Effect of calcination temperature on the physical properties of LiFe5O8 nanostructures

The structural properties of LiFe₅O₈ nanostructures, which were synthesized using a thermal treatment method, were investigated using different characterization methods. The XRD, FESEM and TEM results showed a phase transition from uncompleted α-LiFe₅O₈ and β-LiFe₅O₈ phases to completed α-LiFe₅O₈ phase when the growth calcination temperature shifted from 873 to 973?K. The crystallization was completed at 973?K, revealed by the absence of organic absorption bands in the FT-IR spectra. The results of band gap energy which were studied by UV–vis spectroscopy indicated that when calcination temperature increased, the appraised band gap energy of LiFe₅O₈ nanostructures decreased. Laser Raman analysis was used to determine the peaks of the synthesized LiFe₅O₈ nanostructures accurately and to differentiate between the α-LiFe₅O₈ and β-LiFe₅O₈ phases around 217?cm^?1. The results of a vibrating sample magnetometer (VSM) indicated that the magnetic properties differed between these nanostructures so that saturation magnetization and coercivity increased when the calcination temperature increased. The obtained results from electron paramagnetic resonance (EPR) spectroscopy demonstrated that as the growth calcination temperature shifted from 673 to 873?K, the results of g value and ΔH_pp increased up to the maximum value and then reduced for calcined sample at 973?K.     

Lithium insertion into the spinel LiFe5O8

Lithium has been inserted into the spinel LiFe₅O₈ at both ambient and high temperature. At 50 °C two lithium ions per formula unit can be inserted into the structure; the inserted lithium ions displace the tetrahedral ferric ions of the spinel into neighbouring vacant octahedral sites to yield a rocksalt phase Li₃Fe₅O₈. The long-range order of the lithium and iron ions on the B-sites of the A_tet[B₂]_octX₄ spinel (Fe[Li_0.5Fe_1.5]O₄) is not affected by lithiation. At 400 °C electrochemical insertion of lithium is accompanied by iron extrusion from the oxide lattice. The reaction of two lithium ions per LiFe₅O₈ at this temperature results in a product consisting predominantly of a rocksalt phase of composition Li₂Fe₃O₅ in which the lithium and iron ions are randomly distributed over all the octahedral sites of the structure, and metallic iron.     

Dielectric properties of PMMA/Soot nanocomposites

Dielectric analysis (DEA) of relaxation behavior in poly(methyl methacrylate) (PMMA) soot nanocomposites is described herein. The soot, an inexpensive material, consists of carbon nanotubes, amorphous and graphitic carbon and metal particles. Results are compared to earlier studies on PMMA/multi-walled nanotube (MWNT) composites and PMMA/single-walled nanotube (SWNT) composites. The beta relaxation process appeared to be unaffected by the presence of the soot, as was noted earlier in nanotube composites. The gamma relaxation region in PMMA, normally dielectrically inactive, was "awakened" in the PMMA/soot composite. This occurrence is consistent with previously published data on nanotube composites. The dielectric permittivity, s', increased with soot content. The sample with 1% soot exhibited a permittivity (at 100 Hz and 25 degrees C) of 7.3 as compared to 5.1 for neat PMMA. Soot increased the dielectric strength, deltaE, of the composites. The 1% soot sample exhibited a dielectric strength of 6.38, while the neat PMMA had a value of 2.95 at 40 degrees C. The symmetric broadening term (alpha) was slightly higher for the 1% composite at temperatures near the secondary relaxation and near the primary relaxation, but all samples deviated from symmetrical semi-circular behavior (alpha = 1). The impact of the soot filler is seen more clearly in dielectric properties than in mechanical properties studies conducted earlier.     

Thermal properties of PMMA/montmorillonite clay nanocomposites

Polymer/Clay offer tremendous improvement in wide range of physical and engineering properties for polymers with low filler loading. In nanotechnology polymer/clay nanocomposites use smectitetype clays that have layered structures. In this work, Poly (methyl methacrylate) (PMMA) was synthesized by free radical addition polymerization in the presence of high power ultrasound. The Poly (methyl methacrylate) (PMMA)-Montmorillonite (MMT) clay nanocomposites were synthesized by two different techniques viz., ultrasonic mixing and magnetic stirring. An analysis of the XRD data confirms that the composites are in the nanometer scale. The FTIR spectra show that there is strong interaction between the clay and the polymer that enhances the thermal stability. The thermal stability of the experimental nanocomposite prepared by the two processes is compared. Further analysis of XRD data shows that intercalation as well as exfoliation has taken place in both the types of nanocomposites preparation. An analysis of the TG, DTG curves reveal that the thermal stability is found to increase by nearly 30% for ultrasonic mixing than that of magnetic stirring.     

Synthesis and characterization of SiO2/(PMMA/Fe3O4) magnetic nanocomposites

Magnetic silica nanocomposites (magnetic nanoparticles core coated by silica shell) have the wide promising applications in the biomedical field and usually been prepared based on the famous St?ber process. However, the flocculation of Fe3O4 nanoparticles easily occurs during the silica coating, which limits the amount of magnetic silica particles produced in the St?ber process. In this paper, PMMA/Fe3O4 nanoparticles were used in the St?ber process instead of the "nude" Fe3O4 nanoparticles. And coating Fe3O4 with PMMA polymer beforehand can prevent magnetic nanoparticles from the aggregation that usually comes from the increasing of ionic strength during the hydrolyzation of tetraethoxysilane (TEOS) by the steric hindrance. The results show that the critical concentration of magnetic nanoparticles can increase from 12 mg/L for "nude" Fe3O4 nanoparticles to 3 g/L for PMMA/Fe3O4 nanoparticles during the St?ber process. And before the deposition of silica shell, the surface of PMMA/FeO4 nanoparticles had to be further modified by hydrolyzing them in CH3OH/NH3 x H2O mixture solution, which provides the carboxyl groups on their surface to react further with the silanol groups of silicic acid.     

Optical and magnetic properties of CuO/CuFe2O4 nanocomposites

CuO/c-CuFe₂O₄ nanocomposites have been synthesized via the oxalate precursor route. Effect of synthesis conditions on the crystal structure, microstructure, magnetic and optical properties of the formed powders was studied. The results indicated that pure CuO nanoparticles were obtained from the oxalate precursor annealed at 600 °C for 2 h. However, substitution of Cu²⁺ ion by Fe³⁺ ion (Cu_1?X Fe _X O, where X = 0, 0.05, 0.1 and 0.2) led to form of CuO/CuFe₂O₄ nanocomposites. The microstructures of the powders appeared as a monoclinic like shape. Furthermore, the band gap energy of the obtained CuO nanopowders was 1.41 eV and the value was slightly decreased by Fe³⁺ ion substitution. In addition, the formed CuO particles had weak ferromagnetic characteristics. However, the substitution Cu²⁺ ion by Fe³⁺ ion enhanced the magnetic properties of the formed composite as the result of increasing the CuFe₂O₄ phase formation. Hence, the saturation magnetization was increased from 0.13 to 9.8 emu/g by increasing the Fe³⁺ ion from 0 to 0.2.     

Electrical and mechanical properties of PMMA/reduced graphene oxide nanocomposites prepared via in situ polymerization

We report the effect of filler incorporation techniques on the electrical and mechanical properties of reduced graphene oxide (RGO)-filled poly(methyl methacrylate) (PMMA) nanocomposites. Composites were prepared by three different techniques, viz. in situ polymerisation of MMA monomer in presence of RGO, bulk polymerization of MMA in presence of PMMA beads/RGO and by in situ polymerization of MMA in presence of RGO followed by sheet casting. In particular, the effect of incorporation of varying amounts (i.e. ranging from 0.1 to 2 % w/w) of RGO on the electrical, thermal, morphological and mechanical properties of PMMA was investigated. The electrical conductivity was found to be critically dependent on the amount of RGO as well as on the method of its incorporation. The electrical conductivity of 2 wt% RGO-loaded PMMA composite was increased by factor of 10⁷, when composites were prepared by in situ polymerization of MMA in the presence of RGO and PMMA beads, whereas, 10⁸ times increase in conductivity was observed at the same RGO content when composites were prepared by casting method. FTIR and Raman spectra suggested the presence of chemical interactions between RGO and PMMA matrix, whereas XRD patterns, SEM and HRTEM studies show that among three methods, the sheet-casting method gives better exfoliation and dispersion of RGO sheets within PMMA matrix. The superior thermal, mechanical and electrical properties of composites prepared by sheet-casting method provided a facile and logical route towards ultimate target of utilizing maximum fraction of intrinsic properties of graphene sheets.     

Electrochemically active flame-made nanosized spinels: LiMn2O4, Li4Ti5O12 and LiFe5O8

Electrochemically active LiMn₂O₄, Li₄Ti₅O₁₂, and LiFe₅O₈ particles with spinel structure (normal, mixed and mixed inverse) were made at production rates of 10–20 g h⁻¹ by flame spray pyrolysis (FSP), a scalable, one-step, dry process. These materials were characterized by X-ray diffraction and nitrogen adsorption, and had a primary crystallite size in the range of 8–30 nm and exhibited high temperature stability. Electrochemical properties, as measured by slow cyclic voltammetry, are reported for LiMn₂O₄ and Li₄Ti₅O₁₂ as potential cathode and anode materials, respectively, in secondary lithium-ion batteries. LiFe₅O₈ nanoparticles were made also by FSP containing the electrochemically active β-phase as shown by the corresponding cyclic voltammogram and specific charge–discharge spectra.     

Effect of heat treatment on structure and magnetic properties of FeCoNi/CNTs nanocomposites

Fe₄₆Co₃₅Ni₁₉/CNTs nanocomposites have been prepared by an easy two-step route including adsorption and heat treatment processes. We investigated the effect of heat treatment conditions on structure, morphology, nanoparticle sizes and magnetic properties of the Fe₄₆Co₃₅Ni₁₉ alloy nanoparticles attached on the carbon nanotubes by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy-disperse X-ray spectroscopy (EDS) and vibrating sample magnetometer (VSM). When the reducing temperature changes from 300–450°C, a transition of the crystalline structure from bcc phase to fcc-bcc dual phase and an increase in particle size of Fe₄₆Co₃₅Ni₁₉ nanoparticles together with a local maximum at 350°C are observed. Meanwhile, the saturation magnetization (M _s) for Fe₄₆Co₃₅Ni₁₉ nanoparticles increases with the increase of reducing temperature and the coercivity (H _c) decreases rapidly with a local minimum at 350°C. When the reducing time (tr) changes from 2–5 h, bcc phase is predominant in the Fe₄₆Co₃₅Ni₁₉ alloy particles. Both the particle size and M _s have a maximum at tr = 3 h, and the H _c reaches a maximum at tr = 4 h.     

Electron microscopy of lithium ferrites. Precipitation of LiFe5O8 in α-LiFeO2

α-LiFeO₂, which has the rocksalt structure, loses lithium when it is heated in air at temperatures bove about 1000°C. The consequent non-stoichiometry is retained by rapid quenching, but slower rates of cooling are accompanied by precipitation of the ferri-magnetic spinel, LiFe₅O₈. The size, shape, and structure of the precipitate particles depends upon the thermal treatment of the samples.     

Mechanical and magnetic properties of Ni-Co dispersed Al2O3 nanocomposites

Effects of the fabrication processing on the microstructure and properties of composites were investigated. High-density Ni-Co dispersed-Al₂O₃ (Al₂O₃/Ni-Co) composites were obtained by hydrogen reduction and consolidated using hot pressing and pulse electric current sintering (PECS) of Al₂O₃, Ni(NO₃)₂·6H₂O and Co(NO₃)₂·6H₂O powder mixtures. Microstructural investigations of the hot-pressed composite fabricated using again wet/dry ball-milled powder mixture after calcination revealed that fine Ni-Co particles, about 145 nm in diameter, dispersed homogeneously at the matrix grain boundaries. In particular, fine microstructure of dispersion with the average size of 90 nm was realized for the specimen consolidated by PECS method. High strength of over 1 GPa and hardness of 19 GPa were measured for the nanocomposites prepared from the again ball-milled powder mixture. The ferromagnetism of nano-sized Ni-Co contributes to the magnetic properties of the composites. A change in the coercive force with dispersion size was observed. Also, the extent of magnetic response by an applied stress was strongly influenced by the size of Ni-Co particles. The relations between microstructure and mechanical as well as magnetic properties are discussed.     

Structural, magnetic and electromagnetic wave absorption properties of SrFe12O19/ZnO nanocomposites

Microwave absorption of nanocomposites of strontium ferrite and zinc oxide has been investigated. M-type strontium ferrite powders synthesized by a sol–gel method were combined with different concentrations of ZnO using a new method. The samples were characterized by various experimental techniques including TGA/DTA, X-ray diffraction, transmission electron microscopy, vibrating sample magnetometer and vector network analyzer. Reflection loss of nanocomposites has been measured in two frequency ranges of 8–12 GHz (X-band) and 12–18 GHz (Ku-band). The saturation magnetization of the nanocomposites decreased with increasing concentration of ZnO, but reflection loss in the Ku frequency band is enhanced by up to 5 dB for 15 % of ZnO in the nanocomposites.     

The mechanical properties of MWNT/PMMA nanocomposites fabricated by modified injection molding

This paper established the procedure to fabricate MWNT/PMMA nanocomposite by using both the injection molding and film casting processes. The combined fabrication process could remove demerits while maintaining the merits of each process. Tensile strength of the MWNT/PMMA nanocomposite increased more than 15% and tensile stiffness also increased about 17.5%, compared to the pure PMMA. It was confirmed that this combined fabrication process efficiently dispersed MWNTs in the PMMA matrix, and also maintained the well-dispersed state more effectively. SEM images of the fractural surface show that the degree of dispersion was improved. In addition, a surfactant was used to disperse MWNTs more efficiently, and its effect on mechanical properties was also investigated.     

多壁碳纳米管/聚甲基丙烯酸甲酯复合材料的结构与导电性能

采用超声波辅助溶液共混的方式制备多壁碳纳米管/聚甲基丙烯酸甲酯复合材料,采用扫描电镜及广角X衍射仪对复合材料的微观相态结构进行了分析,对复合材料的物理机械性能及导电性能进行了测试.结果表明:采用溶液混合并用超声辅助分散的方法可使纳米多壁碳纳米管在PMMA基体中分散良好,在碳纳米管含量较低的情况下就可以获得导电性能及物理机械性能良好的复合材料.     

Preparation and magnetic properties of SrFe12O19/SiO2 nanocomposites with core–shell structure

SrFe₁₂O₁₉/SiO₂ nanocomposites with a core–shell structure have been obtained. The core SrFe₁₂O₁₉ nanoparticles were synthesized by a citrate precursor technique with Fe/Sr ratios of 10.8, and silica was coated on SrFe₁₂O₁₉ forming complete coverage by the controlled hydrolysis and condensation of tetraethyl orthosilicate (TEOS). The composition, morphology and structure of the products were characterized by EDS, XRD, TEM, and IR spectroscopy, respectively. The results indicate that the product has a core–shell structure, which is combined through the chemical bond of Fe–O–Si. The magnetic measurements were carried out on a vibrating sample magnetometer (VSM), and the measurement results indicate the reduction of the magnetization of the SiO₂ coated strontium ferrite nanoparticles compared with the uncoated ferrite nanoparticles. High coercivity also shows that the prepared uncoated and coated ferrite nanoparticles are not superparamagnetic.     

微波多元醇法制备单分散Ni1-xZnxFe2O4/MWCNTs与磁性能

以多壁碳纳米管(MWCNTs)为模板,三乙二醇(TREG)为溶剂,采用微波多元醇法制备MWC-NTs负载组成可控的Ni1-xZnxFe2O4(x=0.4、0.5、0.6)纳米复合材料Ni1-xZnxFe2O4/MWCNTs。其结构和形貌通过XRD、SEM、TEM和EDX进行表征,用VSM测试样品的磁性,并探讨了微波功率、微波时间对镍锌铁氧体负载的影响。结果表明立方系尖晶石结构的单分散Ni1-xZnxFe2O4磁性纳米粒子均匀负载在碳纳米管表面,平均粒径约为6nm;其磁性能与镍锌铁氧体的组成有关,随着Zn含量的增加,饱和磁化强度(Ms)先增大后减小,当x=0.5时Ms达到最大值。矫顽力(Hc)都比较小,在室温下表现为超顺磁性。     

Processing and functionalization effect in CNF/PMMA nanocomposites

We compare results for polymer nanocomposites of poly(methyl methacrylate) (PMMA) and carbon nanofibers (CNFs) prepared by three different processing techniques: melt-compounding, solvent casting and in situ polymerization. Moreover, CNFs were used as received and functionalized with oxygen and nitrogen groups. Mechanical properties and rheological behavior of the composites revealed a strong filler-polymer interface interaction in the in situ polymerized composites, even through covalent binding, while was noticed to be weaker in melt-compounding and solvent casting. In addition, in these two further cases, the addition of CNFs, pristine or functionalized, improved toughness of the PMMA.