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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Scoping Studies to Determine Impact of a Low-Alkali Phase Separated Frit on the Behavior of the Frit Slurry and Slurry Mix Evaporator Rheology

The frits used in the vitrification process at the Defense Waste Processing Facility (DWPF) are alkali borosilicate glasses, which are composed mainly of B 2 O 3 , alkali (Li 2 O and Na 2 O) and SiO 2 . As the total alkali concentration in a borosilicate glass is reduced, liquid-liquid immiscibility is exhibited by the glassforming melt, which is analogous to the behavior of oil and water. Upon cooling, the resulting glass matrix is said to be phase separated. The immiscible region is controlled by both composition and temperature. Viscosity of the melt is also a factor as it impacts the reaction rate (kinetics) of phase separation. The reaction rate (kinetics) leading to phase separation is slow for higher viscosity melts, and if such a melt is cooled rapidly (e.g., quenched in water), the resulting glass could be homogeneous, or the scale of the phase separated microstructure could be of no practical significance. Phase separated alkali borosilicate glasses tend to form a more durable silica-rich phase and a less durable alkali borate-rich phase. The overall durability of the phase separated glass depends on the morphology (physical arrangements) of each of these phases. For example, droplets of the alkali borate-rich phase may form within a silicate rich matrix, which would be a more durable glass than a glass with an interconnected alkali borate-rich phase.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2022

Electron-Deficient Ru(II) Complexes as Catalyst Precursors for Ethylene Hydrophenylation

Ruthenium(II) complexes with the general formula TpRu(L)(NCMe)Ph (Tp = hydrido(trispyrazolyl)borate, L = CO, PMe 3 , P(OCH 2 ) 3 CEt, P(pyr) 3 , P(OCH 2 ) 2 (O)CCH 3 ) have previously been shown to catalyze arene alkylation via Ru-mediated arene C–H activation including the conversion of benzene and ethylene to ethylbenzene. Previous studies have suggested that the catalytic performance of these TpRu(II) catalysts increases with reduced electron-density at the Ru center. Herein, three new structurally related Ru(II) complexes are synthesized, characterized, and studied for possible catalytic benzene ethylation. TpRu(NO)Ph 2 exhibited low stability due to the facile elimination of biphenyl. The Ru(II) complex (Tp Br3 )Ru(NCMe)(P(OCH 2 ) 3 CEt)Ph (Tp Br3 = hydridotris(3,4,5-tribromopyrazol-1-yl)borate) showed no catalytic activity for the conversion of benzene and ethylene to ethylbenzene, likely due to the steric bulk introduced by the bromine substituents. (Ttz)Ru(NCMe)(P(OCH 2 ) 3 CEt)Ph (Ttz = hydridotris(1,2,4-triazol-1-yl)borate) catalyzed approximately 150 turnover numbers (TONs) of ethylbenzene at 120 °C in the presence of Lewis acid additives. Here, we compare the activity and features of catalysis using (Ttz)Ru(NCMe)(P(OCH 2 ) 3 CEt)Ph to previously reported catalysis based on TpRu(L)(NCMe)Ph catalyst precursors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRSDate not supplied

Tribological performance of Al2O3-B2O3 composites: Role of CuOand CaO constituents

Al2O3-B2O3 based composites for wear resistant applications (e.g., seal rings and bearings) were manufactured using powder metallurgy route. Four different compositions were considered to control amount of in situ phases, mainly aluminum borate, formed during sintering. The fabricated composites were characterized using X-ray diffraction to identify the phases. Hardness was measured in terms of micro-hardness. The tribological performance of the composites were evaluated by conducting dry sliding tests against alumina balls at different humidity levels (10 – 95% relative humidity). The X-ray spectrum revealed that increase in B2O3 content in the composites increased the amount of aluminum borate phase that enhanced the micro-hardness. Results revealed that aluminum borate enhanced the wear resistance of the composites, whereas the humidity-sensitive alumina phase reduced friction at higher humidity levels. Furthermore, CuO and CaO (2-5 wt.%) were added separately to the composite, resulting in increased density by 22-48 %. Athough the addition of CuO and CaO led to increase in hardness and wear resistance of the composites, the coefficient of friction was negatively affected. The friction and wear performance along with wear mechanism are discussed with respect to observed phases in the composites.

Ashish K. Kasar↗
DOE OSTI2019

SENSITIVITY STUDIES OF HEATER ROD DESIGN FOR TRANSIENT CRITICAL HEAT FLUX EXPERIMENTS IN TREAT

An important area of reactor safety is the cladding-to-coolant heat transfer under fast transient conditions. These conditions can occur during events such as a reactivity-initiated accident (RIA). In this paper we present the work performed under a laboratory directed research and development (LDRD) project, headed by Idaho National Laboratory (INL). The goal was to develop a test matrix to inform on the design of a borated steel heater rod that will induce critical heat flux (CHF) within an experimental capsule filled with water, using the TREAT facility, when submitted to a power pulse. The energy deposition in the rod and occurrence of CHF were identified as the most important key Figures of Merit (FoMs) used in the design process. Energy deposition was varied by using different pulse characteristics and various boron concentrations in the rod. A power coupling factor (PCF) was determined for each boron concentration. A sensitivity study determined the lowest limiting PCF needed to induce CHF in water with different degrees of subcooling while keeping pressure constant. Boron concentrations between 0.1-1.54 wt.% were considered. Additionally, the value of CHF is also known to increase during a rapid transient. A CHF multiplier sensitivity study focused on an example case concluded that CHF is no longer exceeded when the value is between 2.6- and 2.9-times higher. Lastly, a self-shielding study was performed to determine whether a borated tube could be used in place of a solid borated rod. The study determined that the inner 1mm of the rod can essentially be excluded or instrumented without heat generation penalties.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Effect of early hydration temperature on hydration product and strength development of magnesium phosphate cement (MPC)

This paper investigates the effect of early hydration temperatures on hydration products and strength development of magnesium phosphate cement (MPC). MPC paste specimens with borate contents of 3%, 6%, 9% and 12% are prepared and cured in different air temperatures and in the adiabatic condition. The internal hydration temperatures are measured by pre-embedded temperature probes. MPC samples with different hydration temperatures are also obtained by using thin slice samples. The hydration products in MPC samples with different hydration temperatures are analyzed by X-ray diffractometer (XRD) and scanning electron microscope (SEM) and the strength development is also measured. The results show that NH{sub 4}MgPO{sub 4}·6H{sub 2}O is the major hydration product and beneficial to strength development of MPC at hydration temperature below 70 °C. NH{sub 4}MgPO{sub 4}·H{sub 2}O is another major product, which significantly decreases the strength, when the temperature is higher than a critical temperature between 70 °C and 75 °C. NH{sub 4}MgPO{sub 4}·H{sub 2}O can directly form in the MPC paste, and comes from the decomposition of NH{sub 4}MgPO{sub 4}·6H{sub 2}O when the temperature is above 75 °C. With temperature elevation and duration extension, NH{sub 4}MgPO{sub 4}·6H{sub 2}O decomposes rapidly, and even entirely when the temperature is above 100 °C. The borate content has no effect on the types of major hydration products and the critical temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Crystal structures and second-order NLO properties of borogermanates

Borogermanates are a class of very important compounds in materials chemistry. In this paper, the syntheses, structures, and properties of metal borogermanates are reviewed. Organically templated borogermanates with zeolite-like open-frameworks show potential applications as microporous materials. Many compounds in alkali or alkaline-earth borogermanate systems are structurally acentric or polar, some of which exhibit excellent Second Harmonic Generation (SHG) coefficients, wide transparency regions, and high optical-damage thresholds as well as excellent thermal stability. Most of the lanthanide borogermanates are structurally centrosymmetric and not SHG active; however, they are able to emit strong luminescence in visible or near-IR region. In the B-rich compounds, BO{sub 3} and BO{sub 4} groups can be polymerized into a variety of discrete polynuclear anionic cluster units or extended architectures via B-O-B bridges; whereas in the Ge-rich compounds, GeO{sub 4} and GeO{sub 6} polyhedra can also be polymerized. The combinations of borate and germinate afforded rich structural and topological types. - Graphical abstract: Borogermanates are a class of very important compounds in materials chemistry. Both BO{sub x} (x=3, 4) and GeO{sub y} (y=4, 6) polyhedra can be polymerized into a variety of discrete polynuclear anionic cluster units or extended architectures. The combinations of borate and germanate groups in the same oxide framework not only give rise to a rich structural chemistry, but also afford many polar compounds with good SHG properties. Highlights: Black-Right-Pointing-Pointer Borogermanates are a class of new materials. Black-Right-Pointing-Pointer They feature to be the combination of B and Ge atoms into the same oxide framework. Black-Right-Pointing-Pointer They can form a large number of novel 2D and 3D framework structures. Black-Right-Pointing-Pointer Some of them are acentric or polar with moderate strong SHG responses.

36 MATERIALS SCIENCE↗
DOE OSTI2014

The interaction between cations and anionic groups inducing SHG enhancement in a series of apatite-like crystals: A first-principles study

It is an interesting topic to reveal the origin of the SHG intensity enhancement after substitution from alkali and alkali-earth metal atoms to cadmium in a series of apatite-like borates KSr{sub 4}(BO{sub 3}){sub 3}, Ca{sub 5}(BO{sub 3}){sub 3}F, Cd{sub 5}(BO{sub 3}){sub 3}F. Combined with the first-principles method, SHG-density method and real-space atom-cutting method, the electronic structure, the optical properties and the contribution of respective ion and ion groups have been investigated. Second harmonic generation (SHG) responses are mainly attributed to BO{sub 3} groups with π conjugated configuration and their alignment framework. The contributions of A site are more important in CaBOF and CdBOF compounds than in KSrBO. It is also demonstrated that the strong covalent interactions between the boron–oxygen groups and the cadmium atoms contribute the enhancement of SHG responses after substitution from alkali and alkali-earth metal atoms. - graphical abstract: Combined with the first-principles method, SHG-density method and real-space atom-cutting method, the enhancement of SHG response are attributed to the interaction between cadmium and BO{sub 3} groups. - Highlights: • SHG response on a series of apatite-like borates was studied by a SHG-density method. • SHG responses are mainly attributed to BO{sub 3} groups and their alignment framework. • The contributions of A site are more important in CaBOF and CdBOF than in KSrBO. • Covalent interaction between BO and Cd is responsible for SHG of CdBOF.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Luminescence properties in relation to controllable morphologies of the InBO{sub 3}:Eu{sup 3+} phosphor

Graphical abstract: Four kinds of morphologies of Eu{sup 3+} doped indium borate of InBO{sub 3} phosphors have been prepared via a facile flux method only by adjusting the kinds of reaction boron source materials[(a)B{sub 2}O{sub 3}, (b)NH{sub 4}B{sub 5}O{sub 8}·4H{sub 2}O, (c)Li{sub 2}B{sub 4}O{sub 7}, (d)K{sub 2}B{sub 4}O{sub 7}·4H{sub 2}O], in which the monodisperse octahedral sample prepared with K{sub 2}B{sub 4}O{sub 7}·4H{sub 2}O as the boron source and Eu{sup 3+} doping concentration being 5% possesses the higher PL intensity and color purity, which can be used as a potential orange luminescent material. - Highlights: • InBO{sub 3}:Eu{sup 3+} phosphor with four morphologies were prepared by adjusting the boron source. • The doping concentration also has a great influence on the morphology. • The fluorescence performance is strongly correlated with morphology. • The smooth octahedral sample possesses the higher PL intensity and color purity. • InBO{sub 3}:Eu{sup 3+} smooth octahedra can be used as a potential orange luminescent material. - Abstract: Four kinds of morphologies of Eu{sup 3+} doped indium borate of the InBO{sub 3} phosphors have been prepared via a facile flux method only by adjusting the kinds of reaction boron source materials, which have been characterized by XRD, EDS and SEM. In addition, the doping concentration also has a great influence on the morphology of samples. Furthermore, the luminescence properties of the prepared InBO{sub 3}:Eu{sup 3+} samples have been investigated by photoluminescence (PL) spectra. The results show that the fluorescence performance is strongly correlated with morphologies. The prepared InBO{sub 3}:Eu{sup 3+} phosphors show strong orange emissions under ultraviolet excitation at 237 nm, in which the monodisperse octahedra sample prepared with K{sub 2}B{sub 4}O{sub 7}·4H{sub 2}O as the boron source and Eu{sup 3+} doping concentration being 5% possesses the higher PL intensity and color purity, which can be used as a potential orange luminescent material.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Mechanism and Reaction Energy Landscape for Apiose Cross-Linking by Boric Acid in Rhamnogalacturonan II

Rhamnogalacturonan II (RG-II)—the most complex polysaccharide known in nature—exists as a borate cross-linked dimer in the plant primary cell wall. Boric acid facilitates the formation of this cross-link on the apiosyl residues of RG-II’s side chain A. Here, we detail the reaction mechanism for the cross-linking process with ab initio calculations coupled with transition state theory. We determine the formation of the first ester linkage to be the rate-limiting step of the mechanism. Our findings demonstrate that the regio- and stereospecific nature of subsequent steps in the reaction itinerary presents four distinct energetically plausible reaction pathways. This has significant implications for the overall structure of the cross-linked RG-II dimer assembly. Finally, our transition state and reaction path analyses reveal key geometric insights that corroborate previous experimental hypotheses on borate ester formation reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Solvation Environment and Interface Dynamics of Li 2 B 12 H 12 and Li 2 B 12 F 12 Electrolytes Uncovered by Theory and Operando Optical and FTIR Spectroelectrochemistry

In this work, we evaluated two closo-borate salts (Li 2 B 12 H 12 and Li 2 B 12 F 12 ) in propylene carbonate from theoretical and experimental perspectives to understand how the coordination environment influences their spectroscopic and electrochemical properties. The coordination environments of the closo-borate salts were modeled via density functional theory (DFT) and molecular dynamics (MD). Vibrational spectra calculated from the predicted coordination environments are in agreement with experimentally measured steady-state FTIR data. This theoretical investigation also suggested that Li 2 B 12 F 12 would possess a higher ionic conductivity than Li 2 B 12 H 12 , which was corroborated experimentally. Additionally, an electrochemical cell was designed and fabricated that enabled operando optical and FTIR spectroelectrochemical (OP-IR-SEC) measurements. This allowed for the simultaneous measurement of the relative changes of species at a lithium electrode-liquid electrolyte interface and the visualization of lithium plating at the electrode surface. This technique could provide new chemical insights and potentially link optical changes at the electrode–electrolyte interface to specific chemical species in similar electrochemical systems. The Li 2 B 12 F 12 electrolyte was found to have a higher thermal stability, which may find utility in applications for batteries that are subject to high-temperature conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Thermal analysis, spectral characterization and refractive index studies of lithium doped PbO-ZnO-B{sub 2}O{sub 3} glass

Lithium containing lead zinc borate glasseshave been prepared by melt quenching technique. X-ray diffraction reveals the amorphous nature of the glass. Differential scanning calorimeter (DSC) study was carried out in the temperature range RT to 600 deg. C temperature and found glass transition temperature of these glasses decreases with increase in inter substitution of Pb and Zn lithium content. PZB glasses are stable, IR spectra of these glasses show characteristics band originating from borate groups namely [BO{sub 3}] [BO{sub 4}]and B-O-B stretching vibrations respectively, and found that structure is not affected with effect of lithium content. Refractive index of these glasses are in the range of 1.47 with increasing lithium content refractive index decreases indicating decrease in scattering of light.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Synthesis and structural characterization of two half-sandwich nickel(II) complexes with the scorpionate ligands

The synthesis and characterization of two new halfsandwich mononuclear nickel(II) complexes with the scorpionate ligands, [k{sup 3}-N, N',N''-Tp{sup t-Bu}, {sup Me}NiI] (1) and [k{sup 3}-N,N',N''-Tp{sup t-Bu}, {sup Me}NiNO{sub 3}] (2), are reported. These complexes have been fully characterized by elemental analyses and infrared spectra. Their molecular structures were determined by single crystal X-ray diffraction. The nickel(II) ion of complex 1 is in a four-coordinate environment, in which the donor atoms are provided by three nitrogen atoms of a hydrotris(pyrazolyl) borate ligand and one iodide atom, while that of complex 2 is in a five-coordinate environment with three nitrogen atoms from a hydrotris(pyrazolyl)borate ligand and two oxygen atoms from a nitrate ion.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Neutron Absorber Considerations for the DOE Standardized Canister Powerpoint

The DOE Standardized SNF Canister will allow a broad range of DOE-managed fuels to be loaded, stored, transported, and disposed of while avoiding the need to re-open canisters after being sealed. A key safety function of the DOE Standardized SNF Canister is to ensure the material maintains a subcritical configuration for storage, transportation, and disposal. Researchers designed a basket made of a material which should ensure subcriticality (e.g. by geometry control and inclusion of neutron absorber) and be structurally sound. The basket material should resist the corrosive effects of a 10,000 year period in a breached container and still provide adequate neutronic isolation or degrade in a form which prevents a critical configuration of fissile material. This report summarizes the materials evaluated to ensure subcriticality of the DOE Standardized SNF Canister for credible disposal scenarios. Recommendations for future work include performing criticality evaluations using borated stainless steel for the basket material in the DOE Standardized SNF Canister and determining the solubility on boron’s corrosion products. If researchers determine the properties of borated stainless steel are insufficient, ANA needs to undergo more corrosion testing and continue the process to become an ASME code case for welded construction.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

Neutron Absorber Considerations for the DOE Standardized Canister

The Department of Energy (DOE) standardized canister is being re-evaluated to support the management of non-commercial spent nuclear fuel. The standardized canister would allow a broad range of DOE-managed fuels to be loaded, stored, transported, and disposed of while avoiding the need to re-open the canister after initial loading, thus preventing repackaging of the material. A key safety function of this package is to ensure the material maintains a sub-critical configuration for storage, transportation, and disposal. DOE-managed fuels come from a wide range of reactor types, with various cladding materials and enrichments. Many of these reactors, now decommissioned, had unique design features, such as core configuration, fuel element and assembly geometry, moderator and coolant materials, operational characteristics, and neutron spatial and spectral properties resulting in a large diversity of reactor and fuel designs. To adequately address the diversity of DOE spent nuclear fuel (SNF), a number of basket were designed. The basket material needed to have the ability to ensure subcriticality, be structurally sound, and be corrosion resistant. One such option that was investigated in the late-1990s through mid-2000s was a corrosion-resistant, nickel-chromium-molybdenum alloy containing gadolinium, which was termed the advanced neutron absorber (ANA). A number of analyses were performed to verify the structural, corrosive properties, and neutron absorption performances of this material as well as to compare other potential materials to be used for the basket. Gadolinium-containing carbon steel and borated stainless steel were also considered and evaluated. Boral was briefly considered, but due to its corrosive properties. Each of the evaluated materials have strengths and weaknesses. ANA is the best thermal neutron absorber but lacks confirmatory research for corrosion and weldability. Gadolinium containing carbon steel provides excellent moderator exclusion capabilities but does not contain a sufficient supply of phosphate to ensure the gadolinium precipitates. To minimize the probability of a critical configuration, it is highly desirable for the gadolinium to precipate the probability that the materials will remain within the waste packages over the postclosure time periods of interest. Borated stainless steel has structural integrity and impressive corrosion resistance in most environments, but can undergo galvanic corrosion when in close proximity/contact with aluminum and may experience less than desirable corrosion resistance. This report provides an extensive list and comparison of the materials evaluated to ensure sub-criticality of DOE standardized canister in all credible scenarios. More analyses need to be performed using new and updated corrosion information to re-evaluate the neutron absorber that best meets the objectives of the DOE standardized canister.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2013

Investigation of ruthenium dioxide formation mechanisms in containment glass synthesized by liquid feed

The presenting paper focuses on the structural configuration of ruthenium in vitreous matrices with the objective of obtaining more insight into ruthenium incorporation and solubilization mechanisms in borosilicate glasses. To determine the structural effect of an increasing RuO{sub 2} in a borosilicate glass, a series of glass samples were selected from a benchmark composition. {sup 11}B NMR shows that the borate network is influenced by the presence of RuO{sub 2} in the glass: the addition of 2% RuO{sub 2} in a borosilicate glass led to a significant rise of BO{sub 4}. RuO{sub 2} precipitated in the glass does not seem to be the cause of this modification because when RuO{sub 2} increase there is no further change of BO{sub 4} fraction. This effect can be therefore attributed to RuO{sub 2} dissolved in the glass. RuO{sub 2} is known to have a very low solubility in borosilicate glasses (50 to 2000 ppm depending on the temperature, sodium concentration and conditions of synthesis). The link between the ruthenium and the borated network is not yet clearly identified, however, assumptions can be made such as the formation of Ru-O-B when a sufficient quantity of Ru is add (> 400 ppm). Ruthenium could play the role of silicon in increasing the possibility of bridging bond formation with boron coordination number IV.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Major safety and operational concerns for fuel debris criticality control

It can be seen from the criticality control viewpoint that the requirement divides the decommissioning work into two parts. One is the present condition where it is requested to prevent criticality and to monitor subcritical condition while the debris is untouched. The other is future work where the subcritical condition shall be ensured even if the debris condition is changed intentionally by raising water level, debris retrieval, etc. Repair of damages on the containment vessel (CV) walls is one of the most important objectives at present in the site. On completion of this task, it will become possible to raise water levels in the CVs and to shield the extremely high radiation emitted from the debris but there is a dilemma: raising the water level in the CVs implies to bring the debris closer to criticality because of the role of water for slowing down neutrons. This may be solved if the coolant water will start circulating in closed loops, and if a sufficient concentration of soluble neutron poison (borated water for instance) will be introduced in the loop. It should be still noted that this solution has a risk of worsening corrosion of the CV walls. Design of the retrieval operation of debris should be proposed as early as possible, which must include a neutron poison concentration required to ensure that the debris chunk is subcritical. In parallel, the development of the measurement system to monitor subcritical condition of the debris chunk should be conducted in case the borated water cannot be used continuously. The system would be based on a neutron counter with a high sensitivity and an appropriate shield for gamma-rays, and the adequate statistical signal processing.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2015

Understanding the influence of iron on crystallization kinetics of nepheline based glasses - 15472

Hanford site in Washington is home to 55 million US gallons of high level radioactive waste rich in sodium, alumina and iron. The strategy is to vitrify this waste in borosilicate glasses. Crystallization of nepheline/carnegeite (NaAlSiO{sub 4}) in glass melts during vitrification and canister cooling is a big challenge as it severely deteriorates the chemical durability of the glass. As the HLW borosilicate glasses are similar to basalt glass on a borate-free basis and as no borate phase crystallize on the liquidus, the crystallization chemistry of waste glasses can be described by the known phase relations of the geochemical basalt quaternary Na{sub 2}O-Al{sub 2}O{sub 3}-Fe{sub 2}O{sub 3}-SiO{sub 2} system. The objective of this study is to understand the influence of iron on the thermal stability and crystallization kinetics of model sodium- and alumina- rich simplified silicate glasses in the Na{sub 2}O-Al{sub 2}O{sub 3}-Fe{sub 2}O{sub 3}-SiO{sub 2} system designed in the primary crystallization field of nepheline. The results obtained from this study will form the baseline for understanding the nucleation and crystallization kinetics of multicomponent complex nuclear waste glasses in future. A series of glasses with compositions 25Na{sub 2}O-(25-z) Al{sub 2}O{sub 3}-zFe{sub 2}O{sub 3} -50SiO{sub 2} (mol.%) where z varies between 0 -5% has been prepared by melt-quench technique. Glasses have been labelled in reference to their Fe{sub 2}O{sub 3} content, i.e. Fe-z. We could not obtain amorphous glasses with Fe{sub 2}O{sub 3} > 5 mol.% . Glass batches comprising oxides and carbonates were melted at 1650 deg. C in Pt-Rh crucibles for 2 h. The melts were quenched in cold water to yield ∼90 g of glass. Thermal stability and crystallization kinetics of glasses was studied using differential thermal analysis (DTA). Thermal scans (30-1580 deg. C) were collected on glass particles (particle size: 0.5 mm-1 mm) at four different heating rates: 5, 10, 15 and 20 K min{sup -1} in air and inert (N{sub 2}) atmosphere. Non-isothermal crystallization kinetics of the glasses was studied using the Augis-Bennett method and Ozawa method. In accordance with the crystallization data obtained from DTA, glasses were heated in the crystallization temperature range and air quenched. Glasses were also heated from 30 deg. C to 800, 900 and 1000 deg. C for 1 h, respectively, in air and inert (N{sub 2}) atmospheres, at heating rate of 10 K min{sup -1}. Resulting glass-ceramics were characterized for their crystalline phase evolution by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Conversion of melt -to glass-ceramic during cooling DTA data was also collected for all the glasses during their conversion from melt -to -glass-ceramic during cooling at different cooling rates, in air and inert (N{sub 2}) atmosphere. In accordance with the DTA data, conversion of melt to glass-ceramic during cooling was studied by re-melting the glass frit in Pt-Rh crucibles at 1650 deg. C. The melt was allowed to cool at 10 K min{sup -1} and was air quenched at different temperatures (as per DTA data). The as obtained glass-ceramics were characterized by XRD and SEM Incorporation of Fe{sub 2}O{sub 3} in glasses decreases their crystallization temperature and increases their crystallization tendency. Parent glass (stoichiometric nepheline composition) is prone to surface crystallization. Incorporating 5 mol.% Fe{sub 2}O{sub 3} in these glasses transforms the crystallization kinetics from surface to volume nucleation. Crystallization kinetics of glass Fe-2.5 is affected by the environment (N{sub 2} vs. Air) while no significant impact of environment could be seen for glass Fe-5. Devitrification in all the glasses begins with the crystallization of carnegeite (NaAlSiO{sub 4}, orthorhombic) (∼1200 deg. C). Prolonged heat treatments leads to the crystallization of nepheline (NaAlSiO{sub 4}, hexagonal) (∼1200 deg. C) as a secondary phase. Fe{sub 2}O{sub 3} promotes the crystallization of nepheline over carnegeite via formation of magnetite as nucleation site. Iron incorporation pre-nucleates the glasses which upon heat treatment result in the formation of magnetite phase as nucleation sites, thus, shifting the mechanism of crystallization from surface to volume. Unlike carnegeite, the crystal structure of nepheline allows partial substitution of Fe{sup 3+}/Al{sup 3+}. This promotes the crystallization of nepheline over carnegeite in iron-containing glasses. Iron incorporation in nepheline-based sodium aluminosilicate glasses shifts crystallization mechanism from surface to bulk. Our results indicate that atmosphere does affect the crystallization kinetics of iron-containing aluminosilicate glasses but only when Fe{sub 2}O{sub 3} concentration is low. Since nepheline crystal structure can easily accommodate iron in comparison to carnegeite, iron seems to promote nepheline formation in these glasses at the expense of carnegeite through formation of Fe{sub 3}O{sub 4} phase as nucleation site. Future work will be focused on adding compositional complexity to these glasses and studying them further for their nucleation and crystallization behavior.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2021

Small Molecule Activation with Intramolecular “Inverse” Frustrated Lewis Pairs

The intramolecular “inverse” frustrated Lewis pairs (FLPs) of general formula 1-BR 2 -2-[(Me 2 N) 2 C=N]-C 6 H 4 (3-6) [BR 2 = BMes 2 (3), BC 12 H 8 , (4), BBN (5), BBNO (6)] were synthesized and structurally characterized by multinuclear NMR spectroscopy and X-ray analysis. Furthermore, these novel types of pre-organized FLPs, featuring strongly basic guanidino units rigidly linked to weakly Lewis acidic boryl moieties via an ortho-phenylene linker, are capable of activating H-H, C-H, N-H, O-H, Si-H, B-H and C=O bonds. 4 and 5 deprotonated terminal alkynes to form the zwitterionic borates 1-(RC≡C-BR 2 )-2-[(Me 2 N) 2 C=NH]-C 6 H 4 (R = Ph, H) and reacted with ammonia, BnNH 2 and pyrrolidine, to generate the adducts 1-(R 2 HN→BR 2 )-2-[(Me 2 N) 2 C=NH]-C 6 H 4 , where the N-H functionality is activated by intramolecular H-bond interactions. In addition, 5 was found to rapidly add across the double bond of H 2 CO, PhCHO and PhNCO to form cyclic zwitterionic guanidinium borates in excellent yields. Likewise, 5 is capable of cleaving H 2 , HBPin and PhSiH 3 to form various amino boranes. Collectively, the results demonstrate that these new types of intramolecular FLPs featuring weakly Lewis acidic boryl and strongly basic guanidino moieties are as potent as conventional intramolecular FLPs with strongly Lewis acidic units in activating small molecules.

08 HYDROGEN↗