The further developments in nanotechnology in last few years provide usage of nanoscale particles for many applications in various areas such as electronics, pharmaceutical, and biomedical due to their strengthened mechanical, thermal and electrical properties. Boron nitride nanotubes are a good example of nanoparticles. In this study, boron nitride nanotubes were successfully synthesized from the reaction of ammonia gas with mixture of boron and iron oxide. Physical and structural properties of the synthesized materials were determined by X-Ray Diffraction, Energy Dispersive X-Ray Spectroscopy, nitrogen sorption, X-Ray Photoelectron Spectroscopy, Fourier Transform Infrared Spectroscopy, and Scanning Electron Microscopy. Experiments were conducted in a tubular furnace at different temperatures and also at different weight ratios of boron to iron oxide. Qualitative chemical analysis of the reactor effluent stream was carried out using a mass spectrometer. The mass spectrometer analysis of the reaction products proved formation of nitrogen in addition to hydrogen and water during the reaction of ammonia gas with the mixture of boron and iron oxide. XRD results showed that hexagonal and rhombohedral boron nitrides and cubic iron were the solid phases formed in the product. FTIR and XPS results also indicated the presence of boron nitride and the atomic ratio of boron to nitrogen was compatible with the chemical stoichiometric relation between boron and nitrogen. It was observed that the crystanility of the product increased with an increase in temperature. The diameter of the produced nanotubes varied from 64 nm to 136 nm. The synthesized nanotubes exhibited Type II isotherms. The surface areas of the produced boron nitride nanotubes decreased with a decrease in both temperature and the weight ratio of boron to iron oxide. The best temperature and weight ratio of boron to iron oxide to produce boron nitride nanotubes were found to be 1300&deg / C and 20, respectively.

In today&amp / #8217 / s market conditions, higher tool life and durable cutting tools which can stand high cutting speeds are required in chip removal process. In order to improve the performance of cutting tools, coatings are employed extensively. Cubic boron nitride (cBN) is a new kind of coating material for cutting tools due to its outstanding properties and testing of cBN as a hard coating for machining have been increasing in recent years. However, there are some challenges such as compressive residual stress, poor adhesion and limiting coating thickness during the deposition of cBN on substrates. In this study, cubic boron nitride (cBN) coatings are formed on cutting tools from hexagonal boron nitride (hBN) target plates. For this purpose, a physical vapor deposition (PVD) system is utilized. PVD system works on magnetron sputtering technique in which material transfer takes place from target plate to substrate surface. Firstly, cBN coatings are deposited on steel and silicon wafer substrates for measurements and analyses. Compositional, structural and mechanical measurements and analysis are performed for the characterization of coatings. Next, several types of cutting tools are coated by cBN and the effects of cBN coatings on cutting performance are investigated. Finally, it can be said that cubic boron nitride coatings are successfully formed on substrates and the improvement of wear resistance and machining performance of cBN coated cutting tools are observed.

Hexagonal boron nitride (h-BN) formation by carbothermic reduction of B2O3 under nitrogen atmosphere at 1500&deg / C and effect of CaO addition into the initial B2O3 &amp / #8211 / active C mixture were investigated during this study. Reaction products were characterized by powder X-ray diffraction, scanning electron microscopy (SEM) and quantitative chemical analysis. Main aim of this study was to investigate the presence of a second reaction mechanism that catalytically affects h-BN formation during CaO or CaCO3 addition into the initial mixture. It was found that similar to CaCO3 addition, CaO addition has a catalytic effect on carbothermic formation h-BN. In order to investigate the reaction mechanism experiments with B2O3 &amp / #8211 / CaO mixtures without active carbon addition into the mixture were conducted. Furthermore nucleation of h-BN from calcium borate melts had been investigated and experiments were conducted with h-BN addition into CaO &amp / #8211 / B2O3 mixtures. It was concluded that nucleation of h-BN in calcium borate slags under experimental conditions is not possible. Hexagonal BN should be present in the system in order to activate the second nitrogen dissolution followed by h-BN precipitation mechanism. Highest efficiency was achieved in the experiment conducted with CaCO3 addition and largest particle size was observed during the experiment conducted to investigate the effect of nucleation.

Effect of Na2CO3 on formation of hexagonal boron nitride (h-BN) by carbothermic method has been studied by subjecting B2O3-C and Na2CO3-added B2O3-C mixtures to N2 (g) atmosphere. Na2CO3 amount in the mixtures was changed in the range of 0-40 wt. %. Time and temperature were used as experimental variables. Reaction products were analyzed by XRD and scanning electron microscope. Na2CO3 was found to increase both the amount and the particle size of h-BN similar to CaCO3 [1]. Na2CO3 was found to be less effective than CaCO3 in increasing the amount while it was more effective than CaCO3 in increasing the particle size of h-BN forming.

Boron nitride nanotubes (BNNTs), firstly synthesized in 1995, are structural analogues of carbon nanotubes (CNTs) with alternating boron and nitrogen atoms instead of carbon atoms. Besides their structure, mechanical and thermal properties of BNNTs are very similar to the remarkable properties of CNTs. However, BNNTs have higher resistance to oxidation than CNTs. Also, BNNTs are electrically isolating. Therefore, they are envisioned as suitable fillers for the fabrication of mechanically and thermally enhanced polymeric composites, while preserving the electrical isolation of the polymer matrix. In this study, polypropylene (PP) &ndash / boron nitride nanotube (BNNT) composites were prepared using a twin-screw extruder. Mechanical and thermal properties of PP&ndash / BNNT composites were investigated as a function of nanotube loading. The nanotubes used in the composites were synthesized from the reaction of ammonia gas with a powder mixture of elemental boron and iron oxide. X-ray diffraction (XRD) analysis revealed the predominant hexagonal boron nitride in the synthesized product. Multi-wall nanotubes with outer diameters ranging from 40 to 130 nm were observed with SEM and TEM analyses. Tensile testing of PP&ndash / BNNT composites revealed slight increases in the Young&rsquo / s modulus and yield strength of neat PP with 0.5 and 1 wt% of the as-synthesized BNNT additions. On the other hand, due to the agglomeration of BNNTs, elongation at break and tensile strength values of composites decreased with increasing nanotube content. In the case of using 0.5 wt% loading of purified and then surface modified BNNTs, slight improvement in all mechanical properties of neat PP was achieved. Differential scanning calorimetry (DSC) analysis revealed a noticeable increase in the crystallization temperature of BNNT&ndash / added composites. Coefficient of linear thermal expansion (CLTE) of polymeric composites were studied and no significant change in the CLTE of neat PP was observed with the addition of BNNTs. Results of thermal gravimetric analysis (TGA) indicated improvements in the thermal stability of neat PP with BNNT additions.

Carbothermic production of hexagonal BN by using boric acid and ground colemanite mined from Bigadi&ccedil / Region in Turkey was investigated by subjecting pellets prepared from B2O3, activated carbon and colemanite mixtures to nitrogen gas at 1500&deg / C. Similar to CaCO3 addition, colemanite addition to the B2O3-C mixtures resulted in higher amounts of h-BN in the final products. As a result of the experiments conducted with colemanite and CaCO3 additions providing the same quantity of CaO to the initial mixtures, similar amounts of hexagonal BN in the reaction products were observed. As a result of the experiments conducted with different compositions of colemanite- B2O3- C mixtures, 5 wt % colemanite addition was determined to be the optimum composition giving the highest amount of hexagonal BN in the reaction products. Increasing duration of the experiments increased the amount and particle size of h-BN formed in the products. Optimum amount of colemanite addition resulted in higher amounts and coarser particles of h-BN in the products than the optimum amounts of CaCO3 addition.

No description available.

Thesis (M. S.)--Materials Science and Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Cochran, Joe; Committee Member: Berczik, Doug; Committee Member: Sanders, Tom; Committee Member: Sandhage, Ken; Committee Member: Thadhani, Naresh.

The major objective of this thesis is to systematically investigate the effect of hexagonal BN (h-BN) islands on electronic and vibrational properties of single wall carbon Nanotubes. All our investigation are based on first principle Density Functional Theory (DFT) calculations. Our study is motivated by interesting metal-semiconductor transition recently found in periodically patterned graphene with h-BN islands. After reproducing the electronic band structure for pristine single wall zigzag carbon nanotubes (which shows metallic or semiconducting properties depending on their chirality), we investigated their electronic band structure in the presence of h-BN islands. The band structure depends not only on the defect concentration, but also on the pattern of the defect atoms. Our results also suggest that, if we start with a metallic /semiconducting mixture of ZSWCNTs, upon h-BN addition, the sample converts to fully semiconducting. This is a promising result for applications of CNTs in molecular electronics. Fundamental understanding of vibrational properties of nano electronics component is equally important in their applications especially in thermal management and thermoelectric applications. Defect engineering is one of the potential approach for tuning nanoelectronic devices for optimal thermal management and thermoelectric devices. In this work, I present a systematic investigation on how the group velocity and frequency of different phonon modes depend on various h-BN defect concentrations and defect patterns in ZSWCNTs. The study was extended to investigate the effect of hexagonal-C defects on the electronic and vibrational properties of zigzag single wall Boron Nitride nanotubes (ZSWBNNTs).

Doctor of Philosophy / Department of Chemical Engineering / James H. Edgar / Hexagonal boron nitride (hBN) has recently been envisioned for electronic, optoelectronic, and nanophotonic applications due to its strong anisotropy and unique properties. To realize these applications, the ability to synthesize single crystals with large size and low defect density is required. Furthermore, a detailed mechanistic understanding of hBN growth process is helpful for understanding and optimizing the synthesis technique for high quality crystals. In this dissertation, the production of large-scale, high-quality hBN single crystals via precipitation from metal solvents, including Ni-Cr and Fe-Cr, was demonstrated. The use of Fe-Cr mixture provides a lower cost alternative to the more common Ni-Cr solvent for growing comparable crystals. The clear and colorless crystals have a maximum domain size of around 2 mm and a thickness of around 200 μm. Detailed characterizations demonstrated that the crystals produced are pure hBN phase, with low defect and residual impurity concentrations. The temperature-dependent optical response of excitons showed that the exciton-phonon interaction in bulk hBN is in the strong-coupling regime. A new growth method for monoisotopic hBN single crystals, i.e. h¹⁰BN and h¹¹BN, was developed, by which hBN single crystals were grown using a Ni-Cr solvent and pure boron and nitrogen sources at atmospheric pressure. The chemical bonding analysis revealed that the B-N bond in h¹¹BN is slightly stronger than that in h¹⁰BN. The polariton lifetime in our monoisotopic hBN samples increases threefold over the naturally abundant hBN, and the isotopic substitution changes the electron density distribution and the energy bandgap of hBN. The ability to produce crystals in this manner opens the door to isotopically engineering the properties and performance of hBN devices. Atomistic-scale insights into the growth of hBN were obtained from multiscale modeling combining density functional theory (DFT) and reactive molecular dynamics (rMD). The energetics and kinetics of BN species on Ni(111) and Ni(211) surfaces were calculated by DFT. These DFT calculations data were subsequently used to generate a classical description of the Ni-B and Ni-N pair interactions within the formulation of the reactive force field, i.e., ReaxFF. MD simulations under the newly developed potential helped reveal the elementary nucleation and growth process of an hBN monolayer - nucleation initiates from the growth of linear BN chains, which further evolve into branched and then hexagonal lattices. In the end, molecular dynamics simulations demonstrated that the thermodynamic preference of hBN geometries varying from triangle to hexagonal can be tuned by B to N molar ratios, and gas phase N₂ partial pressure, which is also supported by quantum mechanics calculations. The modeling confirms that the nitrogen species indeed plays an important role in dictating sizes and edge terminations of hBN sheets.