MWCNTs/PS复合材料导电性能及导电行为研究

多壁碳纳米管(MWCNTs)与聚苯乙烯(PS)熔融共混,制备试样,部分试样进行热处理。通过导电性能的测试研究了不同测试温度对MWCNTs/PS非结晶复合材料电性能及其导电行为的影响;通过SEM观察了该复合材料的表面形貌。研究结果表明:随着MWCNTs加入量的增加,MWCNTs/PS的体积电阻率(ρ)呈现下降趋势;当MWCNTs加入量达到8.0%,复合材料的ρ降到102数量级;120℃热处理后MWCNTs(10.0%)/PS复合材料的ρ比未经热处理的ρ下降近1个数量级;MWCNTs(10.0%)/PS 1-3型复合材料的PTC行为不明显,但5.0%MWCNTs/PS1-3型复合材料的PTC效应明显,在150℃以后,出现NTC效应。     

Monitoring experiment and simulation on solidification of DNAN based melt-cast explosive with FBG sensors

In order to obtain the change rule of the temperature field and the mechanism of defect formation during the solidification process of melt-cast explosive, the temperature field change data were tested during the solidification process of DNAN based melt-cast explosive by using an arrayed spatially distributed Fiber Bragg Grating (FBG) temperature sensor device. The temperature field variation during the solidification experiment was obtained under the condition that the cooling rate of the boundary water-bath temperature was 0.2 °C/min. On the basis of the solidification experiments, the macroscopic solidification process of small-caliber grenade at different boundary cooling rates was simulated using ProCAST software. The simulation results show that when the boundary cooling rate is 0.2 °C/min, the temperature fields during the solidification process of DNAN based melt-cast explosive are in good agreement with that of the experimental monitoring points; the size of the melt-cast charge defects decreases as the boundary cooling rate becomes smaller; and the location of the charge defects is closer to the tail of the grenade as the cooling rate decreases. In addition, a mesoscopic model of DNAN based melt-cast explosive was established in the paper. At the mesoscopic level, the generation, formation, and evolution of charge defects in DNAN based melt-cast explosive during solidification were investigated. The study results provide theoretical guidance for the formulation design and process optimization of DNAN based melt-cast explosives, as well as for improving the charge quality of ammunition.     

减少双螺杆挤出机螺杆铸造缺陷的一些认识和改进

双螺杆挤出压片机是满足现代橡胶工业大规模生产所需重要设备,特别是对全钢子午线轮胎胶料加工具有极大的优越性,是全钢子午线轮胎胶料加工的关键性设备。螺杆是挤出机的关键部件,其强度和耐磨性有比较高的要求。通常采取铸造成型,螺杆铸件加工后缺陷多,铸件合格率低,本文通过精益六西格玛理论,对此进行分析,找出问题的关键点,加以改进和控制,使螺杆铸件合格率大幅提高。进而为产品质量、交货期、节约制造成本提供了有力保证。     

Thermal conductivity of graphene nanoribbons with defects and nitrogen doping

Thermal conductivity of defective graphene nanoribbons doped with nitrogen for different distributions around the defect edge at nanoscale is investigated using the reverse non-equilibrium molecular dynamics (RNEMD) method, which explores ways to improve thermal management. In addition, thermal conductivity of graphene nanoribbons with both defects and nearby nitrogen doping is investigated in comparison to that of nanoribbons with defects alone. The simulation results are analyzed from three perspectives: phonon match, concentration of N doping, and distribution of N doping. This approach reveals that a coupling effect is the cause of the observed results. Nitrogen doped graphene nanoribbons (both perfect and defective variants) perform better with thermal management than do graphene nanoribbons with defects alone, which is of considerable interest. Based on these investigations, a guide for graphene-interconnected circuits design is implied.     

掺杂、吸附和空位缺陷对碳纳米管导热的影响

采用非平衡分子动力学方法,选用反应经验键序势能,模拟了分别含有掺杂、吸附和空位点缺陷的碳纳米管的导热,并开展了基于第一性原理的声子谱分析;研究了碳管长度、管径、手性以及环境温度等因素的影响。缺陷效应分析表明：与完整无缺陷碳纳米管相比,掺杂、吸附和空位均会导致碳管热导率显著下降,以及碳管轴向温度分布在缺陷处产生非线性的间断性跳跃;缺陷类型对碳管热导率的影响最大,管径次之,管长影响相对最小;而空位、掺杂和吸附对碳管热导率的影响力依次是减小的。     

New NOx sensors based on hematite doped with alkaline and alkaline-earth elements

Alkaline (lithium, potassium, rubidium) and alkaline-earth (magnesium, barium) doped hematite materials were studied for NO₂ sensing application. The synthesized materials were characterized by laser granulometry, X-ray diffraction and scanning electronic microscopy. A temperature of 1300 °C was chosen as the optimal heat treatment in order to obtain the densest material. Humidity dependence of the electrical properties revealed a strong influence in the case of rubidium doped hematite material while the other doped materials were less sensitive.The AC impedance analyses underlined the n-type intrinsic semi-conduction of pure hematite. Alkaline-earth doped hematite materials showed two semi-conducting regions, below and above 500 °C, corresponding to extrinsic and intrinsic n-type semi-conduction, respectively. These electrical analyses associated with SEM observations suggested instability of the ferrites formed in rubidium and potassium doped materials.AC electrical measurements were performed in the 0-500 ppm NO₂ partial pressure range. The alkaline-earth doped hematite materials exhibited the most promising behavior.     

Electrochemical sensors for detection of hydrogen in air: model of the non-Nernstian potentiometric response of platinum gas diffusion electrodes

The potentiometric response of three different platinum gas diffusion electrodes deposited on H₃PO₄ doped polybenzimidazole (PBI) was investigated under humidified atmospheres that contained H₂ or mixtures of H₂ and O₂. Continuum modelling was used to analyse the response. It is shown that the non-Nernstian response under H₂H₂ON₂ mixtures can be explained by a difference of water activity on both sides of the membrane. Under H₂O₂N₂ mixtures, the oxygen mass transport parameters have a strong effect on the electrode sensitivity.     

单层氮化硼空位缺陷的形成与稳定性的研究

本文利用密度泛函理论方法研究了单层氮化硼中多原子空位缺陷的结构和稳定性。研究发现缺陷多为对称结构,并且存在幻数现象。通过对不同尺寸缺陷离解能的回归分析,发现对于尺寸较大的缺陷,周围的氮原子数越多,缺陷越稳定,该结论很好的解释了实验中观察到的现象。     

Synthesis and characterization of calcium double perovskites for the potential application of semiconducting CO2 sensors

A conventional solid-state sintering method was used to prepare double perovskite structured compounds BCN (Ba₂Ca_0.67Nb_1.33O₆), BCNCo (Ba₂Ca_0.67Nb_1.33-xCo_xO_6-δ) and BCNCoFe (Ba₂Ca_0.67Nb_0.67Co_0.66-yFe_yO_6-δ), which exhibit significant chemical stability in nitrogen, air, and 2 % CO₂ (balanced by nitrogen). SEM images show that the Co dopant causes a dense microstructure for BCNCo compounds. In contrast, the introduction of Fe tends to produce a porous and web-like microstructure for the BCNCoFe series. Ba₂Ca_0.67Nb_0.67Co_0.66O_6-δ has a reasonable response (recovery) time at 750 °C and it seems suitable for CO₂ detection at elevated temperatures. Among the BCNCoFe compounds, Ba₂Ca_0.67Nb_0.67Co_0.33Fe_0.33O_6-δ has the largest capacitance as the CO₂ concentration changes from 0 to 2000 ppm, and it exhibits satisfactory sensitivity and repeatability in the temperature range of 450–700 °C with an extra voltage of 0.1 V. To further consider the Ba₂Ca_0.67Nb_0.67Co_0.33Fe_0.33O_6-δ compound for CO₂ sensing, a sol-gel method was utilized. The sol-gel-prepared Ba₂Ca_0.67Nb_0.67Co_0.33Fe_0.33O_6-δ senses CO₂ well, and its concentration changes from 0 to 2000 ppm (or from 0 to 300 ppm) in the temperature range of 400–600 °C. The different CO₂ sensing properties of all prepared double perovskite compounds can be interpreted by the different surface areas that play critical roles in the chemical adsorption of related gaseous species.     

Synthesis and Characterization of Low-Cost Electroactive Hybrid Composites Derived From Polyaniline and NiS

The synthesis and characterization of conducting polyaniline (PANI) salt and nickel sulfide (NiS) hybrid composites are reported in this study. The PANI-NiS hybrid composites showed nearly two orders of magnitude higher than that of pure PANI. The specific conductivities of PANI and PANI-NiS hybrid composites (2% and 20% by weight) were found to be 5.1 × 10^?4, 1.6 × 10^?2, and 3.8 × 10^?2 S/cm. The polarity of Hall voltage of the hybrid composite was found to be negative indicating that the PANI-NiS composite is an n-type semiconductor. The composites pellets were characterized by XRD, SEM and FTIR and the results were compared.     

Conductivity of iron-doped strontium titanate in the quenched and degraded states

The electrical behavior of iron-doped strontium titanate (Fe:SrTiO₃) single crystals equilibrated at 900°C and quenched below 400°C at various oxygen partial pressures () was investigated via impedance spectroscopy and compared to defect chemistry models. Fe:SrTiO₃ annealed and quenched between 1.2 × 10⁻¹⁴ and 2.0 × 10⁻⁴ Pa exhibits a conduction activation energy (E_A) around 0.6 eV, consistent with ionic conduction of oxygen vacancies. However, sudden changes in E_A are found to either side of this range; a transition from 0.6 to 1 eV is found in more oxidizing conditions, while a sudden transition to 1.1 and then 0.23 eV is found in reducing These transitions, not described by the widely used canonical model, are consistent with predictions of transitions from ionic to electronic conductivity, based on first principles point defect chemistry simulations. These models demonstrate that activation energies in mixed conductors may not correlate to specific conduction mechanisms, but are determined by the cumulative response of all operative conduction processes and are very sensitive to impurities. A comparison to electrically degraded Fe:SrTiO₃ provides insight into the origins of the conductivity activation energies observed in those samples.     

Soft sensors model optimization and application for the refinery real-time prediction of toluene content

Industrial facilities nowadays show an increasing need for continuous measurements, monitoring and controlling many process variables. The on-line process analyzers, being the key indicators of process and product quality, are often unavailable or malfunction. This paper describes development of soft sensor models based on the real plant data that could replace an on-line analyzer when it is unavailable, or to monitor and diagnose an analyzer’s performance. Soft sensors for continuous toluene content estimation based on the real aromatic plant data are developed. The autoregressive model with exogenous inputs, output error, the nonlinear autoregressive model consisted of exogenous inputs and Hammerstein–Wiener models were developed. In case of complex real-plant processes a large number of model regressors and coefficients need to be optimized. To overcome an exhaustive trial-and-error procedure of optimal model regressor order determination, differential evolution optimization method is applied. In general, the proposed approach could be, of interest for the development of dynamic polynomial identification models. The performance of the models are validated on the real-plant data.     

The influence of the reaction medium of oxidative methane coupling on the nature of bulk defects of the Li/CaO system

The relationship of the catalytic activity of Li/CaO (0 Li 1.7 at%) in CH₄ oxidative coupling with the defectness of the matrix has been studied. It was shown that the activity of undoped CaO increases with the rise of concentration of anion and cation vacancies. The concentration and nature of defects in the pure CaO are independent of the composition of the gas (O₂, N₂O, CH₄ or reaction mixture). The incorporation of Li ions into the CaO lattice and also the treatment of Li/CaO with the reaction mixture lead to a change of the character of bulk defects and catalytic properties of the oxide. The signals from O ₃ ^– , CO ₂ ^– and LiCO ₃ ^– centers are detected in the EPR spectra of -irradiated Li/CaO catalysts after the contact with the CH₄-O₂ mixture. Such defects are not observed when a CH₄-N₂O mixture is used. Simultaneously, the replacement of O₂ by N₂O in the reaction mixture is accompanied by the decrease of the CO formation rate and the increase of activity in the C₂-product formation.     

Characterization and electron transport properties of polyaniline nanocomposites containing silver chloride nanoparticles embedded on the gelatin surface

ABSTRACT

Polyaniline (PANI) encapsulating silver chloride nanoparticles embedded on the surface of gelatin nanofibers were prepared. The interaction of PANI/gelatin with AgCl and crystallinity of the composites are characterized by FTIR and XRD. The surface framework of the composites was studied by SEM and TEM. Increase of AgCl has brought out significant increase of DC conductivity of the composites. The hydrophilic GEL acts as a plasticizer in the PANI/GeL-AgCl increases the mobility of charge carriers in the composites which influences the conductivity. Such composites are used in electric devices, sensors, and functional coatings for their high electrical conductivity.     

Effect of drawing on the molecular orientation and polymorphism of melt‐spun polyvinylidene fluoride fibers: Toward the development of piezoelectric force sensors

Thin piezoelectric polyvinylidene fluoride fibers containing a high piezoelectric β‐phase content of up to 80% were developed in this work using a melt‐spinning process. After crystallization from the melt, the fibers were subsequently stretched unidirectionally at 120°C between 25 and 75% of their original length. The effects on the molecular orientation, polymorphism and tensile properties of the fibers were investigated. Polarized infra‐red spectroscopy and X‐ray diffraction results show that the conversion of α‐phase to β‐phase occurred during the stretching process as a result of molecular alignment and creation of a dipole induced by the CF₂ groups normal to the fiber direction. These fibers were then integrated into various weave architectures in order to design flexible two‐dimensional textile‐based piezoelectric force sensors. The piezoelectric responsiveness of these materials, tested under impact (70 Newton force, 1 Hz frequency) was very promising, with a maximum output voltage of up to 6 V and an average sensitivity of up to 55 mV/N measured. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of Nd3+ and Cd2+ ions co-substitution on the dielectric and electron transport properties of spinel strontium nanoferrites

The work reports microemulsion synthesis of spinel nanoferrites having a nominal composition of Sr_1−xNd_xFe_2−yCd_yO₄ (0.0≤x≤0.1, 0.0≤y≤1.0). X-ray diffraction (XRD) patterns of powdered products annealed at 1073 K for three hours revealed the cubic Spinel structure with an average crystallite size in the range of 23–35 nm. The room temperature dc resistivity (ρ) has its maximum value for the composition Sr_0.92Nd_0.08Fe_1.2Cd_0.8O_4. However, for this composition the dielectric parameters and ac conductivity have their minimum values. The magnitudes of these parameters decrease with increasing frequency at low frequency region and then show almost independent frequency behavior at higher frequencies. The results are interpreted in terms of dielectric polarization with great detail. Electrochemical impedance spectroscopy results revealed that conduction process is predominantly governed by grain boundary volume. High resistivity and low dielectric constant of investigated material suggests that it may be employed in microwave devices.     

Effect of sintering temperature on the electrical and gas sensing properties of tin oxide powders

Tin oxide is an n-type semiconducting material having superior properties that can be utilized in several applications. The warning and detection of several dangerous gases in the environment are possible by utilizing gas sensors. The comprehensive functionality of these sensors could help to reduce the risk of severe health hazards and unexpected explosion risks. Tin oxide-based gas sensors exhibit reliable gas sensing performances along with respectful sensitivity and selectivity. Tin oxides in micro-and nano-particle forms provide an extremely high surface-to-volume ratio, which is favorable for gas sensors. Processing and synthesis of tin oxide particles accompany high-temperature processes, and this paper focuses on studying the effect of sintering temperatures on the structural and grain size of the commercially available tin oxide particles. The surface morphology of the tin oxide samples sintered at three different temperatures of 1100, 1200, 1300 ^°C shows a clear difference in the grain size and further affecting the dielectric properties of the materials. The gas sensing performances of three tin oxide samples are investigated by fabricating a pellet-type gas sensor. The sensor with the sintering temperature of 1200 ^°C exhibits the best gas-sensing performance with high response and low limit of detection (LOD). Our results suggest that the sintering temperature plays a vital role in deciding the dielectric properties and grain sizes, which are important parameters that affect the gas sensing behavior of tin oxide micro-and nano-particles.     

5．5m捣固焦炉煤塔结构缺陷治理与研究

5．5m捣固焦炉煤塔结构在设计和施工中存在问题,导致深梁底部向外挑出的“牛腿”出现竖向裂缝、振动给料器产生共振、脚手架支承系统失稳等现象。分析问题产生的原因,并通过对“牛腿”裂缝修补、增加剪力墙、改进脚手架支承系统等方法对结构缺陷进行有效的治理。     

Magnetocaloric effect and magnetic properties of the isovalent Sr2+ substituted Ba2FeMoO6 double perovskite

Fine-tuning the charge distribution in Ba₂FeMoO₆ obtained via “isovalent” substitution at the A-site (i.e., Ba) is expected to bring about changes in the physical properties of the system that can be manipulated in magnetic refrigerants. With this motivation, the phase formation, crystal structure, microstructure, magnetic and magnetocaloric properties of the Ba_2−xSr_xFeMoO₆ (0≤x≤0.4) samples fabricated by solid state reaction method have been investigated. The X-ray diffraction analysis confirmed the formation of cubic structure with Fm3m space group in all the fabricated samples. The magnetization measurements and Arrott analysis revealed a second order of ferromagnetic phase transition in all the samples. An increase in magnetization and Curie temperature (T_C) was observed with the increase in Sr-content that was attributed to the increased orbital hybridization and exchange interaction between Fe and Mo ions. The magnitude of the maximum magnetic entropy change at the Curie temperature and the relative cooling power were observed to slightly decrease with the increased Sr doping. The excellent magnetocaloric features and convenient adjustment of Curie temperature make these materials useful for magnetic refrigeration in a wide range of temperature.     

Influence of growth temperature on the microstructure and electrical transport properties of epitaxial NiCo2O4 thin films

In the work reported here, NiCo₂O₄ films were grown epitaxially on LaAlO₃ (111) substrates at temperatures between room temperature and 700?°C. The effects of the substrate temperature (T_sub) on the structural, electrical and magnetic properties and on the Hall effect of the film were investigated. T_sub has a great influence on the cation disorder. High T_sub makes substitution of Ni (Oh) for Co (Td) easier, and changes the relative Ni³⁺/Co³⁺ concentration. The film grown at 400?°C had a relatively larger concentration of Ni³⁺, which lowers the resistivity and enhances the ferrimagnetism of the NiCo₂O₄ film. In addition, a sign change in the Hall coefficient from negative to positive was observed with increasing measurement temperature for each of the samples grown at different substrate temperatures.