Crystallisation effects on rare earth dopants in oxyfluoride glass ceramics

Transparent oxyfluoride glass-ceramic materials are of significant interest for the production of new optoelectronic devices. In this paper we report measurements of the detailed spectroscopy of rare earth dopants in both an oxyfluoride transparent glass ceramic and its glass precursor. We show that several spectroscopically different sites exist for the rare earth even in the glass precursor material, where a significant amount of the rare earth is already coordinated with fluorine. In the glass-ceramic material, these glassy fluorine-coordinated sites are replaced with crystalline sites, but a significant fraction of the rare earth ions are still within the glass phase. The fraction of rare earth ion that is incorporated into the crystalline phase is estimated from the rare earth spectroscopy, and the role of the rare earth coordination in the precursor glass is discussed.     

稀土改性磨碎玻璃纤维对磨碎玻璃纤维/聚四氟乙烯复合材料性能的影响

采用三种表面改性剂,即硅烷偶联剂（PTMS）、含PTMS的稀土改性剂（PTMS-RES）和稀土改性剂（RES）,对磨碎玻璃纤维表面处理,探讨了不同表面处理剂对磨碎玻璃纤维/聚四氟乙烯（MGF/PTFE）复合材料介电性能、热膨胀系数和热导率的影响。测试了RES、未改性的磨碎玻璃纤维和PTMS-RES改性的MGF的FTIR谱图,并采用SEM对MGF/PTFE复合材料的断口形貌进行分析。结果表明：与未经表面改性的MGF/PTFE复合材料相比,经表面改性的MGF/PTFE复合材料的介电性能、热膨胀系数、热导率都得到改善。由于RES特殊的电子层结构以及对阴离子有强吸引作用,RES改性效果比PTMS更好。由于RES与PTMS共同的作用,PTMS-RES比RES能更好地改善MGF与PTFE的界面,促进MGF与PTFE的界面粘结。     

Effect of rare earth dopants on the morphologies and photocatalytic activities of BiFeO3 microcrystallites

Pure and rare earth elements (La, Yb)-doped BiFeO₃ microcrystallites were synthesized by a typical hydrothermal process. The crystal structure, morphologies and photocatalytic activities of these microcrystallites were investigated. The results and analysis revealed that substitution of La and Yb not only changed the energy band gap of BiFeO₃ system, but also affected the morphologies and dimensions of BiFeO₃ microcrystallites. Despite much smaller particle size compared with pure BiFeO₃, the Yb-doped BiFeO₃ microcrystallites exhibited lower photocatalytic efficiency due to much larger energy band gap, which suggests the energy band configuration intensely influences the photocatalytic activity rather than the particle size.     

Effects of rare earth metals on electrical conductivity and mechanical properties of commercial purity aluminium

Abstract

The effects of the addition of rare earth metals on the electrical conductivity and mechanical properties of commercial purity aluminium have been investigated both in the laboratory and in industrial trials. The electrical conductivity of commercial purity aluminium is increased by about 1% on the international annealed copper standard by the addition of lanthanum, and both its tensile strength and elongation are improved considerably by the addition of cerium. Investigation of the microstructure of the alloys containing rare earth metals shows that the apparent improvement in the electrical conductivity of commercial purity aluminium is caused by a decrease in the solid solubility of impurities in the aluminium.

MST/2032     

稀土元素Gd对Al-Si-Mg铸造合金微观组织和力学性能的影响

为了系统地研究稀土Gd对铸造Al-Si-Mg(A357)合金组织和性能的影响,采用OM,SEM,EPMA,XRD,DSC,TEM及拉伸实验等方法对不同Gd含量A357合金进行研究。结果表明:Gd的添加可以细化A357合金的晶粒并减小二次枝晶间距。此外,Gd可以有效地细化合金中的共晶硅,但是对片状共晶硅的形貌影响不大。晶粒和共晶硅的细化及二次枝晶间距的减小使添加Gd后的A357合金的力学性能有了显著的提高。其中,A357-0.5Gd(质量分数/%)合金热处理态抗拉强度为355MPa,相对于未添加Gd元素的A357合金提高了37MPa。当Gd质量分数为1.0%时,尽管组织得到进一步细化,但是大量粗大Al 2Si 2Gd第二相的形成导致了合金力学性能的下降。同时对Gd的细化机制进行探究,结合TEM分析结果可以推断,Gd变质处理后共晶硅上的孪晶密度并不足以引起共晶硅形貌的转变,使得Gd变质效果较弱。而Gd对共晶硅的细化作用可能与Gd增加成分过冷以及形成纳米相阻碍共晶硅生长有关。     

Coloration caused by mechanical stress on rare earth oxysulfides

Oxysulfide powders of yttrium, gadolinium, terbium and lanthanum display distinctive colors when they are either heavily ball-milled or pressed in a steel die. These colors are due to optical absorption bands in the visible region, peak positions of which obey an empirical rule like the Mollowo-Ivey relation of color centers in alkali halides. The c-axis shrinks in the colored samples. The colors are bleached and the cell constants are restored to the original values by heat treatment up to 450°C. Some distortions, however, still remain in the annealed samples.     

Structure, nucleation and Eu luminescence in alkaline earth rare earth borate glass

In La₂O₃-MO-B₂O₃ ternary system, various glasses/ glass ceramics with M=Ca, Sr and Ba have been prepared. In this ternary system, homogeneous nucleation occuring in the B₂O₃ melt appears to be the cause for the formation of nanocrystallites, hence glass ceramics. The nucleation process is very much dependent on the alkaline earth used viz., with smaller alkaline earths like Ca, boron prefers (BO₄)⁵⁻ tetrahedral coordination with oxygen, while in the case of bigger alkaline earths like Ba and Sr, (BO₃)³⁻ triangular coordination seems to be predominant. Eu³⁺ in this glass system yields intense ⁵D₀→⁷F_j emission. A cursory view on the dependence of the various Judd-Ofelt parameters (Ω_k) indicates that Ω₂ parameter is very much dependent on the immediate vicinity of the luminescent ion (Eu³⁺) while Ω₄ is not. Various results based on these are discussed.     

Effect of rare earth Y addition on the microstructure and mechanical properties of high entropy AlCoCrCuNiTi alloys

A series of AlCoCrCuNiTiY_x (x values in molar ratio, x = 0, 0.5, 0.8, 1.0) alloys have been prepared using vacuum arc melting. Classical high entropy diffraction peaks corresponding to a BCC crystal structure and some Cu, Cr peaks are observed for the AlCoCrCuNiTi alloy. However, with the incorporation of rare earth element Y, the BCC diffraction peaks disappeared and were replaced by new compounds like Cu₂Y and AlNi₂Ti. A typical cast dendrite structure with Cu-rich dendritic regions and Cr-rich rosette-like shape precipitations are found in the AlCoCrCuNiTi alloy. In the AlCoCrCuNiTiY_x alloys, Y segregated preferentially to Cu and combined as bulky Cu₂Y compound. The maximum stress of the AlCoCrCuNiTi alloy is 1495 MPa, but reduces intensively after the incorporation of Y due to the formation of bulky Cu₂Y. For all the alloys, the compressive fracture mechanism is observed to be cleavage fracture.     

稀土改性剂对玻璃纤维-SiO2/聚四氟乙烯复合材料性能的影响

采用不同的稀土改性剂（La、Ce、Pr、Nd和Sm）对SiO₂和玻璃纤维（GF）进行改性处理,SiO₂含量为55wt%,GF含量为2wt%。填料改性处理后与聚四氟乙烯（PTFE）分散液在高速分散机中混合,然后通过热压烧结法制得GF-SiO₂/PTFE复合材料。考察了不同的稀土改性剂对GF-SiO₂/PTFE复合材料吸水性、介电性能、热膨胀系数和力学性能的影响。采用FTIR手段对稀土La改性剂,未改性的填料和改性后的填料结构进行了测试。并用SEM和EDS对复合材料的断口形貌及表面处理前后填料的形貌进行观察和能谱分析。结果表明：由于稀土La的电子层结构比其他轻稀土更稳定,对阴离子的吸引作用比其他轻稀土强,稀土La改性剂比其他的稀土改性剂能更好地促进填料GF与PTFE界面粘合,改善GF-SiO₂/PTFE复合材料性能。GF-SiO₂/PTFE复合材料的介电性能受到La含量的影响,当La含量为0.3wt%时介电性能最佳。     

Structure and mechanical properties of ZnAl40Cu3 alloy modified with rare earth elements

The influence of modification of rare earth elements on the structure and mechanical properties of ZnAl40Cu3 alloy is presented in this paper. The ZnAl40Cu3, ZnAl40Cu3SiM and ZnAl40Cu3Si (modified alloy) alloys were tested. The ZnAl40Cu3Si and ZnAl40Cu3 alloys were characterized and revealed a heterogeneous, fine‐grained, dendritic structure. The structure of the alloy ZnAl40Cu3SiM was much more homogeneous. It was found that the addition of silicon reduces the tensile strength. Addition of rare earth elements (REE) to the alloy with silicon resulted in the re‐growth of strength. It was also found that the modification of rare earth elements increases the hardness of the alloy.     

Thermal and dielectric properties of rare earth iodates

The thermal (TGA, DTA and DSC) and dielectric behaviour of all rare earth iodates (except prometheum) has been investigated. The iodates of lanthanum, cerium to europium and gadolinium to lutetium decompose differently and the activation energies for these decomposition reactions have been determined. The DSC measurements have shown that all of the anhydrous iodates undergo one or more exothermic/endothermic changes. From the nature of the DSC profiles, heat of transitions, and powder diffraction data the phase transformations of Ln (IO₃)₃ have been found to occur in four different ways (lanthanum, cerium to europium, gadolinium to terbium, dysprosium to lutetium). Dielectric measurements of Ln (IO₃)₃ at varying temperature have corroborated the observations made with DSC studies. Relatively low dielectric constants of the high-temperature phases probably indicate their centrosymmetric structures. The dielectric behaviour of noncentrosymmetric Ln (IO₃)₃·H₂O (Ln=cerium to samarium) has been investigated in the temperature range 30 to –160° C. They have high dielectric constants (_r, ~ 1800 to 2400) at the ambient temperature and do not show significant change in the entire temperature range of investigation.     

Magnetic properties of some rare earth ferrites

The tetragonal SrEu₂Fe₂O₇ and BaEu₂Fe₂O₇ have been investigated using Mössbauer spectroscopy and magnetic susceptibility techniques. The measurements of magnetic susceptibility have been carried out in the temperature range 100 to 700°K. The data have been fitted to Curie-Weiss law $\text{χ =}\text{C}\text{T}\text{+ θ +}\text{A}$ using a non-linear least square curve fitting procedure. These ferrite compounds are paramagnetic above 534°K and 537°K respectively, with antiferromagnetic ordering below these temperatures.     

高掺量稀土磷酸盐玻璃化学稳定性的研究

稀土掺杂的磷酸盐玻璃作为激光介质和特种光学玻璃材料,其化学稳定性研究是至关重要的.本文主要研究了掺加10mo1%和15mo1%Sm2O3的P2O5-BaO-Al2O3体系玻璃的化学稳定性,研究结果表明:玻璃的耐水性能受玻璃中离子含量的影响较大,Al3 和Sm3 离子的含量越高,结构越稳定,耐水性能越好;玻璃的耐酸性能与结构中阳离子的极化能力(Z2/r)有关,Z2/r越大,耐酸性能越好,而且玻璃的侵蚀是渐缓的,这是由于玻璃表面形成了一层明显的覆盖层所致;玻璃在碱性介质中的侵蚀机理是磷酸盐长链末节的金属离子被水化,产生P-O-P断键,形成正磷酸盐溶解到溶液中,同时,随着稀土离子的增加,耐碱性能变差.     

稀土及硼含量对α-Fe/R2Fe14B纳米晶稀土永磁材料磁性能的影响

分析了自1993年至今国内外文献中报道的α-Fe/R2Fe14B纳米晶稀土永磁薄带的实验数据,研究了稀土含量及硼含量对材料磁性能的影响.结果表明,随稀土含量的增加,纳米晶稀土永磁薄带的矫顽力增加,剩磁趋于减小,稀土含量在8%～9%之间获得最佳的综合磁性能;较高的硼含量有利于获得高矫顽力,但不利于得到高剩磁,硼含量在5%～6%之间为宜.     

Effects of neodymium rich rare earth elements on microstructure and mechanical properties of as cast AZ31 magnesium alloy

Abstract

The effects of neodymium rich rare earth elements [RE(Nd)] on microstructure and mechanical properties of as cast AZ31 magnesium alloy were investigated. The microstructures of as cast AZ31–xRE(Nd) alloys display a dendrite configuration, and the secondary dendrite spacing of the α-Mg phase was decreased with the increasing Nd content. The addition of RE(Nd) resulted in the formation of Al₂Nd and Mg₁₂Nd phases. Mechanical properties were improved significantly due to grain refinement and precipitation of intermetallic phases. When the amount of RE is 1·0 wt-%,The as cast AZ31 alloy reached its maximum tensile strength of 249 MPa at room temperature, yield strength of 169 MPa and elongation of 9·0%.     

Microstructure and mechanical properties of sintered glass

Glass microspheres have been sintered under argon in order to obtain sintered brittle bodies over a large range of density. During sintering, the microstructure evolves from a stacking of spheres to a body containing isolated pores. This evolution of the microstructure is described using image analysis and mathematical morphology. Mechanical properties are also investigated as a function of density. Special attention was paid to fracture toughness because, due to the isotropic behaviour of glass, internal stresses of the second order do not exist. A maximum ofG _IC is observed and it can be correlated with changes in the morphological parameters.     

Catalytic properties of rare earth cobaltites and related compounds

The activity for conversion of methanol to CO₂ on rare-earth cobaltites is greatest for SmCoO₃, which has the highest room-temperature ratio of high-spin to low-spin cobalt ions. The sequence of the activities for Sm_0.5·M_0.5CoO₃ (M=Ca,Sr,Ba), Ba>Sr>Ca, is shown to vary as the amount of high-spin cobalt ion in these compounds at 200°C.     

Synthesis and properties of rare earth doped lamp phosphors

Red, blue and green emitting lamp phosphors such as Eu³⁺ doped Y₂O₃ (red phosphor), Eu²⁺ doped Ba_0·64Al₁₂O_18·64, BaMgAl₁₀O₁₇ and BaMg₂Al₁₆O₂₇ (blue phosphors) and Ce_0·67Tb_0·33MgAl₁₁O₁₉ and Eu²⁺, Mn²⁺ doped BaMgAl₁₀O₁₇ (green phosphors) have been prepared by the combustion of the corresponding metal nitrates (oxidizer) and oxalyl dihydrazide/urea/carbohydrazide (fuel) mixtures at 400°–500°C within 5 min. The formation of these phosphors has been confirmed by their characteristic powder X-ray diffraction patterns and fluorescence spectra. The phosphors showed characteristic emission bands at 611 nm (red emission), 430–450 nm (blue emission) and 515–540 nm (green emission). The fine-particle nature of the combustion derived phosphors has been investigated using powder density, particle size and BET surface area measurements. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995     

Physical properties of some rare earth tellurite glasses

Mossbauer and IR spectra as well as the electrical conductivity have been measured to give an idea about the structure and the electrical properties of some rare earth tellurite glasses containing Fe₂O₃. The glasses denoted [1 – (2x + 0.05)] TeO₂ ·xFe₂O₃ · (x + 0.05) Ln₂O₃, wherex = 0.0 and 0.05 and Ln = lanthanum, neodymium, samarium, europium or gadolinium, were prepared by fusing a mixture of their respective reagent grade oxides in a platinum crucible at 800° C for one hour. The Mossbauer parameters such as isomer shift, quadruple splitting and line width were found to be a function of the polarizing power (charge/radius) of the rare earth cations. The Mossbauer parameters were not affected by the heat treatment of the glass samples. Both of the Te-O-Ln and Te-O-Fe stretching vibrations were obtained from the IR results which indicate that the rare earth oxides and iron oxide are partially covalent. The electrical resistivity was measured as a function of temperature from 293 to 520 K. Both the electrical resistivity and the activation energy were found to be a function of the atomic number (Z) of the rare earth cations. The results were interpreted on the basis of the electronic structure of the glass.