Deprotection of dithioacetals using the tantalum(V) chloride catalyzed oxidation of iodide ion by hydrogen peroxide

Dithioacetals can be deprotected to afford carbonyl groups using the tantalum(V) chloride catalyzed oxidation of iodide ion by hydrogen peroxide under mild conditions.     

Modelling of dynamic ductile fracture and application to the simulation of plate impact tests on tantalum

A model of dynamic damage by void nucleation and growth is proposed for elastic-viscoplastic materials sustaining intense loading. The model is dedicated to ductile materials for which fracture is caused by microvoiding. The material contains potential nucleation sites where microvoids are generated when the local pressure overcomes the nucleation pressure. A probability density function is adopted to describe the fluctuation of the nucleation pressure within the material. The void growth is described by using a hollow sphere model where micro-inertia effects are accounted for. The matrix weakening due to void growth is also included.The model has been first tested under uniaxial deformation. When the strain rate is assumed constant, the pressure inside the material has nearly a linear response up to a maximum. An analytical expression for the maximum pressure is proposed.Finite element simulations of plate impact tests have been carried out and compared to experiments on tantalum. From simulations based on the proposed model, an increase of the spall strength is observed with higher shock intensities. Therefore, the relationship between the velocity pullback and spall strength usually assumed in the literature (based on the acoustic approach) seems to be inadequate. Velocity profiles are simulated for different flyer thicknesses and different impact velocities with close agreement with experiments.     

The electron temperature distribution of laser erosion plume after ablation of a tantalum target with excimer laser in vacuum

The erosion plume resulting from an ablation of a tantalum target in vacuum with an excimer laser radiation (308 nm) was studied using the Langmuir probe technique. The spatial and temporal dependencies of the electron probe currents were obtained in real time. The electron temperature of different plume regions was determined from a series of I–U characteristics taken at different distances between the probe and the target. We determined that the plume electron temperature is non-uniform and has a maximum value in front of the plume.     

The Electrochemical Behavior of Gold Nanoparticle‐Tantalum(V) Phthalocyanine Composites: Applications Towards the Electroanalysis of Bisphenol A

The formation of gold nanoparticle (AuNP) composites with tantalum phthalocyanines (TaPc) complexes { 1a and 1b (Figure 1 )} is reported. The TaPc‐AuNPs conjugates were characterised by atomic force microscopy (AFM) and transmission electron microscopy. The AFM analyses show that conjugates of TaPc with AuNPs are more aggregated when compared to AuNPs alone. The conjugates and TaPc complexes were immobilized on a gold electrode by drop and dry method and these were characterized by electrochemical impedance spectroscopy. The charge transfer behaviour of AuNPs was enhanced in the presence of TaPc complexes. All the modified electrodes showed electrocatalytic oxidation of bisphenol A. The limits of detection for complexes 1a and 1 b were 4.78×10^?10 and 2.76×10^?10 mol L^?1, respectively.     

Effects of deposition parameters on tantalum films deposited by direct current magnetron sputtering in Ar–O2 mixture

The structure, composition, and temperature coefficient of resistance of tantalum films sputtered in Ar–O₂ mixture were studied as a function of deposition parameters and substrates temperature. As the sputtering power increased from 25 to 100 W, the samples deposited at 300 °C only consisted of the β phase, the preferred-growth orientation of films changed from (2 0 0) to (2 0 2) and the temperature coefficient of resistance reduced from −289.8 to −116.7 ppm/°C. The decrease of the oxygen and other impurity in the films was observed as the increase of the sputtering power. In addition, the O/Ta ratio decrease and grain size reduction in the films related to a change of electrical resistivity were observed at substrate temperatures in the range of 300–500 °C. These results suggested that the electrical properties were due to the oxygen and other impurity content and grain size in the films rather than to growth orientation. At 650 °C, the deposited films contained both partial stable body-centered-cubic α phase with low resistivity and tetragonal β phase of Ta. The presence of α phase of Ta causes a sharp decrease of the electrical resistivity and a significant change in the microstructure of the samples.     

Electrical properties and redox stability of tantalum-doped strontium titanate for SOFC anodes

SrTa_xTi_1−xO₃ (STT) with x = 0.01, 0.05, and 0.10, has been investigated as a potential electron conductor for solid oxide fuel cell (SOFC) anodes. STT was found to be chemically stable under oxidizing and reducing conditions and chemically compatible with yttria-stabilized zirconia (YSZ). The coefficient of thermal expansion (CTE) was near that of YSZ, ranging from 11.3 to 11.8 × 10⁻⁶ K⁻¹. The conductive properties of bulk STT and porous STT-YSZ composites were studied under relevant SOFC operating temperatures and redox cycling conditions. In order to achieve reasonable conductivities, samples were initially reduced at 1673 K. Conductivity after redox cycling was higher for lower dopant concentrations. The redox stable conductivity of a porous composite with x = 0.01 was 1.1 S/cm at 1073 K in humidified H₂ (3% H₂O). Fuel cell tests indicated an anode impedance of 0.4 Ω cm² at 973 K in humidified H₂ for STT-YSZ anodes infiltrated with 3 wt.% CeO₂ and 1 wt.% Pd.     

Characterization of oxide coatings formed on tantalum by plasma electrolytic oxidation in 12-tungstosilicic acid

Oxide coatings were formed on tantalum by plasma electrolytic oxidation (PEO) process in 12-tungstosilicic acid. The PEO process can be divided into three stages with respect to change of the voltage-time response. The contribution of electron current density in total current density during anodization results in the transformation of the slope of voltage-time curve. The surface morphology, chemical and phase composition of oxide coatings were investigated by AFM, SEM-EDX, XRD and Raman spectroscopy. Oxide coating morphology is strongly dependent of PEO time. The elemental components of PEO coatings are Ta, O, Si and W. The oxide coatings are partly crystallized and mainly composed of WO₃, Ta₂O₅ and SiO₂. Raman spectroscopy showed that the outer layer of oxide coatings formed during the PEO process is silicate tungsten bronze.     

Base Stabilized σ-Borane Complex of Group 5 Metals: Synthesis and Structure of [(η5-C5Me5)Ta(H3BNC5H4) (C5H4NS)(η2-S2)]

Azametallacyclopropane-containing base stabilized borane complexes of group 5 transition metals have been synthesized and their structural aspects have been described. Treatment of Cp* based Ta and Nb chlorides, Cp*TaCl₄ and Cp*NbCl₄ with [LiBH₄ ⋅ THF] followed by addition of ligands, such as 2-mercaptobenzothiazole, MBT, (C₇H₅NS₂) and 2-mercaptobenzoxazole, MBO (C₇H₅NSO) led to the formation of complexes [Cp*M-[BHS(CH₂ENC₆H₄)(C₇H₄NSE)] ( 1 : M=Ta, E=S; 2 ; M=Nb, E=S; 3 : M=Ta, E=O; 4 ; M=Nb, E=O, Cp*=pentamethyl-η⁵-cyclopentadienyl). By means of UV-vis absorption spectra, the electronic properties of these complexes associated with central metal atoms and heteroatoms (S or O) have been evaluated. In contrast, treatment of Cp*TaCl₄ with 2-mercaptopyridine, MP, (C₅H₅NS) under the same reaction conditions yielded the agostic σ-borane Ta complex, [Cp*Ta(H₃BNC₅H₄) (C5H₄NS)(η²-S₂)], 5 . Unlike 1 – 4 , where the metals interact with boron through bridging sulphur, 5 shows a notable σ-B−H bond interaction with Ta. All spectroscopic data of 1 – 5 along with the X-ray diffraction studies suggest complexes 2 , 4 , and 5 are base (amine) stabilized borane species. Computational studies based on Density Functional Theory (DFT) also supported this conclusion.