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Author: Shanee Danyale Pacley Publisher: ISBN: Category : Carbon-black Languages : en Pages : 113
Book Description
Carbon nanopearls (CNPs), also known as carbon spheres and nanospheres, are of interest to the nanoscience community due to their field emission and tribology capabilities. There have been numerous reports on the properties and potential applications of CNPs; however, there have been few studies on the behavior of the catalyst during synthesis. Carbon nanopearls are limited to being used as cold cathodes and lubricants for tribology if the nickel catalyst remains. This research focused on studying the behavior of the nickel catalyst during chemical vapor deposition of CNPs. Carbon nanopearls were grown at various growth times (10 sec, 30 sec, 60 sec, 90 sec, 120 sec and 300 sec) using two different nickel catalyst sizes (20 nm nickel nanoparticles and 100 nm nickel nanoparticles). Chemical analysis was conducted using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). This enabled observation of the chemical phases as growth time increased. Imaging of the CNPs samples was performed using transmission electron microscopy (TEM). Raman spectroscopy was performed to observe the defects and order in the graphitic structures as growth time varied. The melting temperature of the nickel nanoparticles was investigated experimentally by performing differential scanning calorimetry (DSC) on the nickel catalyst. Theoretically, the melting temperature was calculated using the Gibb-Thomson equation. The question "does the Ni catalyst evaporate during synthesis of carbon nanopearls" was addressed both theoretically and experimentally. Theoretically, the Kelvin effect was used to calculate the vapor pressure of the nickel nanoparticles. The vapor pressure of the nanoparticles was compared to the vapor pressure for bulk nickel, and this helped to determine if the nanoparticles were evaporating. Weight loss experiments were conducted and thermal gravimetric analysis (TGA) was performed on the nickel nanoparticles. These experiments were used to identify the temperature of evaporation. The results from this research showed that during the synthesis process, the Ni oxidized. XRD and XPS showed that the nickel oxide reduced as growth time increased, followed by the formation of a nickel carbide phase. Towards the longer growth times, the carbide decomposed leaving only nickel and graphite. TEM results revealed that the remaining nickel did not exist in the core of the carbon nanopearl, but that it was nickel that had segregated from the CNPs and agglomerated with other nickel particles. DSC identified the melting temperature of the 20 nm nickel nanoparticles to be lower than the bulk melting temperature of nickel. The Gibbs-Thomson effect was used as a guideline for determining the melting temperature of the nanoparticles. Oxidation of the nickel nanoparticles prevented determination of the evaporation temperature. Results from the Kelvin effect indicated that the Ni nanoparticles evaporate sooner than bulk nickel. However, due to XRD identifying Ni at the longer growth times, there was no evidence to conclude that the Ni had evaporated. Finally, a model for CNPs growth was presented based off the results in this research.
Author: Shanee Danyale Pacley Publisher: ISBN: Category : Carbon-black Languages : en Pages : 113
Book Description
Carbon nanopearls (CNPs), also known as carbon spheres and nanospheres, are of interest to the nanoscience community due to their field emission and tribology capabilities. There have been numerous reports on the properties and potential applications of CNPs; however, there have been few studies on the behavior of the catalyst during synthesis. Carbon nanopearls are limited to being used as cold cathodes and lubricants for tribology if the nickel catalyst remains. This research focused on studying the behavior of the nickel catalyst during chemical vapor deposition of CNPs. Carbon nanopearls were grown at various growth times (10 sec, 30 sec, 60 sec, 90 sec, 120 sec and 300 sec) using two different nickel catalyst sizes (20 nm nickel nanoparticles and 100 nm nickel nanoparticles). Chemical analysis was conducted using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). This enabled observation of the chemical phases as growth time increased. Imaging of the CNPs samples was performed using transmission electron microscopy (TEM). Raman spectroscopy was performed to observe the defects and order in the graphitic structures as growth time varied. The melting temperature of the nickel nanoparticles was investigated experimentally by performing differential scanning calorimetry (DSC) on the nickel catalyst. Theoretically, the melting temperature was calculated using the Gibb-Thomson equation. The question "does the Ni catalyst evaporate during synthesis of carbon nanopearls" was addressed both theoretically and experimentally. Theoretically, the Kelvin effect was used to calculate the vapor pressure of the nickel nanoparticles. The vapor pressure of the nanoparticles was compared to the vapor pressure for bulk nickel, and this helped to determine if the nanoparticles were evaporating. Weight loss experiments were conducted and thermal gravimetric analysis (TGA) was performed on the nickel nanoparticles. These experiments were used to identify the temperature of evaporation. The results from this research showed that during the synthesis process, the Ni oxidized. XRD and XPS showed that the nickel oxide reduced as growth time increased, followed by the formation of a nickel carbide phase. Towards the longer growth times, the carbide decomposed leaving only nickel and graphite. TEM results revealed that the remaining nickel did not exist in the core of the carbon nanopearl, but that it was nickel that had segregated from the CNPs and agglomerated with other nickel particles. DSC identified the melting temperature of the 20 nm nickel nanoparticles to be lower than the bulk melting temperature of nickel. The Gibbs-Thomson effect was used as a guideline for determining the melting temperature of the nanoparticles. Oxidation of the nickel nanoparticles prevented determination of the evaporation temperature. Results from the Kelvin effect indicated that the Ni nanoparticles evaporate sooner than bulk nickel. However, due to XRD identifying Ni at the longer growth times, there was no evidence to conclude that the Ni had evaporated. Finally, a model for CNPs growth was presented based off the results in this research.
Author: Stephan Parker Turano Publisher: ISBN: Category : Carbon Languages : en Pages :
Book Description
Carbon nanotubes (CNTs) have become a popular area of materials science research due to their outstanding material properties coupled with their small size. CNTs are expected to be included in a wide variety of applications and devices in the near future. Among these devices which are nearing mass production are electrochemical double layer (ECDL) supercapacitors. The current methods to produce CNTs are numerous, with each synthesis variable resulting in changes in the physical properties of the CNT. A wide array of studies have focused on the effects of specific synthesis conditions. This research expands on earlier work done using bulk nickel catalyst, alumina supported iron catalyst, and standard chemical vapor deposition (CVD) synthesis methods. This work also investigates the effect of an applied voltage to the CVD chamber during synthesis on the physical nature of the CNTs produced. In addition, the work analyzes a novel nickel catalyst system, and the CNTs produced using this catalyst. The results of the effects of synthesis conditions on resultant CNTs are included. Additionally, CNT based ECDL supercapacitors were manufactured and tested. Scanning electron microscope (SEM) analysis reveals that catalyst choice, catalyst thickness, synthesis temperature, and applied voltage have different results on CNT dimensions. Nanotube diameter distribution and average diameter data demonstrate the effect of each synthesis condition. Additionally, the concept of an alignment parameter is introduced in order to quantify the effect of an electric field on CNT alignment. CNT based ECDL supercapacitors testing reveals that CNTs work well as an active material when a higher purity is achieved. The molarity of the electrolyte also has an effect on the performance of CNT based ECDL supercapacitors. On the basis of this research, we conclude that CNT physical dimensions can be moderately controlled based on the choice of synthesis conditions. Also, the novel nickel catalyst system investigated in this research has potential to produce bulk quantities of CNT under specific conditions. Finally, purified CNTs are recommended as a suitable active material for ECDL supercapacitors.
Author: Ayako Nakagawa Publisher: ISBN: Category : Chemical vapor deposition Languages : en Pages : 184
Book Description
Influences of operating conditions on the production of carbon nanotubes (CNTs) were studied using Fe and Fe-Ni bimetallic catalysts supported on silicon monoxide (SiO). The catalysts were prepared in three steps: (1) impregnation of SiO powders with ferric nitride or combinations of ferric and nickel nitrides, (2) oxidation of nitrides in an air stream, and (3) grinding the powders obtained. CNTs were successfully synthesized by catalytic CVD using NH3/CH4 mixtures in a horizontal tubular flow reactor. The following process parameters were varied to investigate their effects on the growth rates of CNTs. The morphologies of catalysts and product CNTs were observed by scanning electron microscope (SEM). The particle size of SiO, metal composition, metal loading, temperature for catalyst oxidation, extent of grinding of catalysts, NH3 pretreatment time, reaction temperature for CNT growth, reaction time, and NH3/CH4 feed ratio. Two different average sizes of SiO particles, 8 [mu]m and 44 [mu]m, were compared based on the growth of CNTs in 5 min. Catalysts supported on 44 [mu]m average sized SiO particles demonstrated higher yields when they were not pretreated in an NH3 stream. When 1 wt% Fe was loaded, aligned CNTs were formed, and a highest growth rate per unit mass of catalyst was observed. The range of oxidation temperature to achieve highest catalyst activities depended on metals and metal contents: 600 - 750°C for 1 wt% Fe, 450 - 600°C for 3 wt% Fe, and 750 - 900°C for Fe-Ni. Grinding catalysts for at least 3 minutes increased the growth rate of CNTs by approximately 40 percent. The growth of CNTs was enhanced when no NH3 pretreatment of catalysts was carried out, regardless of metals and metal contents. However, CNTs did not grow appreciably from methane without ammonia. An NH3/CH4 feed ratio of 0.15 - 0.25 was observed to yield highest growth rates. The reaction temperature to achieve highest CNT growth rates was found to be in the range between 990 and 1000 °C. The growth of CNTs was not linear but decreased with reaction time.
Author: Surya Venkata Sekhar Cheemalapati Publisher: ISBN: Category : Metal catalysts Languages : en Pages : 94
Book Description
A study of the effect of catalyst properties on the synthesis of carbon nanotubes (CNTs) is done in this thesis. Three different metal alloy catalysts, Fe/Ti, Ni/Ti, Co/Ti, have been studied. Various atomic concentrations and thicknesses were cosputter deposited on clean Si wafers using AJA Orion 4 RF Magnetron sputter deposition tool at 5mtorr and 17°C, and the films were characterized using a scanning electron microscope, Energy-dispersive X-ray spectroscopy. All the alloys have been annealed at 650°C and 3 torr in an argon atmosphere at 100 SCCM, followed by ammonia gas plasma etch at different powers at 3 torr and 50 SCCM NH3 flow in a modified parallel plate RF chemical vapor deposition tool for 1 minute. The influence of plasma power, thickness of catalyst and concentration of Ti the secondary metal in the alloy composition, on the surface morphology of the catalyst are investigated by characterizing them with atomic force microscopy. The study has shown that the surface roughness is affected by Ti concentration, thickness and plasma power. The 35 W power NH3 plasma produced rougher surfaces when compared to the 75 W NH3 plasma. The result is interpreted as follows: ion bombardment leads to greater etching of the catalyst surface. Thus, plasma power must be optimized for catalyst thin film and etch time. The study has provided an in depth analysis and understanding of the various factors that influence catalyst surface morphology which can be applied into further study for optimizing parameters for synthesis of single walled CNTs. Following this, a study on catalysts for CNT synthesis was performed using Plasma enhanced chemical vapor deposition and characterized by scanning electron microscope. CNTs were synthesized on Ni, Ni-Ti, Co, Co-Ti and Fe catalyst. Ni, Ni-Ti catalyst produced forest like vertically aligned CNTs whereas Co, Co-Ti produced vertically aligned free standing CNTs. The growth was dense and uniform across the substrate. Initial growth runs on Fe, Fe-Ti alloy did not produce any CNTs until catalyst was restructured with a thicker Ti under layer after an investigation using Secondary ion mass spectrometry of suspected Fe catalyst poisoning due to reaction with Si substrate. A room temperature run was carried out on annealed and plasma etched Ni catalyst and no CNTs were produced indicating the importance of substrate temperature of CNTs. A deeper understanding of factors of influence on CNTs such as catalyst types, structure/morphology, and substrate temperature has been achieved with this study.
Author: GuiPing Dai Publisher: ISBN: Category : Technology & Engineering Languages : en Pages : 0
Book Description
As a new carbon material in the twenty-first century, carbon nanotubes (CNTs) have excellent optical, electrical, magnetic, thermal, chemical, and mechanical properties. There are many synthesis methods to produce CNTs. Compared with other methods, chemical vapor deposition (CVD) is the most effective method that has broad prospects for large-scale control of CNTs in recent years due to its simple equipment, simple operation, and lower cost. In order to gain a comprehensive understanding of the controlling parameters about the formation of CNTs, this chapter reviews the latest progress in the preparation of CNTs by CVD from three of the most important influencing factors: carbon sources, catalysts, and substrates. Among them, the catalyst is the most influential factor for the morphology, structure, and properties of CNTs. It should be pointed out that many growth factors can control the particle size distribution, composition, and structure of the catalysts, such as catalyst substrate, metal transition components added, calcination temperature, etc.
Author: Mahmood Rashid Atiyah Publisher: ISBN: Category : Languages : en Pages : 366
Book Description
Carbon nanotubes (CNTs) are widely synthesized at high temperatures via floating catalyst chemical vapor deposition (FC-CVD) method. It is important to reduce the synthesis temperature of CNTs to allow better control of the reactor's conditions, and to eliminate the formation of carbon by-products as well as reduce the overall cost. Therefore, the main objectives of this work were (i) to synthesize carbon nanotubes at low temperatures using some improvements to the CVD technique, (ii) to investigate the effects of temperature on the synthesis of CNTs and (iii) to simulate the temperature and velocity profile of the FC-CVD system in the absence of reaction. The synthesis temperature of CNTs was examined in the range between 500oC and 600oC at 10oC interval. The preheating set temperature was varied between 150oC and 400oC at 50oC interval. All experiments were conducted at 1 atm and exposed sections were insulated with glass wool covered with aluminum foil. Three O-ring heating mantels were used as a preheater and three ceramic boats were used to collect the product. Temperature in-situ monitoring device was used to monitor the temperature profile in the reactor and provide the exact time to heat up the catalyst and, thus, initiate the reaction. A single heat source for both catalyst and reactor was employed to enhance the growth of CNTs. COMSOL Multiphysics was used to simulate the velocity and temperature profiles of the system in the absence of reaction. The morphology and internal structures of the CNTs formed were analyzed via Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and High Resolution Transmission Electron Microscope (HRTEM). The thermal stability and the purity of the products were analyzed by Thermal Gravimetric Analyzer (TGA). The results of the work showed that CNTs were formed at the synthesis temperature ranging from 530oC to 600oC. Both quality and quantity of CNTs synthesized were increased with the increase in synthesis temperature. The highest amount of carbon deposit was obtained when the preheating and the synthesis temperatures were set at 300oC and 600oC, respectively. However, based on the TGA results, the highest purity of CNTs was achieved when the preheating and the synthesis temperatures were set at 200oC and 600oC, respectively. Well aligned CNTs were found when the preheating temperature was set at 400oC for synthesis temperatures of 570oC and 580oC. The use of single heat source for both catalyst and reactor was found to induce the formation of well aligned CNTs at synthesis temperature of 550oC. The simulation results indicated some regions in the reactor have variation in both temperature and velocity profiles. This, indirectly, affects the formation of CNTs. To conclude, this work has successfully achieved the outlined objectives. The amount of product produced and its quality depend both on the preheating values and the synthesis temperature.
Author: Rasel Das Publisher: Springer ISBN: 3319581511 Category : Technology & Engineering Languages : en Pages : 159
Book Description
This book introduces carbon nanotubes as a matrix for efficient nanohybrid catalysis. The preparation and use of such materials in ultra-grade water purification is described. Simple chemical methods for purification and functionalization of carbon nanotubes prior to their use is also detailed. The author also discusses the potential use of nanotube-based nanobiohybrid catalysts in the removal of organic pollutants.
Author: Shanee Danyale Pacley
Author: Shanee Danyale Pacley
Author: Stephan Parker Turano
Author: Ayako Nakagawa
Author: Surya Venkata Sekhar Cheemalapati
Author: Mauricio Kossler
Author: GuiPing Dai
Author: Mahmood Rashid Atiyah
Author: Rasel Das
Author: Siti Norazlian Ismail
Author: