Variation Of Carbon Nanotubes Research Articles

An enhanced quasi-3D HSDT for free vibration analysis of porous FG-CNT beams on a new concept of orthotropic VE-foundations

The original primary objective of this study is to conduct a comprehensive investigation into the free vibration behavior of beams with porosity, reinforced by carbon nanotubes (CNTs). These beams are supported by an arbitrary orthotropic variable elastic foundation (AOVEF). The focus lies on understanding how the presence of porosity and CNT reinforcement, coupled with the complex support provided by the AOVEF, influences the vibration characteristics of the beams. In addition, we intend to examine the impact of a number of micromechanical models on the vibration properties of these beams. Four carbon nanotube variables are introduced to symbolize several CNT variations. CNTs’ mechanical properties are examined through a variety of micromechanical models. Shear deformation effects are considered into account in the framework of higher-order shear deformation (HSDT) beam theory. The equations of motion are constructed using Hamilton’s concept and the equation system for the FG-CNT beam with supported ends is solved via the Navier methodology. A new approach in elastic foundation modeling is the Arbitrarily Orthotropic Variable Elastic (AOP-VE) foundation. It builds on the Winkler layer concept but introduces the idea of a variable response along the length of the beam foundation. Unlike the Winkler-Pasternak model, AOP-VE allows for control over the directional properties of the Pasternak foundation. The study looks into multiple aspects, involving various distribution kinds of CNTs, the impact of Winkler and Pasternak factors, mode values, side-to-length ratio, porosity, and angle variation. The results indicate that these parameters have a major effect on the inherent vibration features of FG-CNT beams. The study results in various novel findings that improve the understanding of the subject topic and set a standard for future studies.

Pore and phase identification through nanoindentation mapping and micro-computed tomography in nanoenhanced cement

In this work, a methodology is presented in order to assess the microstructure of Portland Cement through advanced characterisation. Nanoindentation is used to determine reduced elastic modulus and hardness, which are involved in the design of construction materials. Elemental mapping and X-ray scanning microtomography were also used to establish structure-property relations through porosity distribution and morphology as well as phase identification by nanoindentation and image analysis. The variation of carbon nanotubes (CNTs) concentration between 0.02 and 1.0 wt% demonstrated alterations in phase composition, and thus the effect of CNTs reinforcement in hydration progress was clarified. Characterisation by all techniques identified 0.5 wt% concentration as promising due to the formation of higher density hydrated phases, even though total porosity was not minimized. This fact was explained by nanoindentation as enhanced Calcium-Silicate-Hydrates connectivity in the porous network was detected. The voids of cement were filled with low stiffness hydrated gel phases as a result of enhanced hydration in the presence of CNTs.

Effect of Multiwalled Carbon Nanotubes (MWCNTs) on the Micro-Hardness and Corrosion Behaviour Mg-Zn Alloy Prepared by Powder Metallurgy

Magnesium Alloys have the potential to be applied in the various fields of applications including biomaterials. Magnesium Alloys are an interesting alloy due to its high strength to density ratio. They have been proposed as a biodegradable implant material due to its friendly effect to human body compared to another alloy. Besides its good biodegradable properties, it has a disadvantage of low hardness and corrosion properties. In order to overcome this, it has been combined with other metals such as Zinc (Zn) or Copper (Cu). To increase mechanical properties, we used Carbon Nanotubes (CNT) as reinforcement. Magnesium-Zinc (Mg-xZn) CNTs composites with several compositions was prepared by using powder metallurgy and sintered in the presence of flowing Argon (Ar) gas in tube furnace. Mg-Zn Alloy with the composition of 4% and 6% of Zn and the variation of CNTs at 0.1%, 0.3 %, and 0.5% was also prepared. Hardness testing by using microvickers showed that CNTs can increase the alloy hardness which the maximum hardness is 53.6 HV. The corrosion rates as low as 175.5 mpy exhibited for the Mg-Alloy with the composition of Mg-4-Zn with 0.1 wt.% of CNTs

Logical Effort Framework for CNFET-Based VLSI Circuits for Delay and Area Optimization

Carbon nanotube field-effect transistors (CNFETs) show great potential to build digital systems on advanced technology nodes with big benefits in terms of power, performance, and area (PPA). However, CNFET-specific additional features such as the number of tubes, pitch (spacing between tubes), tube position, and diameter in array of tubes play a significant role in accurate PPA evaluation. Furthermore, count and density variations in carbon nanotubes (CNTs) due to manufacturing limitations, like the presence of metallic tubes in the CNFET channel, degrade the anticipated PPA benefits. Moreover, modeling the CNFET parameters, CNT variations and etching techniques for CNTs create additional complexity during performance optimization. Hence, for realistic optimization of CNFET circuit’s performance, it is imperative to incorporate the impact of these parameters and variations. In this paper, we propose delay models [pitch-aware logical effort (PALE) and position-aware pitch factor (PAPF)] for fast and accurate performance evaluation by including the impact due to CNFET-specific parameters and CNT variations. These models are developed based on industry standard logical effort framework. Furthermore, we present an optimization tool using PALE and PAPF to minimize the delay and area of CNFET circuits. We deploy several circuit-level techniques prior to optimizing the tubes (CNTs) in the logic gates to achieve globally optimum solution. For better optimization of the circuits, we also include the impact of wire parasitic in estimating the delay of the individual gates. Our optimization tool results in the maximum and average delay improvement by 27% and 17%, respectively, and $2.5\times $ reduction in area for standard ISCAS and OpenSPARC benchmark circuits. Fast and fairly accurate delay computation in our optimization framework offers great runtime benefits as compared to state-of-the-art simulation and statistical-based methods.

Free vibration analysis of arbitrarily shaped Functionally Graded Carbon Nanotube-reinforced plates

Abstract By means of Non-Uniform Rational B-Splines (NURBS) curves, it is possible to describe arbitrary shapes with holes and discontinuities. These peculiar shapes can be taken into account to describe the reference domain of several nanoplates, where a nanoplate refers to a flat structure reinforced with Carbon Nanotubes (CNTs). In the present paper, a micromechanical model based on the agglomeration of these nanoparticles is considered. Indeed, when this kind of reinforcing phase is inserted into a polymeric matrix, CNTs tend to increase their density in some regions. Nevertheless, some nanoparticles can be still scattered within the matrix. The proposed model allows to control the agglomeration by means of two parameters. In this way, several parametric studies are presented to show the influence of this agglomeration on the free vibrations. The considered structures are characterized also by a gradual variation of CNTs along the plate thickness. Thus, the term Functionally Graded Carbon Nanotubes (FG-CNTs) is introduced to specify these plates. Some additional parametric studies are also performed to analyze the effect of a mesh distortion, by considering several geometric and mechanical configurations. The validity of the current methodology is proven through a comparative assessment of our results with those available from the literature or obtained with different numerical approaches, such as the Finite Element Method (FEM). The strong form of the equations governing a plate is solved by means of the Generalized Differential Quadrature (GDQ) method.

Young’s Modulus Variation of Carbon Nanotubes Due to Defects Associated with Atomic Reconstruction of Random Vacancies

This paper studies the effect of three different types of defects on the Young’s modulus of zigzag and armchair single-walled carbon nanotubes. The defects are randomly introduced into the structure with a maximum distribution density of 2%. The defects include monovacancies, before and after reconstruction of dangling bonds, resulting finally to the Stone-Wales defect. As the length of model effects computation time significantly, finite element models are created in pristine and very short tube lengths to investigate the effect of model length on the results obtained. The investigation shows that the introduction of defects generally weakens the elastic strength of tubes but to rather different degrees. However, the structure is capable of restoring its elastic strength by rearranging its atoms in form of the Stone-Wales defect. The use of shorter nanotube models on the other hand can lead to accurate results if appropriate cylindrical boundary conditions are defined.

Rapid Co-Optimization of Processing and Circuit Design to Overcome Carbon Nanotube Variations

Carbon nanotube field-effect transistors (CNFETs) are promising candidates for building energy-efficient digital systems at highly-scaled technology nodes. However, carbon nanotubes (CNTs) are inherently subject to variations that reduce circuit yield, increase susceptibility to noise, and severely degrade their anticipated energy and speed benefits. Joint exploration and optimization of CNT processing options and CNFET circuit design are required to overcome this outstanding challenge. Unfortunately, existing approaches for such exploration and optimization are computationally expensive, and mostly rely on trial-and-error-based ad hoc techniques. In this paper, we present a framework that quickly evaluates the impact of CNT variations on circuit delay and noise margin, and systematically explores the large space of CNT processing options to derive optimized CNT processing and CNFET circuit design guidelines. We demonstrate that our framework: 1) runs over 100x faster than existing approaches, and 2) accurately identifies the most important CNT processing parameters, together with CNFET circuit design parameters (e.g., for CNFET sizing and standard cell layouts), to minimize the impact of CNT variations on CNFET circuit speed with less than 5% energy cost, while simultaneously meeting circuit-level noise margin and yield constraints.

Influence of the variation of carbon nanotubes on the morphology of carbon nanotubes–SiO2hybrid materials

Three different carbon nanotube (CNT)-SiO2 hybrid materials were prepared by a simple sol-gel process using benzyl alcohol as a surfactant, and the variation of morphology of the CNT-SiO2 hybrid materials was investigated. The results showed that the morphology was influenced by the diameter of the different CNTs, and the quality of silica coatings on the CNT surfaces became better when the diameter of CNTs used was larger. We think the detailed understanding of the variation of morphology of CNT-SiO2 hybrid materials should be crucial in order to synthesise ideal CNT-SiO2 hybrid materials for the potential applications in many fields.

Electrical Properties of Carbon Nanotubes-Based Epoxy Nanocomposites for High Electrical Conductive Plate

Electrical properties of carbon nanotubes-based epoxy nanocomposites for high electrical conductive plate were investigated. Dispersion and incorporation mechanism between two conductive fillers with different sizes (CNTs and Graphite) in the polymer matrix are the key factors in the fabrication of high electrical conductivity plate. Different variation of carbon nanotubes (CNTs) (1~10 wt %) and Graphite (G) (60 ~ 69 wt %) loading concentration were added into the epoxy resin. Dispersion of CNTs and G in epoxy resin were conducted by the internal mixer with a Haake torque rheometer. The mixture of G/CNTs/EP was poured into the steel mold, and G/CNTs/EP nanocomposites had been fabricated through compression molding. The electrical conductivity of nanocomposites in terms of variation of G and CNTs concentration were measured by the four point probe for in a plane electrical conductivity. The results revealed that addition of G/CNTs and increasing curing temperature are effective ways to produce high electrical conductive nanocomposites. The highest electrical conductivity was reached on 104.7 S/cm by addition 7.5 wt% of CNTs. Dispersion quality of G and CNTs in the epoxy matrix was observed on the fractured surface by scanning electron microscopic.

Electrical Conductivity and Flexural Strength of Graphite/Carbon Nanotubes/Epoxy Nanocomposites

Carbon nanotubes (CNTs) have excellent mechanical and electrical properties. CNTs reported have excellent properties that can replace conventional conductive filler in advanced engineering applications. The polymer matrix was epoxy resin (EP).Conductive fillers were MWCNTs and synthetic graphite (G). Different variation of CNTs (0~10 wt. %) and graphite (60 ~ 67.5 wt. %) loading concentration were added into the epoxy resin. Dispersion of CNTs and G in epoxy resin were conducted by internal mixer with a Haake torque rheometer. The mixture of G/CNTs/EP was poured into the steel mold, and G/CNTs/EP nanocomposites had been fabricated through compression molding. The electrical conductivity of nanocomposites in term of variation of G and CNTs concentration were measured by the four point probe for in plane electrical conductivity. The results revealed that addition of G/CNTs and increasing curing temperature are an effective ways to produce high electrical conductive nanocomposites. Dispersion quality of CNTs and G in epoxy matrix were observed on the fractured surface by scanning electron microscopic.

The effect of impurities on the Young’s modulus of single-walled carbon nanotubes

The molecular dynamics method was used to investigate the effect of the impurities N,O,Si,P and S on the Young's moduli of armchair (5, 5) and zigzag (9, 0) single-walled carbon nanotubes. The results show that the Young's moduli of armchair (5, 5) and zigzag (9, 0) single-walled carbon nanotubes are 948 and 804 GPa, respectively. When the impurity concentration is less than 10%, the Young's moduli are approximately linearly decreasing with increasing of the impurity concentration, and the greatest decreasing ratio is induced by the impurity Si and the smallest by the impurity N. The decreasing rate of the Young's modulus increases with increase of the impurity atomic number when the impurity element is of the same period with the element C. The effect of the impurities on the Young's modulus of carbon nanotubes is the stronger when the period of the impurity element is different with the element C, and the decreasing rate of the Young's modulus decreases slightly with increasing of the impurity atomic number. The reasons are analyzed by the laws of the Young's potential energy variation of carbon nanotubes with impure and the electron cloud coupling between two atoms from the theory of the local density approximation based on the density functional theory.