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.

Graphite intercalated compounds (GICs) with different stage numbers were prepared from highly oriented pyrolytic graphite (HOPG) and nitric acid using a chemical method. Exfoliated graphite (EG-T) was synthesized from GICs by water treatment followed by thermal shock. The effects of the graphite oxidation depth on the EG-T thermal expansion coefficient, volatile content, and total porosity were examined. However, the main purpose of this work was investigation of the dependence of the inner EG-T pore structure on the level of oxidation. Thus, we studied the micro- and mesopore structure and specific surface area by nitrogen porosimetry and the modern 2D-NLDFT method to calculate the pore size distribution and pore volume. As well, we performed a mercury porosimetry experiment to determine the macropore characteristics. We examined the pore space using a number of scanning electron micrographs of EG-T particle cross-sections using an image processing technique. In this way we showed the strong correlation between the EG-T pore structure parameters and oxidation depth of graphite.

A 2D-NLDFT-HS study is performed of the effect the state of oxidation of the graphite matrix has on the parameters of micro-, meso-, and macropore structures of thermally expanded graphite (TEG). A wide range of the stage numbers of graphite intercalation compounds synthesized from natural flake graphite of the same grade is considered, along with the intercalant that is used and the particle size of the original graphite. The 2D-NLDFT-HS model provides a more accurate description of low-temperature nitrogen adsorption/desorption isotherms than other means.

Introduction. Intumescent flame retardants are intensively used as passive fire protection means. Under fire conditions, these coatings foam and turn into coke, which turns into ash. These products have various fire resistant properties. These transformations are possible due to the foaming process, whose kinetics determines the fire protective characteristics of the compositions used. The paper considers the kinetics of the foaming process in the course of the pyrolysis of four different foaming compositions. The classical triad was used as a thermally expanding agent for the three of them, it includes ammonium polyphosphate, pentaerythritol, and melamine, and the fourth one has intercalated graphite.Research methods. Thermal analysis is widely used to identify and study various materials, substances and fire retardants. However, we have not found any kinetic studies performed using methods of thermal analysis in the literature. In this work, methods of non-isothermal kinetics are used to identify the mechanism of foaming. For this purpose, four series of thermogravimetric tests were carried out at different heating rates for each composition under study. The results of the experiment made it possible to solve inverse and direct kinetic problems and identify mechanisms of the processes.Results and discussion. Methods of non-isothermal kinetics were employed to show that low-temperature stages of thermolysis can be considered as gross-one-stage processes for all samples. The solution of the direct kinetic problem has helped to identify that the limiting foaming stage is described by the Avrami – Erofeev equation for all compositions under study, while the values of kinetic parameters differ significantly. Consequently, foaming proceeds are similar for samples having different compositions. The foaming of the sample containing intercalated graphite depends on heating conditions.Conclusions. It was identified that the studied compositions transform into the viscous-fluid state at high temperatures. In this case, the limiting stage of the foaming process is the nucleation of primary bubbles in the volume of the liquid phase. This process determines the kinetics of foaming, coke properties and its thermophysical characteristics.

A composite material based on expanded graphite (EG) and copper compounds was obtained by natural graphite oxidation with 95% nitric acid, copper (II) nitrate and granular carbamide addition with further rapid heat treatment at three different exfoliation temperatures: 800, 1000 and 1200 °С. It was found that the composition of copper containing graphite material depends on the temperature and the atmosphere of thermal expansion. The formation of copper oxides can be eliminated if rapid heat treatment is conducted in nitrogen at 1200 °С. Thermal conductive properties: thermal diffusivity and specific heat capacity of obtained Cu-expanded graphite samples were measured. It was revealed that the dependence of thermal conductivity (TC) of Cu-graphite material has non-linear character in the studied range of copper content. The incorporation of 3% copper into expanded graphite allows to increase its thermal conductivity by 20% while the further Cu content growth leads to the TC decrease from 6 to 4.5 W/(m∙K). The specific heat capacity is constant at ω(Cu)<3% and reduces in the range (3‒8)% Cu. The advantage of proposed technique of Cu-expanded graphite materials preparation is exclusion graphite intercalation compounds hydrolysis step with further drying because of carbamide addition.

Laser-flash method and thermal analysis were used to determine the heat conductivity and linear thermal expansion coefficient for the low-density carbon-carbon materials based both on the graphite-foam of two types differing by the graphite matrix defective factor and on the pyrolized carbon. It is shown that the thermal conductivity is mostly affected by the density after compression but not by the carbon components ratio. The carbon-carbon material based on electrochemical graphite-foam has a low thermal conductivity λ = 0,5‒2,0 W/(m·K) in a wide temperature range (30‒900 °С) whereas the low thermal conductivity is inherent in the conventional graphite-foam material at high temperatures only.

The laser flash method is used to determine the temperature dependences of the thermal conductivity of graphite foams that differ in the defectiveness of their graphite matrix. It is shown that the heat capacity of the materials which were obtained is independent of the method used to make them. The thermal conductivity of specimens of graphite foam obtained at 1000°C decreases with an increase in temperature, while that of specimens of graphite foam obtained at 400°C remains nearly constant. The thermal conductivity 0.46 W/(m·K) that was achieved is comparable to the thermal conductivity of graphite felt.

The composition of gas evolved upon thermal decomposition of individual and carbamidemodified graphite nitrates was determined. The addition of carbamide was shown to result in the 2-4-fold decrease in the content of nitrogen oxides and the 2-5-fold increase in the content of carbon monoxide. The content of nitrogen oxides in the gas phase decreased when the HNO3 : (NH2)(2)CO molar ratio was equal to 1 : (0.4-1). Combination of carbamide addition with catalytic afterburning provides the 5-fold decrease in the gas-phase amount of nitrogen oxides at the minimum CO content.

The approach for graphite laminated materials strength properties prediction using contact angle measurements was proposed. The tensile strength of laminated materials made of graphite foil and stainless steel with acrylic and silicone adhesives was measured. It was shown that tensile strength depends on energy characteristics of polymer binders, which can be determined by simple and express wetting method. It was found that the highest values of tensile strength, strength of adhesion and the work adhesion to graphite and stainless steel were provided by acrylic adhesive MBM-5C. The delamination occurred when graphite and stainless steel sheets were connected with low surface energy silicone resin, γ = 23 mJ/m2, what was not able to maintain sufficient adhesion level to the both types of attached surfaces: polar steel and non-polar graphite. It was demonstrated that the calculation of the work of adhesion to polar and non-polar model liquids (water and octane respectively) can be applied to optimize the choice of polymer binder and design of laminated materials. It’s quite important that the proposed technique doesn’t require to determine free surface energy for each type of sheet material which is especially difficult and complex task if laminate consists of several different layers.

We present a method for evaluating elastic properties of a composite material produced by molding a resin filled with short elastic fibers. A flow of the filled resin is simulated numerically using a mesh-free method. After that, assuming that spatial distribution and orientation of fibers are not significantly changed during polymerization, effective elastic moduli of the composite material are evaluated. The developed micro-mechanical mathematical modelling of effective moduli is aimed to molding process optimization which results in product quality improvement.

Low density heat-conducting carbon-carbon materials containing coke from 2.8 to 40 wt.% and with density varying in the range from 0.065 to 0.81 g/cm3 are prepared by uniaxial compaction of graphite foam with subsequent impregnation with an acetone solution of propargylated novolac resin and coking. It is shown that mechanical strength of specimens increases in proportion to the coke content within them in the range from 17 to 40 wt.%, and thermal conductivity is almost unchanged and is within the limits of 2.5 – 3.2 W/(m·K).

The elastic moduli of a composite material made of high-temperature modified phenolic resins with short carbon fibers are studied. Several analytical formulas used to determine the effective moduli of such composites are compared and experimentally verified.

Polymeric matrices for composites have a number of unique properties. Their improvement is actual task for researchers. Material with required properties can be gotten by varying matrix composition and proper selection of modifier. It is known that modifier with graphite nature improves electric and thermo conductivity, but its influence on mechanical properties is unsertain. It was shown in this research that strength and fracture toughness of modified polymeric matrices become worse, but tensile and flexure elastic modulus increases. It was found that water absorption of samples increases with modifier addition without dependence of its nature and concentration

This paper examines reactions of stage I and II FeCl3-graphite intercalation compounds (GICs) with intercalants of different strengths: nitric acid and tetrahydrofuran (THF). The reaction of GIC-FeCl3 with nitric acid, a strong intercalant, leads to HNO3 substitution for the FeCl3 in the interlayer spaces of the graphite and formation of a stage II GICs with HNO3. THF, a weak intercalant, does not form any compounds with a stage I or II GIC with FeCl3; instead, it diffuses to intercrystalline regions of the graphite host. Flash heating of the synthesized GICs in air leads to the formation of exfoliated graphite (EG) containing α-Fe2O3 particles, which has low bulk density, down to 6.5 g/L, and high ferric oxide content, up to 33 wt %. Reduction in flowing hydrogen at 600°C leads to the formation of EG with up to 23 wt % α-Fe particles supported on it and with a saturation magnetization of 50 emu/g.

Работа посвящена изучению взаимодействия интеркалированных соединений графита (ИСГ) с FeCl3 I и II ступеней с интеркалатами различной силы: азотной кислотой и тетрагидрофураном (ТГФ). Взаимодействие ИСГ-FeCl3 с сильным интеркалатом азотной кислотой приводит к замещению FeCl3 из межплоскостных пространств графита на HNO3 и образованию ИСГ с HNO3 II ступени. Слабый интеркалат ТГФ при взаимодействии c ИСГ-FeCl3 I и II ступеней не образует новых соединений, а лишь диффундирует в межкристаллитные области графитовой матрицы. При термоударе полученных ИСГ образуется терморасширенный графит (ТРГ) с частицами -Fe2O3, отличающийся низкой насыпной плотностью до 6.5 г/л и высоким содержанием оксида железа до 33 мас. %. При восстановлении данного ТРГ в токе водорода при 600°C происходит образование ТРГ с нанесенными частицами -Fe, содержанием 23 мас. % и намагниченностью насыщения 50 эме/г.

The graphite nitrate of the first step was obtained by anodic oxidation of natural graphite in the 90% solution of nitric acid. Structural, heat-conducting properties of compacted expanded graphite were studied. It was shown that both the plenty of structural defects and low critical density allow to obtain material with reduced thermal conductivity up to 0.4 W/(mK).

The liquid hydrocarbon sorption behavior of expanded graphite (EG) enhanced with iron phases (α-Fe, α-Fe2O3, Fe3O4, and FeOOH) was studied. Iron phases were shown not to affect the porous structure of EG or its sorption capacity. The utilization of the three EG samples with the high magnetic saturation (10.5, 30, and 35emu/g) as magnetic sorbents for the petroleum products spill response was considered. The requirements in values of the magnetic saturation of EG to be attracted by a magnet were estimated. Also, the water sorption of EG was studied, which competes with liquid hydrocarbons for pore spaces. The method of the dynamic contact angle measurement in water is suggested as a useful characterization of EG surface chemistry for this application.