thermocalc — A poor man's approach to computational thermochemistry

We present thermocalc, a Perl module to perform the automated calculation of atomization energies and heats of formation for lists of molecules. The methods used are based on density functional theory and second‐order perturbation theory to ensure that data sets of medium sized to large molecules can be run at reasonable throughput rates. The quantum chemical calculations are performed using the program package TURBOMOLE in a three‐step protocol. In a first step, a pre‐optimization of the structure and a zero‐point energy calculation are performed. As second step, a geometry optimization is being carried out, and the last step is a single point energy calculation. The level of theory used in the different steps can be modified by the user to allow for customized protocols. The performance of example protocols is investigated on different test sets of molecules. In the course of this work, a simple, but efficient one‐parameter correction term based on the shared electron numbers has been developed, which reduces the error of calculated heats of formation significantly. © 2012 Wiley Periodicals, Inc.     

Deterhination of Dibutyltin and Tributyltin Compounds in Sea Water by Graphite Furnace Atomic Absorption Spectrometry

Dibutyltin and tributyltin compounds in artificial sea water were determined at sub-ppb levels. These compounds are separated from matrix elements in aqueous solutions by a simultaneous hydride generation dichloromethane extraction. After dichloromethane is vaporized, the residue is dissolved in hexane and is directly injected into the treated graphite tube and the signal is measured by a Zeeman atomic absorption spectrometer.     

Drop size spectra in sprays from pressure-swirl atomizers

A study on the characterization of sprays from Newtonian liquids produced by pressure-swirl atomizers is presented. The global drop size spectra of the sprays are measured with phase-Doppler anemometry, and global mean drop sizes are derived as moments of the spectra for varying atomizer geometry, liquid flow rate, and physical properties of the liquids. Dimensional analysis provides a correlation for the non-dimensional global Sauter mean diameter. A relationship between the global Sauter mean drop size and the global drop size RMS is established. A method is developed for predicting the global drop size spectra in the sprays, using easily accessible experimental input parameters. The basis for the function defining the spectrum is a gamma distribution, which is known from the literature as physically relevant for ligament-mediated sprays.     

Indirect AAS Determination of Cationic Surfactants in Waste Effluents and Shampoos

Abstract

An indirect atomic absorption spectro-metric (AAS) method using electrothermal atomization (ETAAS) for the determination of cationic surfactants has been proposed. The method involves ion-pair formation between cationic surfactant and sodium hexanitro-cobaltate(III), extraction of the ion-pair into 1, 2-dichloroethane and determination of cobalt con centration in organic phase by ETAAS and hence indirectly relating to the cationic surfactant concentrations. Surfactants of the anionic and nonionic group do not interfere to a great extent, and matrix inter ferences from many other cations, anions and organics are also not observed. The method has been success fully applied to cationic surfactant determination in waste water and hair rinsers. Relative standard deviation values (RSD) of 3.2% for waste water samples and 4.3% for shampoo were observed in these analyses.     

Determination of cadmium in rice and water by tungsten coil electrothermal vaporization-atomic fluorescence spectrometry and tungsten coil electrothermal atomic absorption spectrometry after cloud point extraction

In this work, the microsampling nature of tungsten coil electrothermal vaporization Ar/H₂ flame atomic fluorescence spectrometry (W-coil ETV-AFS) as well as tungsten coil electrothermal atomic absorption spectrometry (W-coil ET-AAS) was used with cloud point extraction (CPE) for the ultrasensitive determination of cadmium in rice and water samples. When the temperature of the extraction system is higher than the cloud point temperature of the selected surfactant Triton X-114, the complex of cadmium with dithizone can be quantitatively extracted into the surfactant-rich phase and subsequently separated from the bulk aqueous phase by centrifugation. The main factors affecting the CPE, such as concentration of Triton X-114 and dithizone, pH, equilibration temperature and incubation time, were optimized for the best extract efficiency. Under the optimal conditions, the limits of detection for cadmium by W-coil ETV-AFS and W-coil ET-AAS were 0.01 and 0.03 μg L⁻¹, with sensitivity enhancement factors of 152 and 93, respectively. The proposed methods were applied to the determination of cadmium in certified reference rice and water samples with analytical results in good agreement with certified values.     

Comparison of electrothermal atomization diode laser Zeeman- and wavelength-modulated atomic absorption and coherent forward scattering spectrometry

Atomic absorption and coherent forward scattering spectrometry by using a near-infrared diode laser with and without Zeeman and wavelength modulation were carried out with graphite furnace electrothermal atomization. Analytical curves and limits of detection were compared. The magnetic field was modulated with 50 Hz, and the wavelength of the diode laser with 10 kHz. Coherent forward scattering was measured with crossed and slightly uncrossed polarizers. The results show that the detection limits of atomic absorption spectrometry are roughly the same as those of coherent forward scattering spectrometry with crossed polarizers. According to the theory with bright flicker noise limited laser sources the detection limits and linear ranges obtained with coherent forward scattering spectrometry with slightly uncrossed polarizers are significantly better than those obtained with crossed polarizers and with atomic absorption spectrometry. This is due to the fact that employing approaches of polarization spectroscopy reduce laser intensity fluctuations to their signal carried fractions.     

雾化角对液体火箭发动机燃烧室压力振荡的影响

针对液氧/煤油火箭发动机模型燃烧室实现了三维非稳态两相燃烧过程的数值模拟,得到的燃烧室截面平均压力和平均速度与实验吻合。在初边值条件不施加任何扰动的情况下,得到了燃烧室压力自激振荡过程,并研究了液氧和煤油喷嘴雾化角对燃烧室压力振荡的影响。计算结果表明:当雾化角为40°或120°时,由于燃料与氧化剂喷雾锥重叠区域较小或较大,导致了推进剂混合很差或很好,不易在燃烧室头部出现局部爆炸性的可燃混气团,致使燃烧室压力振荡强度较弱;而当雾化角为中间值65°时,易于出现爆炸性的可燃气团并导致剧烈的压力振荡,使燃烧室中出现燃烧不稳定性。因此,雾化角的合理设计是抑制燃烧不稳定性的一种途径。     

Synthesis of novel amorphous calcium carbonate by sono atomization for reactive mixing

Droplets of several micrometers in size can be formed in aqueous solution by atomization under ultrasonic irradiation at 2 MHz. This phenomenon, known as atomization, is capable of forming fine droplets for use as a reaction field. This synthetic method is called SARM (sono atomization for reactive mixing). This paper reports on the synthesis of a novel amorphous calcium carbonate formed by SARM. The amorphous calcium carbonate, obtained at a solution concentration of 0.8 mol/dm³, had a specific surface area of 65 m²/g and a composition of CaCO₃•0.5H₂O as determined using thermogravimetric/differential thermal analysis (TG-DTA). Because the ACC had a lower hydrate composition than conventional amorphous calcium carbonate (ACC), the ACC synthesized in this paper was very stable at room temperature.     

Separation of Silver from Chloride and Sulfate Matrices by Fractional Condensation in a Two-Step Graphite Atomizer

The influence of the excess of sodium chloride and potassium sulfate in a sample on the signal of atomic absorption of silver in a two-step graphite atomizer comprising a cup-evaporator and a tube-atomizer heated independently has been investigated. It is shown that the preliminary fractional condensation of the element to be determined in the tube-atomizer can be used to decrease the interferences from the matrix. The undesirable gas-phase condensation of the matrix vapor is eliminated by heating the tube to a temperature close to the temperature of desorption of silver from its surface (700–800°C). The attained level of the influence of the matrix on the signal of atomic absorption is approximately equal to the level of the interferences from the matrix in a graphite atomizer with transverse heating and is higher than that in an atomizer with longitudinal heating.     

Two-Stage Evaporation of Silver Samples in a Graphite Atomizer

A study has been made of the process of separation of silver from the excess in a sample of alkali-earth chlorides and sulfates by two-stage evaporation from the wall of a graphite atomizer and by fractional condensation on its integrated platform. It has been shown that after the condensation on the platform at room temperature the influence of the salts on the signal of atomic absorption is two times higher than that in ordinary one-stage evaporation. The reason for this is the formation of a cloud of condensed salt particles preventing the silver atoms from depositing on the platform. The atoms are deposited on these particles and are removed from the atomizer together with them before the stage of measurement of an analytical signal.