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1.
S.A. Masti A.K. Sharma P.N. Vasambekar A.S. Vaingankar 《Journal of magnetism and magnetic materials》2006
Magnetization and permeability of polycrystalline ferrites with general formula CdxMg1−xFe2−yCryO4 (x=0, 0.2, 0.4, 0.6, 0.8, 1.0; y=0, 0.05 and 0.10) were studied. Study of saturation magnetization reveals that the Neel's two-sublattice model exists upto x=0.4, for y=0, 0.05 and 0.1 and a three-sublattice model (YK-model) is predominant for x>0.4 and y=0, 0.05 and 0.10. The saturation magnetization and magnetic moment were found to decrease with the increase in Cr3+ contents, which is attributed to the dilution of B–B site interaction. Variation of initial permeability with temperature revealed the long-range ferromagnetic ordering in the compounds with x=0.4. The sample with x?0.4 and y=0, 0.05 and 0.10 showed peaking behavior near Curie temperature, which is attributed to the decrease of anisotropy constant K1 to zero. Low-frequency dispersion of initial permeability suggests domain wall displacement. Addition of Cd2+ resulted in a sharp decrease in Curie temperature. With the addition of Cr3+, initial permeability was found to decrease. 相似文献
2.
The electronic states of the Cr overlayers on TiO2(0 0 1) surfaces have been investigated using angle-resolved and resonant photoemission spectroscopy with synchrotron radiation. At lower coverages, Cr deposition on TiO2(0 0 1) creates two well separated in-gap emissions due to the formation of surface Ti3+ (3d1) ions and Cr3+ (3d3) ions. At higher coverages, the in-gap emission is developed into the 2-peak-structure emission of Cr 3d character. The corresponding state is considered to be of metallic nature from the viewpoint of the high ability of oxygen adsorption, but has no Fermi edge, indicating a possibility of forming small Cr clusters on TiO2(0 0 1) at this stage. 相似文献
3.
一次消解测定蔬菜中多种重金属的简捷方法 总被引:1,自引:0,他引:1
针对一般实验室检测人员少,检测任务重的问题,研究了蔬菜通过一次湿化消解后,消解液可以测定多种重金属元素的方法,大大提高了效率,减轻了工作量. 相似文献
4.
Steve Tisserand Célia Billaud J.R. Falck Charles Mioskowski 《Tetrahedron letters》2006,47(29):5177-5180
CrCl2-mediated condensation of γ-chloro-gem-trichloroalkanes with aldehyde generates homoallylic alcohols through a hydride rearrangement followed by a Nozaki-Hiyama allylation. 相似文献
5.
6.
助剂对Cu/Cr催化剂上甲醇部分氧化制氢的活性影响 总被引:4,自引:1,他引:4
曾研究了Cu/Cr二元催化剂上甲醇部分氧化制氢的反应,发现当Cu/Cr比为6:4时,催化剂的Cu^0比表面积最大,呈现出较好的活性。在Cu/Cr(6:4)催化剂中添加Fe,Zn,Al等8种助剂,考察其对甲醇部分氧化制氢催化性能的影响,并着重研究了Zn助剂的作用。实验结果表明,Zn的引入,有利于催化剂活性的提高。当Zn含量为10%时,催化剂活性最好。XRD表征结果表明,Cu/Cr催化剂的失活与其表面上的Cu物种烧结有关,Zn的引入可明显增强Cu/Cr(6:4)催化剂的热稳定性,提高其寿命。 相似文献
7.
Studies were performed to determine the effect of pH on chromium (Cr) binding by native, esterified, and hydrolyzed saltbush (Atriplex canescens) biomass. In addition, X-ray absorption spectroscopy studies were performed to determine the oxidation state of Cr atoms bound to the biomass. The amounts of Cr adsorbed by saltbush biomass were determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES). For Cr(III), the results showed that the percentages bound by native stems, leaves, and flowers at pH 4.0 were 98%, 97%, and 91%, respectively. On the other hand, the Cr(VI) binding by the three tissues of the native and hydrolyzed saltbush biomass decreased as pH increased. At pH 2.0 the stems, leaves, and flowers of native biomass bound 31%, 49%, and 46%, of Cr(VI), respectively. The results of the XAS experiments showed that Cr(VI) was reduced in some extend to Cr(III) by saltbush biomass at both pH 2.0 and pH 5.0. The XANES analysis of the Cr(III) reaction with the saltbush biomass parts showed an octahedral arrangement of oxygen atoms around the central Cr(III) atom. The EXAFS studies of saltbush plant samples confirmed these results. 相似文献
8.
丙烯选择氧化铋钼铁复氧化物催化剂组成,结构及性能的研究 总被引:1,自引:0,他引:1
采用XRD、Raman、XPS及催化剂性能评价等手段,考察了Bi_3(FeO_4)(MoO_4)_2和Fe_2(MoO_4)_3分别存在及两者共存时对Bi-Mo复氧化物体系催化性能的影响.结果表明,这两种含Fe物种的存在都有助于改善Bi-Mo系复氧化物催化剂对丙烯选择氧化反应的催化性能.但两者在作用机理上有所不同.Fe_2(MoO_4)_3本身无催化活性,但在反应条件下可部分还原为FeMoO_4形成Fe~(3+)/Fe~(2+)氧化还原对;且其地结构上与α-Bi_2(MoO_4)_3相匹配,这些因素都有助于促进催化体系中电子和氧物种的传递及催化剂表面活性中心的再生,从而提高催化性能.Bi_3(FeO_4)(MoO_4)_2在反应条件下也可形成Fe~(3+)/Fe~(2+)氧化还原对,但由于其Fe~(3-)所处的化学环境与Fe_2(MoO_4)_3很不相同,且Fe的含量也不及Fe_2(MoO_4)_3,因此它在促进催化体系中电子和氧物种的传递及催化剂表面活性中心的再生等方面的性能较差,但它对提高催化剂表面的活性中心(Bi-Mo对)数目有贡献. 相似文献
9.
Zhong-Le Huang Wolfgang Bensch Hubert Ebert 《Journal of solid state chemistry》2004,177(10):3245-3253
The effect of substitution of the anion Te by Se in non-stoichiometric Cr5Te8 has been investigated with respect to its crystal structure, magnetic properties, and electronic structure. The compounds Cr(1+x)Q2 (Q=Te, Se; Te:Se=7:1; (1+x)=1.234(6), 1.264(6), 1.300(7)) were synthesized at elevated temperatures followed by quenching the samples to room temperature. The crystal structures have been refined with X-ray powder diffraction data with the Rietveld method in the trigonal space group with lattice parameters a=3.8651(1)-3.8831(1) Å and c=5.9917(2)-6.0528(2) Å. The structure is related to the NiAs structure with full and deficient metal layers stacking alternatively along the c-axis. The irreversibility in the field-cooled/zero-field-cooled magnetization suggests that the substitution effects of one Te by one Se is strong enough to cause cluster-glass behavior, from ferromagnetic Cr5Te8 to cluster-glass Cr(1+x)Q2. Non-saturation magnetizations at 5.5 T and the magnetic relaxation results further support the existence of cluster-glass behavior. Accompanying SPR-KKR (spin-polarized relativistic Korringa-Kohn-Rostoker) band structure calculations strongly support the observation that the Cr(1) sites are preferentially occupied by Cr atoms and predict that these compounds are metallic. Results for the spin-resolved DOS and magnetic moments on each crystallographic sites are presented. 相似文献
10.
In the present progress report literature data concerning homogeneous catalyst systems based on vanadium and chromium are reviewed and complemented by a combined study of the magnetic properties and the polymerization activity of such systems. The results show that vanadium forms active species as V (III ) and as V (II ), but chromium only as Cr (II ); models are suggested for the polymerization process. — A comparison with heterogeneous systems (Phillips catalyst) allows the establishment of some general principles concerning the activity of the catalyst and the properties of the polymers. 相似文献