Interferences and their elimination in the determination of the noble metals by atomic-absorption spectrophotometry

A number of serious interferences in the determination of the noble metals by atomic-absorption spectrophotometry have been investigated, and ways of eliminating them considered. The use of the nitrous oxide and acetylene flame reduced many of the interferences but also reduced the sensitivity. Additions of lanthanum, copper sulphate, copper + cadmium sulphate, uranium, and vanadium as releasing agents were effective in the removal of interferences for one or more of the noble metals in the air-acetylene flame. Uranium additions were found to be effective in removing mutual interferences associated with the noble metals (osmium and indium were not tested) whereas vanadium removed mutual and base-metal interferences. The precision and accuracy of methods of analysis based on the use of uranium and vanadium were acceptable, and the application of these methods to the analysis of noble metals collected by various procedures is briefly discussed.     

Ab initio molecular orbital studies for compounds of magnesium

Using a 6-311G** basis set with estimation of correlation energy at the MP2 level, structural and energetic data for 40 molecular species containing magnesium have been calculated. For about half the species studied, further energetic data were obtained using Pople's G2 method. Enthalpy changes at 298.15 K were obtained for isogyric reactions and standard enthalpies of formation were derived from these. Comparison of the standard enthalpies of formation with the sparse literature data suggests the MP2/6-311G** standard enthalpies of formation are accurate to ± 15 kJ mol^?1 and the corresponding G2 enthalpies accurate to ± 10 kJ mol^?1. The calculated ΔH [MgN, g] revealed a gross error in the currently accepted value for this function. It is intended that these results will be used to parameterize the semiempirical molecular orbital package, MOPAC, for the element magnesium. © John Wiley & Sons, Inc.     

Complexes with metal-carbon bonds,part III(1). Preparation and properties of binuclear diarylplatinum(II) compounds

Summary Reaction ofcis-PtCl₂(R₂S)₂, where R=Et, n-Pr or i-Pr, with an excess of PhLi orp-tolylLi in ether yielded the dimeric [PtR₂(R₂S)]₂ complexes where R=Ph orp-tolyl. Usingtrans-PtCl₂(R₂S)₂ under the same conditions with PhLi, both [PtPh₂(Et₂S)]₂ and PtPh₂(Et₂S)₂ were isolated.The dimericcis-[PtR₂(Et₂S)]₂ complexes reacted with a range of neutral ligands to give PtR₂L₂ where L=Et₂S, Me₂S, PPh₃, t-BuNC, 0.5 (bipyridine) or pyridine. With CO, thecis-PtR₂(Et₂S)(CO) compounds were formed. Thecis-Pt(C₆F₅)₂(Et₂S)₂ complex reacted stepwise with PPh₃ and both Pt(C₆F₅)₂(Et₂S)(PPh₃) and Pt(C₆F₅)₂(PPh₃)₂ were isolated.     

Anomalous temperature dependence of sub-critical crack growth in silica glass

The effects of temperature, water vapor, and stress on the rate of sub-critical crack growth (SCG) in fused silica are reported. The crack velocity was measured using the double-cleavage-drilled compression method. In contrast to other inorganic oxide glasses, crack growth velocities (in region I) were found to decrease with increase in temperature. Hence a small temperature rise has the apparent effect of improving the mechanical strength of a stressed-glass part. Despite the anomalous temperature dependence, SCG in fused silica is still likely governed by the established water-enhanced stress-corrosion mechanism; another competing phenomenon is proposed to cause the observed temperature dependence. Measured crack velocities are described using an empirical model (for region I) and a mass-transport model limited by Knudsen diffusion (for region II).     

Single, binary and multi-component adsorption of copper and cadmium from aqueous solutions on Kraft lignin--a biosorbent

A new biosorbent for removing toxic metal ions from water/industrial wastewater has been investigated using by-product lignin from paper production. Lignin was extracted from black liquor waste, characterized and utilized for the removal of copper and cadmium from aqueous solutions in single, binary and multi-component systems. Adsorption studies were conducted at different temperatures, lignin particle sizes, pHs and solid to liquid ratios. All the studies were conducted by a batch method to determine equilibrium and kinetic parameters. The Langmuir and Freundlich isotherm models were applied. The Langmuir model fits best the equilibrium isotherm data. The maximum lignin adsorption capacities at 25 degrees C were 87.05 mg/g (1.37 mmol/g) and 137.14 mg/g (1.22 mmol/g) for Cu(II) and Cd(II), respectively. Adsorption of Cu2+ (68.63 mg/g at 10 degrees C and 94.68 mg/g at 40 degrees C) and Cd2+ (59.58 mg/g at 10 degrees C and 175.36 mg/g at 40 degrees C) increased with an increase in temperature. Copper and cadmium adsorption followed pseudo-second order rate kinetics. From kinetic studies, various rate and thermodynamic parameters such as effective diffusion coefficients, activation energy, and activation entropy were evaluated. Adsorption occurs through a particle diffusion mechanism at temperatures 10 and 25 degrees C while at 40 degrees C it occurs through a film diffusion mechanism. The sorption capacity of black liquor lignin is higher than many other adsorbents/carbons/biosorbents utilized for the removal of Cu(II) and Cd(II) from water/wastewater in single and multi-component systems.     

Sorption of arsenic, cadmium, and lead by chars produced from fast pyrolysis of wood and bark during bio-oil production

Bio-char by-products from fast wood/bark pyrolyses, were investigated as adsorbents for the removal of the toxic metals (As(3+), Cd(2+), Pb(2+)) from water. Oak bark, pine bark, oak wood, and pine wood chars were obtained from fast pyrolysis at 400 and 450 degrees C in an auger-fed reactor and characterized. A commercial activated carbon was also investigated for comparison. Chars were sieved (>600, 600-250, 250-177, 177-149, and <149 microm) and the particle size fraction from 600 to 250 microm was used without further modification for all studies unless otherwise stated. Sorption studies were performed at different temperatures, pHs, and solid to liquid ratios in the batch mode. Maximum adsorption occurred over a pH range 3-4 for arsenic and 4-5 for lead and cadmium. Kinetic studies yielded an optimum equilibrium time of 24 h with an adsorbent dose of 10 g/L and concentration approximately 100 mg/L for lead and cadmium. Sorption isotherms studies were conducted in broad concentration ranges (1-1000 ppb for arsenic, 1x10(-5)-5x10(-3) M for lead and cadmium). Oak bark out-performed the other chars and nearly mimicked Calgon F-400 adsorption for lead and cadmium. In an aqueous lead solution with initial concentration of 4.8x10(-4) M, both oak bark and Calgon F-400 (10 g/L) removed nearly 100% of the heavy metal. Oak bark (10 g/L) also removed about 70% of arsenic and 50% of cadmium from aqueous solutions. Varying temperatures (e.g., 5, 25, and 40 degrees C) were used to determine the effect of temperatures. The equilibrium data were modeled with the help of Langmuir and Freundlich equations. Overall, the data are well fitted with both the models, with a slight advantage for Langmuir model. The oak bark char's ability to remove Pb(II) and Cd(II) is remarkable when considered in terms of the amount of metal adsorbed per unit surface area (0.5157 mg/m(2) for Pb(II) and 0.213 mg/m(2) for Cd(II) versus that of commercial activated carbon.     

Schwefelwasserstoffentwicklung

Ohne Zusammenfassung     

Meron pairs and fermion zero modes

Merons, conjectured as a semiclassical mechanism for color confinement in QCD, have been described analytically by either infinite action configurations or an Ansatz with discontinuous action. We construct a smooth, finite action, stationary lattice solution corresponding to a meron pair. We also derive an analytical solution for the zero mode of the meron pair Ansatz, show that it has the qualitative behavior of the exact zero mode of the lattice solution, and propose the use of zero modes to identify meron gauge field configurations in stochastic evaluations of the lattice QCD path integral.