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.     

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.     

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.     

Assignment of the mechanism of predissociation of the ClO2 molecule by analysis of single-rotational-level lifetimes

Deconvolutions of measured absorption line profiles in the 1ⁿ₀ (n = 0 to 5) and the 3²₀ bands of the òA₂X?²B₁ electronic transition of ClO₂ reveal subnanosecond lifetimes for all rotational levels of the ²A₂ state. Observed ratios of radiationless rates from spin-doublet components identify direct spin-orbit coupling of the ²A₂ state with ²A₁ and/or ²B₁ vibronic states as a predominant predissociation mechanism. Variations of rates with ν′₁ locate an intersection of a second potential surface with that of the ²A₂ state.     

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.     

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.     

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.     

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.     

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.     

Borderline of hydrogen bonding of silanols

Two new silanols bearing very bulky silyl groups, (i-Pr₃ Si)₃SiOH and (t − BuMe₂Si)₃SiOH were prepared by peracidoxidation of their respective silanes. The X − ray crystallographic analysis revealed that (t − BuMe₂Si)₃ SiOH forms a dimeric structure with hydrogen bonding, while (i − Pr₃ Si)₃ SiOH exists as a monomer in the crystal. The effects of the size of the substituents as well as the reactivity of these silanols are discussed.     

Enthalpies of formation of chloride fluorides and of methoxide fluorides of tungsten(VI)

Enthalpies of formation of the tungsten (VI) compounds WF₅Cl, WF₄Cl₂, WF₅(OMe), cis-WF₄(OMe)₂ and cis-WF₂(OMe)₄ are reported. Re-distribution and decomposition reactions in the chloride-fluoride and in the methoxide-fluoride series are discussed in the light of the thermochemical results.     

Power law of nucleation rate of folded-chain single crystals of polyethylene

The number-average molecular weight (M _n) dependence of the primary nucleation rate (I) of polyethylene (PE) folded-chain single crystals was studied in the ordered phase. We observed that the M _n dependence of I is mainly controlled by the diffusion process of polymer chains within the interface between a nucleus and the melt and/or within the nucleus. The results show that I decreases with increasing M _n and follows a power law I∝M _n ^−2.3 for the ordered phase. It is named the power law of the nucleation rate. In a previous article we showed that for the disordered phase I∝M _n ⁻¹. In this article, we concluded that I decreases with increasing M _n and follows a universal power law, I∝M _n ^−H for both ordered and disordered phases. The power H depends on the degree of order of the crystalline phase, which is related to the morphology. Received: 13 September 2000 Accepted: 15 November 2000     

Enthalpies of formation of radicals and the mass spectra of the products of tetrafluoroethylene polymerization in acetone

The mass spectra of the dissociative electron-impact ionization products of telomers formed upon the radiation-chemical telomerization of tetrafluoroethylene in acetone were measured over the range of m/z from 1 to 204. The most intense bands at m/z = 43, 51, and 57 were attributed to the CH₃CO⁺, CF₂H⁺ and CH₃COCH₂⁺ cations—the main dissociation products of the H(C₂F₄) _n CH₂COCH₃ telomers. The telomer composition was consistent with a radical telomerization mechanism, in which chain growth and chain transfer are due to the formation of the CH₃COCH₂^· radical. Based on published data supplemented with quantum-chemical calculations, the enthalpies of formation of the radicals R(CF₂) _n (n = 2–8; R = H, CH₃, CH₃CO, and CH₃COCH₂) were tabulated. The formation of telomers with the same terminal groups is consistent with thermodynamic data and a polymerization mechanism in which the chain growth reaction is diffusion-limited and the chain transfer reaction is activated hydrogen-atom transfer.     

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).     

Kinetics of the thermal decomposition of dinitramide

The kinetic regularities of the heat release during the thermal decomposition of liquid NH₄N(NO₂)₂ at 102.4–138.9 °C were studied. Kinetic data for decomposition of different forms of dinitramide and the influence of water on the rate of decomposition of NH₄N(NO₂)₂ show that the contributions of the decomposition of N(NO₂)₂ ⁻ and HN(NO₂)₂ to the initial decomposition rate of the reaction at temperatures about 100 °C are approximately equal. The decomposition has an autocatalytic character. The analysis of the effect of additives of HNO₃ solutions and the dependence of the autocatalytic reaction rate constant on the gas volume in the system shows that the self-acceleration is due to an increase in the acidity of the NH₄N(NO₂)₂ melt owing to the accumulation of HNO₃ and the corresponding increase in the contribution of the HN(NO₂)₂ decomposition to the overall rate. The self-acceleration ceases due to the accumulation of NO₃ ⁻ ions decreasing the equilibrium concentration of HN(NO₂)₂ in the melt. For Part 2, see Ref. 1. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 395–401 March 1998.     

Effect of temperature of liquid sulphur on kinetics of transformation of chains in its amorphous modification

The rate of transformation of the chains in amorphous sulphur was examined by calorimetry at 298 K. The amorphous samples were remelted at the temperatureT _f in the range from 458 to 573 K. Increase ofT _f decreased the transformation rate. The results satisfy the equationX=1-exp[-(kt)^z] (X=transformation degree,t=time, andk andz=constants). A one-stage transformation was observed for samples remelted atT _f473 K. ForT _f 523 K, transformation in two stages was observed.The effects ofT _f on the kinetics of nucleation and the growth of the nuclei are discussed.     

Investigation of the viscosity of solutions of graft copolymers

Living polystyrene was grafted on fractions of poly(methyl methacrylate) by an anionic grafting reaction. Unreacted polystyrene was separated by fractional precipitation. The composition of copolymer, i.e., the molecular weight of main chains and side chains, was determined. The influence of molecular weight and structure of graft copolymers on the intrinsic viscosity of solutions was examined. This may be expressed in the form [η] = KM^agⁿ. The dependence between a and n in this equation was established.     

Kinetics of vapor nitration of cellulose

The kinetics of vapor nitration of cellulose with nitric anhydride at various pressures was studied under conditions of natural convection in the absence of air, using the nonisothermal kinetic method. The process rate was found to be proportional to the N₂O₅ pressure. The nitration is described by a law of the dη/dt =k ₁/(1+βν) type, wherek ₁ = 10^3.82±0.5 exp[-(36000±(RT)]p _{N 2}O₅ s^?1. β = 10^?7.33±1.4exp[(41300±8000)/(RT)] s^?1, s^?1, within the extents of conversion from 0.04 to 0.4. At high levels of conversion, the nitration occurs with autoacceleration caused by the accumulation of the HNO₃ formed. The diffusion mechanism of vapor nitration of cellulose was suggested and discussed. The values of the effective diffusion constant for N₂O₅ in cellulose and the corresponding activation energy (38.4±2.8 kJ mol^?1) have been estimated.     

Study of formation of nano-quasicrystals and crystallization kinetics of Zr-Al-Ni-Cu metallic glass

The formation of nano-quasicrystals on isothermal annealing of melt-spun ribbons of Zr_69.5Al_7.5Ni₁₁Cu₁₂ metallic glass has been investigated using transmission electron microscopy (TEM). The crystallization study of this metallic glass has been carried out using differential scanning calorimetry (DSC) in non-isothermal (linear heating) mode. It exhibits two-stage crystallization where the first stage corresponds to the precipitation of icosohedral nano-quasicrystalline phase. This has been confirmed with the help of TEM investigations. The crystallization parameters like the activation energy (E _c) and frequency factor (k ₀) have been derived using the Kissinger peak shift analysis. The activation energies for the first and second crystallization peak are found to be 278 and 295 kJ mol^–1, respectively. The frequency factors obtained for the two peaks are respectively 7.16·10¹⁹ and 1.42·10²⁰ s^–1. E _c, k ₀ and the Avrami exponent (n) have also been derived by fitting the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation for the transformed volume fraction (x) to the crystallization data. JMAK results of E _c for the first and second crystallization peak turn out to be 270 and 290 kJ mol^–1 respectively. However, k ₀ and n are found to be heating rate dependent as reported in similar studies. The values of n for the first crystallization stage ranges between 1.66 and 2.57 indicating diffusion-controlled transformation in agreement with earlier reports.