Search

The article presents the synthesis of multi-walled carbon nanotubes (MWCNTs) on the porous nickel foam (3D-Ni) surface using the chemical vapor deposition (CVD) method, followed by the field emission characteristics of the resulting 3D-Ni/MWCNT nanocomposite structures. The characterization of the 3D-Ni/MWCNT morphology showed a uniform distribution of the "moss-like" CNT coating on the walls of the porous 3D-Ni. TEM images showed a high number of walls in MWCNTs, which made such a material resistant to destruction under conditions of strong electric fields during the field emission process. The studies also showed a high degree of chemical purity of the synthesized MWCNTs under the presented technological conditions. An increase in the emission current due to the introduction of CNTs into the structure of porous 3D-Ni is shown. 3D-Ni/MWCNTs field emitter showed a low turn-on field of 5.41 V/μm; a field enhancement factor of 915; and high operating stability. For the first time, the current mode of 3D-Ni-MWCNTs cathode was tested for compliance with the classical field emission law using the Forbes "orthodoxy" test. [ABSTRACT FROM AUTHOR]

Researchers worldwide are studying thermal energy storage with phase change materials because of their substantial benefits in the enhancement of energy efficiency of thermal drying systems. A two-stage convectivevacuum impulsive drying plant is a technology for the manufacturing of chemical and food products with high quality and low energy costs. Energy consumption during the drying process is the main indicator in terms of economy. In this paper, a brief and focused review of the peculiarities of TEAs with PPCMs and opportunities of their application in such drying systems is done and discussed. The paper described the mentioned manufacturing system. The advantages of paraffin wax and thermal conductivity improvement techniques were demonstrated for their use as heat storage materials in CVID drying units. The results of similar previous studies were presented. The results of the experimental studies conducted by the researchers proved that the use of heat accumulators with PCMs increased the overall energy efficiency of drying systems. Finally, integration of TEAs based on modified PPCMs in the CVID system was recommended to intensify thermal energy, reduce thermal influence on the main indicators of the vacuum pump during the evacuation process, and decrease production costs. [ABSTRACT FROM AUTHOR]

The development of reliable and effective functional materials that can be used in various technological fields and environmental conditions is one of the goals of modern nanotechnology. Heating elements' manufacturing requires understanding the laws of heat transfer under conditions of different supply voltages, as this expands the possibilities of such materials' application. Elastomers based on silicon-organic compounds and polyurethane modified with multi-walled carbon nanotubes (MWCNTs) were studied at various concentrations of Ni/MgO or Co-Mo/MgO and voltages (220, 250, and 300 V). It was found that an increase in voltage from 220 to 300 V leads to an initial increase in specific power on one-third followed by a subsequent decrease in a specific power when switched on again to 220 V (for −40 °C) of up to ~44%. In turn, for a polyurethane matrix, an increase in voltage to 300 V leads to an initial peak power value of ~15% and a decrease in power when switched on again by 220 V (for −40 °C) to ~36% (Ni/MgO -MWCNT). The conducted studies have shown that the use of a polyurethane matrix reduces power degradation (associated with voltage surges above 220 V) by 2.59% for Ni/MgO–based MWCNT and by 10.42% for Co-Mo/MgO. This is due to the better heat resistance of polyurethane and the structural features of the polymer and the MWCNT. The current studies allow us to take the next step in the development of functional materials for electric heating and demonstrate the safety of using heaters at a higher voltage of up to 300 V, which does not lead to their ignition, but only causes changes in electrophysical parameters. [ABSTRACT FROM AUTHOR]

The present article considers a comparative analysis of two elastomers, polyurethane (PUС) and organosilicon (OSC), both modified with 1.0–9.0 wt.% multiwall carbon nanotubes (MWCNTs). The MWCNTs‐1 and MWCNTs‐2 were synthesized through CVD method using Co‐Mo/Al2O3‐MgO and Fe‐Co/2,1Al2O3. The results obtained showed that the lowest bulk conductivity (5 × 10−10 S × cm−1) was typical for PUC elastomer modified with 1 wt.% MWCNTs‐2. As for OSC elastomer (modified with 9 wt.% MWCNTs‐1), the lowest bulk conductivity was found to be 0.4 S × cm−1. The maximum temperature field uniformity was established for OSC elastomer modified with 7 wt.% MWCNTs‐2, whereas in the modified PUC‐based elastomer, the nonuniform temperature field took place. This might be caused by local MWCNTs entanglement manifested in the formation of agglomerates or a denser packing of conductive networks. The best combination of the polymer matrix and MWCNTs type was revealed. Finally, it was established that for electric heaters, it is the most efficient to employ OSC modified with 7 wt.% MWCNTs and use MWCNTs‐1 or MWCNTs‐2, depending on the feeding voltage level of 12 or 24 V. This study is of special importance in household purposes, clothing with built‐in heating panels, car/tractor systems, minibus interiors, onboard thermal ventilation systems, clothing, and aircraft industries. [ABSTRACT FROM AUTHOR]

This article describes a technique for the manufacturing of the composites MWCNTs-modified elastomers. The effect of the different MWCNTs mass contents in the elastomer on specific volume and surface electrical resistivity values was investigated. The results on the heaters based on the elastomers and altered with multi-walled carbon nanotubes (MWCNTs) over various catalysts are discussed. It was found that with an increase in the MWCNTs mass content, the maximum power is achieved at a lower voltage value. Besides, temperature fields were measured on the surface of heater samples, and it was established that the temperature variation on the sample surface did not exceed 5 °C, and the heaters had a heating rate of 0.2–0.5 °C/s. Furthermore, a comparison of these heaters with the analogs previously reported by the other researchers is presented, indicating good importance of the reported work. The industrial (commercial) production of such devices is mainly associated with using in fan heaters for domestic purposes, in heaters built into clothes in underfloor heating systems and motor vehicles. The present work will find a good industrial application in the future. [ABSTRACT FROM AUTHOR]

This work represents a new approach for analyzing emission characteristics of multitip field cathodes. The approach is based on using a computerized field emission projector to investigate the behavior of the microscopic emission sites of the field cathode surface. Adsorption-desorption processes on the surface—which influence the emission current level—were investigated by tracking the individual emission sites under conditions of a sharp decrease and increase in the voltage level. An analysis of the transient process showed that emission sites with highest local currents almost do not participate in changing the overall level of emission current, but they became smaller with a decrease in the step voltage contribution of the dimmest sites. Similar dependences were obtained for rising voltage levels but with much faster transitions. [ABSTRACT FROM AUTHOR]

There was a typo error in the second author name. [ABSTRACT FROM AUTHOR]

Exactly 50 years ago, the first article on electrochromism was published. Today electrochromic materials are highly popular in various devices. Interest in nanostructured electrochromic and nanocomposite organic/inorganic nanostructured electrochromic materials has increased in the last decade. These materials can enhance the electrochemical and electrochromic properties of devices related to them. This article describes electrochromic materials, proposes their classification and systematization for organic inorganic and nanostructured electrochromic materials, identifies their advantages and shortcomings, analyzes current tendencies in the development of nanomaterials used in electrochromic coatings (films) and their practical use in various optical devices for protection from light radiation, in particular, their use as light filters and light modulators for optoelectronic devices, as well as methods for their preparation. The modern technologies of "Smart Windows", which are based on chromogenic materials and liquid crystals, are analyzed, and their advantages and disadvantages are also given. Various types of chromogenic materials are presented, examples of which include photochromic, thermochromic and gasochromic materials, as well as the main physical effects affecting changes in their optical properties. Additionally, this study describes electrochromic technologies based on WO3 films prepared by different methods, such as electrochemical deposition, magnetron sputtering, spray pyrolysis, sol–gel, etc. An example of an electrochromic "Smart Window" based on WO3 is shown in the article. A modern analysis of electrochromic devices based on nanostructured materials used in various applications is presented. The paper discusses the causes of internal and external size effects in the process of modifying WO3 electrochromic films using nanomaterials, in particular, GO/rGO nanomaterials. [ABSTRACT FROM AUTHOR]

The article deals with research related to the issues of nanomodification of elastomers as a basis of electric heaters with self-regulating temperature. The effect of multistage mechanical activation of multilayer carbon nanotubes (MCNTs) with graphite on the uniformity of the temperature field distribution on the surface of nanomodified organosilicon elastomer has been studied. The influence of the stages of mechanical action on the parameters of MCNTs is revealed. It has been ascertained that for the MCNTs/graphite bulk material, which has passed the stage of mechanical activation in the vortex layer apparatus, a more uniform distribution of the temperature field and an increase in temperature to 57.1 °C at the supply voltage of 100 V are typical. The distribution of the temperature field in the centrifugal paddle mixer "WF-20B" for mixing MCNTs with graphite has been investigated. It has been found that there is also a thermal effect in addition to the mechanical action on the MCNTs in the paddle mixer "WF-20B". The thermal effect is associated with the transfer of the mechanical energy of friction of the binary mixture MCNTs/graphite on the paddle and the walls of the vessel. The multiplicity of the starting current Ip to the nominal In (Ip/In) is 5 for the first sample, 7.5 for the second sample, and 10 for the third sample at the supply voltage of 100 V. The effect of reducing the starting current and stabilizing the temperature indicates the presence of self-regulation, which is expressed in maintaining a certain level of temperature. [ABSTRACT FROM AUTHOR]