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941.
Kristian Radan 《Journal of fluorine chemistry》2011,132(10):767-771
The compounds, Cd(BF4)(TaF6) and Cd(BF4)(BiF6), have been synthesized and characterized by single-crystal X-ray diffraction and Raman spectroscopy. Both isostructural compounds crystallize in the monoclinic P21/c space group with a = 8.2700(6) Å, b = 9.3691(6) Å, c = 8.8896(7) Å, β = 94.196(3)°, V = 686.94(9) Å3 for Cd(BF4)(TaF6) and a = 8.3412(8) Å, b = 9.4062(8) Å, c = 8.9570(7) Å, β = 93.320(5)°, V = 701.58(11) Å3 for Cd(BF4)(BiF6). Eight fluorine atoms (4 BF4− + 4 AF6−) form a surrounding around the cadmium atom in the shape of distorted square antiprism. These compounds are not isostructural with mixed-anion analogues of Ca, Sr, Ba and Pb studied earlier. 相似文献
942.
Multiple processing by means of successive injection cycles was used to simulate the thermo-mechanical degradation effects on the oligomeric distribution of PLA under mechanical recycling. Likewise, an accelerated thermal ageing over PLA glass transition was performed in order to simulate its service life. MALDI-TOF MS was used for the analysis and the sample preparation procedure was assessed by means of a statistical Design of Experiments (DoE). The quality effects in use for the analysis were signal-to-noise ratio and Resolution. Different matrixes, analyte/matrix proportions and the use of NaTFA as cationization agent were considered. A deep inspection of the statistical results provided a better understanding of the influence of the different factors, individually or in combination, to the signal. The application of DoE for the improvement of the MALDI measurement of PLA stated that the best combination of factors (levels) was the following: matrix (s-DHB), proportion analyte/matrix (1/5 V/V), and no use of cationization agent. Degradation primarily affected the initially predominant cyclic [LAC]n and linear H[LAL]nOH species, where LA stands for a PLA repeating unit. Intramolecular and intermolecular transesterifications as well as hydrolytic and homolytic reactions took place during the formation and disappearance of oligomeric species. In both degradation mechanisms induced by thermal ageing and thermo-mechanical degradation, the formation of H[LAL]nOCH3 by intermolecular transesterifications was highlighted. 相似文献
943.
The bottleneck of applying stir bar sorptive extraction (SBSE) to elemental speciation analysis is lack of suitable extraction phases with good affinities to different elemental species. In this paper, a newly high polar extraction phase of titania immobilized polypropylene hollow fiber (TiO2-PPHF) was prepared by sol–gel immersion and low temperature hydrothermal process and the obtained TiO2-PPHF inherits the adsorption properties of TiO2 and the toughness of PPHF. With a suitable size of stainless steel magnetic bar inserted into the prepared TiO2-PPHF, a disposable TiO2-PPHF coating stir bar was obtained. The prepared TiO2-PPHF was characterized by X-ray diffraction spectrometry and scanning electron microscopy and the significant parameters affecting the extraction efficiency of different arsenic species were studied. Based on the above facts, a new method of SBSE combined with high performance liquid chromatography (HPLC)–inductively coupled plasma mass spectrometry (ICP-MS) was developed for the speciation of phenyl arsenic compounds and their possible transformation products in chicken tissues. Under the optimal conditions, limits of detection (LODs) of the developed method for eight target arsenic species were in the range of 11.4–64.6 ng L−1 with enrichment factors of 8.5–22.3 (theory enrichment factor was 50), and the relative standard deviations (RSDs) were varying from 6.3 to 12.6% (cAsIII/V = 5 μg L−1, cMMA,DMA,p-ASA,4-OH,3-NHPAA,PA,4-NPAA = 10 μg L−1, n = 7). The proposed method was successfully applied to the speciation of arsenic in chicken meat/liver samples and the recoveries for the spiked samples were in the range of 78.5–120.4%. In order to validate the accuracy of the proposed method, a certified reference material of BCR-627 tuna fish tissue was analyzed and the determined values were in good agreement with the certified values. The TiO2-PPHF was demonstrated to be a highly selective coating for the target arsenic species, and could be easily prepared in batches with low cost. In addition, with the disposable coating, the carry-over effect commonly encountered in conventional SBSE was avoided. 相似文献
944.
Tetsuya Kawano 《Journal of solid state chemistry》2011,184(9):2466-2471
Single crystals of new oxyborates, Mg5NbO3(BO3)3 and Mg5TaO3(BO3)3, were prepared at 1370 °C in air using B2O3 as a flux. They were colorless and transparent with block shapes. X-ray diffraction analysis of the single crystals revealed Mg5NbO3(BO3)3 and Mg5TaO3(BO3)3 to be isostructural. The X-ray diffraction reflections were indexed to the orthorhombic Pnma (No. 62) system with a=9.3682(3) Å, b=9.4344(2) Å, c=9.3379(3) Å and Z=4 for Mg5NbO3(BO3)3 and a=9.3702(3) Å, b=9.4415(3) Å, c=9.3301(2) Å and Z=4 for Mg5TaO3(BO3)3. The crystal structures of Mg5NbO3(BO3)3 and Mg5TaO3(BO3)3 are novel warwickite-type superstructures having ordered arrangements of Mg and Nb/Ta atoms. Polycrystals of Mg5NbO3(BO3)3 prepared by solid state reaction at 1200 °C in air showed broad blue-to-green emission with a peak wavelength of 470 nm under 270 nm ultraviolet excitation at room temperature. 相似文献
945.
The symmetry operator Q = Y2 is introduced to re-describe the Heisenberg spin triangles in the {V6} molecule, where Y stands for the Yangian operator which can be viewed as special form of Dzyaloshinsky–Moriya (DM) interaction for spin 1/2 systems. Suppose a parallelogram Heisenberg model that is comprised of four -spins commutes with Q, which mean that it possesses Yangian symmetry, we show that the ground state of the Hamiltonian H4 for the model allows to take the total spin S = 1 by choosing some suitable exchange constants in H4. In analogy to the molecule {V6} where the two triangles interact through Yangian operator we then give the magnetization for the theoretical molecule “{V8}” model which is comprised of two parallelograms. Following the example of molecule {V15}, we give another theoretical molecule model regarding the four -spins system with total spin S = 1 and predict the local moments to be , respectively. 相似文献
946.
The laser clad coating technique can help to produce metallurgical bonding with high bonding strength between the coating layer and the substrate, which has been gradually applied for hydroxyapatite (HA) coating on metallic substrates. In this study, HA powder is mixed with two different binders, namely water glass (WG) and polyvinyl alcohol (PVA), respectively, and is then clad on Ti-6Al-4V substrates using an Nd:YAG laser system under various processing conditions. The microstructure, chemical composition and hardness of the coating layer and transition layer of the various samples are then systematically explored. The experimental results show that the coating layers of the various samples all contain both cellular dendrites and rod-like piled structures, while the transition layers contain only cellular dendrites. For all samples, the coating layer consists mostly of CaTiO3, Ca2P2O7, CaO and HA phases, whereas the transition layer contains primarily CaTiO3, Ca2P2O7, Ti3P, Ti and HA phases. In addition, the transition layer of the WG samples also contains SiO2 and Si2Ti phases. In all of the specimens, the transition layer has a higher average hardness than the substrate or coating layer. Moreover, the transition layer in the WG sample is harder than that in the PVA sample. 相似文献
947.
Sultan F Augath M Murayama Y Tolias AS Logothetis N 《Magnetic resonance imaging》2011,29(10):1374-1381
Combining electrical stimulation with fMRI (esfMRI) has proven to be an important tool to study the global effects of electrical stimulation on neural networks in the brain. Here we extend our previous studies to stimulating the upper superior temporal sulcus (STS) in the anesthetized monkey. Our results show that stimulating area V5/MT and surrounding areas leads to positive BOLD responses in the majority of cortical areas known to receive direct/monosynaptic connections from the stimulation site. We confirm our previous results from stimulating primary visual cortex that the propagation of electrically induced activity is limited in its transsynaptic propagation to the first synapse also for extrastriate areas. 相似文献
948.
基于密度泛函理论的第一性原理的Vienna Ab initio Simulation Package (VASP)软件系统研究了Mg7TMH16 (TM=Sc, Ti, V, Y, Zr, Nb)的晶体结构和电子性能. 分析了结合能和形成焓,计算得到的结合能显示Mg7TiH16和Mg7NbH16的稳定性最强,形成焓的变化表明Mg7TMH16具有比MgH2更低的分解温度,电子态密度显示Mg7TMH16表现出明显的金属特性.
关键词:
第一原理
7TMH16 (TM=Sc,Ti,V,Y,Zr,Nb)')" href="#">Mg7TMH16 (TM=Sc,Ti,V,Y,Zr,Nb)
结合能
形成焓 相似文献
949.
以有机-水为混合溶剂, 采用溶胶-凝胶法制备锂离子电池正极材料Li3V2(PO4)3/C, 选取乙醇、乙二醇和1,2-丙二醇为有机溶剂, 聚丙烯酸(PAA)为碳源和螯合剂. 通过X射线衍射(XRD)、扫描电镜(SEM)、恒流充放电以及循环伏安测试等方法, 研究了产物的结构形貌及电化学性能. XRD测试结果表明所有溶剂制备的样品结晶良好, 有机溶剂的加入不影响Li3V2(PO4)3材料的晶型结构. 恒流充放电结果表明有机溶剂的加入改善了材料的电化学性能. 以1,2-丙二醇-水为溶剂的样品电化学性能最好, 在3.0-4.5 V电压范围内, 0.1C (1C=150 mA·g-1)倍率首次放电比容量为132.89 mAh·g-1, 10C倍率首次放电比容量达125.42 mAh·g-1, 循环700周后容量保持率为95.79%, 具有良好的倍率性能与循环性能; 在3.0-4.8 V电压范围内倍率性能较差. 扫描电镜结果表明混合溶剂制备的样品呈片状和针状, 这种形状有利于锂离子的扩散, 因此提高了材料的电化学性能. 相似文献
950.
M. S. El‐Shahawi A. S. Bashammakh A. A. Al‐Sibaai S. O. Bahaffi E. H. Al‐Gohani 《Electroanalysis》2011,23(3):747-754
A simple adsorptive cathodic stripping voltammetry method has been developed for antimony (III and V) speciation using 4‐(2‐thiazolylazo) – resorcinol (TAR). The methodology involves controlled preconcentration at pH 5, during which antimony(III) – TAR complex is adsorbed onto a hanging mercury drop electrode followed by measuring the cathodic peak current (Ip,c) at ?0.39 V versus Ag/AgCl electrode. The plot of Ip,c versus antimony(III) concentration was linear in the range 1.35×10?9–9.53×10?8 mol L?1.The LOD and LOQ for Sb(III) were found 4.06×10?10 and 1.35×10?9 mol L?1, respectively. Antimony(V) species after reduction to antimony(III) with Na2SO3 were also determined. Analysis of antimony in environment water samples was applied satisfactorily. 相似文献