Characterization and Thermal Conductivity of Modified Graphite/Fatty Acid Eutectic/PMMA Form-Stable Phase Change Material

We prepared and characterized a form-stable composite phase change material （PCM） with higher thermal conductivity. Capric acid（CA）-myristic acid（MA） eutectic as core, poly-methyl methacrylate （PMMA） as supportive matrix and modified graphite （MG） powders serving as the thermal conductance improver were blended by bulk- polymerization method. The composite PCMs with different MG mass fraction （2%, 5%, 7%, 10% and 15%） were characterized by FT-IR, SEM, DSC technique and mechanical tests. Thermal conductivities of the composites were measured by transient hot-wire method. The results indicate that MG powders have been successfully inserted into the CA-MA/PMMA matrix without any chemical reaction with each other. The MG/CA-MA/PMMA composites maintain good thermal storage performance while the thermal conductivity has been enhanced significantly. The composite PCM added with 15 wt% MG powders increases approximately as 195.9% in thermal conductivity. Moreover, the thermal conductivity improvement of the composite PCMs is also verified by the melting-freezing experiment, which is profitable for the heat transfer efficiency in latent heat thermal energy storage system.

Nanosized SnO_2 Particles Dispersed on a Graphite Electrode for Selective Detection of Dopamine and Ascorbic Acid

A novel nano-SnO2/graphite electrode has been prepared via polishing procedure to produce active and stable surface. The modified electrode resolves the overlapping voltammetric response of dopamine and ascorbic acid into two well-defined peaks by 230 mV. The mechanism of discrimination of dopamine from ascorbic acid is discussed. Dopamine and ascorbic acid can be determined simultaneously with the modified electrode. The electrode shows good sensitivity, selectivity and stability.

Poly(lactic acid)-starch/Expandable Graphite (PLA-starch/EG) Flame Retardant Composites

This work reports on the effect of commercial expandable graphite(EG)on the flammability and thermal decomposition properties of PLA-starch blend.The PLA-starch/EG composites were prepared by melt-mixing and their thermal stability,volatile pyrolysis products and flammability characteristics were investigated.The char residues of the composites,after combustion in a cone calorimeter,were analyzed with environmental scanning electron microscopy(ESEM).The thermal decomposition stability of the composites improved in the presence of EG.However,the char content was less than expected as per the combination of the wt%EG added into PLA-starch and the%residue of PLA-starch.The flammability performance of the PLA-starch/EG composites improved,especially at 15 wt%EG content,due to a thick and strong worm-like char structure.The peak heat release rate(PHRR)improved by 74%,the total smoke production(TSP)by 40%and the specific extinction area(SEA)by 55%.The improvements are attributed to the ability of EG to exfoliate at increased temperatures during which time three effects occurred:(i)cooling due to an endothermic exfoliation process,(ii)dilution due to release of H2O,SO2 and CO2 gases,and (iii)formation of a protective intumescent char layer.However,the CO and CO2 yields were found to be unfavorably high due to the presence of EG.

Preparation of lithium-ion battery anode materials from graphitized spent carbon cathode derived from aluminum electrolysis

Graphitized spent carbon cathode(SCC)is a hazardous solid waste generated in the aluminum electrolysis process.In this study,a flotation-acid leaching process is proposed for the purification of graphitized SCC,and the use of the purified SCC as an anode material for lithium-ion batteries is explored.The flotation and acid leaching processes were separately optimized through one-way experiments.The maximum SCC carbon content(93wt%)was achieved at a 90%proportion of−200-mesh flotation particle size,a slurry concentration of 10wt%,a rotation speed of 1600 r/min,and an inflatable capacity of 0.2 m^(3)/h(referred to as FSCC).In the subsequent acid leaching process,the SCC carbon content reached 99.58wt%at a leaching concentration of 5 mol/L,a leaching time of 100 min,a leaching temperature of 85°C,and an HCl/FSCC volume ratio of 5:1.The purified graphitized SCC(referred to as FSCC-CL)was utilized as an anode material,and it exhibited an initial capacity of 348.2 mAh/g at 0.1 C and a reversible capacity of 347.8 mAh/g after 100 cycles.Moreover,compared with commercial graphite,FSCC-CL exhibited better reversibility and cycle stability.Thus,purified SCC is an important candidate for anode material,and the flotation-acid leaching purification method is suitable for the resourceful recycling of SCC.

Electrochemical Determination of Epinephrine with a Pyrolytic Graphite Electrode in the Presence of Ascorbic Acid and Dopamine

A method for determination of epinephrine（EP） in the presence of ascorbic acid （AA） and dopamine （DA） with bare pyrolytic graphite electrodes has been described for the first time. In pH 7.0 phosphate buffer solution, the linear relationship was observed between the reduction peak current of EP and its concentration over the range from 1×10^-4 to 5×10^-7 mol/L, the related coefficient is 0.9992 （N=8）.

Determination of Dopamine in Presence of Uric Acid at Poly (Eriochrome Black t) Film Modified Graphite Pencil Electrode

A simple commercial graphite pencil electrode was used to investigate the electrochemical oxidation of dopamine. The electropolymerised film of eriochrome black t was prepared on the surface of graphite pencil electrode by using cyclic voltammetry technique. The prepared electrode exhibits an excellent electrocatalytical activity towards the determination of dopamine. The effects of concentration, pH and scan rate were investigated. Simultaneous detection of dopamine and uric acid was investigated by using both cyclic voltammetric and differential pulse voltammetry technique. The modified electrode was also used for the detection of dopamine in injection.

Palmitic Acid-Lauric Acid/Expanded Graphite as Form-Stable Composite Phase Change Material for Low-Temperature Energy Storage Applications

Low thermal conductivity of binary fatty acid mixture of palmitic and lauric acids(PA-LA)within the value range of 0.15-0.17 W/(m·K)restricts its wide utilization as thermal energy storage material in the active regime of solar heating applications at low operating temperatures.Nevertheless,this mixture as phase change material(PCM)has a suitable phase-change temperature and heat of 36℃and 176.3 J/g,respectively.Hence,the objective of this study is to formulate a novel form-stable composite PCM with the PA-LA mixture and expanded graphite(EG)as a thermal enhancer.PA-LA eutectic mixture with varied concentrations of EG was prepared and characterized.The thermal conductivity of PA-LA/EG increased gradually with the mass of EG.Optimum thermal properties were observed in PA-LA/(5%EG)composite,where its melting(T_(m)),freezing temperature(T_(t)),latent melting heat and thermal conductivity was 35.53℃,34.84℃,174 J/g,and 1.19 W/(m·K),respectively.Also,the composite PCM is characterized by good chemical-thermal stability and thermal reliability for long-term usage.In conclusion,it can be utilized as a prospective form-stable PCM for thermal energy storage in solar heating systems,overheat treatment systems,and other thermal storage applications at low operating temperatures.

Deposition of Carbon Particulates Surfaces on Zeolites by Electron-Beam Evaporation of Graphite

Disordered carbon particulates were deposited on the surface of natural acid treated zeolite through graphite evaporation by electron beam to improve adsorption properties of the porous material. This study focuses on the development of the new material and not on applications. The effect of acid treatment and carbon deposition on the physical properties of the natural material was investigated. The zeolites were characterized via spectroscopic and microscopic methods, thermal analysis, and gas sorption analysis. Analysis revealed that the surface area and volume increased by a factor of ten after the carbon-coating was deposited onto the zeolite surface and indicated that the Si/Al ratio was higher with the acid treated sample. The acid treatment promoted dealumination of the zeolite and increased overall surface area, whereas the carbon coating re-aluminated the zeolite while adding silica back to the main molecular framework, thus increasing crystallinity and thermal stability and further improving the high surface area produced by the acid treatment.

Organically-Expanded Graphite/Octadecylamine: Structural, Thermal and Relaxation Evaluation

Natural graphite was chemically modified by an acid mixture (H2SO4/HNO3, 4:1) using sonication. The resulting material was then expanded with octadecylamine by the dispersion method. The sample was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry (TG), wide-angle X-ray diffraction (WAXD) and relaxometry—low-field nuclear magnetic resonance (LFNMR). The SEM images revealed the expansion of the graphite layers. The presence of CH absorption was detected in the infrared spectrum of the expanded sample. The WAXD showed an additional diffraction peak at lower 2θ angle, indicating that intercalation of octadecylamine was successful. The thermogravimetry curve revealed three degradation steps. Two of them could be attributed to different structures (delaminated and exfoliated). The relaxometry showed that the relaxation time was dependon the frequency and the curve of the graphite/octadecylamine presented two peaks—approximately before 106 Hz and after 107 Hz. The results permitted inferring that organically modified graphite was achieved.

天然鳞片石墨提纯研究进展

天然鳞片石墨是一种战略资源,对国民经济发展及现代化建设具有重要作用。石墨材料因其具有导电、耐热、抗腐蚀、韧性好、润滑性能好等优异性能,被广泛应用于密封、铸造、防火材料、导电材料等传统工业领域,在新能源、电子信息技术、高端装备技术等新兴领域也具有潜在的应用价值,被誉为“工业黑金”。虽然我国有着丰富的石墨资源,但由于石墨提纯技术落后,石墨深加工产品与国外仍有一定差距。石墨材料纯度越高其应用价值越高,因此,研究高效、节能的石墨提纯技术对我国石墨产业的发展具有十分重要的意义。目前,常用的石墨提纯方法可分为物理提纯法和化学提纯法,其中,物理提纯法包括浮选法、高温法,化学提纯法包括氢氟酸法、酸碱法和氯化焙烧法。分析对比了这几种提纯方法的原理、优点及存在的问题。未来的研究方向主要集中在对单一提纯方法的工艺流程、提纯设备的优化,多种方法联合使用,以及新方法的开发及应用等方面。

力-热场耦合无氟碱酸法石墨提纯试验研究

为了提升碱酸法制备高纯石墨品位,降低环境污染,本试验以萝北石墨浮选精矿为原料,研究了力-热场耦合无氟碱酸法对石墨的提纯效果。结果表明,在NaOH用量为250 kg/t,碱熔温度为750℃,碱融时间为60 min,HCl用量为300 kg/t,酸浸温度为85℃,酸浸时间为4 h的条件下,进行两段超声:第1段为360 W超声强度,80℃温度下洗涤30 min(碱熔后);第2段为180 W超声强度,70℃温度下洗涤20 min(酸浸后),最终制备出的高纯石墨固定碳含量高达99.973%,Si含量为101μg/g,Al含量为31μg/g,Fe含量为29μg/g。

2,2-二甲基乙烯基硼酸电解液添加剂对锂离子电池的影响

为了提高石墨负极与电解液之间的界面稳定性,构建更加均匀稳定的SEI膜,在碳酸酯类电解液中添加了1%(质量分数)的2,2-二甲基乙烯基硼酸(DEBA)。采用恒流充放电、循环伏安法(CV)、交流阻抗法(EIS)进行电化学性能测试,同时采用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)对循环前后的石墨电极进行了表征。研究结果表明,添加DEBA能够提高锂离子电池的放电比容量和循环稳定性,同时能够降低界面阻抗,形成更加均匀稳定的SEI薄膜。0.2 C时添加DEBA的电池首次放电比容量为343.2 mAh/g,循环300次后,放电比容量为285.4 mAh/g,容量保持率为83.2%,表现出比不含添加剂的电池更好的循环性能。

表面包覆碳层孔隙对石墨负极材料倍率性能的影响

为了研究表面包覆碳层孔隙对石墨负极材料倍率性能的影响,引入少量硼酸,在包覆沥青软化阶段形成硼酸气化逸出效应,再通过碳化工艺在天然石墨尾料表面形成具有一定孔隙的包覆碳层,得到具有不同比例孔隙的石墨负极材料。结果表明,硼酸在材料颗粒表面形成了含有孔隙的碳层,其孔隙类型为介孔和大孔;表面碳层中的介孔比例越高,碳层L_(C)中形成Li^(+)的扩散通道数量越多,Li^(+)的扩散阻抗越低,材料倍率性能及循环性能得以改善。

优化碱酸法提纯石墨的研究

【目的】优化天然石墨提纯效果,降低酸在提纯过程中的过多使用对环境造成的影响,满足各行各业对高品质石墨的需求,实现更环保、高效的石墨提纯。【方法】以鳞片石墨为原料,采取NaOH-HCl-HF联合处理的工艺对石墨进行提纯研究,提高石墨的固定碳含量(质量分数,下同),降低石墨中的主要杂质元素如Si、Fe、Al、Cu等的含量,详细考察NaOH的用量以及焙烧温度2个关键因素对该工艺提纯效果的影响;通过扫描电子显微镜(SEM)观察石墨形貌特征,X射线荧光光谱仪(XRF)和电感耦合等离子体原子发射光谱仪(ICP)测定提纯处理前后石墨的杂质含量,X射线衍射仪(XRD)确定石墨及其灰分的晶体结构。【结果】当焙烧温度为500℃、焙烧时间为2.5h,HCl的体积与石墨的质量比为2∶1,氢氟酸的体积与石墨的质量比为2∶1时,石墨的平均固定碳含量从原来的95.3%提高到99.93%;当NaOH与石墨的质量比分别为0.5∶1和0.6∶1时,石墨的平均固定碳含量为99.91%和99.93%;考虑到成本效益等因素,确定当NaOH与石墨的质量比设定为0.5∶1时为理想工艺条件;经过提纯处理后的石墨层结构并不会出现明显的变化,基本性能不变,提纯处理后的石墨相比于提纯处理前的石墨,杂质含量明显地降低。【结论】该碱酸工艺不仅能有效地去除石墨中的杂质,盐酸和氢氟酸的组合还可以显著地提升提纯效果,可有望应用在石墨提纯处理和新能源材料领域。

功能化壳聚糖基聚合物粘结剂在硅碳负极中的性能研究

以壳聚糖为基石,巧妙地引入羧基以提升其水溶性,并进一步接枝苯硼酸基团与羟基封端的聚二甲基硅氧烷(PDMS–OH)进行交联,成功制备出具有三维网状结构的聚合物粘结剂(CFPO)。这一创新设计不仅使粘结剂的水溶性得到显著提升,还增强了其与活性物质之间的相互作用,从而在电池循环过程中实现了更高的稳定性。此外,引入的柔性链段PDMS为锂离子的传输构建了高效通道,而接枝的苯硼酸基团中的硼元素则有助于锂离子的去溶剂化,进一步加速了锂离子的传输。因此,该粘结剂赋予电池卓越的锂离子扩散系数(充放电锂离子扩散系数均达到3.98×109),使电池在高电流密度下仍能维持优异的比容量,显著提升了电池的倍率性能,并实现了高达96.27%的首圈库伦效率。凭借其强大的粘结强度和高锂离子扩散系数,本研究所制备的粘结剂在硅碳负极中表现出色,为电池在高倍率循环时提供了快速且稳定的性能保障,因此,这种CFPO粘结剂无疑是硅碳负极中的杰出之选。

石墨电极粉铺垫混合熔剂助熔测定窑渣中主要成分

本法尝试采用滤纸包裹试样,置于预先用石墨电极粉铺垫好的刚玉坩埚中,于900~950℃的高温炉中熔融10~20 min,至熔融物透明,盐酸浸取,过滤掉少量石墨粉,将滤液加热蒸发至干。在浓盐酸中加动物胶使硅酸凝聚沉淀,经过滤、洗涤、灼烧、称量,计算SiO_(2)的质量分数。所得滤液以氨水沉淀分离,滤液用EDTA标液滴定,计算CaO和MgO的质量分数。氢氧化物沉淀用盐酸溶解,再在氢氧化钠溶液中沉淀分离Al,分取滤液用氟代盐取代EDTA,用铜标液滴定,计算Al_(2)O_(3)的质量分数。

单宁酸改性石墨/聚酰亚胺复合材料的制备及摩擦学性能

通过非共价键改性的方法,将单宁酸(TA)包覆在石墨表面,从而改善石墨(Gr)与聚酰亚胺(PI)基体的界面相容性,并考察单宁酸修饰前后的石墨对PI基复合材料摩擦学性能的影响。结果表明:采用TA对Gr进行非共价修饰可以提高Gr与PI基体中的相容性和界面结合强度,进而提高复合材料的耐热性能和摩擦学性能,当复合体系中TA@Gr质量分数为15%时,材料的摩擦系数达到0.206,磨损率为3.71×10^(-14)m^(3)/(N·m),分别比纯PI降低了21.4%和62.8%,分别比PI/Gr复合材料降低了6.36%和14.7%。

酸处理碳毡阴极增强电芬顿降解左氧氟沙星性能研究

本文通过水热酸处理碳毡(GF),增加其亲水性和表面缺陷数量,增强了电芬顿降解抗生素左氧氟沙星(LEV)性能。采用SEM、XRD、XPS、Raman、FT-IR、接触角等测试技术对酸处理修饰的碳毡(MGF)进行了分析表征,结果表明MGF表面羧基含量和缺陷数量明显增加。在最优的反应条件下,电流0.15 A,pH为2,O_(2)曝气量为0.4 L/min,FeSO_(4)加入量为20 mg/L,该体系反应20 min后,LEV降解率达到96.1%,并且MGF表现出良好的稳定性,经过4个循环LVX降解率仍能达到95.4%。这项工作表明MGF是一种很有前途的电芬顿阴极材料,在水处理领域显示了优异的应用前景。

碱酸湿法制备高纯石墨工艺研究

针对高纯石墨制备,提出碱酸湿法制备工艺。考察了加压碱浸和盐酸浸出除杂时各因素对制备高纯石墨的影响。结果表明,在碱浸温度220℃、碱浓度270 g/L、液固比8、时间2 h、搅拌转速500 r min,铝的脱除率为88.18%,硅的脱除率为89.69%。在常压酸浸温度80℃、酸浓度12%、时间4 h、液固比4的条件下,高纯石墨产品固定碳含量大于99.89%。进行200目标准筛筛分处理后,筛上物灰分含量0.092%、固定碳含量99.91%、水分0.15%,符合鳞片石墨GB T 3518—2008中高纯石墨LC(-)75-99.9产品牌号的技术要求。