Effect of rare earth additives on properties of silicon nitride ceramics

Abstract

Silicon nitride ceramics with rare earth (Re) compound (5 wt-%) and MgO (3 wt-%) additives were fabricated by spark plasma sintering and following heat treatment. The Re compounds included two groups: ReF₃ ((Re?=?La,Nd,Gd) and Re₂O₃ (Re?=?La,Nd,Gd). Specimens show the same tendency in the sintering shrinkage rate, relative density, grain size and bending strength with the increasing Re cation (Re³⁺) radius both in ReF₃ and Re₂O₃ added samples. However, as to aspect ratios and thermal conductivity, the change rules are completely opposite between the two groups of specimens.     

ADSS光缆在特殊跨越条件下的施工技术

介绍了更换光缆中需要跨越带电输电线路、公路、铁路、桥梁等特殊跨越条件下的施工技术。阐述了ADSS光缆特性、连接及展放原则，提出这些特殊条件对施工的影响及相应处理措施。针对抢修工期紧迫，还需采取一些特殊工艺措施，如吊装滑轮法、用工器具作支撑法、利用架空线织网法等。供有关技术人员参考。     

Sol–Gel-Prepared Pure and Lithium-Doped Hexacelsian Polymorphs: An Infrared, Raman, and Thermal Expansion Study of the β-Phase Stabilization by Frozen Short-Range Disorder

Monoclinic and hexagonal forms of celsians (BaAl₂Si₂O₈) were synthesized by hydrolysis–polycondensation of Si/Al alkoxide mixtures. Dilatometry, Raman scattering, IR absorption, and X-ray diffraction techniques were used to identify various hexacelsian phases and their conversion into the monoclinic phase as a function of thermal treatments and doping. Emphasis is given to the relationship between the shrinkage behavior and the static and dynamic short-range disorders in the XO₄ tetrahedra (X = Si/Al) arrangement. The α hexagonal phase exhibits a well-defined α–β_HT transition at about 300°C but a "statically disordered"β_SD form, which does not vary very much with temperature and is very similar to the β_HT form obtained below 300°C for some materials. This statically disordered phase is preferentially observed for fast-sintered lithium-free compositions and transforms gradually in the ordered form by annealing above 1100°C. Such stabilization of the high-temperature phase by the static disorder arising from the peculiar synthesis through alkoxide hydrolysis and the gel route, which freeze the dynamic disorder of gel-forming entities in a static disorder at the gelation step, is discussed in the light of previously observed cases. The thermal expansion behavior is very sensitive to the synthesis conditions, doping, and thermal treatments. The ordered α phase is more easily achieved with lithium-doped compositions, but lithium addition shifts the hexagonal-to-monoclinic phase transformation onset toward lower temperatures and promotes complete transformation with thermal annealing.     

陶瓷金卤灯发展的关键——多晶氧化铝陶瓷泡壳（上）

本文简述了陶瓷金卤灯的特征特性，分析了灯对陶瓷材料的要求，对比了某些陶瓷材料的结构成分及对陶瓷灯的影响，对国产陶瓷材料及泡壳进行了分析研究并给出了部分分析结果。     

Rare-earth doped sol-gel derived oxyfluoride glass-ceramics: Structural and optical characterization

Glass-ceramics containing RE³⁺-doped BaF₂ nanocrystals (RE = Eu, Sm, Dy, Ho and Pr) with the size below 10 nm size have been made by using the controlled crystallization at higher temperatures of the RE³⁺-doped SiO₂-BaF₂ xerogels. Photoluminescence measurements have indicated the incorporation of the RE³⁺ ions in both silica network and in the BaF₂ nanocrystals. Thermoluminescence measurements have shown a peak whose position depends on the nature of RE³⁺-dopant as it follows: 140 °C (for Ho³⁺, Dy³⁺), 340 °C (for Sm³⁺) and 370 °C (for Eu³⁺); in Eu³⁺-doped SiO₂ glass the TL peak is shifted to 383 °C. The peaks in glass-ceramics were assigned to the recombination of the electrons thermal released from the RE³⁺-electron traps located in both glass-matrix and BaF₂ nanocrystals. Within the series the trivalent lanthanide ions act as increasingly deeper electron trapping centres.     

The research center for ultra-high voltage electron microscopy at Osaka University

High-voltage electron microscopy has shown itself advantageous for the study of natural science, including biology, but especially for materials science. The most important advantage for materials science is for in situ experiments about the detailed processes of the phenomena that occur in bulk materials. The present paper is mainly concerned with several types of in situ experiments that have been carried out in the Research Center for Ultra-High Voltage Electron Microscopy, Osaka University. The following subjects have been studied: (a) fundamental problems, such as the conditions necessary for in situ experiments, functional features of specimen treatment devices, and the effects of electron irradiation; (b) the dislocation behavior of crystals under various conditions; (c) high-temperature behavior of refractory materials, mainly ceramic composites; (d) new applications of electron irradiation effects, such as amorphization of crystalline materials and electron-irradiation-induced foreign-atom implantation; (e) environment-matter interaction, mainly chemical amorphization of alloys; and (f) future trends of the in situ experiment, such as combinations with Auger valency electron spectroscopy and high-resolution electron microscopy.     

普通出口陶瓷的现状分析及有关技术问题探讨

分析了中国陶瓷在国际市场上只能处于较低价位的原因，并提出了发展普通出口陶瓷所应采取的对策，尤其对其有关技术问题作了较为详尽的探讨。     

不同铅气氛对PZMN陶瓷压电性能的影响

摘要：采用二次合成法制备了XPMN-(0．2-x)PZN-0．8PZT(x=0．05～0．20)四元系压电陶瓷(PZMN)，系统研究了铅气氛和非铅气氛条件对陶瓷显微组织，介电性能及压电性能的影响规律并探讨了铅气氛作用机制。实验表明在富铅气氛的作用下，PZMN体系具有较优的性能，尤其是x=0．10时，能获得综合优良的压电性能，相对介电常数ε^T33/εo=1000，介电损耗tanδ-0．0050，机电耦合系数Kp=0．52，品质因数Qm=2528，Tc=325℃，可以满足压电变压器等大功率器件应用方面的要求。