁力不可控,存在偏置磁场不够强导致换能效率过低和磁力过强造成操作不方便等问题.提出一种偏置磁场磁力可控的电磁超声换能器,采用电磁铁与永磁铁相结合的方式,达到偏置磁场磁力可控的目的.通过有限元仿真和试验得出,提出的偏置磁场磁力可控的电磁超声换能器,在电磁铁处于关闭模式下,永磁铁能够提供基础磁场;采用增强模式或减弱模式,无被测物时,换能器下表面平均垂直磁通最大分别增强78.58％和减弱19.36％,而提离2 mm检测钢板时,换能器下方钢板表面平均垂直磁通最大分别增强52.99％和减弱38.02％;得出3种模式下,探头磁力随着提离距离缩小而增强的试验曲线;通过增强模式对铝板和钢板进行测厚试验,将检测信号幅值分别提高46.91％和62.01％.所设计的磁力可控电磁超声换能器不仅具有磁力可控的功能,还能够提高检测信号幅值.     

Synthesis of nanopowders with low agglomeration by elaborating Φ values for producing Gd2O3-MgO nanocomposites with extremely fine grain sizes and high mid-infrared transparency

Refining ceramic microstructures to the nanometric range to minimize light scattering provides an interesting methodology for developing novel optical ceramic materials. In this work, we reported the fabrication and properties of a new nanocomposite optical ceramic of Gd₂O₃-MgO. The citric acid sol-gel combustion method was adopted to fabricate Gd₂O₃-MgO nanocomposites with fine-grain sizes, dense microstructures and homogeneous phase domains. Nanopowders with low agglomeration and improved sinterability can be obtained by elaborating Φ values. Further refining of the microstructure of the nanocomposites was achieved by elaborating the hot-pressing conditions. The sample sintered at 65 MPa and 1300 °C showed a quite high hardness value of 14.3 ± 0.2 GPa, a high transmittance of 80.3 %–84.7 % over the 3?6 μm wavelength range, due mainly to its extremely fine-grain size of Gd₂O₃ and MgO (93 and 78 nm, respectively) and high density.     

Colossal dielectric response and relaxation behavior in novel system of Zr4+ and Nb5+ co-substituted CaCu3Ti4O12 ceramics

In this work, we developed a novel system of isovalent Zr⁴⁺ and donor Nb⁵⁺ co-doped CaCu₃Ti₄O₁₂ (CCTO) ceramics to enhance dielectric response. The influences of Zr⁴⁺ and Nb⁵⁺ co-substituting on the colossal dielectric response and relaxation behavior of the CCTO ceramics fabricated by a conventional solid-phase synthesis method were investigated methodically. Co-doping of Zr⁴⁺ and Nb⁵⁺ ions leads to a significant reduction in grain size for the CCTO ceramics sintered at 1060 °C for 10 h. XRD and Raman results of the CaCu₃Ti_3.8-xZr_xNb_0.2O₁₂ (CCTZNO) ceramics show a cubic perovskite structure with space group Im-3. The first principle calculation result exhibits a better thermodynamic stability of the CCTO structure co-doped with Zr⁴⁺ and Nb⁵⁺ ions than that of single-doped with Zr⁴⁺ or Nb⁵⁺ ion. Interestingly, the CCTZNO ceramics exhibit greatly improved dielectric constant (~10⁵) at a frequency range of 10²–10⁵ Hz and at a temperature range of 20–210 °C, indicating a giant dielectric response within broader frequency and temperature ranges. The dielectric properties of CCTZNO ceramics were analyzed from the viewpoints of defect-dipole effect and internal barrier layer capacitance (IBLC) model. Accordingly, the immensely enhanced dielectric response is primarily ascribed to the complex defect dipoles associated with oxygen vacancies by co-doping Zr⁴⁺ and Nb⁵⁺ ions into CCTO structure. In addition, the obvious dielectric relaxation behavior has been found in CCTZNO ceramics, and the relaxation process in middle frequency regions is attributed to the grain boundary response confirmed by complex impedance spectroscopy and electric modulus.     

Microstructure and electric properties of Pr-doped Pb(Zr0.52Ti0.48)O3 ceramics

Improving the piezoelectric activity of lead zirconate titanate (PZT) ceramics is of great importance for practical applications. In this study, the influence of Pr³⁺ doping on the ferroelectric phase composition, microstructure, and electric properties on the A-site of (Pb_1-1.5xPr_x)(Zr_0.52Ti_0.48)O₃ is extensively investigated. A dense and fine microstructural sample is obtained with the introduction of Pr³⁺. The results show that the morphotropic phase boundary (MPB) moves to the rhombohedral phase region. The rhombohedral and tetragonal phases exhibit an ideal coexistence in the 4 mol.% Pr³⁺ doped (PPZT4) samples. Lead vacancy and the reduction of the potential energy barrier are considered to be the key mechanisms for donor doping, which is upheld by the Pr³⁺ doping. Combining the I-E hysteresis loops with the P-E hysteresis loops, it becomes apparent that both contribution maximums of the domain switching and residual polarisation are in PPZT4. Moreover, the thermal aging resistance of PZT is improved by doping, and the temperature stability is optimised from 83% in PZT to 96% in PPZT4. Hence, an appropriate amount of Pr³⁺ doping can effectively improve the piezoelectric activity of PZT ceramics in the MPB area and optimise the performance stability of the material under application temperatures.     

Toughness and R-curve behaviour of laminated Si3N4/SiCw ceramics

Laminated Si₃N₄/SiC_w ceramics were successfully prepared by tape casting and hot-pressing. Its mechanical properties were measured and the impact resistance was discussed. The toughness of the laminated Si₃N₄/SiC_w ceramics was 13.5 MPa m^1/2, which was almost 1.6 times that of Si₃N₄/SiC_w composite ceramics, namely 8.5 MPa m^1/2. Moreover, the indentation strength of laminated Si₃N₄/SiC_w ceramics was not sensitive to increasing indentation loads and exhibited a rising R-curve behaviour, indicating that the laminated Si₃N₄/SiC_w ceramics had excellent impact resistance. The improved toughness and impact resistance of laminated Si₃N₄/SiC_w ceramics was attributed to the residual stress caused by a thermal expansion coefficient mismatch between the different layers, resulting in crack deflection and bridging of SiC whiskers in the interface layer, thus consuming a large amount of fracture work.     

Synthesis of succinic acid-based polyamide through direct solid-state polymerization method: Avoiding cyclization of succinic acid

Succinic acid is an important synthetic monomer but it is difficult to use it as a precursor for synthesizing high molecular weight polyamide, due to its tendency to perform intra-cyclization reaction at high temperature. In order to solve this problem, in this paper, the direct solid-state polymerization (DSSP) method with the initial reactant, nylon salt which was composed of 1, 5-diaminopentane, succinic acid, and terephthalic acid, was applied to synthesize the bio-based copolyamide PA 5T/54. In comparison with the conventional melting polymerization method, the DSSP method can prevent the cyclization reaction of succinic acid effectively due to the lower reacting temperature as well as the restriction effect of the nylon salt. As a result, the product fabricated by DSSP method has higher molecular weight and much lighter color from red to white. Therefore, the DSSP method is advantageous for the synthesis of the polymers or copolymers composed of the succinic acid as the monomer. Furthermore, the polymerization mechanism proposed in this work can serve as a guidance for the design of the molecular structure and control of the polymerization process.     

Enhanced thermal shrinkage behavior of phenolic-derived carbon aerogel-reinforced by HNTs with superior compressive strength performance

A novel carbon/m-HNTs composite aerogel was synthesized by introducing the modified halloysite nanotubes (m-HNTs) into phenolic (PR) aerogels through chemical grafting, followed with carbonization treatment. In order to explore the best proportion of HNTs to phenolic, the micromorphology of PR/m-HNTs were investigated by SEM before carbonization, confirming 10 wt% of m-HNTs is most beneficial to the porous network of aerogels. The interaction between PR and HNTs was studied by FTIR spectra, and microstructure evolution of the target product-carbon/m-HNTs composite aerogel were illustrated by SEM and TEM techniques. SEM patterns indicated that the carbon/m-HNTs aerogels maintain a stable porous structure at 1000 °C (carbonization temperature), while a ~20 nm carbon layer was formed around m-HNTs generating an integral unit through TEM analysis. Specific surface area and pore size distribution of composite aerogels were analyzed based on mercury intrusion porosimetry and N₂ adsorption–desorption method, the obtained results stayed around 500 m²g^?1 and 1.00 cm³g^?1 (pore volume) without significant discrepancy, compared with pure aerogel, showing the uniformity of pore size. The weight loss rate (26.76%) decreased greatly compared with pure aerogel, at the same time, the best volumetric shrinkage rate was only 30.83%, contributed by the existence of HNTs supporting the neighbor structure to avoid over-shrinking. The highest compressive strength reached to 4.43 MPa, while the data of pure aerogel was only 1.52 MPa, demonstrating the excellent mechanical property of carbon/m-HNTs aerogels.     

Enhanced the photocatalytic activity of B–C–N–TiO2 under visible light:Synergistic effect of element doping and Z-scheme interface heterojunction constructed with Ag nanoparticles

In order to enhance the photocatalytic activity of TiO₂ under visible light, Ag nanoparticles were introduced into tridoped B–C–N–TiO₂ (TT) catalyst by photoreduction deposition. Ag/B–C–N–TiO₂ (ATT) catalysts with the functions of reducing band gap and carrier recombination were prepared. At the same time, the effect of the amount of Ag on the photocatalytic performance of ATT catalyst was investigated. Through XRD, XPS, PL and other characterization methods, the (211)/(101)/Ag interface heterojunction mechanism similar to the traditional Z-scheme heterojunction was proposed. The intervention of Ag nanoparticles changed the P–N interface heterojunction between (211)/(101) to the (211)/(101)/Ag Z-scheme interface heterojunction. The results show that ATT catalyst exhibits the highest photocatalytic activity when the molar amount of Ag is 0.005% with the MB degradation rate of the ATT catalyst (0.01707 min^?1), which is 14.59 times of TiO₂ (0.00117 min^?1) and 2.02 times of TT (0.00847 min^?1). In addition, the four cycles efficiencies of ATT for MB degradation were all above 94.00%.This study reveals the possibility of construction of Z-scheme heterojunctions between precious metal nanoparticles and different interfaces of TiO₂, and provides a reference for the construction of Z-scheme interface heterojunctions.     

伊拉克米桑油田水平井钻井关键技术

针对伊拉克米桑油田盐膏层巨厚、钻井液密度窗口窄、存在高压盐水层,储层段漏塌同层导致复杂时效高等问题,通过对比分析国内外盐膏层和窄压力窗口地层钻井技术,总结了米桑油田钻井面临的主要技术难点,从井身结构优化、钻井提速和复杂预防等方面入手,研究形成了适合米桑油田的钻井关键技术,并进行了现场试验应用,取得了显著的效果.伊拉克米桑油田钻井关键技术对该地区钻井技术方案设计和钻井提速提效具有较强的借鉴和指导作用.     

妈祖文化视域下的表情符号设计研究

目的 基于妈祖文化的视角,探究妈祖文化与表情符号设计融合的可能性,打造表情文化产业链,为表情符号的设计开发提供更多的机遇,推动了妈祖文化的对外传播.方法 以妈祖文化为切入点,分析表情符号设计与妈祖文化跨界融合发展的优势.同时,借助具体的案例来阐述两者结合所产生的积极意义,表明巧妙应用妈祖文化的可行性.结论 妈祖文化的融入为表情符号的发展增添了浓墨重彩的一笔,对于增强文化气息及开拓设计思路都发挥着重要作用,易于激发受众的情绪、记忆,引起受众情感和心理的共鸣,从而创造符合受众审美情趣和思维方式的设计作品.由此可见,深入把握两者的关联性,有助于催生新的文化产业形态、传承妈祖文化、开辟表情符号设计新路径.