Glass Constituents Research Articles

Evaluation of Phase- and Element Distribution After Non-Traditional In Situ Vitrification (NTISV) at Los Alamos National Laboratory on a Simulated Adsorption Bed

A cold test demonstration of the Geosafe® Non-TraditionalIn-Situ Vitrification technology (NTISV) was performed at a simulated adsorption bed by using commercial-scale equipment. A successful demonstration of NTISV at Los Alamos National Laboratory (LANL) is expected to provide a useful technology for remediation needs of EM-40 in the U.S. Department of Energy (DOT) complex on legacy buried waste containing organics and radionuclides in geological environments. Therefore, a simulated test bed including surrogates was prepared to evaluate the impact this technology has on immobilizing radionuclides. The total volume of the cold demonstration vitrification was 3.1 m × 4.6 m × 4.9 m resulting in 176,667 kg of glass or glassy constituents. A drill core sample was removed from the glass monolith and divided into 13 samples to gain spatial (vertical) information about (a) vitrification progress, (b) phase distribution, and (c) element distribution. Based upon optical microscopy, least square and Rietveld refinement of the X-ray diffraction data, the phase constitution was determined and a temperature profile estimated. The glass compositions as well as the concentrations of surrogates and trace metals were analyzed by using X-ray Fluorescence Analysis, Electron-beam Microprobe Analysis, and Scanning Electron Microscopy. In the main melting zone, in the depth range 3.7 m to 6.3 m, NTISV successfully vitrified the geological formation (Bandelier Tuffl Unit 2/3 of Tshirege) and convert it mainly into 98-99 wt.-% silicate-based glass and 1-2 wt.-% iron-based metal inclusions. Within this zone the glass compositions have been found to be nearly constant and the surrogate elements (cerium and cesium) are distributed homogeneously.

Nuclear magnetic resonance (NMR) studies of the local structure of phosphorus chalcogenide glasses: an overview

An overview is given on recent nuclear magnetic resonance (NMR) structural studies of phosphorus chalcogenide glasses and melts. The detailed structural speciation of these systems has been derived on the basis of 31P dipolar spin-echo decay spectroscopy, magic-angle spinning (MAS), and variable temperature liquid-state NMR above the glass transition temperature. A specific feature in the binary phosphorus/chalcogen systems is the competition between homo- and heteropolar bond formation, which can be quantitatively described by means of these complementary NMR approaches. The effect of various elemental glass constituents upon these equilibria has been studied in a variety of ternary systems. Finally, MAS in combination with double-quantum (DQ) NMR provides detailed quantitative information on the network structural features present in ionically conducting thiophosphate glasses.

Near net shape production of monolithic and composite high temperature ceramics by hot isostatic pressing (HIP)

Improved properties of high temperature ceramics in general are achieved by compositional and processing research and development—compatible with sintering and forming needs. Pressure can be used to increase the driving force for densification and with hot isostatic pressing (HIP) the form can be closely controlled, even of complex shaped parts, like turbine wheels. Recent development within the EUREKA-AGATA hybrid electric car gas turbine project shows that improved high temperature material properties can be achieved, while at the same time fabricating components like combustion parts and turbine wheels, to near-net-shape. For such components a highly uniform green powder body is desired. Combined with a type of encapsulation during HIP, which does not create shear stresses at the surface of the green body during the shrinkage/sintering to full density, but at the same time prevents penetration into the body, optimal near-net-shape results can be achieved. Recent studies, e.g. by TEM, have confirmed that some encapsulation glass constituents can form new compounds with silicon nitride, at the very surface, which appear to help develop these desired characteristics. Non-homogeneous and non-isotropic ceramics, like fiber reinforced composites, may be fabricated using rigid, shape controlling tools on one or several sides. Particularly for large (and curved) panels such use of a hot isostatic press can be an advantage.

Stoichiometry of the leaching process of fluoride-containing aluminosilicate glass-ionomer glasses.

Dental glass-ionomer cements (GIC) set by an acid-base reaction between a polyalkenoic acid and an ion-leachable glass. The exact relationship between the glass composition and the setting and final properties of GIC is not yet fully elucidated. As part of a systematic study of this relationship, we studied the leaching stoichiometry of glasses used in commercial formulations to correlate the glass composition with its leaching properties. The leaching experiments were performed in acetic acid solutions at pH = 3.4 by means of a pH-stat method. After predetermined time intervals, the suspension was filtered and the filtrate was analyzed for the glass constituents. The usefulness of the pH-stat method for the determination of glass reactivity was corroborated. The deviation of the leaching stoichiometry with respect to the pure glass stoichiometry decreased with increasing relative content of mono- and bivalent glass network dwellers and modifiers. Indications were found that the latter can be leached out independently and preferentially, while the leaching of network dwellers is coupled with the aluminum release. The F content as well as the reactivity of the glass affect the amount of fluoride available for release from a set GIC. It could be concluded that the leaching stoichiometry of GIC glasses can be correlated with their absolute and relative composition.

Free volumes in several ion-conducting glasses

Studies of the packing of atoms in glass have usually been made by assuming that the atoms are spherical. Since spheres contain large spaces into which no nearby atoms or ions can penetrate, cubes rather than spheres are used in this Letter for representing atoms and the free volume is defined as a volume in which no glass constituents exist. It is concluded that alkali ions in alkali borate or silicate glasses occupy the free volume which the glass network-former provides.

Characterisation of surface layers formed under natural environmental conditions on medieval stained glass and ancient copper alloys using SEM, SIMS and atomic force microscopy

Atmospheric corrosion is the result of interactions between a material and the surrounding environment. It involves a number of physical, chemical and electrochemical processes in the interfacial region ranging from the contacting atmosphere over the aqueous adlayer to the material itself. In this contribution surface analytical techniques such as scanning electron microscopy, in combination with energy dispersive X-ray microanalysis (SEM-EDX) and secondary ion mass spectrometry (SIMS) were applied to characterise the corrosion phenomena occurring on medieval stained glass and ancient bronze artefacts. A so-called leached layer has been formed on the glass surfaces due to an ion exchange process, where the potassium and calcium of the glass are replaced by hydrogen bearing species from the moist air. Subsequently, chemical reactions of the leached glass constituents K and Ca with acidifying gases in the ambient atmosphere has led to the formation of a weathering crust. On the surfaces of bronze artefacts a cuprous oxide (mainly) has been built up. Further chemical reactions are leading to crystalline weathering products such as brochantite or malachite depending on the environmental conditions. Additionally, tapping mode atomic force microscopy (TM-AFM) has been applied to study the initial stages of the weathering processes on glass with medieval composition and on pure copper. The task of the present work was not only to develop new analytical strategies and methods, but also to gain additional information of the surface processes involved. Protection against atmospheric corrosion requires such detailed understanding of the role of different corrosion stimulating constituents in the environment, such as humidity, gaseous pollutants and aerosol particulates.

Thermochemical Models for Nuclear Waste Glass Subsystems – MgO-CaO and MgO-Al2O3

AbstractA relatively simple model, the associate species model, is being applied to nuclear waste glass compositions in order to accurately predict behavior and thermodynamic activities in the material. In the model, the glass is treated as a supercooled liquid, with the liquid species allowed to exist below their melting point. The approach requires an initial assembly of binary and ternary oxide liquid solution data that sufficiently reproduce the equilibrium phase diagrams. Two binary oxide subsystems, MgO-CaO and MgO-Al2O3, have been modeled and results compared to published phase diagrams. Computed activities of the glass constituent species are plotted as a function of composition at 1200°C.

Analysis of glass and glass melts during the vitrification of fly and bottom ashes by laser-induced plasma spectroscopy. Part II. Process analysis

Laser-induced plasma spectroscopy (LIPS) is employed for in situ and on-line process analysis of major glass constituents during a vitrification process for fly and bottom ashes from waste incineration. The system is based on an Nd:YAG laser for plasma ignition, while the elemental emissions from the plasma are detected time-resolved by an intensified multichannel analyzer. The perpendicular, single axis, imaging optics allow a remote sensing of the composition of the hot glass melt. Taking into account the plasma characteristics for calibration, good agreement between the LIPS analysis and the established reference analysis is achieved for the concentration ratios of SiO 2, Al 2O 3, and CaO. In addition, LIPS is applied to the analysis of aerosols generated by homogeneous nucleation during the heating-up of the investigated fly ashes. A distinctive temperature dependence of the heavy metal concentration of the aerosols is observed.

Glass formation and local structure in the ternary system P–Se–Al. Solid state NMR studies

Glasses in the system phosphorus–selenium–aluminum have been prepared by ice-water quenching of sealed ampoules. X-ray powder diffraction and differential scanning calorimetry (DSC) of samples indicate a limited region of glass formation in the selenium-rich region of the composition diagram. Structural studies using 27 Al and 31 P solid state NMR reveal that the local environments of both aluminum and phosphorus are dominated by selenium, however, multiple environments are observed for both glass constituents. The presence of aluminum enhances the tendency of phosphorus to become four-coordinate, suggesting that both glass formers interact in the network to some extent. On the other hand, dipolar solid state NMR studies indicate that the P⋯Al interactions are generally smaller than expected on the basis of statistically linked PSe x and AlSe x polyhedra. Together with DSC results, these data favor a structure that is at least partially segregated and/or phase separated.

Analysis of bioactive fluoride-containing calcium aluminosilicate glasses

Different decomposition methods in aqueous solutions were evaluated on their accuracy and reproducibility for the quantitative determination of the constituents of bioactive fluoride-containing glasses used in dental glass ionomer cements. The concentrations of metals can be determined rapidly and accurately by atomic absorption spectrophotometry after degrading the sample in hydrochloric or hydrofluoric acid. The latter degradation method is also suited for the determination of Si. F can be determined with an ion-selective electrode after degrading the samples in 0.5 M HCl. Higher HCl concentrations enhance the risk of HF release.

Review of waste glass corrosion and associated radionuclide release as a part of safety assesment of entire disposal system

Current knowledge on high-level nuclear waste glass corrosion is summarized, and remaining problems are discussed for meaningful predictions of the glass corrosion and associated radionuclide release as a part of safety assessment of entire disposal system. In recent years, much progress has been made in understanding the mechanism of waste glass corrosion in aqueous environments. Glass corrosion models based on the mechanism have been developed for predicting the long-term glass performance, and they are incorporated as part of radionuclide source term in safety assessments of the disposal system. However, these results have not yet allowed meaningful predictions for the long-term release of individual radionuclides from the glass in repository environments, because mechanism of the long-term glass corrosion has not been fully understood and solubilities of actinoids and fission products under disposal conditions are rather uncertain. In addition, the most serious problem is that the effects of various reactions and interactions occurring in the engineered barrier system, such as corrosion of overpack, alteration of backfill and chemical interactions of the released glass constituents with them have not been fully coupled with the glass performance. These reactions may be dominant processes controlling the glass corrosion and associated radionuclide release for the long-term. For the meaningful predictions, we must evaluate the waste glass performance in combination with the effects of various reactions and interactions occurring in the engineered barrier system on the basis of fully understanding of the chemical and geochemical mechanisms.

ジルコニア・セラミックスに対するキャスタブル・セラミックスの鋳接 加熱処理の影響

In order to apply UCC to post and cores or bridges, sintered zirconium (3Y 20 A) was selected as the reinforcing material. In order to combine cast OCC to 3 Y 20 A, it is necessary to line them with dental porcelain as a binder. In order to determine a higher bonding strength, this study was conducted to observe diffusing of ion, to discuss strength of 3Y 20 A itself and bonding strength, and to apply heat treatment (Ht) to the 3Y 20 A specimen bonded to dental porcelain. The results were as follows:1. K and Na ion diffused from dental porcelain to 3Y 20 A at 1, 200°C and 1, 400°C respectively.2. The permeation of glass constituents of porcelain into 3Y 20 A, and the formation of the reacted layerwith growth and transformation of crystalline grains were found according to diffused area at 1, 400°C This factor is improper because the strength of the reacted layer is less than that of dental porcelain.3. Annealing after machining 3Y 20 A is necessary because the strength of surface transformation increased by machining and decreased due to mutual transformation at 1, 200°C.4. In this bonding strength 3Y 20 A/OCC test, Duceratin opaque had a maximum value of 1, 200°C.

Hydroxyapatite ceramics with selected sintering additives

Several sintering additives for hydroxyapatite (HA) have been tested in order to enhance its sinterability without decomposing the HA and/or decreasing bioactivity and biocompatibility, additionally providing a weak interface for HA ceramics. The ion species of sintering additives were selected from those in the mineral constituents of hard tissues and bioactive glasses. After investigation of phase diagrams in the CaO-P 2O 5-additive systems, and analysis of physicochemical properties of the additives, several sintering aids for HA have been chosen. Subsequently, densification, phase composition, grain growth and fracture behaviour of HA containing 5wt% of each additive, sintered at 1000–1100 °C, have been studied. H 3BO 3, CaCl 2, KCl, KH 2PO 4, (KPO 3) n and Na 2Si 2O 5 did not enhance densification of HA. K 2CO 3, Na 2CO 3, KF and sodium phosphates improved the densification significantly. Except for KCl and some sodium phosphates, all the additives caused formation of large quantities of undesired β-tricalcium phosphate or CaO; therefore, they are not appropriate for HA. In the case of sodium phosphate additives, it was possible to avoid formation of CaO or β-tricalcium phosphate by control of the additive quantity and chemical composition. β-NaCaPO 4 has been found to be an effective sintering agent which causes neither decomposition of HA nor formation of other undesired phases.

Particle Size Distribution of Colloids Released in Leachate from Fully Radioactive Waste Glass.

In this study, we have measured the particle size distribution of colloids containing radionuclides and glass constituent elements in the leachate from fully radioactive waste glass using filtration techniques. The fully radioactive waste glass was prepared from high-level liquid waste from the Tokai Reprocessing Plant

Microstructural Evolution of Copper Thick Films Observed by Environmental Scanning Electron Microscopy

A generic copper thick film ink system was formulated to be representative of the inks currently used in industry. The microstructural evolution of two of the copper‐based inks based on the generic composition was investigated using an environmental scanning electron microscope (ESEM) equipped with a hot stage. The first ink, consisting of copper and organic constituents (binder and solvent), oxidized heavily during firing while the second ink, consisting of copper, glass, and organic constituents, oxidized only slightly. The sequence of events observed in firing the ink comprised of copper, glass, and organics is as follows: The burnout process reached completion by about 320°C. Copper oxidation was observed to occur between 500° and 600°C in nitrogen. The glass was observed to soften over the same temperature range. By 700°C, the glass had softened and coated the copper particles. Prior to glass softening, oxidation occurred regardless of the presence of the glass. However, once the glass had softened, copper oxidation was retarded. Cu2O was found to be sufficiently soluble in the glass to allow it to be removed from the surfaces of the copper particles. Thus, the presence of glass facilitated the formation of conductive paths by two mechanisms. It inhibited oxidation and it dissolved the oxide that formed. Both processes allowed effective sintering.

A Glass Durability Model Based on Understanding Glass Chemistry and Structural Configurations of the Glass Constituents

AbstractAn improved structural bond strength (SBS) model has been developed to quantify the correlation between glass compositions and their chemical durabilities. The SBS model assumes that the strengths of the bonds between cations and oxygens and the structural roles of the individual elements in the glass are the predominant factors controlling the composition dependence of the chemical durability of glasses. The structural roles of oxides in glass are classified as network formers, network breakers, and intermediates. The structural roles of the oxides depend on glass composition and the redox state of oxides. A12O3, ZrO2, Fe2O3, and B2O2 are assigned as network formers only when there are sufficient alkalis to bind with these oxides. CaO can also improve durability by sharing non-bridging oxygen with alkalis, relieving Si0 2 from alkalis. The binding order to alkalis is AI2O3>ZrO2>Fe2O 2>B2O2>CaO>SiO2. The percolation phenomenon in glass is also taken into account. The concentration of network formers has to reach a critical value for a glass to become durable; durable glasses are sufficient in network formers and have a complete network structure; poor durability glasses are deficient in network formers and the network is incomplete and discontinuous. The SBS model is capable of correlating the 7-day product consistency test durability of 42 low-level waste glasses with their composition with an R2 of 0.87, which is better than 0.81 obtained with an eight-coefficient empirical first-order mixture model on the same data set.

Mössbauer spectra of tin in float glass

Tin is not a major constituent of window glass, but is found at high concentrations in the lower surface of float glass which has been in contact with the molten tin bath. It does not extend far into the surface, but causes the physical and chemical behaviour to differ from that of the upper surface. It is important, therefore, to understand the structural role of tin in silicate glasses and thus its effect on various properties. Mossbauer spectra were taken of three series of glassy materials, namely binary glasses (SnO and SiO2) in varying proportions, re-melted float glass containing tin, and float glass from a production plant. The binary glasses contained between 20 and 70% tin which was found to be mainly Sn2+, with very small amounts of Sn4+ in some of them. The spectra showed a small decrease in isomer shift with increase in tin content, which is ascribed to the change in molar volume. The re-melted samples were float glass which was mixed with stannous oxalate in appropriate conditions to try and maintain tin in the 2+ state, and contained up to 15% tin by weight. The spectra show both Sn4+ and Sn2+ with rather more in the 4+ oxidation state. The change in the spectra as a function of temperature revealed a large difference in thef-factor (and hence the chemical binding) of the two states. A series of spectra was taken between 17.5 and 900 K for the sample containing 15% tin. From the absorption as a function of temperature thef-factor was determined for both oxidation states, and hence enabled the relative amounts of Sn4+ and Sn2+ present in each sample to be estimated. Measurements of the shift as a function of temperature were also made. The float samples were surface material produced by grinding away all but 0.1 mm of the lower surface of industrially produced float glass. The Mossbauer spectra showed them to be predominantly Sn2+, as expected from the reducing atmosphere in the float plant. The concentration and oxidation state of the tin may be estimated from the value of thef-factors and isomer shifts.

Temperature-induced changes in the composition of floatglass surfaces.

Floatglass is an important kind of commercial glass, comprising the main body of modern flat glass used in buildings and vehicles. The stoichiometry of the surface layer differs from that of the bulk and will usually change due to subsequent high-temperature process steps or attack by water or humidity. Glass samples have been investigated by means of ion beam analysis. Using resonant nuclear reaction analysis ((15)N technique), hydrogen concentration profiles have been determined. Profiles of the heavier glass constituents, especially sodium and tin, have been obtained by RBS. Changes in the composition of the floatglass surfaces caused by subsequent temperature treatment (up to 700 ( degrees )C) and by controlled hydration treatment are reported. Possible mechanisms of hydrogen uptake and release are discussed.

Interfacial reactions between glass coatings and steel substrates induced by laser cladding

Interfacial reactions between glass and metal have not yet been clarified. On the basis of a composition determination using electron probe microanalysis, the present paper investigates interfacial reactions glass coatings and carbon steel or commercial pure iron substrates induced by laser cladding. The interfacial redox reactions take place between the glass coatings and the substrates at elevated temperatures prevailing in the melt pool under laser irradiation because of the physical chemical property difference between the glass melt and the substrates. As a result,the Fe and C in the substrates are oxidized; the glass constituents Na 2O, K 2O, CaO, SiO 2, Al 2O 3, CoO and NiO are reduced. The glass phase has penetrated into the substrates, especially the carbon steel substrate. This results because the substrates are corroded and dissolved along grain boundaries or into the grain bulk by glass melt during laser cladding.

Hydrodesulfurization of model systems using slurry-phase catalysts

An attempt has been made to assess the accuracy of the particle-induced X-ray emission (PIXE) fundamental parameters with standards approach to quantifying major- and minor-element constituents of silicate glasses and minerals. A deviation from linearity at low energies in the channel-energy calibration relationship was identified as a source of undesired residues in GUPIX-fitting. A correction for this effect was developed using a general-purpose spectrum fitting program and was incorporated in GUPIX. The PIXE spectra of sixteen well-characterized electron microprobe standards were then processed. Complementary electron probe micro-analysis (EPMA) measurements were used to support the comparison of the PIXE results with previous characterizations. Major element concentrations were found to differ on average from literature values as follows: SiO2 (−0.28 ± 0.12%), Al2O3 (0.72 ± 0.74%), MgO (0.11 ± 0.63%), Na2O (−2.6 ± 1.2%), K2O (1.1 ± 0.7%), CaO (−0.35 ± 0.37%), TiO2 (2.5 ± 1.9%), MnO (0.8 ± 4.7%), FeO (0.98 ± 0.93%). These results indicate that major and minor elemental analysis can be achieved with high accuracy using the present Guelph micro-PIXE setup.