Home – Home – Jornals – Advanced Search

Two methods for the transition of aqueous solutions of polyvinyl alcohol (PVA) from the liquid state of aggregation to the solid state are considered. Freezing an aqueous solution of PVA at a negative temperature and subsequent thawing at a positive temperature result in the formation of rubber-like cryogels. Another way is chemical crosslinking of kinetically individual PVA macromolecules to spatial networks having elastic properties. Sodium tetraborate was used to structure aqueous PVA solutions. The rheological properties of a two-component aqueous solution of PVA were studied. The study shows that the polymer solution exhibits the properties characteristic of non-Newtonian liquids. The kinetics of gelation of the products of chemical structuring of aqueous PVA solutions with an aqueous sodium tetraborate solution was studied. It is shown that viscosity increases with time as a consequence of chemical interaction. The mechanical properties of carbon-containing composite materials obtained by various methods have been investigated. It has been determined that the most durable materials are those formed by the cryotropic method and those chemically structured after cryogenic treatments. The stress-strain and moisture-resistant properties of carbon materials enable their use as fuel briquettes with a minimum amount of a binder. They can also serve as high-energy fuels for domestic and industrial purposes. The chemical method of structuring a PVA solution can be used for dust control in coal mines.

The procedure for obtaining humic (HA), hymatomelanic (HmA) and fulvic acids (FA) that allows achieving their high yield has been developed and tested with the brown coals of the Kansk-Achinsk and the South Ural basins. The highest yield of humic substances is achieved for naturally oxidized brown coal of the Tisul deposit: HA - 60.9 %, HmA - 11.3 %, FA - 9.6 %. The composition of native brown coals, as well as HA, HmA and FA obtained from them, was studied using proximate and ultimate analysis, FTIR spectroscopy and ¹³C NMR (CPMAS) spectroscopy. It is established that the chemical and structural-group composition of HA, HmA and FA has significant differences. The samples of HmA and FA are characterized by relatively high content of oxygen-containing aliphatic groups with the predominance of carboxylic acids and esters in comparison with HA. Higher content of carbon, hydrogen and aromatic fragments is characteristic of HA. The samples of HmA and FA have similar elemental and structural group composition, however, HmA has a higher content of carbon and aromatic fragments.

Integrated studies of green coke have been carried out by means of X-ray diffractometry, electron microscopy, electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR). It is determined by EPR spectroscopy that two types of radical structures are present in the samples: low-molecular aromatic radicals and conjugated polyaromatic structures in which the unpaired electron is delocalised. Analysis of line shapes in the EPR spectra reveals differences between the green coke samples under investigation. EPR is shown to be highly sensitive method allowing one to follow the changes of molecular structure during the production of green coke. The results obtained in the work with the help of EPR are in good agreement with the results of NMR spectroscopic studies. It is concluded that evaluation of the molecular structure of intermediate coking products is necessary to improve the composition of initial raw material and technological operations.

The article reports the results of the study of the morphology, porous structure and electrical capacitance characteristics of highly porous carbon matrices (HPCMs) obtained from coal raw materials with different degrees of metamorphism and nanostructured composites (NSCs) based on them, the surface of which is decorated with gold or manganese oxide nanosized particles (NP), accumulating electrical charge during polarization in the electrolyte via two mechanisms (formation of an electrical double layer (EDL) and involvement of pseudo-capacitance component during Red-Ox reactions on electrodes). The samples of HPCMs were obtained by high-temperature (800 ^oC) alkaline activation (the mass ratio KOH/C = 2 : 1) of fossil coal from the coal basins of the Kemerovo Region and the Republic of Sakha (Yakutia): CAK - based on anthracite of the Kiyzasskiy open-pit mine (Kuzbass), with the highest coalification degree; CBK - based on boghead (a kind of sapropel coal ) from the Taymylyr deposit (Yakutia) with the lowest degree of metamorphism; CDK - based on long-flame coal (Kuzbass) occupying an intermediate position in the metamorphism series. Results obtained by scanning electron microscopy, small-angle X-ray scattering in combination with sorptometry showed that the NSC morphology is largely determined (except for submicron aggregates) by the porous structure of the matrices. The shape of cyclic voltammetry (CVA) curves for HPCMs CDK, CBK and Au-NP filled NSC based on them indicated a significant contribution from EDL into capacitance; the contribution of pseudo-capacitance is observed for the composite MnO_x/CDK electrode. The features of CVA curves for microporous CAK HPCM and NSC based on it are probably caused by hindered diffusion. The specific electrical capacitance is higher as a result of the polarization of CDK and CBK HPCM with large proportions of mesopores, as well as NSCs on their basis, than that resulting from the polarization of microporous CAK and the corresponding composites. For all three HPCMs, the introduction of fillers causes an increase in the electrode capacitance. The effect is more significant for NSCs obtained from hard coals with a low level of metamorphism (an increase up to 1.8 and 1.6 times with respect to the capacitance of initial matrices for NSCs based on CDK and CBK, respectively, according to the impedance measurement data), which is due to a decrease in the active resistance and the charge transfer resistance of the cells, and, in general, to the active component of the impedance.

The morphology of nanoparticles, structural-phase properties, and phase transformations that occur during heating in the nanostructured CoPt and CoPd systems rich in precious metals, obtained by co-reduction of aqueous precursor solutions by hydrazine hydrate, were studied by X-ray phase analysis and X-ray structural analysis, small-angle X-ray scattering, and high-resolution transmission electron microscopy. The results obtained are of interest for the development of the fundamentals of materials science of bimetallic nanoalloys, and provide a key to understand the processes of the formation of FePt, CoPt and FePd nanoalloys while heating intermetallic compounds with a highly ordered structure L1₀, which possess record-setting magnetic and magneto-optical properties.

The work is concerned with the development of a new type of iron-containing catalyst (Ct) based on lignin for the hydrogenation of carbon monoxide. Catalytic systems were obtained by hydrothermal synthesis and studied using a set of physicochemical methods (Fourier transform IR spectroscopy, Raman spectroscopy, low-temperature nitrogen adsorption, elemental analysis, atomic absorption analysis, X-ray phase analysis, X-ray photoelectron spectroscopy, transmission electron microscopy). Brunauer-Emmett-Teller (BET) surface area analysis, elemental analysis, atomic absorption analysis, X-ray fluorescence (XRF), transmission electron microscopy (TEM). It is shown that the formed catalysts are fine-grained, non-pyrophoric, non-hygroscopic, black powders. The catalytic systems are determined to exhibit high activity in carbon monoxide hydrogenation: the conversion is close to 100 %, the productivity with respect to С₅₊ hydrocarbons reaches 131.6 g/(kg Ct ∙ h).

The effect of hydrothermal carbonisation temperature (190-250 °C) on the properties of biochar produced from hydrolytic lignin was studied. Biochar was investigated using a set of physicochemical methods, its elemental, proximate and thermal analysis was carried out. It is shown that an increase in the temperature of hydrothermal treatment has a negative effect on biochar yield but allows obtaining a more thermally stable product with fuel characteristics comparable with those of brown coal.

Ni-, Co- and Ni–Co-containing catalysts for steam reforming of isobutanol were obtained by biochar impregnation with water-alcohol solutions of metal salts. Biochar was synthesised by the hydrothermal carbonisation of cellulose with subsequent thermal treatment of the obtained materials under the conditions of limited oxygen access. The catalysts were characterised using a complex of physicochemical methods (IR spectroscopy, BET, temperature programmable desorption of ammonia, scanning electron microscopy in combination with local electron microprobe analysis, X-ray phase and X-ray fluorescence analysis). It is found that the sample 2.5Ni-2.5Co/C (where the number before the metal symbol means its mass content calculated for the mass of reduced catalyst, %) provides a high yield of hydrogen (58%) from isobutanol reforming.

To develop an effective catalyst for the resource-saving conversion of coal-industry methane into hydrogen-containing gas, the materials Ce_0.2Ni_0.8O_1.2/Al₂O₃ were synthesized, their physicochemical and functional properties were studied depending on the nature of the precursors of active components (nickel(II) nitrate hexahydrate, nickel(II) ammonium oxide) and promoters (cerium(III) nitrate hexahydrate, ammonium cerium(IV) nitrate). It is shown that the nature of the precursor affects the textural and structural characteristics of the samples, their catalytic activity in the steam-carbon dioxide reforming of methane and resistance to the formation of carbon deposits. The optimal composition of precursors (nickel(II) nitrate hexahydrate, cerium(III) nitrate hexahydrate) has been established, the use of which in the synthesis of the Ce_0.2Ni_0.8O_1.2/Al₂O₃ catalyst ensures a decrease in the average particle size of the Ni active component (25 → 6.5 nm) and the degree of catalyst carbonisation (2.9 → 0.5%), high hydrogen yield (95%) at 800 °C in the steam-carbon dioxide reforming of methane.

The effect of the temperature regimes of hardwood sawdust thermochemical treatment (hydrothermal carbonization and torrefaction) on biochar properties and combustion characteristics are investigated. The mass yields of biochars were considered from the viewpoint of the processes that take place during thermochemical treatment, along with the changes in the elemental composition resulting from these processes. The optimal method and temperature regime of thermochemical treatment were determined. The effect of the method and temperature of sawdust thermochemical treatment on the composition of gaseous products from biochar combustion was assessed by FTIR spectroscopy combined with thermogravimetric analysis. Two main stages of biochar combustion were detected: the phase of removal and combustion of volatile substances (up to 400 °C) and the phase of semi-coke combustion (above 400 °C). The analysis carried out by means of FTIR spectroscopy during combustion allowed us to determine the released components of the gaseous mixture and to observe thermochemical decomposition of biochar components in the real time mode. Investigation of biochar combustion showed that an increase in sawdust processing temperature reduces the formation of gaseous products at the first stage of combustion and promotes an increase in the amount of carbon dioxide at the second stage.