Internal bias field relaxation in poled Mn-doped Pb(Mn1/3Sb2/3)O3–Pb(Zr,Ti)O3 ceramics

The frequency, electric field cycling and temperature dependences of the polarization–electric field (P–E), strain–electric field (S–E) loops in poled Mn-doped 0.05Pb(Mn_1/3Sb_2/3)O₃–0.50PbZrO₃–0.45PbTiO₃ ceramics have been investigated. The P–E and S–E loops are strongly asymmetric corresponding to the presence of an internal bias field E_i after poling and aging, indicating that the domain walls are strongly pinned by preferentially oriented defect dipoles formed by the acceptor dopant ions (Mn²⁺/Mn³⁺) and O²⁻ vacancies. Whereas, the loops exhibit a tendency of changing from asymmetric shapes to normal symmetric ones with increasing electric field amplitude or decreasing frequency. Repeated electric field cycling as well as high temperature results in a similar effect. Meanwhile, the E_i reduces consequently, providing evidence of domain depinning or internal bias field relaxation. It is suggested that the reorientation of the defect dipoles and depinning of domain walls arising from high temperature or electric field cycling are responsible for this extrinsic internal bias field relaxation process.     

具有梯度孔结构多孔陶瓷膜支撑体的制备

采用平均粒径为0.56μm的Al2O3为原料,研究了不同固相含量的Al2O3悬浮液的流变性能.在此基础上,采用含10%(质量分数,下同)Al2O3的悬浮液,通过重力沉降和真空抽吸过程,成功制备出具有梯度孔结构的片状Al2O3支撑体.对具有梯度孔结构支撑体的微观结构进行了表征,并研究了支撑体的孔隙率和渗透性能随烧成温度的...     

Different microstructure BaO–B2O3–SiO2 glass/ceramic composites depending on high-temperature wetting affinity

In this work, we propose a simple but effective method to fabricate BaO–B₂O₃–SiO₂ glass/ceramic composites with different microstructures that depend on the high-temperature wetting affinity. The experimental results showed that the wetting affinity between oxide ceramic and the BaO–B₂O₃–SiO₂ glass matrix could strongly affect the driving force of densification and crystallization and finally the microstructure of the glass/ceramic composites. It was found that suitable amounts of alumina powders could obviously increase the driving force for sintering of glass by increasing the capillary pressure. In this case, the contact angle between alumina and glass matrix is about 24° at high temperature and a densified and homogeneous microstructure of glass/alumina composite was obtained. On the contrary, rutile powders additive was found to result in higher phase separation and crystallization during the sintering of glass/rutile composites. In this case, the contact angle between rutile and glass matrix is about 124° at high temperature, and the sintered body has a lower dielectric loss than the sample with alumina additive. Therefore, the microstructure and dielectric property of glass/ceramic composites could be controlled by adjusting the ceramic composition and wetting affinity between ceramic additive and glass matrix in our study.     

Enhanced electrical properties related to structural distortion of CaBi2Nb2O9-based piezoelectric ceramics

CaBi₂Nb₂O₉ (CBN)-based high Curie temperature piezoelectric ceramics with formula Ca_0.8-xSr_x(Li_0.5Ce_0.15Bi_0.35)_0.2Bi₂Nb_1.94Ta_0.04W_0.02O₉ were prepared by conventional solid-state reaction method. The effects of strontium substitution for calcium in CBN pseudo-perovskite structure A-site were systematically studied. Results showed that the addition of Sr²⁺ ions lead to an improvement of the tetragonality of lattice structure, which resulted in an enhancement of piezoelectric and ferroelectric properties together with high Curie temperature T_C and good resistance to thermal depolarization. The analysis of dielectric spectrums revealed that the space charge polarization induced an additional dielectric anomaly occurred below T_C. The composition with x = 0.025 showed good integrated performance, the piezoelectric coefficient d₃₃ and T_C were ~17.5 pC/N and ~917°C, respectively. Even though the as-studied ceramics underwent high depolarizing temperature reached up to 875°C, d₃₃ decreased by 8% merely. The remanent polarization 2P_r and the resistivity ρ at 650°C were on the order of ~10 μC/cm² and 3 × 10⁵ Ω cm, respectively.     

纳米薄层SAPO-5分子筛的离子热合成及催化性能

以小剂量的丁二酸、氯化胆碱和四乙基溴化铵复配形成的低共熔混合物为溶剂和模板,以水热法合成的纳米薄层SAPO-5分子筛作为晶种,使用离子热法在微波加热功率为400 W、温度为180℃和晶化时间为20 min的条件下,高效合成了具有六角花瓣状的纳米薄层SAPO-5分子筛。采用XRD、SEM、N2物理吸/脱附和NH3-TPD对合成样品的物相、形貌、孔结构和酸性进行了分析。结果表明,所合成的样品SC2-T180-t20-P400是一种同时含有微孔-介孔-大孔结构的多级孔SAPO-5分子筛,其外表面积高达85m2/g。分子筛产物中无机物的原子利用率达到88%。该样品在苯与苯甲醇的烷基化反应中,苯甲醇转化率和二苯甲烷选择性分别达到99.9%和94.0%,表现出比传统水热法合成的纳米薄层SAPO-5催化剂更为优异的催化性能。     

蚕沙基多孔炭表面氧化改性对农药噻虫嗪吸附及缓控释影响

选用桑蚕废弃物蚕沙为炭源,通过炭化活化的方式获得了一种高比表面的中微双孔道生物炭材料SCSE,并采用不同氧化剂对其表面氧化处理以调控材料孔径和表面积对农药噻虫嗪分子的吸附作用力,以实现SCSE材料对农药噻虫嗪的缓控释,并系统研究了氧化改性后材料的比表面积、孔径和表面基团性质的变化对材料吸附噻虫嗪的热力学和动力学平衡以及噻虫嗪的释放动力学等性能的影响。结果表明：SCSE孔隙结构发达,其BET比表面和孔容分别为1290.95 m²/g和0.690 cm³/g;在室温下,该材料对噻虫嗪分子的吸附容量达到560 mg/g。噻虫嗪在四种SCSE上的释放动力学可分为快速持续释放过程和慢速释放过程两个过程,其中快速持续释放过程的释放动力学常数约是慢速释放过程的29～34倍;其中硝酸改性后的SCSE-HN对噻虫嗪的释放比例最大,释放速度最快。本实验所获得的四种SCSE材料对噻虫嗪的释放均表现出长效释放效力。按照一般农作物的需药量,该吸附剂只要按照0.5 g/（d·m²）的投入量便能很好地对农作物进行长效的虫害防治（>40 d）。     

氧化铝、氮化硅和碳化硅的疲劳特性与寿命预测

分析了几种典型的结构陶瓷在长期载荷下的失效特性和差别。认为长期失效的本质是强度衰减,建立了一个疲劳失效的强度衰减模型和提出了寿命预测方法。分别研究了氧化铝、氮化硅和碳化硅几种常用工程陶瓷在常温和高温下的疲劳特性和差异。采用三点弯曲的受力方式测试了不同载荷水平下的断裂时间。结果表明：碳化硅的疲劳门榄值超过强度的80％,而且受温度影响最小;氧化铝的静疲劳受微小裂纹扩展控制;氮化硅的高温疲劳主要是蠕变机制导致强度衰减,疲劳门槛值不超过强度50％。由实验研究了氮化硅的高温静疲劳、动疲劳和循环疲劳三者在相同温度和相同应力峰值变化下的寿命关系,结果与计算一致。     

多孔介质中流体流动的格子气自动机模拟

介绍了 13-Bit正六边形多速格子气自动机模型的特点 ,讨论了多孔介质流体流动的格子气自动机模型的渗透率等参量算方法 ,应用该模型对计算机产生的多孔介质几何构型和焦炭多孔介质中的流体流动进行了模拟 ,其结果既可以给出多孔介质中的流动细节 ,也可统计得到表征多孔介质宏观流动特征的物理参量 .初步研究表明 :格子气自动机模型可用于模拟复杂边界条件下多孔介质的流体流动     

Synthesis and properties of lanthanum hexaaluminate ceramic La1−xCaxAl11−y−zMgyTizO18

The aim of the present work is to obtain ceramic materials with a hexagonal structure and high density, hardness and mechanical strength at lower synthesis temperature. Ceramic samples with nominal composition La_1−xCa_xAl_11−y−zMg_yTi_zO₁₈ (x=0–1; y=0–3; z=0–3,5) are prepared. The samples are sintered at temperature 1500 °C by one-stage and two-stage ceramic technology. By X-ray diffraction and scanning electron microscopy, predominant phase LaAl₁₁O₁₈ and second phases LaAlO₃ and -Al₂O₃ are identified. Ceramic materials are characterized with high physico-mechanical properties and may be find application for production of mill bodies and materials for immobilization of nuclear waste.     

掺锰(Ba,Sr)TiO_3系PTCR瓷的研究

本文研究了掺锰(Ba,Sr)TiO_3系PTC热敏电阻瓷的性质。讨论了不同SrO量的Tc和ar的变化。烧成温度和保温时间对(Ba,Sr)TiO_3瓷的PTC特性有重大影响。当SrO量0.10 mol、Sb_2O_3 0.135wt.％、MnO_2 0.04和0.06wt.％、SiO_20.38wt.％以及Al_2O_3 0.215wt.％时,(Ba,Sr)TiO_3半导瓷具有二次PTC现象。