A New Ferroelectric Phase of YMnO3 Induced by Oxygen‐Vacancy Ordering

Manganese oxides are good candidates of strongly correlated electron materials due to the uniqueness of electronic structure of manganese and the mobility of oxygen among lattice sites under external impacts. Here, we used electron beam as the excitation source to explore the structural evolution of YMnO₃ and identified a new phase under the radiation of electron beam in the transmission electron microscope. Analyses of the electron energy‐loss spectra reveal that this phase originates from ordered oxygen vacancy. We applied the first principles calculation to pick out the optimized stable structure with a lower polarization, and verified its correctness by electron diffraction and image simulations. Analyses of density of states indicate that weak Y–O covalence is favorable for the existence of ferroelectricity, supporting the electrostatic nature of ferroelectricity in the YMnO₃.     

腈纶的氧化处理及其耐酸和耐有机溶剂性能研究

分析了腈纶的预氧化工艺,测试了氧化过程各阶段纤维的物理机械性能,并进行了氧化纤维的耐酸和耐有机溶剂的试验。     

Electrochemical synthesis of polyacrylonitrile (PAN)–copper composite conductive film

Polyacrylonitrile–copper composite film was synthesized by electrochemical reduction of a swollen film made by blend solution of a polyacrylonitrile–copper(II) ion which was coated on a electrode surface. The morphological structure of this composite film in the cross section was measured by a scanning electronic microscope and it showed three composite layers: a densely deposited layer, a transition layer, and an undeposited layer. The deposited layer consisted of the copper element and gave a high conductivity (10⁰ S-cm⁻¹). In the transition layer, there was a great amount of a tree-shaped copper deposit, but no such deposit can be found in the undeposited layer. The experiment data showed that the conductivity of the film increases with increase of electrochemical reduction time and decreases with increase of ratio of nitrile group to the copper(II) ion. The viscosity of polyacrylonitrile-copper(II) ion solution is enhanced by a decrease of the ratio of the nitrile group to the copper(II) ion. © 1996 John Wiley & Sons, Inc.     

Surface crystalline characteristics of polyurethane investigated by atomic force microscopy

A polyester—urethane was synthesized by the reaction of 2,4-toluylene diisocyanate (TDI) with poly(butylene glycol adipate) (PBGAD) using 1,4-butanediol (BDO) as a chain extender. Atomic force microscopy was employed to examine the surface morphologies of polyurethane (PU) films formed by heat treatment as well as at room temperature. At both conditions the surface of the PU film appeared as a spherulitic structure with a varied diameter and vertical height. Furthermore, the crystalline structure of heat-treated film was denser than that of the film formed at ambient. © 1996 John Wiley & Sons, Inc.     

晶态介孔材料研究新进展

有序介孔材料从非晶态向结晶态的转变无疑是介孔材料这一领域的重大突破.对目前国内外在晶态介孔材料研究领域的新进展进行了综述,着重介绍了具有代表性的晶态硅基和钛基介孔材料,展望了介孔材料在21世纪的发展及应用趋势.     

正泰BHQ-S-C型电机保护器原理及检修

0引言 正泰BHQ-S-C型电机保护器具有过截保护、过压保护、断相保护等功能,对一般中小型电机具有较全面的保护作用,广泛地应用于生产中.     

电压互感器的配置原则及常见的事故处理方法

1互感器的配置原则 TV的配置原则是:①应满足测量、保护、同期和自动装置的要求;②保证在运行方式改变时,保护装置不失压、同期两侧都能方便地取压.通常配置如下:     

C/SIC复合材料结构动态特性研究

针对C/SiC轻质复合材料结构,将三维编织C/SiC复合材料看作是组分材料的空间结构物,由有序的细观结构单胞叠合而成.采用细观结构单胞作为离散单元对三维编织复合材料结构进行宏观网格剖分,利用有限元方法研究复合材料悬臂板动态特性.计算结果与理论值符合较好.     

核电厂通用老化经验报告分析与编制建议

美国核管会编制发布的通用老化经验报告是美国核电厂运行执照更新的基石文件,对指导核电厂设计、运行和延寿,包括水化学管理、在役检查等老化管理工作具有重要意义.同时国际原子能机构也组织各成员国共同开发国际通用老化经验报告,而国内尚未编制中国核电厂通用老化经验报告.本文从报告适用性、老化经验积累与反馈、老化管理和科研水平提升等...     

噪声信号的故障分析系统

噪声监测由于其测取方便、非接触式测量和携带信息丰富等特点在故障分析与诊断中逐渐受到重视.首先介绍了故障分析中的声信号处理方法,包括时域处理方法和频域处理方法,然后列举了一个具体的基于发动机噪声的故障分析系统的实现方案,主要通过傅立叶变换和小波变换对发动机噪声进行故障分析,证明了利用噪声监测来进行故障分析的可行性.