Rheological behaviors and electrical conductivity of epoxy resin nanocomposites suspended with in-situ stabilized carbon nanofibers

Epoxy resin nanocomposites suspended with carbon nanofibers (CNFs) have been prepared. A bifunctional coupling agent, 3-aminopropyltriethoxysilane, is used to treat the acid oxidized fibers. The dispersion quality of the CNFs with and without surface modification is monitored by an oscillatory rheological investigation. The addition of fibers is observed to influence the rheological behaviors of the suspensions drastically. Newtonian fluid behavior disappears as the fiber loading increases. A significant increase of the complex viscosity and storage modulus is observed, especially when the temperature increases to 50 °C and 75 °C. In-situ reaction between the amine-terminated functional groups on the silanized fibers and the resin, is justified by the FT-IR analysis and is responsible for the improved fiber dispersion and network formation. A decreased rheological percolation is observed after silanization due to the improved fiber dispersion quality. The electrical conductivity percolation is well correlated to the rheological percolation for the as-received fiber resin suspensions. However, with an insulating organic coating on the fiber surface, the conductivity increases slightly and lacks the correlation to the rheological percolation.     

Effect of double doping on crystal structure and electrical conductivity of CaO and WO3-doped Bi2O3

The atomic arrangement of WO₃-doped Bi₂O₃ was found similar to that of the fluorite structure. However, the electrical conductivity of WO₃-doped Bi₂O₃ is significantly lower than that of commonly used Y₂O₃-doped Bi₂O₃. The structure and electrical conductivity of samples formulated as (Ca_xW_0.15Bi_0.85−x)₂O_3.45−x (x = 0, 0.1, 0.2 and 0.3) were investigated. The as-sintered (W_0.15Bi_0.85)₂O_3.45 and (Ca_0.1W_0.15Bi_0.75)₂O_3.35 exhibit similar single tetragonal structure that is isostructural with 7Bi₂O₃·2WO₃. Therefore, (W_0.15Bi_0.85)₂O_3.45 and (Ca_0.1W_0.15Bi_0.75)₂O_3.35 formed a superstructure consisting of 10 enlarged cubic fluorite subcells. However, the as-sintered samples consist of a tetragonal structure and tetragonal CaWO₄ for x = 0.2 and 0.3 because the oxygen vacancy concentration increases. The conductivities of (Ca_xW_0.15Bi_0.85−x)₂O_3.45−x (x = 0, 0.1, 0.2 and 0.3) did not exhibit linear dependence with x value. The best conductivity is 2.35 × 10⁻² S cm⁻¹ at 700 °C for x = 0.1 that is higher than that of Ca-free (W_0.15Bi_0.85)₂O_3.45. The higher conductivity of (Ca_0.1W_0.15Bi_0.75)₂O_3.35 than (W_0.15Bi_0.85)₂O_3.45 may result from the higher anion vacancy concentration and more symmetrical structure.     

A feasible approach to fabricate two-dimensional WS2 flakes: From monolayer to multilayer

Tungsten disulfide (WS₂), with indirect-direct bandgap transition when thinned down to atomically thin flake, provides intriguing applications in next-generation optoelectronics. Here, we develop a feasible approach to fabricate two-dimensional (2D) WS₂ flakes by the evaporation and sulfurization of W film using S powder. The layer number and lateral dimension of the as-grown WS₂ flakes are confirmed by Raman spectroscopy, photoluminescence (PL), optical microscopy, and atomic force microscopy (AFM). The evolution of the layer number and edge length of the flakes is attributed to the concentration gradient of W vapor on the substrate surface in the atmosphere. Our result opens a novel pathway to fabricate other 2D transition metal dichalcogenides (TMDs) and construct 2D TMDs-based heterostructures.     

The synergistic effect of dual substitution of Al and Sb on structure and ionic conductivity of Li7La3Zr2O12 ceramic

Li₇La₃Zr₂O₁₂ (LLZO) with cubic garnet type structure is a promising solid electrolyte. In this work, Li_6.925-3xAl_xLa₃Zr_1.925Sb_0.075O₁₂ (0 ≤ x ≤ 0.1) electrolytes were prepared by conventional solid-state reaction. The influence of Sb-Al cosubstitution on the structure, microstructure and conductivity of Li₇La₃Zr₂O₁₂ were investigated by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and impedance spectroscopy. Single cubic phase has been achieved for Li_6.925-3xAl_xLa₃Zr_1.925Sb_0.075O₁₂ (x = 0–0.075). Suitable amount of Al-Sb cosubstitution accelerates densification and improves the ionic conductivity. Li_6.775Al_0.05La₃Zr_1.925Sb_0.075O₁₂ exhibits highest relative densities (96.7%) and total ionic conductivity (4.10 × 10^?4 S/cm at 30 °C).     

Effects of carbon nanotubes and interphase properties on the interfacial conductivity and electrical conductivity of polymer nanocomposites

L_c is the minimum length of carbon nanotubes (CNTs) required for efficient transfer of filler conductivity to polymer matrix in polymer CNT nanocomposites (PCNTs). In this work, L_c is correlated with the dimensions of the CNTs and the interphase thickness. Subsequently, the interfacial conductivity as well as the effective length and concentration of CNTs are expressed by CNT and interphase properties. Moreover, a simple model for the tunneling conductivity of PCNTs is developed with these effective terms. The impacts of all parameters on L_c, the interfacial conductivity, the fraction of CNTs in the networks and the conductivity of the PCNT are explained and justified. In addition, the predictions of the percolation threshold and conductivity are compared with the experimental results of several samples. The desirable values of interfacial conductivity are achieved by thin, short and super‐conductive CNTs, high waviness and a thick interphase. However, thin and long CNTs, low waviness, a thick interphase, poor tunneling resistivity due to the polymer matrix and a short tunneling distance advantageously affect the conductivity of PCNTs, because they produce large conductive networks. The predictions also show good agreement with the experimental measurements of percolation threshold and conductivity, which confirms the developed equations. © 2020 Society of Chemical Industry     

Nitrogen-doped-CNTs/Si3N4 nanocomposites with high electrical conductivity

Novel highly electrically conducting nanocomposites consisting of a silicon nitride (Si₃N₄) ceramic matrix containing up to 13.6 vol.% of nitrogen-doped multi-walled carbon nanotubes (CNx) were fabricated. As-synthesized CNx were treated with hydrogen peroxide in order to efficiently detach/isolate the nanotubes from bundles, then they were mixed with the ceramic powders and fully densified using the spark plasma sintering (SPS) technique. Composites containing 13.6 vol.% CNx reached an electrical conductivity of 2174 S m⁻¹ that is the highest value reported hitherto for carbon nanotubes/Si₃N₄ nanocomposites. The nitrogen doping also favored a strong mechanical interlocking between the nanotubes and the Si₃N₄ matrix; when compared to the undoped carbon nanotubes. These novel nanocomposites could be used in devices associated to power generation or telecommunications.     

Electrical conductivity relaxation in PVOH-LiClO4-Al2O3

We report on electrical conductivity relaxation measurements of solid polymer electrolytes (SPE) based on poly(vinyl alcohol) (PVOH) and LiClO₄ in which nanoporous Al₂O₃ particles with average pore diameter of 58 Å were dispersed. A power law frequency dependence of the real part of the electrical conductivity is observed as a function of temperature and composition. This behaviour is typical of systems in which correlated ionic motions in the SPE bulk material are responsible for ionic conductivity. This variation is well fitted to a Jonscher expression σ′(ω) = σ₀[1 + (ω/ω₀)^p] where σ₀ is the dc conductivity, ω₀ the characteristic angular frequency relaxation and p is the fractional exponent between 0 and 1. For a prototype membrane with composition 0.9PVOH − 0.1LiClO₄ + 7 wt.%Al₂O₃, it was found that the temperature dependence of σ₀ and ω₀, may be described by the VTF relationship, ? = ?₀ exp[−B/(T − T₀)], with approximately the same constant B and reference temperature T₀, indicating that ion mobility is coupled to the motions of the polymer chains. Moreover, p decreased with increasing temperature, from 0.68 at T = 319 K, to 0.4 at T = 437 K, indicating weaker correlation effects among mobile ions when the temperature is increased.     

保温时间对聚对亚苯基/LiNi-铁氧体纳米复合材料输运性能的影响

以溶剂热法合成聚对亚苯基/LiNi_0.5Fe₂O₄纳米复合材料,分别对放电等离子烧结时不同保温时间制备的样品的电导率和热导率进行了研究。发现,保温时间不同对聚对亚苯基/ LiNi_0.5Fe₂O₄纳米复合材料的电导率没有明显的影响,但对热导率具有一定的影响,保温时间越长热导率越大。保温时间延长,导致铁氧体晶粒长大,使材料体系的声子平均自由程增加,因此声子热导率增加,从而导致总热导率的增加。由于铁氧体具有较差的电输运特性,因此晶粒长大对电导率大小没有明显的影响。     

微滴乳液聚合制备PDMS/SiO2纳米复合材料

采用超声分散的方法,以少量八甲基环四硅氧烷(D₄)对硅溶胶粒子进行表面接枝改性。然后在改性硅溶胶存在下,以十二烷基苯磺酸(DBSA)为乳化剂兼催化剂进行D₄的微滴乳液聚合,得到聚硅氧烷(PDMS)/二氧化硅(SiO₂)纳米复合乳液。采用FTIR、TGA、纳米粒度仪、TEM和拉力机分别对样品进行了表征。结果表明:采用超声分散的方法,能够有效地实现硅溶胶粒子的表面改性。通过微滴乳液聚合得到的复合乳胶粒是聚合物包覆二氧化硅粒子的核壳结构形态。SiO₂的引入提高了有机硅复合膜力学性能,增强了热稳定性。     

Preparation and properties of polypropylene/montmorillonite layered nanocomposites

Polypropylene (PP)/montmorillonite (MMT) nanocomposites have been prepared by melt intercalation using organomontmorillonite and conventional twin screw extrusion. The dispersibility of silicate layers of the montmorillonite in the composites was investigated by using X‐ray diffractometer and transmission electron microscopy (TEM). The silicate layers of montmorillonite are dispersed at the nanometer level in the PP matrix, as revealed by X‐ray and TEM results. The tensile strength of PP/MMT is not much improved compared with pure PP or conventional filled composites. However, the impact strength is greatly improved at lower content of MMT. © 2000 Society of Chemical Industry     

Preparation, structure and electrical conductivity of pyrochlore-type Gd1−xEu2xSm1−xZr2O7 ceramics with a constant lattice parameter

A novel series of Gd_1−xEu_2xSm_1−xZr₂O₇ (x = 0, 1/3, 1/2, 2/3, 1) ceramics with a constant lattice parameter are prepared by solid-state reaction, and are then evaluated as possible solid electrolytes. The microstructure and electrical properties of Gd_1−xEu_2xSm_1−xZr₂O₇ ceramics have been investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and complex impedance analysis. Gd_1−xEu_2xSm_1−xZr₂O₇ ceramics exhibit a single phase of pyrochlore-type structure. The total conductivity of Gd_1−xEu_2xSm_1−xZr₂O₇ ceramics obeys the Arrhenius relation, and gradually increases with increasing temperature from 723 to 1173 K. At 973–1173 K, the composition has little effect on electrical conductivity of Gd_1−xEu_2xSm_1−xZr₂O₇ ceramics. Gd_1−xEu_2xSm_1−xZr₂O₇ ceramics are oxide-ion conductors in the oxygen partial pressure range of 1.0 × 10⁻⁴ to 1.0 atm at all test temperature levels. The maximum total conductivity of Gd_1−xEu_2xSm_1−xZr₂O₇ ceramics is about 1.01 × 10⁻² S cm⁻¹ at 1173 K in air.     

Preparation,structural, and electrical studies of polyaniline/ZnFe2O4 nanocomposites

Polyaniline/ZnFe₂O₄ nanocomposites were synthesized by a simple and inexpensive one‐step in situ polymerization method in the presence of ZnFe₂O₄ nanoparticles. The structural, morphological, and electrical properties of the samples were characterized by wide angle X‐ray diffraction (WAXD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). WAXD and SEM revealed the formation of polyaniline/ZnFe₂O₄ nanocomposites. Infrared spectroscopy indicated that there was some interaction between the ZnFe₂O₄ nanoparticles and polyaniline. The dc electrical conductivity measurements were carried in the temperature range of 80 to 300 K. With increase in the doping concentration of ZnFe₂O₄, the conductivity of the nanocomposites found to be decreasing from 5.15 to 0.92 Scm⁻¹ and the temperature dependent resistivity follows ln ρ(T) ∼ T^−1/2 behavior. The nanocomposites (80 wt % of ZnFe₂O₄) show a more negative magnetoresistance compared with that of pure polyaniline (PANI). These results suggest that the interaction between the polymer matrix PANI and zinc nanoparticles take place in these nanocomposites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Electrical conductivity and thermal properties of spark plasma sintered Al2O3-SiC-CNT hybrid nanocomposites

In this study, we report the electrical conductivity and thermal properties of Al₂O₃-SiC-CNT hybrid nanocomposites processed via ball milling (BM) and spark plasma sintering (SPS). The initial powders and consolidated samples were characterized using transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM), respectively. A multifunction calibrator and a high-resolution digital multimeter were used to measure the electrical conductivity. The thermal properties were measured using a thermal constants analyser. The SiC and CNT-reinforced alumina hybrid nanocomposites exhibited a significant increase in their room-temperature electrical conductivity, which made them suitable for electrical discharge machining. The Al₂O₃-5SiC-2CNTs had a high electrical conductivity value of 8.85 S/m compared to a low value of 6.87×10⁻¹⁰ S/m for the monolithic alumina. The addition of SiC and CNTs to alumina decreased its room-temperature thermal properties. The increase in temperature resulted in a decrease in the thermal conductivity and thermal diffusivity but an increase in the specific heat of the monolithic alumina and the hybrid nanocomposites. These properties were correlated with the microstructure, and possible transport mechanisms were discussed.     

Electrical discharge machining of B4C-TiB2 composites

The interrelationships between the microstructure and electrical discharge machining (EDM) behaviour of B₄C-TiB₂ composites with respectively 30, 40 and 60 vol.% TiB₂ are investigated. Special attention was given to the influence of the grain size on the EDM behaviour by producing composites with an ultrafine TiB₂ phase using in situ synthesis during PECS. The experimental work revealed that 40 vol.% of TiB₂ results in an optimal material removal rate while the surface roughness for rough cut EDM decreases with increasing TiB₂ content. The finer microstructure of the ultrafine composite shows higher MRR's and lower R_a values than the commercial powder based composites. The major material removal mechanism for the PECS based composites was melting. The 3 point bending strength of all composites after grinding, EDM rough cut and EDM finish cut was not statistically different and about 800 MPa. The EDM recast layer was analysed by X-ray photoelectron spectroscopy.     

The thermal conductivity of Nylon 6/clay nanocomposites

Nylon 6/clay nanocomposites (NCNs) of different clay loadings are prepared by melt compounding. The effects of clay loading and dispersion on the thermal conductivity of NCNs are investigated using XRD, TEM, DSC, and POM. The results show that the thermal conductivity of the exfoliated NCNs decreases with an increase of clay content; but the thermal conductivity of the intercalated NCNs does not decrease, indeed, it increase markedly at high clay content. Such results observed in the exfoliated NCNs are opposite to the expectation of the classic Maxwell thermal conduction model. The further investigations indicate that such decrease observed in the exfoliated NCNs is due mainly to the exfoliation of clay layers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Enhancement of density and ionic conductivity for garnet-type Li5La3Ta2O12 solid electrolyte by self-consolidation strategy

Garnet-type Li₅La₃Ta₂O₁₂ (LLTaO) solid electrolyte is a potential candidate component for future all-solid-state batteries due to its extraordinary stability against the reaction with molten lithium. In contrast with traditional cold isostatic pressing (CIP) method, which generally pursues ultra-high pressure, this paper tries to enhance the density and ionic conductivity of LLTaO by self-consolidation strategy without the assistance of any pressing operations. A LLTaO bulk with a relative density of 95% is obtained. SEM images reveal that the bulk sample is assembled by large dense particles in size of tens of microns indicating that the interstitial space among the particles has been dramatically minimized. Accordingly, the total ionic conductivity and the bulk ionic conductivity at 30?°C are promoted up about one order of magnitude higher to 2.63?× 10^?5 S?cm^?1 and 1.41?×?10^?4 S?cm^?1, respectively. Moreover, the lithium ionic migration network in the crystalline unit cell of LLTaO is first explored from its assembled way. A hexagon-like basic unit with tetrahedral Li1 joint sites and Li1- - Li1 edges is identified. The tetrahedral Li1 sites act as crucial junctions for the transportation of lithium ions. This work would significantly stimulate the development of LLTaO electrolyte membrane technology.     

Structural anomaly and electrical relaxation in (Na2/3Pb1/3)(Mn1/2Nb1/2)O3 ceramics

The X-ray diffraction patterns of (Na_2/3Pb_1/3)(Mn_1/2Nb_1/2)O₃ ceramics were measured within 15–850 K temperature range. The anomaly in the thermal expansion temperature dependence occurred in 250–365 K range. The generalised Cole–Cole model was proposed to describe the measured effective electric permittivity influenced by high electric conduction and the coexistence of two contributions ?*(T,f) = ?*_lattice + ?*_carriers was considered. The analysis of the electric permittivity and conduction exhibited two relaxation processes. The electric conduction relaxation characteristic time values indicated the small polaron mechanism with τ₀ ≈ 10⁻¹³ s occurring in 240–345 K range and the ionic mechanism with τ₀ ≈ 10⁻¹¹ s involved in the other relaxation occurring in the 320–510 K range. The ionic relaxation process was ascribed to a subsystem of defects, which was weakly interrelated to the anomaly in thermal expansion of the (Na_2/3Pb_1/3)(Mn_1/2Nb_1/2)O₃ ceramics. The Gate model was proposed to describe the ionic relaxation mechanism.     

Inclusions of Nanometer-Sized Al2O3 Particles in a Crystalline (Sc,Lu)2(WO4)3 Matrix

Nanometer-sized Al₂O₃ particles were successfully synthesized as crystalline inclusions by mixing both components to form the nanometer-sized particles and the (Sc,Lu)₂(WO₄)₃ matrices in a crystal lattice by preparing a solid solution of (Sc,Lu)₂(WO₄)₃ and Al₂(MoO₄)₃ and then decomposing the solid solution. The particles were dispersed uniformly and without agglomeration, which is commonly observed with conventional preparation techniques. The average particle size of the Al₂O₃ was 3.5 nm, and the standard deviation was estimated to be 1.1 nm.     

Synthesis and electrochemical studies of a layered spheric TiO2 through low temperature solvothermal method

This paper demonstrates a low temperature solvothermal method for the synthesis of a layered spheric TiO₂. The crystal structure and morphology of the material were characterized by using X-ray diffraction (XRD) and scanning electron miscopy (SEM). Electrochemical performances of the TiO₂ when used as anode material in lithium ion batteries were investigated by galvanostatic charge/discharge and cyclic voltammetry experiments. A discharge capacity of 179 mAh g⁻¹ was obtained in the potential range between 3.0 and 1.5 V. No significant capacity decay was observed in the successive 30 cycles showing satisfactory cycling performance of the electrode.     

Electrochemical lithium insertion in (PO2)4(WO3)2m (2 ≤ m ≤ 10): Relation among the electrochemical insertion process and structural features

In this work it is presented a review of the main results obtained during the electrochemical lithium insertion in the family of monophosphate tungsten bronzes (PO₂)₄(WO₃)_2m (2 ≤ m ≤ 10). This family of oxides is a good system in order to study the relation among the electrochemical processes observed in the course of lithium insertion and the changes of bronzes structures. By means of X-ray diffraction experiments, the nature of Li_x(PO₂)₄(WO₃)_2m phases has been elucidated and a correlation with the reversible/irreversible processes observed during the electrochemical insertion has been established. The electrical properties of the inserted Li_x(PO₂)₄(WO₃)_2m phases were measured and a relation with the amount of lithium inserted and m was also found.