The scalable production of high-quality nanographite by organic radical-assisted electrochemical exfoliation.

One of the promising ways to produce graphene is the technology of graphite splitting or exfoliation, both by physical or mechanical and chemical, including electrochemical methods. The product of electro exfoliation is nanographite, which is transformed into multigraphene at the subsequent stage of liquid-phase mechanical and ultrasonic disintegration. This approach demonstrates a successful method of obtaining multigraphene from available graphite raw materials. Since, already at a potential of 1.23V, during the electrolysis of water on a graphite anode, the hydroxyl anion is discharged with the formation of a very active hydroxyl radical oxidizer, it is not surprising that when the graphite electro exfoliation process is overvolted at 10V, graphite oxidation products are formed. In order to control the defectiveness of the graphene lattice by oxidation products, we carried out processes of graphite exfoliation in the presence of both a number of reducing agents ascorbic acid, sodium borohydride, hydrazine hydrate, and in the presence of industrial antioxidants radical traps (2,2,6,6-tetramethylpiperidine-1-il)oxyl (TEMPO), (2,2,6,6-tetramethyl-4 oxo-piperidine-1-yl)oxyl (IPON), a mixture of 5,8,9-bis isomers[(2,2,6,6-tetramethyl - 4 oxo-piperidine-1-yl)]-{5,8,9-[1,1’- bi(cyclopentylidene)]-2,2’,4,4’- tetraene}(YARSIM-0215). It should be noted, that the best result of preventing the oxidation of nanographite in electro exfoliation technology in our studies is the ratio of carbon to oxygen (C/O) about 69.

Development of rGO/Fe3O4 Composites as Glucose Biosensors

The rGO/Fe3O4 composite is one type of composites that can be used as a biosensor material, especially glucose sensors. The main ingredients of the composite synthesis are graphite and iron sand. The synthesis process of Fe3O4 was done using the coprecipitation method, while the graphite oxidation process was accomplished using the modified Hummer's method. The composites were formed using the ex-situ wet mixing method. The formed iron sand and graphite were characterized using FTIR and XRD, and it was found that Fe3O4 was formed from the appearance of the Fe-O bond, the oxidation process of graphite was seen from the appearance of the C=O bond, and the detection of Fe peaks corresponded to the cubic crystal plane. Likewise, the composites formed were also characterized using FTIR and XRD for identification of the rGO/Fe3O4 composite formation. It was proven from the presence of Fe-O and C-O bonds and the appearance of an amorphous peak of rGO in the XRD results. The performance of the rGO/Fe3O4 composites as the glucose biosensor was examined by varying the mass of Fe3O4 on the composite, using UV-Vis spectroscopy. The performance of the rGO/Fe3O4 composite biosensor in absorbing glucose reached optimum at a mass variation of 0.3 grams of Fe3O4, as demonstrated by by the lowest absorbance peak with an intensity of 0.0048 at a wavelength of 440 nm, corresponding to glucose entrappment of 7.1 mg/gram.

High Temperature Aged Leakage Relaxation Screening Tests on Confined Flexible Graphite Gaskets

Flexible graphite-based gaskets are used extensively in high-temperature applications as a replacement of asbestos based gaskets. The effect of aging and temperature exposure of flexible graphite sheet gaskets was the subject of a previous work [1,2], however, the effect when flexible graphite is in a confined gasket configuration is not known. This study outlines the performance evaluation of the elevated temperature behavior of flexible graphite-based gaskets under a confined configuration and exposed over a long period employing HALR (High temperature Aged Leakage Relaxation) fixture. This ARLA-like fixture can retain the mechanical feature of the ATRS/HATR while allowing the cold leakage rate and weight loss measurement. Four different confined gasket configurations, namely corrugated metal, spiral wound, kammprofile and double jacketed, are evaluated within a temperature range of (427 to 649 °C) 800 to 1200 °F and exposure time of 2500 hours. Graphite weight loss, gasket thickness change, leakage and tightness parameter, creep and relaxation measurements were taken at regular intervals for each gasket style. To better understand the aging process, these critical mechanical and leakage properties are scrutinized; the degradation process related to mainly graphite oxidation is further discussed, and a conclusion is drawn.

Analysis of methods for increasing the oxidation resistance of carbon-graphite products used in metallurgical and chemical units

This review study analyses the existing methods for increasing the oxidation resistance of carbon-graphite products, as well as assesses their applicability in metallurgical and chemical units. The reseach basis was the data published on the oxidation mechanism of carbon-graphite materials, conditions for their use in metallurgical and chemical processes, as well as existing technologies aimed at improving the oxidation resistance of artificial graphites. The existing ideas about the kinetics of carbon graphite oxidation are described depending on temperature conditions. A review of existing technologies for increasing the oxidation resistance of materials and their economic efficiency, taking into account the conditions of their operation, was carried out. Prospects of the presented solutions for the units of metallurgical and chemical industries were analysed. Three modes of oxidation of graphitised materials were distinguished on the basis of operating conditions, chemical and physical properties. According to this classification, the most rational method for increasing oxidation resistance consists in the impregnation of carbon-graphite materials with the formation of a protective glassy coating in the volume of through pores or with the formation of a coating (a continuous layer on the surface of the product) due to the occurrence of a chemical reaction with the reagents used. For most metallurgical and chemical units, the impregnation of carbon-graphite materials with the formation of borate and phosphate glasses is preferable, primarily due to lower economic costs. The applicability of this method is currently limited by temperature conditions, at which the protective properties and continuity of the formed glassy coatings are preserved. Therefore, additional research is required to adapt the conventional technological and technical solutions to the high-temperature conditions of metallurgical units (over 800°C).

Accelerated Synthesis of Graphene Oxide from Graphene

Graphene oxide (GO) is an oxygenated functionalized form of graphene that has received considerable attention because of its unique physical and chemical properties that are suitable for a large number of industrial applications. Herein, GO is rapidly obtained directly from the oxidation of graphene using an environmentally friendly modified Hummers method. As the starting material consists of graphene flakes, intercalant agents are not needed and the oxidation reaction is enhanced, leading to orders of magnitude reduction in the reaction time compared to the conventional methods of graphite oxidation. With a superior surface area, the graphene flakes are quickly and more homogeneously oxidized since the flakes are exposed at the same extension to the chemical agents, excluding the necessity of sonication to separate the stacked layers of graphite. This strategy shows an alternative approach to quickly producing GO with different degrees of oxidation that can be potentially used in distinct areas ranging from biomedical to energy storage applications.

Thermodynamic Analysis of Radioactive Graphite Oxidation in NiO-NaCl-KCl-Na2CO3-K2CO3 Melt in the Atmosphere of Argon

Behavior of U, Pu radionuclides was investigated when heating radioactive graphite in NaCl – KCl – Na2CO3 – K2CO3 melt with NiO additives using the thermodynamic modeling method. Calculations were made by the TERRA software that is used for the determination of phase composition, thermodynamic and transport properties, taking into account chemical and phase changes in temperature range 373 – 3273 K. Calculation of equilibrium phase composition and parameters of equilibrium was carried out using reference information about properties of the individual substances (INVATERMO, HSC, etc.). This study demonstrates that at a temperature of 1273 K the condensed carbon burns down with the formation of CO and CO2. Increasing temperature to 1673 K causes the condensed compounds of uranium to evaporate. This study determined that uranium exists in the form of ionized UO−3 in temperature range from 1673 to 3273 K. Plutonium exists in the form of gaseous PuO2, PuO in temperature range 2373 – 3273 K. Keywords: thermodynamic modeling, radionuclides, radioactive graphite