Titanium and boron nitride and carbide, titanium diboride were synthesized by carbothermic reduction as single phase as well as mixtures intended to form composite materials. The aim of the project is to study the physical chemistry of carbothermic reduction for the production of pure nonoxide ceramic powders and also for the in-situ formation of ceramic/ceramic partially-densified composites. The thermodynamic and kinetic factors that govern the phase constituents are discussed and the effect of processing parameters on the morphology and extent of reduction are also established. The first part of the present investigation is aimed at the production of titanium nitride, carbonitride and carbide powders and the in-situ formation of TiN/TiC partially-densified composites by the carbothermic reduction of titania in suitable nitriding atmospheres. The investigation includes the aspects of the thermodynamics and kinetics of the nitriding reaction and points out the reaction mechanism by identifying the phase formed after the nitridation process. The microstructures produced after the reduction-nitridation process have been correlated with the thermodynamic and kinetic parameters. The synthesized titanium nitride powder was identified as the carbonitride phase, Ti(CxN1_x), having a range of composition. The rate of reduction of TbO2 was found to be determined by the rate of oxygen diffusion in the sub-oxide lattice and the derived value of activation energy in the temperature range 1473K to 1773K from the Arrhenius plot is 120 kJ-mole-1 of T102. TI305 was found as a high temperature precursor phase for the formation of titanium nitride. The use of iron chloride as catalyst and activated charcoal in the mixtures of oxide increased the yield of titanium nitride phase by enhancing the rate of reduction of titanium oxides. The morphology of titanium carbonitride particles was dependent upon the reactivity of carbon and the temperature. The calculated equilibrium phase fields were found to be in agreement with the experimental data and provide a means to select the variables for the reduction condition for designing a required ceramic microstructure. The microstructure of boron nitrides is closely related to the structural chemistry of carbon and nitriding agent. The main aim of the second part of the project was to synthesize boron nitride and carbide powders and whiskers by carbothermic reduction of boric anhydride (6203) in nitrogen atmosphere and also to understand a relation between the processing parameters and the phases produced. The effect of processing conditions such as the gas composition, reactivity of carbon, reaction temperature and time as well as the composition of starting materials on the synthesis of boron nitride and carbide phases were studied. The reactivity of carbon, B/C ratio and gas composition were the most important variables that determined the formation, structure and morphology of the nitride. During the nitridation process, boron carbide phase also formed and played a significant role. The investigation also reports the evidence for the formation of metastable forms of BN i. e wurtzite and cubic BN. We also report the results of the solubility of nitrogen in C-saturated B4C structure. The third part of the present work is aimed at the production of TiB2 powders. Aspects of the formation of two or three ceramic phase mixtures were also examined together with the relative stability of the single phase mixed diborides with respect to pure diboride phase. The central aim of this part is to establish the mechanism of the synthesis reaction leading to the formation of uniform size of titanium diboride crystals. Titanium boride (TiB2) powder was produced in the powder form by the reduction of ingredient oxides with carbon via a gas-solid phase reaction. For the production of the composite microstructure, the nitrogen partial pressure was found to be the most critical factor. In the composite microstructure, the titanium nitride particles have a submicrometer size whereas the boride particle size is only a few micrometers with predominantly hexagonal morphology. Some calculated equilibrium phase fields have been experimentally verified. The empirical verification is a useful tool to establish the correctness of the calculated phase diagram. The theoretical approach therefore enables to identify the condition for the formation of phase mixtures. The constituent phases depend on the reduction conditions. For example, nitrides in equilibrium with Ti62 can only form above a critical nitrogen partial pressure whereas TiC or B4C form in the inert atmospheres. This result is applicable to all other ceramics. The investigation also shows the viability of production of the composite powder mixture via the oxide co-reduction technique. The synthesis of TIB2/TiN, TiB2ýC, TB2/TN/BN and mixed diboride composites is possible by employing the reduction route.

An experimental study of the low lying excited states of C¹¹ has been made using the B¹⁰(d ,nɣ )C¹¹ reaction at a deuteron bombarding energy of 0.8 Mev. Measurements were made of the n- ɣangular correlations of the ground state gamma transitions from the 6.49 and 4.32 Mev levels, and of the gamma ray branching ratios of the 6.49, 4.81 and 4.32 Mev levels. The apparatus used for the measurements was a combination of a NaI(T1) gamma ray spectrometer and an improved fast neutron time-of-flight spectrometer, developed by the author. Theoretical analysis of the n-ɣ angular correlations showed that the 6.49 Mev and 4.32 Mev levels are formed by the capture of p½ protons This restricts the Jπ values of these levels to (5/2)¯ or (7/2)¯. The parities of the states observed in this experiment are all known to be negative from the high energy stripping data of Cerineo and Maslin et al. A comparison of the experimental branching ratios with the theoretical branching ratios predicted by the intermediate coupling shell model is consistent with the following spin and parity assignments in C¹¹ : g.s. (3/2)¯, 2.00 Mev (1/2)¯, 4.32 Mev (5/2)¯, 4.81 Mev (3/2*)¯ and 6.49 Mev (7/2)¯. These assignments are in agreement with other recent results. The correspondence of these levels in C¹¹ with those of B¹¹ is consistent with the hypothesis of the charge independence of nuclear forces. The experimental results agree in some cases and disagree in others with the intermediate coupling shell model calculations of Kurath. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The growth of single and multilayer BN films on several substrates was investigated. A typical atomic layer deposition (ALD) process was demonstrated on Si(111) substrate with a growth rate of 1.1 Å/cycle which showed good agreement with the literature value and a near stoichiometric B/N ratio. Boron nitride films were also deposited by ALD on Cu poly crystal and Cu(111) single crystal substrates for the first time, and a growth rate of ~1ML/ALD cycle was obtained with a B/N ratio of ~2. The realization of a h-BN/Cu heterojunction was the first step towards a graphene/h-BN/Cu structure which has potential application in gateable interconnects.

Thesis advisor: James Morken / This dissertation details two different alkene difunctionalization strategies that are utilized in the synthesis of three types of organoboron species in racemic and enantioenriched fashion. Chapter one will introduce the carbohydrate and DBU co-catalyzed transition-metal-free enantioselective diboration reactions of unactivated alkenes. Mechanistic insights guided reaction condition design will be discussed. In chapter two, a nickel-catalyzed conjunctive cross-coupling of 9-BBN borane and carboxylic acid derivatives is presented. Its development and detailed mechanistic studies, along with the efforts in asymmetric induction will be covered. Finally, the first enantio- and diastereoselective synthesis of 1,2-anti-silylboronates enabled by palladium-catalyzed conjunctive cross-coupling will be described. The optimization of chemo-, enantio- and diastereoselectivity in the reactions and their following transformations (e.g. oxidation and amination) is demonstrated. / Thesis (PhD) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Thesis advisor: James P. Morken / This dissertation describes the development of a method for the stereoselective synthesis of organoboronates and the applications of these products to target-oriented synthesis. The first chapter discusses an investigation of the palladium-catalyzed conjunctive cross-coupling reaction by kinetic analysis. This reaction enables the asymmetric synthesis of organoboronates by utilizing the 1,2-metallate rearrangement of borates as a mechanistic step in a cross-coupling reaction. The second chapter describes the application of the conjunctive cross-coupling reaction to the asymmetric synthesis of tertiary boronic esters. In chapter three, the conjunctive cross-coupling reaction of 1,2-disubstituted alkenyl boronates is presented. Such a substrate class is susceptible to the undesired Suzuki-Miyaura cross-coupling reaction, and this challenge led to the development of a novel diol ligand for boron as an effective solution. The final chapter details the progress toward the total synthesis of the sarcodictyin natural products, which display promising anti-cancer activity. The synthetic route utilizes reactions of organoboronates for powerful C–C bond formations; the construction of a fully-cyclyzed advanced intermediate is achieved in eight steps. / Thesis (PhD) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

<p>Adoption of conservation tillage systems is known to result in increased soil K stratification. Yet, there have been few investigations into the optimization of K management in these tillage systems, particularly regarding the placement and timing of K-based fertilizer applications. Additionally, there are many unknowns regarding the influence of tillage timing with/ without K fertilizer application. Increased availability of fertilizers containing both macro- and micro-nutrients, such as Aspire™ (which includes both K and B), has coincided with new questions about potential micronutrient deficiencies in maize (<i>Zea mays</i> L.) production. Previous research has investigated the influence of K and B individually; however, few university studies utilize multi-nutrient fertilizer sources. These knowledge gaps prompted a series of field investigations into the impacts of alternative tillage/ placement of Aspire™ on maize growth and development. Because K stratification is thought to potentially limit K availability to maize, tillage/fertilizer placement treatments involving no till (NT), fall strip-till (FST), spring strip-till (SST), and fall chisel (FC) were compared with at least two application rates of Aspire™ (ranging from 0 to 108 kg K ha^-1) from 2016 to 2019 on Indiana soils with moderate exchangeable K concentrations. Maize was grown in rotation with unfertilized soybean (<i>Glycine max </i>L) planted after strip-till.</p><p>Although tillage systems, other than no-till, were intended to decrease stratification, little change in vertical stratification for in-row samples was observed in the strip-till systems when Aspire™ was band applied at the time of strip-till (indicating fertilizer application was limited to the top several centimeters of soil). Few interactions were evident in maize response between tillage/placement and Aspire™ applications; however, superior V6-stage growth/nutrition responses to Aspire™ application occurred in fall tillage systems (FST or FC). The latter was especially true when comparing the two strip-till timings (FST and SST) at three rates. In addition to early season plant nutritional benefits, plant stature also benefited from Aspire™ across tillage/ placement systems (e.g., ~20% increase in height at V8, plus a leaf area index (LAI) gain at V14 of ~10%) reflecting on the potential to increase the source capacity of fertilized maize plants. By R1, there was little synergism between treatments in the tested parameters, indicating little difference among the tillage/ placement methods (and strip-till timing), and few immediate consequences from 50% rate reduction for Aspire™ in the strip-till systems. Although grain yield increases of 4-8% were common when Aspire™ was applied, yield component analysis showed little interaction between tillage/placement and Aspire™. Grain yields were shown to be more highly correlated and had significant relationships to earleaf K at R1, and less so with minor changes in B concentrations at R1.</p><p>Aspire™ application at the full and 50% rate commonly benefited plant nutrition and grain yield, but little synergism between Aspire™ application and tillage/ placement system was evident. Although rate reduction did not show immediate consequences to plant nutrition in either strip-till timing, longer-term research is necessary to better understand future consequences from this management practice. The lack of differences in response to strip-till timing (fall vs. spring) shows the potential for flexible timing when optimum tillage conditions are present. This research confirmed the importance of K fertilization to maize performance, but the efficient management of K requires further inquiry.</p>

The search for alternative methods of synthesizing cubic boron nitride (cBN), one of the hardest known materials, at low thermo-baric conditions has stimulated considerable research interest due to its great potential for numerous practical industrial applications. The practical applications are motivated by the material’s amazing combination of extraordinarily superior properties. The cBN phase is presently being synthesized from graphite-like boron nitride modifications at high thermo-baric conditions in the presence of catalytic solvents or by ion–beam assisted (chemical and physical) deposition methods. However, the potential and performance of cBN have not been fully realized largely due to central problems arising from the aforementioned synthesis methods. The work reported in this dissertation is inspired by the extensive theoretical investigation of the influence of defects in a ecting the transformation of the hexagonal boron nitride (hBN) phase to the cBN phase that was carried out by Mosuang and Lowther (Phys Rev B 66, 014112 (2002)). From their investigation, using an ab-initio local density approach, for the B, C, N, and O simple defects in hBN, they concluded that the defects introduced into hBN could facilitate a low activation–energy hexagonal-to-cubic boron nitride phase transformation, under less extreme conditions. We use ion implantation as a technique of choice for introducing ‘controlled’ defects into the hot–pressed polycrystalline 99.9% hBN powder samples. The reasons are that the technique is non–equilibrium (not influenced by dilusion laws) and controllable, that is the species of ions, their energy and number introduced per unit area can be changed and monitored easily. We investigate the structural modifications of hBN by ion implantation. Emphasis is given to the possibilities of influencing a low activation–energy hBN-to-cBN phase transformation. The characterization of the structural modifications induced to the hBN samples by implanting with He+ ions of energies ranging between 200 keV and 1.2 MeV, at fluences of up to 1.0 1017 ionscm2, was accomplished by correlating results from X-Ray Di raction (XRD), micro-Raman (-Raman) spectroscopy measurements, and two-dimensional X-Y Raman (2D-Raman) mapping measurements. The surface to pography of the samples was investigated using Scanning Electron Microscopy (SEM). E orts to use Surface Brillouin Scattering (SBS) were hampered by the transparency of the samples to the laser light as well as the large degree of surface roughness. All the implantations were carried out at room temperature under high vacuum. 2D-Raman mapping and -Raman spectroscopy measurements done before and after He+ ion irradiation show that an induced hBN-to-cBN phase transformation is possible: nanocrystals of cBN have been observed to have nucleated as a consequence of ion implantation,the extent of which is dictated by the fluences of implantation. The deviationof the measured spectra from the Raman spectra of single crystal cBN is expected, has been observed before and been attributed to phonon confinement e ects. Also observed are phase transformations from the pre-existing hBN modification to: (a) the amorphous boron nitride (aBN), (b) the rhombohedral boron nitride (rBN) modifications, (c) crystalline and amorphous boron clusters, which are a result of the agglomeration of elementary boron during and immediately after ion implantation. These transformations were observed at high energies. Unfortunately, the XRD measurements carried out could not complement the Raman spectroscopy outcomes probably because the respective amounts of the transformed materials were well below the detection limit of the instrument used in the former case.

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23026号 / 理博第4703号 / 新制||理||1674(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 北川 宏, 教授 吉村 一良, 教授 有賀 哲也 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

On-board hydrogen storage presents a challenging barrier to the use of hydrogen as an energy source because the performance of current storage materials falls short of platform requirements. Because boron is one of the lightest chemical elements that can form strong covalent bonds with hydrogen, it provides an excellent opportunity to design new lightweight materials on the basis of novel boron hydride building blocks. Realizing this potential requires an understanding of the electronic structure, chemical bonding, and stability of neutral and anionic BxHy clusters with variable stoichiometry. While a large number of boron hydride compounds are known, there are still entire classes of yet unknown neutral and anionic BxHy clusters and molecules with various new x/y ratios which may be good candidates for hydrogen storage or as intermediates of borane de-hydrogenation. The primary aim of this dissertation was to search for neutral and anionic BxHy clusters that are thermochemically stable towards hydrogen release and to understand the chemical bonding in these novel clusters. These goals were accomplished by performing an unbiased search for neutral and anionic global minimum BxHy clusters using ab initio methods. In addition to finding a rich variety of new neutral and anionic BxHy (x = 3 – 6 and y = 4 – 7) clusters that could be building blocks for novel hydrogen-boron materials during the course of conducting this research, optical isomerism was discovered in select neutral and anionic boron-hydride clusters. Furthermore, the transition from planar to 3- dimensional geometries in global minimum B6Hx - clusters was discovered using ab initio techniques during this study. Chemical bonding analysis using the AdNDP method was performed for all global minimum structures and low-lying isomers. The chemical bonding pattern recovered by the AdNDP method in all cases is consistent with the geometric structure. The theoretical vertical detachment energies presented in this dissertation may help interpret future photoelectron spectroscopic studies of the anions presented here.

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