Microstructure and Composition of Primary and Recycled Single Grains of YBCO,GdBCO‐Ag,and SmBCO‐Ag Bulk Superconductors

The widespread use of single grain RE‐Ba‐Cu‐O [(RE)BCO] bulk superconductors, where RE is typically Sm, Gd, or Y, is, in part, limited by the relatively high costs of precursor powders and the low success rate of the manufacturing process. Both these problems can be addressed by recycling primary‐processed grains in which the initial growth process has failed in some way. Key to the use of recycled grains in practical applications is an assurance that their properties and performance are not inferior to those of primary grown grains. In this work, we describe the differences between the growth process, microstructure, and properties of primary and recycled (RE)BCO single grains. We observe that the mechanism of growth is the same for both primary and recycled single grain samples in all three RE‐based systems investigated. In the recycling process additional liquid‐rich phase powder is provided beneath a failed sample, whereby this liquid phase infiltrates upwards and contributes a sufficient concentration of additional RE species at the growth front to enable samples to grow relatively easily in the form of single grains by producing a more uniform composition at the growth front, which leads directly to an increased tolerance to the presence of Ag and Ce‐rich agglomerates. Importantly, we observe that the recycled samples have a much more uniform composition, and therefore exhibit more uniform superconducting properties, than single grain samples fabricated by a primary grown process.     

Improved mechanical properties through recycling of Y-Ba-Cu-O bulk superconductors

The success rate of the growth of single grain Y–Ba–Cu–O (YBCO) bulk superconductors, applied typically as trapped field magnets, by melt processing techniques is often rather low. To ensure that the rare earth elements used in these materials are not wasted, and to improve the economics of production, therefore, an effective way of recycling such “failed” samples is essential for the long-term sustainability of the bulk process. In the present paper, a detailed study of the microstructural and mechanical properties of recycled YBCO samples has been made and their properties compared to those of primary grown samples. Recycled YBCO samples exhibit trapped magnetic fields of ～ 70 – 80 % of those observed in primary grown samples. Microstructural investigations reveal a significant reduction in the porosity and a simultaneous improvement in the distribution of Y₂BaCuO₅ second phase inclusions throughout the microstructure of recycled, single grain YBCO samples. This means that, while the superconducting properties of the recycled samples are generally inferior to those of primary grown samples, somewhat surprisingly the mechanical properties such as flexural strength, hardness and tensile strength of the recycled samples can be improved. The recycled YBCO samples studied here exhibited an average flexural strength of 75 MPa, which is almost 50 % higher compared to primary grown YBCO, which has significant implications for their use in practical applications that involve large mechanical forces, such as levitation. Good correlations were observed between the microstructural parameters and measured mechanical properties in both primary grown and recycled YBCO samples.     

Grain boundary conductivity of Ce0.8Ln0.2O2−δ ceramics (Ln = Y, La, Gd, Sm) with and without Co-doping

The acetylacetone precursor method was used to obtain powders of different ceria-based Ce_0.8Ln_0.2O_2−δ (Ln = Y, Gd, Sm, La) compositions, and these powders were used to prepare disks which were sintered at 1150 °C after addition of Co nitrate, or at 1500 °C, without Co. These materials were characterized by impedance spectroscopy to distinguish the bulk and grain boundary behaviours. Arrhenius representations of bulk conductivity data show a gradual slope change, indicating defect interactions on cooling to intermediate and relatively low temperatures. Though data for different doped-ceria samples converge in the high temperature range, significant differences in conductivity and activation energy were found at low temperatures. The grain boundary behaviour shows dependence on the trivalent additive (Y, La, Gd or Sm), and the highest grain boundary conductivity for samples obtained without addition of cobalt nitrate was found for samples with La. However, addition of cobalt nitrate and sintering at relatively low temperature enhances the grain boundary conductivity of the remaining materials. The highest specific grain boundary conductivity was then found for samples containing Sm. Differences in grain boundary behaviour were interpreted based on differences in segregation of the rare earth additives for samples without Co-doping and preferential segregation of Co for Co-doped samples.     

Preparation, Characterization, and Microwave Properties of RETiNbO6 (RE = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Y, and Yb) Dielectric Ceramics

Microwave ceramic dielectric resonators (DRs) based on RETiNbO₆ (RE = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Y, and Yb) have been prepared using the conventional solid-state ceramic route. The DR samples are characterized using XRD and SEM methods. The microwave dielectric properties are measured using resonant methods and a net work analyzer. The ceramics based on Ce, Pr, Nd, and Sm have dielectric constants in the range 32–54 and positive coefficient of thermal variation of resonant frequency (τ_f). The ceramics based on Gd, Tb, Dy, Y, and Yb have dielectric constants in the range 19–22 and negative τ_f.     

Stability and Oxidation Properties of RE-α-Sialon Ceramics (RE = Y, Nd, Sm, Yb)

Oxidation studies of hot-pressed RE-α-sialons, RE _x -Si_{12-4.5 x} Al_{4.5 x} O_{1.5 x} N_{16-1.5 x} (with x = 0.40 for RE = Nd, Sm, Yb; and x = 0.48 for RE = Y) were carried out in oxygen in a TG apparatus for ca. 20 h. Very good oxidation resistance was found for the Yb-doped samples, with parabolic rate constants K _p similar/congruent 0.09 10^-6-3 10^-6 mg²cm^-4s^-1 in the temperature range 1250-1350°C. The promising performance of this material was corroborated by long-term oxidation experiments (5 days) in air at 1350°C. Although the oxidation kinetics can be described by simple equations related to the parabolic rate law (e.g., the arctan equation, Δ W / A ₀=α arctan bt + c t ), the oxidation process in these materials is likely to be complex. The significantly lower oxidation resistance of the RE = Nd, Sm doped α-sialons, especially at higher temperatures, is related to the formation of melilite, RE₂Si_{3− y} Al _y O_{3+ y} N_{4− y} ( y ∼ 1), in these systems. The melilite phase is also responsible for the thermal instability of the Nd- and Sm-α-sialons.     

A Comparison of 0°–0° and 45°–45° bridge‐Seeded,YBCO single grains

A variety of multiseeding techniques have been investigated over the past 20 yr in an attempt to enlarge bulk (RE)BCO superconducting samples fabricated by the top‐seeded melt growth (TSMG) process for practical applications. Unfortunately, these studies have failed to establish whether technically useful values of trapped field can be achieved in multiseeded bulk samples. In this work specially designed, 0°–0° and 45°–45° bridge seeds of different lengths have been employed to produce improved alignment of the seeds during the TSMG process. The ability of these bridge‐seeded samples to trap magnetic field, which is the key superconducting property for practical applications of bulk (RE)BCO, is compared for the samples seeded using 0°–0° and 45°–45° bridge seeds of different lengths. The grain boundaries produced by these bridge seeds are analyzed in detail, and the similarities and differences between the two bridge‐seeding processes are discussed.     

Luminescence properties and tunable emission of Ag NCs in oxyfluoride glass through REF3 (RE = Y,La and Gd) doping

In this research, series of Ag nanoclusters (Ag NCs) contained oxyfluoride glasses were prepared using the melt quenching method, in which the REF₃ (RE = Y, La, and Gd) were selected as dopants to control their size distribution. The absorption, steady and time‐resolved PL spectra were carried to investigate the size dependent luminescence properties of Ag NCs. The spectral results indicated that the super broadband emission of Ag NCs is contributed by the spin‐allowed (blue side) and the spin‐forbidden (red side) transitions, respectively. Besides, the introduction of REF₃ (RE = Y, La, and Gd) can promote the formation of Ag NCs with different sizes and therefore modulated their luminescence properties. The maximum external quantum yields of Ag NCs with emissions at 430, 510, 520, and 570 nm were evaluated to be 24.6%, 40.7%, 56.3% and 30.7%, respectively, which can be obtained in SAg, SAgLa, SAgGd, and SAgY.     

Analysing metals in bottle‐grade poly(ethylene terephthalate) by X‐ray fluorescence spectrometry

After a rigorous cleaning process, recycled food‐grade poly(ethylene terephthalate) (PET), can be mixed with virgin PET resin in different concentrations and used for packaging of soft drinks. Therefore, it is important to have an experimental method to distinguish the presence of recycled polymer in a batch and to check its “true quality.” One of the issues to be verified is the presence of inorganic contaminants due to the recycling process. X‐ray fluorescence technique is one alternative for this kind of analysis. The results obtained in this work show that bottle‐grade PET samples (PET‐btg) are made either via direct esterification or by a transesterification process. Samples that were subjected to thermo‐mechanical processings (superclean® processing, PET‐btg blends processed in our laboratory and soft drink PET packaging) present Fe Kα emission lines with higher intensities than those presented by virgin bottle‐grade PET. After applying principal component analysis, it can be concluded that Fe is an intrinsic contaminant after the recycling process, furnishing a way to indicate class separations of PET‐btg. A calibration and validation partial least squares model was constructed to predict the weight percent of post‐consumption bottle‐grade PET in commercial PET samples. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A Coated Infiltration Growth Technique for Fabricating Single‐Grain Y–Ba–Cu–O Bulk Superconductor

A coated infiltration growth technique was proposed to fabricate single‐grain Y?Ba?Cu?O bulk superconductor, in which a liquid source coated Y₂BaCuO₅ (Y‐211) preform was employed and the liquid source composition was 3BaO + 5CuO. Experimental results indicated that, the sample exhibited a single‐grain morphology on the top surface, and the liquid source coating always existed surrounding the bulk which contributed to the complete growth of the sample. The homogeneous distribution of fine Y‐211 inclusions in microstructure and a satisfactory J_c performance of 5.67 × 10⁴ A/cm² in self‐field at 77 K have also been observed.     

Modified Pechini Synthesis of Proton‐Conducting Ba(Ce,Ti)O3 and Comparative Studies of the Effects of Acceptors on its Structure,Stability, Sinterability,and Conductivity

The phase structure, chemical stability, sinterability, and electrical performance of the proton‐conducting Ba(Ce,Ti)O₃ solid solution with a series of acceptors M (M = In, Y, Sm) synthesized by a modified Pechini method were systematically investigated. The substitution of cerium with titanium was proved as an effective way to improve the stability of BaCeO₃. Especially for the BaCe_0.95Ti_0.05O_3?δ sample doped with In, no change in the phase was found even after treatment in the atmosphere containing both CO₂ and H₂O at 700°C for 10 h. Thanks to the highly sinteractive powders with particle size of ~100 nm, dense ceramics were easily acquired. Moreover, compared with the undoped BaCe_0.95Ti_0.05O₃ sample, In, Y, and Sm dopants further improved the sinterability of the solid solution. In particular, In played a role of sintering aid and led to the largest linear shrinkage of the ceramics. As to the electrical performance, the transport properties of the samples under various atmospheres were analyzed and compared. The impedance tests demonstrated the best electrical performance of the Y‐doped samples.     

Reactivity between rare‐earth oxides based thermal barrier coatings and a silicate melt

The reactivity between rare‐earth (RE‐) oxide stabilized ZrO₂ or HfO₂ thermal barrier coatings (TBCs) and a calcium‐magnesium‐aluminum‐silicate (CMAS) melt was studied at 1310°C. These reactions are representative of the ingestion of siliceous materials by the intake air of gas turbines (e.g., in aircraft engines) at high temperatures (>1200°C). These materials can melt and react with coated components in the hot section, resulting in premature failure. The goal of this work was to probe the effect of various RE (RE = Y, Yb, Dy, Gd, Nd, and Sm) oxides in the melt phase equilibrium and stability of the top‐coating system. Thermodynamic calculations of the phase assemblage of the (1?x) ZrO₂‐xY₂O₃ coating materials and CMAS melt are compared with the experimental findings. CMAS was found to penetrate the samples at the grain boundaries and dissolve the coating materials to form silicate phases containing the RE elements. Furthermore, apatite and garnet crystalline phases formed in the samples with total RE‐oxide content higher than 16 mol% in the reaction zone for the ZrO₂ system. In general, samples with nominal compositions ZrO₂‐9Dy₂O₃, HfO₂‐7Dy₂O₃, ZrO₂‐8Y₂O₃, HfO₂‐6Er₂O₃, ZrO₂‐9.5Y₂O₃‐2.25Gd₂O₃‐2.25Yb₂O₃, and ZrO₂‐30Y₂O₃ exhibited lower reactivity, or more resistance, to CMAS than the other coating compositions.     

A Novel Top‐Seeded Infiltration Growth Technique for Fabricating Y–Ba–Cu–O Single‐Grain Superconductor Nano‐Composites

Top‐seed infiltration and growth technique (TSIG) is proposed to fabricate Y–Ba–Cu–O (YBCO) single‐grain superconductor nano‐composites, in which a solid source composition of nano‐Y₂O₃ + BaCuO₂ and a liquid source composition of Y₂O₃ + 10BaO + 16CuO are employed. As can be seen, this novel technique uses just one source of precursor powder of BaCuO₂, so it is more simplified and efficient. Microstructural observation indicates that fine Y₂BaCuO₅ (Y‐211) inclusions with a size from dozens of nanometers to about one hundred nanometers are successfully introduced in YBa₂Cu₃O_7?x (Y‐123) superconducting matrix, which can act as more effective pinning centers for improving the bulk performance. Superconducting property measurement shows that, a maximum trapped field of 0.36044 T is present at the center of the sample after magnetization by a permanent magnet (B = 0.5 T). These results prove that our proposed TSIG technique is a practical method for fabricating YBCO bulk superconductor nano‐composites with high performance.     

RE[TsGlyH]3Cl3·nH2O（RE=La,Nd,Sm,Eu,Gd,Er）配合物燃烧热测定及其标准生成焓的研究

在298.15 K下,用氧弹热量计测定了稀土配合物RE[TsGlyH]3Cl3·nH2O（RE=La,Nd,Sm,Eu,Gd,Er）的恒容燃烧热-△cU,其结果依次为15 918.2,15 879.3,15 526.7,15 246.9,15 492.4,11 727.8 J/g。并据此计算出标准摩尔生成焓-△fHmθ分别为1 977.05,1 939.71,2 189.36,2 352.82,2 123.04,5 743.50 kJ/mol。这些结果为配合物的稳定性和热化学数据关系提供了实验依据。     

Low temperature coefficient dielectric materials,PbRETiTaO7 (RE=Y,La, Nd,Sm, Gd,or Dy) having pyrochlore type structure

Abstract

The present work investigates the dielectric properties of pyrochlore type oxides, PbRETiTaO₇ (RE=Y, La, Nd, Sm, Gd, or Dy) in the low frequency region (100 kHZ–1 MHz) at temperatures between 30 and 100°C and the microwave frequency region. The 1 MHz dielectric constants (K) are in the range 43–99 and show somewhat low variation with temperature (30–100°C) as well as frequency (1 kHz to 1 MHz). The temperature coefficient of dielectric constant (TCK) over the temperature range 30–100°C is negative and varies in the range, ?72 to ?342 ppm °C^?1. The dielectric constant in the microwave frequency region is in the range 23–43. Among the samples, PbGdTiTaO₇ shows very good quality factor (Q×f) of 4008 in the microwave frequency region. They all have cubic pyrochlore type structure as indicated by powder X-ray diffraction patterns. The sintered microstructure shows well formed grains without much porosity.     

Effect of Rare Earth Doping on the Catalytic Activity of Copper‐Containing Hydrotalcites in Phenol Hydroxylation

The copper‐containing hydrotalcites (Cu‐HTLcs) are synthesized under microwave irradiation, the effect of rare earth elements (RE) on the synthesis of Cu‐HTLcs, wherein RE stands for rare earth elements, e.g., La, Y, Sm and Ce, is also investigated in the present work. The hydrotalcite structure of the synthesized samples is verified by XRD and FT‐IR. The results of their catalytic performances in phenol hydroxylation show that the doped rare earth elements can promote the catalytic activity of Cu‐HTLcs, exhibiting a good trend as follows: La>Y>Sm>Ce. XPS results show that the Cu⁺ species are produced after the interaction of La‐Cu‐HTLcs with H₂O₂. Combining with the catalytic test results, we propose a new mechanism about the generation of HO ^. radicals in phenol hydroxylation, it is assumed that HO‐Cu⁺‐OH species are first formed by the reduction of HO‐Cu²⁺‐OH located in hydrotalcites in the presence of H₂O₂, and then react with H₂O₂ to give rise to HO^. radicals.     

Significant Improvement of Superconducting Properties in Nano‐NiFe2O4‐Doped Y–Ba–Cu–O Single‐Grain Superconductor

Introduction of refined second‐phase particles in superconducting YBa₂Cu₃O_7?x (Y‐123) matrix is known to be an effective route to improve the δl‐type pinning and the performance of Y–Ba–Cu–O (YBCO) single‐grain superconductors, while the δT_c‐type pinning induced by spatial fluctuations in matrix composition is also important and contributes to the in‐field J_c performance and high‐field applications of bulk superconductors. In this communication, chemical doping of nano‐sized NiFe₂O₄ (mean size 50 nm) in single‐grain YBCO superconductor is performed using a novel top‐seeded infiltration growth (TSIG) technique based on a solid source pellet (SSP) of nano‐Y₂O₃ + BaCuO₂. The results indicate that, significant improvement of bulk performances including levitation force (33.93 N) and trapped field (0.3628 T) has been observed in the 0.2 wt% nano‐NiFe₂O₄‐doped sample, which are much higher than the undoped sample (28.81 N and 0.2754 T). T_c measurement indicates that, a decreased onset T_c of about 87.5 K and a broadened transition width of about 5 K are observed in the NiFe₂O₄‐doped sample, indicating appearance of weak superconducting regions in superconducting matrix caused by Ni and Fe substitutions in Y‐123 crystal lattice. This study supplies a practical approach to increase the YBCO bulk performance significantly.     

过渡金属氧化物对苯并恶嗪热稳定性影响研究

将过渡金属氧化物TiO2、MnO2、CuO、Cu2O、ZnO、ZrO2以及Y2O3、CeO2、Sm2O3、Gd2O3分别添加到苯酚/4,4'-二苯甲烷二胺型苯并恶嗪(BB)中间体中,制备了过渡金属氧化物/BB固化物,通过FTIR、TGA和DMA分析研究了过渡金属氧化物对苯并恶嗪热稳定性的影响。结果表明,这些氧化物的添加不改变BB固化物的化学结构;除ZnO外,其他氧化物均使BB的热稳定性和800℃残炭率降低,这是由于过渡金属氧化物与BB中N原子间配位作用的形成削弱了C—N键,使其更易断裂。     

Re‐using bauxite residues: benefits beyond (critical raw) material recovery

Since the world economy has been confronted with an increasing risk of supply shortages of critical raw materials (CRMs), there has been a major interest in identifying alternative secondary sources of CRMs. Bauxite residues from alumina production are available at a multi‐million tonnes scale worldwide. So far, attempts have been made to find alternative re‐use applications for bauxite residues, for instance in cement / pig iron production. However, bauxite residues also constitute an untapped secondary source of CRMs. Depending on their geological origin and processing protocol, bauxite residues can contain considerable amounts of valuable elements. The obvious primary consideration for CRM recovery from such residues is the economic value of the materials contained. However, there are further benefits from re‐use of bauxite residues in general, and from CRM recovery in particular. These go beyond monetary values (e.g. reduced investment / operational costs resulting from savings in disposal). For instance, benefits for the environment and health can be achieved by abatement of tailing storage as well as by reduction of emissions from conventional primary mining. Whereas certain tools (e.g. life‐cycle analysis) can be used to quantify the latter, other benefits (in particular sustained social and technological development) are harder to quantify. This review evaluates strategies of bauxite residue re‐use / recycling and identifies associated benefits beyond elemental recovery. Furthermore, methodologies to translate risks and benefits into quantifiable data are discussed. Ultimately, such quantitative data are a prerequisite for facilitating decision‐making regarding bauxite residue re‐use / recycling and a stepping stone towards developing a zero‐waste alumina production process. © 2018 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Self-Propagating High-Temperature Synthesis of α-SiAlON Doped by RE (RE=Eu,Pr,Ce) and Codoped by RE and Yttrium

Self-propagating high-temperature synthesis (SHS) was applied to synthesize α-SiAlON powders doped by RE (RE = Eu,Pr,Ce) and codoped by RE and yttrium. The results showed that the weight ratio of α-SiAlON to (α-SiAlON +β-SiAlON) decreased from 70%, 55%, and 25% for europium-, praseodymium-, and cerium-doped α-SiAlON compositions, respectively, and the weight percentage of α-SiAlON phase increased to 100% for both (Eu,Y) and (Pr,Y) systems and 94% for the (Ce,Y) system, indicating SHS is a promising approach for synthesizing α-SiAlONs stabilized by the cations that could not be incorporated into the α-SiAlON structure by conventional sintering methods.     

Towards thermal barrier coating application for rare earth silicates RE2SiO5 (RE= La,Nd, Sm,Eu, and Gd)

Rare earth (RE) silicates X1-RE₂SiO₅ (RE = La, Nd, Sm, Eu, and Gd) are comprehensively investigated as promising thermal barrier coating candidates. The mechanical, thermal, and corrosion resistance properties are evaluated by theoretical exploration and experimental measurement. Mechanical properties and corrosion resistance to calcium-magnesium alumino-silicates (CMAS) melts of X1-RE₂SiO₅ are linearly correlated with ionic radius of RE elements. Elastic moduli increase with the decrease of ionic radius of RE³⁺. X1-RE₂SiO₅ with larger RE³⁺ exhibits better resistance to molten melts corrosion. For thermal properties, they are not obviously sensitive to RE species. All X1-RE₂SiO₅ demonstrate low thermal conductivities and their magnitudes are significantly modified by concentration of defects. Thermal expansion coefficients of X1-RE₂SiO₅ are more or less close and are compatible with the value of superalloy. The results highlight X1-RE₂SiO₅ as potential thermal barrier coating candidates with overall properties.