Influence of the Degree of Dehydroxylation of Kaolinite on the Properties of Aluminosilicate Glasses

The degree of dehydroxylation of kaolinite, D_TG and D_IR, respectively, is characterized by thermogravimetric analysis (TG) and Fourier transform infrared spectroscopy (FTIR). The relation between DTG and DIR based on the infrared absorptions at 3600–3700, 915, 810, and 540 cm⁻¹ is established. Three regions can clearly be distinguished: the dehydroxylation region (D_TG<0.9), the metakaolinite region (0.9<D_TG<1) and the ‘spinel’ region(D_TG=1). The effect of the degree of dehydroxylation of kaolinite on the amount of reactive material is measured by the reaction enthalpy, ΔH, of the low-temperature reaction of the dehydroxylated kaolinite with a potassium silicate solution using differential scanning calorimetry (DSC). |ΔH| increases almost linearly with DTG in the dehydroxylation region. In the metakaolinite region, ΔH and thus the amount of reactive material, becomes constant. |ΔH| is sharply decreasing when metakaolinite transforms into other phases in the ‘spinel’ region. No significant differences in the reactivity of the dehydroxylates is detected with DSC. According to FTIR, the use of partially dehydroxylated kaolinite is not influencing the molecular structure of the low-temperature synthesized aluminosilicates, but residual kaolinite is retrieved as an additive. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study of kinetics of glass transition of metallic glasses

In this study, the kinetics of glass transitions of Ti₅₀Cu₂₀Ni₃₀ and Fe₆₇Co₁₈B₁₄Si₁ metallic glasses are studied using thermal analysis technique, i.e., differential scanning calorimetry, by means of continuous heating of the sample at various heating rates. In the present study, based on the heating rate dependence of glass transition temperature (T _g), the activation energy (E) of the glass transition region is determined by two most frequently used approaches, i.e., Moynihan's method and Kissinger's equation. The fragility index, m, is also calculated using T _g, which is a measure of glass-forming ability of the given system. The result shows that the fragility index, m, of the given systems is <16. This indicates that the given systems are strong liquids with excellent glass-forming ability.     

Hydrogenation of complexes of diastereotopicN-benzoyldehydrodipeptides

The replacement of theN-acetyl group by anN-benzoyl group inN-acyldehydrodipeptides results, first, in an increase in the asymmetric induction in their hydrogenation in the case ofN-Bz-Phe-(S)-Glu.N-Bz-(S)-Phe-(S)-Glu is obtained with a diastereomeric excess (de) of 52 %. Second, no poisoning of the Pd-catalyst by sulfur inN-Bz-Phe-(S)-Met occurs, andN-Bz-(R)-Phe(S)-Met is obtained with ade of 26 %. The formation of complexes ofN-Bz-Phe-AA with Ca²⁺ and Mg²⁺ ions does not, as a rule, affect the diastereoselectivity of the hydrogenation. The structure of the dehydrodipeptides has been determined on the basis of¹H NMR spectra, potentiometric titration, and molecular mechanics calculations.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 884–887, May, 1994.This work was carried out with the financial support of the Russian Foundation for Basic Research (Project 93-03-4646).     

Graphical representation of the state of orientation of polymer systems

The orientation distribution function for noncrystalline structural units in polymer systems cannot be determined completely from any experimental source; only the second and/or fourth moments of the distribution function, i.e., the second and/or fourth orders of the generalized orientation factors F_lm^j, can be evaluated. It is there-fore necessary to estimate the distribution function from F_2m^j and F_4m^j. In this paper, a graphical representation of the state of orientation is first discussed in terms of plots of F₄₀^j against F₂₀^j for several types of distribution functions for uniaxial orientation. These are three types of extreme concentration of the distribution at particular polar angles θ₀ given by θ₀ = 0, 0<θ₀<π/2, and θ₀ = π/2; five types of rather realistic distributions having single maxima at θ_j = 0, θ₀, π/2 and double maxima at θ_j = 0, π/2, and a single minimum at θ_j = θ₀; and four types of more realistic distributions including Kratky's floating rod model in an affine matrix. Second, estimation of the distribution function for uniaxial orientation from F₄₀^j and F₂₀^j is discussed quantitatively in terms of the mean-square error by three approximation methods: (a) expansion of the distribution function in finite series of spherical harmonics through the fourth order, (b) approximation of the distribution function as a composite of two components, random orientation and a particular orientation distribution given by N_a (cos²θ_j)^a, N_a being a constant, and (c) approximation of the distribution function by N_a (cos²θ_j)^a alone. It is concluded that when the orientation distribution is sharp, estimation by the second method of approximation gives a smaller error than the first.     

The construction of graph models for calculations of the properties of substitution isomers of basis structures on the basis of additivity of energy contributions

A method for the construction of additive models for calculations of the properties of substitution isomers of basis structures is described for the example of a series of X-substituted methylsilanes CH_{3 − k} X _k -SiH_{3 − l} X _l (where X = CH₃, F, Cl, …, k, l = 0, 1, 2, 3). The method is based on similarity of subgraphs in graphs of several molecules and the arrangement of polygonal numbers (triangular, tetrahedral) of the Pascal triangle. Parameters taking into account multiple nonvalence interactions (-C-Si<, >C-Si<, …) through two atoms along the molecular chain of an X-substituted methylsilane (X = CH₃) were for the first time explicitly included in the calculation scheme. Taking these interactions into account allows us to completely differentiate all the structural isomers of certain molecules and obtain numerical parameter values for predicting properties P under consideration in various approximations. Numerical calculations of Δ_f H _{g,298 K}^o were performed for 16 alkylsilanes (as X-substituted methylsilanes), including 7 compounds not studied experimentally.     

Neutral diterpenoids of oleoresins of five species of conifers of Transcarpathia

The compositions of the neutral diterpenoids of the oleoresins of five species of conifers growing in the Transcarpathia have been studied. It has been found that the oleoresins ofAbies alba M.,Larix decidua M., andPicea excelsa L. contain more than 50% of neutral diterpenoids. The group and qualitative compositions of the oxygen-containing diterpenoids have been determined. In the oleoresins ofAbies alba,Picea excelsa, andPicea abies tertiary alcohols — cis-abienol and isocembrol — predominate, while inLarix decidua the main component is the hydroxy ester larixyl acetate. Primary alcohols related to the resin acids have been found in all the oleoresins investigated. Features of the distribution of diterpenoids according to the species of conifers have been revealed. The results obtained are necessary for the chemotaxonomy of conifers of the family Pinceae.Novosibirsk Institute of Organic Chemistry, Siberian Branch, Academy of Sciences of the USSR. Translated from Khimiya Prirodynkh Soedinenii, No. 6, pp. 812–816, November–December, 1988.     

Types of rotary crystal state of solid solutions of paraffins

Thermal deformations and polymorphous transformations of solid solutions of paraffins in C₁₇–C₁₉, C₁₉–C₂₁, C₂₁–C₂₃, C₂₂–C₂₄, and C₂₃–C₂₄ systems are investigated by thermal X-ray diffractometry using a temperature step of several tenths of a degree. It is examined how the length of a molecular chain of a homolog (n) and the difference in length (Δn) between the chains as well as the molecular composition of a solid solution affect these transitions, and the data are compared with those for the individual homologs of paraffins. St. Petersburg University. Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 3, pp. 380–394, May–June, 1998. This work was supported by RFFR grant No. 97-05-65534 and ISSEP grants No. 156p and a97-2633.     

Kinetics of the Formation of Goethite in the Presence of Sulfates and Chlorides of Monovalent Cations

The synthesis of goethite by oxidation of Fe²⁺in presence of metallic iron was undertaken in an aqueous medium containing indifferent salts such as Na₂SO₄, (NH₄)₂SO₄, NaCl, and NH₄Cl. Temperature and bubbling air rate were maintained, respectively, at 70°C and 1 L/min. The influence of anions and cations on the kinetics of each step of the process has been followed distinctly, the iron dissolution rate has been determined by the variation of the medium acidity, and the precipitation of goethite has been determined by gravimetric measurements. With respect to Cl⁻, the SO₄²⁻anion decreases the rate of the two reactions. NH₄⁺acts as an inhibitor when it is present at low concentrations and as an accelerator for higher concentrations; the limit corresponding to the change of NH₄⁺behavior depends on the nature of the counter ion. The reaction product is composed of pure goethite in the presence of sulfate salts, whereas a mixture of goethite and lepidocrocite, respectively, 60–70 and 40–30%, was observed in the presence of chloride salts.     

Influence of polarity of medium on fluorescence characteristics of alkylaminobenzophenones

A study has been made of the instantaneous fluorescence spectra of 4,4′-bis-dimethylaminobenzophenone (Michler’s ketone, MK), 4,4′-bis-diethylaminobenzophenone (DEAB), and 4-dimethylaminobenzophenone (DMAB) in various solvents, at room temperature. It has been shown that an increase of the solvent polarity leads to an increase of fluorescence intensity and a shift of the fluorescence band maximum toward longer wavelengths. The presence of traces of water in the solutions increases the fluorescence intensity and gives a red shift of the maximum. From the relationships found between the position of the fluorescence maximum and the polarity of the solvent, estimates have been made of the dipole moment of the luminescent state, which is 1.6·10⁻²⁷ C·m for the MK, 2.1·10⁻²⁷ C·m for the DEAB, and 0.8·10⁻²⁷ C·m for the DMAB. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of the Ukraine, 31 Nauka Prospect, 252039 Kiev, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 1, pp. 36–40, January–February, 1997.     

Thermodynamic characterization of the melting of a series of polyesteramides

The changes in enthalpy, entropy and volume upon melting have been determined by dilatometric and differential scanning calorimetry measurements for four polyesteramides of the type:

$\text{-[-}\text{COφCONH(CH}{}_2\text{)}{}_{\mathrm{n}}\text{}\text{NHCOφCOO(CH}{}_2\text{)}{}_{\mathrm{m}}\text{}\text{O}\text{-]-}{}_{\mathrm{x}}$

with the following values for n and m; 6-6, 12-2, 12-6 and 12-12. The changes in each state function vary quite regularly with the number of CH₂ groups/repeating unit. A comparison is made between experimental data on the entropy of fusion and theoretical predictions. There is emphasis on the influence on the thermodynamics of melting of the rigidity of the -OCO-φ-CONH- residues and, in particular, of the persistence in the molten state of many interchain hydrogen bonds.     

Structure of the blue forms of bisphthalocyanines of rare-earth elements

Using electron spectroscopy, X-ray photoelectron spectroscopy, and ESR spectroscopy, the blue forms of bisphthalocyanines of rare-earth elements were found to have structures of sandwich-type complexes with isoelectronic phthalocyanine ligands linked with tetravalent metal ions, [Pc^2–Ln⁴⁺Pc^2–]⁰. A comparative spectral and electrochemical study of the blue and green forms oftert-butyl-substituted bisphthalocyanines was carried out for almost the whole series of rare-earth metals. Lutetium octa(perfluoro-tert-butyl)- and perchlorobisphthalocyanines were synthesized for the first time.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 425–430, March, 1995.This study was financially supported by the Russian Foundation for Basic Research (grant No. 94-03-08903).     

Heat of formation of lanthanum-lead alloys

In the La? Pb system the heats of formation were measured, using a differential direct isoperibol calorimeter, and checking composition and state of the samples by chemical, metallographic and X-ray analyses. For the various compounds the _H (for the reaction among solid phases at 300 K) correspond to the following values (Kcal/g · at.): La₅Pb₃ = ?17.2₅ ± 0.5, La₄Pb₃ = ?16.7 ± 0.5, La₅Pb₄ = ?16.5 ± 0.5, La₃Pb₄ = ?15.3 ± 0.5, LaPb₂ = ?14.4 ± 0.5, LaPb₃ = ?13.7 ± 0.5. The results obtained are briefly discussed and compared with those calculated using the method suggested by MIEDEMA .     

Synthesis of CeO2 by thermal decomposition of oxalate and kinetics of thermal decomposition of precursor

CeO₂ was synthesized by calcining Ce₂(C₂O₄)₃·8H₂O above 673 K in air. The precursor and its calcined products were characterized using thermogravimetry and differential scanning calorimetry, Fourier transform infrared spectra, X-ray powder diffraction, scanning electron microscopy, and UV–Vis absorption spectroscopy. The result showed that cubic CeO₂ was obtained when the precursor was calcined above 673 K in air for 2 h. The UV–Vis absorption spectroscopy studies showed that superfine CeO₂ behaved as an excellent UV-shielding material. The thermal decomposition of the precursor in air experienced two steps, which are: first, the dehydration of eight crystal water molecules, then the decomposition of Ce₂(C₂O₄)₃ into cubic CeO₂. The values of the activation energies associated with the thermal decomposition of Ce₂(C₂O₄)₃·8H₂O were determined based on the Starink equation.     

Construction of different types of ion-selective electrodes and validation of direct potentiometric determination of phenytoin sodium

The construction and performance characteristics of phenytoin sodium selective electrodes are detailed. Two types of electrodes: plastic membrane I and coated wire II, were constructed based on the incorporation of phenytoin sodium with tungstosilicic acid. The influence of membrane composition, kind of plasticizer, pH of the test solution, soaking time and the electrodes’ foreign ions were investigated. The electrodes showed a Nernstian response with a mean calibration graph slope of 30.9±0.1 and 28.9±0.1 mV decade⁻¹ at 25°C for electrode I and II respectively, over a phenytoin sodium concentration range of 5×10⁻³−5×10⁻⁶ M and 1×10⁻³−1×10⁻⁶ M with a detection limit 1.3×10⁻⁶ M and 2.5×10⁻⁷ M for electrode I and II, respectively. The electrodes gave average selective precision and were usable within the pH range 6–10. Interference studies from common cations, alkaloids, sugars, amino acids and drug excipients are reported. The results obtained by the proposed electrodes were also applied successfully for the determination of the drug in pharmaceutical preparations and biological fluids.     

Description of structures in terms of polyhedrapacking

The structures of alloys can be described in terms of polyhedrapacking. We studiedall structure types found in the binary systemsT ⁵ orT ⁶ withB ³ orB ⁴ (T ⁵: V, Nb, Ta;T ⁶: Cr, Mo, W;B ³: Al, Ga, In, Tl;B ⁴: Si, Ge, Sn, Pb) elements. Most of the structures examined until now could be built up with one or two polyhedra, only in a few cases more than two polyhedra are required. It is found that there are two types: a three-dimensional distribution of discrete polyhedra sharing corners, edges or faces and a layer-like distribution. This model proved valid for all structure types studied. Classification of the structures according to their polyhedrapacking criteria is introduced (Table 1). Table 2 includes the coordination numbers of all atoms in the studied structures.     

The heat of fusion of polytetrafluoroethylene

The heat of fusion of virgin and melt-processed polytetrafluoroethylene (PTFE) was determined using the Clapeyron equation. Experimental data were obtained from PVT experiments and high-temperature x-ray diffraction measurements. For virgin, as-polymerized PTFE, the melting temperature is given by where, for T_m in degrees Celsius, A = 346.3±1.2, B = 0.095±0.003, and P is the pressure in kilograms per square centimeter. At the end of the atmospheric-pressure melting interval, the amorphous and crystalline specific volumes V₁ and V_c are 0.6517 and 0.492 cm³/g, respectively. Thus the heat of fusion is 24.4 cal/g, or nearly twice the value reported previously. The increases in enthalpy and volume at the melting point both indicate a degree of crystallinity of about 75–80% although infrared, x-ray, and NMR data give much higher levels. Data from calorimetry, NMR, and dynamic mechanical measurements indicate that in virgin PTFE some of the crystals continue to experience torsional oscillations at temperatures below the room-temperature transitions. This indicates that there are at least two kinds of crystalline regions. For previously melted PTFE, T_m is determined by A = 328.5±0.7 and B = 0.095±0.002, the volumes are V_am = 0.6349 and V_cr = 0.4855 cm³/g, and the heat of fusion is 22.2 cal/g. The entropy of fusion for PTFE is much closer to that of polyethylene than was previously believed.     

Kinetics of Formation of Peroxyacetic Acid

The kinetics of the reaction of acetic acid with hydrogen peroxide, leading to peroxyacetic acid, were studied at various molar reactant ratios (AcOH-H₂O₂ from 6 : 1 to 1 : 6) at 20, 40, and 60°C and sulfuric acid (catalyst) concentrations of 0 to 9 wt %. The reaction is reversible, and the equilibrium constant decreases as the temperature rises: K = 2.10 (20°C), 1.46 (40°C), 1.07 (60°C); Δ_r H ⁰ = − 13.7±0.1 kJ mol⁻¹, Δ_r S = −40.5±0.4 J mol⁻¹ K⁻¹. The maximal equilibrium concentration of peroxyacetic acid (2.3 M) is attained at 20°C and a molar AcOH-to-H₂O₂ ratio of 2.5 : 1. The rate constants of both forward and reverse reactions increase with increase in sulfuric acid concentration from 0 to 5 wt %. Further raising the catalyst concentration does not affect the reaction rate. The reaction mechanism is discussed.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 7, 2005, pp. 1187–1193.Original Russian Text Copyright © 2005 by Dul’neva, Moskvin.     

Effect of the nature of the support on the activity of palladium catalysts for oxidation of carbon monoxide

We have studied the catalytic activity of TiN_0.65, TiO₂, Al₂O₃, and palladium catalysts supported on them in the oxidation of carbon monoxide. The order in which the activities of the supported catalysts vary, Pd/Al₂O₃>Pd/TiO₂>Pd/TiN_0.65, is the reverse of the activity series for the supports. This is explained by the effect of transfer of electron density from the palladium to the substrate. Taras Shevchenko Kiev University, 64 Vladimirskaya ul., Kiev 252033, Ukraine, G. V. Kurdyumov Institute of the Physics of Metals, National Academy of Sciences of Ukraine, 36 Akademika Vernadskogo bul’var, Kiev-142 252642, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 34, No. 2, pp. 118–121, March–April, 1998.     

Synthesis of phenolic components of Grains of Paradise

Two vanilloids, (5E)-8-(4-hydroxy-3-methoxyphenyl)oct-5-en-4-one (1) and 4-[3-hydroxydecyl]-2-methoxyphenol (2), isolated from the dried seeds of Grains of Paradise (Aframomum melegueta), were synthesized; the latter compound was made as the S-enantiomer and the material derived from the seeds was found to be a 1:1.7 mixture of the R and S isomers. The synthetic route used should allow the preparation of analogs having extended alkyl chains and consequently different lipophilicity, and 3, a homolog of 2, was also prepared.