Graphite Pellets Research Articles

Holistic valorization of fayalitic slag to pig iron and glass fibers

A valorization process for fayalitic copper slags is presented. A primary copper slag is reduced via carbothermic reduction thus creating a pig iron phase and a secondary copper slag, which is used for glass fiber production. The carbothermic reduction is carried out with graphite pellets or carbon fibers as an alternative reduction agent in crucibles within a furnace using inductive heating. The experiments are prepared and evaluated using FactSage 8.1. Carbon is used with an excess of 10% of the calculated value. The effect of temperature variation and turbulence on the carbothermic reduction process are studied. Glass fiber drawing is realized manually after remelting the secondary copper slag. The threshold for successful glass fiber production lays at a FeOx content below 10 wt%. The produced pig iron phase as well as the resulting glass fibers are characterized, while their industrial applicability is discussed.

Investigation of Reduction Mechanism and the Effect of NaCl-CaCl2 Mixture on Tungsten Production from Tungsten Sulfide

Tungsten powder production from its sulfide by constant voltage electrochemical reduction was studied in CaCl2-NaCl salt solutions by varying composition at 750 °C. The mechanism of the reduction process was investigated by means of linear sweep voltammetry analysis using three electrodes; tungsten reference, graphite and WS2 porous pellet in eutectic CaCl2-NaCl salt mixture. The characterization studies were performed by X-ray Diffraction analysis and Scanning Electron Microscope. The produced powder contained tungsten produced by the complete reduction of WS2 with some by-products containing mainly Ca compounds. Tungsten could be separated successfully from the by-products after an acid treatment using dilute HCl. Furthermore, it was observed that the increase in CaCl2 could lead to an approximate doubling of the reduction rate within the parameter ranges covered in this study.

Chemical interaction of Y2O3 coating with U-Zr-Nd metallic fuel during casting

The interaction between molten metals and ceramic coating materials was studied to minimize fuel material loss and develop a reusable crucible for fuel melts. U-Zr-Nd alloy and pure Nd were used as metal melts while the substrate pellets were Y2O3-plasma-spray-coated graphite. The metals were melted using the sessile drop test method on Y2O3-coated graphite pellets. All Y2O3 coating layers of the specimens detached from the graphite specimens and attached to the molten metals because of their reactivity. Furthermore, a microstructural analysis of the specimens was performed after droplet testing. The results revealed that (Nd,Y)2O3 compounds were formed by the reaction between Nd and Y2O3 coating during the U-Zr-Nd fuel melting on the substrate.

Crumpled few-layer graphene: Connection between morphology and optical properties

Comprehensive characterization of crumpled graphene materials is required to understand their morphologically dependent properties. This study connects the optical properties of crumpled few-layer graphene (FLG) aerosols and colloidal suspensions with particle morphology. The mass absorption cross-section (MAC) of crumpled FLG was measured in the aerosol phase and it is shown that such aerosols absorb visible light more efficiently than soot aerosols. The UV–Vis spectra of FLG suspensions in ethanol were correlated with the mean nanoparticle layer number and the lateral size. The measured optical properties were also simulated using discrete dipole approximation (DDA) applied to volume-reconstructed particles with refractive indices of graphene and graphite from literature. The measurements were more closely reproduced using the refractive index of graphite pellets rather than flat graphene on a substrate. Moreover, we show that a simpler Rayleigh–Debye–Gans (RDG) model can predict the wavelength dependence of the crumpled FLG absorption cross-section.

A scalable electron beam irradiation platform applied for allotropic carbon transformation

The design of solid-state materials whose properties and functions can be manipulated in a controlled manner by the application of electron beam irradiation is important in modern materials chemistry and physics. In this paper, we present a progress in the development of scalable electron beam irradiation platform to obtain innovative materials for technological and industrial applications, since one of the problems to be solved in this research area is the scalability of these new nanomaterials induced by electron beam irradiation (EBI). In particular, we focus on carbon structures due to its excellent and exciting properties applied in the technological area in the last years, where we show for the first time a new strategy for carbon allotropic transformation through the portable EBI. This new platform is particularly effective, fast, versatile, clean and easy-to-use, facilitating the preparation of many types of nanomaterials that cannot be obtained by conventional chemical and physical methods. The EBI on flat graphite pellets resulted in a covering of it surface with rod-like particles composed of different allotropic forms of carbon. Furthermore, the developed system allowed the implantation of the Fe as a catalytic material through steel sputtering of the high voltage acceleration anode during the EBI process. It was observed by HRTEM analyses that the rod-like particles are preferentially composed of highly oriented graphite in its bottom, polycrystalline graphite in its middle and magnetite nanoparticles in its top.

Effect of Using Rice Husk Char as an Additive on Phosphate Recovery from Swine Wastewater by Magnesium Metal Corrosion

The recovery of phosphate from swine wastewater is highly significant in order to alleviate eutrophication in aquatic ecosystems, and the increasing scarcity in phosphorus resources. This study reports on a strategy to recover phosphate from swine wastewater using rice husk char as an additive via magnesium metal corrosion. The results demonstrated high levels of recovery efficiency at relatively low cost. When the mass ratio of rice husk char to magnesium was 2:1, the pH of this solution increased to 9.75, and the phosphate recovery efficiency from real swine wastewater reached 96.80% at a Reynolds number of 13931 without aeration. Evaluation of economic feasibility revealed that the proposed method was $0.79 kg−1 of PO4-P. Approximately 57.98% of the cost may be saved compared with the use of magnesium metal pellets coupled with graphite pellets.

Graphite-loaded cotton wool: A green route to highly-porous and solid graphite pellets for thermoelectric devices

The high porosity of thermoelectric materials is a valuable feature to ideally reduce thermal conductivity without degrading electrical conductivity. This paper describes a unique low-temperature and direct method for making highly porous yet solid graphite pellets. Cotton wools were loaded with graphite particles, and pressed to yield low-density graphite pellets. The electrical and thermal properties of the resulting pellets have been studied. A significant reduction in the heat flow through the pellets has been observed as compared to a pure graphite pellet. For the porous pellets, the electrical conductivity was slightly lower than that of pure graphite pellets due to the charge scattering processes of the highly porous network, yet the thermal conductivity was drastically reduced with enhancements in Seebeck coefficients hence, a significant improvement in the thermoelectric property. Overall, the power factor was found to increase from 0.303 μWm−1K−2 for solid graphite pellet to 0.424 μWm−1K−2 for porous graphite pellet, showing a simultaneously improved power factor and reduced thermal conductance. The approach can be extended for other good thermoelectric materials to achieve further enhancements in their properties and useful to reduce material cost.

A study of the relationship between microstructure and oxidation effects in nuclear graphite at very high temperatures

Graphite is used in the cores of gas-cooled reactors as both the neutron moderator and a structural material, and traditional and novel graphite materials are being studied worldwide for applications in Generation IV reactors. In this study, the oxidation characteristics of petroleum-based IG-110 and pitch-based IG-430 graphite pellets in helium and air environments at temperatures ranging from 700 to 1600 °C were investigated. The oxidation rates and activation energies were determined based on mass loss measurements in a series of oxidation tests. The surface morphology was characterized by scanning electron microscopy. Although the thermal oxidation mechanism was previously considered to be the same for all temperatures higher than 1000 °C, the significant increases in oxidation rate observed at very high temperatures suggest that the oxidation behavior of the selected graphite materials at temperatures higher than 1200 °C is different. This work demonstrates that changes in surface morphology and in oxidation rate of the filler particles in the graphite materials are more prominent at temperatures above 1200 °C. Furthermore, possible intrinsic factors contributing to the oxidation of the two graphite materials at different temperature ranges are discussed taking account of the dominant role played by temperature.

Dual-trap system to study charged graphene nanoplatelets in high vacuum

We discuss the design and implementation of a system for generating charged multilayer graphene nanoplatelets and introducing a nanoplatelet into a quadrupole ion trap in high vacuum. Levitation decouples the platelet from its environment and enables sensitive mechanical and magnetic measurements. The platelets are generated via liquid exfoliation of graphite pellets and charged via electrospray ionization. A single platelet is trapped at a pressure of several hundred millitorr and transferred to a trap in a second chamber, which is pumped to UHV pressures for further study.

Influence of target thickness on the release of radioactive atoms

Nowadays, intense exotic beams are needed in order to study nuclei with very short half-life. To increase the release efficiency of the fission products, all the target characteristics involved must be improved (e.g. chemical composition, dimensions, physicochemical properties such as grain size, porosity, density…). In this article, we study the impact of the target thickness. Released fractions measured from graphite and uranium carbide pellets are presented as well as Monte-Carlo simulations of the Brownian motion.

Interfacial Lithium-Ion Transfer Between Graphite Negative Electrode and Sulfide Solid Electrolyte

Introduction All-solid-state lithium secondary batteries using inorganic solid electrolytes instead of liquid electrolytes have been expected as next-generation secondary batteries with high safety and high reliability. Among the inorganic solid electrolytes, sulfide-based solid electrolyte such as Li2S-P2S5 based glass solid electrolyte has received much attention due to the high lithium-ion conductivities and room temperature pressure sintering [1]. Graphite has been used as the negative electrode materials in commercial lithium-ion batteries, and the improvement in interfacial lithium-ion transfer reaction between graphite and liquid electrolyte is recognized as an important issue and this issue should be considered in all-solid-state lithium secondary batteries. In this study, interfacial reaction between graphite and sulfide solid electrolyte was investigated. Experimental A layered electrolyte consists of 75Li2S-25P2S5 glass pellet and 1 mol dm-3 LiClO4/propylene carbonate (PC) was used in order to use lithium metal electrode as reference electrode. A three-electrode cell was assembled by using graphite sheet as working electrode, lithium metal as counter and reference electrodes. Cyclic voltammetry and electrochemical impedance spectroscopy were carried out. Results Figure 1 shows the cyclic voltammogram of the three-electrode cell using graphite sheet as working electrode. An oxidation-reduction current was observed between 0 – 0.5 V (vs. Li/Li+). Since lithium ion cannot intercalate into graphite sheet in LiClO4/PC, this oxidation-reduction peak indicates that lithium-ion intercalation/de-intercalation proceeded at the interfacial between graphite sheet and 75Li2S-25P2S5 glass pellet. In the Nyquist plot, one semi-circle was observed and assigned to interfacial lithium-ion transfer process. In the meeting, the activation energy for the interfacial lithium-ion transfer process will be discussed. Reference [1] A. Sakuda et al., Sci. Rep., 3, 2261 (2013). Acknowledgement This work was financially supported by ALCA-SPRING of the JST. Figure 1

Compatibility of Lead-Bismuth Eutectic with SiC-Coated Graphite at Elevated Temperature

Uniform coating of β-silicon carbide (β-SiC) was formed over a graphite pellet through slurry-based silicon coating followed by in situ reaction at 1873 K (1600 °C). The coated pellet was exposed to molten lead-bismuth eutectic (LBE) at 1173 K (900 °C) in static condition for 200 h. Weight loss measurement, X-ray diffraction, and secondary electron microscopy–energy-dispersive spectroscopy confirmed that the SiC coating could effectively prevent molten LBE from attacking the inner graphite material.

Mid infrared emission spectroscopy of carbon plasma

Mid infrared time-resolved emission spectra were recorded from laser-induced carbon plasma. These spectra constitute the first study of carbon materials LIB spectroscopy in the mid infrared range. The carbon plasma was induced using a Q-switched Nd: YAG laser. The laser beam was focused to high purity graphite pellets mounted on a translation stage. Mid infrared emission from the plasma in an atmospheric pressure background gas was detected by a cooled HgCdTe detector in the range 4.4–11.6μm, using long-pass filters. LIB spectra were taken in argon, helium and also in air. Despite a gate delay of 10μs was used there were strong backgrounds in the spectra. Superimposed on this background broad and noisy emission bands were observed, the form and position of which depended somewhat on the ambient gas. The spectra were digitally smoothed and background corrected. In argon, for instance, strong bands were observed around 4.8, 6.0 and 7.5μm. Using atomic spectral data by NIST it could be concluded that carbon, argon, helium and nitrogen lines from neutral and ionized atoms are very weak in this spectral region. The width of the infrared bands supports molecular origin. The infrared emission bands were thus compared to vibrational features of carbon molecules (excluding C2) of various sizes on the basis of previous carbon cluster infrared absorption and emission spectroscopic analyses in the literature and quantum chemical calculations. Some general considerations are given about the present results.

Crystallization and precipitation of phosphate from swine wastewater by magnesium metal corrosion.

This paper presents a unique approach for magnesium dosage in struvite precipitation by Mg metal corrosion. The experimental results showed that using an air bubbling column filled with Mg metal and graphite pellets for the magnesium dosage was the optimal operation mode, which could significantly accelerate the corrosion of the Mg metal pellets due to the presence of graphite granules. The reaction mechanism experiments revealed that the solution pH could be used as the indicator for struvite crystallization by the process. Increases in the Mg metal dosage, mass ratio of graphite and magnesium metal (G:M) and airflow rate could rapidly increase the solution pH. When all three conditions were at 10 g L–1, 1:1 and 1 L min–1, respectively, the phosphate recovery efficiency reached 97.5%. To achieve a high level of automation for the phosphate recovery process, a continuous-flow reactor immersed with the graphite-magnesium air bubbling column was designed to harvest the phosphate from actual swine wastewater. Under conditions of intermittently supplementing small amounts of Mg metal pellets, approximately 95% of the phosphate could be stably recovered as struvite of 95.8% (±0.5) purity. An economic analysis indicated that the process proposed was technically simple and economically feasible.

군용 연료전지 적용을 위한 Mg-Graphite 펠렛의 가수분해 반응을 이용한 수소생산

On board hydrogen generation from the hydrolysis of an active metal is very attractive due to its economical, convenient, and safe reasons. A Mg-graphite pellet has been designed as a hydrogen source for portable fuel cell. Mg (1 g) + 0.10 g graphite pellet showed an excellent hydrogen generation rate that is equivalent to 15.8 ml/g.min from its hydrolysis. The hydrogen generation rate of the pellet is significantly increased due to the galvanic corrosion by galvanic cells between Mg anode and graphite cathode in a 10.wt. % NaCl solution at a room temperature.

Thermochemical performance of magnesium hydroxide–expanded graphite pellets for chemical heat pump

Expanded graphite (EG) was used to enhance the thermal conductivity in the packed bed reactors of magnesium oxide–water (MgO–H2O) chemical heat pumps (CHP). An expanded graphite–magnesium hydroxide composite (EM) was obtained by mixing a precursor CHP material of magnesium hydroxide (Mg(OH)2) powder and EG. The composite was pelletized to achieve a diameter (ϕ) of 7.1 mm and thickness (l) ranging of 3.5–4.5 mm. Mg(OH)2 dehydration and MgO hydration in the EM pellets were investigated on the packed bed reactor of a 100-W-scale CHP experimental apparatus. The temperatures measured in the packed beds of the EM pellets, as well as the dehydration and hydration kinetics, were compared with the results obtained using a packed bed of pure Mg(OH)2 pellets (ϕ = 1.9 mm, l = 5–10 mm). The thermochemical performances of the EM pellets were analyzed as a function of the mass mixing ratio of Mg(OH)2 to EG (4:1, 8:1, and 16:1) used for preparing the EM. In both dehydration and hydration, the EM pellets showed a higher reaction rate and more homogeneous temperature distribution in the packed bed than did the pure Mg(OH)2 pellets. Consequently, a greater final material conversion was achieved. A higher reactivity enhancement was measured with the addition of a greater quantity of EG in the EM preparation. From the experimental results, it was calculated that the bed comprising EM pellets (having a mass mixing ratio of 8:1) had a heat-storage capacity of 881kJ/kgMg(OH)2, gross heat output of 714kJkgMg(OH)2, and mean power output rate of 132W/kgMg(OH)2. These values were higher correspondingly than the 755, 505, and 94W/kgMg(OH)2 values calculated for the bed comprising pure Mg(OH)2 pellets. It was demonstrated that the EM pellets had higher reactivity than pure Mg(OH)2 pellets because of their higher thermal conductivity.

A Kinetic Study on Carbothermic Reduction of Hematite with Graphite Employing Thermogravimetry and Quadruple Mass Spectrometry

AbstractThe reduction of hematite–graphite pellet was investigated from a kinetic viewpoint in the temperature range of 1173–1473 K (900–1200°C). The experimental procedure included thermogravimetric analysis (TGA) for measuring the weight change of the pellet and quadruple mass spectrometry (QMS) for monitoring the compositional change of the product gases. By applying a uniform internal reduction model to the current system, the activation energies for the reduction of Fe3O4 to wustite and for that of wustite to Fe were evaluated to be 91.0 and 25.9 kJ mol−1, respectively. Due to the product gas analyses by QMS, it was observed that the reduction rate of hematite–graphite pellet was accelerated up to the equilibrium concentration of CO determined by the carbon gasification curve. Changeover of reduction mechanism with increasing reduction degree was explained in terms of a schematic diagram based on the results obtained in the current study.

Characterization of the carbonization process of expandable graphite/silicone formulations in a simulated fire

The fire performance of curable-silicone based coatings containing expandable graphite (EG) is evaluated in hydrocarbon fire scenario (standard UL1709) using a lab-scale furnace test. From 5% to 25% of expandable graphite is incorporated in the silicone matrix to make the coating swell during the fire experiment. Fire performance of 25%EG/silicone-based coating is better than that of commercial intumescent paint used as reference. This is explained by a high swelling velocity (18%/s), a high expansion (3400%), an impressive cohesion of the char and a low heat conductivity at high temperature (0.35 W/K m at 500 °C). To elucidate this way of charring, the residue after fire testing was analyzed by scanning electron microscopy, transmission electron microscopy, energy dispersive spectrometry, X-ray photoelectron spectroscopy and X-ray diffraction. It is shown that the char is composed of two main parts: the top is composed of quartz and amorphous silica which coat graphite flakes and the heart of the char is composed of graphite flakes embedded in degraded silicone forming a complex structure. It is shown that, the good cohesion of the char is due to: (i) the presence of the undegraded silicone matrix; and (ii) the coating of graphite pellets by silicone.

Microstructure and morphology changes in MgH2/expanded natural graphite pellets upon hydrogen cycling

Compacted mixtures based on ball-milled magnesium hydride (MgH2) have gained significant research interest as suitable materials for hydrogen storage tanks. The issue related to their stability during practical service conditions is one of paramount relevance. In this work, we investigate the microstructure and morphology of pellets obtained by the compaction of ball-milled MgH2/Nb2O5 powders mixed with expanded natural graphite. The pellets are subjected to repeated hydrogen sorption cycles to measure hydrogen storage properties and its stability with cycling. Moreover, the effect of air-exposure on the hydrogen sorption behavior is studied. Electron microscopy observations of as-prepared and cycled pellets point to a dramatic modification of the material's microstructure upon repeated hydrogen cycling. In particular, the appearance of MgH2 particles depleted of the Nb2O5 catalyst and the formation of hollow MgO shells are highlighted. These findings are discussed by a simple model which takes into account the basic mechanisms intervening during the metal-hydride transformation in the pellet.

Wavelength dependence of polyyne preparation by liquid-phase laser ablation using pellet targets

The amount of polyynes produced by Nd:YAG laser (355, 532, and 1064 nm) ablation of fullerene and graphite pellet targets was the largest for 1064 nm ablation, contrary to the powder target in the previous report. This result is believed to come from the difference in the main polyyne-production area in liquids in the optical cell, depending on the pellet and powder targets.