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71.
V Babizhetskyy 《Journal of solid state chemistry》2004,177(2):415-424
Solid state phase equilibria in the ternary Gd-Si-B phase diagram have been proposed at 1270 K using X-ray diffraction, scanning electron microscopy and electron probe microanalysis. Prior to this work, the binary systems Gd-B, Gd-Si and Si-B have also been reinvestigated. The main characteristic of the ternary diagram is the occurrence of two new ternary compounds Gd5Si2B8 and Gd5Si3B0.64. The former crystallizes in tetragonal symmetry, space group P4/mbm with unit cell parameters a=7.2665(3), c=8.2229(7) Å, the second one presents hexagonal symmetry, space group P63/mcm with unit cell parameters a=8.5080(4),c=6.4141(2) Å. The X-ray structures of the two structurally related phases Gd5Si3B0.64 and host binary Gd5Si3 have been refined from three-dimensional single-crystal intensity data to the final R values of 0.036 (Rw=0.046) and 0.046 (Rw=0.055) for 457 and 401 reflections, respectively with [F>4σ(F)]. Both structures exhibit the Mn5Si3-type structure, with in addition for Gd5Si3B0.64 a partial occupancy by boron of the normally vacant interstitial site at the center of the Gd6 octahedron, which corresponds to the origin of the unit cell. Bonding between the interstitial boron atoms and the gadolinium ones forming the Gd6B polyhedra is indicated by the decrease in the corresponding Gd-Gd distances and consequently in the unit cell volume. Finally, the Gd-Si-B phase diagram is compared with the previously reported Er-Si-B, at 1070 K. 相似文献
72.
A novel class of platinum-based initiating systems for the ring-opening polymerization of a wide variety of heterocyclic compounds including epoxides, oxetanes, and 1,3,5-trioxane have been discovered. In addition to a platinum complex as a catalyst, a cocatalyst, consisting of a compound or polymer containing silicon-hydrogen bonds must also be present. This article reports on a preliminary survey of the scope and limitations of these new initiator systems. Particular emphasis in this article has been placed on the ring-opening polymerization of epoxides which have been studied in some detail and which proceed rapidly and exothermically at room temperature. A number of mechanistic studies have been conducted and the best current evidence suggests that polymerization proceeds by a cationic mechanism. Evidence is also presented which suggests that platinum metal colloids may function as the active initiating species. 相似文献
73.
Dithiocarbamate functions were incorporated into different polyacrylamide matrices crosslinked with a flexible and hydrophilic
crosslinking agent, tetraethyleneglycol diacrylate (TEGDA), and their complexation behaviours were investigated. Crosslinked
polyacrylamides with varying extents of the tetrafunctional TEGDA crosslinks were prepared by free radical solution polymerization
at 60°C using potassium persulphate as initiator in ethanol. The dithiocarbamate functionality was incorporated into these
polyacrylamides by a two-step polymer-analogous reaction involving (i)trans-amidation with ethylenediamine and (ii) dithiocarbamylation of the aminopolyacrylamide with carbon disulphide and alkali.
The complexations of dithiocarbamate with Cu(II), Ni(II), Zn(II), Co(II) and Hg(II) ions were followed under different conditions.
The metal ion intake varied with the extent of the crosslinking agent and the observed trend in complexation is Hg(II) > Cu(II)>
Zn(II)> Co(II)> Ni (II). The time-course of complexation, the possibility of recycling, swelling characteristics, and spectral
and thermal analyses were carried out. The thermal stability increases upon complexation with metal ions. 相似文献
74.
Brad M. Rosen Virgil Percec 《Journal of polymer science. Part A, Polymer chemistry》2007,45(21):4950-4964
Atom transfer radical polymerization (ATRP) and single electron‐transfer living radical polymerization (SET‐LRP) both utilize copper complexes of various oxidation states with N‐ligands to perform their respective activation and deactivation steps. Herein, we utilize DFT (B3YLP) methods to determine the preferred ligand‐binding geometries for Cu/N‐ligand complexes related to ATRP and SET‐LRP. We find that those ligands capable of achieving tetrahedral complexes with CuI and trigonal bipyramidal with axial halide complexes with [CuIIX]+ have higher energies of stabilization. We were able to correlate calculated preferential stabilization of [CuIIX]+ with those ligands that perform best in SET‐LRP. A crude calculation of energy of disproportionation revealed that the same preferential binding of [CuIIX]+ results in increased propensity for disproportionation. Finally, by examining the relative energies of the basic steps of ATRP and SET‐LRP, we were able to rationalize the transition from the ATRP mechanism to the SET‐LRP mechanism as we transition from typical nonpolar ATRP solvents to polar SET‐LRP solvents. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4950–4964, 2007 相似文献
75.
76.
We have carried out some photon interaction measurements using 59.54 keV γ-rays from a 241Am source. These include γ attenuation studies as well as photoelectric absorption studies in various samples. The attenuation
studies have been made using leaf and wood samples, samples like sand, sugar etc., which contain particles of varying sizes
as well as pellets and aqueous solutions of rare earth compounds. In the case of the leaf and wood samples, we have used the
γ-ray attenuation technique for the determination of the water content in fresh and dried samples. The variation of the attenuation
coefficient with particle size has been investigated for sand and sugar samples. The attenuation studies as well as the photoelectric
studies in the case of rare earth elements have been carried out on samples containing such elements whose K-absorption edge
energies lie below and close to the γ-energy used. Suitable compounds of the rare earth elements have been chosen as mixture
absorbers in these investigations. A narrow beam good geometry set-up was used for the attenuation measurements. A well-shielded
scattering geometry was used for the photoelectric measurements. The mixture rule was invoked to extract the values of the
mass attenuation coefficients for the elements from those of the corresponding compounds. The results are consistent with
theoretical values derived from the XCOM package. 相似文献
77.
本文用数字散斑相关方法测量了五种不同幂硬化指数韧性金属材料(铝和铜),双边裂纹尖端细观区域内应变场.对所得结果用韧性损伤模型进行了分析.在此法中以金属自然表面结构为散斑场,不同加载状态的散斑场进行比较,得到相对变形与应变.图象之间相关性 C 是变形参数或是位移及其导数的泛函.使其相关性 C 取最大值的试凑变形即为其真实变形场.这一方法在细观测量中应用得到满意的结果. 相似文献
78.
Sahadev R. K. Sharma S. K. Sindhwani 《Monatshefte für Chemie / Chemical Monthly》1992,123(10):883-889
Summary The chelation behaviour of some trivalent lanthanide and yttrium metal ion with biologically active 2-hydroxy-1-naphthaldehyde thiosemicarbazone (HNATS) has been investigated by potentiomotric measurements at 20±0.5°C in 75% (v/v) dioxane-water medium at various ionic strengths of sodium perchlorate. The method of Bjerrum and Calvin, as modified by Irving and Rossotti has been used to find out the values of
(average number of ligand bound per metal ion) andpL (free ligand exponent). The formation constants of metal chelates have been computed on a PC-XT computer, using a program patterned after that of Sullivan et al. to give
n
values using weighted least squares method. TheS
min
values (S
min
=2) have been calculated. The order of formation constants of chelates was found to be: La3+3+3+3+3+3+3+3+3+3+. The formation constants of the chelates formed have been correlated to size and ionization potentials of the metal ions.
Potentiometrische Untersuchungen der Komplexierungsgleichgewichte zwischen einigen trivalenten Metallionen und biologisch aktivem 2-Hydroxy-1-naphthaldehyd-thiosemicarbazon (HNATS)
Zusammenfassung Es wurde das Chelierungsverhalten einiger trivalenter Lanthanidenionen mit biologisch aktivem 2-Hydroxy-1-naphthaldehyd-thiosemicarbazon (HNATS) mittels potentiometrischer Messungen bei 20±0.5°C in 75% (v/v) Dioxan-Wasser bei verschiedener Ionenstärke an Natriumperchlorat untersucht. Die Methode nach Bjerrum und Calvin in der Modifikation nach Irving und Rossotti wurde zur Ermittlung der Werte (mittlere Anzahl an Liganden pro Metallion) undpL (Exponent an freiem Liganden) verwendet. Die Komplexbildungskonstanten wurden in Anlehnung an Sullivan et al. an einem PC-XT Computer errechnet. DieS min-Werte (S min=2) wurden ebenfalls bestimmt. Die Reihung der Chelatbildungskonstanten war: La3+相似文献3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+ 3+. Die Bildungskonstanten sind mit der Größe und dem Ionisierungspotential der Metallionen zu korrelieren.
79.
80.
纳米二氧化钛粒子分散性能的研究 总被引:15,自引:0,他引:15
以四氯化钛为原料,采用溶胶-凝胶法技术合成路线,获得了平均粒径为63nm的二氧化钛粉末。采用分散技术,不仅可以改善粒子的分散性能,而且对粒子的生长也起到一定的抑制作用。研究表明:(1)采用SDS作为分散剂时,其极性基团和非极性基团分别与水和纳米TiO2粒子相结合,从而阻隔了TiO2粒子的团聚,起到分散作用。(2)以稀土元素La作为分散剂,其独特的轨道结构,不仅扩大了能量吸收的范围,更重要的是它与TiO2形成的络合物,使其成为相对独立的小团体,而它本身很小的固溶度使其难于形成合金化组元,结果被释放出来,从而形成更小的纳米TiO2粒子,起到分散纳米TiO2粒子的作用,并同时抑制纳米TiO2粒子的生长。 相似文献