A Simple Quasi-2D Numerical Model of a Thermogage Furnace

A simple quasi-2D model for the temperature distribution in a graphite tube furnace is presented. The model is used to estimate the temperature gradients in the furnace at temperatures above which contact sensors can be used, and to assist in the redesign of the furnace heater element to improve the temperature gradients. The Thermogage graphite tube furnace is commonly used in many NMIs as a blackbody source for radiation thermometer calibration and as a spectral irradiance standard. Although the design is robust, easy to operate and can change temperature rapidly, it is limited by its effective emissivity of typically 99.5–99.8%. At NMIA, the temperature gradient along the tube is assessed using thermocouples up to about 1,500°C, and the blackbody emissivity is calculated from this. However, at higher operating temperatures (up to 2,900°C), it is impractical to measure the gradient, and we propose to numerically model the temperature distributions used to calculate emissivity. In another paper at this conference, the model is used to design an optimized heater tube with improved temperature gradients. In the model presented here, the 2-D temperature distribution is simplified to separate the axial and radial temperature distributions within the heater tube and the surrounding insulation. Literature data for the temperature dependence of the electrical and thermal conductivities of the graphite tube were coupled to models for the thermal conductivity of the felt insulation, particularly including the effects of allowing for a gas mixture in the insulation. Experimental measurements of the temperature profile up to 1,500°C and radial heat fluxes up to 2,200°C were compared to the theoretical predictions of the model and good agreement was obtained.     

Multiwalled Nanotubes: Their Formation by Irradiating Graphite with High Doses of Electrons

We report the production of carbon nanotubes by high dose of electron irradiation. The irradiation was performed with a 2 MeV Van de Graaff accelerator, while the irradiation conditions were the following: voltage 1.3 MeV, current 5 µA, dose rate 25 kGy/min, and total dosage 1000 kGy. The samples were analyzed in a high-resolution transmission electron microscope. The main features observed on the samples, were huge nanotubes of several nanometer long and few nanometer wide, which are capped at one end. It is good to point out, that at this level of irradiation, we were not able to find either onion-like or particle structures throughout the material, as it is usual in similar hexagonal structures. This behavior could be attributed to the level of irradiation used to create the nanotubes under investigation.     

Properties of Graphite‐Strengthened Magnesium

Mg was dispersion‐strengthened with graphite by powder metallurgy. The material was produced by ball milling Mg micropowder (median particle diameter 40 μm) with 3 vol.‐% graphite powder (median particle diameter 1–2 μm). After 8 h ball milling the product was consolidated by hot extrusion. Structural analysis revealed that a submicrocrystalline structure developed during ball milling. Tensile tests showed that the material was brittle even up to 300 °C and, therefore, most mechanical tests were carried out under compression. Under those conditions the reinforced material showed yield stresses of 270 MPa at ambient temperature, 170 MPa at 150 °C, and 125 MPa at 300 °C. Mg processed under the same conditions, but without graphite addition, had significantly lower yield stresses. The dispersion‐strengthened Mg showed a marked increase in creep resistance: at 200 °C and a stress, σ_c, of 100 MPa, the secondary creep rate, ?_s, was in the lower 10^–9 s^–1 range and at 300 °C and σ_c of 80 MPa, ?_s values of up to 1 × 10^–8 s^–1 were measured. The results are discussed.     

Structural Analogies and Differences Between Graphite Oxide and C60 and C70 Polymeric Oxides (Fullerene Ozopolymers)

A brief survey of the chemical structural analogies and differences between graphite oxide and fullerene ozopolymers or polymeric fullerene oxides (PFO) is presented. Graphite oxide is the product of oxidation of graphite prepared with strong oxidizing agents while PFO is the products formed by prolonged ozonation of C₆₀ or C₇₀ in solution. Notwithstanding the different starting substrates and oxidation conditions, elemental analyses, FT-IR spectroscopy and ¹³C-NMR spectroscopy suggest a very similar chemical structure for graphite oxide and PFO. A further analogy is the possibility to perform reduction or oxidation reactions on both substrates considered. Graphite oxide and PFO have also in common the ability to act as ion exchangers and as metal ion binders. Even the thermal behavior is comparable. However, X-ray powder diffraction has confirmed that graphite oxide still has a layered structure derived from graphite but with the graphene sheets at much bigger distance from each other due to the intercalation of oxidized groups and solvent molecules, while PFO do not show at all any sign of layered structure either from the X-ray spectra and also by its behavior in solution which is strikingly different from that shown by graphite oxide.     

Modified g-C3N4 derived from ionic liquid and urea for promoting visible-light photodegradation of organic pollutants

In this work, modified g-C₃N₄ was fabricated successfully by calcination of ionic liquid (IL) and urea. The addition of IL changed the polymerization mode of urea, induced the self-assembly of urea molecules, modified the morphological structure of the tightly packed g-C₃N₄, and extended the electron conjugation system. When using 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) as a modifier, the heteroatom Cl could be inserted into the g-C₃N₄ to optimize the electronic structure. The results of characterizations indicate that the unique structure of modified g-C₃N₄ has an expanded electron delocalization range, introduces an interlayer charge transmission channel, promotes the charge transmission, reduces the band gap, enhances the absorption of visible light, and inhibits electron-hole recombination. Modified g-C₃N₄ showed excellent photocatalytic performance for the degradation of rhodamine B and tetracycline. Furthermore, the effect of different anions in 1-butyl-3-methylimidazolium salts ([Bmim]Cl, [Bmim]Br, [Bmim][BF₄], and [Bmim][PF₆]) on the structure and function of g-C₃N₄ are discussed.     

Technology for recycling and regenerating graphite from spent lithium-ion batteries

With the annual increase in the amount of lithium-ion batteries (LIBs), the development of spent LIBs recycling technology has gradually attracted attention. Graphite is one of the most critical materials for LIBs, which is listed as a key energy source by many developed countries. However, it was neglected in spent LIBs recycling, leading to pollution of the environment and waste of resources. In this paper, the latest research progress for recycling of graphite from spent LIBs was summarized. Especially, the processes of pretreatment, graphite enrichment and purification, and materials regeneration for graphite recovery are introduced in details. Finally, the problems and opportunities of graphite recycling are raised.     

炭黑对ASA/天然石墨复合材料的电磁屏蔽性能影响

通过熔融共混方法制备导电高分子复合材料丙烯腈-苯乙烯-丙烯酸酯共聚物(ASA)/天然石墨(NGR)/炭黑(CB),采用电磁屏蔽测量仪、四探针电阻率测量仪和动态热机械分析仪对复合材料的电性能和力学性能进行详细研究。结果表明,ASA/NGR复合材料的体积电阻率随着炭黑含量增加而增加;同时在30 MHz~1500 MHz范围内,复合材料的电磁屏蔽性能从28 dB提高到38 dB,符合商业要求。炭黑的加入大大改善了材料力学性能,弯曲强度从31 MPa增加到41 MPa;动态储能模量从4.6 GPa增加到14.5 GPa。     

Electrochemical insertion of lithium ions into disordered carbons derived from reduced graphite fluoride

Both covalent (obtained by direct fluorination at high temperature) and semi-ionic carbon fluorides (synthesized at room temperature) were reduced in order to obtain disordered carbons containing very small content of fluorine and different physical properties according to the reduction treatment (chemical, thermal or electrochemical). After a physical characterization (X-ray diffraction, electron spin resonance and FT-IR spectroscopies), the electrochemical behaviours of the pristine carbon fluorides and of the treated samples were investigated during the insertion of lithium using liquid carbonate-based electrolytes (LiClO₄-EC/PC, 50:50%, v/v). Both galvanostatic and voltammetric modes were performed and revealed that the voltage profiles and the capacities differed according to the starting material and the reduction treatment. Semi-ionic carbon fluoride treated in F₂ atmosphere for 2 h at 150 °C and then chemically reduced in KOH exhibits high reversible capacities (the reversible capacity is 530 mAh g⁻¹ in the second cycle); in this case, the voltage profiles show a large flat portion at potentials lower than 0.3 V which is attributed to the insertion/deinsertion of lithium ions between the small graphene sheets and/or the absorption of pseudo metallic lithium into the microporosity of the sample. Nevertheless, a part of the lithium ions are removed at potentials higher than 0.5 V versus Li⁺/Li limiting the useful capacity.     

浸渍增重率和反渗率研究

对浸溃过程中浸渍剂沥青的浸入率和反渗率进行了分析与探讨。提出了理想增重率、理论增重率与实际增重率的概念和计算方法。并比较了实际增重率与操作增重率的差别。同时分析了抽真空的绝对压力与施压的绝对压力对各项增重率和反渗率的影响。     

Novel tin-graphite composites as negative electrodes of Li-ion batteries

For the purpose of obtaining an improved performance of the graphite negative electrode of Li-ion batteries, a novel graphite-tin composite has been synthesized by reduction of tin chloride (SnCl₂) with KC₈ in THF medium. This composite contains nano-sized tin particles dispersed on the graphite surface and free tin aggregates. Lithium electrochemical insertion occurs both in graphite and in tin. An experimental reversible specific charge of 489 mA h g⁻¹ is found stable upon cycling. Such a value is lower than the maximum theoretical one of 609 mA h g⁻¹ suggesting that only a part of tin is involved in the lithium insertion/extraction process. This part of active tin responsible for the stable capacity could be that bound to graphite. To the contrary, free tin aggregates could contribute to an extra capacity that decreases upon cycling in relation with the volume changes that occurs during alloying/dealloying.