Determination of cadmium in coal using solid sampling graphite furnace high-resolution continuum source atomic absorption spectrometry

This work describes the development of a method to determine cadmium in coal, in which iridium is used as a permanent chemical modifier and calibration is performed against aqueous standards by high-resolution continuum source atomic absorption spectrometry (HR-CS AAS). This new instrumental concept makes the whole spectral environment in the vicinity of the analytical line accessible, providing a lot more data than just the change in absorbance over time available from conventional instruments. The application of Ir (400 g) as a permanent chemical modifier, thermally deposited on the pyrolytic graphite platform surface, allowed pyrolysis temperatures of 700 °C to be used, which was sufficiently high to significantly reduce the continuous background that occurred before the analyte signal at pyrolysis temperatures <700 °C. Structured background absorption also occurred after the analyte signal when atomization temperatures of >1600 °C were used, which arose from the electron-excitation spectrum (with rotational fine structure) of a diatomic molecule. Under optimized conditions (pyrolysis at 700 °C and atomization at 1500 °C), interference-free determination of cadmium in seven certified coal reference materials and two real samples was achieved by direct solid sampling and calibrating against aqueous standards, resulting in good agreement with the certified values (where available) at the 95% confidence level. A characteristic mass of 0.4 pg and a detection limit of 2 ng g^–1, calculated for a sample mass of 1.0 mg coal, was obtained. A precision (expressed as the relative standard deviation, RSD) of <10% was typically obtained when coal samples in the mass range 0.6–1.2 mg were analyzed.Dedicated to the memory of Wilhelm Fresenius     

Spectroscopic Investigation of Sublimated Products of Ultradisperse Polytetrafluoroethylene

The structure of fractions isolated by thermal sublimation of ultradisperse polytetrafluoroethylene (UPTFE) powder has been studied by IR spectroscopy. At 50°C–160°C, fractions of highly amorphous fragments are condensed on a cold receiver; the fragments are constructed from branched chains with terminal olefin groups. Fractions isolated at 300°C and higher are close in structure to PTFE and are highly crystalline. It is assumed that sample amorphism is due to the irregular distribution of the fractions of fragments with terminal olefin and lateral fluoromethyl groups in the structures.Original Russian Text Copyright © 2004 by L. N. Ignatieva, A. K. Tsvetnikov, O. N. Gorbenko, T. A. Kaidalova, and V. M. Buznik__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 830–836, September–October, 2004.     

Radiolytic gas formation under γ-irradiation of oxalic acid solutions

Radiolytic gas formation under -irradiation (10⁴–10⁶ Gy) of 10^–2–10^–4 M aqueous solutions of oxalic acid at 25–60°C was studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 11, 2004, pp. 1836–1839.Original Russian Text Copyright © 2004 by Popova, Voronin, Byvsheva.     

Mechanism of the Effect of Thermal Treatment on the Formation of Strong Acid Sites in the Surface Layers of Sulfated Metal Oxides

Strong acid catalysts were synthesized by the impregnation of hydrated ZrO₂ and TiO₂ with sulfuric acid followed by thermal treatment at different temperatures. The surface acidity and crystallochemical characteristics of the catalysts were studied by potentiometry and X-ray diffraction analysis, respectively. It was found that the surface acidity gradually increased as the temperature of thermal treatment was increased from 350 to 600°C for SO^2– ₄/ZrO₂ or to 200°C for SO^2– ₄/TiO₂; this increase correlated with the degrees of crystallinity of the samples. A hypothesis was proposed to explain the gradual accumulation of acid sites in the surface layer in the course of thermal treatment. It was assumed that, because of crystallographic changes that caused the weakening or even rupture of Zr–O–S and Ti–O–S bonds in modified surface layers, these layers exhibited an enhanced reactivity in contact with water vapor. Subsequently, this resulted in the formation of strongly acidic grafted M–O–SO₃–H⁺ groups.     

Surface Area Study of High Area Cobalt Aluminate Particles Prepared by the Sol-Gel Method

Cobalt aluminate particles were prepared by the sol-gel method, starting from aluminum sec-butoxide and cobalt salts with a Co:Al ratio of 1:3. Samples with the same composition were also prepared by the citrate-gel method from cobalt and aluminum nitrates and citric acid. The particles were calcined to temperatures between 400 and 1000°C, for the formation of the mixed oxide having spinel structure. The surface properties of the different samples (BET surface area and pore size distribution) were measured. The highest BET surface area obtained (about 339 m²/g) corresponds to a sample prepared by cobalt acetate and aluminum sec-butoxide, calcined at 400°C. The surface area of the sample is reduced progressively as the sample is calcined to higher temperatures (to about 65 m²/g at 1000°C). Narrow pore size distributions were observed with average pore radius ranging from 17–20 Å, for samples heated to 400°C, to about 55–65 Å, for samples heated to 1000°C. The different surface areas and porosities obtained for particles prepared by different methods, different precursors or calcination temperatures, are discussed.     

The first ionization constant from 25 to 200°C and 2000 bar for orthophosphoric acid

The ionization constant of orthophosphoric acid, determined by conductivity measurements, decreased from 7.11×10^–3 at 25°C to 6.2×10^–4 mol-kg^–1 at 200°C. The pressure effect to 2000 bar was also measured and the ratio K₂₀₀₀/K₁ is 2.7 at 25°C and 3.7 at 200°C. The standard partial molar volume change for the ionization at 1 bar, , changes from –16.1 at 25°C to –33.3 cm³-mol^–1 at 200°C. The partial molar compressibility change for the ionization, , varies from –3.8×10^–3 to –8.3×10^–3 cm³-mol^–1 bar^–1 over the same temperature range.     

Active centers on the surface of thermoactivated silica. Their reactivity toward organoaluminum compounds

Interaction between organoaluminum compounds (triethylaluminum, ethoxydiethylaluminum, and diethoxyethylaluminum) and the surface of silica activated at various temperatures (200–800 °C) was studied by IR spectroscopy, mass spectrometry, and quantum chemistry. Formation of structural silanon defects on the surface of silica activated at 800 °C was considered. It was established that the fraction of terminal silanol groups involved in the interaction with organoaluminum compounds on the surface of silica thermoactivated above 600 °C is low, and siloxane bonds and structural surface defects play a determining role. The thermodynamic favorability of coordination of organoaluminum compounds on these active surface centers is shown. The structure and routes of decomposition of aluminum-containing surface intermediates were studied.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1906–1911, October, 1995.The work was financially supported by the Russian Foundation for Basic Research (Project No. 94-03-08847).     

Effect of heat treatment on thermal stability of limestone

The nature of the anomalous effect exerted by the heat treatment of limestone at 500 and 600°C on its thermal stability at 825°C was studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 9, 2004, pp. 1435–1437.Original Russian Text Copyright © 2004 by Kabanov.     

The Relationship between the State of Active Species in a Ni/Al2O3Catalyst and the Mechanism of Growth of Filamentous Carbon

The formation of active particles and their changes in the course of 1,3-butadiene decomposition on a Ni/Al₂O₃catalyst at temperatures from 400 to 800°C were studied by high-resolution electron microscopy. It was found that carbon filaments of different types were formed at 400–800°C. The growth of thin filaments (20–30 nm in diameter) takes place at 400–600°C on a conical Ni particle located at the growing end of the filament, whereas di-symmetrical filaments 50–100 nm in diameter grow on biconical metal particles. As the carbonization temperature was increased to 700–800°C, graphite nanotubes 5–20 nm in diameter were formed. It was found that the mechanism of formation and the structure of filaments are related to the state of catalytically active species, which consist of a solid solution of carbon in the metal. It is suggested that the metastable surface nickel carbide Ni₃C_{1 – x} is an intermediate compound in the catalytic formation of graphite filaments from 1,3-butadiene. Upon termination of the reaction, the metastable Ni₃C_{1 – x} microphase is decomposed with the formation of hexagonal nickel microinclusions. The role of epitaxy in the nucleation and growth of a graphite phase on the metal is discussed. Models are presented for the growth of structurally different carbon filaments depending on the formation of active metal species at various temperatures. Considerable changes in the structure of carbon and the formation of nanotubes at 700–800°C are related to the appearance of a viscous-flow state of metal–carbon particles.     

Effect of the Measurement Temperature on the Dispersive Component of the Surface Free Energy of a Heat Treated SiO2 Xerogel

The surface free energy of a monolithic silica xerogel treated at 1000°C has been measured by inverse gas chromatography in the temperature range 25–150°C using n-alkanes. Values of the dispersive component, _S ^D, vary from 49.07 mJ·m^–2 at 25°C to 17.20 mJ·m^–2 at 150°C. The _S ^D value obtained at 25°C is lower than that found for amorphous and crystalline silicas but higher than that found for glass fibres meaning that the heat treatment at 1000°C changes drastically the structure of the silica xerogel showing a surface similar to a glass. However, the higher value of _S ^D in comparison to glass fibres can be attributed to the mesoporous structure present in the silica xerogel. In the temperature range of 60–90°C there exists an abrupt change of the _S ^D values as well as in the dispersive component of the surface enthalpy, h _S ^D. Such abrupt change can be attributed to an entropic contribution of the surface free energy.     

Mechanism of solid-state conversion of non-stoichiometric hydroxyapatite to diphase calcium phosphate

Two non-stoichiometric hydroxyapatites (n-HA) with Ca/P molar ratios of 1.50 and 1.58 and one stoichiometric hydroxyapatite (s-HA) with Ca/P = 1.67 were prepared from chemically pure CaHPO₄·2H₂O and KOH. After sintering at 1050 °C for 4 h, n-HA with Ca/P = 1.50 was transformed into -Ca₃(PO₄)₂, n-HA with Ca/P = 1.58 was converted to diphase calcium phosphate (DCP), while s-HA underwent no chemical transformations. The sintered and unsintered samples of hydroxyapatite were studied by IR spectroscopy, chemical analysis, and X-ray diffraction analysis. The crystallite dimensions were calculated, and a model for the DCP structure was proposed. The mechanism of the solid-state n-HA to DCP conversion was proposed on the basis of this model and published values of the volume diffusion coefficients of the OH^–, Ca²⁺, and PO₄ ^3– ions at 1000 °C.     

Thermal Evolution of Hybrid Organic-Inorganic Gels Derived from Reaction of 1,4 Butanediol with Tetraethoxysilane

Transparent monolithic discs of organic-inorganic hybrid gels have been prepared by hydrolysis-condensation reactions of tetraethyl orthosilicate with 1,4 butanediol. The gels and glasses have been characterized by infrared spectroscopy and ²⁹Si MAS NMR. The characterization of the gels by infrared spectroscopy showed the incorporation of carbonaceous groups in the polymeric structure and Si–C bonding in the glasses. Pyrolysis of the gels has been studied using thermal analysis. It showed that the pyrolysis of the gels occurs in two temperature domains. The first is below 400°C due to condensation reactions and second is in the temperature range 450–550°C due to decomposition of carbonaceous groups and crosslinking. Pyrolysis of the gels at 1000°C resulted in X-ray amorphous, hard black glasses similar to oxycarbide glasses obtained by pyrolysis of siloxanes. On further heat treatment to 1400–1600°C, development of cristobalite structure and crystalline silicon carbide is observed in the otherwise amorphous black mass. The pyrolysed materials have been found to exhibit good resistance towards oxidation at 1000°C.     

Polychronous kinetics of oxidative delignification of coniferous kraft cellulose with hydrogen peroxide

The kinetics of oxidative delignification of coniferous kraft cellulose with hydrogen peroxide in the temperature range 60–100°C was studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 10, 2004, pp. 1739–1742.Original Russian Text Copyright © 2004 by Shcherbakova, Demin, Mikhailov.     

Studies on recrystallised aluminium trihydroxide precipitates: The energetics of dissolution by sodium hydroxide solutions

Summary Aluminium hydroxide gels were recrystallised in high pH solution for 2–1000 hr to give a series of gibbsite powders of different surface areas, 1`11/2, P11/8, P11/48, P11/360 and P11/X; their average platelet lengths were 30, 60, 130, 260 and 450 nm. The dissolution equilibria of these powders in sodium hydroxide solutions of C=1-8 M were studied at 20° to 80°C.The equilibrium constants (for formation of diaquo-tetrahydroxoaluminate anion) increased with temperature and with increasing surface area; the K value for P11/2 was about four times that of P 11/X at 20 °C and about three times (that for P 11/X) at 80 °C. The dissolutions were endothermic; however, the value over this temperature range increased from –29.5 kJ mol<sup>–1</sup> (for P11/X) to –24.7 kJ (for P 11/2). This increase was related to the appreciable surface energies of the high surface-area materials.The (– G°) values increased with increasing temperature and in turn with increasing surface area; the (– G°) values for 1`11/2 dissolution at any temperature were about 4 kJ mol^–1 higher than those for P11/X dissolution.With 1 figure and 1 table     

Forms of iron occurrence in a series of binary tellurides Fe<Subscript>x</Subscript>Ti<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript>1.45</Subscript>

Nonstoichiometric tellurides Fe_xTi_1–x Te_1.45 synthesized at 850°C were studied by X-ray phase and X-ray fluorescence analysis and by ⁵⁷Fe Mössbauer spectroscopy. The mutual iron-titanium substitution is limited in this series. The system contains four individual phases in which iron is in three different states: Fe²⁺ in an asymmetric environment, Fe²⁺ in a symmetric environment, and Fe⁰. The distribution of various iron states in the system depends not only on the Fe : Ti ratio, but also on the structure of phases.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 11, 2004, pp. 1761–1764.Original Russian Text Copyright © 2004 by Pankratova, Zabolotnaya, Panchuk, Semenov, Zvinchuk, Suvorov.This revised version was published online in April 2005 with a corrected cover date.     

Nucleophilic Addition to Acetylenes in Superbasic Catalytic Systems: XIV. Vinilation of Diols in a System CsF-NaOH

A new catalytic system CsF-NaOH was developed for the synthesis of mono- and divinyl ethers of alkanediols exceeding in efficiency KOH. The nucleophilic addition of diols to acetylene in the presence of this system occurs both at enhance pressure (without solvent, 140–160°C) and atmospheric pressure (in DMSO medium, 100°C) of acetylene. Conditions were established of a selective preparation in a high yield of divinyl ethers from diols.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 5, 2005, pp. 677–683.Original Russian Text Copyright © 2005 by Oparina, Khil’ko, Chernyshova, Shaikhudinova, Parshina, Preiss, Henkelmann, Trofimov.     

IR spectroscopic study of the conformational lability of 4′-ethyl-4-cyanobiphenyl

The conformational lability of 4-ethyl-4-cyanobiphenyl molecules in solid crystal (SC) and isotropic liquid (IL) states was investigated by IR spectroscopic techniques (experiment and theory). IR absorption spectra were measured at 28°C–95°C in the frequency range 400 cm^–1–4000 cm^–1. Spectrum simulation was performed using the fragment method with allowance for the conformational fluctuations of molecules. The experimental and calculated spectra were compared and analyzed, and it was shown that in the IL, the samples are mixtures of conformers. The temperature changes in the spectra in the stated range are caused by the conformational lability of molecules.Original Russian Text Copyright © 2004 by L. M. Babkov, I. I. Gnatyuk, G. A. Puchkovskaya, and S. V. TrukhachevTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 398–405, May–June, 2004.     

Structure of the Potassium Hydroxide-Dibenzo-18-crown-6 Complex

Dibenzo-18-crown-6 reacts with potassium hydroxide in methanol to give the C₂₀H₂₄O₆ ⋅ KOH ⋅ MeOH complex which was characterized by the ¹H NMR, UV, and IR spectra. Depending on the conditions, the reaction of the same compounds in toluene gave products with the compositions 4 C₂₀H₂₄O₆ ⋅ KOH ⋅ 3 H₂O (3 h, reflux) and 11C₂₀H₂₄O₆ ⋅ KOH (1 h, 80°C, 1 h).__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 4, 2005, pp. 620–625.Original Russian Text Copyright © 2005 by Nosyreva, Mal’kina, Sinegovskaya, Trofimov.     

Dielectric investigation of the glass relaxation in poly(vinyl acetate) and poly(vinyl chloride) under high hydrostatic pressure

Measurements of the complex relative permittivity of poly(vinyl acetate) from 35 °C to 190 °C and poly(vinyl chloride) from 90 °C to 150 °C in the frequency range 10^–2 –10⁷ Hz and the pressure range 1–5000 bar are reported. Details of the pressure generating system and of the dielectric equipment are described.     

Structural Characteristics of Hydrated Complexes of Aminoacids in Aqueous Solutions

Aqueous solutions of nine α-aminoacids were studied in a diluted range of concentrations (from 0. 01 m to 0.1 m) at 5°C, 15°C, 25°C, 35°C, and 45°C based on the model that uses molar adiabatic compressibility (β _s V _m ) as a measure of hydration of the solute. For the resulting hydrated complexes of aminoacids, structural characteristics have been determined. At increased concentrations of the acid, variation of its hydration number is the chief factor affecting the molar compressibility of the hydrated complex.Original Russian Text Copyright © 2004 by V. N. Afanasiev, E. Yu. Tyunina, and V. V. Ryabova__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 883–888, September–October, 2004.