Effect of IR Radiation on the Properties of Polyacrylonitrile and Membranes on Its Basis

The effect of processing of polyacrylonitrile membranes by IR radiation at a temperature of 100–150°С is studied. The influence of the processing temperature on the film structure is ascertained. In a film heated at 100°С, a small amount of the double C=N bonds is found. Its further heating to 120°С is accompanied by a change in the chain conformation and an increase in the content of C=N bonds. It is shown that, upon IR processing at 120°С, polyacrylonitrile ceases to dissolve in N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethyl sulfoxide. Heating at 150°С gives rise to the appearance of conjugated С=N–C=N bonds. The analysis of AFM micrographs demonstrates that the processing of the membranes by IR radiation makes their surface rougher, while the size of pores changes slightly. The permeability of the membranes in various media is measured.     

Colorimetric analysis of thermal degradation of plasticized poly(vinyl chloride): Potentials and limitations

The kinetics of formation and consumption of polyenes is studied by measuring the change in color coordinates and color difference during the thermal aging of plasticized poly(vinyl chloride) at a temperature of 60–130°С under vented conditions and in a closed volume. It is shown that the initial rate of accumulation and the quasi-stationary concentration of polyenes at 100–130°С grow with temperature. The energy of activation of dehydrochlorination is 70 ± 3 kJ/mol. At a lower temperature (60–80°С), the intensity of color of the samples that are preliminarily aged at increased temperatures decreases. The reduction in the rate of this process with temperature in the range of 60–80°С and the presence of the quasi-stationary level at 100–130°С are related to competition of the processes of formation and oxidation of polyenes.     

Influence of curing conditions and dibutyl phthalate concentration on the properties of cured epoxy resin

The influence of the curing conditions and dibutyl phthalate additions on the physicomechanical properties of cured polyepoxides based on ED-20 resin and 4,4'-diaminodiphenylmethane curing agent was examined. An increase in the curing temperature over 150°С does not noticeably influence the physicomechanical properties of the cured resin, and keeping of the reaction mixture at 180°С for 12 h leads to a considerable decrease in the glass transition temperature of the polymer. Addition of dibutyl phthalate in concentrations of up to 10 wt % decreases the glass transition teperature of the polymer by 44°C, but with increasing concentration of dibutyl phthalate the elastic modulus increases and the breaking strain slightly decreases. The dependence of the ultimate strength on the dibutyl phthalate concentration passes through a maximum at 3 wt % dibutyl phthalate.     

Thermally stable phthalonitrile matrixes containing siloxane fragments

New low-melting phthalonitrile monomers suitable for the production of high-temperature matrixes for polymer composite materials are synthesized. After the introduction of siloxane bridges into a monomer, the glass-transition temperature decreases to–1–27°С, depending on the type of substituent at the silicon atom. These compounds are found to be sufficiently hydrolytically stable, despite the presence of sensitive siloxane bonds. The cured resin retain properties featured to the class of phthalonitriles, such as a high onset tеmperature of degradation (>530°С in argon), a high heat deflection temperature (>420°С), and char yield. The considered compounds make it possible to widen the temperature window for processing of phthalonitrile resins without any change in the properties of the final material.     

Kinetics of Curing of Epoxy Oligomer by Diaminodiphenyl Sulfone: Rheology and Calorimetry

Diaminodiphenyl sulfone is used as a curing agent to obtain an epoxy-resin-based binder with improved thermal stability. The kinetics of curing of this composition is studied by rheokinetic and calorimetric methods. It is shown that complete conversion is attained at a temperature of 200°С or higher. The rate of viscosity increase in the course of time in curing under flow conditions does not depend on the shear rate; the viscosity changes monotonically. The curing reaction occurs in the homogeneous mode without separation of a crosslinked polymer; it is described by a second-order equation with self-deceleration at low temperatures. The rheokinetic characteristics and temperature dependences of kinetic parameters of the process are determined.     

Influence of the structure of oxirane-containing compounds on curing of poly-<Emphasis Type="Italic">N</Emphasis>-methyl-5-vinyltetrazole

Comparative analysis of the curing performance of epoxy-containing cross-linking agents of different structure in vulcanization of a promising binder for energetic systems, poly-N-methyl-5-vinyltetrazole prepared by the modification procedure and containing residual N–H-unsubstituted tetrazole fragments, was made. Cross-linking of polymer chains of the binder is a result of alkylation of the residual N–H-unsubstituted tetrazole rings in poly-N-methyl-5-vinyltetrazole macromolecules with oxirane rings of the second reactant. Curing of poly-N-methyl-5-vinyltetrazole in the presence of macromolecular curing agents, carbon-chain polymers containing oxirane rings in pendant chains, at temperatures lower than 100°С occurs in a considerably narrower time interval compared to curing with low-molecular-mass epoxy resin.     

Novel 1D coordination polymer {Tm(Piv)3}n: Synthesis,structure, magnetic properties and thermal behavior

The new 1D coordination polymer {Tm(Piv)₃}_n (1), where Piv=OOCBu^t?, was synthesized in high yield (>95%) by the reaction of thulium acetate with pivalic acid in air at 100 °С. According to the X-ray diffraction data, the metal atoms in compound 1 are in an octahedral ligand environment unusual for lanthanides. The magnetic and luminescence properties of polymer 1, it’s the solid-phase thermal decomposition in air and under argon, and the thermal behavior in the temperature range of ?50…+50 °С were investigated. The vaporization process of complex 1 was studied by the Knudsen effusion method combined with mass-spectrometric analysis of the gas-phase composition in the temperature range of 570–680 K.     

Specifics of reactions of cerium sulfate and europium sulfate with hydrogen

Reactions of cerium sulfate and europium sulfate with hydrogen have been studied. Diagrams showing the evolution of phase composition of the polycrystalline products of reaction between europium sulfate and hydrogen are constructed. The reaction of Ce₂(SO₄)₃ with hydrogen at 600°С consecutively yields Ce₂O₂S and Ce₂O₃ phases. At 800°С the batch is >95 mol % Ce2O3. At 480-500°С, a single-phase sample of EuSO4 is prepared; at 600-1000°С, Eu₂O₂S is prepared; and at 1050°С, the batch is >95 mol % Eu₂O₂S and up to 5 mol % Eu₂O₃. Atomic-force microscopy shows that europium sulfate grains, which represent agglomerates of particles 10-20 μm in size, are degraded upon reaction with hydrogen into individual ovalshaped particles sized 40-60 × 130-200 nm.     

Synthesis and characterization of α-, β-, and γ-Ga2o3 prepared from aqueous solutions by controlled precipitation

α, β and γ-Ga₂O₃ have been successfully obtained in an easily scalable synthesis using aqueous solution of gallium nitrate and sodium carbonate as starting materials without any surfactant and additive. α and β-Ga₂O₃ were obtained by calcination at 350 and 700 °С, respectively, of α-GaOOH, prepared by controlled precipitation at constant pH 6 and T = 55 °С, with 24 h of aging. Aging was necessary to fully convert the initially preciptated gel into a well-crystalline and phase-pure material. γ-Ga₂O₃ was obtained after calcination at 500 °С of gallia gel, synthesized at constant pH 4 and T = 25 °С, without aging. These three polymorphs have a for gallia relatively high surface area: 55 m²/g (α-Ga₂O₃), 23 m²/g (β-Ga₂O₃) and 116 m²/g (γ-Ga₂O₃). The combination of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), nitrogen physisorption and thermogravimetry (TG) was employed to characterize the samples and their formation.     

Study of simultaneous solubility of salts in the ammonium nitrate–ammonium chloride–water system

Ternary eutectic of the NH₄NO₃–NH₄Cl–H₂O system at–23.6°С has been found using a set of theoretical and experimental methods. According to the data of visual-polythermal and differential thermal analyses data, crystallization surface of the system has been plotted at–23.6 to 100°С.     

Phase Equilibria in the K,Cа∥SO<Subscript>4</Subscript>,CO<Subscript>3</Subscript>,HCO<Subscript>3</Subscript>–H<Subscript>2</Subscript>O System at 25°С

Phase equilibria in the system K,Cа∥SO₄,CO₃,HCO₃–H₂O have been studied at 25°С. This system at 25°С involves 7 invariant points, 21 monovariant curves, and 22 divariant fields. The data gained served to plot the first phase diagram (phase complex) of the studied system at 25°С.     

On the fracture mechanism of partially healed interfaces of glassy polymers: an ATR-FTIR investigation

Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) has been employed to analyse the surfaces of poly(2,6-dimethyl-1,4-phenylene-oxide) (PPO) samples prior to contact and after fracture of the PPO–PPO auto-adhesive joints which formed during the contact of two identical PPO samples at temperatures of 146 or 156 °С that are lower than the PPO bulk glass transition temperature by 70 or 60 °С, respectively. The differences in the intensity of ATR-FTIR spectra for the original and fractured PPO surfaces found have been discussed in the frameworks of the molecular mechanisms of fracture.     

Study of Viscosity-temperature Properties of Oil and Gas-condensate Mixtures in Critical Temperature Ranges of Phase Transitions

Transport of oil and gas-condensate mixtures of various compositions is found to be accompanied by a slight increase in viscosity in the coldest period when ground temperatures at depth of a condensate pipeline reach 0 – minus 4°С. Fall in temperature of oil fluids under study to minus 10 – minus 30°С is accompanied by a sharp increase in all structural and rheological parameters of the mixture. Even a slight amount of oil added to a gas-condensate mixture causes a significant decrease in viscosity in the negative temperature range. As a result, cloud and pour point of a mixture falls, its amount decreases, the structure of paraffin deposits changes.     

Polyacrylonitrile-based FeCo/C nanocomposites: Preparation and magnetic properties

Metal–carbon nanocomposites that represent FeCo alloy nanoparticles uniformly distributed over the carbon matrix, were prepared by the IR pyrolysis of precursors comprising polyacrylonitrile (PAN), iron acetylacetonate, and cobalt acetate (the metal ratio in the precursors was Fe: Co = 1: 1, 3: 1). The composition of FeCo alloy nanoparticles satisfies the tailored ratio Fe: Co. The FeCo phase is formed at synthesis temperatures in the range 500–600°С; at T ≤ 500°С only FCC-Co-base solid solutions are observed. The nanocomposites prepared at T ≥ 600°С simultaneously contain FeCo intermetallic nanoparticles and an insignificant amount of a FCC-Co phase or a cobalt-base solid solution phase. The saturation magnetization of FeCo/C metal–carbon nanocomposites is determined by the mean nanoparticle size and the alloy composition, and ranges from 36 to 64 (A m²)/kg (when Fe: Co = 1: 1) and from 35 to 52 (A m²)/kg (when Fe: Co = 3: 1) at synthesis temperatures in the range 600–800°С.     

Performance of a zeolite-containing catalyst and catalysts based on noble metals in intermolecular hydrogen transfer between С<Subscript>6</Subscript> hydrocarbons

The activities of a zeolite-containing catalyst and catalysts containing a noble metal in intermolecular hydrogen transfer between С₆ hydrocarbons are compared. The zeolite-containing catalyst is ineffective in hydrogen transfer from cyclohexane to 1-hexene and in cyclohexene conversion at <400°С. Cyclohexene disproportionation at Т < 200°С takes place only over catalysts containing a noble metal. The cyclohexene conversion selectivity depends strongly on the support type. Using deuterated compounds, it has been demonstrated that intermolecular hydrogen transfer via the dehydrogenation–hydrogenation mechanism involves only the initial cyclohexene.     

CO oxidation by oxygen of the catalyst and by gas-phase oxygen over (0.5–15)%CoO/ZrO<Subscript>2</Subscript>

CO adsorption on (0.5–15)%CoO/ZrО₂ catalysts has been investigated by temperature-programmed desorption and IR spectroscopy. At 20°С, carbon monoxide forms carbonyl and monodentate carbonate complexes on Co _m ²⁺ O _n ^2- clusters located on the surface of crystallites of tetragonal ZrO₂. With an increasing CoO content of the clusters, the amount of these complexes increases and the temperature of carbonate decomposition, accompanied by CO₂ desorption, decreases from 400 to 304°С. On the 5%CoO/ZrО₂ sample, the carbonyls formed on the Со²⁺ and Со⁺ cations and Со⁰ atoms decompose at 20, 90, and 200–220°С, respectively, releasing CO. At 20°С, they are oxidized by oxygen to monodentate carbonates, which decompose at 180°С. Adsorbed oxygen decreases the temperature of their decomposition on oxidation sites by ~40°C, and the sample remains in an oxidized state ensuring the possibility of subsequent CO adsorption and oxidation. The rate of the oxidation of 5%CoO/ZrО₂ containing adsorbed CO by oxygen is higher than the rate of the oxidation of the same sample reduced by carbon monoxide, because the latter reaction is an activated one. In view of the properties of the complexes, it can be concluded that the carbonates decomposing at 180°С are involved in CO oxidation by oxygen from the gas phase in the presence of hydrogen, a process occurring at 50–200°С. The rate-limiting step of this process the decomposition of the carbonates, which is characterized by an activation energy of 77–94 kJ/mol.     

Phase Diagram of an Ethylene Glycol–Hexamethylphosphorotriamide System

The phase diagram of an ethylene glycol (EG)–hexamethylphosphorotriamide (HMPT) system is studied over two wide temperature intervals (+25°С…?90°С…+40°С) and (?150°С…+40°С) by means of differential scanning calorimetry using INTERTECH DSC Q100 and METTLER TA4000 DSC instruments (Switzerland) in the DSC30 mode with variable cooling/heating rates. Substantial overcooling of the liquid phase, a glass transition, and different types of interaction are observed in the system. No thermal effects are observed in intermediate range of concentrations during the slow cooling/heating processes, and the system remains liquid until the glass transition. The presence of such a metastable phase is attributed to a sharp rise in the viscosity of the system due to different kinds of interaction between the components. HMPT: 2EG and HMPT: EG compounds with crystallization temperatures of +5 and ?0.5°С, respectively, are observed upon rapid cooling and slow heating. Changes in enthalpy are calculated for all of the observed thermal effects. The distinction from the phase diagram of H₂O–HMFT (literary data) is explained by the difference in the interactions between system components and by the structural differences between EG and H₂O.     

Synthesis of highly porous zinc–carbon composites based on modified pine wood

Highly porous materials containing zinc oxide were prepared form modified pine wood. The growth dynamics of zinc oxide microcrystallites in the course of carbonization of pine sawdust mixed with ZnCl₂ was studied. The hexagonal wurtzite-type ZnO phase is formed at 400°С and is broken down at approximately 800°С. The synthesized composite material has a high specific surface area, up to 1900 m² g^–1. The relationships of the porous structure formation in the composite in relation to the temperature and subsequent treatment with water were revealed. Opening of the porous structure of the composite in the course of carbonization of modified pine sawdust is associated with the formation of crystal-like phases of carbon and ZnO.     

Temperature-dependent ratcheting of PTFE gaskets under cyclic compressive loads with small stress amplitude

Uniaxial stress-controlled ratcheting experiments on PTFE gaskets under cyclic compressive loads with small stress amplitude were performed. The effect of temperature on the deformation behavior was considered. Results showed that the compressive modulus decreases rapidly when the temperature increases from 100 °C to 200 °C. Compressive ratcheting deformation with cycles increase significantly with the increases of temperature. The ratcheting deformations at 100 °C, 150 °C and 200 °C are nearly two, three and five times that at room temperature, respectively. Most of ratcheting deformation mainly occurs during the first 20 cycles because the subsequent ratcheting rate and strain range are small and much less than those in the previous cycles. The accumulated deformation under cyclic loads with small stress amplitude is relatively approach to the static compressive creep with the same peak stress. Therefore, the accumulated deformation with time of PTFE gaskets obtained by cyclic compression with small stress amplitude can be estimated by the corresponding static creep deformation with good accuracy under the approximate stress rate and the same temperature, especially at room temperature.