Search

The results of experimental and theoretical studies on the influence of the surface density of a thin porous sheet of thermally expanded graphite on the acoustic wave transmission coefficient are presented. The applicability of thin film theory for describing the processes of acoustic wave propagation through porous sheet media in the low-frequency region and for small thicknesses is demonstrated. An assessment of the influence of the operating frequency on the sensitivity of the transmission coefficient to the surface density of the sheet is conducted. [ABSTRACT FROM AUTHOR]

Carbon materials with a graphite-like structure have the highest thermal stability in a non-oxidizing environment, sufficient structural strength, are easily processed, etc., and therefore they are widely used in various fields of technology. There are two methods of obtaining such materials: pyrolysis or carbonization of hydrocarbons and processing of natural graphite, so-called “thermo-expanded graphite technology” (TRG), which consists of successive reactions of intercalation, hydrolysis and heat treatment of natural graphite, leads to modification of the surface of TRG particles and provides the ability to their pressing and rolling on rollers to form dense materials. Natural graphite with a carbon content of 99.0–99.5 % by mass is used for the production of TRG, from which sealing materials are obtained for the equipment of enterprises of general industrial purpose: the fuel and energy complex, the petrochemical industry, utilities, etc. In the equipment of nuclear power plants, materials from TRG, of so-called “atomic purity”, are used, in which the carbon content must be at least 99.85 % by mass. Therefore, the purpose of the work is to obtain thermally expanded graphite of high purity by the method of electrochemical oxidation and further purification of flotation-enriched graphite. The production process took place in two stages: electrochemical intercalation of graphite with concentrated sulfuric acid followed by hydrolysis, and chemical further purification using ammonium bifluoride and Trilon B as cleaning reagents. Combining into one process of electrochemical oxidation of graphite and its further purification allows obtaining high purity TRG with a carbon content of 99.94–99.96 % by mass. In order to find the regularities of the interaction of Trilon B with metal ions included in the composition of graphite impurities, quantum chemical modeling of these processes was carried out. The energy effect of the interaction of the iron (III) cation is greater in absolute value (–969.1 kJ/mol) than for the case with the aluminum cation (–748.3 kJ/mol) both in the aqueous medium and in the adsorbed state on the surface of the graphene plane (–816.9 for Fe3+ and –621.2 kJ/mol for Al3+). Regardless of the nature of the cation, its interaction with Trilon B is thermodynamically more likely in an aqueous solution than in an adsorbed state on the surface of a graphene-like plane. [ABSTRACT FROM AUTHOR]

The stress–strain diagram of a polymer composite material based on rubber PDI-3A filled with thermally expanded graphite or potassium chloride has been studied before and after microwave treatment for 300, 600, 900, and 1200 s. It has been found that the ultimate tensile strength and strain increase twofold after a 300-s microwave treatment and testing at 223 K. A significant decrease in the stress–strain properties of the synthesized composites with an increase in the test temperature or microwave treatment time is observed. [ABSTRACT FROM AUTHOR]

The physical and mechanical properties and structural condition of flexible graphite foils produced by processing natural graphite with nitric acid, hydrolysis, thermal expansion of graphite and subsequent rolling were studied. The processes of obtaining materials and changing their characteristics has been thoroughly described and demonstrated. The structural transformations of graphite in the manufacture of foils were studied by X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). A decrease in the average size of the coherent scattering regions (CSR) of nanocrystallites was revealed during the transition from natural graphite to thermally expanded graphite from 57.3 nm to 20.5 nm at a temperature of 900 °C. The rolling pressure ranged from 0.05 MPa to 72.5 MPa. The thickness of the flexible graphite foils varied from 0.11 mm to 0.75 mm, the density—from 0.70 to 1.75 g/cm3. It was shown that with an increase in density within these limits, the compressibility of the graphite foil decreased from 65% to 9%, the recoverability increased from 5% to 60%, and the resiliency decreased from 10% to 6%, which is explained by the structural features of nanocrystallites. The properties' anisotropy of graphite foils was studied. The tensile strength increased with increasing density from 3.0 MPa (ρ = 0.7 g/cm3) to 14.0 MPa (ρ = 1.75 g/cm3) both in the rolling direction L and across T. At the same time, the anisotropy of physical and mechanical properties increased with an increase in density along L and T to 12% with absolute values of 14.0 MPa against 12.5 MPa at a thickness of 200 μm. Expressed anisotropy was observed along L and T when studying the misorientation angles of nanocrystallites: at ρ = 0.7 g/cm3, it was from 13.4° to 14.4° (up to 5% at the same thickness); at ρ = 1.3 g/cm3—from 11.0° to 12.8° (up to 7%); at ρ = 1.75 g/cm3—from 10.9° to 12.4° (up to 11%). It was found that in graphite foils, there was an increase in the coherent scattering regions in nanocrystallites with an increase in density from 24.8 nm to 49.6 nm. The observed effect can be explained by the coagulation of nanocrystallites by enhancing the Van der Waals interaction between the surface planes of coaxial nanocrystallites, which is accompanied by an increase in microstrains. The results obtained can help discover the mechanism of deformation of porous graphite foils. The obtained results can help discover the deformation mechanism of porous graphite foils. We assume that this will help predict the material behavior under industrial operating conditions of products based flexible graphite foils. [ABSTRACT FROM AUTHOR]

A novel conductive composite based on PEDOT:PSS, BSA, and Nafion for effective immobilization of acetic acid bacteria on graphite electrodes as part of biosensors and microbial fuel cells has been proposed. It is shown that individual components in the composite do not have a significant negative effect on the catalytic activity of microorganisms during prolonged contact. The values of heterogeneous electron transport constants in the presence of two types of water-soluble mediators were calculated. The use of the composite as part of a microbial biosensor resulted in an electrode operating for more than 140 days. Additional modification of carbon electrodes with nanomaterial allowed to increase the sensitivity to glucose from 1.48 to 2.81 μA × mM−1 × cm−2 without affecting the affinity of bacterial enzyme complexes to the substrate. Cells in the presented composite, as part of a microbial fuel cell based on electrodes from thermally expanded graphite, retained the ability to generate electricity for more than 120 days using glucose solution as well as vegetable extract solutions as carbon sources. The obtained data expand the understanding of the composition of possible matrices for the immobilization of Gluconobacter bacteria and may be useful in the development of biosensors and biofuel cells. [ABSTRACT FROM AUTHOR]

The composite materials based on a thermosetting binder mark SFP and thermally expanded graphite and containing 50–70% of the filler are prepared by the method of hot pressing. It is studied how the physicochemical and mechanical characteristics of the composite depend on the method of filler introduction. The materials prepared by mixing air-dry components are shown to exhibit the high conductivity (up to 195 S/cm) and strength (above 25 mPa), the low interface contact resistance (less than 10 mΩ cm2), and the corrosion current not exceeding 1 µA/cm2, which allows the high efficiency of energy conversion in SPFC to be reached. [ABSTRACT FROM AUTHOR]

Graphite-graphene composites (GGC) have been obtained as a result of mechanical treatment of thermoexpanded graphite (TEG). Raman spectroscopy proves the presence of ordered graphene in the GGC. The predominant formation of no more than 5 graphene sheets in the material is concluded from Raman data and SEM micrographs. Electrochemical tests of GGC samples show that in spite of quite low specific discharge capacity (290 mAhg−1), a 20-fold increase in current density (from 50 to 1000 mA g−1) does not lead to a change in the specific capacity upon deintercalation of lithium ions. This feature favorably differs the material studied from existing analogues. A decrease in the specific capacity during cycling of the GGC at a current density of 100 mA g−1 after 95 cycles has not been noted. Exceptionally low decrease in the specific capacity upon the increase of the power load, perfect cycling stability and high Coulombic efficiency supported by electrochemical impedance analysis indicate good prospects of using GGC as a lithium-ion battery anode and for utilizing graphene additives to electrode materials of lithium-ion batteries operating at high discharge currents. [ABSTRACT FROM AUTHOR]

Previous studies have shown that mixture of hydrogenated Ti and thermally expanded graphite (TEG) can be used as a material for cathodes of thermophotoemission energy converters and allows reducing significantly the temperature of the start of electron emission. In the present work, the changes in the structural state and electronic properties of nanostructured material based on hydrogenated Ti with 0.53 wt.% TEG during the vacuum annealings of it at different temperatures in a furnace are studied. By comparing the experimental and theoretical values of electrical conductivity for different densities of the powder material, it is shown that the hydrogenated Ti--TEG mixture can form a composite. The reason for this is the important role of interfaces between the components of the composite as well as the charge transfer through these interfaces. As found, the short-term increase of temperature changes significantly and irreversibly the structure of each component of the composite and its electrical conductivity, but the composite does not show significant irreversible changes during such heating. As shown, the long-term (1.5 h) annealing of the material in a vacuum furnace at ≅ 700 K and 900 K leads to the loss of above-mentioned thermal stability of composite. As established, the specific electroconductivity of the composite is increased after long-term vacuum annealing at a temperature of 700 K, and, when the annealing temperature is near 900 K, it is decreased compared to the previous case. According to the results of the specific electroconductivity temperature dependences' analysis, activation energies of electrokinetic phenomena in the studied material are established and, for the first time, the important role of electronic subsystem in investigated composite formation and in changes of its properties under various thermal influences is proved experimentally that is important to create 'cold' emitters of electrons. [ABSTRACT FROM AUTHOR]

We present results of studying the sensitivity of an acoustic method for gaging the density of thermally expanded graphite (TEG) samples based on recording changes in the amplitude of a signal transmitted through the sample due to a change in density. They show that the maximum sensitivity of the method is comparable with the error of measurement of density and mass by the direct weight method, 26 kg/m3 and 0.02 g, respectively. The unevenness of the density distribution over the area of TEG samples of various thicknesses was estimated, while the deviation of the amplitude of the signal transmitted through the sample, proportional to the density deviation, reached up to 50% for some sheets, 30% for mats, and the smallest did not exceed 10%. During the scanning process, an inversely proportional dependence of the amplitude of the transmitted acoustic signal on the average sample density was revealed. This dependence was most pronounced for small thicknesses of TEG mats and sheets. [ABSTRACT FROM AUTHOR]

Methods for dispersing of the thermally expanded graphite (TEG) in a dilute alcohol medium and for modifying the surface of a TEG with an ultradisperse dielectric - silicon dioxide (SiO2) are proposed. The new polymer nanocomposites (PNC) obtained based on polychlortrifluoroethylene (PCTFE) with a low content of dispersed TEG and a modified filler TEG/SiO2 are characterized by high rates of electrophysical properties. Using electron microscopy and X-ray photoelectron spectroscopy, the features of the electronic structure of the surface of composites are investigated. Using the two-contact method in the kilohertz frequency range, the features of change in the electrophysical properties of composites depending on the content of fillers and temperature have been established. Based on research and comparative analysis of thermophysical properties (specific heat capacity c, temperature coefficient of linear expansion a) of the systems, the influence of the structural-morphological state of the components and their concentration, the level of interfacial interaction on the physical properties of nanocomposites was investigated. The fact of the appearance of interfacial polarization in the PCTFE-TEG/SiO2 interfacial layers due to the appearance of the TEG/SiO2 and PCTFE-SiO2 interphase layers is established, which, while preserving the complex of properties inherent to the polymer materials, increases the overall electrical conductivity of the composites. It was also established that the modified nanofiller exhibits greater activity in relation to the polymer matrix than the unmodified one. It is shown that the composites exhibit a dual effect of the modified nanofiller on the matrix structure, which manifests in the formation of a powerful crystalline structure in the zones of influence of the nanofiller and amorphization of the polymer matrix in the peripheral zones. It was found that the result of amorphization of the matrix is a decrease in the area of the peaks of temperature reflexes on the temperature dependences of the specific heat capacity and an increase in the absolute value of the temperature coefficient of linear expansion with an increase in the concentration of modified TEG. [ABSTRACT FROM AUTHOR]

The size of mosaic blocks along the graphite layers (that is, the average diameter of crystallites in the basal plane) was determined by two methods for specially made model materials based on narrow fractions of flake graphite powders and milled pyrographite with lamellar particles. The first method consisted in the calculation of mosaic block sizes from a minimum of the temperature dependence of electrical conductivity using an empirical law according to Mason; the second method based on mathematical modeling used the values of the magnetoresistance of carbon materials at temperatures of 80 and 300 K. The correspondence between the sizes of mosaic blocks calculated by these methods along the graphite layers in the considered materials was shown. A correction for the lamellar shape of graphite crystallites was determined to calculate the sizes of mosaic blocks in the direction perpendicular to the graphite layers from the 002 peak broadening in the diffraction pattern. [ABSTRACT FROM AUTHOR]

Graphite intercalated compounds (GICs) with different stage numbers are prepared chemically from highly oriented pyrolytic graphite (HOPG), natural flaked graphite (FG) and nitric acid. Exfoliated graphite samples (EG-T) are synthesized from GICs via water treatment followed by thermal shock. The aim of this work is to investigate the dependence of the inner EG-T pore structure on the extent of oxidation and type of graphite by processing scanning electron microscopy (SEM) micrographs of EG-T cross sections. A procedure is developed on the basis of a deep convolutional neural network that speeds up image processing with no appreciable loss of accuracy. A strong correlation is found between EG-T pore structure parameters, the depth of oxidation, and the type of graphite. [ABSTRACT FROM AUTHOR]

Oil spills necessitate the development of effective methods for preventing their damaging effects on the environment. A number of physical, chemical, thermal, and biological methods are used to combat oil spills. Among them, sorption is considered to be efficient in removing thin oil films from water surfaces. Currently, there is an urgent need for simple methods of obtaining oil sorbents that include a magnetosensitive component to optimize the process of removing oil from the water surface. The purpose of the work is to obtain and research oil sorbents resistant to destruction, with increased bulk density and complex magnetosensitivity, based on thermally expanded graphite (TEG) with the inclusion of micro- and nano-particles of iron and its oxides. The structure and composition of the new composite material was characterized using scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffractometry, thermogravimetric analysis, and laser diffraction particle sizing. The composite sorbent comprised TEG with the inclusion of iron-containing magnetosensitive particles. Metal-carbon nanoparticles (MCN) were used as the magnetosensitive component; they had a magnetosensitive iron core covered with a carbon shell. We used two methods of synthesis, namely (i) mechanical mixing of the TEG flakes and MCN particles, and (ii) applying a thermal shock (microwave processing) to the mixture of graphite intercalated with sulphuric acid and micro- and nanoparticles of iron and iron oxides. In the first case, MCN particles were fixed on the faces, edges, and other surface defects of the TEG flakes due to intermolecular forces, coordinate bonds, and electrostatic interaction. The strong adhesion of magnetosensitive iron/iron oxide and TEG particles in the second case was due to the mutual dissolution of iron and carbon components during the thermal shock, which formed an interfacial layer in which iron carbide is present. The presence of magnetosensitive components in the structure of the proposed oil sorbents allows the use of magnetic separation for the localization and removal of oil spills, increases the density of sorbents, and, accordingly, leads to a decrease in windage while retaining the advantageous properties of thermally expanded graphite. According to the results of laboratory studies, the efficiency of removing oil from the water surface is not lower than 95–96%. [ABSTRACT FROM AUTHOR]

The stability of Nafion–carbon composites is important for the efficient functioning of fuel cells. The thermal decomposition of Nafion, nanostructured carbon materials, such as multi-walled carbon nanotubes, graphene-like materials, and their composites, have been studied using constant heating rate thermogravimetry in air. Materials were characterized by quantitative and qualitative analysis methods, such as thermogravimetry, X-ray photoelectron spectroscopy, scanning, and transmission electron microscopy with field emission. In Nafion–carbon composites, an increase in the thermal stability of the Nafion polymer is observed due to the formation of surface compounds at the Nafion–carbon interface. In this case, the degree of stabilization is affected by both the component composition of the composite and the structure of the nanocarbon material. The greatest effect was obtained in the case of using thermally expanded graphite (few-layer graphene). Nafion is distributed to a greater extent over the surface of the carbon material due to its high structural accessibility. The most thermally stable composite is Nafion–graphene in a mass ratio of components 1:4 with one stage Nafion degradation at 422 °C, whereas the degradation of pristine Nafion occurs in three stages at 341, 413, and 430 °C. The dependences of thermal stability and features of thermal degradation on the composition and structure of composites are discussed. [ABSTRACT FROM AUTHOR]

The adsorption properties of powdered and composite sorbents in sorption from dilute solutions and in sorption of oils were studied. Acetic acid solutions and such oils as liquid paraffin and MS-20 industrial oil were chosen as examples. The sorbents were based on thermally expanded graphite prepared from hydrolysis lignin using thermal and electrochemical technologies. High adsorption performance of thermally expanded graphite and its ability for regeneration after the sorption from solutions were proved. The influence of the density of the composite sorbents on their ability to adsorb oils was examined. An equation was obtained for calculating the oil absorption coefficient after keeping the composite sorbents in oils for different times, and the constants of this equation, which depend on the sorbent density and kind of oil, were calculated. [ABSTRACT FROM AUTHOR]

A technology for obtaining graphene by means of ultrasonic dispersion of thermally expanded graphite in the presence of a surface-active polymer Nation is presented. The technology makes it possible to obtain large amounts of low-layer (1–3 layers) graphene in a relatively short time. An approach to control the dispersion process based on UV spectroscopy of dispersions is described. A mechanism is proposed for the effect of a surface-active polymer on the production of low-layer graphene by ultrasonic dispersion. [ABSTRACT FROM AUTHOR]

The paper presents the results of the study of the dependence of the properties of polymer composites of the linear high-pressure polyethylene (LHPPET) system – graphite fillers of various types: natural GAK-2, thermally expanded (TEG) and with ultrasonic treatment. The test samples contained a filler in a wide concentration range (5–35 wt. %). Samples were manufactured using rolling, pressing and powder technology methods. Electrical resistance was measured by the four-probe potentiometric method at constant current. It is shown that the electrical resistance decreases sharply in a narrow concentration interval of 5–15 wt. % from 6.77·1010 to 4.9·10² Ω·m (for compositions obtained by rolling), from 2.96·1010 to 1.2 Ω·m (for pressed samples), from 2.87·109 to 0.14 Ω·m (for compositions obtained by powder technology). For samples of the LHPPET – GAK-2 system, a rapid decrease in electrical resistance is observed at filler concentrations of 5–30 wt. % from 1.36·1012 Ω·m to 2.79·10² Ω·m. Using thermally expanded graphite with and without ultrasonic treatment (and to a lesser extent GAK-2) it is possible to obtain polymer composite materials (PCM) with volume resistivity ranging from 6.77 to 1.9·10–3 Ω·m. It has been experimentally confirmed that electrical conductivity largely depends on the PCM manufacturing technology. The established dependences of the current conductivity of composites, depending on the manufacturing method, are associated with the corresponding structural differences. These structural differences are manifested in an increase in the number and area of contacts of filler particles – graphite and in a change in the thickness of the layers of the polymer matrix. Dry powder technology is the most effective method of obtaining LHPPET – graphite compositions. The optimal composition of the composition is 25 wt. % TEG and 75 wt. % LHPPET. Directions of practical use of the obtained results can be effectively used in industry and housing and communal economy. [ABSTRACT FROM AUTHOR]

The introduction of polymer-composite materials makes it possible not only to solve the problem of increasing durability, reducing the mass and cost of machines, but also, by introducing fillers, to adapt them to the required operating conditions. At the same time, there is a problem regarding the high cost of technologies for obtaining composites, which limits their widespread implementation. That is why the object of this research is the processes of influence of the filler on the characteristics and properties of polymer-composite materials. Complex laboratory studies of physical and mechanical characteristics, tribological and thermophysical properties of the developed polymer-composite materials based on Phenylone C2 were carried out. The dependence of the coefficient of friction and wear of the material based on Phenylone C2, containing thermally expanded graphite, on the pressure and nature of counter-bodies during friction with lubrication and without it was established. It was revealed that the minimum amount of wear of the material, with friction with lubrication, is achieved under the pressure on tribojunction of 5 MPa. It was established that with an increase in the concentration of filler from 5 to 25 wt% the coefficient of thermal conductivity increases by 4–40.8 %, compared with that non-filled with Phenylone C2. It was found that the introduction of thermally expanded graphite into Phenylone C2 in the amount of 5 wt % leads to a decrease in heat capacity by 34 %. The proposed technology of obtaining polymer-composite materials in the electromagnetic field provides sufficient physical and mechanical characteristics, tribological properties and low cost of finished products (parts). The results reported here make it possible to adapt the physical and mechanical characteristics, thermophysical and tribological properties of polymer-composite materials to certain modes of operation of movable junctions. [ABSTRACT FROM AUTHOR]

The formation of carbon-containing composites based on metals opens the prospect of combining the advantages of their components and manifesting new electrophysical properties, which are not characteristic of the original materials. Mechanical synthesis of hydrogenated titanium (TiH) and thermally expanded graphite (TEG) powders leads to such composites formation. As shown, the increase by 1.65 and 6.3 times in their electrical conductivity is observed in comparison with original TiH and TEG components, respectively. It is due to an increase of free electrons in the TEG because of their transport from the metal component. [ABSTRACT FROM AUTHOR]

The current trend of replacing metal alloys with composite materials in the manufacture of various types of plain bearings, sealing elements of Assembly units, anti-friction bushings, and other machine parts is very promising for the development of many industries. However, in the manufacture of composite material products by modern methods, such as extrusion, pressing, and injection molding, various types of defects characteristic of these types of processing occur, resulting in the required parameters of the quality of the working surfaces of parts are not provided. This leads to the need for additional mechanical processing the quality of which largely depends on the reliability and durability of the functioning of parts and mechanisms. The article analyzes the main parameters that affect the quality of the surface obtained during turning for metal alloys, as well as for composite materials. The method of obtaining blanks by pressing from the material under consideration was developed, the technological equipment necessary for the research was designed and manufactured, a plan was developed for conducting a full-factor experiment with the creation of a model in the Mathcad program, and an active experiment was carried out to determine the influence of cutting mode parameters on surface roughness. Given the results of the study on the basis of which conclusions about the dependence of various cutting parameters on the quality of the surface layer, defined by the nuances of turning the considered composite material, practical recommendations that will positively affect the timing and success of implementation of fabrication of parts from this material.

The article touches upon the problem of working area air pollution by pathogenic microorganisms. The problem’s solution requires increased efficiency of filtration materials. Using thermally expanded graphite and Cribrol® polymer composite material, we analyzed air purification quality of multifunctional rooms in comparison with traditional activated carbon. The filtration materials properties were studied using a set of analytical methods. The air was pumped through tested materials in a volume of 500–2000 liters with the use of PU-1B sampling device depositing microorganisms on the nutrient medium. We showed that activated graphite and Cribrol® are effective in cleaning the air from bacteria (cell sizes do not exceed 1 micron), as well as larger microorganisms (from 3 microns or more). Activated graphite completely trapped microorganisms in all test variants. The filtration capacity of the new materials turned out to be higher than that of traditional activated carbon, which indicates the prospects for their further research and practical application.

The results of obtaining membrane electrodes based on thermally expanded graphite by thermolysis of pastes represented by graphite bisulfate, various binders, and solvents are reported. The microstructure and elemental composition of the electrodes were examined and their chemical purity was proven. The method of thermogravimetric analysis demonstrated the high thermal stability of the electrodes. The effectiveness of the use of membrane electrodes in the electrosynthesis of organic compounds is shown. [ABSTRACT FROM AUTHOR]

Bacterial cellulose (BC) produced by the Komagateibacter sucrofermentas VKPM B-11267 bacteria was used as a carrier for immobilization of acetic acid bacteria Gluconobacter oxydans in amperometric biosensors. The bioreceptor was formed on the surface of a screen-printed graphite electrode modified with thermally expanded graphite (TEG) or on the surface of a porous three-dimensional material, nickel foam (NF). Structural features of these materials contributed to the creation of a firm contact between the electrode material and the surface of the BC on which the bacterial cells were immobilized. Scanning electron microscopy showed that bacteria not only sorb on the surface of BC but are also able to penetrate the inner volume of the film. Conductivity of both types of biosensors was studied using impedance spectroscopy and the resistance of the graphite electrode was shown to decrease by three orders of magnitude after its surface is modified with TEG. Bioelectrodes containing BC were used in the construction of an amperometric biosensor for glucose determination. The sensitivity of the biosensor was 3 μA/mM × cm2. Thus, BC in combination with TEG and NF can be used to create three-dimensional electrodes of bioelectrocatalytical devices. [ABSTRACT FROM AUTHOR]

Thermal degradation of multiwalled carbon nanotubes, thermally expanded graphite, Nafion proton-conducting polymer, and binary composites based on it (Nafion + carbon nanotubes, Nafion + thermally expanded graphite) in air was studied. The temperature dependence of the lifetime of the materials was estimated. The structure of the materials studied was characterized by field emission scanning and transmission electron microscopy, thermal gravimetric analysis, and differential scanning calorimetry. The degradation kinetics was examined using nonisothermal kinetic analysis; the activation energy and pre-exponential factor of the Arrhenius equation were determined. The thermal stability of Nafion in its binary composites with carbon materials is enhanced owing to the formation of surface compounds on the Nafion–carbon interface. The degree of stabilization, or the composite lifetime, depends on the component composition of the composite and on the structure of the nanocarbon material. The largest effect was reached when using a composite with thermally expanded graphite at the component weight ratio of 1 : 4. Its lifetime at 80°C was 1014.4 min, exceeding by 4 orders of magnitude the lifetime of straight Nafion (1010.4 min). In the case of the composite with thermally expanded graphite at the component weight ratio of 1 : 4, Nafion polymer is distributed over the surface of the carbon material to a greater extent compared to the other compositions because the better surface accessibility. Introduction of carbon and carbon–polymer composites with mixed conductivity in the course of fabrication of electrochemical electrodes enhances their heat resistance and limiting operation temperature, thus allowing the operation life to be prolonged and production cost of the items to be reduced. [ABSTRACT FROM AUTHOR]

Electropolymerized neutral red, thionine, and aniline were used as part of hybrid nanocomposite conductive polymers, to create an amperometric reagent-less biosensor for glucose determination. The structure of the obtained polymers was studied using infrared (IR) spectroscopy and scanning electron microscopy. Electrochemical characteristics were studied by cyclic voltammetry and impedance spectroscopy. It was shown that, from the point of view of both the rate of electron transfer to the electrode, and the rate of interaction with the active center of glucose oxidase (GOx), the most promising is a new nanocomposite based on poly(neutral red) (pNR) and thermally expanded graphite (TEG). The sensor based on the created nanocomposite material is characterized by a sensitivity of 1000 ± 200 nA × dm3/mmol; the lower limit of the determined glucose concentrations is 0.006 mmol/L. The glucose biosensor based on this nanocomposite was characterized by a high correlation (R2 = 0.9828) with the results of determining the glucose content in human blood using the standard method. Statistical analysis did not reveal any deviations of the results obtained using this biosensor and the reference method. Therefore, the developed biosensor can be used as an alternative to the standard analysis method and as a prototype for creating sensitive and accurate glucometers, as well as biosensors to assess other metabolites. [ABSTRACT FROM AUTHOR]

The article discusses the synthesis and properties of electrically conductive polymer composite materials based on low-ash graphite grade GSM-1, modified with acids using bisulfate technology. Investigations of the influence of such technological methods as pressing and rolling on rollers with a variable gap on the conductivity of composite materials based on thermally expanded graphite and thermally expanded polymer-graphite compositions containing acid-modified graphite have been carried out. It is shown that, by applying to polymer composites the technological methods of thermal expansion, pressing, and rolling on rollers, it is possible, firstly, to combine fillers of different nature, shapes, and sizes and, secondly, to obtain composites with the required conductivity of an electrically conductive polymer composite. The paper shows the advantage of using thermally expanded graphite in comparison with other forms of graphite to obtain highly conductive polymer compositions. [ABSTRACT FROM AUTHOR]

Dispersions of graphene nanoparticles were obtained by liquid phase exfoliation of thermally expanded graphite in ethanol as well as tert-butanol via sonication. Initial thermally expanded graphite was obtained by heat treatment in the shock mode of ternary graphite nitrate intercalation compound with formic and acetic acids. Investigation of the graphite nitrate intercalation compound and thermally expanded graphite structural characteristics by X-ray diffraction analysis has been carried out. The microstructure and morphology of the obtained graphene particles were studied by transmission electron microscopy.

Oil spills necessitate the development of effective methods for preventing their damaging effects on the environment. A number of physical, chemical, thermal, and biological methods are used to combat oil spills. Among them, sorption is considered to be efficient in removing thin oil films from water surfaces. Currently, there is an urgent need for simple methods of obtaining oil sorbents that include a magnetosensitive component to optimize the process of removing oil from the water surface. The purpose of the work is to obtain and research oil sorbents resistant to destruction, with increased bulk density and complex magnetosensitivity, based on thermally expanded graphite (TEG) with the inclusion of micro- and nano-particles of iron and its oxides. The structure and composition of the new composite material was characterized using scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffractometry, thermogravimetric analysis, and laser diffraction particle sizing. The composite sorbent comprised TEG with the inclusion of iron-containing magnetosensitive particles. Metal-carbon nanoparticles (MCN) were used as the magnetosensitive component; they had a magnetosensitive iron core covered with a carbon shell. We used two methods of synthesis, namely (i) mechanical mixing of the TEG flakes and MCN particles, and (ii) applying a thermal shock (microwave processing) to the mixture of graphite intercalated with sulphuric acid and micro- and nanoparticles of iron and iron oxides. In the first case, MCN particles were fixed on the faces, edges, and other surface defects of the TEG flakes due to intermolecular forces, coordinate bonds, and electrostatic interaction. The strong adhesion of magnetosensitive iron/iron oxide and TEG particles in the second case was due to the mutual dissolution of iron and carbon components during the thermal shock, which formed an interfacial layer in which iron carbide is present. The presence of magnetosensitive components in the structure of the proposed oil sorbents allows the use of magnetic separation for the localization and removal of oil spills, increases the density of sorbents, and, accordingly, leads to a decrease in windage while retaining the advantageous properties of thermally expanded graphite. According to the results of laboratory studies, the efficiency of removing oil from the water surface is not lower than 95–96%.

The work considered the properties of a biosensor based on a novel nanomaterial—modified thermally expanded graphite (TEGM). The main focus was on whether the procedure of additional graphite thermal expansion would affect the electrochemical properties of biosensors based on membrane fractions of acetic acid bacteria Gluconobacter oxydans. Raman spectroscopy, scanning electron microscopy and electrochemical analysis were used for the study. Raman spectra showed that the formation of TEGM led to its stratification into smaller particles and a better orderly layered structure with high "graphenization" degree. Modification of TEG led to the formation of additional cavities into which bacterial cells or bacterial membrane fractions could be immobilized and affect the electrical conductivity of the biosensors positively. Calculation of the heterogeneous charge transfer constants showed that processes occurring on the electrodes are quasi-reversible. The limiting stage of these processes is the transfer of an electron from a biological component on the electrode surface, not the diffusion of the analyte from the solution to the active centers of the enzyme. We showed the possibility of developing third-generation mediator-free biosensors for glucose detection based on TEGM, as well as of second-generation mediator biosensors for glucose, ethanol and glycerol detection. [ABSTRACT FROM AUTHOR]

Polyamides are widely used as matrix polymers of composite and structural materials in many industrial technologies. One of the features of polyamide polymers is their noticeable ability to absorb water from the environment in a liquid or gaseous state. The results of the study of the kinetics of water absorption of composites with a polyamide matrix filled with products of thermal modification of hydrolytic lignin in the temperature range of 273–313 K are reported. Graphite from hydrolytic lignin, graphite bisulfate, and thermally expanded graphite, were examined as composite fillers. The plasticizer was vaseline oil. The maximum water absorption after 650 h exposure was 1.1 and 2.2 wt % of water at temperatures of 293 and 313 K, respectively, for the composite filled with lignin-derived graphite with 9% oil. The minimum values ​?of water absorption constants were determined for a composite filled with thermally expanded graphite from lignin with 20% oil. The use of thermally expanded graphite as a filler makes it possible to significantly increase the oil content in the blend, since its oil absorption is significantly higher compared to that of other graphite materials. The rate constants of water absorption were calculated and equations that describe this process for the studied composites were derived. It has been proven that the ability of polyamides to absorb water significantly decreases with an increase in the oil plasticizer content therein, i.e., oil blocks the polar CONH groups of polyamide macromolecules, which reduces the probability ​of water absorption constants were determined for a composite filled with thermally expanded graphite from lignin with 20% oil. The use of thermally expanded graphite as a filler makes it possible to significantly increase the oil content in the blend, since its oil absorption is significantly higher compared to that of other graphite materials. The rate constants of water absorption were calculated and equations that describe this process for the studied composites were derived. It has been proven that the ability of polyamides to absorb water significantly decreases with an increase in the oil plasticizer content therein, i.e., oil blocks the polar CONH groups of polyamide macromolecules, which reduces the probability of hydrogen bond formation in the structure of polyamide composites. [ABSTRACT FROM AUTHOR]

A synthesis method has been developed, and the electrochemical properties of a nanocomposite coating based on polyaniline (Pani) and thermally expanded graphite (TEG) on a substrate of anodized graphite foil in an aprotic lithium electrolyte have been studied. Stable suspensions of Pani–TEG were obtained by mixing a solution of Pani base in formic acid with TEG and subsequent ultrasonic treatment and deposited on the porous surface of activated (anodized) graphite foil. The specific electrochemical capacity of the coating attained 675 F/g at a charge–discharge current of 0.5 mA/cm2 in an aprotic electrolyte of 1 M LiClO4 in propylene carbonate. Upon long cycling for a week (more than 300 cycles), the drop in capacity was not higher than 4%. [ABSTRACT FROM AUTHOR]

Thermal degradation in air of Nafion proton-conducting polymer in composites containing nanostructured carbon materials [carbon black of Vulcan XC-72 grade and a graphene-like material (thermally expanded graphite)] and platinum nanoparticles was studied by nonisothermal kinetic analysis. The effect of the contact of Nafion with one or another material of the composite on the degradation kinetics was examined. The activation energy of Nafion desulfonation was calculated in relation to the component composition. The temperature dependence of the polymer lifetime for materials of different component compositions was evaluated. The materials were characterized by scanning and transmission electron microscopy and by differential thermal analysis. The presence of carbon materials enhances the heat resistance of Nafion and narrows the temperature interval of its degradation. The presence of various forms of carbon material (carbon black, thermally expanded graphite) and of platinum nanoparticles influences the Nafion desulfonation and its kinetic characteristics differently. The mechanism of thermal stabilization of Nafion in the presence of carbon materials was suggested. [ABSTRACT FROM AUTHOR]

As a result of the research, the possibility of directional control of the operational properties of epoxy composites by the use of small additives of thermally expanded graphite-graphene structures has been proved, providing the bending failure stress increases by 32% and the bending elastic modulus increases by 44%, the compression strength increases by 49%, the tensile strength increases by 74% and the tensile elastic modulus increases by 34%, impact resilience increases by 78%. The addition of thermally expanded graphite increases thermal, fire and heat resistance as well as the coefficient of heat-conducting epoxy composite. [ABSTRACT FROM AUTHOR]

Based on the data of electron scanning and transmission microscopy, X-ray energy-dispersive spectroscopy (EDS), voltammetry, and electrochemical impedance spectroscopy the structures of composite electrode materials are modeled. Materials with a mixed (electron and proton) conductivity, which contain platinum nanoparticles on carbon black (Pt/C, electron conductor), the proton-conducting polymer Nafion (fluorocarbon polymer containing sulfo groups), and two types of additives of nanostructured carbon materials (carbon nanotubes (CNTs) and thermally expanded graphite (TEG)) are investigated. Concentration profiles of elements (EDS data) obtained by scanning sample surfaces and features of the dependences of the electrochemically active platinum surface area and concentration dependences of the electron and proton resistance on the Nafion concentration in the material are analyzed. It is shown that the structure of the material, in particular, the proton-conducting polymer Nafion, depends on the type of the additive. Structural models of the materials studied are proposed. [ABSTRACT FROM AUTHOR]

The compositions of antifriction biocompatible polyamide matrix composites filled with graphite nanocomponents obtained by modified industrial phytogenic waste—hydrolytic lignin—are developed. Paraffin oil and polysiloxane fluid were used as safe plasticizing agents and lubricating components. The oil absorption of the obtained materials and the tribological characteristics of the composites are studied. The composites are studied using thermogravimetric analysis, infrared spectroscopy, and microstructural analysis. It is shown that the composites filled with thermally expanded graphite from lignin and plasticized with a blend (paraffin oil + PES-5) in the amount of a 5–15% additive have average friction factors of 0.072 and 0.074 with a specific load of 2.33 and 0.33 MPa respectively. With an increase in the additive content, the friction factor grows slightly. Therefore, to increase composite durability, the recommended composite plasticizer content should be 28–30%. [ABSTRACT FROM AUTHOR]

This work considers the effects of various carbon nanomaterials and fibres on bioelectrocatalytic and respiratory activity of bacterial cells during the oxidation of ethanol in the presence of an electron transport mediator. Gluconobacter oxydans sbsp. industrius VKM B‐1280 cells were immobilised on the surfaces of graphite electrodes and had an adsorption contact with a nanomaterial (multi‐walled carbon nanotubes, thermally expanded graphite, highly oriented pyrolytic graphite, graphene oxide, reduced graphene oxide). The electrochemical parameters of the electrodes (the polarisation curves, the value of generated current at the introduction of substrate, the impedance characteristics) were measured in two‐electrode configuration. Modification by multi‐walled carbon nanotubes led to the increase of microbial fuel cell (MFC) electric power by 26%. The charge transfer resistance of modified electrodes was 47% lower than unmodified ones. Thermally expanded and pyrolytic graphites had a slight negative effect on the electrochemical properties of modified electrodes. The respiratory activity of bacterial cells did not change in the presence of nanomaterials. The data can be used in the development of microbial biosensors and MFC electrodes based on Gluconobacter cells. [ABSTRACT FROM AUTHOR]

Abstract—The results of comparative triboengineering tests of chromium coatings formed using electroplating deposition and electrodeformation cladding with a flexible tool (EDCFT) are given in this work. In the formation of coatings by the EDCFT method, sintered bars of chromium powder doped with additives of ultradispersed diamond graphite mixture (UDGM) and thermally expanded graphite were used as coating materials (donors). It has been established that, when rubbing without a lubricant, sprays of rubber on the surface of specimens with a coating with the lowest values of the coefficient of sliding friction fsl and total weight wear Δm have samples with chromium coatings formed by electroplating (ftr = 0.37, Δm = 0.2 × ten–3 d) using the EDCFT method from a donor doped with the ultradispersed diamond-graphite mixture UDGM (ftr = 0.35, Δm = 0.23 × ten–3 d). Bench tests of hydraulic cylinders with full-scale stock samples with a coating formed by the EDCFT method from chromium doped with UDGM have established full compliance of the prototypes of hydraulic cylinders with the specifications. [ABSTRACT FROM AUTHOR]

Recent years have witnessed an ever-increasing interest in developing electrochemical biosensors based on direct electron transfer-type bioelectrocatalysis. This work investigates the bioelectrocatalytic oxidation of glucose by membrane fractions of Gluconobacter oxydans cells on screen-printed electrodes modified with thermally expanded graphite and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Electrooxidation of glucose was shown to occur without the presence of electron transport mediators. Chronoamperometric and cyclic voltametric characteristics showed an increase of anodic currents at electrode potentials of 0–500 mV relative to the reference electrode (Ag/AgCl). The direct electron transfer effect was observed for non-modified PEDOT:PSS as well as for PEDOT:PSS linked with crosslinkers and conductive fillers such as polyethylene glycol diglycidyl or dimethyl sulfoxide. Bioelectrodes with this composite can be successfully used in fast reagent-free glucose biosensors.

The influence of the pulse energy on the performance of copper electrodes with added graphite in the electrospark piercing of tool steel is studied. With increase in the pulse current, the electrode wear increases, if the other parameters are unchanged. In absolute terms, the wear is less in the presence of thermally expanded graphite and greater in the presence of colloidal graphite. [ABSTRACT FROM AUTHOR]

The influence of the turning parameters on the surface roughness of composites based on thermally expanded graphite is considered. The dependence of the cutting force on the turning parameters is determined. A formula is proposed for the cutting force on composites based on thermally expanded graphite as a function of the selected machining conditions. [ABSTRACT FROM AUTHOR]

To create a fire retardant coating that can be applied in the hydrocarbon fire, the nanocomposites of the ethylene-vinyl acetate (EVA) copolymer with montmorillonite (MMT), thermally expanded graphite (EG) are synthesized and their structure, physicochemical and thermal properties are studied. Using IR spectroscopy and X-ray phase analysis, it is found that the EVA nanocomposites with montmorillonite and nanographite obtained in solution and melt have the same structure. Thermal-oxidative degradation of the EVA copolymer and nanocomposites on its basis in the temperature range of 100-700 °C is investigated. It is proved that nanoclay and nanographite as a part of nanocomposites increase thermal characteristics of the original polymers. The thermal stability of the studied compounds increases in the series: polymer

The electrical and thermal conductivities of polymer nanocomposites based on ultrahigh molecular weight polyethylene (UHMWPE) and high-density polyethylene (HDPE) were studied with a segregated and random distribution of the nanofiller, which was taken as thermally expanded graphite (TEG). The segregated structure has an ordered 3D distribution of filler particles in a framework in a polymer matrix with a high local concentration φloc, which is significantly higher than the average φ for the entire volume of the composite, φloc » φ. Concentration dependence of electrical conductivity is describedby the percolation equation with percolation thresholds-0.5 and 6.9 vol.%, critical exponent σ0-4.0 and 2.6, parameter ς0 - 530 and 0.43 S/cm for the segregated and statistical systems, respectively. Thermal conductivity for both systems is describedby a parallel model, which can be explained by the lengthy structure of the filler in the volume of the polymer. The segregated structure has a higher thermal conductivity of the filler λ, = 33 W/m-K versus λf = 15 W/m-K for the random distribution of the filler. The higher values of conductivity parameters λf σ0, and lower percolation threshold φc for the segregated structure are explained by the high local concentration of filler particles in the framework, which ensures better transfer of electrical and heat flow through the presence of direct contacts of particles in the framework compared to its random distribution. [ABSTRACT FROM AUTHOR]