A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2016. / This study has explored the CVD synthesis of carbon nanofibres (CNFs) using Eskom’s waste coal fly ash as a catalyst with acetylene and hydrogen as the carbon source and carrier gas, respectively. In the process, a possible growth mechanism for these carbon nanofibres was sought. CNFs were successfully synthesised from fly ash and were found to have an average diameter of 22±7 nm. The growth mechanism of these CNFs was studied using EDS, TEM and laser Raman spectroscopy. It was observed that CNFs grew via root growth on spherical particles of fly ash and by tip growth on irregular-shaped metal oxide agglomerates. Both of these were found, through EDS analysis, to be Fe-rich. CNFs were functionalised between 2-12 h under reflux at 110 °C using a 3:1 (v/v) combination of HNO3 and H2SO4 in order to introduce functional groups onto their surfaces to act as anchors for hydrophilic reactants. The functionalisation of these CNFs was studied using TEM, laser Raman spectroscopy, ATR-FTIR spectroscopy, PXRD, BET, XRF and TGA. ATR-FTIR spectroscopy showed that some carbonyl functional groups were present on the surfaces of these CNFs after functionalisation. The functionalised CNFs (fCNFs) were then treated using a simple hydrothermal method to deposit 10% (m/m) of TiO2 nanoparticles onto their surface. This hydrothermal method employed the drop-wise addition of TiCl4 to a cold water-fCNFs mixture, which was then refluxed at 115 °C for 2-12 h. Laser Raman spectroscopy confirmed the presence of both TiO2 (phase pure anatase) and CNFs. ATR-FTIR spectroscopy provisionally revealed the presence of covalent Ti-O-C bonds. Studies where the duration of exposure to TiCl4 and the functionalisation time of CNFs were examined showed that the particle size and agglomeration of the TiO2 nanoparticles did not affect the surface area of the CNF-TiO2 hybrids significantly. However, CNF-TiO2 hybrids which were shown by TGA to have high fly ash content were observed to have low surface areas. fCNFs functionalised at 2 h had the highest surface area, at all fixed durations of exposure to TiCl4 by comparison with fCNFs which had been functionalised for longer periods. / GR2016

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfillment for the degree of Master of Science in Chemistry, 2017 / The aim of this study was to synthesize helical carbon nanofibers with controlled diameter by using copper nanoparticles contained inside hollow carbon sphere. In this work, different methods have been explored to synthesize copper nanoparticles contained inside mesoporous hollow carbon spheres in order to minimize the sintering effect of the copper nanoparticles. Mesoporous hollow carbon spheres were used not only as a support for the copper nanoparticles but to stabilize and disperse these nanoparticles to prevent the formation of aggregates. Mesoporous hollow carbon spheres were synthesized using a hard templating method, in which mesoporous silica spheres or polystyrene spheres were used as a sacrificial template. Carbon nanofibers with different morphologies, including straight and helical fibers were obtained by a chemical vapor deposition method where acetylene was decomposed over copper nanoparticles contained inside mesoporous hollow carbon spheres catalyst at 350 °C. The synthesized carbon nanofibers were grown on the surface of the mesoporous hollow carbon spheres as the methods used to synthesize the catalyst failed to incorporate copper nanoparticles inside the spheres. Differences in the diameter of the straight and helical carbon nanofibers were observed from both catalysts. This supports the important effect of particle size on influencing the shape of the synthesized carbon nanofibers. / XL2018

No description available.

Carbon nanotubes (CNTs) and carbon nanofirbers (CNFs) have excellent properties (mechanical, electrical, magnetic, etc.), which can make them effective nanoreinforcements for improving the properties of materials. The incorporation of CNT/Fs in a wide variety of materials has been researched extensively in the past decade. However, the past study on the reinforcement of cementitious materials with these nanofilaments has been limited. The findings from those studies indicate that CNT/Fs did not significantly improve the mechanical properties of cementitious materials. Two major parameters influence the effectiveness of any discrete inclusion in composite material: The dispersion quality of the inclusions and the interfacial bond between the inclusions and matrix. The main focus of this dissertation is on the dispersion factor, and consists of three main tasks: First a novel thermodynamic-based method for dispersion quantification was developed. Second, a new method, incorporating the utilization of silica fume, was devised to improve and stabilize the dispersion of CNFs in cement paste. And third, the dispersion quantification method and mechanical testing were employed to measure, compare, and correlate the dispersion and mechanical properties of CNF-incorporated cement paste produced with the conventional and new methods. Finally, the main benefits, including the increase in strength and resistance to shrinkage cracking, obtained from the utilization of CNFs in cement paste will be presented. The investigations and the corresponding results show that the novel dispersion quantification method can be implemented easily to perform a wide variety of tasks ranging from measuring dispersion of nanofilaments in composites using their optical/SEM micrographs as input, to measuring the effect of cement particle/clump size on the dispersion of nano inclusions in cement paste. It was found that cement particles do not affect the dispersion of nano inclusions in cement paste significantly while the dispersion of nano inclusions can notably degenerates if the cement particles are agglomerated. The novel dispersion quantification method shows that, the dispersion of CNFs in cement paste significantly improves by utilizing silica fume. However, it was found that the dispersion of silica fume particles is an important parameter and poorly dispersed silica fume cannot enhance the overall dispersion of nano inclusions in cementitious materials. Finally, the mechanical testing and experimentations showed that CNFs, in absence of moist curing, even if poorly dispersed, can provide important benefits in terms of strength and crack resistance.

No description available.

In this study, we developed the manufacturing pathways of carbon nanofibers (CNF) and activated carbon nanofibers (ACNF) via the ¡§melt-spinning¡¨ method. A novel route based on the solvent-free core/sheath melt-spinning of polypropylene/ (phenol formaldehyde-polyethylene) (PP/(PF-PE)) to prepare CNF. The approach consists of three main steps: co-extrusion of PP (core) and a polymer blend of PF and PE (sheath), followed by melt-spinning, to form the core/sheath fibers; stabilization of core/sheath fibers to form the carbon fiber precursors; and carbonization of carbon fiber precursors to form the final CNF. Both scanning electron microscopy and transmission electron microscopy images reveal long and winding CNF with diameter 100 - 600 nm and length greater than 80 £gm. With a yield of ~ 45 % based on its raw material PF, the CNF exhibits regularly oriented bundles which curl up to become rolls of wavy long fibers with clean and smooth surface. Results from X-ray diffractometry, energy dispersive X-ray, Raman spectroscopy, and selected area electron diffraction patterns further reveal that the CNF exhibits a mixed phase of carbon with graphitic particles embedded homogeneously in an amorphous carbon matrix. The carbon atoms in CNF are evenly distributed in a matrix having a composition of 90 % carbon element and 10 % in oxygen element. A series of ACNF have also been prepared based on the chemical activation on the thus-prepared CNF; their morphological and microstructure characteristics were analyzed by scanning electron microscopy, atomic force microscopy (AFM), Raman spectroscopy, and X-ray diffractometry, with particular emphasis on the qualitative and quantitative AFM analysis. The effect of activating agent, potassium hydroxide and phosphorous acid, is compared; factors affecting the surface morphology and microstructure of ACNF are analyzed. The ACNF also exhibits a mixed phase of carbon with graphitic particles embedded homogeneously in an amorphous carbon matrix. The resulting ACNF consists of 73 % C element and 27 % O element. The total pore volume of the all activated ACNF is larger than that of un-activated CNF. It can be inferred that chemical activation by KOH results in increased micropore volume in carbon nanofibers; while the micropores produced by the chemical activation of H3PO4 may further be activated and then enlarged to become the mesopores at the expense of micropore volume. For the concentration effect of KOH on ACNF, it can be inferred that high concentration KOH activation results in increased SBET and micropore volume in carbon nanofibers. The average pore diameter of ACNF gradually decreases as the KOH concentration increases.

The focus of the proposed research will be on exploring the use of nanotechnology-based nano-filaments, such as carbon nanotubes (CNTs) and nanofibers (CNFs), as reinforcement in improving the mechanical properties of portland cement paste as a construction material. Due to their ultra-high strength and very high aspect ratios, CNTs and CNFs have been used as excellent reinforcements in enhancing the physical and mechanical properties of polymer, metallic, and ceramic composites. Very little attention has been devoted on exploring the use of nano-filaments in the transportation industry. Therefore, this study aims to bridge the gap between nano-filaments and transportation materials. This will be achieved by testing the integration of CNTs and CNFs in ordinary portland cement paste through state-of-the-art techniques. Different mixes in fixed proportions (e.g. water-to-cement ratio, air content, admixtures) along with varying concentrations of CNTs or CNFs will be prepared. Different techniques commonly used for other materials (like polymers) will be used in achieving uniform dispersion of nano-filaments in the cement paste matrix and strong nano-filaments/cement bonding. Small-scale specimens will be prepared for mechanical testing in order to measure the modified mechanical properties as a function of nano-filaments concentration, type, and distribution. With 0.1 percent CNFs, the ultimate strain capacity increased by 142 percent, the flexural strength increased by 79 percent, and the fracture toughness increased by 242 percent. Furthermore, a scanning electron microscope (SEM) is used to discern the difference between crack bridging and fiber pullout. Test results show that the strength, ductility, and fracture toughness can be improved with the addition of low concentrations of either CNTs or CNFs.

Uniform and aligned nanofibers have been obtained by eletrospinning. Activated carbon nanofibers (ACNFs) have been used as electrode materials for battery and electric double layer due to its porous properties. A high value of surface area can be attained (1000 - 3000 nm) by activation, due to the presence of micropores on the surface of nanofibers. A series of nanofibers have been prepared using different polymer precursors and concentrations by electrospinning in this study. Morphological study by SEM reveals a uniform and aligned fibrous structure for the PAN-based CNF (11 wt%) and a curved and twisted fibrous structure for the PAN-based CNF (8 wt%) and the acrylic-based CNF (9 wt%). Thus, the microstructure of CNF can be greatly influenced by the concentration of polymer precursor; high quality of nanofibers can be produced with higher polymer concentration and higher viscosity. The diameter of PAN-based nanofibers is gradually decreased from 400 to 200 nm during stabilization, carbonization, and activation, due mainly to the degradation and condensation. Surface of CNF becomes rough after activation due to the etching by potassium ions at high temperatures. Microstructural study by X-ray diffraction and Raman spectroscopy indicates a discernible diffraction peak at d002 = 0.356 nm and the ratio ID/IG = 1.83 of ACNFs, showing an amorphous and disordered structure, and leading to a low conductivity. Adsorption/desorption isotherms obtained from BET measurements under nitrogen atmosphere suggests a relatively small surface area of 8-10 m2/g, indicating that there might be no adsorption on the porous ACNF or the porous structure has been destroyed after carbonization. This leads to a relatively low conductance of 17 Faraday/g measured from the cyclic voltammetry.

Submitted by Juliana Bovi de Oliveira null (juliana_bovi@hotmail.com) on 2016-04-28T03:07:28Z No. of bitstreams: 1 Dissertação de Mestrado - Juliana B Oliveira.pdf: 3628116 bytes, checksum: 38a7295f033a2a9bda4b4118db7acee0 (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-05-02T11:57:44Z (GMT) No. of bitstreams: 1 oliveira_jb_me_guara.pdf: 3628116 bytes, checksum: 38a7295f033a2a9bda4b4118db7acee0 (MD5) / Made available in DSpace on 2016-05-02T11:57:44Z (GMT). No. of bitstreams: 1 oliveira_jb_me_guara.pdf: 3628116 bytes, checksum: 38a7295f033a2a9bda4b4118db7acee0 (MD5) Previous issue date: 2016-03-08 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Nos últimos anos, reforços constituídos de nanoestruturas em carbono, tais como nanotubos de carbono, fulerenos, grafenos e nanofibras de carbono, vêm sendo muito pesquisados devido às suas elevadas propriedades mecânicas, elétricas e térmicas. Uma vez que, as nanofibras de carbono consistem em um reforço contínuo (ou na forma de mantas) de elevada área superficial específica, associado ao fato de que estas podem ser obtidas a um baixo custo e em grandes quantidades, estas vêm se mostrando vantajosas quando comparadas aos tradicionais nanotubos de carbono. Assim, as nanofibras de carbono são ótimas candidatas para a obtenção de materiais avançados, podendo estas serem utilizadas como reforços em compósitos com diversas aplicações, tais como em implantes neurológicos e ortopédicos, como suportes de catalisadores, artefatos para aplicações aeroespaciais, dentre outras. Desta forma, o objetivo principal deste trabalho é a produção de nanofibras de carbono, empregando como precursora a manta de poliacrilonitrila (PAN) obtida pelo processo de eletrofiação via solução polimérica, com posterior utilização como reforço em compósitos poliméricos. Neste trabalho, uma manta de poliacrilonitrila com nanofibras de diâmetro de aproximadamente (375 ± 85) nm foi obtida por eletrofiação, sendo esta posteriormente carbonizada. A massa residual resultante do processo de carbonização foi de aproximadamente 38% em massa, com uma redução de 50% nos diâmetros das nanofibras após a queima das mantas de PAN, sendo que as mesmas apresentaram um rendimento de 25%. Na análise da estrutura cristalina do material carbonizado, verificou-se que o material apresentou uma desorganização estrutural. E a partir do ensaio de condutividade elétrica da manta carbonizada, concluiu-se que o material se comporta como um semi-condutor. O compósito de nanofibras de carbono/resina epóxi processado apresentou módulo de elasticidade de (3,79 ± 0,48) GPa, temperatura de transição vítrea (Tg) na faixa de 108,9 a 135,5°C, e um coeficiente de expansão térmica linear entre a faixa de 68 x 10-6/°C e 408 x 10-6/°C. / In recent years, reinforcement consisting of carbon nanostructures, such as carbon nanotubes, fullerenes, graphenes, and carbon nanofibers has been very researched due to its mechanical, electrical and thermal properties, besides having good thermal conductivity, mechanical resistance and high surface area. Since the carbon nanofibers comprise a continuous reinforcing with high specific surface area, associated with the fact that they can be obtained at a low cost and in large amounts, they have shown to be advantageous compared to traditional carbon nanotubes. Thus, the carbon nanofibers are excellent candidates in order to obtain advanced materials, and these can be used as reinforcements in composites with several applications such as for example, neurological and orthopedic implants, integrates in catalysts systems, devices for aerospace applications, among others. So, the main objective of this work is the processing of carbon nanofibers, using PAN as a precursor, obtained by the electrospinning process via polymer solution, with subsequent use for applications as reinforcement in polymer composites. In this work, PAN nanofibers were produced by electrospining with a diameter of approximately (375 ± 85) nm. The resulting residual weight after carbonization was approximately 38% in mass, with a diameters reduction of 50%, and the same showed a yield of 25%. From the analysis of the crystallinity structure of the carbonized material, it was found that the material presented a disordered structure. From the electrical conductivity results of the specimens, it was concluded that the material behaves as a semi-conductor. The epoxy resin/carbon nanofiber composite presented an elastic modulus value of (3.79 ± 0.48) GPa, a glass transition temperature (Tg) in the range from 108.9 to 135 5 ° C and a linear thermal expansion coefficient within the range of 68 x 10-6/°C and 408 x 10-6/°C.

Electronic skin (e-skin) materials have gained a wide range of attention due to their multiple applications in different areas, including soft robotics, skin attachable electronics, prosthetics, and health care. These materials are required to emulate tactile perceptions and sense the surrounding environments while maintaining properties such as flexibility and stretchability. Current e-skin fabrication techniques, such as photolithography, screen printing, lamination, and laser reducing, have limitations in terms of costs and manufacturing scalability, which ultimately preventing e-skin widespread usage. In this work, we introduce conductive stretchable 3D printable skin-like nanocomposite material. Our nanocomposite is easily 3D printed, cost-effective, and actively senses physical stimuli, such as strain and pressure, which gave them the potential to be used in prosthetics, skin-attachable electronics, and soft robotics applications. Using the conductive properties of carbon nanofibers, alongside a polymeric matrix based on Smooth-on platinum cured silicone and crosslinked PDMS, we can obtain a flexible and stretchable material that resembles human skin and can conduct electricity. A great advantage in our composite is the ability to tune its mechanical properties to fit the desired application area through varying PDMS's chain lengths and composition ratios in the nanocomposite. Also, the interconnecting network of micrometer-long nanofibers allows the measurement of resistivity changes upon physical stimuli, granting the nanocomposite sensing abilities. Moreover, we explored and optimized 3D printing of the nanocomposite material, which offering simplicity and versatility for fabricating complex 3D structures at lower costs.