Limited Oxidation of Irradiated Graphite Waste to Remove Surface Carbon-14

Tara E. Smith,Shilo Mccrory,Mary Lou Dunzik-Gougar 한국원자력학회 2013 Nuclear Engineering and Technology Vol.45 No.2

Large quantities of irradiated graphite waste from graphite-moderated nuclear reactors exist and are expected to increase in the case of High Temperature Reactor (HTR) deployment [1,2]. This situation indicates the need for a graphite waste management strategy. Of greatest concern for long-term disposal of irradiated graphite is carbon-14 (14C), with a half-life of 5730 years. Fachinger et al. [2] have demonstrated that thermal treatment of irradiated graphite removes a significant fraction of the 14C, which tends to be concentrated on the graphite surface. During thermal treatment, graphite surface carbon atoms interact with naturally adsorbed oxygen complexes to create COx gases, i.e. “gasify” graphite. The effectiveness of this process is highly dependent on the availability of adsorbed oxygen compounds. The quantity and form of adsorbed oxygen complexes in pre- and post-irradiated graphite were studied using Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Xray Photoelectron Spectroscopy (XPS) in an effort to better understand the gasification process and to apply that understanding to process optimization. Adsorbed oxygen fragments were detected on both irradiated and unirradiated graphite; however,carbon-oxygen bonds were identified only on the irradiated material. This difference is likely due to a large number of carbon active sites associated with the higher lattice disorder resulting from irradiation. Results of XPS analysis also indicated the potential bonding structures of the oxygen fragments removed during surface impingement. Ester- and carboxyl- like structures were predominant among the identified oxygen-containing fragments. The indicated structures are consistent with those characterized by Fanning and Vannice [3] and later incorporated into an oxidation kinetics model by El-Genk and Tournier [4]. Based on the predicted desorption mechanisms of carbon oxides from the identified compounds, it is expected that a majority of the graphite should gasify as carbon monoxide (CO) rather than carbon dioxide (CO2). Therefore, to optimize the efficiency of thermal treatment the graphite should be heated to temperatures above the surface decomposition temperature increasing the evolution of CO [4].

LIMITED OXIDATION OF IRRADIATED GRAPHITE WASTE TO REMOVE SURFACE CARBON-14

Smith, Tara E.,Mccrory, Shilo,Dunzik-Gougar, Mary Lou Korean Nuclear Society 2013 Nuclear Engineering and Technology Vol.45 No.2

Large quantities of irradiated graphite waste from graphite-moderated nuclear reactors exist and are expected to increase in the case of High Temperature Reactor (HTR) deployment [1,2]. This situation indicates the need for a graphite waste management strategy. Of greatest concern for long-term disposal of irradiated graphite is carbon-14 ($^{14}C$), with a half-life of 5730 years. Fachinger et al. [2] have demonstrated that thermal treatment of irradiated graphite removes a significant fraction of the $^{14}C$, which tends to be concentrated on the graphite surface. During thermal treatment, graphite surface carbon atoms interact with naturally adsorbed oxygen complexes to create $CO_x$ gases, i.e. "gasify" graphite. The effectiveness of this process is highly dependent on the availability of adsorbed oxygen compounds. The quantity and form of adsorbed oxygen complexes in pre- and post-irradiated graphite were studied using Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Xray Photoelectron Spectroscopy (XPS) in an effort to better understand the gasification process and to apply that understanding to process optimization. Adsorbed oxygen fragments were detected on both irradiated and unirradiated graphite; however, carbon-oxygen bonds were identified only on the irradiated material. This difference is likely due to a large number of carbon active sites associated with the higher lattice disorder resulting from irradiation. Results of XPS analysis also indicated the potential bonding structures of the oxygen fragments removed during surface impingement. Ester- and carboxyl-like structures were predominant among the identified oxygen-containing fragments. The indicated structures are consistent with those characterized by Fanning and Vannice [3] and later incorporated into an oxidation kinetics model by El-Genk and Tournier [4]. Based on the predicted desorption mechanisms of carbon oxides from the identified compounds, it is expected that a majority of the graphite should gasify as carbon monoxide (CO) rather than carbon dioxide ($CO_2$). Therefore, to optimize the efficiency of thermal treatment the graphite should be heated to temperatures above the surface decomposition temperature increasing the evolution of CO [4].

그라파이트/구리 복합재료의 기계적 특성에 미치는 그라파이트 형상과 복합재료 제조방법의 영향

손유한,한준현,Sohn, Youhan,Han, Jun Hyun 한국재료학회 2018 한국재료학회지 Vol.28 No.10

To study the effects of graphite shape and the composite fabricating method on the mechanical properties of graphite/copper (Gr/Cu) composites, a copper composite using graphite flakes or graphite granules as reinforcing phases is fabricated using mechanical mixing or electroless plating method. The mechanical properties of the Gr/Cu composites are evaluated by compression tests, and the compressive strength and elongation of the Gr/Cu composites using graphite granules as a reinforcing phase are compared with those of Cu composites with graphite flakes as a reinforcing phase. The compressive yield strength or maximum strength of the Gr/Cu composites with graphite granules as a reinforcing phase is higher than that of the composites using graphite flakes as a reinforcing phase regardless of the alignment of graphite. The strength of the composite produced by the electroless plating method is higher than that of the composite material produced by the conventional mechanical mixing method regardless of the shape of the graphite. Using graphite granules as a reinforcing phase instead of graphite flakes improves the strength and elongation of the Gr/Cu composites in all directions, and reduces the difference in strength or elongation according to the direction.

Synthesis and Characterization of Fluorinated Graphite with High Crystallinity

송은지,정민정,이영석 한국공업화학회 2018 한국공업화학회 연구논문 초록집 Vol.2018 No.0

In this study, the direct fluorination on graphite was suggested for high fluorine contents on graphite surface and crystallinity. The prepared graphite were labelled as G-4F (fluorinated graphite at 400 °C) and G-4F-6V (Heat treatment at 600 °C in vacuum after fluorination). From XPS data, after fluorination at 400 °C, 19.1 at.% of fluorine was introduced on graphite. G-4F-6V has 20.0 at.% of fluorine, most of the fluorine remains in G-4F-6V. After fluorination at 400 °C, it can be confirmed that the graphite structure collapses. However, the XRD result of G-4F-6V was similar to graphite structure. In case of the G-4F-6V, despite changing to graphite structure after heat treatment in a vacuum state, high contents of fluorine are present on the surface. It is believed that the fluorinated graphite is recovered to the graphite structure as fluorocarbon exits from the fluorinated graphite while the unstable decomposition gas such as F₂ re-reacts with the graphite surface.

Effects of solvent extraction on the microstructure of bituminous coal-based graphite

Wang Lipeng,Yao Zongxu,Guo Zhimin,Shen Xiaofeng,Li Zhiang,Zhou Zhengqi,Wang Yuling,Yang Jian-Guo 한국탄소학회 2022 Carbon Letters Vol.32 No.3

Coal-based graphite has become the main material of emerging industries. The microstructure of coal-based graphite plays an important role in its applications in many fields. In this paper, the effect of carbon disulfide/N-methyl-2-pyrrolidone solvent mixture extraction on the microstructure of bituminous coal-based graphite was systematically studied through preliminary extraction coupled with high-temperature graphitization. The graphitization degree g (75.65%) of the coal residue-based graphite was significantly higher than that of the raw coal-based graphite. The crystallite size La of the coal residue-based graphite was reduced by 47.06% compared with the raw coal-based graphite. The ID/ IG value of the coal residue-based graphite is smaller than that of the raw coal-based graphite. The specific surface area (16.72 m2/g) and total pore volume (0.0567 m3/g) of the coal residue-based graphite are increased in varying degrees compared with the raw coal-based graphite. This study found a carbon source that can be used to prepare coal-based graphite with high graphitization degree. The results are expected to provide a theoretical basis for further clean and efficient utilization of the coal residue resources.

Expanded Graphite 산화물과 자성 나노입자의 복합화와 자기적 특성

노일표(Il Pyo Roh),임현준(Hyun Joon Yim),강명철(Myung Chul Kang),이찬혁(Chan Hyuk Rhee),심인보(In-Bo Shim) 한국자기학회 2012 韓國磁氣學會誌 Vol.22 No.1

The composites of expanded graphite oxide and magnetic nanoparticle (Ni and Co) were synthesized by using simple chemical method. From the raw material natural graphite, the expanded graphite was fabricated using sulfuric acid and 1st heat treatment at 600 ℃ for 1 hour. The expanded graphite was changed to expanded graphite oxide by 2<SUP>nd</SUP> heat treatment at 1050℃ for 15 sec and chemical oxidation. The expanded graphite oxide/1-methyl-2-pyrrolidone solution reacts with the magnetic nanoparticle to form a magnetic graphite oxide composite. These graphite-based materials were characterized by x-ray diffractometer, Raman spectroscopy, transmission electron microscope, and vibration sample magnetometer. We expect that these results of this paper were become basis research of graphite oxide composite.

On the Mechanism of the Formation of Widmanstatten Graphite in Flake Graphite Cast Irons

Jr Carl R.Loper,Park, Junyoung 대한금속재료학회 2003 METALS AND MATERIALS International Vol.9 No.4

The mechanism whereby Widmanstatten graphite develops during the solidification of flake graphite cast irons has been found to involve the preferential segregation and a complex interaction of specific elements at the surface of the graphite flake during solidification and the development of the plate like appendages in the solid austenite adjacent to the graphite flake. The literature has suggested that lead, calcium and hydrogen may bc causal to the formation of Widmanstatten graphite. hut has the interaction of these elements has not been effectively documented. While the formation of this degraded graphite is often attributed to the presence of a sufficient amount of lead alone, it has been observed that Widmansatten graphite develops only in conjunction with a combination of factors operative at the graphite-austenite intertace. Commercial flake graphite cast irons may exhibit Widmanstatten graphite as a function of lead and calcium content in the iron, moisture content in the molding media, solidification cooling rate and the rate of cooling immediately after solidification, etc. Lead contamination of cast irons was also observed to increase the chilling tendency of the iron. The detrimental effects of lead can be counteracted by the presence of rare earths in the iron, where rare eanh elements react with lead to form stable. high melting point compounds.

Artificially-built solid electrolyte interphase via surface-bonded vinylene carbonate derivative on graphite by molecular layer deposition

Chae, Seulki,Lee, Jeong Beom,Lee, Jae Gil,Lee, Tae-jin,Soon, Jiyong,Ryu, Ji Heon,Lee, Jin Seok,Oh, Seung M. Elsevier 2017 Journal of Power Sources Vol.370 No.-

<P><B>Abstract</B></P> <P>Vinylene carbonate (VC) is attached in a ring-opened form on a graphite surface by molecular layer deposition (MLD) method, and its role as a solid electrolyte interphase (SEI) former is studied. When VC is added into the electrolyte solution of a graphite/LiNi<SUB>0.5</SUB>Mn<SUB>1.5</SUB>O<SUB>4</SUB> (LNMO) full-cell, it is reductively decomposed to form an effective SEI on the graphite electrode. However, VC in the electrolyte solution has serious adverse effects due to its poor stability against electrochemical oxidation on the LNMO positive electrode. A excessive acid generation as a result of VC oxidation is observed, causing metal dissolution from the LNMO electrode. The dissolved metal ions are plated on the graphite electrode to destroy the SEI layer, eventually causing serious capacity fading and poor Coulombic efficiency. The VC derivative on the graphite surface also forms an effective SEI layer on the graphite negative electrode via reductive decomposition. The detrimental effects on the LNMO positive electrode, however, can be avoided because the bonded VC derivative on the graphite surface cannot move to the LNMO electrode. Consequently, the graphite/LNMO full-cell fabricated with the VC-attached graphite outperforms the cells without VC or with VC in the electrolyte, in terms of Coulombic efficiency and capacity retention.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ring-opened VC is chemically bonded on graphite surface through MLD method. </LI> <LI> The attached VC copies reduction behavior of VC as additives generating SEI via C=C. </LI> <LI> VC-attached graphite outperforms the pristine graphite in both half cell and full cell. </LI> <LI> VC molecules added in electrolyte generate acid when oxidized. </LI> <LI> The acid generated by VC oxidation accelerates transition metal dissolution from LNMO. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Bulk graphite: materials and manufacturing process

Sang-Min Lee,Dong-Su Kang,Jea-Seung Roh 한국탄소학회 2015 Carbon Letters Vol.16 No.3

Graphite can be classified into natural graphite from mines and artificial graphite. Due to its outstanding properties such as light weight, thermal resistance, electrical conductivity, thermal conductivity, chemical stability, and high-temperature strength, artificial graphite is used across various industries in powder form and bulk form. Artificial graphite of powder form is usually used as anode materials for secondary cells, while artificial graphite of bulk form is used in steelmaking electrode bars, nuclear reactor moderators, silicon ingots for semiconductors, and manufacturing equipment. This study defines artificial graphite as bulk graphite, and provides an overview of bulk graphite manufacturing, including isotropic and anisotropic materials, molding methods, and heat treatment.

Surface engineering of graphite anode material with black TiO_2-x for fast chargeable lithium ion battery

Kim, Dae Sik,Chung, Dong Jae,Bae, Juhye,Jeong, Goojin,Kim, Hansu Elsevier 2017 ELECTROCHIMICA ACTA Vol.258 No.-

<P><B>Abstract</B></P> <P>One of the most important challenges in the improvement of the lithium ion battery (LIB) for electric vehicle (EV) applications is its fast charging capability. However, currently used graphite anode materials cannot meet this requirement for EVs. Herein, we demonstrate that surface modification of graphite using oxygen-deficient black titanium oxide (TiO<SUB>2−x</SUB>) is an efficient way to improve the fast charging capability of graphite anode material for LIB. The proposed surface engineered anode material, 1 wt% TiO<SUB>2-x</SUB> coated graphite anode material, at a high rate of 5 C-rate, exhibited 98.2% of the capacity obtained at a rate of 0.2 C without any degradation of other performances. Full cell tests adopting LiCoO<SUB>2</SUB> as a cathode material with TiO<SUB>2-x</SUB> coated graphite anode material also confirmed that the TiO<SUB>2-x</SUB> coating layer can improve the fast charging capability of graphite anode material. Such an improvement in the fast charging capability has mainly been attributed to the modified interface between the anode and the electrolyte by surface-engineering of the TiO<SUB>2-x</SUB> layer on the surface of graphite. These results show that the approach presented in this work, interfacial engineering of graphite using oxygen deficient TiO<SUB>2-x</SUB>, deserves to be regarded as one of the most promising ways to develop an anode material with fast charging capability for high power LIB for EV applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Core shell structured TiO<SUB>2-x</SUB>@graphite was synthesized via sol-gel method. </LI> <LI> TiO<SUB>2-x</SUB>@graphite anode showed much improved fast charging capability. </LI> <LI> Fast charging capability of TiO<SUB>2-x</SUB>@graphite was confirmed using full cell. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>