Mineralogical and petrographic analysis on the flake graphite ore from Saba Boru area in Ethiopia

The mineralogy and petrography of natural graphite in Saba Boru of Ethiopia indicate that there exists flake graphite with a slightly oval structured fine size according to our study on thin and polished sections. Herein, for estimating the carbon content in graphite, the ASTM-C561, the test method for ash in a graphite sample, was used. For characterizing graphite, x-ray diffraction, x-ray fluorescence, inductively coupled plasma mass spectroscopy, and scanning electron microscopy were also used. Chemical analysis of ore samples determined that the average compositions are 63.35% SiO₂, 15.45% Al₂O₃, 2.36% Fe₂O₃, 2.07% K₂O, less than1% others, and loss-on-ignition (LOI) in the range of ~4.74%–37.42%. The total carbon content of graphitic ore ranged from 4.11% to 33.14%. Importantly, when graphite is concentrated through floatation, its average purity and recovery are 92.97% and 90.82%, respectively. Furthermore, once the graphite concentrates are treated with hydrofluoric acid, the average value attains a high grade of 96.48% C. Moreover, the average ash content is 81.93% (pre-flotation) and 3.1% (post-flotation), respectively. Finally, after beneficiation, a silica is identified as a major gangue (85.88%), usable as a raw material for other purposes such as cement. Hence, these graphite-bearing rocks seem to be worth exploring for commercialization opportunities.     

Hybrid UV photodetector with high photo-to-dark current ratio based on ordered TiO2 nanorod arrays and polystyrene sulfate

Vertically aligned TiO₂ nanorods arrays were successfully synthesized on FTO glass by wet-chemical method. Based on polystyrene sulfate (PSS) functionalized TiO₂ nanorods arrays, a sandwich-structured hybrid UV photodetector was fabricated. The photo-to-dark current ratio of the device increases by more than 3 orders of magnitude with typical case, while the dark current is about 10 nA at 1 V bias. The high photoresponse together with the low dark current could probably contribute a large photocurrent and low-power application. The high performance of the hybrid material and facile low-cost fabrication of the UV detector make the devices promising for large-area UV photodetection applications.     

Influence of crucible material on the microstructure and properties of iron rich glass-ceramics

Slag glass melting is usually performed on a laboratory scale in crucibles, which are economically viable tools for the production of slag glass-ceramics. In this work, quaternary CaO-Al₂O₃-MgOSiO₂ (CAMS) glass-ceramics were prepared by melting the tailing of Bayan Obo mine tailing, blast furnace slag, and fly ash in alumina and graphite crucibles. The effect of the crucible material on the microstructure and properties of the glass-ceramics was investigated using differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and inductively coupled plasma atomic emission spectroscopy. Results indicated that the contents of Al₂O₃ and Fe₂O₃ in the initial glass were significantly changed by the corrosion of the alumina crucibles during the glass melting process and by the reducing action of the graphite crucibles. The main crystal phases of glass-ceramics melted in alumina crucibles and graphite crucibles were Ca (Mg, Fe, Al) (Si, Al)₂O₆, coesite and Ca (Mg, Al) (Si, Al)₂O₆, respectively. According to these findings, we conclude that the microstructure and properties of the glass-ceramics are affected by the crucibles.     

Preparation and electrochemical properties of Co3O4/graphite composites as anodes of lithium ion batteries

Co₃O₄/graphite composites were synthesized by precipitation of cobalt oxalate on the surface of graphite and pyrolysis of the precipitate, and the effects of graphite content and calcination temperature on the electrochemical properties of the composites were investigated. The samples were characterized by thermogravimetry and differential thermal analysis (TG/DTA), X-ray diffractometry (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and charge/discharge measurements. With increasing the graphite content, the reversible capacity of the Co₃O₄/graphite composites decreases, while cycling stability improves dramatically, and the addition of graphite obviously decreases the average potential of lithium intercalation/deintercalation. The reversible capacity of the composites with 50% graphite rises from 583 to 725 mA·h/g as the calcination temperature increases from 300 to 500 °C, and the Co₃O₄/graphite composites synthesized at 400 °C show the best cycling stability without capacity loss in the initial 20 cycles. The CV profile of the composite presents two couples of redox peaks, corresponding to the lithium intercalaction/deintercalation for graphite and Co₃O₄, respectively. EIS studies indicate that the electrochemical impedance decreases with increasing the graphite content.     

煤系石墨氧化过程中结构变化研究

以湖南新化、郴州两地不同石墨化程度的煤系隐晶质石墨为原料,采用改进Hummers法,制备出系列氧化石墨,然后利用X射线衍射(XRD)、扫描电镜(SEM)、傅里叶变换红外光谱(FT-IR)等对石墨原料及系列氧化产物进行表征。结果表明,经氧化后两个地区石墨化不同的石墨结构层上均接有羟基(C-OH)、环氧(C-O-C)、羧基(COOH)或羰基(C=O)等含氧官能团,高锰酸钾的用量和原矿的石墨化程度对氧化石墨的难易和产物的结构无序程度均有影响。低石墨化程度的石墨较高石墨化程度的石墨易于被氧化。随着KMnO_4用量的增加,两种石墨的结构无序程度都逐渐增加,但在相同的KMnO_4用量下,低石墨化度的石墨氧化产物的结构无序程度更高。推测一方面是隐晶质石墨的粒径偏小,与高锰酸钾及溶液的接触面积较大,另一方面是低石墨化度石墨C-C多,化学活性较强,易被氧化。此外,高石墨化程度的石墨氧化后的最大层间距大于低石墨化度石墨氧化后的最大层间距。     

不同方法制备LiNO3NaCl/EG复合相变储热材料的热物性分析

选用LiNO_3-NaCl(87:13)二元混合相变熔盐作为相变材料,高导热系数的膨胀石墨作为复合基载材料,分别采用机械混合熔融法和超声波粉碎法制备了LiNO_3-NaCl/EG复合相变材料。通过热重及同步热分析仪对复合材料的热物性进行了测试分析。进而比较了不同制备方法的优缺点,并通过相变理论对材料的相关物性进行了分析。     

Fabrication of Ni-, Co- and NiCo-coated graphite microspheres by heterogeneous precipitation

The precursors with NiCO₃·2Ni(OH)₂·2H₂O, Co₂(OH)₂CO₃, or both NiCO₃·2Ni(OH)₂·2H₂O and Co₂(OH)₂CO₃ coated graphite microspheres were prepared respectively by the aqueous heterogeneous precipitation using nickel sulfate, cobalt nitrate, sodium carbonate, ammonium bicarbonate and graphite microspheres as the main starting materials. Subsequently, Ni-, Co- and NiCo-coated graphite microspheres were successfully obtained by thermal reduction of the as-prepared precursors at 500 °C for 2 h, respectively. These metal-coated graphite microspheres were characterized with a smooth, cohesive surface consisting of fine metallic particles. Optimized precipitation processing parameters of the concentration of graphite microspheres (10 g/L), the rate of adding reactants (3 mL/min) and pH value (8.0) were determined by a trial and error method. The thermal analysis of the precursors was investigated by TG. Powders of the precursors and the resultant metal-(Ni, Co and NiCo alloy) coated graphite microspheres were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Funded by the Post-graduate Innovation foundation of Jiangsu Province of China (No. CX07B_085z)     

Kinetic study of LiMn2O4 in process of lithium intercalation

Exchange current density of spinel LiMn₂O₄ was studied by linear polarization. The relationship of the kinetic property with the structure of spinel LiMn₂O₄ was investigated by studying the effect of the doping and surface coating on the kinetic properties of electrode material. The results show that the exchange current density of spinel LiMn₂O₄ electrode increases with the increase of the amount for lithium intercalation at first, and then decreases. The maximal exchange current density appeares at the 80%–90% lithium intercalation. The similar phenomenon was observed on the doped spinel LiMn₂O₄ electrode. Doping can enhance the exchange current density of spinel LiMn₂O₄ material. However, the degree of the doping effect varies with the doped element varying. Surface coating can also enhance the exchange current density of spinel material, and the increment of value is higher than that of doped ones. Foundation item: Project(50302016) supported by the National Natural Science Foundation of China     

ItX型气缸盖蠕墨铸铁铣削应用研究

HX型柴油机所使用的气缸盖是其核心部件之一,选用材料为蠕墨铸铁,结构中各型腔布局复杂,加工精度要求高,是典型的多面多孔系的箱体类零件。结合公司现有设备资源配置,从现场生产需求着手,以提高加工工序中铣削效率为目的,应用SANDVIK无涂层刀片和涂层刀片,通过对蠕墨铸铁进行铣削加工过程中产生的切屑形态和工件所受的切削力进行综合分析和研究。     

Investigation on the electrocatalytic characteristics of SnO<Subscript>2</Subscript> electrodes with nanocoating prepared by electrodeposition method

SnO₂ electrodes have many advantages in the degradation of toxic or bio-refractory organic wastewater, and SnO₂ is a kind of anode material which has the potential to be widely used. Electrocatalytic efficiency and service life of TiSnO₂ electrodes are key factors that can influence its applications. In order to enhance the electrocatalytic characteristics of TiSnO₂ electrodes, a type of electrocatalytic electrode with nanocoating was prepared by direct current (DC) electrodeposition method and thermal oxidation technique. With phenol as the model pollutant, the electrochemical degradation efficiencies of electrodes with nanocoating and non-nanocoating were investigated. It was demonstrated that the electrodes with nanocoating have higher efficiency than that of electrodes with non-nanocoating. The degradation time was decreased 33.3% for the same amount of phenol’s degradation. The crystal structure of surface coating, the micrograph of electrode surface and the chemical environment of Sn and Sb in the electrode surface were analyzed with the help of XRD, SEM and XPS. The results showed that the surface of electrode was mainly SnO₂ crystal with rutile structure and that much adsorbed oxygen in nanocoating was the dominant factor for enhancing the electrocatalytic characteristics. Supported by the Excellence Young Teacher Foundation of China Education Ministry and Research Foundation for Outstanding Young Scholars of Heilongjiang Province (Grant No. JC-02-04)     

Microstructure evolution of graphite intercalated by TiO2 and its photocatalytic activity

An intercalative composite of graphite oxide (GO) as host intercalated by an object of TiO₂ nanoparticles was obtained at low temperature by mixing GO with Ti(SO₄)₂ solution, and by another object of Ti₂O₃ while mixing with TiCl₄ ethanol solution. Microstructures of the GO and its intercalative composites at different C/Ti ratio were studied by XRD, SEM, AFM and FT-IR, and the evolution of these lamellar structures was studied based on the temperature change. The photocatalytic activity of the intercalative composites was characterized according to the degradation of methyl orange. The intercalative composite formed by Ti(SO₄)₂ solution presents an excellent photocatalytic reactivity, while that formed by TiCl₄ presents no observablly photocatalytic reactivity. The electric conductivity variation of different composites was checked, in order to investigate the role of the possible electron transfer between the graphite layer and TiO₂ nanocrystal during TiO₂ excited by UV light irradiation. Funded by The National Natural Science Foundation of China (No.50572070 and No.50672066)     

Supercapacitors based on high-surface-area graphene

Exfoliated graphite oxide was prepared by an improved Hummers method and was then reduced to graphene with hydrazine in the presence of ammonium hydroxide.N2adsorption–desorption measurement showed that graphene so obtained had a specific surface area as high as 818 m2/g.Galvanostatic charge/discharge curves demonstrated that the as-prepared graphene exhibited a specific capacitance of 186.9 F/g at a current density of 0.1 A/g and that about 96%of the specific capacitance was retained after 2000 cycles at a current density of 5 A/g.     

Full-solution-processed high mobility zinc-tin-oxide thin-film-transistors

The full solution-processed oxide thin-film-transistors(TFTs) have the advantages of transparency, ease of large-area fabrication, and low cost, offering great potential applications in switching and driving fields, and attracting extensive research interest. However, the performance of the solution-processed TFTs is generally lower than that of the vacuum-deposited ones. In this article, the full-solution processed TFTs with zinc-tin-oxide(ZTO) semiconductor and aluminium(Al_2O_3) dielectrics were fabricated, and their mobilities in the saturation region are high. Besides, the effect of the Al_2O_3 dielectrics' preparation technology on ZTO TFTs' performance was studied. Comparing the ZTO TFTs using the spin-coated Al_2O_3 dielectrics of 1–4 layers, the ZTO TFT with 3-layer Al_2O_3 dielectrics achieved the optimal performance as its field-effect carrier mobility in the saturation region is 112 cm~2/V s, its threshold voltage is 2.4 V, and its on-to-off current ratio is 2.8×105. This is also the highest reported carrier mobility of the solution-processed ZTO TFTs.     

ZnO films on transferable and low thermal resistance graphite substrate grown by ultrasonic spray pyrolysis

ZnO thin films were deposited on graphite substrates by ultrasonic spray pyrolysis method with Zn(CH 3 COO) 2 ·2H 2 O aqueous solution as precursor. The crystalline structure, morphology, and optical properties of the as-grown ZnO films were investigated systematically as a function of deposition temperature and growth time. Near-band edge ultraviolet(UV) emission was observed in room temperature photoluminescence spectra for the optimized samples, yet the usually observed defect related deep level emissions were nearly undetectable, indicating that high optical quality ZnO thin fi lms could be achieved via this ultrasonic spray pyrolysis method. Considering the features of transferable and low thermal resistance of the graphite substrates, the achievement will be of special interest for the development of high-power semiconductor devices with suffi cient power durability.     

Photocatalytic activity of porous magnesium oxychloride cement combined with AC/TiO<Subscript>2</Subscript> composites

As a decorative material, magnesium oxychloride cement was used as a photocatalyst supporter to purify the pollutants indoors. Due to excellent adsorption properties of activated carbon (AC), the photocatalytic composties, TiO₂/AC, were prepared and introduced into the porous magnesium oxychloride cement (PMOC) substrate to composite a sort of photocatalytic cementitious material (PCM). The optimal composite processes were assessed by gas chromatograph, using toluene as the target. By comparing the perspective of toluene purification and thorough decomposition, it can be found that the optimal mass ratio for TiO₂/AC composites is 4/25, and the heat treatment to TiO₂/AC sample at 350 °C can play the optimal synergetic role of adsorbents in photocatalytic process. The synergistic effect of TiO₂, AC and magnesium oxychloride cement (MOC) was also evaluated by gas chromatograph. One-take molding process was adopted to introduce the TiO₂/AC into PMOC substrate, and its optimal mass fraction was 4 wt%, while the appropriate density of substrate was 0.35 g/cm3. Toluene degradation showed that the prepared PCM can degrade pollutants efficiently. The appropriate treatment process of TiO₂/AC, mass of TiO₂/AC, substrate density, and stable pore structure should be coordinated to maximize the adsorption-photodegradation performance. The combination of photocatalytic materials, adsorbents, and building materials provided a new idea for the application of photocatalysis.     

Characteristics and Microstructure of Graphite Encapsulated Iron Nanoparticles

The graphite encapsulatedα-Fe particles were prepared by reduction of stage-2 and stage-3 FeCl 3 graphite intercalation compounds(GICs)with metallic potassium.X-ray diffraction analysis(XRD),energy dispersive X-ray spectroscopy(EDS)investigation and transmission electron microscopy(TEM) observation show that the reduction products of stage-2 FeCl 3 -GICs contains more abundantα-Fe nanoparticles than those of stage-3.High-resolution TEM(HRTEM)observation reveals that the nanoparticle ofα-Fe was polycrystals or twins,which was real or quasi two-dimension in shape,and whose space orientation was strictly controlled by the graphene.Based on the experiment results,a possible growth model of the graphite encapsulatedα-Fe was proposed.     

新型离子液体用于碳糊电极的直接电化学研究

以1,2-二甲基咪唑、正溴丁烷和三氟甲基磺酰亚胺锂盐为原料,合成了液态范围宽、热稳定性好、无酸性质子的疏水性离子液体1-n-丁基-2,3-二甲基咪唑三氟甲基磺酰亚胺.将该离子液体作为黏合剂,制备离子液体/碳糊电极(CILE)和葡萄糖氧化酶/离子液体/碳糊电极(GOD-CILE),分别以铁氰酸钾溶液、磷酸氢二钠/磷酸二氢钾溶液(PBS,pH值为6.98)为电化学探针,研究CILE和GOD-CILE的直接电化学性能和电极表面形态.结果表明,与传统黏合剂石蜡相比,离子液体能有效地将石墨粉黏结,形成均匀平整界面,咪唑环和石墨层之间形成"π-π环" 相互作用,使得电子在电极内的传递速率大大加快,电流响应明显增加;GOD吸附在CILE表面可保持生物活性,表现出一对峰形良好的准可逆氧化还原峰.离子液体良好的导电能力、"π-π环"相互作用和黏合性质促进了离子液体在第三代传感器中的研发.     

Calibration and uniqueness analysis of microparameters for DEM cohesive granular material

The differential evolution (DE) algorithm was deployed to calibrate microparameters of the DEM cohesive granular material. 4 macroparameters, namely, uniaxial compressive strength, direct tensile strength, Young’s modulus and Poisson’s ratio, can be calibrated to high accuracy. The best calibration accuracy could reach the sum of relative errors RE_sum < 0.1%. Most calibrations can be achieved with RE_sum < 5% within hours or RE_sum < 1% within 2 days. Based on the calibrated results, microparameters uniqueness analysis was carried out to reveal the correlation between microparameters and the macroscopic mechanical behaviour of material: (1) microparameters effective modulus, tensile strength and normal-to-shear stiffness ratio control the elastic behaviour and stable crack growth, (2) microparameters cohesion and friction angles present a negative linear correlation that controls the axial strain and lateral strain prior to the peak stress, and (3) microparameters friction coefficient controls shear crack friction and slip mainly refers to the unstable crack behaviour. Consideration of more macroparameters to regulate the material mechanical behaviour that is dominated by shear crack and slip motion is highlighted for future study. The DE calibration method is expected to serve as an alternative method to calibrate the DEM cohesive granular material to its peak strength.     

Water-oxygen interaction on marcasite(101) surface: DFT calculationOA

Marcasite (Fe S₂) is widespread in nature,its oxidation plays a vital role in acid mine drainage,mineral resource recovery,and photoelectric material applications.In this paper,the oxidation mechanism of marcasite has been studied for the first time using density functional theory (DFT).It is found that,unlike the oxidation of pyrite,the oxidation of marcasite merely occurs at surface S atoms.Under the coexistence of water and oxygen,S atoms around surface Fe atoms are replaced by O a...     

Manufacturing microporous foam zinc materials with high porosity by electrodeposition

In order to get foam zinc materials of porous metal electrode, a novel method for preparing foam zinc was proposed, in which the polyurethane foam with diameter of 0.3 mm as substrate was processed by degreasing, roughening, activating, electroless plating and electrodeposition. The main factors affecting the process, such as ZnSO₄ content, temperature, pH value, current density, and electrodes distance, were investigated comprehensively. The optimal process conditions are 250 g/L ZnSO₄, 20 g/L Al₂(SO₄)₃, 40 g/L KAl(SO₄)₂, 30 g/L Na₂SO₄, pH=3.5, 4.0 cm of electrodes distance and 0.04 A/cm² current density at 30 °C. The result shows that adding ultrasonic on the process can elevate the deepening plating ability and current efficiency. Foam zinc material with a high porosity of 92.2% and a three-dimensional network structure can be fabricated by electrodeposition.