Synthetic Investigations in Borates, Borate Germanates, Gallium Oxonitrides, and Intermetallic Phases at Extreme Conditions

Multianvil Hochdruck-/Hochtemperatur Untersuchungen an Seltenerd Boraten, Borat Germanaten, Gallium Oxonitriden und Intermetallischen Phasen. Im Speziellen werden die neuen Borate alpha-Nd2B4O9, beta-Nd(BO2)3, delta-La,Ce(BO2)3 und Pr4B10O21 vorgestellt. Die Erweiterung des Systems durch Germanium führte zum neuen Borat Germanat Ce6(BO4)2Ge9O22. Im Bereich der Gallium Oxonitride konnte eine Spinell-Phase realisiert werden. Hochdruck-/Hochtemperatur Untersuchungen zeigten Phasenumwandlungen vom TiNiSi- und NdPtSb-Typ in den ZrNiAl-Typ bei Drücken von 7-14 GPa und 1000-1400 °C

Effect of temperature and time on zinc borate species formed from zinc oxide and boric acid in aqueous medium

The effect of temperature and time of heating of zinc oxide and boric acid in aqueous medium on product type, dehydration behavior, crystal morphology, and structure was investigated for the production of flame retardant and smoke suppressant zinc borate. Two different products dehydrated at 140 and 350°C were obtained and characterized by thermal gravimetric analysis, X-ray diffraction, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy

Synthesis and Characterization of One Dimensional Boron-Based Nanomaterials

One dimensional (1D) metal borate and boride nanomaterials have attracted tremendous attention due to their good chemical inertness, high-temperature stability, excellent mechanical properties, and low thermal expansion coefficient. Beta-BaB2O4 (BBO) is a well-known nonlinear optical material with a high second-order nonlinear susceptibility, wide transparency range, and high damage threshold. Using a low temperature, organic-free hydrothermal technique, single-crystalline barium polyborate Ba3B6O9(OH)6 (BBOH) nanorods were synthesized. It was found that BBO nanospindles can be achieved by annealing the BBOH nanorods at a relatively low temperature of 810 oC. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques were used to characterize these nanomaterials. The formation mechanisms are discussed in conjunction with the crystallographic characteristics and surface energy of the BBOH nanorods and BBO nanospindles. UV-vis absorption spectra demonstrated that both BBOH nanorods and BBO nanospindles are transparent from the ultraviolet to the visible regions. Single crystalline strontium borate (SrB2O4) nanorods were synthesized for the first time via a sol-gel route at low temperature. The SrB2O4 nanorods have a good crystalline nature and they are transparent from the ultraviolet to the visible regimes. Nanoscale three-point bending tests were performed directly on individual nanorods to probe their mechanical properties using an atomic force microscope. The elastic modulus of SrB2O4 nanorods was measured to be 158.2 ± 7.9 GPa, exhibiting a significant increase compared with other borate nanostructures and bulk borates. We calculated the Young\u27s moduli of bulk SrB2O4 and SrB2O4 nanorods with consideration of surface stress effect of nanorods by density functional theory. The simulated results were found consistent with the experimental values. Zirconium diboride (ZrB2) is a highly covalent refractory and ultrahigh temperature ceramic material with a hexagonal crystal. This along with its relatively low density of ~6.09 g/cm3 and good high temperature strength makes it a candidate for high temperature aerospace applications such as hypersonic flight or rocket propulsion systems. We present the synthesis and structural characterization of ZrB2 nanorods. Single crystalline ZrB2 nanorods were synthesized for the first time via a simple route at a relatively low temperature of 800 oC. The XRD analysis revealed that the as-synthesized nanorods have hexagonal phase of ZrB2. In this Dissertation, the mechanical properties of ZrB2 nanorods were also characterized by atomic force microscope-based nanoindentation technique. Furthermore, the Young\u27s modulus of ZrB2 nanorods was calculated with consideration of surface stress effect of nanorods by density functional theory. This theoretical prediction agrees well with the experimental results

ELECTRON PARAMAGNETIC RESONANCE (EPR) SPECTROSCOPIC INVESTIGATION OF DEFECT CENTERS IN SELECTED BORATES AND BOROSILICATES

This thesis presents the results of a single-crystal electron paramagnetic resonance (EPR) spectroscopic investigation of defect centers in selected borates and borosilicates (i.e., datolite, danburite, and jeremejevite). The research brings new complementary data to the current understanding of defect structures in minerals, which are not only important to Earth Sciences but also directly relevant to environmental applications (e.g., nuclear waste disposal) and materials science. Single-crystal EPR spectra of a gamma-ray-irradiated datolite from Bergen Hill, New Jersey, USA, reveal the presence of a boron-oxygen hole center (BOHC). Spin-Hamiltonian parameters obtained from single-crystal EPR spectra and radiation-dose-dependence experiments allow us to confirm the BOHC center in datolite as the [BO4]0 type, involving hole trapping on the hydroxyl oxygen atom after the removal of the hydrogen atom: via a reaction O3BOH --> O3BO• + H0, where • denotes the unpaired electron. Density functional theory (DFT) calculations support the proposed structural model, and the calculated 11B hyperfine coupling constants are in excellent agreement with the experimental results. Also, isochronal and isothermal annealing experiments provide information about the thermal stability and decay kinetics of the [BO4]0 center in datolite. The confirmation of the [BO4]0 center and its formation from the O3BOH precursor in datolite are compared with other BOHCs in minerals and are discussed with relevance to the implications for not only understanding of BOHCs in alkali borosilicate glasses but also their applications to nuclear waste disposal. A combined study by use of synchrotron X-ray absorption spectroscopy (XAS), single-crystal EPR and pulse electron spin echo envelope modulation (ESEEM) spectroscopy provides compelling evidence for lattice-bound arsenic in danburite from Charcas, San Luis Potosi, Mexico. Arsenic K-edge X-ray absorption near-edge (XANES) spectra show that the dominant oxidation state is +3, and modeling of the extended X-ray absorption fine structure (EXAFS) spectra suggests that As3+ mainly occupies the Si site. Detailed single-crystal EPR spectra, measured before and after gamma-ray irradiation, reveal three arsenic-associated paramagnetic electron centers (I, II and III). Centers I and II are varieties of the [AsO2]2 radicals, formed from electron trapping on a substitutional As3+ ion at the Si site. This model is also supported by the 11B superhyperfine structures determined by ESEEM spectra at 80 K. Center III is the [AsO3]2 radical, originated from electron trapping on a [AsO4]3¬ group after removal of the O4 atom during gamma-ray irradiation. Therefore, arsenic in danburite is present in both the +3 and +5 oxidation states and preferentially occupies the Si site. Single-crystal EPR spectra of jeremejevite from Cape Cross, Namibia, reveal an S = 1/2 hole center characterized by a hyperfine structure arising from interaction with two equivalent 27Al nuclei. Our results suggest that this aluminum-associated oxygen hole center represents hole trapping on a hydroxyl oxygen atom linked to two equivalent octahedral Al3+ ions, after the removal of the proton (i.e., a VIAl−O−−VIAl center). Periodic ab initio UHF and DFT calculations confirmed the experimental 27Al hyperfine coupling constants and directions, supporting the proposed structural model. Also, isochronal annealing experiments provide information about the thermal stability of the VIAl−O−−VIAl center. These data obtained from the VIAl−O−−VIAl center in jeremejevite provide new insights into analogous defects that have been documented in several other minerals

Investigation of the reaction of boron oxide with aluminium powder and method development for boron determination in the reaction mixture

Thesis (Master)--İzmir Institute of Technology, Chemistry, İzmir, 2007Includes bibliographical references (leaves: 60-62)Text in English; Abstract: Turkish and Englishxi, 62 leavesIn this study, a cheap method for the synthesis of elemental boron by the reduction of boron oxide with aluminum was investigated. However after various optimization studies, detectable boron amounts could not be found in the reaction mixtures by XRD and SEM-EDX analysis. Meanly aluminum borates were formed as products and these products were leached by 6 M HCl, however removel of borates could not be achieved. We think that the reason of this outcome is that we worked with simple experimental setup, therefore could not achieving the suitable experiment conditions and because of this we failed in the sythesis of boron. In the second part of the study, a new method for the direct determination of boron was investigated. 96 %pure boron and KBr were mixed and analyzed with Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). No distinct differences for boron was observed in the DRIFT spectra. Then, different sample compositions were prepared with different amounts of boron and KBr. These samples were split as validation and calibration sets and their spectra were collected by DRIFTS. All collected spectral data were processed in a different computer where the data proccessing programs were installed. The genetic inverse least square (GILS) method was used inorder to generate calibration model. Results obtained showed that boron amounts could be directly determined with maximum 3-4 % error. Afterwards, same procedure was also tried for boron and boron oxide binary mixtures and boron, boron oxide and aluminum ternary mixtures. In the binary mixture, determination of boron could be successfully achieved, however boron oxide determination could not be achieved as good as boron determination. In the ternary mixture, better results were obtained compared to binary mixture. Finally, the method was tried with the original samples, but not very satisfactory results were obtained. We think this result is due to the malfunction of FTIR instrument and personal error in the preparation of similar samples. More sample preparation and measurement could not be achieved because the FTIR instrument is not functioning at present

Development of method for boron determination in basalt fibers

The main objective of the present thesis was to develop a method to determine the boron content of boron doped basalt fibers. Two types of samples were investigated: natural basalt powders doped with H3BO3 were used for method development and the method was applied to basalt fiber samples from two different fiber producers. Na2O2 based alkaline fusion with different sample masses and the use of HCl and HNO3 for dissolution of fusion residues was investigated. The results show that using 10:1 flux to sample ratio and HCl as dissolving acid allows for full digestion of sample and determination of boron content by MP-AES analysis. Results from the analysis of commercial basalt fibers revealed that fibers from one producer, contrary to the suppliers claim, did not contain any boron, highlighting the need for quality check and the development of method to do that

Quasicrystalline Approach to Predicting the Spinel-Nepheline Liquidus: Application to Nuclear Waste Glass Processing

The crystal-melt equilibria in complex fifteen component melts are modeled based on quasicrystalline concepts. A pseudobinary phase diagram between acmite (which melts incongruently to a transition metal ferrite spinel) and nepheline is defined. The pseudobinary lies within the Al{sub 2}O{sub 3}-Fe{sub 2}O{sub 3}-Na{sub 2}O-SiO{sub 2} quaternary system that defines the crystallization of basalt glass melts. The pseudobinary provides the partitioning of species between the melt and the primary liquidus phases. The medium range order of the melt and the melt-crystal exchange equilibria are defined based on a constrained mathematical treatment that considers the crystallochemical coordination of the elemental species in acmite and nepheline. The liquidus phases that form are shown to be governed by the melt polymerization and the octahedral site preference energies. This quasicrystalline liquidus model has been used to prevent unwanted crystallization in the world's largest high level waste (HLW) melter for the past three years while allowing >10 wt% higher waste loadings to be processed