HN型催化剂催化α——蒎烯制苎烯的初步研究

本文用ＨＮ型催化剂低温催化α－蒎烯异构化制苎烯，考察了反应温度、反应时间、催化剂种类对反应结果的影响。实验结果表明在７０℃、反应４ｈ以上，苎烯的选择性仍保持在３５％以上。     

相容剂对PS／PP共混合金混容形态和性能的影响

研制了马来酸酯接枝聚丙烯相容剂，并将其用于聚苯乙烯／聚丙烯的共混改性；通过力学性能测试、透射电镜分析、差示扫描量热分析等方法研究了相容剂对ＰＳ／ＰＰ合金的混容形态和力学性能的影响。结果表明：相容剂的加入，使ＰＳ／ＰＰ由不相容的独立聚集的两相变为相畴很小的细分散相，共混高分子的链段运动也表现为趋于均相结构的运动方式。加入相容剂后共混材料的冲击强度有明显提高，拉伸强度也有所上升。相容剂的含量对性能也有较大影响，相容剂用量为８％时，力学性能最好，从ＤＳＣ测试中可以看到此时共混物趋向均相体系；继续增大相容剂用量，合金的力学性能反而下降。     

Nanocrystalline buildup,relaxor behavior,and polarization characteristic in PZT–PNZN quaternary ferroelectrics

The Pb(Zr_0.47Ti_0.53)O₃–Pb[(Ni_0.6Zn_0.4)_1/3Nb_2/3]O₃ (PZT–PNZN) quaternary ferroelectrics presenting the high piezoelectric coefficients are the active element in a range of piezoelectric devices. However, the buildup of nanoceramics with stable perovskite structure is still a big challenge, which prohibits the miniaturization of piezoelectric devices. In this work, the high dense PZT–PNZN nanoceramics with average grain size of 130 nm were prepared by a combination of high‐energy ball milling (HEBM) and spark plasma sintering (SPS). The domain configuration and relaxor behavior in this nanoceramic are reported for the first time. Although the noncubic crystal structure and dielectric anomaly suggest a ferroelectric behavior, only very slim polarization–electric (P–E) hysteresis loops are observed. The suppression of macroscopic ferroelectric polarization mainly originates from the decrease in crystal tetragonality and the enhanced clamping effect on domain wall motion. The piezoelectric properties, d₃₃=65 pC/N and k_p=17%, raise the possibility of PZT–PNZN nanoceramics for application in multilayer piezoelectric devices.     

Submicron crystalline buildup and size‐dependent energy harvesting characteristic in PZN–PZT ternary ferroelectrics

Piezoelectric energy harvester converts low‐frequency vibrational energy in the environment into electrical energy, enabling the purpose of self‐supplying power for low‐energy consumption devices. The key to miniaturizing energy harvester is the buildup of the submicron‐grained ceramic with a high transduction coefficient (d×g), which is still a big challenge from a technical point of view. In this work, the popular ternary system of Pb(Zn_1/3Nb_2/3)O₃–Pb(Zr_0.5Ti_0.5)O₃ (PZN–PZT) has been selected as objective compound, and the submicron‐grained ceramics were prepared by a combination of high‐energy ball milling and pressureless sintering technology. The results revealed that nanocrystalline PZN–PZT powders can be synthesized by one step mechanochemical route without the calcination stage. Using these nanopowders as precursors, dense ceramics with different grain size have been prepared through tailoring the sintering temperature. The study of size‐dependent energy harvesting characteristic evidenced an optimum transduction coefficient of 7980×10^?15 m²/N was obtained for 950°C sintered specimen, which has uniform microstructure with mean grain size of 0.33 μm. In the mode of the cantilever‐type energy harvester constructed by this material, the output power at low frequency of 89 Hz was as high as 69 μW at an acceleration of 10 m/s², showing the suitability for piezoelectric generators harvesting environmental vibrational energy.     

预吸水轻骨料对高强混凝土早期收缩的影响

基于等强度原则,设计了内养护水灰比分别为0、0.04、0.08和0.12的4组高强混凝土,研究了密封和干燥两种养护条件下,预吸水轻骨料的体积掺量对混凝土早龄期自由收缩、内部湿度及弹性模量的影响。结果表明：随着内养护水引入量的增大,28 d龄期内高强混凝土内部湿度下降和早期总收缩变形均得到明显缓解,且对密封养护混凝土的影响更明显;但混凝土的弹性模量随轻骨料掺量增大而下降,应用中应优化选择预吸水轻骨料的掺量。在干燥环境条件下,轻骨料预吸水内养护法并不能根除干燥收缩,内养护高强混凝土中可能存在较大的内部湿度梯度及近表面干燥现象。     

Mechanical properties of carbon fiber composites modified with nano-SiO2 in the interphase

The performance of carbon fibers-reinforced composites is dependent to a great extent on the properties of fiber–matrix interface. To improve the interfacial properties in carbon fibers/epoxy composites, nano-SiO₂ particles were introduced to the surface of carbon fibers by sizing treatment. Atomic force microscope (AFM) results showed that nano-SiO₂ particles had been introduced on the surface of carbon fibers and increase the surface roughness of carbon fibers. X-ray photoelectron spectroscopy (XPS) showed that nano-SiO₂ particles increased the content of oxygen-containing groups on carbon fibers surface. Single fiber pull-out test (IFSS) and short-beam bending test (ILSS) results showed that the IFSS and ILSS of carbon fibers/epoxy composites could obtain 30.8 and 10.6% improvement compared with the composites without nano-SiO₂, respectively, when the nano-SiO₂ content was 1 wt % in sizing agents. Impact test of carbon fibers/epoxy composites treated by nano-SiO₂ containing sizing showed higher absorption energy than that of carbon fibers/epoxy composites treated by sizing agent without nano-SiO₂. Scanning electron microscopy (SEM) of impact fracture surface showed that the interfacial adhesion between fibers and matrix was improved after nano-SiO₂-modified sizing treatment. Dynamic mechanical thermal analysis (DMTA) showed that the introduction of nano-SiO₂ to carbon fibers surface effectively improved the storage modulus of carbon fibers/epoxy.     

聚甲醛/可反应性纳米SiO2复合材料的非等温结晶动力学及动态力学性能

采用熔融共混法制备了聚甲醛(POM)/可反应性纳米二氧化硅(RNS)复合材料。通过差示扫描量热仪(DSC)研究了RNS对聚甲醛非等温结晶行为的影响;分别用修正Avrami方程的Jeziorny法和Mo法研究了POM及其复合材料的非等温结晶动力学。结果表明,两种方法均能较好地描述复合材料的非等温结晶动力学,RNS的加入对POM结晶起到了异相成核作用,使得复合材料在较高的温度下即开始结晶,同时RNS又具有抑制结晶的作用,使得复合材料的结晶速率降低,半结晶时间t1/2增大。Avrami指数n有所降低,说明RNS改变了POM的结晶和生长过程。动态力学分析(DMA)研究结果表明,POM复合材料的储能模量也有所增加,Tg向高温方向移动,说明RNS与POM之间存在着较强的相互作用。     

Large electrocaloric effect with ultrawide temperature span in Na1/2Bi1/2TiO3-based lead-free ceramics

Innovative cooling technologies are recognized by many industries as a crucial part of their system design. A large electrocaloric effect (ECE) and extended working temperature are the key issues hindering the realization of electrocaloric refrigeration technology. In this work, large ECE (ΔT = 0.8–0.9°C @ 4 kV/mm) with an ultrawide temperature span from 30 to 120°C is noted for lead-free (Na_1/2Bi_1/2)_0.80Sr_0.20(Zn_1/3Nb_2/3)_xTi_1-xO₃ ceramics. The excellent ECE performance can be ascribed to the evolution of polar nanoregions. Our work suggests that this material is promising for applications in solid-state refrigeration systems with a broad range of operating temperatures.     

Capping Groups Induced Size and Shape Evolution of Magnetite Particles Under Hydrothermal Condition and their Magnetic Properties

Three simple capping molecules (urea, 3-aminopropanol, and polyethylene glycol) with different functional groups (−NH₂ for urea, −NH₂ and −OH for 3-aminopropanol, and −O− for polyethylene glycol) have been designed to prepare magnetite (Fe₃O₄) particles with various shapes. The crystal structure, morphologies, and magnetic properties of the products have been characterized by X-ray diffraction, electron microscopy, and vibrating sample magnetometer. The results indicate that the capping functional groups play a major role in determining the size, shape, and thus magnetic properties of the magnetite nanocrystals. The morphology evolution of the magnetite under the hydrothermal condition is discussed in detail, particularly for the interaction between the various capping groups and surface structure and chemistry of the nanocrystals.     

掺杂对Na0.5Bi0.5TiO3基无铅压电陶瓷弛豫性的影响

对(Na0.5Bi0.5)TiO3-BaTiO3(NBBT)二元系压电陶瓷在准同型相界附近进行不同量的La,Mn掺杂,通过XRD、电学性能测试等,研究了掺杂对陶瓷微观结构及介电性能的影响.结果表明,La,Mn掺杂后,相变的弥散程度增大,体系的弛豫性增强.铁电体的弛豫性与基体内极性微区的有序度及尺寸、数量密切相关,对NBBT这种A位复合体系而言,La离子的介入在一定程度上引起电荷不平衡,促使微区长大;但是由于La的分隔作用,A位与B位的耦合作用大大减弱,体系整体有序度降低,弛豫性增强.Mn离子的B位掺杂有助于建立新的(AA')(BB')O3复合体系,因此也影响体系的弛豫性.