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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Magnetic behavior of erbium-zinc-borate glasses and glass ceramics

Glasses of the system (Er{sub 2}O{sub 3}){sub x}⋅(B{sub 2}O{sub 3}){sub (60−x)}⋅(ZnO){sub 40} (3 ≤ x ≤ 15 mol%) were prepared by conventional melt quenching and subsequently converted to glass ceramics by heat treatment of glass samples at 860 °C for 2 h. The magnetic behaviour of the studied glasses and glass ceramics were investigated using a vibrating sample magnetometer (VSM) and a Faraday-type magnetic balance. Magnetic data show that erbium ions are involved in negative superexchange interactions in all the investigated samples, being antiferromagnetically coupled. For all studied samples the experimental values obtained for the effective magnetic moments are lower than the value corresponding to free Er{sup 3+} ions and decrease with the increasing of Er{sub 2}O{sub 3} content. The decrease is more pronounced in heat treated samples than untreated ones.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Transport properties of lithium- lead-vanadium-telluride glass and glass ceramics

Glasses with the chemical composition 35Li{sub 2}O-(45-x)V{sub 2}O{sub 5−}20PbO-xTeO{sub 2} (where x = 2.5, 5, 7.5, 10, 15 mol %) have prepared by conventional melt quenching method. The electrical conductivity of Li{sup +} ion conducting lead vanadium telluride glass samples has been carried out both as a function of temperature and frequency in the temperature range 503K-563K and over frequencies 40 Hz to 10 MHz. The electronic conduction has been observed in the present systems. When these samples annealed around 400°C for 2hour become the glass ceramic, which also shows increase tendency of conductivity. SEM confines glass and glass ceramic nature of the prepared samples.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Synthesis and structural studies of multi-component strontium zinc silicate glass-ceramics

Glass having composition 40SrO-10ZnO-40SiO{sub 2}-2B{sub 2}O{sub 3}-2Al{sub 2}O{sub 3}-2TiO{sub 2}-2Cr{sub 2}O{sub 3}-2Y{sub 2}O{sub 3}, (mol %) was prepared by melt-quench technique and converted into glass-ceramics by subjecting it to varying heat treatments. Thermal properties were measured by thermo-mechanical analyzer and differential thermal analyzer. The XRD revealed that initially Sr{sub 2}ZnSi{sub 2}O{sub 7} phase at lower temperature and later SrSiO{sub 3}/Sr{sub 3}Si{sub 3}O{sub 9} phase crystallized. The structural elucidation by Raman spectroscopy shows the presence of mainly Q{sup 1} structural units along with Q{sup 2} and Q{sup 0} units in the base glass. Raman spectra revealed that during crystallization initially crystalline phase having Q{sup 1} structural units (corresponding to Sr{sub 2}ZnSi{sub 2}O{sub 7} phase) are formed and later crystalline phase having Q{sup 2} structural units with 3 member ring type structure crystallizes. Thus, Raman spectroscopy and XRD together confirm that in early stage of crystallization, Sr{sub 2}ZnSi{sub 2}O{sub 7} phase and later Sr{sub 3}Si{sub 3}O{sub 9} phase formed in the glass-ceramics.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Assessing the Validity of the Simplified Potential Energy Clock Model for Modeling Glass-Ceramics

Glass-ceramic seals may be the future of hermetic connectors at Sandia National Laboratories. They have been shown capable of surviving higher temperatures and pressures than amorphous glass seals. More advanced finite-element material models are required to enable model-based design and provide evidence that the hermetic connectors can meet design requirements. Glass-ceramics are composite materials with both crystalline and amorphous phases. The latter gives rise to (non-linearly) viscoelastic behavior. Given their complex microstructures, glass-ceramics may be thermorheologically complex, a behavior outside the scope of currently implemented constitutive models at Sandia. However, it was desired to assess if the Simplified Potential Energy Clock (SPEC) model is capable of capturing the material response. Available data for SL 16.8 glass-ceramic was used to calibrate the SPEC model. Model accuracy was assessed by comparing model predictions with shear moduli temperature dependence and high temperature 3-point bend creep data. It is shown that the model can predict the temperature dependence of the shear moduli and 3- point bend creep data. Analysis of the results is presented. Suggestions for future experiments and model development are presented. Though further calibration is likely necessary, SPEC has been shown capable of modeling glass-ceramic behavior in the glass transition region but requires further analysis below the transition region.

36 MATERIALS SCIENCE↗
DOE OSTI2021

A constitutive model for glass–ceramic materials

Glass–ceramics have received recent attention for use in glass–ceramic to metal hermetic seals. Due to their heterogeneous microstructure, these materials exhibit a number of advantageous responses over conventional glass based seals. Key amongst them is the possibility of a controllable thermal strain response and apparent coefficient of thermal expansion which may be used to minimize thermally induced residual stresses for aforementioned seals. Furthermore, these behaviors result from an inorganic glass matrix and variety of crystalline ceramic phases including silica polymorph(s) that may undergo reversible solid-to-solid transformations with associated inelastic strain. Correspondingly, these materials exhibit complex thermomechanical responses associated with multiple inelastic mechanisms (viscoelasticity and phase transformation). While modeling these behaviors is essential for developing and analyzing the corresponding applications, no such model exists. Therefore, in this work a three-dimensional continuum constitutive model for glass–ceramic materials combining these various inelastic mechanisms is developed via an internal state variable approach. A corresponding fully implicit three dimensional numerical formulation is also proposed and implemented. The model is used to simulate existing experiments and validate the proposed formalism. As an example, the simple seal problem of a glass–ceramic seal inside a concentric metal shell is explored. Finally, the impact of the cooling rates, viscoelastic shift factors, and inelastic strain on final residual stress state are all investigated and the differing contributions highlighted.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Cold crucible induction melter studies for making glass ceramic waste forms: A feasibility assessment

Glass ceramics are being developed to immobilize fission products, separated from used nuclear fuel by aqueous reprocessing, into a stable waste form suitable for disposal in a geological repository. This work documents the glass ceramic formulation at bench scale and for a scaled melter test performed in a pilot-scale (approximately 1/4 scale) cold crucible induction melter (CCIM). Melt viscosity, electrical conductivity, and crystallization behavior upon cooling were measured on a small set of compositions to select a formulation for melter testing. Property measurements also identified a temperature range for melter operation and cooling profiles necessary to crystallize the targeted phases in the waste form. Bench scale and melter run results successfully demonstrate the processability of the glass ceramic using the CCIM melter technology.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2017

Sealing glass-ceramics with near-linear thermal strain, part III: Stress modeling of strain and strain rate matched glass-ceramic to metal seals

Thermal mechanical stresses of glass-ceramic to stainless steel (GCtSS) seals are analyzed using finite element modeling over a temperature cycle from a set temperature (T set ) 500°C to -55°C, and then back to 600°C. There are two glass-ceramics that have an identical coefficient of thermal expansion (CTE) at ~16 ppm/°C but have very different linearity of thermal strains, designated as near-linear NL16 and step-like SL16, and were formed from the same parent glass using different crystallization processes. Stress modeling reveals much higher plastic strain in the stainless steel using SL16 glass-ceramic when the GCtSS seal cools from T set . Upon heating tensile stresses start to develop at the GC-SS interface before the temperature reaches T set . On the other hand, the much lower plastic deformation in stainless steel accumulated during cooling using NL16 glass-ceramic allows for radially compressive stress at the GC-SS interface to remain present when the seal is heated back to T set . Finally, the qualitative stress comparison suggests that with a better match of thermal strain rate to that of stainless steel, the NL16 glass-ceramic not only improves the hermeticity of the GCtSS seals, but would also improve the reliability of the seals exposed to high-temperature and/or high-pressure abnormal environments.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Effect of heat treatment time on microstructure and electrical conductivity in LATP glass ceramics

Glass-ceramic is prepared by heat treatment of melt quenched 14Li{sub 2}O−9Al{sub 2}O{sub 3}−38TiO{sub 2}−39P{sub 2}O{sub 5} glass in the vicinity of crystallization temperature. Growth of ceramic phase is controlled by tuning heat treatment time at fixed temperature. Ceramic phase was identified to be LiTi{sub 2}(PO{sub 4}){sub 3} from X Ray Diffraction analysis. Microstructural evolution of this phase with hold time was observed under high resolution Scanning Electron Microscope. DC conductivity is observed to increase by 4-5 orders of magnitude in this glass-ceramic compared to parent glass. However, formation of pores and cracks with very large heat treatment time seem to hinder further increase of conductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Preparation and characterization of novel foamed porous glass-ceramics

Foamed glass-ceramics without using foaming agent have been synthesized in a novel glass system of SrO-CaO-Al{sub 2}O{sub 3}-TiO{sub 2}-B{sub 2}O{sub 3}-SiO{sub 2}-P{sub 2}O{sub 5}-M{sub x}O{sub y} (where M = Ba, Mg, La, Ce and Ni) by a simple process of powder sintering. The glass and glass-ceramics are characterized by dilatometry, differential scanning calorimetry (DSC), heating stage microscopy (HSM), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), optical microscopy and Fourier transformed infrared spectroscopy (FTIR). All the glasses formed are amorphous and the glass transition temperature and dilatometric softening temperature of these glasses are found to be in the range 673–678 °C and 706–728 °C respectively. The glasses are highly stable as indicated by the DSC evaluated glass stability parameters of the range 195–240 °C. Quantitative sintering study of glass powder compacts revealed swelling in the samples with NiO and CeO{sub 2} corresponding to a geometry change of 75 and 108% around 900 °C respectively. With reference to this finding the glass powder compacts are heated to 900 °C and the foamed glass-ceramics are obtained. Characteristic crystalline silicate phases have been identified in the XRD studies and their microstructures are recorded by FESEM. Optical microscope study of the foamed samples revealed formation of bigger foamed cavity with residual pores in samples with NiO and CeO{sub 2} in comparison to samples with BaO, MgO and La{sub 2}O{sub 3}. The mean pore diameters of the samples with NiO and CeO{sub 2} are determined to be 43 and 32 μm, and their respective porosities are 2.34 and 1.82 cm{sup 3}/g respectively. Thus NiO and CeO{sub 2} are found to be very effective to obtain foamed glass-ceramics without using foaming agent by the viscous flow sintering of fine glass powder compacts along with the reduction of the respective polyvalent ions. - Highlights: • Synthesis of foamed porous glass-ceramics without foaming agent by sintering method • Only powder compact yielded foamed porous glass-ceramics but bulk glass did not. • Glasses containing NiO and CeO{sub 2} exhibited significant foaming efficiency. • Bloating of entrapped gas during viscous flow sintering is the origin of foaming. • Residual void created pores in the sintered glass-ceramics as evidenced in FESEM.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Development of a sintering process for recycling oil shale fly ash and municipal solid waste incineration bottom ash into glass ceramic composite

Highlights: • Glass ceramic composite is prepared from oil shale fly ash and MSWI bottom ash. • A novel method for the production of glass ceramic composite is presented. • It provides simple route and lower energy consumption in terms of recycling waste. • The vitrified slag can promote the sintering densification process of glass ceramic. • The performances of products decrease with the increase of oil shale fly ash content. - Abstract: Oil shale fly ash and municipal solid waste incineration bottom ash are industrial and municipal by-products that require further treatment before disposal to avoid polluting the environment. In the study, they were mixed and vitrified into the slag by the melt-quench process. The obtained vitrified slag was then mixed with various percentages of oil shale fly ash and converted into glass ceramic composites by the subsequent sintering process. Differential thermal analysis was used to study the thermal characteristics and determine the sintering temperatures. X-ray diffraction analysis was used to analyze the crystalline phase compositions. Sintering shrinkage, weight loss on ignition, density and compressive strength were tested to determine the optimum preparation condition and study the co-sintering mechanism of vitrified amorphous slag and oil shale fly ash. The results showed the product performances increased with the increase of sintering temperatures and the proportion of vitrified slag to oil shale fly ash. Glass ceramic composite (vitrified slag content of 80%, oil shale fly ash content of 20%, sintering temperature of 1000 °C and sintering time of 2 h) showed the properties of density of 1.92 ± 0.05 g/cm{sup 3}, weight loss on ignition of 6.14 ± 0.18%, sintering shrinkage of 22.06 ± 0.6% and compressive strength of 67 ± 14 MPa. The results indicated that it was a comparable waste-based material compared to previous researches. In particular, the energy consumption in the production process was reduced compared to conventional vitrification and sintering method. Chemical resistance and heavy metals leaching results of glass ceramic composites further confirmed the possibility of its engineering applications.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2012

Glass Ceramic Formulation Data Package

A glass ceramic waste form is being developed for treatment of secondary waste streams generated by aqueous reprocessing of commercial used nuclear fuel (Crum et al. 2012b). The waste stream contains a mixture of transition metals, alkali, alkaline earths, and lanthanides, several of which exceed the solubility limits of a single phase borosilicate glass (Crum et al. 2009; Caurant et al. 2007). A multi-phase glass ceramic waste form allows incorporation of insoluble components of the waste by designed crystallization into durable heat tolerant phases. The glass ceramic formulation and processing targets the formation of the following three stable crystalline phases: (1) powellite (XMoO 4 ) where X can be (Ca, Sr, Ba, and/or Ln), (2) oxyapatite Y x, Z (10-x) Si 6 O 26 where Y is alkaline earth, Z is Ln, and (3) lanthanide borosilicate (Ln 5 BSi 2 O 13 ). These three phases incorporate the waste components that are above the solubility limit of a single-phase borosilicate glass. The glass ceramic is designed to be a single phase melt, just like a borosilicate glass, and then crystallize upon slow cooling to form the targeted phases. The slow cooling schedule is based on the centerline cooling profile of a 2 foot diameter canister such as the Hanford High-Level Waste canister. Up to this point, crucible testing has been used for glass ceramic development, with cold crucible induction melter (CCIM) targeted as the ultimate processing technology for the waste form. Idaho National Laboratory (INL) will conduct a scaled CCIM test in FY2012 with a glass ceramic to demonstrate the processing behavior. This Data Package documents the laboratory studies of the glass ceramic composition to support the CCIM test. Pacific Northwest National Laboratory (PNNL) measured melt viscosity, electrical conductivity, and crystallization behavior upon cooling to identify a processing window (temperature range) for melter operation and cooling profiles necessary to crystallize the targeted phases in the waste form.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2017

Corrosion Behavior and Microstructure Influence of Glass-Ceramic Nuclear Waste Forms

Glass ceramic waste forms present a potentially viable technology for the long term immobilization and disposal of liquid nuclear wastes. Through control of chemistry during fabrication, such waste forms can have designed secondary crystalline phases within a borosilicate glass matrix. In this work, a glass ceramic containing powellite and oxyapatite secondary phases was tested for its corrosion properties in dilute conditions using single pass flow through testing (SPFT). Three glass ceramic samples were prepared using different cooling rates to produce samples with varying microstructure sizes. In testing at 90 °C in buffered pH 7 and pH 9 solutions, it was found that increasing pH and decreasing microstructure size (resulting from rapid cooling during fabrication) both led to a reduction in overall corrosion rate. The phases of the glass ceramic were found, using a combination of solutions analysis, SEM and AFM, to corrode preferably in the order of powellite > bulk glass matrix > oxyapatite.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2013

Glass-Ceramic Waste Forms for Uranium and Plutonium Residues Wastes - 13164

A program of work has been undertaken to treat plutonium-residues wastes at Sellafield. These have arisen from past fuel development work and are highly variable in both physical and chemical composition. The principal radiological elements present are U and Pu, with small amounts of Th. The waste packages contain Pu in amounts that are too low to be economically recycled as fuel and too high to be disposed of as lower level Pu contaminated material. NNL and ANSTO have developed full-ceramic and glass-ceramic waste forms in which hot-isostatic pressing is used as the consolidation step to safely immobilize the waste into a form suitable for long-term disposition. We discuss development work on the glass-ceramic developed for impure waste streams, in particular the effect of variations in the waste feed chemistry glass-ceramic. The waste chemistry was categorized into actinides, impurity cations, glass formers and anions. Variations of the relative amounts of these on the properties and chemistry of the waste form were investigated and the waste form was found to be largely unaffected by these changes. This work mainly discusses the initial trials with Th and U. Later trials with larger variations and work with Pu-doped samples further confirmed the flexibility of the glass-ceramic. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗