Journal of Nano Research Vol. 26

Abstract: This work considers the study of the diffusion of carbon dioxide in polypropylene and amorphous polymers containing carbon nanoparticles, particularly carbon nanofibres and graphene, as well as nanoclays, to be used in microcellular foaming. The diffusion of CO₂ out and into the nanocomposites was studied during high pressure CO₂ dissolution, as the amount of CO₂ dissolved into the nanocomposite and CO₂ desorption rate are crucial in order to have a proper control of foaming. Comparatively, platelet-like nanoparticles slowed down the desorption of CO₂ out of the nanocomposites by means of a physical barrier effect, enabling a higher concentration of CO₂ to remain in the polymer and be used in foaming. As a consequence of the higher amount of CO₂ retained in the polymer and the cell nucleation effect promoted by the nanoparticles, polymer nanocomposite foams presented finer microcellular structures, in the case of PMMA even sub-microcellular, and higher specific moduli and electrical conductivities when compared to their pure counterparts.

Abstract: Nanostructured iron based alloy, elaborated from pure elemental powders by mechanical milling at high energy was studied. The materials obtained were characterized by several techniques, such as X-ray diffraction (XRD), which allowed the dissolution of chromium in the iron phase as a function of milling time. The peaks indicate that the obtained solid solution has the body centred cubic (bcc) structure, for a speed of 250 rpm after 24 hours milling time. The Williamson - Hall analysis method was used to exploit the recorded XRD patterns. The crystallite size of about 14 nm and the microstrain of about 0.90% were obtained for 48 hours of milling. Scanning electron microscopes (SEM) and EDX analysis have confirmed the refining of milled particles as a function of milling time and the homogenization of our powders. The measurement of reflection coefficient has revealed an increase in the microwave absorption versus milling time and has confirmed the formation of our alloy during 24 hours of milling.

Abstract: An experimental facility to examine the effect of carbon nanotubes (CNT) on the performance of a horizontal V-grooved heat pipe was build. The circular heat pipe was made of copper with an inner diameter of 10 mm and equipped with 10 axial V-grooves with 1 mm depth and 1 mm mouth. The experiment was performed using water as working fluid with mass percentage of CNT of 0%, 1%, 3% and 5%. The optimum fill ratio of the heat pipe was first determined by examining the fill ratio effect on the total resistance. This optimum fill ratio was then used throughout the whole experiment. The evaporator of the heat pipe was heated using a copper heater block equipped with 6 cartridge heaters. The power input to the evaporator was varied from 60 W to 240 W in steps of 60 W with maintaining steady-state operation at each power level. The condenser was cooled by a water jacket fed by a chiller. The surface temperature of the heat pipe was measured by 7 K-type self-adhesive thermocouples connected to data acquisition system. The experimental results showed that the performance of the heat pipe improved with the use of CNT-water mixture in terms of a reduction in the thermal resistance. The results also showed that this enhancement is a function of the amount of CNT additive.

Abstract: Oil recovery in offshore environments can be increased by using nanofluids with electromagnetic waves generated from an antenna in the oil reservoir. In the case of offshore environments, these constraints can be avoided if a horizontal antenna is towed close to the seabed, which maximises the electromagnetic energy transferred from the overburden to the reservoir and nanofluids in the reservoir. In this research, a new enhanced antenna is used with iron oxide (Fe₂O₃) and zinc oxide (ZnO) nanofluids for oil recovery applications at the laboratory scale. In the antenna study, it was observed that the curve antenna with magnetic feeders gave a 1978% increase in the magnetic field signal strength compared to the case without magnetic feeders. The curve antenna with magnetic feeders produced a 473% increase in the electric field signal strength compared to the case without magnetic feeders. Iron oxide (Fe₂O₃) nanoparticles were prepared by the sol-gel method. The iron oxide (Fe₂O₃) nanoparticle sizes were in the range of 30.27-37.60 nm. FESEM and HRTEM images show that the samples have good crystallinity and that the grain size increased as temperature increased. Iron oxide (Fe₂O₃) samples sintered at 500°C showed a high initial permeability and Q-factor and a low loss factor compared to samples sintered at 500°C. The sample had a very high initial permeability and a low loss at low frequencies; therefore, it was suitable for the preparation of the nanofluid and oil recovery applications. Oil recovery through the usage of 0.1 % (w/w) iron oxide (Fe₂O₃) nanofluid with an EM field generated from the curve antenna with magnetic feeders was 33.45% of OOIP (original oil in place). In a similar case where 0.1 % (w/w) zinc oxide (ZnO) nanofluid with an EM field was used, 22.46 % of OOIP was recovered. These results imply that injecting 0.1% w/w iron oxide nanofluid coupled to the curve antenna with magnetic feeders has potential for oil recovery for improved water flooding systems because the high magnetic flux density that acts on the nanoparticles is proportional to the magnetic field strength.

Abstract: A major challenge for the oil industry is increasing the oil recovery from reservoirs. Nanofluid injection with the aid of electromagnetic (EM) waves can improve oil recovery. Nanoparticles of zinc oxide (ZnO) were synthesised using a sol-gel method and characterised using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Nanofluids of SWCNT and zinc oxide (ZnO) were used in this oil recovery study. It was observed that curved antennae with magnetic feeders gave a 472% larger D-field signal than those without magnetic feeders. The Dmol3 simulations showed that the band gap of ZnO is 1.088 eV, and the band gap of the SWCNT was 0.326 eV. The particle sizes of the ZnO nanoparticles were in the range of 30-39 nm. FESEM and HRTEM images showed that the samples were highly crystalline, and the grain size increased as the temperature increased. As a result, these nanoparticles were suitable for the preparation of the nanofluid and oil recovery applications. Oil recovery using 0.001% (w/w) ZnO nanofluid and EM was 16.10 % of OOIP, and using 0.01% SWNT nanofluid yielded an oil recovery of 23 ROIP %. These results imply that injecting a ZnO oxide nanofluid of 0.001% w/w coupled with a curved antenna and magnetic feeders has the potential to improve oil recovery in waterflooding systems.

Abstract: Research on the application of nanoparticles, specifically magnetic nanoparticles in enhanced oil recovery has been increasing in recent years due to their potential to increase the oil production despite having to interact with reservoirs of high salinity, high pressure and temperature and un-natural pH. Unlike other conventional EOR agents e.g. surfactants and polymers, a harsh environment will cause degradation and failure to operate. Magnetic nanoparticles which are activated by a magnetic field are anticipated to have the ability to travel far into the oil reservoir and assist in the displacement of the trapped oil. In this work, ferromagnetic Co²⁺_xFe²⁺_1-xFe³⁺₂O₄ nanoparticles were synthesized and characterized for their morphological, structural and magnetic properties. At a composition x = 0.75, this nanomaterial shows its best magnetisation parameters i.e. highest value of saturation magnetization, remanence and coercivity of 65.23 emu/g, 12.18 emu/g and 239.10 Oe, respectively. Subsequently, a dispersion of 0.01 wt% Co²⁺_0.75Fe²⁺_0.25Fe³⁺₂O₄ nanoparticles in distilled water was used for core flooding test to validate its feasibility in enhanced oil recovery. In a core flooding test, the effect of electromagnetic waves irradiation to activate the magnetization of Co²⁺_0.75Fe²⁺_0.25Fe³⁺₂O₄ nanofluid was also investigated by irradiating a 78 MHz square wave to the porous medium while nanofluid injection was taking place. In conclusion, an almost 20% increment in the recovery of oil was obtained with the application of electromagnetic waves in 2 pore volumes injection of a Co²⁺_0.75Fe²⁺_0.25Fe³⁺₂O₄ nanofluid.

Abstract: For electromagnetic absorbing and shielding applications, carbon nanotubes (CNT) are widely used due to their excellent electrical and physical properties. Fabrication of microwave absorbing materials involves the use of compounds capable of generating dielectric and/or magnetic losses when impinged by an electromagnetic wave. The presence of lattice defects e.g. vacancies and dislocations contributes to the loss and attenuation in the electromagnetic waves, which in turn remarkably enhance the absorption ability of the material. With the CVD technique which is known to produce several lattice defects in the final product, aligned MWCNTs were successfully synthesized by pyrolizing toluene and ferrocene in an inert argon environment. The morphology analysis of the aligned MWCNTs was conducted via FESEM and TEM analysis, to reveal the average length of approximately 295 μm, with diameters in the range of 60-200 nm. EDS analysis indicates the high yield of CNTs, with more than 90% in weight composition, with less than 5 % Fe impurities presence. Textural properties of MWCNTs were studied by measuring pore size and BET surface area. To understand the response of CNTs to an electromagnetic field, permeability and permittivity measurement were conducted in the frequency range of 100 Hz to 110 MHz. In conclusion, the presence of defects in MWCNTs is desirable for enhanced electromagnetic absorption ability.

Abstract: Hydrogen interaction with defects and structural development of Pd films with various microstructures were investigated. Nanocrystalline, polycrystalline and epitaxial Pd films were prepared and electrochemically loaded with hydrogen. Structural changes of Pd films caused by absorbed hydrogen were studied by in-situ X-ray diffraction combined with acoustic emission and measurement of electromotorical force. Development of defects during hydrogen loading was investigated by positron annihilation spectroscopy. It was found that hydrogen firstly fills open volume defects existing already in the films and subsequently it occupies also interstitial sites in Pd lattice. Absorbed hydrogen causes volume expansion, which is strongly anisotropic in thin films. This introduces high stress into the films loaded with hydrogen. Acoustic emission measurements revealed that when hydrogen-induced stress achieves a certain critical level rearrangement of misfit dislocations takes place. The stress which grows with increasing hydrogen concentration can be further released by plastic deformation and also by detachment of the film from the substrate.

Abstract: Enhanced oil recovery (EOR) refers to the recovery of oil that is left behind in a reservoir after primary and secondary recovery methods, either due to exhaustion or no longer economical, through application of thermal, chemical or miscible gas processes. Most conventional methods are not applicable in recovering oil from reservoirs with high temperature and high pressure (HTHP) due to the degradation of the chemicals in the environment. As an alternative, electromagnetic (EM) energy has been used as a thermal method to reduce the viscosity of the oil in a reservoir which increased the production of the oil. Application of nanotechnology in EOR has also been investigated. In this study, a non-invasive method of injecting dielectric nanofluids into the oil reservoir simultaneously with electromagnetic irradiation, with the intention to create disturbance at oil-water interfaces and increase oil production was investigated. During the core displacement tests, it has been demonstrated that in the absence of EM irradiation, both ZnO and Al₂O₃ nanofluids recovered higher residual oil volumes in comparison with commercial surfactant sodium dodecyl sulfate (SDS). When subjected to EM irradiation, an even higher residual oil was recovered in comparison to the case when no irradiation is present. It was also demonstrated that a change in the viscosity of dielectric nanofluids when irradiated with EM wave will improve sweep efficiency and hence, gives a higher oil recovery.

Abstract: In this study, numerous types of straight hetero-junction carbon nanotubes (CNTs) and their fundamental CNTs were investigated by the finite element method (FEM). By applying the FEM, the shear behavior of these hetero-junctions was obtained thorough numerical simulation. The behavior of hetero-junctions and their constituent CNTs were investigated. The investigations revealed that the twisting angle of straight hetero-junction CNTs lies within the range of twisting angle of their fundamental CNTs. In addition, change of boundary conditions did not significantly change the value of obtained twisting angle of hetero-junctions. It was also concluded that the shear behavior of straight hetero-junctions and their constituent CNTs increases by increasing the chiral number of both armchair and zigzag CNTs. The current study provides a better insight towards the prediction of straight hetero-junction CNTs behavior.