Carbon nanotube and nanofiber growth on Zn based catalysts

In this study, acetylene gas was delivered to a catalyst network consists of NaCl-support and Zn nanoparticles in a temperature range of 500-700°C by means of a chemical vapor deposition (CVD). A principle feature that delineated this CVD study from prior studies lay, first in the method used to support the catalyst and secondly the choice of the catalyst metal. In particular, NaCl was deliberately retained and exploited in subsequent manipulations for the reason that it performed remarkably well as a support medium. The catalytic activity of Zn towards production of CNT/CNFs appeared to be promoted as a result of using molten ionic substrate

Trace elements in Turkish biomass fuels: Ashes of wheat straw, olive bagasse and hazelnut shell

Ash contents of wheat straw, olive bagasse and hazelnut shells were 7.9%, 3.9%, 1.2%, respectively, which seemed to be within the average values of ash of biomass. The microstructure of ashes included smooth, polygonal, granular and molten drop structures. A large percentage of particles present in ashes are commonly 1–20 lm in size. SEM/EDS analyses performed on the major ash forming elements in different ashes indicated that Si, Ca, K and Mg and P were generally the most abundant species. Trace element levels in ash samples of various biomass types such as hazelnut shell, wheat straw, olive bagasse were analysed using ICP spectroscopy. The elements determined were some of those considered being of great environmental concern such as, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pb. In all of the ashes studied Fe had the highest concentration among other trace elements, Mn was the second element that exhibited higher concentrations. The order of concentration of elements in the ashes from the highest to the lowest values was as follows: Fe > Mn > Zn > Cu > Ni > Cr > Pb > Co

Fuel supply chain analysis of Turkey

In spite of its natural sources, Turkey depends on other countries in terms of energy production, and a transfer from conventional fossil sources to sustainable energy sources is strongly necessary. Among the sustainable energy sources, biomass is the subject of this study. The characteristics, logistic aspects, environmental aspects, economical, legal and technical aspects are investigated in order to show that the possible biomass co-firing is very important for the construction of economic, sustainable and environmentally friendly energy systems

BeamSwitch: System solution for energy-efficient directional communication on mobile devices

Directional communication has the potential to improve both the energy efficiency of wireless communication without sacrificing its quality. We present a system solution, BeamSwitch, for directional communication on mobile devices. BeamSwitch employs a special multi-antenna system that consists of multiple identical directional antenna or beams, a single regular omni antenna, and a single RF chain. It uses one of the directional beams for transmitting data frames and receiving their acknowledgments and the regular antenna for all other transceiving. BeamSwitch tracks the signal strength of incoming frames and selects the right beam for data transmission. We report an extensive evaluation of BeamSwitch including both measurements with a prototype with three beams and Qualnet-based simulation. Our evaluation shows that BeamSwitch with three 6 dBi directional antennas can improve the energy efficiency of a commercial 802.11 adapter by over 20% and simultaneously provide better or close communication quality. BeamSwitch achieves this under diverse radio propagation environments and extreme mobility (up to 360° per second direction change)

Production of templated carbon nano materials, carbon nanofibers and super capasitors

i. Porous carbons are usually obtained via carbonization of precursors of natural or synthetic origin, followed by activation. To meet the requirements, a novel approach, the template carbonization method, has been proposed. Replication, the process of filling the external and / or internal pores of a solid with a different material, physically or chemically separating the resulting material from the template, is a technique that is widely used in microporosity and printing. This method has been used to prepare replica polymers [1,2] metals [3] and semiconductors [4] and other materials [5,6]. Zeolites represent an interesting case for replication processes, because the dimensions of their cages and channels are quite similar to those organic molecules that constitute the replica. If such as nanospace in a zeolite is packed with carbon and then the carbon are extracted from the zeolite framework, one can expect the formation of a porous carbon whose structure reflects the porosity of the original zeolite template. Owing to the disordered and inhomogeneous nature of the starting materials,\ud the resulting carbon has a wide and poorly controlled distribution of pore sizes. Zeolites with three-dimensional pore structures were found to be suitable as templates [7,8], whereas zeolites with one-dimensional structures were not effective [9]. These carbons obtained using zeolite templates with three-dimensional pore structures retained the shapes of zeolite particles, but did not retain their internal periodic structure. ii. Many methods have been proposed for carbon nanofiber (CNF) production, among them, we have chosen chemical vapor deposition (CVD) method for CNF synthesis because of its potential for scaling up the production and low cost[10]. Recent developments showed that alignment, positional control on nanometer scale, control over the diameter, as well as the growth rate of the carbon nanotubes (CNT) and CNFs can be achieved by using CVD[11-13]. Many catalysts supports and metal catalysts were proposed for CNF production through CVD technique. Silica (SiO2) [14], alumina (Al2O3) [15], quartz [16], titania (TiO2) or calcium oxide (CaO) [17] were used as the catalyst support because of their chemical inertness and high-temperature resistance. However, all of these support materials require harsh chemical treatment i.e. concentrated bases (NaOH) or strong acids (HF) to remove them, and these reagents may also damage the carbon nanostructure. Additionally, strong acids and bases are less desirable for large-scale production due to environmental concerns. Our goal in synthesizing CNFs is to achieve a control in tailoring the diameter, and morphology at the same time. We believe that understanding the chemistry involved in the catalyst and nanofiber growth process is the critical point to be able to produce defectless, property controlled CNFs. Thus, knowing the effect of the catalyst on CVD production of carbon nanofibers is very important for producing the desired CNFs. A very unique material, NaCl in the field of catalytic CVD process for carbon materials production, was selected as the support material which provides easy production and easy removal properties to the catalyst system. Together with the support material, the metal catalyst preparation step was differentiated from the conventional wet catalyst methods in which a liquid solution containing the catalyst in salt form is applied to the substrate via spray coating [16,18,19], spin coating [20-22], or microcontact printing [23] as well. The most active metals that were used previously in the catalytic CVD process for carbon materials production were Fe, Co [24], and Ni. The reason for choosing these metals as catalyst for CVD growth of nanotubes was the thermodynamic behavior of the metals at high temperatures, in which carbon is soluble in these metals and this solubility leads to the formation of metal-carbon solutions and therefore the desired carbon nanomaterial formation nucleates. In this study, transition metal based organometallic complex catalysts of Fe, Co, Ni and Cu were synthesized by a new approach of simultaneous synthesis of the support material and the catalyst. Therefore an easy production method for catalyst to use in CVD was developed by using only wet chemistry. iii. Electrochemically conducting polymers (ECPs) are of interest in late years and they are promising materials for realization of high performance supercapacitors, as they are characterized by high specific capacitances, by high conductivities in the charged states and by fast charge-discharge processes. The charge processes pertain to the whole polymer mass and not only to the surface. These features suggest the possibility to develop devices with low ESR and high specific energy and power. However, the long-term stability during cycling is a major demand for an industrial application of ECPs. Swelling and shrinkage of ECPs, caused by the insertion/deinsertion of counter ions required for doping the polymer, is well known and may lead to degradation of the electrode during cycling. This obstacle has been over overcome to some level by using composite materials made of carbon materials such as CNTs or activated carbons with CPs. Carbon material in the bulk both ensures a good electrical conductivity even the CP is in its insulating state and improves the mechanical properties of the electrodes. As mentioned in the earlier chapters, using carbon nanotubes, CPs, or both as composites for the active material of the supercapacitor applications comes with some disadvantages as well as the advantages. CPs although being a promising energy source for the job, lack the flexibility for insertion/deinsertion of the dopant ions resulting in shorter recycling life times than desired. CNTs are the employed to gain more flexibility however whether they are used as active materials solo, or engaged in a composite with a CP, they could not supply enough energy for the job. Therefore, the objective of this study is, to obtain a new material for supercapacitor active material; by depositing a conducting polymer, polypyrrole, on to carbon nanotubes via electropolymerization. By this method, the problem of bulk charging in conducting polymers is aimed to be overcomed. Since the coating is in magnitudes of nanometers, only surface charging will exist, which is desirable for supercapacitor applications

Active and Passive Control of Machine Tool Vibrations for High Speed and Accuracy

High-performance mechatronic systems are widely used in precision manufacturing equipment such as CNC machine tools, 3D-Printers, photolithography systems, industrial robots, and Coordinate Measuring Machines (CMMs). These equipment are utilized in producing parts and components for aviation, semiconductor, optics, and many other emerging industries, with geometric features and surface properties within micrometer-, or even in some cases nanometer-level accuracy. To keep up with the rapidly increasing productivity and accuracy demands, it is crucial that mechatronic systems of these manufacturing equipment deliver high-speed motion with high precision. In this dissertation, motion control strategies are presented to increase dynamic positioning accuracy and productivity of such mechatronic systems. First, a novel trajectory generation method is presented to avoid exciting low frequency structural vibration modes of machine tools and 3D-Printers, without compromising from productivity. The trajectory generation problem is posed as a convex optimization problem, and a practical windowing method is presented to implement the proposed strategy in real-time for long and realistic manufacturing scenarios. The proposed algorithm is validated on an industrial 3-Axis machine tool, and 4-6 times attenuation of the column vibration mode is achieved with 1[g] acceleration commands, without increasing the cycle time compared to state-of-the-art trajectory generation methods. This is followed by proposition of a data-driven trajectory shaping algorithm designed to eliminate dynamic positioning errors induced by flexible motion transmission components (such as ball-screw drives) and nonlinear friction forces typically caused by mechanical bearings and guiding units. The proposed algorithm is used for optimizing trajectory pre-filters through machine-in-the-loop iterations, in a data-driven fashion, and therefore it can be applied on a wide variety of systems without requiring elaborate dynamic modeling. Effectiveness of the proposed technique is validated on a linear-motor-driven planar motion stage and an industrial 3-Axis machine tool, and it is shown that dynamic errors are reduced by 3-5 times compared to industry-standard approaches. Finally, an active tool position control strategy is proposed to mitigate self-excited (chatter) vibrations for improving stability margins of turning processes. Two motion control algorithms are developed to control the dynamic process defined by the interaction of the tool and the workpiece. An industrial lathe (turning center) is utilized for validating the effectiveness of proposed algorithms. A piezo-actuator driven tool-assembly is utilized to control tool position during the machining process, utilizing tool acceleration feedback, and the experiments show that 4-5 times increase in productivity (widths of cut) is achieved by the proposed strategy