Mechanical and electrical properties of carbon nanotube reinforced epoxide resin composites

Carbon nanotubes （CNTs）/epoxide resin composites were prepared, the mechanical and electrical properties of the composites were investigated. The effects of concentration and dispersion state of CNTs on the tensile strength, tensile modulus and electrical resistance of the composites were studied. The results indicate that the CNTs can be dispersed well in the epoxide resin matrix by ultrasonic method, and the mechanical and electrical properties of epoxide resin matrix can be improved significantly. The tensile tests show that the tensile strength and tensile modulus are higher than those of epoxide resin if the content of CNTs is less than 1.75% （mass fraction）. When the content of CNTs is 0.75%, the conditional best results are obtained, the tensile strength of the composite is the highest, increased by 18.3% and the tensile modulus is increased by 20.5% compared with the matrix. With the increase of CNTs, the electrical resistance of the composites decreases greatly, while the conductivity of the composite increases. The percolation threshold values of electrical characteristic transformation for this composite material were determined for the first time.     

Measurement of electrical conductivity of micron-scale metallic wires

Electrical conductivltles of micron-scale aluminum wires were quantitatively measured by a four-point atomic force microscope （AFM） probe. This technique is a combination of the principles of the four-point probe method and standard AFM. This technique was applied to the 99.999% aluminum wires with 350 nm thickness and different widths of 5.0, 25.0 and 50.0 μm. Since the small dimensions of the wires, the geometrical effects were discussed in details. Experiment results show that the four-point AFM probe is mechanically flexible and robust. The four-point AFM probe technique is capable of measuring surface topography together with local electrical conductivity simultaneously. The repeatable measurements indicate that this technique could be used for fast in-situ electrical properties characterization of sensors and microelectromechanical system devices.     

Preparation of nanocrystal modificator and its modification mechanism

In order to increase the modifying effect, the Cu-P master alloy was rapidly solidified with melt-spin method, and the nano-sized ribbon was gained at 10^5-10^6 ℃/s. Subsequently, ZL109 alloy was modified by nanocrystal and massive Cu-P master alloy, respectively, with molten metal casting method. The results show that the microscopic structure of ZL109 alloy modified by nanocrystal Cu-P master alloy is better than that modified by massive Cu-P master alloy, the original crystal silicon and eutectic silicon are refined more effectively and the mechanical properties are increased evidently： the tensile-strength is increased by 25%, the elongation is increased by 32.26% and the hardness is increased by 17.2%. Therefore, the melt-spin treatment is a feasible method to improve the modifying effect of Cu-P master alloy.     

Decomposition process of zircon sand concentrate with CaO-NaOH

The decomposition process for zircon sand concentrate using mixed base of sodium hydroxide partly replaced by calcium oxide was inrestigated.It is found that the decomposition rate of zircon gradually increased with the increase of the reaction temperature and time.The decomposition rate is over 97% with the conditions that CaO/zircon molar ratio is 0.25 ～ 0.75 at 800 ℃ for 1 h.Whereas the decomposition rate decreased when the molar ratio was more than 0.75.Also,thermogravimetry-differential thermal analysis（TG-DTA） and X-ray diffraction（XRD） were used to study the reaction mechanism of zircon decomposition process with CaO-NaOH.The results showed that Na₂O,which was generated by the reaction of CaO and Na₄SiO₄,increased the decomposition rate of zircon owing to its spread to the surface of zircon and played a role in decomposition process.     

Preparation and conductivity of nanocrystalline rare earth mixed oxides SmFe1—xCoxO3—δ

Nanocrystalline rare earth mixed oxides SmFe1-xCoxO3-δ were prepared by sol-gel method at 1073K for 2h calcination and characterized by X-ray diffraction(XRD) and scanning electron microscope(SEM).The results show that SmFe1-xCoxO3-δhas the structure of perovskite type.The conductivity of the materials increases with the temperature rising and the maximum conductivity at 1073 K is 2.6 S/cm with the best mole ratio of Fe^3 to Co^3 being 1:4.This kind of oxide is a conductive ceramic material by means of conduction of electron and oxygen anion.     

ARTIFICIAL NEURAL NETWORK MODEL OF CONSTTTUTIVE RELATIONSHIP FOR 2A70 ALUMINUM ALLOY

The hot deformation behavior of 2A70 aluminum alloy was investigated by means of isothermal compression tests performed on a Gleeble-1500 thermal simulator over a wide range of temperatures 360-480℃ with strain rates of 0.01-1s-1 and the largest deformation of 60%, and the true stress of the material was obtained under the above-mentioned conditions. The experimental results shows that 2A70 aluminum alloy is a kind of aluminum alloy with the property of dynamic recovery; its flow stress declines with the increase of temperature, while its flow stress increases with the increase of strain rates. On the basis of experiments, the constitutive relationship of the 2A70 aluminum alloy was constructed using a BP artificial neural network. Comparison of the predicted values with the experimental data shows that the relative error of the trained model is less than ±3% for the sampled data while it is less than ±6% for the non- sampled data. It is evident that the model constructed by BP ANN can accurately predict the flow stress of the 2A70 alloy.     

Preparation of Y2O3：Eu^3＋ phosphor by molten salt assisted method

A kind of fine and quasi-spherical Y2O3：Eu^3＋ phosphor was prepared by firing a preparative precursor at 1 200 ℃ for 2 h with the molten salts of Na2CO3, S and NaCl. The precursor was obtained by homogeneous precipitation of yttrium and europium with oxalic acid when using EDTA, citric acid or starch as complexant. The structure and morphology of the phosphors were characterized by XRD and SEM, respectively. The influence of complexing environment, firing temperature and molten salts on formation of the phosphor Y2O3：Eu^3＋ was discussed. The result show that the prepared Y2O3：Eu^3＋ phosphor is of quasi-spherical structure with size of 2-3 μm. Its luminescent intensity is 30% higher than that of the same phosphor prepared by the same procedure but without molten salts, and is 5% higher than that of commercial Y2O3：Eu^3＋ red phosphor.     

Electro-Optics and Band Gap Energies of Nanosilver-Coated TiO_2 Nanotubes on Titanium Metal

TiO_2 nanotubes on Ti metal surface were prepared by the electrochemical anodization method. Then, nanosilver was deposited onto the nanotubes by the electroless dip coating and the anodization. The obtained TiO2 nanotubes were examined by using scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, cyclic voltammetry, and UV–Vis. The electrochemical band gap(E_g~(CV)) of the nanosilver-coated TiO_2 nanotubes prepared by the anodization was found as 1.54 eV. Using the UV–Vis measurements, the optical band gap energy(E_g~(op).) was calculated as 1.51 eV for the Ag/TiO_2 nanotubes obtained by electroless dip coating. The electrical conductivity of the TiO_2 nanotubes also increased from 3.0 9 10-4 to 34.7 S/cm after nano Ag deposition by the anodization method.These Ag/TiO_2 nanotubes with low band gap and high electrical conductivity are desirable for the applications in electronics, Li-ion batteries, and solar cells.     

The Influence of Nano-Al2O3 Additive on the Adhesion between Epoxy Resin and Steel Substrate

The influence of nano-A1203 additive on the adhesion between epoxy resin and steel substrate has been investigated. The results of tensile testing indicated that the adhesion strength was increased dramatically by addition of Al2O3 nanoparticles in epoxy resin compared with that of the unmodified resin. The highest adhesion strength was obtained with 1 wt% nano-Al2O3 added in epoxy adhesive, more than two times higher than that of the unmodified. Scanning electronic microscope (SEM) revealed that a boundary layer exists between epoxy and steel substrate, energy spectrum analysis indicates there is enrichment of the nano-Al2O3 particle. Those results confirmed that the nano-Al2O3 additive was closely related to the change of interface morphology and the improvement of adhesion strength. The reason for adhesion improvement was also be discussed.     

Strategy to Improve the Performance of Dye-sensitized Solar Cells Based on TiO2 Films Prepared by Room Temperature Cold Spray

Dye-sensitized solar cells(DSCs)are promising photochemical solar cells owing to their high efficiency and low cost.In this study,the influence of cell geometry,electrolyte composition,and counter electrode(CE)characteristics on the performance of DSCs was investigated to aim at improving the cell efficiency.Using an U-type cell geometry proposed decreased the internal resistance of DSCs and therefore increased the fill factor and energy conversion efficiency.The addition of DMPII to the I-/I3-based electrolyte increased the open-circuit voltage by decreasing the dark current.Compared to the DSCs with the Pt CE prepared by the thermal decomposition of H2PtCl6,the DSCs with the sputtered Pt CE showed a higher fill factor and short-circuit current density,owing to the high electrical conductivity and enhanced light-reflecting ability of the mirror-like sputtered Pt CE.Based on these results,the energy conversion efficiency of the DSC with the TiO2 porous films fabricated by a room temperature cold spray method was increased from 3.93%to 5.11%.The relatively high efficiency shows that the room temperature cold spray is a prospective method in fabricating nanocrystalline TiO2 films for flexible DSCs.     

溶胶-凝胶法合成导电SrVO3 粉末

通过溶胶-凝胶法结合热处理合成了导电SrVO₃粉末。在溶胶配制过程,对Sr:V摩尔比进行精确调控,再通过对凝胶热分解行为的表征,确定其煅烧温度和除去残余碳,从而获得前驱体粉末,再将其在H₂中还原以获得最终产物。研究了煅烧温度、Sr:V摩尔比对产物形貌、结构和组成的影响,并采用标准直流四探针技术对样品的电导率进行测试。结果表明,当Sr:V摩尔比为1:1.06,煅烧温度500 ℃,再在850 ℃氢气还原,可以制备没有残余碳或钒的氧化物杂质的单相SrVO₃粉末。SrVO₃粉末的电导率达到714.3 S/cm,比石墨粉末的电导率（500 S/cm）高。     

Ho添加对Al-Zn-Mg-Cu合金均匀化热处理过程中微观组织和性能演变的影响

通过SEM、OM和DSC,研究添加Ho的Al-Zn-Mg-Cu合金均匀化热处理制度,测试不同均匀化热处理过程中合金的电导率和硬度变化。结果表明,铸态合金中存在4种第二相：T(AlZnMgCu),Al₇Cu₂Fe,Al₈Cu₄Ho 及S (Al₂CuMg),第二相导致合金元素分布存在严重微观偏析。合金在475 ℃均匀化热处理20 h后,T相完全回溶基体且未观察到S相,仅剩余Al₇Cu₂Fe和Al₈Cu₄Ho。硬度和电导率随T相的回溶而变化,T相的回溶使得合金硬度升高,电导率降低。同时,在475 ℃均匀化热处理5~20 h过程中,Al₃Ho相析出,这一现象引起硬度和电导率的升高。结合均匀化动力学分析,确定合金适宜的均匀化热处理制度为470~475 ℃/20~25 h。     

Microstructure and Properties of Porous Ni50Cr50-Al2O3 Cermet Support for Solid Oxide Fuel Cells

The microstructure of the cermet support significantly influences the performance of solid oxide fuel cells (SOFCs). The properties required for the support include high electrical conductivity, necessary permeability, good match of thermal expansion with other layers, and high strength. In this study, a flame-sprayed porous Ni50Cr50-Al₂O₃ cermet was designed as the support of SOFCs. The effect of cermet microstructure on its gas permeability, electrical conductivity, thermal expansion coefficient (TEC), and bending strength was investigated. Results show that the gas leakage rate of the cermet increased with the increase of polyester content in the starting powder. The cermet exhibited a thermal expansion coefficient of 11.39 × 10^?6 K^?1 from 25 to 1000 °C. Moreover, the electrical conductivity of the cermet increased significantly and reached 1015 S/cm after sintering at 1000 °C for 15 h. The bending strength of the cermet reached 171 MPa. The cermet stability at high temperatures and SOFCs’ performance are discussed.     

High-Temperature Electrical Insulation Behavior of Alumina Films Prepared at Room Temperature by Aerosol Deposition and Influence of Annealing Process and Powder Impurities

Alumina (Al₂O₃) is a widely used material for highly insulating films due to its very low electrical conductivity, even at high temperatures. Typically, alumina films have to be sintered far above 1200 °C, which precludes the coating of lower melting substrates. The aerosol deposition method (ADM), however, is a promising method to manufacture ceramic films at room temperature directly from the ceramic raw powder. In this work, alumina films were deposited by ADM on a three-electrode setup with guard ring and the electrical conductivity was measured between 400 and 900 °C by direct current measurements according to ASTM D257 or IEC 60093. The effects of film annealing and of zirconia impurities in the powder on the electrical conductivity were investigated. The conductivity values of the ADM films correlate well with literature data and can even be improved by annealing at 900 °C from 4.5?×?10^?12 S/cm before annealing up to 5.6?×?10^?13 S/cm after annealing (measured at 400 °C). The influence of zirconia impurities is very low as the conductivity is only slightly elevated. The ADM-processed films show a very good insulation behavior represented by an even lower electrical conductivity than conventional alumina substrates as they are commercially available for thick-film technology.     

Development of thermoelectric module based on dense Ca3Co4O9 and Zn0.98Al0.02O legs

Ca₃Co₄O₉ (p-type) and Zn_0.98Al_0.02O (n-type) pellets were prepared by conventional sintering (CS) and Spark Plasma sintering (SPS) starting from the oxides. The best p-type sample was SPS Ca₃Co₄O₉ obtained from pre-sintered pellets, with electrical conductivity σ = 144 S/cm and Seebeck coefficient S = 172 μV/K at 800 °C, while thermal conductivity κ = 2.00 W/m×K and figure of merit ZT = 0.23. The best n-type sample was CS Zn_0.98Al_0.02O showing σ = 83 S/cm and S = ?268 μV/K at 800 °C, while = 5.03 W/m×K and ZT = 0.127. The output power of a module based on SPS Ca₃Co₄O₉ and CS Zn_0.98Al_0.02O legs was 2.26 mW (with T = 500 °C, ΔT = 248 °C).     

NaF·AlF3-Al2O3-CaF2-ZrO2熔盐体系的电导率

采用改进的固定电导池常数法研究 NaF-AlF3-CaF2-Al2O3-ZrO2熔盐体系的电导率。结果表明, NaF-AlF3-3%Al2O3-3%CaF2-ZrO2熔盐体系的电导率随着ZrO2含量（0~5%）的增加呈降低趋势。每增加1%氧化锆,电导率相应地降低约0.02 S/cm。温度每增加1°C时电导率相应降低约0.004 S/cm。随着NaF与AlF3摩尔比的增加,体系的电导率随之增加。最后采用二次回归正交设计方法,建立分子比相同时电解质的电导率与温度和氧化锆浓度关系的回归方程。     

Study on synthesis and anticorrosion properties of polymer nanocomposites based on super paramagnetic Fe2O3·NiO nanoparticle and polyaniline

In this study, Fe₂O₃·NiO/PANi nanocomposites were prepared and their anticorrosion properties were investigated. The Fe₂O₃·NiO nanoparticles were synthesized by precipitation–oxidation methods. Fe₂O₃·NiO–PANi nanocomposites were prepared by in situ polymerization of aniline monomer in the presence of Fe₂O₃·NiO nanoparticle. The structure of the polymer nanocomposite was characterized by SEM and X-ray method. The electrical conductivity, magnetic properties and anticorrosion properties of the materials were examined by the conventional four probe method, vibrating magnetometer and by impedance measurement method. The results show that the Fe₂O₃·NiO nanoparticles have the uniform size with the size ranging from 50 to 60 nm. By the formation of polymer nanocomposite, the Fe₂O₃·NiO phase is well dispersed in the PANi polymer matrix. But the Fe₂O₃·NiO nanoparticles are not exfoliated from its agglomerate structure. The polymer nanocomposite showed both magnetic and conductive properties. With increasing Fe₂O₃·NiO content, both the saturated magnetization and the coercive force increase and reach the value of 0.31 emu/g and 162.56 Oe by the Fe₂O₃·NiO content of 5%, respectively. In contrast, the electrical conductivity of the polymer nanocomposite decreases with increasing Fe₂O₃·NiO content from 0.353 S/cm of neat PANi to 0.075 S/cm by the Fe₂O₃·NiO content of 5%. From the anticorrosion investigation, it was revealed that the protective performance of polyurethane paint containing Fe₂O₃·NiO/PANi nanocomposite was significantly improved with increasing Fe₂O₃·NiO/PANi content.     

A Comparative Study on the Reduction Mechanism of Fe2O3 Under Different Heating Methods

The mechanisms for magnetizing roasting of Fe₂O₃ into Fe₃O₄ under microwave heating and electrical heating have been studied through thermogravimetric analyses, x-ray diffraction (XRD) measurements, and reaction kinetic calculations. In the reduction process, activated carbon was used as a reducing agent and argon as the protective gas. The results of heating tests indicated that the temperature heating speed during microwave heating is 50 times faster than that of electrical heating. The maximum conversion ratio of Fe₂O₃ by microwave heating is 24.5% higher than that by electrical heating. XRD results showed that the required temperature for Fe₂O₃ to completely convert into Fe₃O₄ by microwave heating is 200°C lower than that by electrical heating. Reaction kinetics parameters calculation results showed that the controlling step of microwave magnetizing is a phase boundary reaction of the contracted ball at 250–450°C with an apparent activation energy of 45 kJ/mol, whereas the controlling step of electrical magnetizing is a chemical reaction of stochastic coring at 450–650°C with an apparent activation energy of 225 kJ/mol.     

Electrical properties of amorphous carbon films

Aromatic polyimide films, Upilex S partially carbonized between 700°C and 1000°C. Electrical conductivity is higher at higher temperatures. The electrical conductivity s could be expresses as s = s_o exp (−E/kT), where k is the Boltzmann constant, t is the absolute measuring temperature. s_o and E are found to be 4 × 10⁻¹ Ω⁻¹ m⁻¹ and 0.02eB, respectively. The experimental data show that the Hall coefficient R is negative, and this implies that the carriers are negatively charged, i.e. electrons. The specimens are n-type semiconductors. The carrier density η is given by η = 1/(|e|R) and the mobility μ is μ is s/(η|e|), where |e| is the absolute value of the electron charge and s is the electrical conductivity. Fitting the data, η = A₁ exp (−E₁/κT) and μ = A₂ exp (E₂/κT). E₁ and E₂ depend on carbonized temperature. The polyimide films are not completely carbonized but partially carbonized at 700°C. The partially carbonized polyimide is an n type donor. It is concluded that the “impurity level” lies about 0.36eV below the conduction band.     

Enhancement of electrical conductivity of polypyrrole film by stretching: Counter ion effect

The effect of counter ions on the structure and properties of polypyrrole films was investigated. Various aliphatic and aromatic sulfonates as well as some typical inorganic ions such as BF₄⁻, ClO₄⁻and PF₆⁻ were employed as the counter ions. The films were prepared by anodic oxidation of pyrrole in propylene carbonate containing tetraethylammonium salt of the corresponding counter ion and 1 vol.% of water at −20 °C. The electrical conductivity and elongation of the films were highly dependent upon the structure of the counter ions. Among the counter ions investigated, PF₆⁻ gave a film with the highest conductivity (4.0 × 10² S/cm) and elongation (135%). The film stretched up to 2.5 times its original length showed a conductivity of 1.6 × 10³ S/cm in the stretch direction. A linear relationship was observed between the d-spacing measured by X-ray diffraction and the size of the counter ion. Films with smaller counter ions, both unstretched and stretched, showed higher conductivity, although the anisotropy in conductivity of the stretched films was independent of the size of the counter ion.