Biogeochemical migration of Al, Hf, Sc, Th and rare-earth metals in the profile of the deep-seated eutrophic marsh in the interfluve of the Ob and Tom rivers

Aluminum, Sc, Th, Hf, and lanthanoids belong to groups of elements that are, slightly, very slightly, and moderately captured in marsh ecosystems. In the genesis of the peatbog the biogeochemical migration of elements is mainly determined by the quality of the humus barriers as well as by the capability to form intermetallic compounds of widely varying compositions. In the surface layer (10 cm) of the peatbog the highest content of Al, Hf, Ce, and Sm over the entire history of marsh development was observed. This fact reflects the modern tendency to forming technogenic streams of the above content.     

Biogeochemical migration of metals of the iron group during the peatbog accumulation in the eutrophic marsh of Western Siberia

In a eutrophic marsh, Fe, Mn, Ni, and Co are the elements of moderate biological capture and Cr is the element of weak biological capture. Over the history of the peatbog formation migration of elements is determined by the oxidation-reduction zonality of the peatbog thickness, the quality of humous barriers, and the carbonate equilibrium in the stagnant waters. No technogenic degradation of the marshes in the southern taiga of Western Siberia has been detected.     

氟化络合-ICP-MS法测定稀土金属中的难熔金属杂质元素Ta、Mo、W、Ti、Nb

针对稀土金属中难熔金属杂质元素Ta、Mo、W、Ti、Nb在HCl或HNO3中不易溶解的性质,本文在前人工作基础上,采用HF络合-ICP-MS结合的方法,有效地将上述元素溶解在溶液中,并利用ICP-MS高灵敏度和多元素同时测定的优势,成功建立了稀土金属中难熔金属杂质元素Ta、Mo、W、Ti、Nb的测定方法。其操作过程较传统化学方法简便,灵敏度也更高。本文分析了氢氟酸的络合过程,试验了稀土氟化物沉淀对被测元素的吸附作用和内标法的校正作用。方法检出限在0.3～1.5ng／mL,测定下限0.0005％～0.0010％,回收率在89.2％～118.9％,相对标准偏差为4.6％～9.7％。     

ChemInform Abstract: Structure and Bonding in Dinuclear Oxoanions of V,Nb, Ta,Mo, and W

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

氧化钪中Ti,Mo,W,V,Zr等难熔杂质光谱分析

本用提高样品蒸发速率的方法提高氧化钪中难熔杂质光谱分析灵敏度。采用一种特殊的阴极设计，配合使用Ｎ２＋Ａｒ气氛控制，在旋流气室中放电激发，取样仅５ｍｇ的条件下，光谱测定氧化钪中难烷质Ｔｉ，Ｚｒ，Ｍｏ，Ｗ，Ｖ灵敏度可达（１－３）×１０＾－４％。测定的相对标准偏差为９％－２７％。     

Supercooling measurement in W, Ta, Nb and Re liquid metals by stereophotocalorimetric method

The technique of crystal growth coupled with a stereophotocalorimetric method has been used in a series of supercooling measurements on pure refractory metals. The cooling history of these metals is recorded on photographic films which are calibrated as a function of the temperature. High absolute amounts of supercooling has been observed in W, Ta, Nb and Re liquid droplets. It is noted that the brightness traces of the solidification process for highly supercooled Re droplets evidence of two successive phase transformations (Re cfc to Re hc) shows.We thank the Fonds National de Recherche Scientifiques of Switzerland.     

Electronic Structure of TiAl-2M(M=V,Nb,Ta,Cr,Mo,W,Mn) Alloy

1INTRODUCTIONTitaniumaluminidesbasedonY-TiAlarereceivingconsiderableattentionaspo-tentialcandidatesformaterialsinhightemperatureaerospaceapplication.Theirlowdensity,hightemperaturescreepresistance,highoxidationresistanceandstrengthmakesthemexcellentpotentialenginematerials.Howevertheirlowductilityandlowfracturetoughnessatroom'temperaturesaremajorhindrancestotheirpracticaluti-lization.TheTiAlalloymayhaveanelongationabout2%t'},furtherimprovementisnecessarybeforethesematerialscouldbeusedin…     

Isotopenverh?ltnismessung von Mo, V, Ti und Zr sowie deren Konzentrationsbestimmung in W?ssern mit einem Thermionen-Quadrupol-Massenspektrometer

Summary Negative MoO ₃ ^– and positive V⁺, Ti⁺, and Zr⁺ thermal ions are produced in a double-filament ion source to determine the isotope ratios of these elements in a quadrupole mass spectrometer. The average relative standard deviation for all isotope ratio measurements is 0.5%. The ratio Me⁺/MeO⁺ (Me=V, Ti, Zr) is followed dependent on the temperature of the ionization filament. A linear plot is obtained for log (Me⁺/MeO⁺) versus 1/T with increasing Me⁺/MeO⁺ ratios for higher temperatures using a single and a double-filament arrangement. An analytical procedure is developed, which allows the simultaneous measurement of Mo and V, and of Ti and Zr as well from one filament by a stepwise variation of the filament temperatures. Mo, V, Ti, and Zr traces in the ng/g and pg/g level of different water samples could be analysed with isotope dilution mass spectrometry using enriched isotopes of⁹⁷Mo,⁵⁰V,⁴⁷Ti, and⁹¹Zr. The precision lies usually in the range of 1 to 6% and the detection limits are 0.002 ng/g for Mo, 0.02 ng/g for V, 0.05 ng/g for Ti, and 0.01 ng/g for Zr using sample amounts of 250 g.     

Oxygen reduction behavior of RuO2/Ti,IrO2/Ti and IrM (M: Ru,Mo, W,V) Ox/Ti binary oxide electrodes in a sulfuric acid solution

Some oxide catalysts, such as RuO₂/Ti, IrO₂/Ti and IrM(M: Ru, Mo, W, V)O_x/Ti binary oxide electrodes, were prepared by using a dip-coating method on a Ti substrate. Their catalytic behavior for the oxygen reduction reaction (ORR) was evaluated by cyclic voltammetry in 0.5 M H₂SO₄ at 60 °C. These catalysts were found to exhibit considerably high activity, and the most active one among them was Ir_0.6V_0.4O₂/Ti prepared at 450 °C, showing onset potential for the ORR at about 0.86 V–0.90 (vs RHE).     

Plasma etching of refractory metals (W,Mo, Ta) and silicon in SF6 and SF6-O2. An analysis of the reaction products

The etching rates and reaction products of refractory metals (W, Mo, and Ta) and silicon have been studied in a SF₆-O₂ r.f. plasma at 0.2 torr. The relative concentrations of WF₆ and WOF₄ and the intensities of the WF _n ⁺ (n=3–5), WOF _m ⁺ (m=1–3), MoF _n ⁺ , and MoF _m ⁺ ions have been measured by mass spectroscopy. An analysis of the neutral composition of the plasma during etching of these metals and a comparison with the results obtained for silicon show that at least two species are involved for W and Mo etching: fluorine and oxygen atoms. A reaction scheme is proposed.     

Determination of Ti,V, Zn and W traces by proton activation analysis

Procedures are described for determining traces of titanium in scandium, vanadium in titanium, zinc in copper and tungsten in tantalum, utilizing activation with 11 Me V protons. Experimental data on⁴⁸V,⁵¹Cr,⁶⁶Ga and¹⁸²Re yields and analytical sensitivities are reported.     

Catalytic Dehydrogenation of Ethylbenzene in Helium and Reductive Dealkylation in Hydrogen on Nb, Mo, Ta, W, and Re Halide Clusters

Halide clusters of [(Nb₆Cl₁₂)Cl₂(H₂O)₄]4H₂O and (H₃O)₂[(M₆Cl₈)Cl₆] 6H₂O (M=Mo, W), which have an octahedral metal framework, and Re₃Cl₉, which has a triangular metal framework, developed catalytic activity for the dehydrogenation of ethylbenzene selectively to yield styrene when the halide clusters were treated in a stream of helium at 450°C. In the case of the Mo cluster, this catalytic activity appeared at 300°C. The activity increased with increasing temperature. Above 400°C, the catalytic activity decreased with time, and the selectivity for benzene increased noticeably. The reduction in the activity was caused by the formation of coke attributable to ethylene produced as a by-product. When the Nb and Ta clusters of the same structure were treated in a stream of hydrogen in the same way, no catalytic reaction proceeded. However, the Mo and W clusters in a stream of hydrogen catalyzed reductive dealkylation of ethylbenzene selectively yielding toluene and benzene. In the case of the Mo cluster, the catalytic activity appeared at 400°C, and increased with increasing temperature. The activity did not decrease with time even at high temperatures. The Re cluster, which was reduced to the metal by the treatment in hydrogen, catalyzed ring-opening degradation to yield gaseous hydrocarbons.     

Electronic structures and properties of eight-coordinate metal-polyarsenic complexes MAs8n- (M = V,Nb, Ta,Cr, Mo,W, Mn,Tc, Re)

The eight-coordinate early transition metal polyarsenic complexes, MAs(8)3- (M = V, Nb, Ta), MAs(8)2- (M = Cr, Mo, W), and MAs8- (M = Mn, Tc, Re), have been studied using density functional theory (DFT). The geometry optimizations of these complexes indicate that in the most stable structures the transition metal atoms are trapped in a crownlike cavity consisting of a zigzag eight-membered ring of As8 cluster. The scalar-relativistic effects and spin-orbit coupling effects on the electronic structures and energy levels were taken into account. The stabilities of gas-phase MAs8n- ions and bonding between the As8 ring and early transition metals are discussed on the basis of population analysis, atomization energies, and decomposition reaction energies. All these complex ions are found to be diamagnetic with notable HOMO-LUMO energy gaps. The vibrational frequencies and infrared absorption intensities of the MAs8n- series are predicted theoretically. Brief theoretical calculations of the similar MoA(8)2- pnictide ions indicate that the analogous P, Sb, and even Bi complexes are likely to be stable, whereas the crownlike MoN(8)2- is not a stable complex.     

EPR study of dithiophosphate,dithiocarbamate, and xanthate complexes of Cr(V), Mo(V), and W(V)

Liquid and frozen solutions of diethyl dithiophosphate, diethyl dithiocarbamate, and butyl xanthate complexes of Cr(V), Mo(V) and W(V) were studied by the EPR method in the temperature range from 293–77dg K. The spin-Hamiltonian parameters were determined. Conclusions were drawn about the structure of these complexes and about the bond character within the complexes. A multiplicity of the hyperfine splitting constants from Cr⁵³, Mo^95,97, and W¹⁸³ to the constant of additional hyperfine splitting from the p³¹ isotope is observed in diethyl phosphate complexes.     

Manufacturing corrosion-resistant electrode materials on the Basis of Ti, Ta, Nb, and W covered with thin electrodeposited platinum layers

The electrodeposition of thin platinum coatings onto Ti, Ta, Nb, and W supports with an ordered microstructure and reliable adhesion is studied. The coatings can be applied in adverse electrolysis conditions for synthesizing oxidants and for other purposes. Optimum conditions for a support pretreatment and a platinum deposition from an electrolyte based on platinum diamminedinitrite are found. All other deposition conditions being the same, the support pretreatment affects the coating microstructure (ordering, size of Pt crystallites, roughness coefficient). On polished Nb supports, the grain size of Pt crystallites is smaller, the coating is more compact, and the roughness coefficient drops to nearly 5–8, which is typical for bulk platinum. However, the Nb support must be preliminarily oxidized in a strictly specified mode, for preventing hydrogen sorption during platinum electrodeposition, if one is to deposit reliable poreless platinum coatings with strong adhesion     

Electronic structure and bonding in heteronuclear dimers of V, Cr, Mo, and W: a CASSCF/CASPT2 study

Heteronuclear dimers like CrMo, CrW, MoW, VCr, VMo, VW, and their anions have been investigated by means of multiconfigurational quantum chemistry methods, using the complete active space self-consistent field followed by second-order perturbation theory, CASSCF/CASPT2. We explored in great detail several spectroscopic properties such as bond length, potential energy surfaces, dissociation energies, ionization potentials, electron affinities, low-lying excited states, vibrational frequencies, and dipole moments. All proposed dimers show ground states with a pronounced multireference character. The group VI heterodimers have a (1)Σ(+) ground state, while the mixed group V-group VI heterodimers show a (2)Δ ground state. Among all dimers, only VCr presents a potential energy profile with a deep minimum in the d-d region and a shelf-like potential in the s-s region. All the remaining dimers show only the short-range minimum. The largest effective bond order is obtained for the MoW, with a value of 5.2, that is, a weak sextuple bond. Most of the obtained results are valuable tools to drive future experimental investigations.     

钛锡钼钨同时测定多元统计与滤波分辨法比较

采用多元线性回归、主成份回归、偏最小二乘、目标因子分析和自适应滤波等多元统计及滤波分辨法,借金属离子-苯基荧光酮PF-CTMAB显色体系同时测定钼钨钛锡四组分,结果良好。并进行了方法比较。     

On line ion exchange separation of short-lived Zr, Hf, Mo, Ta and W isotopes as homologs of transactinide elements

The short-lived isotopes of W and their descendants have been separated from nuclear reaction products arising in the bombardment of samarium target with²⁴Mg ions at the U-400 cyclotron of JINR-Dubna. Chemical separations were performed using previously elaborated fast and continuous ion exchange. In similar way products of²³⁵U fission, obtained at the microtron MT-25 during irradiation of²³⁵U target with photoneutrons were separated.