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.

Detection of heavy metals in water samples by laser-induced breakdown spectroscopy combined with annular groove graphite flakes

The use of laser-induced breakdown spectroscopy(LIBS) for the analysis of heavy metals in water samples is investigated. Some factors such as splashing, surface ripples, extinction of emitted intensity, and a shorter plasma lifetime will influence the results if the water sample is directly measured. In order to avoid these disadvantages and the ‘coffee-ring effect', hydrophilic graphite flakes with annular grooves were used for the first time to enrich and concentrate heavy metals in water samples before being analyzed by LIBS. The proposed method and procedure have been evaluated to concentrate and analyze cadmium, chromium, copper, nickel, lead,and zinc in a water sample. The correlation coefficients were all above 0.99. The detection limits of 0.029, 0.087, 0.012, 0.083, 0.125, and 0.049 mgl^(-1) for Cd, Cr, Cu, Ni, Pb, and Zn,respectively, were obtained in samples prepared in a laboratory. With this structure, the heavy metals homogeneously distribute in the annular groove and the relative standard deviations are all below 6%. This method is very convenient and suitable for online in situ analysis of heavy metals.

Enhanced Thermal Conductivity and Bending Strength of Graphite Flakes/aluminum Composites Via Graphite Surface Modification

The effect of graphite surface modification on the thermal conductivity(TC) and bending strength of graphite flakes/Al composites(Gf/Al) prepared by gas pressure infiltration were investigated. Al3 Ni and Al4C3 phase may form at the interface in Ni-coated Gf/Al and uncoated Gf/Al composites, respectively, while the Al-Cu compound cannot be observed in Cu-coated Gf/Al composites. The Cu and Ni coatings enhance TC and the bending strength of the composites in the meantime. TC of Cu-coated Gf/Al composites reach 515 Wm^-1·K^-1 with 75 vol% Gf, which are higher than that of Ni-coated Gf/Al. Meanwhile, due to Al3 Ni at the interface, the bending strength of Ni-coated Gf/Al composites are far more than those of the uncoated and Cu-coated Gf/Al with the same content of Gf. The results indicate that metal-coated Gf can effectively improve the interfacial bonding between Gf and Al.

Nanosheet-stacked flake graphite for high-performance Al storage in inorganic molten AlCl_(3)-NaCl salt

Aluminum storage systems with graphite cathode have been greatly promoting the development of state-of-the-art rechargeable aluminum batteries over the last five years;this is due to the ultra-stable cycling,high capacity,and good safety of the systems.This study discussed the change of electrochemical behaviors caused by the structural difference between flake graphite and expandable graphite,the effects of temperature on the electrochemical performance of graphite in low-cost AlCl_(3)-NaCl inorganic molten salt,and the reaction mechanisms of aluminum complex ions in both graphite materials by scanning electron microscopy,X-ray diffraction,Raman spectroscopy,cyclic voltammetry,and galvanostatic charge-discharge measurements.It was found that flake graphite stacked with noticeably small and thin graphene nanosheets exhibited high capacity and fairly good rate capability.The battery could achieve a high capacity of^219 mA·h·g^(-1) over 1200 cycles at a high current density of 5 A·g^(-1),with Coulombic efficiency of 94.1%.Moreover,the reaction mechanisms are clarified:For the flake graphite with small and thin graphene nanosheets and high mesopore structures,the reaction mechanism consisted of not only the intercalation of AlCl4^-anions between graphene layers but also the adsorption of Al Cl4^-anions within mesopores;however,for the well-stacked and highly parallel layered large-size expandable graphite,the reaction mechanism mainly involved the intercalation of AlCl4^-anions.

Effect of Nano Carbon Black and Graphite Flake on Properties of Low Carbon Al2O3-C Refractories

Low carbon Al2O3 - C refractories specimens were prepared with tabular alumina （3. 0 - 1.0, 1.0 - 0. 5, 0.6-0.2, ≤0.3, ≤0. 045 and ≤0. 02 mm）, active alumina micropowder （≤2 μm ） and silicon （ 〈≤0. 045 mm ） as main raw materials. Nano carbon black （N220） and natural graphite flake （ 〈≤0. 074 mm ） were adopted as the carbon sources. The specimens were treated at 800, 1 000, 1 200 and 1 400 ℃ under coke embedded atmosphere. The effects of additions of nano carbon black and graphite flake on mechanical properties and thermal shock resistance of the specimens were stud- ied. Their mechanical properties were measured by three- point bending test and thermal shock resistance was de- termined by water quenching method. The phase compo- sition of the specimens was analyzed with X-ray diffrac- tion and microstruetures were observed through FESEM. The results reveal that： （1） the strengths of A1203 - C refractories with these two carbon sources show no big differences when coked at lower than 1 000 ℃ ; when coked at over 1 200 ℃ , the strengths of the specimens with graphite added are much higher than those of the specimens containing carbon black due to much more sil- icon carbide whiskers formed; （2） since the nano carbon black has small particle size, they can be filled into in- terstice of Al2O3 particles to form the nano carbon net- work structure, absorbing and relieving the thermal stressgenerated from expansion and contraction and reducing the thermal expansion coefficient of the specimens, thus their thermal shock resistance is better than that of the specimens containing graphite ; （ 3 ） low carbon Al2 O3 - C refractories with good mechanical properties and excellent thermal shock resistance can be prepared with combi- nation of nano carbon black and graphite flake.

Sintering behavior and thermal conductivity of nickel-coated graphite flake/copper composites fabricated by spark plasma sintering

Nickel-coated graphite flakes/copper（GN/Cu） composites were fabricated by spark plasma sintering with the surface of graphite flakes（GFs） being modified by Ni–P electroless plating. The effects of the phase transition of the amorphous Ni–P plating and of Ni diffusion into the Cu matrix on the densification behavior, interfacial microstructure, and thermal conductivity（TC） of the GN/Cu composites were systematically investigated. The introduction of Ni–P electroless plating efficiently reduced the densification temperature of uncoated GF/Cu composites from 850 to 650℃ and slightly increased the TC of the X–Y basal plane of the GF/Cu composites with 20 vol%–30 vol% graphite flakes. However, when the graphite flake content was greater than 30 vol%, the TC of the GF/Cu composites decreased with the introduction of Ni–P plating as a result of the combined effect of the improved heat-transfer interface with the transition layer, P generated at the interface, and the diffusion of Ni into the matrix. Given the effect of the Ni content on the TC of the Cu matrix and on the interface thermal resistance, a modified effective medium approximation model was used to predict the TC of the prepared GF/Cu composites.

Replacement of Flake Graphite in Aluminacarbon Refractories by Hexagonal Boron Nitride

Three kinds of composite alumina refractories were prepared with tabular alumina （3-1 and 1-0 mm） as aggregates,tabular alumina powder,α-Al2 O3 micropowder,and Si powder as matrix,adding 3 mass％ hexagonal boron nitride （h-BN）,3 mass％ flake graphite and 10 mass％ flake graphite,respectively.Cold physical properties,hot modulus of rupture,oxidation resistance,thermal shock resistance and slag corrosion resistance of the specimens were compared.The results show that：（1） physical properties and hot modulus of rupture of Al2 O3-h-BN refractories are slightly different from those of low carbon Al2 O3-C refractories,but better than those of traditional Al2 O3-C refractories with 10 mass％ graphite ; （2） Al2 O3-h-BN refractories have better thermal shock resistance and oxidation resistance than the carbon containing refractories,while similar slag resistance with low carbon Al2 O3-C refractories ; （3） h-BN can replace flake graphite as a starting material for the preparation of composite alumina refractories,considering the overall properties of the material.

Calculating the effective thermal conductivity of gray cast iron by using an interconnected graphite model

A new theoretical model of gray cast iron taking into account a locally interconnected structure of flake graphite was designed,and the corresponding effective thermal conductivity was calculated using the thermal resistance network method.The calculated results are obviously higher than that of the effective medium approximation assuming that graphite is distributed in isolation.It is suggested that the interconnected structure significantly enhances the overall thermal conductivity.Moreover,it is shown that high anisotropy of graphite thermal conductivity,high volume fraction of graphite,and small aspect ratio of flake graphite will cause the connectivity effects of graphite to more obviously improve the overall thermal conductivity.Higher graphite volume fraction,lower aspect ratio and higher matrix thermal conductivity are beneficial to obtain a high thermal conductivity gray cast iron.This work can provide guidance and reference for the development of high thermal conductivity gray cast iron and the design of high thermal conductivity composites with similar locally interconnected structures.

降低石墨微细鳞片含量的再磨工艺优化研究

对黑龙江某石墨粗精矿进行了立式搅拌磨机再磨试验。以陶瓷球为磨矿介质,研究了磨机转速、介质球直径、磨矿时间等工艺参数对石墨磨矿-浮选效果的影响。结果表明,石墨磨矿的优化工艺参数为:采用慢-快-慢交替的磨机转速,陶瓷介质球直径8~10 mm,磨矿时间5 min,在该优化条件下进行磨矿-浮选开路试验,获得了固定碳含量95.83%、-0.045 mm粒级含量24.51%、大鳞片(+0.15 mm)含量14.27%的石墨精矿。

天然鳞片石墨特征对球形加工的影响

以萝北(LB)、双鸭山(SYS)、鸡西(JX)、吉林(JL)4个地区浮选石墨精矿及其球化产品为研究对象。通过偏光显微镜(PLM)、扫描电镜(SEM)、X射线衍射(XRD)分析了脉石状态、片径大小、鳞片厚度、结晶程度,探究天然鳞片石墨特征对球形化石墨产品的影响。结果表明,4个地区石墨浮选精矿固定碳含量为JX>JL>SYS>LB,片径为JX>LB>JL>SYS,球形化时脉石矿物被包裹,恶化产品品质。一定粒径范围,大鳞片石墨成球效果更好;石墨鳞片厚成球颗粒更“实心”,鳞片薄成球颗粒内部缺陷更多。球形化过程中,石墨层间结构稳定程度高低为LB>SYS>JL>JX。LB石墨成球效果更好,更适合制备球形石墨。

非洲某鳞片石墨矿梯级回收工艺研究

以非洲某鳞片石墨为研究对象,开展了不同粒级石墨资源梯级回收工艺研究。结果表明,原矿固定碳含量为32.54%,其中大鳞片石墨主要呈片状或条带状结构与脉石矿物相互交代连生;粗选适宜条件为:磨矿细度-0.074 mm粒级占72.87%,煤油用量50 g/t,2#油用量150 g/t;浮选工艺为一粗一扫四精,其中粗精矿经精选1直接浮选后进行筛分分离出大鳞片石墨,筛下产物依次再进行三次磨矿三次精选获得细鳞片石墨。闭路试验结果显示,精矿中+0.150 mm大鳞片石墨和-0.150 mm细鳞片石墨固定碳含量分别达96.53%和96.21%,其中大鳞片石墨回收率达22.74%,比传统再磨再选工艺提高了7.66个百分点。

高导热多孔石墨预制体的制备及其性能

以天然鳞片石墨、酚醛树脂以及中间相碳微球为主要原料,制备多孔石墨预制体,经石墨化处理后再与环氧树脂复合,获得高导热石墨/环氧树脂复合材料。研究了素坯成形密度和粉末组成对多孔石墨预制体X-Y方向的导热性能与孔隙率的影响。结果表明:预制体内部石墨片定向排列,酚醛树脂与中间相碳微球连接其间,形成定向多孔网络结构,实现高导热、高孔隙与大孔径的协同。当素坯成形密度为1.4 g/cm^(3),天然鳞片石墨、酚醛树脂、中间相碳微球的含量分别为67.5 mass%、17.5 mass%和15 mass%时,多孔石墨预制体X-Y方向导热性能达到286.97 W/(m·K),气孔率达到44.56%;此时,石墨/环氧树脂复合材料X-Y方向导热性能达到116.81 W/(m·K)、抗压强度为26 MPa,在电子封装领域具有潜在的应用前景。

原生矿泥对鳞片石墨浮选影响机制研究

我国风化石墨矿储量大,成分复杂,石墨精矿固定碳回收率低。为高效利用风化石墨矿,本文以萝北县云山石墨矿风化矿石矿泥中所含石英、云母、绿泥石、褐铁矿、高岭土等矿物为对象,研究原生矿泥对石墨浮选效果的影响机制,并探索了减小矿泥影响的方法。研究表明,影响石墨浮选的主要原因是矿泥和石墨发生了异相凝聚,云母、高岭石和褐铁矿在石墨表面罩盖严重,长石和绿泥石在石墨表面发生了微弱罩盖,石英和透辉石由于泡沫夹带上浮的可能性较大;水玻璃和六偏磷酸钠作为组合抑制剂使用能有效改善矿泥对石墨选矿的影响。

高压辊磨对细鳞片石墨解离的影响

为了研究高压辊磨对细鳞片石墨的粉碎特征,通过对比不同粉碎产物的粒度组成和浮选精矿的粒度组成,得出高压辊磨产物和球磨产物的分离和护片效果。通过浮选动力学实验研究了高压辊磨产物和球磨产物的浮选率。在此基础上,利用扫描电镜对球磨浮选精矿和高压辊磨产物的微观形貌进行了表征,揭示了细鳞片石墨的解离和保护机理。研究结果表明:基于石墨鳞片本身的韧性和高压辊磨粉碎过程的线接触,高压辊磨对石墨鳞片有明显的保护作用,促进石墨的解离。浮选动力学试验表明:高压辊磨产物在实际生产中显著提高了细鳞片石墨的浮选速率和浮选指标。扫描电镜分析结果表明:高压辊磨促进裂隙沿着石墨和脉石的共生界面产生,促进了石墨的解离和鳞片的保护。该研究为细鳞片石墨保护和高效解离提供了理论指导。

鳞片石墨矿的工艺矿物学特征研究

鳞片石墨的片径越大,价值越高,故在鳞片石墨矿的加工过程中要严格保护鳞片。本文对鸡西地区的大块石墨矿进行矿物学研究,采用矿物解离分析仪(MLA)检测石墨薄片的矿物组成、形貌、分布和粒度,分析其矿物学特征对石墨解离、鳞片破坏及浮选作业的影响。分析结果表明,鸡西石墨矿样品的品位为5.05%。其中,0.15mm以上粒度达到51.68%,而细颗粒石墨多数被脉石矿物包裹,选择合适的磨矿方式对细颗粒石墨的解离以及大鳞片石墨的保护至关重要。

晶质石墨闪速浮选扩大连续试验研究

为防止石墨鳞片在浮选富集过程中多次磨矿而受到严重破坏,设计开发有效容积5 L的闪速浮选装备,将其应用于磨矿分级回路中提前回收已经单体解离石墨,并开展日处理量1.5 t扩大连选试验,采用1粗1扫8次精选部分中矿集中再选的工艺流程。通过和常规不含闪速浮选流程进行对比发现,在精矿固定碳质量分数和固定碳回收率相当的前提下,采用闪速浮选工艺流程,精矿中+0.15 mm粒级产率提高1.99百分点。说明闪速浮选工艺实施有效防止磨矿分级回路中石墨鳞片过磨,实现了将沉砂中已经单体解离石墨提前回收,对于大鳞片的保护具有重要意义。

微细鳞片石墨纳米气泡浮选与传统浮选的对比研究

微细鳞片石墨资源将是未来利用的主要石墨资源,为了实现微细鳞片石墨高效回收,探究了纳米气泡对微细鳞片石墨浮选强化行为的影响。通过浮选动力学、激光粒度分析仪、Zeta电位仪以及接触角分析仪研究了纳米气泡浮选和传统浮选行为的差异。结果表明,纳米气泡比传统浮选提前25 s完成微细鳞片石墨浮选。传统浮选精矿回收率和碳含量分别为87.89%和72.31%,纳米气泡浮选精矿回收率和碳含量分别为92.91%和73.40%,相比传统浮选精矿回收率高约5百分点,碳含量高约1百分点。纳米气泡可以有效团聚微细鳞片石墨,增大其表观尺寸,改善浮选效果。纳米气泡可以回收传统浮选不能有效回收的10μm以下微细鳞片石墨,进而提高了回收率。纳米气泡浮选精矿表面接触角比传统浮选精矿表面接触角高6.92°,有利于柴油在石墨表面的吸附,改善了石墨表面疏水性。纳米气泡降低了微细鳞片石墨颗粒间的静电斥力,有利于微细鳞片石墨疏水性团聚体的稳定结构,从而提高浮选概率。

晶质石墨浮选柱机联合与常规流程对比研究

晶质石墨矿是我国重要的非金属矿产资源。在浮选富集的过程中,由于磨矿段数多等原因造成鳞片破坏。萝北某地晶质石墨矿原矿品位为11.37%,属于细鳞片石墨矿。为提高精选作业段中鳞片的含量,开展了精选作业柱机联合流程和全机流程对比连选试验研究。两个流程处理量和药剂制度相同,在精矿固定碳含量和固定碳回收率相当的前提下,柱机联合流程的+0.15 mm粒级产率提高了1.05个百分点。柱机流程相较全机流程精选作业减少了一段浮选和一段磨矿。磨矿段数的减少是鳞片得以保护的关键因素。柱机流程除了能提高鳞片产率外,浮选柱在运行能耗、维护成本等方面同样优势明显,因此有望在晶质石墨浮选中实现工业应用。

Field electron emission from bunchy flake-like nano-carbon films

This paper reports that bunchy flake-like nano-graphite crystallite films （BNGCFs） were deposited on Si substrates by using the microwave chemical vapour deposition technique. Furthermore the BNGCFs were characterized by x-ray diffraction spectra, scanning electron microscopy, Raman spectra and field emission （FE） I-V measurements, and a lowest turn-on field of 1.5 V/μm, and a high average emission current density of 30 mA/cm2 at a macroscopic electric field of 8.0V/μm were obtained. The J-E data did not follow the original Fowler-Nordheim （F-N） relation since they were not well represented in the F-N plot by a straight line. A model considering the F-N mechanism, and the statistic effects of FE tip structures has been applied successfully to explain all the FE data observed for E 〈 8.SV/μm.

黑龙江鸡西平安鳞片石墨矿工艺矿物学研究

为了查明黑龙江平安鳞片石墨矿工艺矿物学特征,在化学分析的基础上,采用自动矿物解离分析仪(mineral liberation analyser,MLA)系统研究了原矿矿物组成、粒度分布和矿石嵌布特性等.结果表明:原矿有价元素固定碳的质量分数为17.7%,主要以石墨形式存在.主要脉石矿物为长石、石英,其质量分数分别为34.32%,20.83%.该石墨矿大鳞片石墨(粒度大于0.15 mm)的颗粒数占比为46.17%;当粒度为0.18 mm<d≤0.4 mm时石墨单体的解离度为70%,粒度为0.074 mm<d≤0.18 mm时解离度达95%.石墨主要为松散的片状集合体,与脉石矿物嵌布关系较为复杂,影响石墨的回收率及石墨精矿的质量.