Download or read book Surface Investigations of the Mechanism of Single Walled Carbon Nanotube Growth by CO Disproportionation Over a Co Mo Catalyst written by José Efraín Herrera and published by . This book was released on 2003 with total page 546 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Single Walled Carbon Nanotubes written by Yan Li and published by Springer. This book was released on 2019-05-16 with total page 333 pages. Available in PDF, EPUB and Kindle. Book excerpt: The series Topics in Current Chemistry Collections presents critical reviews from the journal Topics in Current Chemistry organized in topical volumes. The scope of coverage is all areas of chemical science including the interfaces with related disciplines such as biology, medicine and materials science. The goal of each thematic volume is to give the non-specialist reader, whether in academia or industry, a comprehensive insight into an area where new research is emerging which is of interest to a larger scientific audience. Each review within the volume critically surveys one aspect of that topic and places it within the context of the volume as a whole. The most significant developments of the last 5 to 10 years are presented using selected examples to illustrate the principles discussed. The coverage is not intended to be an exhaustive summary of the field or include large quantities of data, but should rather be conceptual, concentrating on the methodological thinking that will allow the non-specialist reader to understand the information presented. Contributions also offer an outlook on potential future developments in the field.

Download or read book Investigation Into the Growth Mechanisms of Carbon Nanotubes Formed Using Thermal Chemical Vapour Deposition written by William Murray Whyte and published by . This book was released on 2011 with total page 288 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Dissertation Abstracts International written by and published by . This book was released on 2004 with total page 854 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Nanotechnology for Chemical Engineers written by Said Salaheldeen Elnashaie and published by Springer. This book was released on 2015-07-03 with total page 285 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book describes the basic principles of transforming nano-technology into nano-engineering with a particular focus on chemical engineering fundamentals. This book provides vital information about differences between descriptive technology and quantitative engineering for students as well as working professionals in various fields of nanotechnology. Besides chemical engineering principles, the fundamentals of nanotechnology are also covered along with detailed explanation of several specific nanoscale processes from chemical engineering point of view. This information is presented in form of practical examples and case studies that help the engineers and researchers to integrate the processes which can meet the commercial production. It is worth mentioning here that, the main challenge in nanostructure and nanodevices production is nowadays related to the economic point of view. The uniqueness of this book is a balance between important insights into the synthetic methods of nano-structures and nanomaterials and their applications with chemical engineering rules that educates the readers about nanosclale process design, simulation, modelling and optimization. Briefly, the book takes the readers through a journey from fundamentals to frontiers of engineering of nanoscale processes and informs them about industrial perspective research challenges, opportunities and synergism in chemical Engineering and nanotechnology. Utilising this information the readers can make informed decisions on their career and business.

Download or read book Carbon Nanostructured Materials written by Alexander Khovavko and published by Springer Nature. This book was released on with total page 163 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Effect of Catalyst Properties on the Synthesis of Carbon Nanotubes by Plasma Enhanced Chemical Vapor Deposition written by Surya Venkata Sekhar Cheemalapati and published by . This book was released on 2012 with total page 94 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Chemical Engineering Progress written by and published by . This book was released on 2005 with total page 460 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Rational Catalyst Design for Carbon Nanotube Carpet Growth and Fischer Tropsch Synthesis written by Xu Li and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The first part of this research involves the growth of vertically aligned carbon nanotube (CNT) arrays (or CNT carpets) that are desired in many important applications. Growth of high-quality, dense CNT carpets via catalytic chemical vapor deposition (CCVD) has been largely limited to catalysts supported on amorphous alumina or silica. Although catalyst design and CCVD process optimization have been extensively investigated, scalable growth of CNT carpets especially on nontraditional substrates remains largely a challenge. To develop a rational basis for designing efficient CNT catalysts, a deeper understanding of the role of substrates in CNT carpet growth during CCVD is required. In this study, a fundamental investigation of the effects of substrate properties on CNT carpet growth from supported catalysts under different reaction conditions and feedstock is carried out. To illuminate the interrelationships between properties of catalyst supporting layers on CNT carpet growth behaviors, CNT growth experiments from Fe catalyst supported on a variety of nontraditional substrates including stainless steel (SS), MgO, MgAl2O4 (100, 110, and 111 crystalline phases), and ZrO2 were carried out. This study reveals that ion beam bombardment of 316 SS decreases the film thickness of AlxOy required for CNT growth to 5 nm AlxOy. The role of ion beam bombardment is to transform a highly crystalline surface into an amorphous surface, resulting in favorable catalyst-substrate interactions that enhances CNT growth. Our results reveal that Fe catalyst supported on different phases of MgAl2O4 spinel substrates show different CNT growth behaviors due to their different surface chemistries and surface energies. The second part of this research is motivated by the drive to seek new routes that yield clean fuels and chemicals via Fischer-Tropsch synthesis (FTS). FTS provides a pathway for the transformation of biomass, coal or natural gas into fuels and chemicals using a transition metal catalyst. Co-based catalysts are of interest because they exhibit relatively higher activity and selectivity to long-chain paraffins, high resistance to deactivation, and a low water-gas shift (WGS) reaction activity. Catalytic performance is sensitive to the catalyst preparation method and type of catalyst precursor. To investigate the effect of the type of catalyst precursor used during synthesis on physicochemical properties and efficiency of FTS process, SiO2-supported Co catalysts were synthesized via an incipient wetness impregnation method from four different precursors: Co(NO3)2 (Co-Nit), Co(C2H3O2)2 (Co-Ace), CoCl2 (Co-Chl), and Co(OH)2 (Co-Hyd). This study reveals the type of Co precursor used during synthesis has significant effects on catalyst dispersion, size, crystalline phase, reducibility, stability, and FTS performance (CO conversion, C5+ selectivity, turnover frequency, and catalyst lifetime). Prenatal and postmortem characterization of the catalyst reveal sintering and formation of Co2C in all catalysts except Co-Nit, which may explain the various degrees of deactivation observed. Further, XANES and EXAFS data confirm the superior structural stability of Co-Hyd and presence of hydroxyl groups even after reaction.

Download or read book Reliable Growth of Vertically Aligned Carbon Nanotube Arrays by Chemical Vapor Deposition and In situ Measurement of Fundamental Growth Kinetics in Oxygen free Conditions written by JUNG BIN. IN and published by . This book was released on 2011 with total page 196 pages. Available in PDF, EPUB and Kindle. Book excerpt: Vertically-aligned carbon nanotube (VACNT) arrays are both an important technological system, and a fascinating system for studying basic principles of nanomaterial synthesis. However, despite continuing efforts for the past decade, important questions about this process remain largely unexplained. Recently, nanotube research investigations have been conducted, aiming at revealing the underlying growth mechanisms, rather than merely studying the feasibility on new growth methods. Nonetheless, growth deactivation and the accompanying termination mechanisms still remain a topic of nanotube synthesis science. Due to the extremely small size, however, direct characterization of various transport and conversion events occurring at the catalyst surface is not an easy task. Thus investigations on growth kinetics are the first step to resolve questions about growth mechanism. Before exploring kinetic aspects of the growth process, one must achieve reliable growth conditions since growth non-reproducibility retards obtaining reliable growth data and undermines the scientific value of the data. In order to improve growth reliability, several factors that may contribute to growth non-reproducibility were identified and thereafter mitigated. Firstly, a simulation study was conducted to achieve insight into temperature and velocity profile of gases inside the reactor since gas flow dynamics can render growth environment near the substrate non-uniform. Interestingly, when argon gas was used as the main carrier gas, natural convective flow emerged, generating flow circulation before the gas reached the substrate placed at the center of the tube reactor. This flow circulation was not favorable for controlled gas introduction. This problem could be resolved by using a more heat- and momentum- conductive gas such as helium. Secondly, atomic force microscopy of annealed catalyst revealed that the aluminum sub-layer was not thermally stable at the growth temperature although this material has been widely used as a barrier layer to avoid silicide formation of catalyst on silicon substrates. In this respect, aluminum oxide should be a better choice, but under-stoichiometry of the aluminum oxide layer, which originated from sputter target degradation, affected thermal stability of the layer. Reactive sputtering by oxygen addition greatly enhanced thermal stability, and finally defect-free catalyst nanoparticles were formed by thermal annealing. Thirdly, the effect of the small part-per-million levels of oxygen-containing species on VACNT growth revealed that oxygen-containing gas impurities in nominally pure gas sources have a great influence on growth kinetics in a positive way; their presence increases catalyst lifetime and growth yield. However, the kinetic behavior that is highly sensitive to gas purity is prone to showing an interfering kinetic trend where the real mechanism is masked by the significant gas impurity effect. The stark difference in catalytic lifetime after the introduction of high-performance gas purifiers shows that extremely tight control of the reaction gas composition purity is necessary to obtain controlled growth of CNTs under atmospheric chemical vapor deposition (CVD) conditions. Finally, more reliable growth of VACNTs was achieved, and thereafter the next step for fundamental growth kinetics measurement was followed. Finally, the CVD system was equipped with an optical micrometer that enables in-situ measurement of the height of growing VACNTs, which have advantageous structure facilitating measurement of growth kinetics since the array height has a robust correlation with growth yield and thereby growth rate. Various ethylene and hydrogen combinations were examined to capture growth kinetics related to different gas environment. The measured initial growth rates were linearly proportional to ethylene concentration, whereas a reciprocal relation was observed with respect to hydrogen concentration. The apparent activation energy was higher than reported in references. Flow rate variation experiments revealed that gas phase reaction is involved as the crucial growth step, which supports the observed high activation energy. Consequently, a growth model was proposed so that it could reasonably fit the initial growth rate data. Kinetic aspects related to growth deactivation were explored by measuring the final growth height and catalyst lifetime. Unlike growth with unpurified gases, growth became much less sensitive to gas composition after purification. Importantly, it was observed that growth deactivates by deficit of carbon source when relatively low ethylene was introduced. This result is surprising since ethylene pressure should be high enough at the catalyst, considering the calculated sticking coefficient of ethylene is very low, approximately 10^-5. Thus it substantiates the idea that catalyst-mediated gas pretreatment process is critical to sustain nanotube growth. Importantly, this idea challenges the widely accepted growth termination concept whereby nanotube stops growing due to catalyst encapsulation by excessive carbon. Indeed, reduced flow rate of gas mixture increased growth yield remarkably by promoting the gas pretreatment over the catalyst. Catalyst ripening, or steric hindrance by interaction of nanotubes can be an alternative reason for growth termination, but analysis of morphologies of the annealed catalyst and as-grown nanotubes revealed that their effects were not significant for the corresponding growth conditions.

Download or read book Physical Properties Of Carbon Nanotubes written by G Dresselhaus and published by World Scientific. This book was released on 1998-07-22 with total page 273 pages. Available in PDF, EPUB and Kindle. Book excerpt: This is an introductory textbook for graduate students and researchers from various fields of science who wish to learn about carbon nanotubes. The field is still at an early stage, and progress continues at a rapid rate. This book focuses on the basic principles behind the physical properties and gives the background necessary to understand the recent developments. Some useful computational source codes which generate coordinates for carbon nanotubes are also included in the appendix.

Download or read book Carbon Nanotubes and Related Structures written by Dirk M. Guldi and published by John Wiley & Sons. This book was released on 2010-01-26 with total page 562 pages. Available in PDF, EPUB and Kindle. Book excerpt: Written by the most prominent experts and pioneers in the field, this ready reference combines fundamental research, recent breakthroughs and real-life applications in one well-organized treatise. As such, both newcomers and established researchers will find here a wide range of current methods for producing and characterizing carbon nanotubes using imaging as well as spectroscopic techniques. One major part of this thorough overview is devoted to the controlled chemical functionalization of carbon nanotubes, covering intriguing applications in photovoltaics, organic electronics and materials design. The latest research on novel carbon-derived structures, such as graphene, nanoonions and carbon pea pods, round off the book.

Download or read book Relationship Between the Micro structure of Co Mo Catalysts Supported on Silica and the Selectivity Towards Single walled Carbon Nanotubes written by Giulio Lolli and published by . This book was released on 2007 with total page 324 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Graphite Fibers and Filaments written by Mildred S. Dresselhaus and published by Springer Science & Business Media. This book was released on 2013-03-08 with total page 391 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book was begun after three of the present authors gave a series of in vited talks on the subject of the structure and properties of carbon filaments. This was at a conference on the subject of optical obscuration, for which submicrometer diameter filaments with high length-to-diameter ratios have potential applications. The audience response to these talks illustrated the need of just one scientific community for a broader knowledge of the struc ture and properties of these interesting materials. Following the conference it was decided to expand the material presented in the conference proceedings. The aim was to include in a single volume a description of the physical properties of carbon fibers and filaments. The research papers on this topic are spread widely in the literature and are found in a broad assortment of physics, chemistry, materials science and engineering and polymer science journals and conference proceedings (some of which are obscure). Accordingly, our goal was to produce a book on the subject which would enable students and other researchers working in the field to gain an overview of the subject up to about 1987.

Download or read book Surface Chemistry of Metal Catalyst Under Carbon Nanotube Growth Conditions written by Tyson Cody Back and published by . This book was released on 2010 with total page 143 pages. Available in PDF, EPUB and Kindle. Book excerpt: The catalyst nanoparticle is critical to the yield, type, and diameter in the growth and nucleation of carbon nanotubes. The objective of this study is focused on determining what changes take place with the catalyst chemistry under growth conditions typically seen in chemical vapor deposition, CVD, experiments. It is well known that catalyst poisoning can occur and in turn effects the catalytic activity of the nanoparticle. A complete description of this mechanism is as of yet undetermined. In order to elucidate this process iron films were deposited onto Si substrates that contained a support layer of Al2O3 or SiO2. These samples were investigated with various surface chemistry techniques such as X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and electron energy loss spectroscopy (EELS). In addition, structural characteristics were investigated with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The surface techniques were used in-situ in order to observe chemistries that might not be observable outside a CVD reactor. Two sets of experiments were performed on the silica and alumina supports. The first consisted of carbon nanotube growth at near atmospheric pressure, while the second was performed under vacuum. The oxide support was shown to have an affect on the type of nanotubes grown under identical conditions. The silica support films produced more MWNT, while the alumina support films produced more SWNT. This difference was due to the amount of ripening that takes place on the oxide supports. Also in-situ XPS revealed differences in the chemistry of iron catalyst during growth and these differences were attributed to substrate interactions between alumina and iron. Finally, in-situ XPS analysis showed no evidence of carbides or oxides acting as a catalyst during the nucleation process.

Download or read book Nanohybrid Catalyst based on Carbon Nanotube written by Rasel Das and published by Springer. This book was released on 2017-05-23 with total page 159 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Phase Stability of Iron carbon Nanocarbides and Implications for the Growth of Carbon Nanotubes written by Neha Awasthi and published by . This book was released on 2007 with total page 250 pages. Available in PDF, EPUB and Kindle. Book excerpt: Catalyst nanoparticles play a crucial role in the synthesis of single-walled carbon nanotubes by chemical vapor deposition technique. Understanding the thermal behavior of the nano-catalysts, their interaction with Carbon and stability of nanocarbides can give better insight into the growth mechanism and control over selective, yield of nanotubes. In this work, we present results using first-principle calculations and classical molecular dynamics simulations to understand the thermodynamics of free and Al2O3 supported Fe-C nanoparticles. We observe that the substrate plays an important role during the growth reaction by increasing the melting temperatures of small and medium size Fe nanoparticles. We investigate Fe-C phase diagrams for small Fe nanoparticles (d∼2nm) and discover that as the size of the Fe nanoparticle is reduced, the eutectic point shifted significantly toward lower temperatures, as expected from the Gibbs-Thomson law, and also toward lower concentrations of C. We devise a simple model based on the Young-Laplace pressure-radius relation, to predict the behavior of the phases competing for stability in Fe-C nanoclusters at low temperature. We identify ranges of nanoparticle sizes which are compatible for steady state-, limited- and no-growth of SWCNTs corresponding to unaffected, reduced and no solubility of C in the Fe nanoparticles. We also calculate Fe-Mo-C ternary phase diagrams to investigate the behavior of bimetallic Fe:Mo catalyst nanoparticles. Our results show that addition of Mo (upto small concentrations) lowers the minimum radius when stable carbides nucleate and poison the catalyst, which enables a larger range of catalyst nanoparticles sizes to nucleate nanotubes. We also find that pure Fe has the highest surface concentration in Fe:Mo nanoparticles and is likely to be the active nucleation site for nanotubes.