Joule heating in electromagnetic casting

According to the experimental analysis oftemperature distribution in an Al ingot ofelectromagneticcasting, the induction thermal profile in the horizontal and vertical directions is studied. The influence ofinductor currents on the thermal distribution ofthe ingot is also analyzed. The relation between the average temperature in the ingot cross-section and the metal height is studied. Finally, the gross Joule heating is calculated from the experimental and regression curve.     

Diamond electrophoretic microchips—Joule heating effects

Microchip electrophoresis (MCE) has become a mature separation technique in the recent years. In the presented research, a polycrystalline diamond electrophoretic microchip was manufactured with a microwave plasma chemical vapour deposition (MPCVD) method. A replica technique (mould method) was used to manufacture microstructures in diamond. A numerical analysis with CoventorWare™ was used to compare thermal properties during chip electrophoresis of diamond and glass microchips of the same geometries. Temperature distributions in microchips were demonstrated. Thermal, electrical, optical, chemical and mechanical parameters of the polycrystalline diamond layers are advantageous over traditionally used materials for microfluidic devices. Especially, a very high thermal conductivity coefficient gives a possibility of very efficient dissipation of Joule heat from the diamond electrophoretic microchip. This enables manufacturing of a new generation of microdevices.     

Controlling electron-beam-induced carbon deposition on carbon nanotubes by Joule heating

Electron-beam-induced deposition (EBID) of carbon on the surface of carbon nanotubes was well controlled by passing different electrical currents through the nanotubes. The control is due to Joule heating and the temperature of the carbon nanotubes was estimated. The deposition rate was found to increase and then decrease with the temperature and was maximized at about 310?K and approached zero at about 400?K. The method can be used to control the deposition rate of EBID in nanowelding and nanofabrication and to eliminate amorphous carbon contamination in in situ study of nanostructures.     

Arc-instability generated during the Joule heating induced crystallization of amorphous silicon films

Joule heating induced crystallization (JIC) was accomplished by applying an electric field to a conductive layer located beneath the amorphous silicon film. This study found that an intense arc is generated at the interface between the silicon and the electrode. The artificial modification of a JIC-sample structure led us to the finding that arc generation is caused by the dielectric breakdown of a SiO₂ layer that is sandwiched between the transformed polycrystalline silicon and a conductive layer at high temperatures during Joule heating.     

Influence of Joule heating during electromigration evaluation of silver lines

In the present study, the kinetics and failure mechanism of silver (Ag) thin film metallization have been determined under various temperature conditions. Failure was due to evaporation of metal assisted by agglomeration. The effect of Joule heating on the activation energy (E_a) for failure is determined. The Ag metallization appears to experience bimodal failure (0.46 and 0.89 eV) when Joule heating effect is not considered. However, upon incorporation of the temperature rise due to Joule heating, the E_a is determined to be 0.51 eV indicating a single failure mechanism.     

Geometrical effects in a Joule heating problem from miniature soldering

The soldering of small, delicate electronic devices by means of a blade thermode (a small, thin, rectangular or requires the lower side of the thermode to have a uniform temperature distribution. This is not easily obtained: during start-up the corners tend to be too hot, and too cold in the stationary phase. In the present study the various aspects that determine the heat flow and the temperature distribution are analysed, both for the dynamic and the stationary cases.For a temperature-independent (linear) material, approximate solutions are obtained for the dynamic problem. For the stationary problem, an exact solution is utilized that includes temperature-dependent (nonlinear) material. Practical design rules based on these solutions are proposed. The analysis compares very well with a numerical finite-element simulation.     

Finite element modeling of melting crack tip under thermo-electric Joule heating

The finite element modeling of the melting crack tip under thermo-electric Joule heating is presented in this paper. It is necessary to consider the AC input, temperature-dependent material constants and crack contact conditions. The shape of the melting crack tip zone may be either circular or elliptical. As the crack length relative to the plate width becomes too small, the crack tip may not melt. Finally, this paper demonstrates that the electric current density factor cannot be used to estimate the crack tip temperature and melting condition.     

Joule Heating Activation of Template-Mediated Carbon Fibers with Significantly Enhanced Capacitive Performance

Carbon fibers (CFs) have been innovated in the application of fiber-shaped and wearable energy storage devices recently. However, time- and energy-consuming activation process under harsh conditions is generally required to modify the surface structure of the CF. Herein, a fast and effective Joule heating activation method is proposed with the nickel–cobalt layered double hydroxide-derived nanometal particles as the template. The resultant Joule heating-activated CF (JACF) demonstrates excellent capacitive performance with an electrode capacitance of 268 F g⁻¹. After assembling into a solid-state fiber-shaped supercapacitor (FSC), the device shows both enhanced specific capacitance and energy/power densities, as well as the long cycling stability of over 5000 cycles. The Joule heating method reported in this work is time and energy saving for CF activation compared with the traditional chemical etching or high-temperature annealing processes, and it is promising for the large-scale production of high-performance fiber-shaped and wearable energy devices.     

Simulation of continuum electrical conduction and Joule heating using DEM domains

This paper proposes an original method to simulate the electrical conduction in continuums with the Discrete Element Method (DEM). The proposed method is based on the graphs theory applied to electrical resistance network, where the resistance between two discrete elements is estimated through the notion of ‘transmission surface’ to assume the discrete domain as a continuous medium. In addition to the electrical conduction, the Joule heating of a DEM domain has also been developed to take full advantage of the electrical conduction. The proposed method has been implemented in the free DEM software named ‘GranOO’. The numerical results were compared against analytical approaches when applicable, or against Finite Element Method if the geometries become more complex or in case of dynamic loadings. The results are found satisfactory with errors around 3% for the electrical conduction and Joule heating of reasonably complex domains and loading cases. When it comes to more complex domains, such as electrical constriction, whilst the results remain close to those obtained with reference solutions (around 6%), they highlight the importance of taking care about the domains discretization. Finally, the proposed method is applied to detect cracks onset on a cylindrical rod torsion test to show how to take advantage of the proposed work. Copyright © 2016 John Wiley & Sons, Ltd.     

Metal oxide coating on carbon nanotubes by a methanol-thermal method

A methanol-thermal method has been developed to fabricate one-dimensional composite nanowires by coating multiwalled carbon nanotubes with lanthanum oxide and iron oxide, respectively. The coating structure and composition have been investigated by transmission electron microscopy and the X-ray energy dispersive spectrum. Magnetic measurement for the iron oxide coatings indicated that the coercivity has been enhanced after coating. The method reported here provides a novel procedure for the fabrication of one-dimensional composite nanostructures.     

The effect of nanotube radius on the constitutive model for carbon nanotubes

We investigate the effect of nanotube radius on the constitutive model of single wall carbon nanotubes. We adopt a modified Cauchy–Born rule to incorporate the interatomic potential into the continuum analysis, and such an approach ensures the equilibrium of atoms. It is shown that the nanotube radius has little effect on the mechanical behavior of single wall carbon nanotubes subject to simple tension or pure torsion, while the nanotube orientation has somewhat larger influences.     

表面覆铪改善碳纳米管膜发射性能

研究了表面沉积铪膜并进行后处理对碳纳米管膜场电子发射性能的影响.研究结果表明在适当的退火温度下碳纳米管表面形成了碳化铪,并显著提高了碳纳米管的发射电流密度、发射均匀性和发射稳定性.我们认为碳纳米管表面发射性能的提高归功于表面碳化铪膜良好的导电性、化学惰性和低逸出功.     

Effect of substrate and catalyst on the transformation of carbon black into nanotubes

Structural transformation of carbon black (CB) into nanotubes and nano-onion like structures in the presence of bimetallic catalysts (Fe and Ni) is reported and the influence of the substrate (alumina and stainless steel) in the structural transformation is studied. In addition, the importance of a specific weight ratio of CB to catalyst in the transformation of amorphous CB into graphitic nanostructures is verified. The experiments were carried out at 1,000 °C in a horizontal tube furnace under N₂ atmosphere. The samples were characterized by transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, Raman spectroscopy and also thermomagnetic analysis (Curie-temperature determinations) were done to assess thermally induced magnetic phase changes. All the characterization techniques showed the resulting structures were influenced by the substrate and weight ratio for CB to catalysts. However, there was no significant difference in the magnetic performance of the resulting structures obtained on different substrates.     

利用感应加热技术进行炭纤维连续石墨化

采用感应加热技术研制出炭纤维连续高温热处理专用设备石墨化炉，最高使用温度3000℃。对PAN基炭纤维T300进行了连续石墨化处理，热处理温度为2000℃～3000℃，制备出力学性能相当于日本东丽公司M40的石墨纤维，验证了该设备的技术可行性。考察了热处理温度对炭纤维力学性能、密度和直径的影响，用SEM观察了石墨化前后炭纤维表面微观形态的变化。结果表明：随热处理温度的提高，炭纤维的密度增大、直径减小，弹性模量升高，而抗拉强度下降。经3000℃高温热处理后，纤维的弹性模量高达450GPa。     

Thermodynamic properties of amorphous silicon investigated by pulsed laser heating

Nanosecond (=347 nm, =25 ns) and picosecond (=532 nm, =20 ps) pulsed laser irradiation have been used to induce surface melting in ion implanted and annealed amorphous silicon layers. Time-resolved reflectivity technique was employed to detect the melting onset, from which the melting temperatures of the amorphous phases have been evaluated. Thermal properties of the relaxed amorphous have also been investigated, and in particular, the differences in the heat capacity and in the thermal conductivity of the relaxed amorphous with respect to the as-implanted one were determined. Using these results, the free energy diagram of both relaxed and unrelaxed amorphous silicon has been constructed.Paper presented at the Second Workshop on Subsecond Thermophysics, September 20–21, 1990, Torino, Italy.     

Structure of chiral single-walled carbon nanotubes under hydrostatic pressure

We investigate the structural parameters, i.e., bond lengths and bond angles of chiral tubes of various chiralities using a procedure based on helical and rotational symmetries and Tersoff potential. The results indicate that at ambient conditions, there are equal bond lengths and three unequal bond angles in the structure of chiral tubes. This bond length depends significantly on the chirality and insignificantly on the tube radius. Length of the tubes does not play very significant role on bond length and bond angles. These C–C bonds were recalculated under hydrostatic pressure. The bond length compresses with pressure while the bond angles remain practically unchanged. We also carry out analysis regarding the cross sectional shape of chiral tubes and its pressure dependence. It is found that at some pressures, transition from circular to oval cross section takes place. The transition pressure is found to strongly depend on the radius and chirality of tube. At this transition, corresponding to given elliptical cross section, the bond length for all chiral tubes of various chiralities and radius approaches nearly a fixed value of 1.434 Å.     

Homogenization of helical beam-like structures: application to single-walled carbon nanotubes

This work is devoted to the computation of axial stiffness of helical beam-like structures. Starting from the homogenization theory of periodic slender domains and taking benefit of the property of helical symmetry, the overall elastic behavior can be obtained from the solution of three-dimensional problems posed on a reduced basic cell. The mechanical analysis of this reduced basic cell performed using a concise FE model allows therefore to compute easily the anisotropic beam homogenized stiffness coefficients. The accuracy and usefulness of this approach is demonstrated by comparisons with reference solutions and large FE model results for two numerical volume structure examples: a wire spring and a stranded “6 + 1” rope. The homogenization procedure is then applied to single-walled carbon nanotubes and it is shown from the two helical symmetries that their basic cell can be reduced to three beam elements.     

Transmission electron microscopy study of individual carbon nanotube breakdown caused by Joule heating in air

We present repeated structural and electrical measurements on individual multiwalled carbon nanotubes, alternating between electrical measurements under ambient conditions and transmission electron microscopy (TEM). The multiwalled carbon nanotubes made by chemical vapor deposition were manipulated onto cantilever electrodes extending from a specially designed microfabricated chip. Repeated TEM investigations were then made of the progressive destruction of the nanotube structure induced by Joule heating in air. The electrical measurements indicate that the studied nanotubes behave as diffusive conductors with remarkably predictable electrical properties despite extensive structural damage.