Carbon nanotube-epoxy composites: The role of acid treatment in thermal and electrical conductivity

Wet acid oxidation treatment methods have been widely reported as an effective method to purify and oxidize the surface of industrial multi-walled carbon nanotubes. This work examines the use of a concentrated HNO₃/H₂SO₄ mixture in an attempt to optimize the purification procedure of industrial multi-walled carbon nanotubes with diameter distribution statistics. It is shown that acid treatments of several hours are enough to purify the nanotubes. The electrical and thermal conductivities of epoxy composites containing 0.05–0.25 wt% of an acid-treated multi-walled carbon nanotube have been studied. The electrical conductivity of the composites decreases by more than three orders, whereas the thermal conductivity of the same specimen increases very modestly as a function of the filler content.     

Effect of nano‐modified SiO2/Al2O3 mixed‐matrix micro‐composite fillers on thermal,mechanical, and tribological properties of epoxy polymers

Thermo‐mechanically durable industrial polymer nanocomposites have great demand as structural components. In this work, highly competent filler design is processed via nano‐modified of micronic SiO₂/Al₂O₃ particulate ceramics and studied its influence on the rheology, glass transition temperature, composite microstructure, thermal conductivity, mechanical strength, micro hardness, and tribology properties. Composites were fabricated with different proportions of nano‐modified micro‐composite fillers in epoxy matrix at as much possible filler loadings. Results revealed that nano‐modified SiO₂/Al₂O₃ micro‐composite fillers enhanced inter‐particle network and offer benefits like homogeneous microstructures and increased thermal conductivity. Epoxy composites attained thermal conductivity of 0.8 W/mK at 46% filler loading. Mechanical strength and bulk hardness were reached to higher values on the incorporation of nano‐modified fillers. Tribology study revealed an increased specific wear rate and decreased friction coefficient in such fillers. The study is significant in a way that the design of nano‐modified mixed‐matrix micro‐composite fillers are effective where a high loading is much easier, which is critical for achieving desired thermal and mechanical properties for any engineering applications. Copyright © 2016 John Wiley & Sons, Ltd.     

IR Reflective LaPO4 Ceramic Colorant Reinforced Polymer Composite Coatings on Glass and Metal Substrates for Heat Management Applications

LaPO₄ ceramic colorants were processed in the vibrant shades of green and brick red, and subsequently embedded in polymer resins for the fabrication of heat management coatings. The IR/UV shielding characteristics of these ceramic colorants and polymer coatings were analysed and it was found that the ceramic dispersoids enhance the IR reflectance quality of polymer resins by 20 to 25 times. The nano ceramic green colorant-reinforced polymer coating on glass panels offers the stringent property, i. e., optical transparency and heat reflectance combined, when exposed to direct sunlight. Other photophysical properties were also studied and analysed. The brick red colorant entrenched resin coating on metal substrate offered heat reflectance and corrosion resistance characteristics. XPS studies provided the chemical environment of the systems. Surface morphology, crystallinity and particle size of the products were investigated using SEM, TEM, XRD and DLS techniques. The polymer resin coating of these ceramic colorants offers thermal stability and colorfastness properties.     

Effect of substrate temperature on the properties of reactively sputtered TiN/NbN multilayers

TiN/NbN multilayer coatings were deposited with various substrate temperatures by DC reactive magnetron sputtering method onto Si (111) and glass substrates. The effect of substrate temperature on the structural and optical properties of TiN/NbN multilayers was investigated by X‐ray diffraction, X‐ray photoelectron spectroscopy, Field emission scanning electron microscopy and Photoluminescence measurements. The composition was analyzed by X‐ray photoelectron spectroscopy. X‐ray diffraction results showed that the layers crystallized in cubic structure for TiN and hexagonal structure for NbN. It was found that grain size increased with increase in substrate temperature. The surface morphology of the TiN/NbN thin films showed a dense and smooth surface with substrate temperature upto 200 °C but after 300 °C, the grains became larger and coarse surface was observed. The TiN/NbN multilayer coatings exhibited the characteristic peaks centered at 180, 210 and 560 cm^‐1. Red band emission peaks were observed in the wavelength range of 700‐710 nm. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A General Integral Method for one dimensional ablation

Heat and Mass Transfer - Ablation of a semi infinite medium subject to a time varying heat flux at its surface is considered. It is shown that a general integral method can be formulated to...     

Photo‐enhanced catalytic activity of spray‐coated Cu2SnSe3 nanoparticle counter electrode for dye‐sensitised solar cells

Cu₂SnSe₃ nanoparticles are synthesised using oleylamine as both a solvent and capping agent and spray coated to form dye‐sensitised solar cell (DSSC) counter electrodes (CEs) using earth‐abundant elements. The film requires annealing at only 400 °C in nitrogen, which is a lower temperature than previous reports of both Cu₂SnSe₃and Cu₂ZnSnSe₄ films, also avoiding the use of Se gas. The composition and phase of the material is confirmed to be kesterite Cu₂SnSe₃. DSSCs using Cu₂SnSe₃ CEs give a power conversion efficiency of 4.87%, compared to 5.35% when using Pt. Electrochemical impedance spectroscopy indicates that the performance of the Cu₂SnSe₃ CE is enhanced under illumination, leading to a drop in the charge transfer resistance. This illumination‐induced enhancement of the catalytic activity provides a novel mechanism for the enhancement of CE performance in DSSCs.

     

Effect of nano/micro‐mixed ceramic fillers on the dielectric and thermal properties of epoxy polymer composites

Nano/micro ceramic‐filled epoxy composite materials have been processed with various percentage additions of SiO₂, Al₂O₃ ceramic fillers as reinforcements selected from the nano and micro origin sources. Different types of filler combinations, viz. only nano, only micro, nano/micro, and micro/micro particles, were designed to investigate their influence on the thermal expansion, thermal conductivity, and dielectric properties of epoxy polymers. Thermal expansion studies were conducted using thermomechanical analysis that revealed a two‐step expansion pattern consecutively before and after vitreous transition temperatures. The presence of micro fillers have shown vitreous transition temperature in the range 70–80°C compared with that of nano structured composites in which the same was observed as ~90°C. Similarly, the bulk thermal conductivity is found to increase with increasing percentage of micron‐size Al₂O₃. It was established that the addition of micro fillers lead to epoxy composite materials that exhibited lower thermal expansion and higher thermal conductivity compared with nano fillers. Moreover, nano fillers have a significantly decisive role in having low bulk dielectric permittivity. In this study, epoxy composites with a thermal expansion coefficient of 2.5 × 10^?5/K, thermal conductivity of 1.18 W/m · K and dielectric permittivity in the range 4–5 at 1 kHz have been obtained. The study confirms that although the micro fillers seem to exhibit good thermal conductivity and low expansion coefficient, the nano‐size ceramic fillers are candidate as cofillers for low dielectric permittivity. However, a suitable proportion of nano/micro‐mixed fillers is necessary for achieving epoxy composites with promising thermal conductivity, controlled coefficient of thermal expansion and dielectric permittivity. Copyright © 2013 John Wiley & Sons, Ltd.     

A facile approach to hexagonal ZnO nanorod assembly

Nanocrystalline ZnO nanorods were successfully grown by ultrasonication using an acidic ethanolic zinc acetate precursor solution followed by a flow coating process and annealing at 600 °C. The ZnO nanorods obtained were hexagonal in shape and showed a high degree of uniformity in size and distribution. These samples were characterized by X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Raman spectrophotometry and the results are discussed. This approach appears to be the easiest way to fabricate bulk ZnO nanorods.     

Approximate solution of nonlinear transient heat conduction in one dimension

Three approximate methods, viz. the Heat Balance Integral method (HBI), the Modified Heat Balance Integral method (MHBI) and the Double Integral Method (DIM) in combination with hybrid profiles (HP - consisting of an exponential and polynomial) are evaluated for relative merits in solving the onedimensional heat diffusion equation. Applications to two linear test problems (TP1 - semi-infinite solid with constant heat flux at its boundary, TP 2 - semi-infinite solid with step change in its surface temperature) yield the HP-MHBI as the most desirable combination. Applications to nonlinear problems show that these combinations are ideally suited for obtaing reliable and accurate appoximate solutions.

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Näherungslösung von eindimensionaler nicht linearer transienter Wärmeleitung

Zusammenfassung Es wurden drei Näherungsmethoden, die Heat Balance Integral-Methode (HBI), die Modified Heat Balance IntegralMethode (MHBI) und die Double Integral-Methode (DIM) in Verbindung mit hybriden Profilen (HP - bestehend aus Exponentialund Polynomfunktionen) ausgewählt, um die eindimensionale Wärmediffusionsgleichung zu lösen. Anwendungen auf zwei lineare Testprobleme (TP 1 - halb-unendlicher Festkörper mit konstantem Wärmestrom an dessen Grenze, TP2 - halb-unendlicher Festkörper mit sprunghaftem Wechsel der Oberflächentemperatur) ergaben, daß die HP-MHBI-Methode die erwünschte Kombination darstellt. Anwendungen auf nichtlineare Probleme zeigen, daß diese Kombination ideal für das Erzielen zuverlässiger und aussagekräftiger Näherungslösungen ist.