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.     

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.     

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).     

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.     

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.     

Association constants and heats of formation of heteroassociates of anions of sulphophthaleine dyes

The tendency of anions of sulphophthaleine dyes to heteroassociation was studied in aqueous solutions of phenol red, bromophenol blue, bromocresol green, bromocresol purple, and bromothymol blue. It was spectrophotometrically determined that single-(Han⁻) and double-charged anions (An²⁻) of sul-phophthaleines can form stable heteroassociates of composition Ct⁺ · HAn⁻ and (Ct⁺)₂ · An²⁻ with cations (Ct⁺) of polymethine dyes, pinacyanol, and quinaldine red. The values of enthalpy formation of ions of dyes and heteroassociates were calculated using semi-empirical methods, then correlated with experimentally determined values of equilibrium association constants.     

Kinetic Analysis of the Decomposition of Chelates of Di-alkyldithiocarbamate of Cd(II)

The thermal decomposition kinetics of the solid complexes Cd(S₂ CNR₂ )₂ , where R =C₂ H₅ , n -C₃ H₇ , n -C₄ H₉ or iso -C₄ H₉ , was studied by using isothermal and non-isothermal thermogravimetry. The superimposed TG/DTG/DSC curves revealed that thermal decomposition reactions occur in the liquid phase. The kinetic model that best fitted the experimental isothermal TG data was the one-dimensional phase-boundary reaction-controlled process R₁ . The thermal analysis data suggested the thermal stability sequence Cd(S₂ CNBuⁿ ₂ )₂ >Cd(S₂ CNPrⁿ ₂ )₂ >Cd(S₂ CNBuⁱ ₂ )₂ >Cd(S₂ CNEt₂ )₂ , which accords with the sequence of stability of the apparent activation energies. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Relative stability of isomers of polynuclear complexes of molybdenum oxides

Molybdenum(VI) oxide MoO₃ has been studied and the composition of polynuclear molybdenum oxides in the gas phase Mo _x O_{3x ? y} (x = 1–6, y = 0–2) has been determined by laser desorption/ionization time-of-flight mass spectrometry. Quantum-chemical calculations of bond energies, interatomic distances, charge distributions, and molybdenum-molybdenum bond orders for the isomers of neutral polynuclear molecular compounds Mo _x O3 _{x ? y} have been performed with the use of the PBE functional with a relativistically corrected potential implemented as the PRIRODA program package. On the basis of the bond energies, the relative stability of the isomers has been estimated. For the Mo _x O _y isomers (x ≥ 3), cyclic structures have been predicted to be more favorable. For the predicted most stable isomers of each Mo _x O _y composition, the bond energies of their positive and negative ions have been calculated. The positive ionization of Mo _x O _y leads to a considerable decrease in the bond energy of the isomer and the negative ionization, to its increase by about 0.1 au.     

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 .     

Studies of thermal decomposition of hydrazidocarbonates of some first row transition elements

The thermal properties of some hydrazidocarbonates of copper, Cu(N₂H₃COO)₂.0.5H₂O, nickel, Ni(N₂H₃COO)₂.2N₂H₄, and iron, Fe(N₂H₃COO)₂ and N₂H5[Fe(N₂H₃COO)₃].H₂O, were studied in an inert argon atmosphere. The TG, DTG and DSC curves for these compounds were taken. In the case of N₂H₅[Fe(N₂H₃COO)₃].H₂O, intermediates were observed and isolated during the decomposition. The end-products were metal powders oxidized to a greater or lesser degree.

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Zusammenfassung In einer inerten Argonatmosphäre wurden die thermischen Eigenschaften einiger Hydrazidocarbonate von Kupfer, Cu(N₂H₃COO)₂.0.5H₂O, Nickel Ni(N₂H₃COO)₂.2N₂H₄ und Eisen Fe(N₂H₃COO)₂ bzw. N₂H₅[Fe(N₂H₃COO)₃].H₂O ermittelt, d.h. TG-, DTG- und DSC-Kurven wurden angefertigt. Im Falle von N₂H₅[Fe(N₂H₃COO)₃].H₂O konnten während der Zersetzung auch Zwischenprodukte beobachtet und isoliert werden. Die Endprodukte waren mehr oder weniger oxydierte Metallpulver.

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Paper presented at the 6th World Conference for Thermal Analysis, Capri, 1989.

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This work was supported by the Research Council of Slovenia.     

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.     

Heats of formation of multi-substituted positive ions of organic species

The difference (ΔΔ_fH°) between heats of formation of many multi-substituted odd- and even-electron positive ions can be described by a linear equation: ΔΔ_fH° = A + Bm, where m is the number of substituents or ligands, relative to the unsubstituted reference ion, and m = 1, 2 or 3; A and B are the intercept and slope, respectively. The correlation quality for 59 types of odd- and 26 types of even-electron ions, which involve C, Si, Sn, H, F, Cl, Br, I, O, S, N and P atoms, was analyzed. Unknown heats of formation of related ions and the proton affinities of some organic molecules were predicted using the linear equation.     

Transformations of isobutylene in the presence of various types of zeolites

Conclusions In contrast to zeolites with ultrahigh silica content, type A, X, Y, and M zeolites in the Na form and also those modified by decationization, cation exchange, and addition of-Al₂O₃, Al₂O₃-SiO₂, Pt, and Rh show a low activity in the aromatization reaction of C₃-C₄ olefins at 450–550°C at times of contact of 2–14.4 sec. The zeolites studied become rapidly deactivated as the result of intense coke formation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1300–1304, June, 1981.     

Synthesis of some derivatives of the C-terminal tetrapeptide of the hormone gastrin

Summary The synthesis has been effected of the C-terminal tetrapeptide of gastrin Trp · Met · Asp · PheNH₂ · HCl (I) and its derivatives Boc-Trp · Met · Asp · PheNH₂ (II), C₂H₅OCO-Trp · Met · Asp · PheNH₂ (III), C₂H₅OCOCHNH₂CO-Trp · Met · Asp · PheNH₂ (IV), and Boc--Ala · Trp · Met · Asp · PheNH₂ (V).Institute of Organic Synthesis, Academy of Sciences of the Latvian SSR. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 94–97, January, 1971.     

The high temperature pyrolysis of 1,3-butadiene: heat of formation and rate of dissociation of vinyl radical

The high temperature pyrolysi of 1,3-butadiene has been investigated in the shock tube with two time-resolved diagnostic techniques: laser schlieren measurements of density gradient with 1, 2, 4, and 5% C₄H₆ in Ar or Kr, 0.26 < P₂ < 0.66 atm, over 1550–2200 K, and time-of-flight mass spectra for 3% C₄H₆–Ne, P₅ ～ 0.4 atm, 1400–2000 K. When combined with a recent single-pulse shock tube product analysis covering 1050–2050 K, these measurements permit a complete modeling of major species in C₄H₆ pyrolysis. Extrapolated density gradients and product analyses show initiation is dominated by C₄H₆ → 2C₂H₃., significant falloff and Arrhenius curvature being seen in the derived rates. A restricted rotor, Gorin model RRKM fit to these rates with reasonable parameters generates The derived barrier, ΔH${}_{\text{0}}^{\text{º}}$ = 99 ± 4 kcal/mol, translates to ΔH${}_{\text{f}}^{\text{º}}$ _,298 = 63.4 ± 2 kcal/mol for the heat of formation of vinyl radical. A mechanism for the formation of all products detected in the above experiments is given, together with a successful but semiquantitative kinetic model for major products. The measurements require the rate of vinyl radical dissociation, C₂H₃ + M → C₂H₂ + H + M, to be extremely low, k < 10⁹ cm³/mol s for 1600 K, so that the dominant chain carrier in C₄H₆ pyrolysis is vinyl radical.     

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.     

Synthesis of anthrathiopyrantriones by heterocyclization of alkynoyl derivatives of chloroanthraquinones

A procedure was developed for the synthesis of 2-substituted, including 2-alkenyl-substituted, 4H-anthra[1,2-b]thiopyran-4,7,12-triones and 4H-anthra[2,3-b]thiopyran-4,6,11-triones by cyclocondensation of vic-alkynoylchloroanthraquinones with Na₂S.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2205–2209, October, 2004.     

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.