Effect of sintering condition on microstructure and dielectric properties of BSTN composite ceramics

The effect of sintering condition on the phase composition, microstructure and dielectric properties of barium strontium titanate niobate (BSTN) composite ceramics, in which the perovskite phase and the tungsten bronze phase coexisted, was investigated by XRD, SEM and LCZ Meter. The results show that more Sr²⁺ ions dissolved from the grain boundaries into the crystal lattice of the pervoskite phase and the tungsten bronze phase, especially, into the lattice of the pervoskite phase with the increasing of sintering temperature and sintering time, respectively. So the Curie temperature point decreases with the increasing of sintering temperature. The crystal growth rate of the tungsten bronze phase is higher than that of the perovskite phase in BSTN composite ceramics as the sintering temperature increases. The reasonable sintering temperature is about 1275 °C for BSTN composite ceramics. The activation energy to setting up polarization in BSTN composite ceramics increases with the increase of the applied frequency.     

便携式钢筋强度检测仪的研制及应用

介绍了一种新型的基于钢材表面硬度检测理论研制的钢筋强度检测仪器,该仪器应用于现场无损检测混凝土中钢筋的抗拉强度、屈服强度,并概述了该测试仪的检测原理、结构构成及检测结果,指出了其推广应用前景。     

Synthesis of (BaxSr1−x)(Zn1/3Nb2/3)O3 ceramics by reaction-sintering process and microstructure

(Ba_xSr_1−x)(Zn_1/3Nb_2/3)O₃ complex perovskite ceramics produced by reaction-sintering process were investigated. Secondary phases ZnNb₂O₆ and (Cu₂Zn)Nb₂O₈ were found at the perovskite matrix grain boundaries. 98.5–99.8% of the theoretical density was obtained. In (Ba_0.5Sr_0.5)(Zn_1/3Nb_2/3)O₃ and (Ba_0.7Sr_0.3)(Zn_1/3Nb_2/3)O₃, the amount and volume of second phases decreased clearly at 1500 °C.     

Efficient field emission from tetrapod-like zinc oxide nanoneedles

Tetrapod-like zinc oxide (ZnO) nanoneedles were fabricated using a simple and economical method of rapid heating high purity zinc powders at 900 °C. No catalyst and vacuum were employed in the experiment. Field-emission measurements showed that the turn-on field of the synthesized tetrapod-like ZnO nanoneedles was as low as 1.8 V/μm at the emission current density of 1.0 μA/cm² and the emission current density reached 1.0 mA/cm² under an applied field of about 3.9 V/μm. The low turn-on field, high emission current density, and good electron emission stability make the ZnO nanoneedles one of the promising candidates for field-emission displays.     

The electrode/sample contact effects on the dielectric properties of the CaCu3Ti4O12 ceramic

In this paper, the contact effects at the electrode/sample interfaces on the dielectric properties of the CaCu₃Ti₄O₁₂ (CCTO) ceramic were studied. The experimental results provide clear evidence that the colossal dielectric constant in CCTO is related to the ceramic itself; however, it may also partly originated from the electrode/sample contact effects which depends on the surface resistivity of the sample. When the surface resistivity of the ceramic is as high as 1.2 × 10⁸ Ω cm, no obvious mobile space charges can be observed, and the dielectric properties of the sample is inert to the different metal electrodes and various sample thicknesses, indicating the colossal dielectric constant (near 2000 at 10 kHz) at room temperature is due to the true properties of the ceramic itself. However, after the surface resistivity is lowered to 3.1 × 10⁷ Ω cm through post-annealing the sample in N₂ atmosphere at 750 °C, obvious mobile space charges can be observed, and the dielectric properties of the sample become sensitive to the different types of contacts. The dielectric constant of the sample with Pt electrode shows a significant enhancement (up to 5000 at 10 kHz), comparing with that of the sample with Ag electrode. Clearly, in this case, the extrinsic contact contributes partly to the colossal dielectric constant of CCTO ceramic.     

Three-dimensional BEM for piezoelectric fracture analysis

A boundary element approach with quadratic isoparametric elements, quarter-point elements and singular quarter-point elements for three-dimensional crack problems in piezoelectric solids under mechanical and electrical loading conditions, is presented in this paper for the first time. The procedure is based on Deeg's fundamental solution for anisotropic piezoelectric materials, and the classical extended displacement boundary integral equation. Stress and electric displacement intensity factors are directly evaluated as system unknowns, and also as functions of the computed nodal displacements and electric potentials at crack faces. Special attention is paid to the fundamental solution evaluation. Several three-dimensional crack problems in transversely isotropic bodies under mechanical and electrical loading conditions are analysed. Numerical solutions computed for prismatic cracked 3D plate problems with a plane strain behaviour are in very good agreement with their corresponding 2D BE solutions. Results for a penny shape crack in a piezoelectric cylinder are presented for the first time. The proposed approach is shown to be a simple, robust and useful tool for stress and electric displacement intensity factors evaluation in piezoelectric media.     

The influence of mo additive on the microstructure and property of Ti/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite

The influence of Mo on the microstructure, bending strength and HV of Ti/Al₂O₃ composite was studied, and the influence mechanism was analyzed. The results indicate that after the addition of Mo, the composite organization is finer and phases distribution is better-proportioned which make the microstructure denser, the bending strength and HV of composite are also increased to a degree. But the bending strength increases first then decreases with the increasing of Mo content, so the appropriate Mo content for the Ti/Al₂O₃ composite is to be further confirmed. WANG Zhi: Born in 1962 Funded by Natural Science Foundation of China (No. 50232020) and Natural Science Foundation of Shandong Province (No. 2002F21)     

现代煤油气相干燥工艺及设备（上）

阐述了煤油气相干燥的原理，特点及主要工艺参数，对传统和现代的干燥工艺及其所使用的设备进行了对比，最后对ＭＩＣＡＦＩＬ公司的最新专利产品作了简要介绍。     

数控转塔冲床主传动的发展

对数控转塔冲床主传动部件的发展历程进行了综述,并分析了三种传动方式的优劣。提出将交流伺服控制系统用于数控转塔冲床,采用大规模集成化技术及智能化功率模块,实现对交流伺服的位置环、速度环和电流环的全数字化控制,提高冲床的加工精度及效率。     

机械电子设备中的电气干扰及抗干扰措施

从电源干扰、电磁干扰、接地错误三个方面介绍了机械电子设备中的电气干扰的来源及传输途径；从滤波、电气隔离、屏蔽、接地等四个方面介绍了具体的抗干扰措施。