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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Sol–gel synthesis of silver nanocrystals embedded in sodium borosilicate monolithic transparent glass with giant third-order optical nonlinearities

Highlights: • We prepared Ag-doped sodium borosilicate monolithic glass. • The influence of temperature on the SPR absorption peak intensity was studied. • Nonlinear optical properties of the glass were investigated. • A mechanism for the formation of Ag quantum dots glass was proposed. - Abstract: We report the preparation of uniform spherical shape silver nanocrystals doped sodium borosilicate monolithic transparent glass by sol–gel method. The characterization of the resulting Ag nanocrystals was accomplished by using X-ray powder diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and energy dispersive X-ray spectrum. Surface plasma resonance absorption peaks of the silver nanocrystals glass at about 406 nm have been obtained from ultraviolet–visible absorption spectrometer and their intensity is changed with different heat treatment temperatures. We have investigated the nonlinear optical properties of silver quantum dots doped glass using Z-scan technique. Third-order nonlinear optical susceptibility χ{sup (3)} of the glass was estimated to be 1.01 × 10{sup −11} esu. In particular, a mechanism for the formation of Ag quantum dots glass is proposed. This work will significantly promote the obtained material applications in optical devices.

36 MATERIALS SCIENCE↗
NASA NTRS1982

Manufacture of large glass honeycomb mirrors

The problem of making very large glass mirrors for astronomical telescopes is examined, and the advantages of honeycomb mirrors made of borosilicate glass are discussed. Thermal gradients in the glass that degrade the figure of thick borosilicate mirrors during use can be largely eliminated in a honeycomb structure by internal ventilation (in air) or careful control of the radiation environment (in space). It is expected that ground-based telescopes with honeycomb mirrors will give better images than those with solid mirrors. Materials, techniques, and the experience that has been gained making trial mirrors and test castings as part of a program to develop 8-10-m-diameter lightweight mirrors are discussed.

Angel, J. R. P.↗
DOE OSTI2017

Simulations of the surfaces of soda lime aluminoborosilicate glasses exposed to water

Molecular dynamics simulations of 7 compositionally different sodium calcium alumino–borosilicate glasses showed formation of 4 B and 5 Al more consistent with experimental data without compromising the other structural features that match experimental results observed in recent simulations of these glasses. Analysis of the dry surfaces of these glasses show a lack of 4 B in the top 5–6 Å of the surface in comparison to the bulk concentration for all glasses and no 5 Al. Upon exposure to water, the simulations show that the 3 B in the top 5–6 Å of the glasses are preferentially attacked, decreasing the number of B bonds to O originally from the glass, indicating a change in the glass network. Inclusion of all B–O bonds in the top 5–6 Å (i.e., including O from water) shows a decrease in 3 B but an increase in 4 B that is consistent with NEXAFS analysis, which the simulations show are hydroxylated. Furthermore, there is an increase in the concentration of 3 Al in the dry surface in comparison to the bulk, but exposure to water converts almost all of these 3 Al to 4 Al. Hydroxyl concentrations vary from 2.6/nm 2 to 4.1/nm 2 , with SiOH and BOH dominating these surface hydroxyls. Upon exposure to water, network linkages to B are preferentially ruptured. This, and the preferential loss of the nonbridging oxygen sites attached to Na, provide atomistic evidence of the initial stages of removal of B and Na from glass surfaces exposed to water.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Potential-induced degradation of Cu(In,Ga)Se 2 can occur by shunting the front i-ZnO and by damaging the p-n junction

In this work we test field-relevant potential-induced degradation (PID) behavior by encapsulating laboratory Cu(In,Ga)Se 2 (CIGS) solar cells and applying +1000 V uniformly on the face of the front glass. In this configuration, we find that K-rich borosilicate glass reduces the extent of PID relative to Na-rich soda-lime glass. We also find that the standard testing protocol of stressing cells at short-circuit leads to faster PID than stressing cells at open-circuit. We characterize two types of CIGS PID: The first, front shunting PID, is driven by front-glass stress and occurs when alkali metal cations accumulate in the i-ZnO buffer, where they increase shunt conductance to reduce fill factor. The second, p-n junction PID, results from back-glass stress as alkali metal cations pile up near the CIGS surface/CdS buffer, where they reduce charge carrier concentration, open-circuit voltage, and fill factor to degrade efficiency ~160 times faster than front shunting PID.

14 SOLAR ENERGY↗
NASA NTRS1977

Integral glass encapsulation for solar arrays

Electrostatic bonding has been used to join silicon solar cells to borosilicate glass without the aid of any organic binders or adhesives. The results of this investigation have been to demonstrate, without question, the feasibility of this process as an encapsulation technique. The potential of ESB for terrestrial solar arrays was clearly shown. The process is fast, reproducible, and produces a permanent bond between glass and silicon that is stronger than the silicon itself. Since this process is a glass sealing technique requiring no organics it makes moisture tight sealing of solar cells possible.

Young, P. R.↗
DOE OSTI2022

The Effects of Mixing Multi-Component HLW Glasses on Spinel Crystal Size

The Hanford Waste Treatment and Immobilization Plant will vitrify radioactive waste into borosilicate glass. The high-level waste (HLW) glass formulations are constrained by processing and property requirements, including restrictions aimed at avoiding detrimental impacts of spinel crystallization in the melter. To understand the impact of glass chemistry on crystallization, two HLW glasses precipitating small (?5 µm) spinel crystals were individually mixed with a glass that precipitated large (?45 µm) spinel crystals in ratios of 25, 50, and 75 wt%. The size of spinel crystals in the mixed glasses varied from 5 to 20 µm. Small crystal size was attributed to: (1) high concentrations of nuclei due to the presence of ruthenium oxide and (2) chromium oxide aiding high rates of nucleation. Results indicate that the spinel crystal size can be controlled using chromium oxide and/or noble metal concentrations in the melt, even in complex mixtures like HLW glasses. Small crystals tend to settle slowly, so they are acceptable in the melter without a risk of failure. Allowing higher concentrations of spinel-forming waste components in the waste glass enables glass compositions with higher waste loading, thus increasing plant operational flexibility. An additional benefit to the presence of chromium oxide in the glass composition is the potential for the oxide to protect melter walls against corrosion.

Lonergan, Charmayne E.↗
DOE OSTI2017

Defense waste processing facility (DWPF) liquids model: revisions for processing higher TIO 2 containing glasses

Radioactive high level waste (HLW) at the Savannah River Site (SRS) has successfully been vitrified into borosilicate glass in the Defense Waste Processing Facility (DWPF) since 1996. Vitrification requires stringent product/process (P/P) constraints since the glass cannot be reworked once it is poured into ten foot tall by two foot diameter canisters. A unique “feed forward” statistical process control (SPC) was developed for this control rather than statistical quality control (SQC). In SPC, the feed composition to the DWPF melter is controlled prior to vitrification. In SQC, the glass product would be sampled after it is vitrified. Individual glass property-composition models form the basis for the “feed forward” SPC. The models transform constraints on the melt and glass properties into constraints on the feed composition going to the melter in order to guarantee, at the 95% confidence level, that the feed will be processable and that the durability of the resulting waste form will be acceptable to a geologic repository. This report documents the development of revised TiO 2 , Na 2 O, Li 2 O and Fe 2 O 3 coefficients in the SWPF liquidus model and revised coefficients (a, b, c, and d).

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1979

Repairing cracked glass

Filing procedure consisting of machined lightweight fused-silica tiles coated with thin-layer of borosilicate glass produces homogeneous seal in thin glass. Procedure is useful in repairing glass envelopes, X-ray tub windows, Dewar flasks, and similar thin glass objects.

Helman, D. D.↗
DOE OSTI2019

Potential-Induced Degradation Depends on Leakage Current and Light/Electrical Bias in Cu(In,Ga)Se 2 Devices

Potential-induced degradation (PID) of encapsulated Cu(In,Ga)Se 2 (CIGS) solar cells was researched for different substrates: soda-lime glass (SLG), SLG with an Al 2 O 3 diffusion barrier, and borosilicate glass (BSG). The Al 2 O 3 and BSG samples increased the time to PID failure by 5x and 30x, respectively. The relationship among PID and coulombs transferred from the substrate to the device through leakage current differed depending on the sample type. When the (unrepresentative) dark PID stress test was interrupted to characterize devices with light/electrical bias, PID was partially reversed. Furthermore, applying high voltage stress to open-circuit devices was less damaging, relative to forward-biased and short-circuited cells. Light/electrical bias may therefore reduce PID by driving alkali metal cations away from the p-n junction to diminish their degrading effects. These results show that device light/electrical bias should be carefully controlled during CIGS PID testing, as it affects PID in addition to leakage current.

14 SOLAR ENERGY↗
DOE OSTI2023

Optimization Efforts at DWPF to Ensure Waste Tank Closure by 2037 – 24404

At the Savannah River Site (SRS) in Aiken, South Carolina, the Defense Waste Processing Facility (DWPF) produces a glass-form product by processing high-level liquid waste (HLW) with borosilicate glass in a high-heated Melter, then putting the vitrified waste into stainless-steel canisters. Since 1996, DWPF has performed this vitrification process for the liquid waste mission at the SRS; the overall objective for this mission is to reduce the volume in the upstream waste tanks, so those tanks can be emptied and operationally closed. This mission seeks to eliminate the single biggest environmental risk in the state of South Carolina, which requires a robust processing strategy within the DWPF, along with optimal interface between the other facilities in the liquid waste organization (LWO). As of the end of July 2023, DWPF has safely remediated 63.7 MCi of HLW, and filled 4,319 canisters (We project that about 4,000 more canisters are needed to be filled to reach the closure goal.)

Armstead, III, Frank L.↗
DOE OSTI2013

Silane Modification of Glass and Silica Surfaces to Obtain Equally Oil-Wet Surfaces in Glass-Covered Silicon Micromodel Applications

The wettability of silicon and glass surfaces can be modified by silanization. However, similar treatments of glass and silica surfaces using the same silane do not necessarily yield the same wettability as determined by the oil-water contact angle. In this technical note, surface cleaning pretreatments were investigated to determine conditions that would yield oil-wet surfaces on glass with similar wettability to silica surfaces treated with the same silane, and both air-water and oil-water contact angles were determined. Air-water contact angles were less sensitive to differences between silanized silica and glass surfaces, often yielding similar values while the oil-water contact angles were quite different. Borosilicate glass surfaces cleaned with standard cleaning solution 1 (SC1) yield intermediate-wet surfaces when silanized with hexamethyldisilazane, while the same cleaning and silanization yields oil-wet surfaces on silica. However, cleaning glass in boiling concentrated nitric acid creates a surface that can be silanized to obtain oil-wet surfaces using HDMS. Moreover, this method is effective on glass with prior thermal treatment at an elevated temperature of 400oC. In this way, silica and glass can be silanized to obtain equally oil-wet surfaces using HMDS. It is demonstrated that pretreatment and silanization is feasible in silicon-silica/glass micromodels previously assembled by anodic bonding, and that the change in wettability has a significant observable effect on immiscisble fluid displacements in the pore network.

contact angle↗
DOE OSTI2018

Structural features of ISG borosilicate nuclear waste glasses revealed from high-energy X-ray diffraction and molecular dynamics simulations

Vitrification is a widely accepted method to immobilize nuclear waste. Detailed structural information is critical to understand the physical and chemical behaviors, including the long-term chemical durability of these glasses that are to be stored in geological storage sites. High-energy X-ray diffraction studies are used to obtain accurate structural information of the International Simple Glass (ISG), a six-component borosilicate model nuclear waste glass with a composition (mol%) of 60.2SiO 2 -16.0B 2 O 3 -12.6Na 2 O-3.8Al 2 O 3 -5.7CaO-1.7ZrO 2 . Classical molecular dynamics (MD) simulations with recently developed effective potentials are utilized to generate structural models of the ISG glasses to provide interpretation of the high-energy X-ray structural data and additional short and medium range structural details. The atomic structure model generated from MD simulations shows an excellent agreement with high-energy X-ray diffraction, measured for the first time for ISG, with an R x value of 5.5%. Systematic investigations of the medium-range structural features of ISG are performed, built upon recent study of the short-range structure. In particular, the glass former cation oxygen polyhedral analysis show that [SiO 4 ]-[SiO 4 ] and [BO 4 ]-[SiO 4 ] connections are the most abundant while [ZrO 6 ] octohedra having higher probability to connect to another [SiO 4 ], [BO 4 ] and [BO 3 ]. Moreover, we have studied the ISG surface structure using MD simulations. Noticeable differences in terms of both chemical compositions and structural features between the bulk and surface are observed. There exist increased small-sized rings, under coordinated Si species, high 3-coordinated boron content (86.5%) on the surface. Very importantly, sodium ions are found to be enriched on the glass surface, consistent with recent experimental results. Furthermore, both bulk and surface structural information are discussed in terms of the dissolution and corrosion mechanisms of ISG and related nuclear waste glasses.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Iron polyphosphate glasses for waste immobilization

Abstract Iron polyphosphate glasses resist attack by water, can dissolve large concentrations of species that are otherwise insoluble in borosilicate glass melts, and can be processed at relatively low temperatures (1000‐1200°C), and so are viable hosts for vitrifying hazardous and radioactive wastes. The properties of iron polyphosphate glasses depend on the distributions of phosphate anions and the nature of the bonds between those anions and various metal polyhedra, and quantitative information can be obtained about those structures using a variety of spectroscopic, diffraction, and chromatographic techniques. This structural information helps explain compositional trends in properties, including dissolution rates, electrical conductivity, thermal properties and crystallization tendency. Studies of waste forms made with low activity and high level wastes are reviewed and related back to an understanding of the structures and properties of simpler iron polyphosphate glasses.

Brow, Richard K.↗
DOE OSTI2025

Advanced Computational Modeling of High-Level Waste Vitrification at the Hanford Site

The U.S. Department of Energy (DOE) has selected vitrification for stabilizing legacy tank waste at the Hanford site, where radioactive waste from plutonium production was historically stored in underground tanks. This waste will be separated into low-activity waste (LAW) and high-level waste (HLW) fractions and processed at the Waste Treatment and Immobilization Plant (WTP). At WTP, glass melters are used for the vitrification of radioactive tank waste, transforming it into a stable borosilicate glass form for safe long-term storage. The melter vessel is constructed from highly durable and heat-resistant materials, where the vitrification process occurs. The main regions that are modeled are the melt pool, plenum, cold cap, riser/discharge chamber, and surrounding structure with insulation layers. Forced convection induced by air bubblers at the base of the melter ensure uniform temperature distribution and provide heat to the cold cap layer. The cold cap is a region of reacting batch feed that floats on top of the molten glass and is where the batch-to-glass reactions occur. Joule heating provided by electrodes mounted along the vertical walls of the melter and immersed directly in the glass, generates the necessary heat for the net endothermic conversion processes that occur in the cold cap. The high temperatures, radioactivity, and opaque nature of the glass prevent direct observation inside the melters. Therefore, computational models are essential for providing insight into factors that affect melter throughput. Thermocouples in the plenum provide operators with plenum temperature measurements. Operational adjustments include bubbling rate, voltage supplied to the electrodes, feed adjustments, and glass removal rate. Different computational fluid dynamics (CFD) models have been developed, each serving a specific purpose. There are CFD models of different scale melters, as well as models that capture the two-phase flow interfaces of rising bubbles in the molten glass or models with a simplified molten glass region so that the surrounding structure and plenum can be feasibly incorporated. Pilot-scale melter models have been developed to serve as validation of the methods employed in the simulation of the full-scale WTP melters. Models incorporating resolved bubbling are used to develop momentum source terms to implement into a single phase, multi-region, steady-state flow model that is being validated by measured process parameters such as glass production rate, voltage, input power, plenum temperatures, etc. The resolved bubbling model uses the multiphase volume of fluid approach to model the system with a high-resolution interface capturing scheme to maintain sharp interfaces between the molten glass and the air phase. The suite of CFD models is continually being improved to incorporate more realistic physics and achieve faster turnaround time. For example, an incremental controller is implemented to automatically adjust electrode voltage within the simulation to a molten glass set point temperature of 1150°C. Newer models feature improved meshes to ensure conformal meshes between regions and eliminate unnecessary mesh refinement in areas that are not of interest (such as boundary layers in offgas ports). Instead of explicitly modeling the structural, refractory, and insulation layers of the melter, a thermal resistance approach is used with published correlations used for boundary conditions. The development of robust and efficient CFD models will be instrumental in enabling the WTP to successfully fulfill its mission of safely stabilizing legacy nuclear waste.

12 - MGMT OF RADIOACTIVE AND NON-RADIOACTIVE WASTE↗
DOE OSTI2019

Effects of Sulfate on Rhenium Incorporation into Low-Activity Waste Glass

Technetium-99 (99Tc) is a major radionuclide of concern in the Hanford low-activity waste (LAW), which will be vitrified into borosilicate glass at the Waste Treatment and Immobilization Plant (WTP). Sulfate content in LAW has been known to be a critical factor affecting the volatile loss of 99Tc during melting of the LAW glass feed (a mix of liquid LAW and mineral/chemical additives). We investigated rhenium (a nonradioactive surrogate for 99Tc) incorporation into glass by performing crucible melting tests of two representative simulated LAW glass feeds, each prepared with varied sulfur levels. The sulfate content varied from the original content to half of the original (½S) and to zero (0S), in the range of 0 to 0.8 mass % SO3 in glass if 100% retained. The slurry feeds were dried at 105°C and heated to 400–1100°C. Deionized water leach at room temperature and at 80°C was conducted on the dried feed and heat-treated samples to analyze the chemical compositions of soluble and insoluble phases separately and to profile the partitioning of various components into different phases during the melting process. Different partitioning behavior of rhenium, sulfate, and chlorine is discussed in connection with major feed-to-glass conversion reactions. The mechanism on how sulfate affects rhenium incorporation during feed-to-glass conversion reactions, and so final retention of rhenium in glass, is proposed based on the two hypotheses that segregated sulfate-rich phase forms during feed conversion reactions and Re preferentially partitions to this sulfate-rich phase.

Jin, Tongan↗