稀土元素对钯的力学性能的影响

研究了０．１－０．６ａｔ％ＲＥ元素对Ｐｄ的力学性能的影响。稀土不仅提高Ｐｄ的室温强度和弹性模量，也提高Ｐｄ的高温瞬时强度，蠕变寿命和激活能以及Ｐｄ的延伸率。在稀浓度范围内，强度性随浓度呈线性增高。按０．１ａｔ％ＲＥ归一化处理ＰｄＲＥ合金强度性质有反常的影响：在所有Ｐｄ－ＲＥ合金中，Ｐｄ－Ｅｕ合金有最高的强度性质，其次为Ｐｄ－Ｙｂ和Ｐｄ－Ｃｅ合金。稀土在合金中的作用机制，如净化杂质，提高再结晶温度，     

Fabrication and characterisation of neodymium-doped silica glass by sol-gel process

 Neodymium-doped silica glass possesses many properties ideal for high-power laser applications. These include low thermal expansion coefficient, high temperature stability, and low nonlinear index of refraction. For the first time, the sol-gel process has been successfully employed to prepare highly doped neodymia silica glass, up to 5wt% Nd for homogeneous dopant distribution. The optical characteristics of the silica glass and its in-process gel, including the UV/VIS absorption spectra, infrared absorption spectra, fluorescence emission spectrum and the fluorescence lifetime, are measured and analyzed. The structure of the sample is also characterized by means of XRD and SEM. A porous gel is observed to have formed when the heat treatment temperature reaches 300^oC. Wavelength shifts in the absorption peak corresponding to the ⁴I_9/2 to ⁴F_5/2 transition have been observed during the densification process and for different Nd weig ht contents. The FTIR spectra have shown that high temperature heat treatment can greatly reduce the amount of OH groups and organic residue in the silica. We have also shown that a high OH content contributes to weak fluorescence intensity and short fluorescence lifetimes. Received: 3 March 1997 / Accepted: 27 May 1997     

Cations in Inorganic Solids

Abstract

Until recently, cations have been considered as small “isolated” entities, occupying the spaces in close-packed arrays of large anions. An inspection however of cation subarrays reveals that some kind of interaction must exist between them, as they reproduce both the topology and the distances of their parent metal structures.

Up to now, the existence of clusters has been identified with metal-rich compounds or with compounds in which the metal atoms have unsaturated valences. However, from the results reported here, it can be stated that cations recognize themselves in forming aggregates in such a way that the world of clusters also comes into the field of fully ionic compounds, wherein metal atoms have saturated valences.

This kind of interaction has already been observed in silver(I) and gold(I) compounds (and is known as the auriphilic effect or as d ¹⁰-d ¹⁰ interactions); but examples are reported here of similar interactions between cations of the alkaline-earth metals. Group 13 elements, lanthanides, Sc, Ti and Y, indicating that this effect is a general feature of inorganic solids. Although some explanations have been reported, the reasons for such interactions remain unclear. This is an open question challenging theoretical chemists.

These new ideas are placed in the context of similar ones developed recently, which give to cations a more relevant ôle in determining crystal structures. Thus, the old ideas of Lebedev regarding the protagonism of “large” cations in the formation of crystal structures is discussed together with the more recent ideas of O'Keeffe and Hyde which describe the crystal structures of oxides as oxygen-stuffed alloys.

In many oxides, the cations occupy octahedral or tetrahedral holes in close-packed arrays of anions. It is true that in many other structures, the cations reproduce the topology of the structures of elements or simple alloys, but it is also true that the structure of the parent metal is often preserved in its oxides.     

Ratiometric optical thermometer with high-sensitive temperature sensing based on tunable luminescence of Ce3+-Eu2+ in KSr4B3O9 phosphors

It is a challenge to develop a new type of non-contact temperature sensor and the related materials with the advantages of high detection sensitivity, spatial resolution, non-invasive and fast response. In this work, a moderate solid-state method was utilized to prepare a novel Ce³⁺/Eu²⁺ co-doped KSr₄B₃O₉ phosphor for efficient dual-emission temperature-sensing application. According to the different activation energy and the energy transfer process from Ce³⁺ to Eu²⁺, two non-overlapping emission bands with respectively distinctive temperature responses were realized. By using the significant difference in the fluorescence intensity ratio between Eu²⁺ and Ce³⁺, a strong shift of the CIE coordinate from (0.3701, 0.4311) at 293 K to (0.2623, 0.2465) at 443 K could be read out. Meanwhile, the maximum absolute (S_a) and relative sensitivities (S_r) were fitted to be 0.0118 and 2.25 % K^?1 with a large chromaticity shift from 293 to 443 K (ΔE = 0.1652). The configuration coordinate diagram in KSr₄B₃O₉ was adopted to explain the temperature quenching mechanism in detail. The outstanding temperature-sensing characteristic indicates that KSr₄B₃O₉: 1.75 %Ce³⁺/1.75 %Eu²⁺ phosphor has the potential to be applied in a thermometric probe.     

Computational Design of Rare-Earth Reduced Permanent Magnets

Multiscale simulation is a key research tool in the quest for new permanent magnets. Starting with first principles methods, a sequence of simulation methods can be applied to calculate the maximum possible coercive field and expected energy density product of a magnet made from a novel magnetic material composition. Iron (Fe)-rich magnetic phases suitable for permanent magnets can be found by means of adaptive genetic algorithms. The intrinsic properties computed by ab initio simulations are used as input for micromagnetic simulations of the hysteresis properties of permanent magnets with a realistic structure. Using machine learning techniques, the magnet’s structure can be optimized so that the upper limits for coercivity and energy density product for a given phase can be estimated. Structure property relations of synthetic permanent magnets were computed for several candidate hard magnetic phases. The following pairs (coercive field (T), energy density product (kJ·m⁻³)) were obtained for iron-tin-antimony (Fe₃Sn_0.75Sb_0.25): (0.49, 290), L1₀-ordered iron-nickel (L1₀ FeNi): (1, 400), cobalt-iron-tantalum (CoFe₆Ta): (0.87, 425), and manganese-aluminum (MnAl): (0.53, 80).     

稀土氧化物在功能陶瓷中的应用分析

综述了稀土氧化物在压电陶瓷，导电陶瓷，AlN陶瓷，ZrO2氧敏陶瓷，微波介质陶瓷中的应用现状，详细讨论了稀土的作用机理，再现了稀土氧化物掺杂改性的规律，为利用稀土氧化物掺改性功能陶瓷提供一定的参考和指导作用，并且为稀土氧化物的应用指明了方向，简述了该领域应用研究的发展方向。     

天然气蒸汽转化催化剂抗积炭性能研究

用程序升温表面裂解和程序升温表面反应的方法研究催化剂上ＣＨ４裂解和沉积炭与水汽反应过程。试验结果表明：在转化催化剂上，ＣＨ４裂解从２２０℃开始，３６０℃时明显加速，５４０℃时速度达极大值；     

Effect of rare-earth element oxides (La2O3, Ce2O3) on the structural and physico-chemical characteristics of Pd/Al2O3 monolithic catalysts of nitrogen oxide reduction by methane

It is shown that introduction of additives of rare-earth element oxides (La₂O₃, CeO₂) enables regulating the structural and functional characteristics of Pd/Al₂O₃-catalysts (applied on ceramic monoliths of honeycomb structure) of nitrogen oxide reduction by methane. Modifying additives provide increase of thermal stability of porous structure of both highly dispersed Al₂O₃, as the second support, and the catalyst as a whole.

Contribution of La₂O₃ and CeO₂ in increasing the thermal stability is of an additive nature, and lanthanum oxide shows the higher efficiency than cerium one. According to X-ray phase analysis data, stabilizing action is conditioned by occurrence of rare-earth element oxides into lattice of Al₂O₃, which retards diffusional processes leading to phase transitions of low-temperature crystalline modifications of alumina into high-temperature ones with a low specific surface. For the catalyst samples modified with La₂O₃ an effect of thermal activation is observed, which is revealed by increase in catalytic activity as a result of annealing at 850 °C. Such a phenomenon, as shown by means of X-ray photoelectron spectroscopy technique, can be explained via stabilization of palladium in singly charged state in the form of groups of Pd⁺O₂⁻ and corresponding increase in concentration of active centers.     

稀土稳定剂及有机酸对无毒低发泡UPVC发泡体系的影响

介绍了无毒低发泡UPVC发泡体系的分解特性，研究了稀土稳定剂及有机酸对发泡体系、加工流变行为的影响。结果表明，稀土稳定剂的加入使复合发泡剂的分解趋向高温、分解速率降低，同时促进塑化，有利于低发泡UPVC的加工。