掺杂Tb3+的混合碱土金属钨酸盐的合成和性质

合成了掺杂Ｔｂ（３＋）的混合碱土金属钨酸盐，测定了其发射光谱和激发光谱，用粉末Ｘ射线衍射和电子衍射法表征了其晶体结构，并对钨酸钙钡单晶体进行了Ｘ射线能谱成份分析．探讨了碱土金属钨酸盐的溶混性成因以及在这些晶体中Ｔｂ（３＋）发光和能量传递机理．     

掺杂铕（Ⅲ）的同多钨酸钠的合成及其发光特性

Ｎａ＿２Ｗ＿４Ｏ＿（１３）的合成及结构已见文献［１，２］，但关于掺杂稀土离子的同多钨酸盐的合成及其发光特性的研究未见报道。本工作旨在采用高温固相反应法合成Ｎａ＿２Ｗ＿４Ｏ＿（１３）：Ｅｕ荧光体，探讨掺杂稀土离子的发光机理。     

掺杂Eu3+的Na24As2Mo22O83的合成及其发光特性

本文在固相合成掺杂稀土离子的单钨酸盐,混合碱土金属钨酸盐^[1-3]等体系的的系统研究基础上,采用固相反应法合成掺杂Eu^3 离子的Na24As2Mo22O83荧光体结晶粉末,并经元素分析,IR和X射线粉末衍射等分析手段确定了它的结构,探讨了Eu^3 离子在Na24As2Mo22O83中的发光和能量传递机理。     

粉状白钨酸的研究(Ⅻ)——某些聚钨酸有机铵盐的合成和性质

以粉状白钨酸和三种有机铵--乙二胺、乙醇胺和异丙胺为原料,分别合成了偏钨酸盐和仲钨酸盐。通过紫外,红外光谱、核磁共振谱以及极谱测定,研究了三种不同类型有机胺聚钨酸盐的组成与性质,发现乙醇胺和异丙胺的偏钨酸盐具有光敏性。     

掺杂Eu~(3+)的Na_(24)As_2Mo_(22)O_(83)的合成及其发光特性

本文在固相合成掺杂稀土离子的单钨酸盐、混合碱土金属钨酸盐[1～ 3 ] 等体系的系统研究基础上 ,采用固相反应法合成掺杂Ｅｕ3 + 离子的Ｎａ2 4Ａｓ2 Ｍｏ2 2 Ｏ83 荧光体结晶粉末 ,并经元素分析 ,ＩＲ和Ｘ射线粉末衍射等分析手段确定了它的结构 ,探讨了Ｅｕ3 + 离子在Ｎａ2 4 Ａｓ2 Ｍｏ2 2 Ｏ83 中的发光和能量传递机理。1　实验部分1 1　试剂及样品的制备先将Ｎａ3 ＡｓＯ4 ·1 2Ｈ2 Ｏ (分析纯 )和Ｎａ2 ＭｏＯ4 ·2Ｈ2 Ｏ(分析纯 )在 2 5 0℃下灼烧 30ｍｉｎ脱水制得Ｎａ3 ＡｓＯ4 和Ｎａ2 ＭｏＯ4 结晶粉末 ,再按一定物质的量比 ( 9…     

硅钨酸盐的合成及其在醇的四氢吡喃化反应中的催化性能

用硅钨酸分别与硝酸铜、硝酸锌和硝酸铝采用复分解法合成了相应的硅钨酸盐．结合红外光谱、紫外光谱和热重等分析手段对这三种硅钨酸盐结构进行了表征,并考察了三种硅钨酸盐在醇的四氢毗喃化反应中的催化性能．结果表明：用0．7g具有Keggin结构的硅钨酸盐作催化剂,在室温无溶剂条件下,催化二氢吡喃（33mmol）与醇（30mmol）的反应,反应条件温和,工艺简单,催化效果好,无副产物生成．     

白钨矿结构物相含稀土异价固溶体的形成规律

运用原子参数-支持向量机算法(SupportVectorMachine,SVM)和熔盐相图智能数据库技术,研究了白钨矿型钼酸盐、钨酸盐和含稀土钼酸盐、钨酸盐形成异价固溶体的条件,建立了碱金属-稀土钼酸盐和钨酸盐的晶型以及这些化合物与稀土钼酸盐或钨酸盐形成连续固溶体的判据,并求得这类化合物的晶胞参数的计算式。计算表明:各组分元素的离子半径和电负性是影响固溶体形成、晶型和晶胞参数的主要因素。根据本文所得经验式估计TlPr(MoO4)2-Pr2(MoO4)3系固溶体情况与实测结果一致。     

光促进十聚钨酸盐催化的C—H键官能团化反应

近年来,十聚钨酸盐作为催化剂在光催化有机合成领域引起了广泛关注.在光照下,十聚钨酸盐可以活化反应物中的C—H键,通过"氢原子转移"作用产生自由基,进而实现C—H键官能团化反应.对近年来十聚钨酸盐在光诱导下催化C—H键官能团化,构筑C—C、C—N、C—F键等的研究进展进行了综述.     

粉状白钨酸的研究——ⅩⅫ.六聚钨酸二甲基亚砜加合物的制备

1968年,Fuchs等首次用控制水解法从WO(CH_3)_4中获得了六聚钨酸盐,它的阴离子W_6O_(19)~(2-)结构也已被测定。迄今六钨酸盐主要还是局限于几个多碳有机胺盐。以粉状白钨酸为原料,在二甲基亚砜(DMSO)中制得了一系列DMSO配位的多价金属的六钨酸盐晶体,并测定了其中部分盐类的晶体结构。但六聚钨酸仍未     

白钨矿型钨酸盐和钼酸盐纳米晶/微晶制备研究进展

综述近年来自钨矿型钨酸盐和钼酸盐纳米晶/微晶制备技术领域的研究进展,重点介绍熔盐法、有机配合物前驱法、模板法、微乳液法、水热法、溶剂热法和微乳液.溶剂热法的原理和技术特点,比较各种方法的异同点,并提出白钨矿型钨酸盐和钼酸盐纳米晶/微晶制备技术的发展趋势.     

Electronic band structures and photovoltaic properties of MWO4 (M=Zn, Mg, Ca, Sr) compounds

Divalent metal tungstates, MWO₄, with wolframite (M=Zn and Mg) and scheelite (M=Ca and Sr) structures were prepared using a conventional solid state reaction method. Their electronic band structures were investigated by a combination of electronic band structure calculations and electrochemical measurements. From these investigations, it was found that the band structures (i.e. band positions and band gaps) of the divalent metal tungstates were significantly influenced by their crystal structural environments, such as the W-O bond length. Their photovoltaic properties were evaluated by applying to the working electrodes for dye-sensitized solar cells. The dye-sensitized solar cells employing the wolframite-structured metal tungstates (ZnWO₄ and MgWO₄) exhibited better performance than those using the scheelite-structured metal tungstates (CaWO₄ and SrWO₄), which was attributed to their enhanced electron transfer resulting from their appropriate band positions.     

Thermochemical Study of Gaseous Salts of Oxygen-containing Acids: XIII. Molybdates and Tungstates of Alkaline-Earth Metals

Gas-phase reactions involving molybdates and tungstates of alkaline-earth metals were studied by high-temperature mass spectrometry. The standard enthalpies of formation and atomization of these salts were determined.     

Comprehensive Study of Third-Order Nonlinear Tungstates: Relationship between Structural and Vibrational Properties in Raman Shifters

Although tungstates are now well known as laser Raman shifters, their physicochemical properties (especially the vibrational ones) were not often studied. We have carried out a comprehensive and systematic study of tungstate Raman spectra, thanks to which, structural and vibrational properties could be correlated. It was shown that the Raman scattering characteristics of these compounds are directed by simple physical chemistry parameters. They change logically with easy interpolation. The optimization of the search for tungstates as new efficient Raman shifters was realized through a figure of merit: a map where the Raman frequency is described versus a normalized parameter representative of the Raman gain.     

Role of crystal structure on the thermal expansion of Ln2W3O12 (Ln = La, Nd, Dy, Y, Er and Yb)

The negative thermal expansion material Y₂W₃O₁₂ belongs to Ln₂W₃O₁₂ family of compositions. The thermal expansion behavior of Ln₂W₃O₁₂ (Ln = La, Nd, Dy, Y, Er and Yb) members synthesized by the solid-state reaction have been studied and correlated to their crystal structure. The lighter rare earth tungstates (Ln = La, Nd and Dy) crystallize in monoclinic structure (C2/c) whereas the heavy rare earth tungstates (Ln = Y, Er and Yb) form the trihydrate orthorhombic Ln₂W₃O₁₂3H₂O at room temperature and above 400 K transforms to unhydrated orthorhombic structure (Pnca). The hot pressed (1273 K and 25 MPa) ceramic pellets have been studied for thermal expansion property by dilatometry and high temperature X-ray diffraction. The heavy rare earth tungstates show a large initial expansion up to 400 K, followed by a thermal contraction. The light rare earth tungstates, on the other hand, show thermal expansion. The difference in the thermal expansion behavior in Ln₂W₃O₁₂ series is attributed to the difference in the structural features. The heavy rare earth tungstates have corner sharing of LnO₆ octahedra with WO₄ tetrahedra, where the now well established mechanism of transverse vibrations operate. The light rare earth tungstates have edge sharing of LnO₈ polyhedra where in such a mechanism is absent.     

Study of the reduction of tungsten trioxide doped with MCl (M=Li,Na, K)

Thermodynamic calculations predict the formation of hydrochloric acid gas and alkali tungstates during hydrogen reduction of WO₃ doped with alkali chlorides MCl (M=Li, Na, K). The formation of HCl was proved experimentally by simultaneously coupled TG-MS measurements from RT to 1200°C. The formation of HCl is the result of the reaction between MCl, WO₃ and water. Ubiquitous traces of moisture in the gas are sufficient for reaction according to WO₃+(2+2n)MCl +(1+n)H₂O→M_2+2nWO_4+n+(2+2n)HCl (n=0, 1, 2). Laboratory reduction tests showed that the formed tungstates differ. NaCl and KCl form monotungstates (n=0), while LiCl produces more lithium-rich compounds (n=1, 2). Temperature and humidity, among other process factors, control subsequent reduction of the tungstates to metals. This revised version was published online in July 2006 with corrections to the Cover Date.     

An x-ray diffraction study of the kinetics of formation of barium-calcium aluminates and tungstates

Summary By making use of x-ray phase analysis it is possible to determine the technological conditions for preparing barium-calcium tungstates and aluminates. It has been shown that the preparation of barium-calcium aluminates by combined precipitation of substances which form the aluminates on subsequent ignition makes it possible to increase the purity of the product obtained and to decrease the temperature and shorten the duration of the ignition. This is probably related to the fact that during the combined precipitation, thorough mixing of the original components takes place, facilitating the course of the reaction in the solid phase. In the preparation of tungstates by the combined precipitation method, however, no significant decrease in the temperature or duration of ignition were obtained.Translated from Zhurnal Strukturnoi Khimii, Vol. 1, No. 2, pp. 178–182, July–August, 1960     

Paradoxes and paradigms: observations on pyrohydrolysis,oxygen bomb combustion,and alkaline carbonate fusion,most frequently used decomposition methods for subsequent determination of fluorine and accompanying thermochemistry

Pyrohydrolysis, oxygen bomb combustion, and alkaline carbonate fusion are the most frequently used methods for decomposition of fluorine containing materials. The efficiency of these methods was proven by the determination of fluorine content in certified reference materials of clay and vegetation. Possible reactions proceeding during decomposition were suggested and accompanying thermochemistry discussed. The Gibbs energies were estimated to establish if suggested reactions are thermodynamically favorable or not. In addition, linear relationships between the enthalpies of formation of metal fluorides and the balanced values of the enthalpies of formation of the plausible reaction products (metal tungstates, metal oxides, or metal carbonates), electronegativity of metals, and number of fluorine atoms in metal fluorides were established. These equations were suggested for the estimation of the enthalpies of formation of metal tungstates, metal oxides, or metal carbonates, for which experimental data are not available.     

Orientation of tungsten trioxide thin films fabricated by sol–gel method using aqueous sols of colloidal layered tungstates

Oriented monoclinic WO₃ thin films were fabricated by sol–gel method using aqueous sols of colloidal layered tungstates. The colloidal tungstate sols were prepared by reacting different alkylamines with layered tungstic acid H₂WO₄ in water. With decreasing the alkyl chain length of the alkylamines, the colloidal layered tungstate became smaller. Alkylamines with a short alkyl chain provided transparent aqueous sols. Furthermore, the WO₃ thin films fabricated from the obtained aqueous sols had a high (100)-orientation. However, upon annealing H₂WO₄ crystals applied on a glass substrate with the tungstate layers parallel to the substrate, highly (001)-oriented WO₃ layers were obtained. Since both of the A- and C-planes of WO₃ have a similar structure to the layers of H₂WO₄, the orientation of the WO₃ thin films and layers probably resulted from the topotactic structural conversion of the tungstates. Interestingly, the preferential orientation of the thin films was dependent on the presence or absence of interlayer alkylamines in the tungstates.     

Electrochemical lithium intercalation into WO3 and lithium tungstates Li x WO3+ x /2 of various structures

Hexagonal and monoclinic tungsten trioxides WO₃ and hexagonal lithium tungstates Li _x WO_{3+ x /2} (x = 0.10–0.42) from a soft chemistry route were used as the active cathode material in secondary lithium batteries. The hexagonal structures, regardless of their being an oxide or a tungstate, showed higher specific capacities and better cycling behavior in Li⁺ intercalation reactions than the monoclinic form. The presence of pre-allocated lithium (as Li₂O) in hexagonal tungstates decreased the capacity for lithium intercalation. Additionally, the plot of open-circuit voltage (OCV) against the depth of intercalation (n) for anhydrous tungstates showed two straight lines with different slopes that can be related to the structural changes in lithium intercalation. The effective diffusion coefficients of lithium insertion into the host structure, D˜, were also found to be dependent on the structure and the composition of these compounds. Received: 28 November 1997 / Accepted: 6 March 1998