Development of a Pulsed Laser Ablation Technique for the Formation of Carbon Nanotubes

The objective of this work was to develop a pulsed laser ablation technique for the formation of carbon nanotubes (CNTs). This study was divided into three parts. The first part involved the development of pulsed laser ablation (PLA) system. The second part dealt with the growth of CNTs by using the pulsed laser ablation technique, and finally the last part dealt with the analysis of microstructure and surface morphology of the deposited sample collected and the influence of the laser ablation on the surface morphology of the sample target. A vacuum chamber was designed for the formation of CNTs. The stainless steel chamber used in this system has a cylindrical shape, with diameter of about 15cm and 45cm length. CNTs were formed by laser ab!ation using a graphite pellet, graphite-Ni, graphite-Co and graphite-Ni-Co, each with 10 weight percentage catalysts. The Nd:YAG laser with 532nrn wavelength, 10.24 W laser power was used to ablate the target to form the CNTs. Argon (Ar) gas was kept flowing into the chamber, keeping the pressure inside chamber at 4 Torr.Web-liked CNTs were found in the deposited sample collected after 30 minutes laser ablation by using the graphite pellet and the graphite filled with mono-catalyst and bi-catalyst. The XRD pattern for the deposited sample shows the CNTs peak located at about 26.5". The SEM micrograph show that the diameter size of the CNTs formed by the Co, Ni, NiCo catalysts and without catalyst follow the order C>CCo>CNi>CNiCo. The range of the diameters of the CNTs was found to be about 35-150nm. The sphere-liked carbon structures were found deposited in the substrate after laser ablation without the Ar gas flowing into the chamber during the ablation process. TEM micrograph confirmed the formation of CNTs. It was found that by using a bi-metal catalyst (Ni-Co), a bamboo-like structure of CNTs was formed

Phase evolution and crystallite size of La-substituted YIG at differentcalcination temperatures.

Yttrium iron garnet (YIG) substituted lanthanum ions (La3+) Y3-xLaxFe5O12 were synthesized at different temperatures. The effect of calcination temperature on crystalline structures was investigated by using X-ray diffraction (XRD). The results show that the crystallization of the samples La-substituted YIG x=0.0 and x=0.5 is more completed when the calcination temperature increases. However, Fe2O3 phase was formed in the sample with La substitution of x=1.0 when the temperature increases. The sizes of substituted YIG particles calculated from Scherrer equation were ranged from 29 to 71 nm and it was found increased with the increasing of calcination temperature

Numerical solutions of linear Fredholm Integral Equations using half-sweep arithmetic mean method

In this paper, performance of the 2-Point Half-Sweep Explicit Group (2-HSEG) iterative method with first order composite closed Newton-Cotes quadrature scheme for solving second kind linear Fredholm integral equations is investigated. The formulation and implementation of the method are described. Furthermore, numerical results of test problems are also presented to verify the performance of the method compared to 2-Point Full-Sweep Explicit Group (2-FSEG) method. From the numerical results obtained, it is noticeable that the 2-HSEG method is superior to 2-FSEG method, especially in terms of computational time

Synthesis, morphology, characterisation and evaluation of carbon nanotubes-substituted YIG-PVA composites as electromagnetic wave absorbing materials

It is of interest whether carbon nanotubes (CNTs) and Yttrium Iron Garnet (YIG) containing polymer composite would produce any significant electromagnetic wave absorption effects in the composite. Therefore, in this work, carbon nanotubes-substituted YIG-PVA composites (YIG(La)-CNTs-PVA and YIG(Bi)-CNTs-PVA composites) were fabricated. Morphology and its electromagnetic properties as electromagnetic wave materials were studied. Yttrium iron garnet (YIG) substituted with lanthanum and bismuth namely Y3-xLaxFe5O12 and Y3-xBixFe5O12 (where x=0.0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0) were synthesized via sol gel technique. The phase formation, surface morphology and magnetic properties of as-prepared YIG nanoparticles were studied using X-Ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM), respectively. The synthesized single phases YIG(La) and YIG(Bi) particles have spherical shapes with particles size in the range of 35-80nm. The saturation magnetization of YIG(La) and YIG(Bi) were 17.72emu/g and 18.57emu/g, respectively. Carbon nanotubes (CNTs)which are used as filler for the composites were synthesized by the decomposition of methane over Co-Mo/MgO catalyst using chemical vapor deposition (CVD) technique. The ratio of Co to Mo supported on MgO and the catalytic reaction time were studied to optimize a CNTs yields. The optimization of CNTs yields was obtained by using the Co:Mo catalyst at ratio 1:1 supported on MgO and the catalytic reaction time of 180min. The microstructure and particles sizes of as-prepared CNTs were determined using TEM. 6M HNO3 and 6M H2SO4 in a volume ratio of 1:3 were used to purify and functionalise the as-prepared CNTs. The purity of CNTs and the functional group introduced on CNTs after purification were determined by using Thermogravimetric Analysis (TGA) and identifying the groups using Fourier Transform Infrared Spectroscopy (FTIR), respectively. High purity CNTs of about 98.57% together with COOH and OH functional groups were obtained after purification process. The highest dielectric loss of CNTs-PVA composite was obtained with addition 3wt% of CNTs, while the highest dielectric and magnetic losses of YIG(La)-CNTs-PVA and YIG(Bi)-CNTs-PVA composites were obtained when 3wt% of CNTs were used. The highest tan δ obtained at YIG(La)-CNTs-PVA and YIG(Bi)-CNTs-PVA were 6.75 at frequency 100MHz and 1.12 at frequency 300MHz, respectively. It is suggested that the dielectric loss of the composites understudied are due to the interfacial polarisation of YIG(Bi) or YIG (La), CNTs and PVA within composite and magnetic losses are due to the domain wall movement of YIG(La) or YIG(Bi) in composite

A Comparative Study on the Crystalline and Surface Properties of Carbonized Mesoporous Coconut Shell Chars

In the present work, the facile thermal decomposition of raw coconut shells was carried out for the exploitation of the role of inert gas in the carbonization process and its role in determining the morphology, crystallographic parameters, and surface area of biochar before activation. The comparative investigation of mesoporous carbonized products synthesized with the muffle and tube furnace was carried out at a similar temperature and an assessment was made with a commercial carbon. The focus of the work was aimed at the interpretation of surface morphology, elemental identification, phase composition, interplanar spacing, full-width half maximum, crystallite size, lateral size, number of layers, dislocation density, microstrain, packing density, crystallinity index, and the specific surface area of the product obtained from two different approaches. It was revealed that the carbonized coconut shell chars obtained from the tube furnace have better characteristics to be activated further for carbon black synthesis. So, the flow of inert gas in a tube furnace is demonstrated to have a key role in improving the attributes of coconut shell chars

Anti-Wear and Anti-Erosive Properties of Polymers and Their Hybrid Composites: A Critical Review of Findings and Needs

Erosion caused by the repeated impact of particles on the surface of a substance is a common wear method resulting in the gradual and continual loss of affected objects. It is a crucial problem in several modern industries because the surfaces of various products and materials are frequently subjected to destructively erosive situations. Polymers and their hybrid materials are suitable, in powdered form, for use as coatings in several different applications. This review paper aims to provide extensive information on the erosion behaviors of thermoset and thermoplastic neat resin and their hybrid material composites. Specific attention is paid to the influence of the properties of selected materials and to impingement parameters such as the incident angle of the erodent, the impact velocity of the erodent, the nature of the erodent, and the erosion mechanism. The review further extends the information available about the erosion techniques and numerical simulation methods used for wear studies of surfaces. An investigation was carried out to allow researchers to explore the available selection of materials and methods in terms of the conditions and parameters necessary to meet current and future needs and challenges, in technologically advanced industries, relating to the protection of surfaces. During the review, which was conducted on the findings in the literature of the past fifty years, it was noted that the thermoplastic nature of composites is a key component in determining their anti-wear properties; moreover, composites with lower glass transition, higher ductility, and greater crystallinity provide better protection against erosion in advanced surface applications

Preparation Methods for Graphene Metal and Polymer Based Composites for EMI Shielding Materials: State of the Art Review of the Conventional and Machine Learning Methods

Advancement of novel electromagnetic inference (EMI) materials is essential in various industries. The purpose of this study is to present a state-of-the-art review on the methods used in the formation of graphene-, metal- and polymer-based composite EMI materials. The study indicates that in graphene- and metal-based composites, the utilization of alternating deposition method provides the highest shielding effectiveness. However, in polymer-based composite, the utilization of chemical vapor deposition method showed the highest shielding effectiveness. Furthermore, this review reveals that there is a gap in the literature in terms of the application of artificial intelligence and machine learning methods. The results further reveal that within the past half-decade machine learning methods, including artificial neural networks, have brought significant improvement for modelling EMI materials. We identified a research trend in the direction of using advanced forms of machine learning for comparative analysis, research and development employing hybrid and ensemble machine learning methods to deliver higher performance

Neutron-Induced Nuclear Cross-Sections Study for Plasma Facing Materials via Machine Learning: Molybdenum Isotopes

In this work, we apply a machine learning algorithm to the regression analysis of the nuclear cross-section of neutron-induced nuclear reactions of molybdenum isotopes, 92Mo at incident neutron energy around 14 MeV. The machine learning algorithms used in this work are the Random Forest (RF), Gaussian Process Regression (GPR), and Support Vector Machine (SVM). The performance of each algorithm is determined and compared by evaluating the root mean square error (RMSE) and the correlation coefficient (R2). We demonstrate that machine learning can produce a better regression curve of the nuclear cross-section for the neutron-induced nuclear reaction of 92Mo isotopes compared to the simulation results using EMPIRE 3.2 and TALYS 1.9 from the previous literature. From our study, GPR is found to be better compared to RF and SVM algorithms, with R2=1 and RMSE =0.33557. We also employed the crude estimation of property (CEP) as inputs, which consist of simulation nuclear cross-section from TALYS 1.9 and EMPIRE 3.2 nuclear code alongside the experimental data obtained from EXFOR (1 April 2021). Although the Experimental only (EXP) dataset generates a more accurate cross-section, the use of CEP-only data is found to generate an accurate enough regression curve which indicates a potential use in training machine learning models for the nuclear reaction that is unavailable in EXFOR