钨钼室温脆性的研究

对不同实验条件下制备的钨和钼的试样作扫描电镜、透射电镜和俄歇电子能谱分析。断口形貌分析表明,在室温下烧结态和再结晶态的断口呈典型的晶间脆性断裂,低形变及再结晶试样为晶间脆断和穿晶解理的混合型断裂,高度形变的试样断口呈纤维状韧性断裂特征,是纤维束撕裂、分层,而后单个纤维出现缩颈、微孔合并所致。在10~(-9)Torr高真空度下对新鲜断口作俄歇电子能谱分析证实,间隙杂质磷、氧和碳是钨的主要晶界杂质,而钾、氧和碳则在掺杂钨的晶界明显富集,可以确认这些在晶界大量富集的杂质是削弱晶界强度,造成钨钼室温脆性的基本原因.文中还分析了晶粒结构和亚结构对室温脆性的影响。     

新的极谱催化体系连续测定岩溶地下水中钨和钼

钨、钼-二苯基乙醇酸-2,2′-联吡啶-钛铁试剂连测体系还未见报道。本文提出了在0.05mol/L的硫酸中,钨与二苯基乙醇酸,2,2′-联吡啶的络合物在-0.79V(vs.SEC)产生一个极其灵敏的极谱催化波,测定完钨后,加入少量钛铁试剂测定钼。钼于-0.20V(vis.SEC)处产生极灵敏的阴极化导数波,波形尖锐对称,易于测量。采用此种连测体系,钨钼的灵敏度都可满足要求,钨和钼的检出限分别为0.004、0.01μg/L。确定最佳条件和拟定了不经分离富集直接测定岩溶地下水中痕量钨和钼的方法。此外还对极谱波性质进行了探讨,讨论了阴、阳离子表面活性物质对极谱催化波的作用机理。     

Microstructure evolution and dielectric properties of Ba<Subscript>5-x</Subscript>Na<Subscript>2x</Subscript>Nb<Subscript>10</Subscript>O<Subscript>30</Subscript> ceramics with different Ba–Na Ratios

The tetragonal tungsten bronzes of Ba5−xNa_2x Nb₁₀O₃₀ (BNN, 0.5≤ x≤1.3) ceramics were synthesized using the solid state reaction method. The sintering behavior and dielectric characteristics of the BNN ceramics, as a function of the Ba-Na ratio, were examined. Densification of the samples with excess compositions of Ba and Na was higher than that of the stoichiometric BNN sample. The maximum dielectric constant and the Curie temperature showed highest values at the stoichiometric composition and decreased as the composition shifted away from the stoichiometry. in order to obtain a quantitative evaluation of the diffuse phase transition (DPT) behavior of the BNN ceramics, γ and C/κ_max were calculated. The weakest DPT behavior was observed in the stoichiometric composition. An increase in the DPT is in correlation with the increase in the number of ways of cation distribution by the disordered occupation of Ba and Na and the vacancies in the A1 and A2 sites of the tungsten bronze structure.     

Tunable magnetic properties of arrays of Fe(1 1 0) nanowires grown on kinetically grooved W(1 1 0) self-organized templates

We report a detailed magnetic study of a new type of self-organized nanowires discussed briefly previously [B. Borca et al., Appl. Phys. Lett. 90 (2007) 142507]. The templates, prepared on sapphire wafers in a kinetically limited regime, consist of uniaxially grooved W(1 1 0) surfaces, with a lateral period here tuned to 15 nm. Fe deposition leads to the formation of (1 1 0) 7 nm-wide wires located at the bottom of the grooves. The effect of capping layers (Mo, Pd, Au, Al) and underlayers (Mo, W) on the magnetic anisotropy of the wires was studied. Significant discrepancies with figures known for thin flat films are evidenced and discussed in terms of step anisotropy and strain-dependent surface anisotropy. Demagnetizing coefficients of cylinders with a triangular isosceles cross-section have also been calculated, to estimate the contribution of dipolar anisotropy. Finally, the dependence of magnetic anisotropy with the interface element was used to tune the blocking temperature of the wires, here from 50 to 200 K.     

Luminescence properties of Ba2NaNb5O15 crystals activated with Sm, Eu, Tb or Dy ions

Single crystals of Ba₂NaNb₅O₁₅ (BNN) singly doped with Sm³⁺, Eu³⁺, Tb³⁺ or Dy³⁺ have been grown by means of the flux growth method. Their visible emission and excitation spectra and the decay profiles of the luminescence have been measured at room temperature. All spectral features are significantly inhomogeneously broadened in consequence of the structural disorder of the host and of the doping mechanisms. The analysis of the observed spectra allows formulating an hypothesis about the site occupancy of the active ions in the BNN lattice.     

Microstructure and corrosion properties of thick WC composite coating formed by plasma cladding

The thick Ni-coated WC coatings, in a matrix of Nickel-based alloys, were prepared on AISI 1045 steel using plasma cladding equipment. A pre-placed layer of uniform mixture, with different weight fractions of Ni-coated WC powder and Nickel-based alloy powder, on the steel substrate was melted at the high temperature of the plasma jet. The coating composition, microstructure and microhardness were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS) and microhardness testing. The experimental results show that the metallurgical bond was formed between the coating and substrate. The XRD results show that the coatings contain γ-Ni, carbides (such as M₂₃C₆ and M₇C₃) and boride (such as Fe₂B, Fe₃B phases). SEM shows that all the coatings are crack-free with lower porosity (<1%). It is found that the microhardness and the electrochemical behavior of the coatings are depended on the content of Ni-coated WC powder. The corrosion mechanism for the coatings may be due to the microgalvance corrosion between the phases in the cladding coatings.     

采用软化学法制备WO3和其锂化物及其结构稳定性的研究

通过两种方法合成了六方形和单斜氧化钨的水化物WO3·yH2O(y=0.50～1.20):(1) 用强酸(1～3 mol/L HCl) 将0.25 mol/L Li2WO4在100 ℃进行酸化; (2) 将1 mol/L Li2WO4置于高压反应釜中,控制pH为1.5,在100 ℃进行水热合成. 对于水热法,温度较高时(125～200℃),得到组分为LixWO3+x/2·yH2O(x=0.10～0.50,y=0.50～0.90)的锂化氧化钨. 合成产物的结构和组分与酸的浓度和后处理(加热、超声波)有关. 在350 ℃加热时六方形氧化钨完全转化为单斜氧化钨. 将温度在150 ℃以上时通过水热法合成的氧化钨前驱体进行超声波处理,产物的含锂量恒定为每单元0.18摩尔. 锂的引入有利于锂化氧化钨的结构和组分的稳定.     

Facile synthesis of mesoporous WO3@graphene aerogel nanocomposites for low-temperature acetone sensing

Nanocomposites constructed by combining mesoporous metal oxides and graphene have received tremendous attention in wide fields of catalysis,energy storage and conversion,gas sensing and so on.Herein,we present a facile interface-induced co-assembly process to synthesize the mesoporous W03@graphene aerogel nanocomposites(denoted as mW03@GA),in which graphene aerogel(GA) was used as a macroporous substrate,mesoporous W03 was uniformly coated on both sides of graphene sheets through a solvent evaporation-induced self-assembly(EISA) strategy using diblock copolymer poly(ethylene oxide)-b-polystyrene(PEO-b-PS) as a template.The resultant mW03@GA nanocomposites possess well-interconnected macroporous graphene networks covered by mesoporous W03 layer with a uniform pore size of 19 nm,high surface area of 167 m~2/g and large pore volume of 0.26 cm~3/g.The gas sensing performance of mW03@GA nanocomposites toward acetone and other gases was studied,showing a high selectivity and great response to acetone at low temperature of 150℃,which could be developed as a promising candidate as novel sensors for VOCs detection.     

Further experimental evidences of thermal spreading of tungsten oxide on zirconia

The effects brought about by the time of thermal treatment as well as the water content in the gas phase during the thermal spreading of WO₃ on zirconia were investigated. Diffuse reflectance UV-vis spectroscopy evidenced the thermal spreading phenomenon and revealed the formation of polymeric tungsten dispersed species. Neither the thermal treatment time nor the water content showed to influence the nature of the dispersed species, which reveal to present thermodynamically preferential molecular structures. Infrared spectroscopy analysis of adsorbed pyridine evidenced that the polytungstate species lead to the generation of Brönsted acid sites. Lewis acid sites stronger than those naturally present on zirconia could also be detected in addition to weaker Lewis sites, which were associated to the WO₃ still present in the catalysts as showed by X-ray diffraction.     

Synthese und spektroskopische Charakterisierung einiger Pentacarbonylwolfram(0)-Komplexe mit verschiedenen 1H-Phosphiren-Liganden,Kristallstrukturen von,und

Synthesis and Spectroscopic Characterization of some Pentacarbonyltungsten(0) Complexes with Various 1H-Phosphirene Ligands: Crystal Structures of , and The tungsten(0) complex 1 reacts upon heating with acetylene derivatives 2a–f in toluene to form benzonitrile and the complexes 4a–f ( 4a : R¹ ? Ph, R² ? H; 4b : R¹ ? Ph, R² ? CH₃; 4c : R¹ ? OEt, R² ? H; 4d : R¹ ? Ph, R² ? CO₂Et; 4e : R¹, R² ? CO₂Me; 4f : R¹, R² ? SiMe₃), which have been isolated by chromatography. Spectroscopic and mass spectrometric data are discussed. The crystal structures of the compounds 4a, b and d were determined by X-ray single crystal structure analysis ( 4a : space group P2₁/n, Z = 4, a = 937,5(2) pm, b = 2202,4(6) pm, c = 1266,3(4) pm, β = 108,94(4)°; 4b : space group P2₁/c, Z = 4, a = 1293,9(2) pm, b = 923,5(1) pm, c = 2223,4(3) pm, β = 92,385(6)°; 4d : space group P2₁/c, Z = 4, a = 955,2(2) pm, b = 3190,9(4) pm, c = 930,7(2) pm, β = 99,64(1)°).