Magnetic behavior of tetrahedral Cr4+ compounds: Sr2CrO4, Ba2CrO4, and Ba3CrO5

The preparation of the compounds Sr₂CrO₄, Ba₂CrO₄, and Ba₃CrO₅ is described. The characterization of these three Cr⁴⁺ compounds by X-ray and magnetic susceptibility experiments has been conducted. The magnetic moments for Sr₂CrO₄, Ba₂CrO₄, and Ba₃CrO₅ were determined to be in good agreement with the calculated value expected for a tetrahedral Cr⁴⁺ ion. Weak antiferromagnetic ordering for all three compounds is indicated from the small paramagnetic Weiss constants determined from the susceptibility data in the temperature region 80–300 K. Distortions of the tetrahedra from ideality, as determined from the structural features, further cause a reduction in the magnetic moments from the theoretical values.     

Pretreatment of wastepaper and pulp mill sludge by aqueous ammonia and hydrogen peroxide

Pretreatment of two different softwood-based lignocellulosic wastes (newsprint and Kraft pulp mill sludge) was investigated. Pretreatment was done by aqueous ammonia and hydrogen peroxide (H₂O₂), two delignifying reagents that are environmentally benign. Three different treatment schemes were employed: aqueous ammonia alone (ammonia recycled percolation [ARP]), mixed stream of aqueous ammonia and H₂O₂ and successive treatment with H₂O₂ and aqueous ammonia. In all cases there was a substantial degree of delignification ranging from 30 to 50%. About half of the hemicellulose sugars were dissolved into the process effluent. Retention of cellulose after pretreatment varied from 85 to 100% for newspaper feedstock and from 77 to 85% for the pulp mill sludge. After treatment with aqueous ammonia alone (ARP), the digestibility of newspaper and the pulp mill sludge was improved only by 5% (from 40 to 45% for the former and from 68 to 73% for the latter), despite a substantial degree of delignification occurring after the ARP process. The lign in content thus did not correlate with the digestibility for these substrates. Simultaneous treatment with H₂O₂ and aqueous ammonia did not bring about any significant improvement in the digestibility over that of the ARP. A succcessive treatment by H₂O₂ and ARP showed the most promise because it improved the digestibility of the newspaper from 41 to 75%, a level comparable to that of α-cellulose.     

Separation of uranium from molybdenum using a diamine functional group bonded to controlled-pore glass

A method for selective extraction of uranium from carbonate solutions containing molybdate is reported. A liquid chromatography column, packed with N-β-aminoethyl-γ-ammopropyltrimethoxysilane immobilized on a glass substrate, was utilized in a continuous How system. The selective retention of the uranyl carbonate species [UO₂(CO₃)₂? 2H₂O]^2- and UO₂(CO₃)^4- on protonated immobilized diamine is the basis for this separation Recoveries of uranium and molybdenum from synthetic samples ranged from 96.7 to 113.4% for uranium and from 96.7 to 110.5% for molybdate for a range of recommended conditions.     

Hemin-phytic Acid Functionalized Porous Conducting Polymer Hydrogel With Good Biocompatibility for Electrochemical Detection of H2O2 Released From Living Cells

A novel hemin/phytic acid doped polyaniline (PA-PANI) hydrogel composite was prepared through a simple chemical and self-assembly method, which was modified onto electrode for electrochemical detection of H₂O₂ released from living cells. It showed good analytical performance with high sensitivity, selectivity and a rapid response for the analysis of H₂O₂ in the range of 2 to 102 μM, with the detection limit of 1.2 μM. The favorable results mainly originated from both the high conductivity of PA-PANI hydrogel and its network structure preventing hemin from self-dimerization to provide active catalytic species. Furthermore, PA-PANI with good biocompatibility allowed living cells to adhere and resulted in a short diffusion distance between H₂O₂ released from cells and electrode.     

The heat capacity of lead from 300 to 850°k: conversion of cp to cv for liquid lead

Abstract

Recent measurements of the heat capacity at constant pressure C_p for lead from 300 to 850°K have shown that C_p for liquid lead decreases continuously from the melting point to 850°K. Using data in the literature of density and velocity of sound, the dilation correction has been applied to C_p to obtain the heat capacity at constant volume C_v for liquid lead. Application of the dilation correction to solid lead gives a C_v curve which uncreases only about one joule/gm-atom-°K from 300 to 600°K, whereas the C_v curve for liquid lead decreases almost 5 joules/gm-atom-°K from 600 to 850°K. A careful assessment of the uncertainty in the quantities used in the dilation correction leads to an uncertainty in C_v of ± 2.5% (about one joule/gm-atom-°K), and thus the decrease in C_v for liquid lead is quite real.     

Electron scattering on C6F6 and SF6 molecules

Total absolute cross sections for electron scattering on hexafluorobenzene, C₆F₆, and sulfur hexafluoride, SF₆, molecules, have been measured as a function of impact energy from 0.6 to 250 eV. The total cross section for C₆F₆ exhibits a very broad peak stretching from 10 to 100 eV with some weak features near 9.5 and 15 eV superimposed on the peak. Apart from the well-known low-energy resonant structures in the SF6 total cross section function, a new weak resonant feature close to 25 eV has been noticed in the present experiment, in accordance with earlier theoretical calculations.     

Direct reuse of LiFePO4 cathode materials from spent lithium-ion batteries: Extracting Li from brine

Due to the serious imbalance between demand and supply of lithium, lithium extraction from brine has become a research hotspot. With the demand for power lithium-ion batteries (LIBs) increased rapidly, a large number of spent LiFePO₄ power batteries have been scrapped and entered the recycling stage. Herein, a novel and efficient strategy is proposed to extract lithium from brine by directly reusing spent LiFePO₄ powder without any treatment. Various electrochemical test results show that spent LiFePO₄ electrode has appropriate lithium capacity (14.62 mg_Li/g_LiFePO4), excellent separation performance (α_Li-Na = 210.5) and low energy consumption (0.768 Wh/g_Li) in electrochemical lithium extraction from simulated brine. This work not only provides a novel idea for lithium extraction from brine, but also develops an effective strategy for recycling spent LIBs. The concept of from waste to wealth is of great significance to the development of recycling the spent batteries.     

Improving the robustness of a partial least squares (PLS) model based on pure component selectivity analysis and range optimization: case study for the analysis of an etching solution containing hydrogen peroxide

Pure component selectivity analysis (PCSA) was successfully utilized to enhance the robustness of a partial least squares (PLS) model by examining the selectivity of a given component to other components. The samples used in this study were composed of NH₄OH, H₂O₂ and H₂O, a popular etchant solution in the electronic industry. Corresponding near-infrared (NIR) spectra (9000-7500 cm⁻¹) were used to build PLS models. The selective determination of H₂O₂ without influences from NH₄OH and H₂O was a key issue since its molecular structure is similar to that of H₂O and NH₄OH also has a hydroxyl functional group. The best spectral ranges for the determination of NH₄OH and H₂O₂ were found with the use of moving window PLS (MW-PLS) and corresponding selectivity was examined by pure component selectivity analysis. The PLS calibration for NH₄OH was free from interferences from the other components due to the presence of its unique NH absorption bands. Since the spectral variation from H₂O₂ was broadly overlapping and much less distinct than that from NH₄OH, the selectivity and prediction performance for the H₂O₂ calibration were sensitively varied depending on the spectral ranges and number of factors used. PCSA, based on the comparison between regression vectors from PLS and the net analyte signal (NAS), was an effective method to prevent over-fitting of the H₂O₂ calibration. A robust H₂O₂ calibration model with minimal interferences from other components was developed. PCSA should be included as a standard method in PLS calibrations where prediction error only is the usual measure of performance.     

Matrix-assisted laser desorption mass spectrometry of homopolymer oligodeoxyribonucleotides. Influence of base composition on the mass spectrometric response

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has the potential for providing a rapid alternative to gel electrophoresis for DNA sequence analysis provided that an intense mass spectrometric response can be obtained from mixtures of DNA fragments containing up to 300 nucleotides. MALDI-MS has not yet proved viable for such analyses because the MS response falls off rapidly for mixed-base DNA fragments containing more than 20–30 nucleotides. Previous studies have demonstrated that base composition is a critical factor in the MALDI-MS response of oligodeoxyribonucleotides. This paper describes an investigation of the physical roots of the observed influence of base composition on the mass spectrometric response, focusing on homopolymer oligodeoxyribonucleotides (dT₇, dT₁₀, dT₁₈, dT₃₆, dG₇, dG₁₀, dG₁₈, dI₁₈ and dU₁₈) and dT₅G₅. Forty-eight different matrix compounds were tested for their ability to produce laser desorption masses spectra from such homopolymer oligodeoxyribonucleotides. Considerably stronger mass spectrometric responses were obtained from polydeoxythymidines than from polydeoxyguanosines, polydeoxycytidines and polydeoxyadenosines. Although mass spectral peaks corresponding to dT₁₈ were observed from 20 of the matrices studied, no discernible response was observed for dG₁₈ from any of these matrices. To elucidate the physical basis for origins of the observed differences in response, a number of factors were investigated including the ionization efficiency, the tendency towards fragmentation and the extent to which the oligodeoxyribonucleotides were incorporated into the matrix crystals. The results of these experiments indicate that low ionization efficiency is not a likely main contributor to the low response to polydeoxyguanosines, fragmentation is a likely main contributor to the low response to polydeoxyguanosines, the overall incorporation of polydeoxyguanosines into matrix crystals is comparable to that for polydeoxythymidines and the exocyclic amino group of guanosine, adenosine and cytidine has a strong inhibitory effect on the mass spectrometric response.     

Synthesis,structure and spin-crossover transition of The Cluster Compound Nb6I11−xBrx (0 ⩽ x ⩽ 2.7)

The homogeneous phase Nb₆I_11?xBr_x (0 ? x ? 2.7) is synthesized from Nb₃Br₈, Nb₃I₈ and Nb in sealed Nb capsules at 1 130 K. A second-order phase transition is found as for the composition Nb₆I₁₁ itself, changing the space group from P2₁cn (low temperatures) to Pccn, accompanied by a spin-crossover from a doublet to a quartet state. With increasing Br content the lattice constants decrease and the transition temperature shifts from 274 to 170 K while the transition interval is broadened simultaneously. Single crystal investigations for x = 0.5 and 2.3, each at 110 and 298 K, indicate a preferred substitution of one of the bridging I positions (I6) by Br atoms.     

Ternary phase equilibria for the sodium chloride–sodium sulfate–water system at 200 and 250 bar up to 400°C

Phase equilibria in the NaCl–Na₂SO₄–H₂O system were investigated at 200 and 250 bar for total salt concentrations ranging from 5 to 20 wt.% total salt over temperatures ranging from 320 to 400°C. In addition to providing data for this ternary system, the experiments also added information on the phase behavior of the two binary systems: NaCl–H₂O and Na₂SO₄–H₂O. For salt mixture compositions which were rich in sodium sulfate, a solid phase was observed to nucleate from the homogeneous liquid phase. Salt mixture compositions which had a high fraction of sodium chloride exhibited a vapor separation from a homogeneous liquid phase. By fitting curves to the solid–liquid and vapor–liquid separation temperatures, the temperature and composition of a constrained invariant point where liquid, solid salt and vapor are in equilibrium were estimated. These estimates were performed at discrete compositions of 5, 10, 15 and 20 wt.% total salt at pressures of 200 and 250 bar. The temperature and composition of the invariant point increased with increasing pressure following a simple thermodynamic model for boiling point elevation in a nearly ideal solution.     

Evaluation and applications of a gaseous mercuric chloride source

In this study, a diffusion-type device for generating gaseous mercuric chloride (HgCl₂) was systematically evaluated and applied to validate the annular denuder method for sampling gaseous HgCl₂ species in a synthetic gas stream. The results show that it takes at least 48 h for the system to reach a steady-state condition after the diffusion cell reaches the temperature set-point and the carrier gas is activated. The primary Hg species from the source was proven to be HgCl₂. In the temperature range from –5.00 to 11.80 °C, the Hg emission rates from the source vary from 1.8 to 14.2 pg min^–1. It is shown that, under the experimental conditions examined, KCl-coated annular quartz denuders designed for ambient reactive gaseous mercury (RGM) collection could quantitatively collect HgCl₂. It is also demonstrated that the impactors used to remove coarse airborne particulate matter could lead to a loss of up to one third of the HgCl₂ in the gas stream.     

Calculations of electron inelastic mean free paths. XII. Data for 42 inorganic compounds over the 50 eV to 200 keV range with the full Penn algorithm

We have calculated inelastic mean free paths (IMFPs) for 42 inorganic compounds (AgBr, AgCl, AgI, Al₂O₃, AlAs, AlN, AlSb, cubic BN, hexagonal BN, CdS, CdSe, CdTe, GaAs, GaN, GaP, GaSb, GaSe, InAs, InP, InSb, KBr, KCl, MgF₂, MgO, NaCl, NbC_0.712, NbC_0.844, NbC_0.93, PbS, PbSe, PbTe, SiC, SiO₂, SnTe, TiC_0.7, TiC_0.95, VC_0.76, VC_0.86, Y₃Al₅O₁₂, ZnS, ZnSe, and ZnTe) for electron energies from 50 eV to 200 keV. These calculations were made with energy-loss functions (ELFs) obtained from measured optical constants for 15 compounds while calculated ELFs were utilized for the other 27 compounds. Checks based on ELF sum rules showed that the calculated ELFs were superior to the measured ELFs that we had used previously. Our calculated IMFPs could be fitted to a modified form of the relativistic Bethe equation for inelastic scattering of electrons in matter for energies from 50 eV to 200 keV. The average root-mean-square (RMS) deviation in these fits was 0.60%. The IMFPs were also compared with a relativistic version of our predictive Tanuma-Powell-Penn (TPP-2M) equation. The average RMS deviation in these comparisons was 10.7% for energies between 50 eV and 200 keV. This average RMS deviation is almost the same as that found in a similar comparison for a group of 41 elemental solids (11.9%) although relatively large deviations were found for cubic BN (65.6%) and hexagonal BN (34.3%). If these two compounds are excluded in the comparisons, the average RMS deviation becomes 8.7%. We found generally satisfactory agreement between our calculated IMFPs and values from other calculations and from experiments.     

Simultaneous determination of aflatoxins and ochratoxin A in baby foods and paprika by HPLC with fluorescence detection: a single-laboratory validation study

Mycotoxins are toxic secondary metabolites of fungal origin, the major mycotoxins of food concern are aflatoxins and ochratoxin A. Due to the wide range of matrices susceptible to mycotoxin contamination, the possible co-occurrence, and the very wide range of concentration, validated versatile multi-mycotoxin and multi-matrix methods are strongly requested. A reversed phase HPLC method for the simultaneous determination of aflatoxins and ochratoxin A in baby foods and paprika was set up. Three bulk samples were prepared according to commercial availability, one for paprika and for baby foods, two different bulks were set, a corn based and a multi-cereal based baby food. A single-laboratory validation was performed, for each investigated level ten analyses were performed, relative standard deviations of repeatability (RSD_r) and recovery factors were calculated; RSD_r values ranged from 2% to 10% for AFB₁ and from 3% to 10% for OTA, while the recovery factors ranged from 86% to 96% for AFB₁ and from 77% to 96% for OTA. The checked compliance of the RSD_r and recovery with the values reported in the current EU Regulations confirmed the fitting for purpose of the method. Limit of detection and LoQ values of the method were respectively 0.002 and 0.020 μg/kg for AFB₁ and 0.012 and 0.080 μg/kg for OTA in baby foods; and 0.002 and 0.200 μg/kg for AFB₁ and 0.012 and 0.660 μg/kg for OTA in paprika. The current method represents a good example of the possibility of a multi-mycotoxin and/or a multi-matrix analysis depending on the laboratory research or official control purposes.     

Electric Properties of Solid Solutions in the Systems Li6MoN4−Li7NbN4 and Li6WN4−Li7TaN4

The phase balance and electric properties of products in the systems Li₆MoN₄–Li₇NbN₄ and Li₆WN₄–Li₇TaN₄ are studied. It is shown that continuous series of solid solutions whose lithium-cation conductance decreases during mutual doping exist in either system. The activation energies for the long- and short-range motion of lithium charge carriers, determined from the electroconductance and ⁷Li NMR data, equal 55 and 46 or 25 and 14 kJ mol^–1 for the initial compounds of the first and second systems, respectively. The difference that large is attributed to a large contribution of the coulombic correlation for the hops of lithium charge carriers in both systems. Basic parameters of the correlation (time, distance, relaxation time) are calculated from experimental data. The strong correlation in the systems is presumed to stem from a weak screening of the coulombic field in the nitrides, rather than from a high concentration of charge carriers.     

Graphene grafted silica‐coated Fe3O4 nanocomposite as absorbent for enrichment of carbamates from cucumbers and pears prior to HPLC

In this paper, a novel graphene (G) grafted silica‐coated Fe₃O₄ nanocomposite was fabricated by the chemical bonding of G onto the surface of silica‐coated Fe₃O₄ nanoparticles. Some carbamates (metolcarb, carbaryl, pirimicarb, and diethofencarb) in cucumber and pear samples were enriched by this nanocomposite prior to their determination by HPLC with UV detection. Experimental parameters that may affect the extraction efficiency were investigated. Under the optimum conditions, a linear response was achieved in the concentration range of 0.5–100.0 ng/g for metolcarb, carbaryl, and diethofencarb, and 1.0–100 ng/g for pirimicarb with the correlation coefficients (r) ranging from 0.9956 to 0.9984. The LOD (S/N = 3) of the method were found to be in the range from 0.08 to 0.2 ng/g. The RSDs were in the range from 2.4 to 5.8%. The results indicated that the G grafted silica‐coated Fe₃O₄ nanocomposite was stable and efficient for magnetic SPE and has a great application potential for the preconcentration of other organic pollutants from real samples.     

Spectroscopic studies of the AlCl3 · NH3 complex

A normal coordinate analysis for the AlCl₃ · NH₃ complex is performed. Calculations for a hypothetical complex with a planar AlCl₃ ligand are included. A deviation from planarity is found in the realistic complex. Force fields for free NH₃ and AlCl₃ molecules are employed in the construction of an initial approximate force field. The theory of kinematic coupling is used to study the frequency shifts from free to complexed ligands. A final force field is developed so as to reproduce exactly a set of observed frequencies from the literature. Calculations on mean amplitudes and perpendicular amplitude correction coefficients are reported.     

Ozone source attribution during a severe photochemical smog episode in Beijing, China

Beijing,the capital of China,frequently suffers from the high levels of ozone in summer.A 3-D regional chemical transport model,the Comprehensive Air Quality Model with extensions(CAMx),has been used to simulate a heavy O3 pollution episode in Beijing during June 26―July 2,2000.Ozone Source Apportionment Technology(OSAT) and Geographic Ozone Assessment Technology(GOAT) were applied to quantify the contributions of the precursor emissions from different regions to O3 concentrations in Beijing,to identify the...     

Generation and detection of gaseous W12O 41 −· and other tungstate anions by laser desorption ionization mass spectrometry

The presence of a peak centered near m/z 2862, observed for the first time for the caged dodecatungstate radical-anion, [W₁₂O₄₁]^−·, enables distinguishing WO₂ from WO₃ by Laser Desorption Ionization mass spectrometry (LDI-MS). In addition to WO₂, laser irradiation of dry deposits made from aqueous ammonium paratungstate, and calcium and lead orthotungstate also produce the [W₁₂O₄₁]^−·. In contrast, spectra recorded from deposits made from aqueous Na₂WO₄, sodium metatungstate, and WO₃, or non-aqueous calcium and lead orthotungstate, and ammonium paratungstate, failed to show the m/z 2862 peak cluster. These observations support the hypothesis that polycondensation reactions to form [W₁₂O₄₁]^−· occur solely in the presence of water. Although dry spots are irradiated for ionization, the solvent used for sample preparation plays an important role on the chemical composition endowed to ions detected. For example, the m/z 2862 peak seen from deposits made from aqueous ammonium paratungstate, and calcium and lead orthotungstate, is absent in the spectra recorded either from pristine deposits or those derived from solutions made with organic solvents such as acetonitrile or ethanol.     

Determination of the thermodynamic activity of sulfuric acid in the H2SO4-H2O-HCHO system by an indicator method

The ionization of N,N-dimethyl-2,4-dinitroaniline in water-formaldehyde solutions of H₂SO₄ consists in the addition of a H₂SO₄ molecule to an indicator molecule. The logarithm of the indicator ratio for identical molality of the acid in a water-formaldehyde solution and in water varies linearly as a function of the logarithm of the thermodynamic activity of the acid for a molar ratio of free water to methylene glycol >-10. A method is presented for calculation of the thermodynamic activity of the acid in the H₂SO₄,-H₂O-methylene glycol system in the H₂SO₄, molality range from 1 to 4 for the given molar ratio of free water to methylene glycol.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 987–991, May, 1990.