Fe/C复合纳米材料的制备研究

以强酸为絮凝剂，将碱性溶液中的水性中间相沥青絮凝，从而使水性中间相沥青在酸性介质中形成炭基溶胶和凝胶。将此炭基溶胶和硝酸铁溶液混合形成复合溶胶、凝胶，进而采用醇水交换和超临界干燥制备出粒度为5nm-20nm的Fe/C复合纳米材料。考察了硝酸铁和水性中间相沥青的比例，以及热处理条件对Fe/C复合纳米材料织构和结构的影响。利用透射电镜、物理吸附、ICP－AES、X－射线衍射、热重等表征手段对Fe/C复合纳米材料特性和热处理的变化规律进行了研究。结果表明：通过改变炭基溶胶中硝酸铁的加入量可以制备不同铁含量的Fe/C复合纳米材料；在惰性气氛下，于较低温度热处理时，Fe/C复合纳米粉中铁是以Fe2O3的形式存在，热处理温度升高（900℃）后Fe2O3被还原为单质铁，且金属颗粒团聚长大，在高温（1300℃）时，铁以Fe3C的形式存在，颗粒进一步长大且有部分炭石墨化。在还原性气氛下，在300℃－500℃热处理范围内，随温度的升高铁被还原为单质铁。     

SiO2气凝胶/中间相沥青基泡沫炭复合材料的制备与表征

以正硅酸乙酯、乙醇和去离子水为原料,采用溶胶-凝胶法制备了SiO2溶胶;并以煤沥青为原料,采用自挥发发泡法制备了中间相沥青基泡沫炭。然后采用浸渍工艺将SiO2溶胶和中间相沥青基泡沫炭在常压下进行复合,制备了SiO2气凝胶/中间相沥青基泡沫炭复合隔热材料。利用XRD、SEM、热导仪和万能试验机等设备分别研究了SiO2气凝胶、中间相沥青基泡沫炭以及SiO2气凝胶/中间相沥青基泡沫炭复合材料的结构和性能。结果表明,所制备的复合材料具有一定的力学性能,同时其隔热性能优于单一泡沫炭的隔热性能,有望成为一种新型的隔热材料。     

水相炭基溶胶—凝胶法制备纳米炭粉的研究

以高温煤焦油沥青为炭源,经浓硝酸和浓硫酸混合物在30℃氧化制备出较高收率的水性中间相沥青。将水怀中间相沥青溶于氨水溶液得到水相炭基凝胶,经过乙醇与水直接交换后超临界干燥和热处理制备出颗粒分布均匀、平均尺寸在10nm左右的无定型碳纳米粉。并采用透射电子显微镜、傅立叶红外光谱、热重、物理吸附、X－射线衍射等分析手段对纳米炭原粉在热处理过程中的物理化学变化规律进行了表征。     

由沥青制备炭基凝胶的研究

以煤焦油沥青为原料,经过氧化、碱溶制备出水性中间相沥青,着重考察了制备条件对水性中间相沥青在水相中凝胶化的影响。结果表明：氧化温度、浓度和溶胶的pH值对水性中间相沥青的凝胶化有影响;水性中间相沥青（AMP）可以在较宽的pH值范围内形成凝胶。在碱性条件下,氧化温度降低、pH值升高和AMP浓度提高均可缩短炭基凝胶的凝胶时间;以强酸为絮凝剂在酸性条件下水性中间相沥青絮凝为炭基凝胶;在中性条件下,给溶胶中加入乙醇可形成炭基凝胶。     

由中间相沥青制备泡沫炭:Fe(NO3)3的影响

以中间相沥青为前驱体制备高性能泡沫炭，在考察中间相沥青、Fe（NO3）3及其混合物热分解行为的基础上，着重研究了Fe（NO3）3对制备中间相沥青基泡沫炭的影响，揭示了Fe（NO3）3对泡沫炭孔泡结构的影响规律及其作用机制，初步研究了在泡沫炭炭化过程中形成的Fe／C之物相结构及其石墨化行为。结果表明，在不同的炭化温度下，Fe在泡沫炭中的存在形态各异；Fe物种的存在有利于提高泡沫炭的石墨化程度。     

溶胶-凝胶法制备纳米复合永磁材料中溶液pH值的影响

用溶胶-凝胶法制备了纳米复合永磁材料FesmO3/Fe2O3,通过XRD、TG/DTG、SEM及VSM的表征,研究了溶液pH值对凝胶形态、焙烧温度和磁性能的影响.实验结果表明,溶液pH值对焙烧温度和样品相态有显著的影响,在低pH值分段焙烧时,可得纳米复合永磁材料FeSmO3/Fe2O3,当pH值升到7时,只能得到单相粉体FeSmO3.分段焙烧400℃、2h及650℃、1h后,得到平均粒径在30nm、软磁相与硬磁相发生强烈的交换耦合作用的纳米复合永磁材料,由于交换耦合作用使纳米复相具有优异于单相的磁性能.     

炭二氧化硅复合气凝胶的合成及结构分析

将二氧化硅溶胶和间苯二酚-甲醛溶液混合,经溶胶凝胶反应得到复合湿凝胶. 再经超临界干燥和炭化得到炭-二氧化硅复合气凝胶. 分别用氢氟酸刻蚀和空气烧蚀复合气凝胶中的二氧化硅和炭,得到结构完整的炭气凝胶和二氧化硅气凝胶. 复合湿凝胶经常压干燥、炭化和氢氟酸刻蚀能得到炭干凝胶. 利用透射电镜和低温氮气吸附对上述凝胶的微结构进行了表征. 结果表明：复合气凝胶中,炭和二氧化硅纳米网络各自连续并相互嵌套. 由于二氧化硅纳米网络的支撑作用,复合凝胶在超临界干燥和高温炭化过程中体积收缩减小,网络塌陷降低. 所得炭气凝胶具有高比表面（934m²/g）和高孔容（3.9cm³/g）的特点.     

纤维素磁性纳米复合膜的研究进展

目的综述了纳米Fe3O4磁性粒子的制备方法和机理,找出纤维素磁性纳米复合膜的基本复合方法。方法比较分析沉淀法、水热反应法、微乳液法、溶胶凝胶法、高温分解法等制备纳米Fe3O4磁性粒子的优缺点。结果总结了纤维素磁性纳米复合膜研究和应用进展,并为今后纤维素磁性纳米复合膜的发展提出了建议和新思路。结论采用原位复合的方法制备纤维素磁性纳米复合膜是目前的研究热点,具有显著的意义和广阔的发展前景。     

氧化硅包裹四氧化三铁微球的制备及表征

在室温下,采用H2O2氧化Fe(OH)2悬浮液的方法制备得到了粒径23nm左右的磁性纳米粒子,经X射线衍射检测制备得到的是Fe3O4磁性纳米粒子,粒子的饱和磁化强度为59.05emu/g。先用硅烷偶联剂KH560修饰Fe3O4,提高粒子在乙醇溶液中的单分散性,在此基础上采用溶胶凝胶法通过TEOS水解制备得到分散性佳、尺寸均匀、粒径为25nm左右核壳结构的氧化硅包覆Fe3O4纳米粒子的磁微球。     

不同酸对γ-Fe_2O_3/SiO_2纳米复合粉体特性的影响

以正硅酸乙酯及铁盐为原料,通过溶胶-凝胶法制备γ-Fe2O3/SiO2纳米复合粉体。采用红外吸收光谱、X射线衍射仪、透射电镜及振动样品磁强计等对复合粉体进行表征。结果表明:以不同铁盐为前驱体得到不同晶型的Fe2O3;不同酸对磁性复合粉体的性能有重要影响:加硝酸时,γ-Fe2O3大小为15nm,其饱和磁化强度大;加入醋酸时得到的γ-Fe2O3颗粒为5nm,且粒度分布变窄,但其饱和磁化强度明显下降;并对γ-Fe2O3在SiO2中的合成机理进行了探讨。     

Interaction of diamond with ultrafine Fe powders prepared by different procedures

We have studied the interaction of synthetic diamond crystals with ultrafine Fe powders during catalytic diamond gasification in a hydrogen atmosphere at 900°C. The Fe powders were prepared by three procedures: reduction of Fe₂O₃ nanopowder; evaporation using an ELV-6 electron accelerator, followed by condensation; and reduction of ferric chloride. The surface-processed diamond crystals were examined by electron microscopy. The results indicate that ultrafine powders produced by the first two procedures cause predominantly lateral etching of diamond. The Fe particles prepared by the third procedure penetrate into the bulk of diamond crystals and produce etch pits and “tunnels,” thereby markedly increasing the specific surface area of the crystals.     

Rapid synthesis and characterization of maghemite nanoparticles

Fe2O3-SiO2 nanocomposites were prepared by a sol-gel method using various evaporation surface to volume (S/V) ratios ranging from 0.03 to 0.2. The Fe2O3-SiO2 sols were gelated at various temperatures ranging from 50 degrees C to 70 degrees C, and subsequently they were calcined in air at 400 degrees C for 4 hours. The structure and the magnetic properties of the prepared Fe203-SiO2 nanocomposites were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), differential thermal analysis (DTA), and vibrating sample magnetometer (VSM) measurements. The gelation temperature of the Fe2O3-SiO2 sols influenced strongly the particle size and crystallinity of the maghemite nanoparticles. It was observed that the particle size of maghemite nanoparticles increased with the increasing of the gelation temperature of the sols, which may be due to the agglomeration of the maghemite particles at elevated temperatures inside the microporosity of the silica matrix during the gelation process, and the subsequent calcination of these gels at 400 degrees C resulted in the formation of large size iron oxide particles. Magnetization studies at temperatures of 10, 195, and 300 K showed superparamagnetic behavior for all the nanocomposites prepared using the evaporation surface to volume ratio (S/V) of 0.1, 0.2, 0.09, and 0.08. The saturation magnetization, Ms, values measured at 10 K were 5.5, 8.5, and 9.5 emu/g, for the samples gelated at 50, 60, and 70 degrees C, respectively. At the gelation temperature of 70 degrees C, gamma-Fe2O3 crystalline superparamagnetic nanoparticles with the particle size of 9 +/- 2 nm were formed in 12 hours for the samples prepared at the S/V ratio of 0.2.     

Preparation of alumina–silica–nickel nanocomposite by in situ reduction through sol–gel route

Ceramic based composites with dispersion of nano sized metal/metal carbide particles have generated wide technological interest for their improved mechanical properties — hardness, fracture strength as well as fracture toughness, superior electrical properties and magnetic properties. In the present investigation alumina–silica gels have been prepared along with nickel chloride and dextrose distributed in the nanometric pores of the gel. The gels are prepared with different molar proportions of alumina and silica containing 5 wt% of nickel chloride and 50 wt% excess dextrose. During heat treatment at a temperature of 9008C for half an hour in nitrogen atmosphere, nickel chloride is reduced to metallic nickel by in situ generated hydrogen in the silica–alumina matrix. X-ray analyses indicate that no nickel chloride reduction is possible upto 50 mol% silica in alumina–silica matrix. Beyond this range, higher the silica content, higher is the reduction of nickel chloride. The presence of metallic nickel has been substantiated further by SAD analysis. Particle size analysis based on X-ray diffraction as well as transmission electron micrograph shows the presence of nickel particles of size ,20 nm distributed in the alumina–silica nanocomposite.     

Composition and tempering of Fe---C and Fe---Ni---C fine particles prepared by spark erosion

Fe---C and Fe---Ni---C powders prepared by spark synthesis from pure Fe, Fe---Ni and C as electrodes were investigated. They exhibit a wide variety of particles differing in form, size and phase composition. The as-prepared powders consist of graphite, carbides, - and γ-Fe, non-magnetic phases and a new ferromagnetic component. Carbides dominate among the ferromagnetic phases. The fractions exhibiting superparamagnetic behaviour contain fine Fe and Fe---C particles in graphite. Changes in the phase composition due to tempering at elevated temperatures lead to the Fe---C equilibrium.     

Synthesis of Nano Crystalline Ni and Fe by Levitational Gas Condensation Method

Nanocrystalline Ni and Fe were synthesized by the levitaional gas condensation (LGC) method using wire feeding (WF) and micron powder feeding (MPF) systems. The magnetic properties have been characterized using a vibrating sample magnetometer (VSM) and Moumlssbauer spectroscopy. The X-ray diffraction and saturation magnetization results indicate the small amount of oxidized phases such as amorphous NiO and Fe₃O₄ on the surface of metal powders. The size and shape of the nano powders were investigated by transmission microscopy (TEM). It was found that particles have a mean crystallite size about 22 and 24 nm for Fe and Ni. The surface effect might influence the magnetic hysterisis behavior of Ni and Fe     

Hydrothermal synthesis of magnetite nanoparticles via sequential formation of iron hydroxide precipitates

A novel method for preparing fine magnetite nanoparticles without using any additives and organic solvents has been developed. In this method, a sequential precipitates formation method, ferrous and ferric hydroxides are not coprecipitated but sequentially formed in an alkaline solution, and then the resulting suspension is subjected to a hydrothermal treatment. The obtained magnetite nanoparticles were characterised through scanning electron microscopy observation and X-ray diffraction analysis, and the particle size and magnetic properties were measured with a dynamic light scattering particle size analyser and a superconducting quantum interference device magnetometer, respectively. In order to prepare fine magnetite nanoparticles with a uniform size, both the formation sequence of ferrous and ferric hydroxide precipitates and the supersaturation of ferric hydroxide in the solution were essential. The ferromagnetic magnetite nanoparticles with a median size 8.5?nm were relatively easily obtained in the formation process in which a ferric sulphate solution was rapidly poured into a suspension of ferrous hydroxide particles prepared beforehand using ferric chloride and sodium hydroxide, whereas the median size of magnetite nanoparticles prepared via conventional coprecipitation route was 38.6?nm.     

Preparation of alumina–silica–nickel nanocomposite by in situ reduction through sol–gel route

Ceramic based composites with dispersion of nano sized metal/metal carbide particles have generated wide technological interest for their improved mechanical properties — hardness, fracture strength as well as fracture toughness, superior electrical properties and magnetic properties. In the present investigation alumina–silica gels have been prepared along with nickel chloride and dextrose distributed in the nanometric pores of the gel. The gels are prepared with different molar proportions of alumina and silica containing 5 wt% of nickel chloride and 50 wt% excess dextrose. During heat treatment at a temperature of 900°C for half an hour in nitrogen atmosphere, nickel chloride is reduced to metallic nickel by in situ generated hydrogen in the silica–alumina matrix. X-ray analyses indicate that no nickel chloride reduction is possible upto 50 mol% silica in alumina–silica matrix. Beyond this range, higher the silica content, higher is the reduction of nickel chloride. The presence of metallic nickel has been substantiated further by SAD analysis. Particle size analysis based on X-ray diffraction as well as transmission electron micrograph shows the presence of nickel particles of size ∼20 nm distributed in the alumina–silica nanocomposite.     

On the formation of M2+ -Sb3+ -alkoxide precursors and sol-gel processing of M-Sb oxides with M = Cr,Mn, Fe,Co, Ni,Cu and Zn

Binary alkoxide complexes of compositions close to MSb(OEt)₅, with M = Mn, Fe, Co and Ni, have been prepared and characterized by their i.r. and u.v.-VIS spectra, while Cr, Cu and Zn do not form similar ethoxide complexes with Sb(OEt)₃. The Mn and Fe complexes must be prepared in inert atmosphere as they are very easily oxidized. The Fe complex is metastable and decomposes within a few hours. The Co complex can only be prepared in the presence of acetonitrile. X-ray amorphous gels were formed upon hydrolysis of solutions containing M to Sb species in the ratio 12 for M = Mn, Fe, Co and Ni. The gels consisted of agglomerated particles of sizes from 75 to 300 nm. The decomposition of the gels in air and in nitrogen has been monitored by means of thermogravimetric measurements. Samples of heated gels were quenched from various temperatures in the region 50–950°C, and the formed oxides were characterized by their X-ray powder patterns and by their infrared spectra. At 950 °C MSb₂O₆ was formed in air, while in nitrogen MSb₂O₄ (M = Mn, Co and Ni) was formed at intermediate temperatures. At higher temperatures the latter compound decomposed and Sb₂O₃ sublimated.     

Preparation and optical properties of iron-modified titanium dioxide obtained by sol–gel method

In this paper twelve TiO₂:Fe powders prepared by sol–gel method were analyzed being into consideration the kind of iron compound applied. As a precursor titanium (IV) isopropoxide (TIPO) was used, while as source of iron Fe(NO₃)₃ or FeCl₃ were tested. Fe doped TiO₂ was obtained using two methods of synthesis, where different amount of iron was added (1, 5 or 10% w/w). The size of obtained TiO₂:Fe particles depends on the iron compound applied and was found in the range 80–300 nm as it was confirmed by SEM technique. TiO₂:Fe particles were additionally investigated by dynamic light scattering (DLS) method. Additionally, for the TiO₂:Fe particles UV–vis absorption and the zeta potential were analyzed. Selected powders were additionally investigated by magnetic force microscopy (MFM) and X-ray diffraction techniques. Photocatalytic ability of Fe doped TiO₂ powders was evaluated by means of cholesteryl hemisuccinate (CHOL) degradation experiment conducted under the 30 min irradiation of simulated solar light.     

Fe3O4/CdTe磁性荧光纳米复合物的逐步杂凝聚法合成及其表征

采用逐步杂凝聚法合成了Fe3O4/CdTe磁性荧光纳米复合物.以化学共沉淀法制备Fe3O4纳米颗粒,经油酸修饰后分散在表面活性剂中形成磁流体.CdTe量子点以巯基乙酸为稳定剂制得.最后以聚乙烯亚胺(PEI)为联接剂,成功制备了Fe3 O4 /CdTe磁性荧光双功能纳米复合物颗粒.该复合物颗粒平均尺寸为(30±5)nm,荧光产率为0.186,饱和磁化强度为15.745emu/g,该纳米粒子既具有优异的荧光特性,也具有较强的超顺磁性.