Determination of Pd,Rh, Pt,Au in road dust by electrothermal vaporization inductively coupled plasma mass spectrometry with slurry sampling

Inductively coupled plasma mass spectrometry coupled with ultrasonic slurry sampling electrothermal vaporization (USS-ETV-ICP-MS) has been applied to determine Pd, Rh, Pt and Au in 0.5% m/v slurries of several road dust samples. 2% m/v ammonium pyrrolidine dithiocarbamate (APDC) was used as the modifier to enhance the ion count. The influence of instrument operating conditions, slurry preparation and interferences on the ion count was reported. This method has been applied to the determination of Pd, Rh, Pt and Au in BCR 723 Road Dust and NIST SRM 2709 San Joaquin Soil reference materials and two road dust samples collected locally. The analysis results of the standard reference materials agreed with the certified values. Precision between sample replicates was better than 10% for all the determinations. The method detection limits estimated from standard addition curves were 0.9, 0.4, 0.6 and 0.4 ng g⁻¹ for Pd, Rh, Pt and Au, respectively, in original dust samples.     

Mechanism of copper underpotential deposition at Pt(<Emphasis Type="Italic">hkl</Emphasis>)-electrodes: Quantum-chemical modelling

Mechanism of copper underpotential deposition at stepped faces of platinum single crystals Pt(hkl) is studied using cyclic voltammetry, scanning probe microscopy, and quantum-chemical modelling. It is shown that the first stage of UPD is one-dimensional decoration of the (100)- or (110)-orientated steps, then copper monolayer forms at (111)-terraces. The final stage is the secondary step decoration. Quantum-chemical modelling, with the using of long-distance potentials of the Cu-Pt and Cu-Cu pair interactions, allows estimating the energy of copper adsorption at different structure elements of the substrate (steps, kinks, terraces) and revealing the succession of the adatom monolayer formation; it also provides additional information for the identifying of the nature of voltametric peaks for different stages of the copper adsorption-desorption.     

Microwave assisted volatilization of silicon as fluoride for the trace impurity determination in silicon nitride by dynamic reaction cell inductively coupled plasma-mass spectrometry

A low pressure microwave assisted vapor phase dissolution procedure for silicon nitride and volatilization of in situ generated SiF₄ has been developed using H₂SO₄, HF and HNO₃ for the determination of trace impurities present in silicon nitride. Sample was taken in minimum amount (0.5 mL for 100 mg) of H₂SO₄ and treated with vapors generated from HF and HNO₃ mixture in presence of microwaves in a closed container. An 80 psi pressure with ramp and hold times of 30 min and 60 min respectively, operated twice, resulted in 99.9% volatilization of Si. Matrix free solutions were analyzed for impurities using DRC-ICP-MS. The recoveries of Cr, Mn, Fe, Ni, Co, Cu, Zn, Sr, Y, Cd, Ba and Pb were between 80 and 100% after volatilization of Si. The blanks were in lower ng g⁻¹ with method detection limits in lower ng g⁻¹ to sub ng g⁻¹ range. The method was applied for the analysis of two silicon nitride samples.     

求解复杂湍流的非线性涡黏性系数模型和代数应力模型

非线性涡黏性系数模型和代数应力模型联系了线性涡黏性系数湍流模型和完整的微分 雷诺应力模型.随着它们受到日益关注,其形式也越来越多样化.本篇综述的目的是对这些模 型加以总结并比较它们之间的共同点及不同之处,指出它们与完整微分雷诺应力模型之间的 关系,以及相对于线性涡黏性系数模型而言它们在预报流场上所具有的优势.     

Fusion around the barrier for 7Li+12C

Fusion cross-sections for the ⁷Li + ¹²C reaction have been measured at energies above the Coulomb barrier by the direct detection of evaporation residues. The heavy evaporation residues with energies below 3 MeV could not be separated out from the α-particles in the spectrum and hence their contribution was estimated using statistical model calculations. The present work indicates that suppression of fusion cross-sections due to the breakup of ⁷Li may not be significant for ⁷Li + ¹²C reaction at energies around the barrier.