Glassy Forms Research Articles

Multiphase synergistic immobilization of complex trialkyl phosphine oxide end-waste into an iron-containing aluminosilicate glass-ceramic

The objective of this study was to address the challenges associated with complex TRPO waste, by utilizing a natural aluminosilicate material to produce glass-ceramic waste forms. When the simulated waste content was below 30 wt.%, glassy waste forms were successfully obtained. Ce and Fe played crucial roles in the formation of Si–O–Ce bonds and [FeO4]-tetrahedra in the glass network, which effectively immobilized other waste elements. However, when the waste content exceeded 30 wt.%, the waste was incorporated into feldspar, iron-manganese crystals, fluorite ceramic, and glass. This combination of ceramic and glass matrices synergistically immobilized the waste, resulting in excellent mechanical performance and chemical durability. The leaching rates of LRCe and LRNd were remarkably low around ∼10−6 to 10−7 g m−2 d−1, after 42 d. Furthermore, the study also investigated the role of multi-valence elements, such as Ce, Fe, and Mn, in the formation of iron-containing aluminosilicate glass-ceramics. The findings offer a novel approach to effectively immobilize complex nuclear waste.

Fast heating inhibits endothermic solid-solid polymorphic transition giving a melting of low temperature polymorph with the next cold crystallization

Heating at the rate of several hundred Kelvin per second in fast scanning calorimetry (FSC) experiments was found to change the route of polymorphic transformation. Upon the increase of the heating rate first the endothermic solid-state polymorphic transition is hindered to give a consecutive melting of low-temperature form and crystallization of high temperature polymorph. At higher heating rates, only melting of low-temperature polymorph is observed much below an equilibrium melting point. This thermal behavior with depression of final melting point by 30 K was observed for tert‑butylthiacalix[4]arene tetrasubstituted with (ethoxycarbonyl)methoxy groups (1), which does not sublimate at heating. A similar shift of the endothermic solid-state polymorphic transition by temperature at fast heating was found for caffeine (2), however the melting of low-temperature polymorph is not observed due to sublimation of the compound at elevated temperatures. The heating rates, at which a significant depression of the melting points of 1 and 2 may be expected in absence of sublimation, were calculated using equations of thermal kinetics derived from the data of conventional differential scanning calorimetry. The results give a practical guide for the preparation of glassy forms of the substances capable of endothermic solid-solid transition below melting point of high-temperature form.

Analysis of Vibrational Spectra of Tetrafluoroethane Glasses Deposited by Physical Vapor Deposition.

This paper presents the results obtained in the study of structural phase transitions in thin films of R134A. The samples were condensed on a substrate by physical deposition of R134A molecules from the gas phase. Structural phase transformations in samples were investigated by observing the changes in characteristic frequencies of Freon molecules in the mid-infrared range with the help of Fourier-transform infrared spectroscopy. The experiments were carried out in the temperature range from 12 to 90 K. A number of structural phase states, including glassy forms, were detected. The changes in thermogram curves at fixed frequencies of half-widths of absorption bands of R134A molecules were revealed. These changes indicate a large bathochromic shift of these bands at frequencies of ν = 842 cm-1, ν = 965 cm-1, and ν = 958 cm-1 and a hypsochromic shift of the bands at frequencies of ν = 1055 cm-1, ν = 1170 cm-1, and ν = 1280 cm-1 at temperatures from T = 80 K to T = 84 K. These shifts are related to the structural phase transformations in the samples.

Phase separation in mullite-composition glass

Aluminosilicates (AS) are ubiquitous in ceramics, geology, and planetary science, and their glassy forms underpin vital technologies used in displays, waveguides, and lasers. In spite of this, the nonequilibrium behavior of the prototypical AS compound, mullite (40SiO2-60Al2O3, or AS60), is not well understood. By deeply supercooling mullite-composition liquid via aerodynamic levitation, we observe metastable liquid–liquid unmixing that yields a transparent two-phase glass, comprising a nanoscale mixture of AS7 and AS62. Extrapolations from X-ray scattering measurements show the AS7 phase is similar to vitreous SiO2 with a few Al species substituted for Si. The AS62 phase is built from a highly polymerized network of 4-, 5-, and 6-coordinated AlOx polyhedra. Polymerization of the AS62 network and the composite morphology provide essential mechanisms for toughening the glass.

Preparation and characterization of glassy waste forms based on SrF2-Fe2O3-PbO/Bi2O3-P2O5 system

Glassy waste forms based on SrF2-Fe2O3-PbO/Bi2O3-P2O5 system were prepared by using a one-step melting quench method. Glass forming ability, actual composition, structure and thermal stability of the samples were studied by using X-Ray fluorescence (XRF) spectroscopy, X-Ray diffractometry (XRD), infrared spectroscopy (IR), dilatometry and differential thermal analysis (DTA). Water resistance of the samples was evaluated by using dissolution rate and Product Consistency Test (PCT) methods. Melting temperature of the simulated 90SrF2 waste forms was reduced to 1000–1050 °C and their melting time was shortened to 0.5 h. Water resistance of the waste forms met the requirements of national industrial standard EJ1186–2005, while their thermal stability was much higher than those of the phosphate waste forms vitrified with >20 wt.% halide wastes reported in the open literature. It is concluded that waste forms with mixed structure of orthophosphate and pyrophosphate glasses have high water resistance and high thermal stability.

Geochemistry of aerodynamically distorted Australasian microtektites: Implications for ejecta on Mars and Venus

We report microtektites recovered from a large area of the deep seafloor (Central Indian Ocean) that appear to have undergone aerodynamic distortion during re-entry into the atmosphere. Considering the geographic locations, stratigraphic position and chemical compositions these glassy forms belong to the Australasian tektite strewn field. The microtektites are elongated to lengths of cms, sometimes flattened, bent, folded and fused at both ends suggesting that this side could have been the Earth-facing side during the re-entry. The presence of flow lines and distortional features are indicative of high atmospheric pressures experienced by the microtektites. The location where these microtektites were recovered constitute distal ejecta, and the shape distortion, that occurred during re-entry of the ejecta, seems to have affected only a few amongst the extensive collection of microtektites. Most of the specimens contain lechatelierite inclusions and higher volatile oxides, which are indicative of incomplete homogenization after melting and lower temperatures of formation vis-a-vis other specimens at the same location. The element distribution patterns in aerodynamically distorted microtektites suggest that ablation was similar to normal spherical tektites in which volatile elements are preserved. In contrast, aerodynamically ablated forms of Australasian ejecta show skin melting where thin layers of the anterior portions of samples flow back giving rise to the familiar button shapes. Our observation of delicate, elongated, flattened, and viscously deformed specimens is perhaps the first to imply that at the distal end of ejecta, each spot in the specimens has undergone different levels of trajectories, heating and ablation. These investigations could have implications to understand ejecta emplacement characteristics on planetary surfaces that contain appreciable atmospheres such as Mars and Venus.

The fate of Si and Fe while nuclear glass alters with steel and clay

The French concept developed to dispose high-level radioactive waste in geological repository relies on glassy waste forms, isolated from the claystone host rock by steel containers. Understanding interactions between glass and surrounding materials is key for assessing the performance of a such system. Here, isotopically tagged SON68 glass, steel and claystone were studied through an integrated mockup conducted at 50 °C for 2.5 years. Post-mortem analyses were performed from nanometric to millimetric scales using TEM, STXM, ToF-SIMS and SEM techniques. The glass alteration layer consisted of a crystallized Fe-rich smectite mineral, close to nontronite, supporting a dissolution/reprecipitation controlling mechanism for glass alteration. The mean glass dissolution rate ranged between 1.6 × 10−2 g m−2 d−1 to 3.0 × 10−2 g m−2 d−1, a value only 3–5 times lower than the initial dissolution rate. Thermodynamic calculations highlighted a competition between nontronite and protective gel, explaining why in the present conditions the formation of a protective layer is prevented.

Synthesis and characterization of Co–B–Fe–Ti nanosized alloyed powders

AbstractIn this study, novel Co60Fe18Ti18B4alloy powders have been synthesized with high compositional homogeneity using a high-energy ball milling technique. The structural, morphological and mechanical properties of the nanosized alloyed powders were examined using different analytical techniques, including scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectrometry and X-ray diffraction. According to the X-ray diffraction analysis for both Co powder and Co60Fe18Ti18B4alloy powders, with increasing milling time, the content of Co-based (hcp) solid solution decreased and Co-based (fcc) solid solution increased. The mechanical properties of the material were also investigated by Vickers micro-hardness testing. The micro-hardness value of the Co60Fe18Ti18B4alloy was found as 120.08 HV. After sintering (1 h– 1000 °C), the hardness improved remarkably (536.32 HV). Furthermore, results indicate that the synthesized Co-based alloy powder has both glassy and nanocrystalline phase forms.

Differentiating Fukushima and Nagasaki plutonium from global fallout using 241Pu/239Pu atom ratios: Pu vs. Cs uptake and dose to biota

Plutonium (Pu) has been released in Japan by two very different types of nuclear events – the 2011 Fukushima accident and the 1945 detonation of a Pu-core weapon at Nagasaki. Here we report on the use of Accelerator Mass Spectrometry (AMS) methods to distinguish the FDNPP-accident and Nagasaki-detonation Pu from worldwide fallout in soils and biota. The FDNPP-Pu was distinct in local environmental samples through the use of highly sensitive 241Pu/239Pu atom ratios. In contrast, other typically-used Pu measures (240Pu/239Pu atom ratios, activity concentrations) did not distinguish the FDNPP Pu from background in most 2016 environmental samples. Results indicate the accident contributed new Pu of ~0.4%–2% in the 0–5 cm soils, ~0.3%–3% in earthworms, and ~1%–10% in wild boar near the FDNPP. The uptake of Pu in the boar appears to be relatively uninfluenced by the glassy particle forms of fallout near the FDNPP, whereas the 134,137Cs uptake appears to be highly influenced.Near Nagasaki, the lasting legacy of Pu is greater with high percentages of Pu sourced from the 1945 detonation (~93% soils, ~88% earthworm, ~96% boar). The Pu at Nagasaki contrasts with that from the FDNPP in having proportionately higher 239Pu and was distinguished by both 240Pu/239Pu and 241Pu/239Pu atom ratios. However, compared with the contamination near the Chernobyl accident site, the Pu amounts at all study sites in Japan are orders of magnitude lower. The dose rates from Pu to organisms in the FDNPP and Nagasaki areas, as well as to human consumers of wild boar meat, have been only slightly elevated above background. Our data demonstrate the greater sensitivity of 241Pu/239Pu atom ratios in tracing Pu from nuclear releases and suggest that the Nagasaki-detonation Pu will be distinguishable in the environment for much longer than the FDNPP-accident Pu.

Influence of long-term aqueous leaching of irradiated graphite on surface properties and behavior of radionuclides

AbstractSamples of real irradiated (i-)graphite from bushings of RBMK reactor after several types of decontamination treatments were put in contact with aqueous solutions modelling underground water of Nizhnekansky massif (Russia) equilibrated with bentonite for periods up to 1.5 years. Leach rates of radionuclides and evolution of graphite surface morphology and oxidation state were monitored using nuclear spectroscopy, SEM and XPS. After the experiment, less than one third of surface carbons remains unoxidised. Extensive precipitation of secondary phases (alumosilicates, carbonates) was observed on some samples and is possibly correlated with surface oxidation extent. The leach rates of dose-forming 14C and 36Cl are comparable with the leach rates of radionuclides in glassy waste forms. According to the current study i-graphite could be regarded as a waste form, which is suitable for near-surface disposal.

Compositional Dependence of Solubility/Retention of Molybdenum Oxides in Aluminoborosilicate-Based Model Nuclear Waste Glasses.

Molybdenum oxides are an integral component of the high-level waste streams being generated from the nuclear reactors in several countries. Although borosilicate glass has been chosen as the baseline waste form by most of the countries to immobilize these waste streams, molybdate oxyanions (MoO42-) exhibit very low solubility (∼1 mol %) in these glass matrices. In the past three to four decades, several studies describing the compositional and structural dependence of molybdate anions in borosilicate and aluminoborosilicate glasses have been reported in the literature, providing a basis for our understanding of fundamental science that governs the solubility and retention of these species in the nuclear waste glasses. However, there are still several open questions that need to be answered to gain an in-depth understanding of the mechanisms that control the solubility and retention of these oxyanions in glassy waste forms. This article is focused on finding answers to two such questions: (1) What are the solubility and retention limits of MoO3 in aluminoborosilicate glasses as a function of chemical composition? (2) Why is there a considerable increase in the solubility of MoO3 with incorporation of rare-earth oxides (for example, Nd2O3) in aluminoborosilicate glasses? Accordingly, three different series of aluminoborosilicate glasses (compositional complexity being added in a tiered approach) with varying MoO3 concentrations have been synthesized and characterized for their ability to accommodate molybdate ions in their structure (solubility) and as a glass-ceramic (retention). The contradictory viewpoints (between different research groups) pertaining to the impact of rare-earth cations on the structure of aluminoborosilicate glasses are discussed, and their implications on the solubility of MoO3 in these glasses are evaluated. A novel hypothesis explaining the mechanism governing the solubility of MoO3 in rare-earth containing aluminoborosilicate glasses has been proposed.

Allegories of Creation: Glassmaking, Forests, and Fertility in Webster’sThe Duchess of Malfi

Allegories of Creation: Glassmaking, Forests, and Fertility in Webster’s<i>The Duchess of Malfi</i>

Vermicular kaolinite relics in fly ash derived from Bokaro and Jharia coals (Jharkhand, India)

During a study of fly ash from two pulverized fuel power plants (Bokaro and Chandrapura) burning coal from the Bokaro Coalfield in Jharkand state, India, glassy and vermicular mineral forms were found associated with the char. A combination of optical microscopy, XRD, SEM/EDS, and XRF analysis has shown that this morphotype, reported here for the first time, originated from kaolinite that expanded during heating inside the furnace chamber under relatively low combustion temperatures. The morphotype has an internal structure that resembles the fanning-out structure formed during vermicular kaolinite development.

Correlation of some opto-electrical properties of Se–Te–Sn glassy semiconductors with the average single bond energy and the average electronegativity

Studies of some electrical and optical properties of Se90Te10−xSnx (x = 2, 4, 6 and 8) glassy alloys, in bulk and thin film forms, were performed at room temperature. Pellets of a diameter ∼1.3 cm and different thicknesses ranging from 0.04 cm to 0.06 cm of these compositions were obtained. Measurements of I–V characteristics of these pellets have been carried out at room temperature. Ohmic behavior was observed in low voltage range (0–5 V) while a deviation from ohmic towards non-ohmic behavior was observed at higher voltage range (6–20 V). This deviation can be interpreted in terms of space charge limited conduction (SCLC) mechanism whereas the plots of ln (I/V) vs. V were found to be straight lines. The room temperature DC electrical conductivity σDC has been calculated from the linear region of the I–V characteristic curves. In addition, thin films of a thickness ∼1100 Å of the alloys under investigation were prepared and the optical band gap Eopt of these thin films is obtained from Tauc plot (αhν)2 = B (hν − Eopt) after the determination of the absorption coefficient α over a wavelengths range of 440–1100 nm. Analysis of the experimental data shows that σDC increases while Eopt decreases with increasing Sn content. These results are explained in terms of the decrease in the values of average single bond energy HS/<r> and average electronegativityχm.

Investigation of Nitramine‐Based Amorphous Energetics

AbstractTo date, the use of high explosives (HEs) has been largely limited to their crystalline forms. The glassy forms of these materials have not received much attention. While the highest density and stability of HEs is only attainable in the crystalline state, the unique properties exhibited by glasses may offer significant practical advantages. In this work, the production and properties of glassy molecular dispersions based on CL‐20 with HMX and polyvinyl acetate additives were investigated. The glassy form was achieved by rapid precipitation of the composite ingredients using spray drying. The role of the additives on glass formation was examined. Characterization revealed multiple novel properties in comparison to the traditional crystalline HE‐based compositions. Differential scanning calorimetry (DSC) analysis showed that in the glassy state the materials have a higher configurational enthalpy, by as much as 42 J g−1. Thermomechanical analysis (TMA) results indicate that the glassy materials undergo a glass transition at around 50 °C, during which a transformation from a rigid to a liquid‐like state occurs. The glasses showed a tendency to crystallize, as was observed with TMA and DSC analysis. It was observed that the stability of the amorphous phase with respect to crystallization improved with increasing pellet density. These findings serve to highlight the unique opportunity presented by glassy energetics to achieve improvements beyond those attainable with traditional crystalline materials.

Comparative study of the rare earth environment in rare earth metaborate glass (REB3O6, RE = La, Nd) and in sodium borate glasses

The RE environment in the RE-metaborate glass (RE=La3+ or Nd3+) has been characterized by Nd LIII-edge EXAFS and Nd3+ and Eu3+ optical spectroscopy. The spectroscopic data have been compared with that of crystalline RE-metaborate and of two sodium borate glasses containing RE, a Na-poor borate glass (20mol% Na2O) bearing almost no NBOs (non-bridging oxygens), and a Na-rich borate glass (35mol% Na2O) bearing a significant number of NBOs. Spectroscopic data indicate that the RE–O ionicity and mean distance increase in the order Na-rich borate glass<RE-metaborate glass<Na-poor borate glass<RE-metaborate crystal. The distribution of RE3+ sites in the RE-metaborate glass is wider than in the two sodium borate glasses, as revealed by a larger RE–O distance distribution and larger inhomogeneous widths of optical transitions. Data are consistent with a model in which both NBOs and BOs take part to the coordination sphere of RE3+, like in the crystalline RE-metaborate phase, but they point out stronger RE3+–NBO bonds. The structural and bonding differences involving the RE3+ ions, between the glassy and crystalline forms of RE-metaborate, may be the basis of the high nucleation barrier observed in this congruent composition.

Crystallization Kinetics of Fe76.5−x C6.0Si3.3B5.5P8.7Cu x (x = 0, 0.5, and 1 at. pct) Bulk Amorphous Alloy

The influence of Cu on crystallization kinetics of Fe76.5−x C6.0Si3.3B5.5P8.7Cu x (x = 0, 0.5, and 1 at. pct) bulk amorphous alloys was investigated by isothermal and isochronal differential scanning calorimetry combined with X-ray diffraction. The thermal analysis revealed that the crystallization of the amorphous matrix proceeds through at least two exothermic events. The Cu-free glassy alloy forms by primary crystallization the metastable Fe23C6 phase, while upon 0.5 at. pct Cu addition the primary crystallized phase is α-Fe. The activation energy for crystallization, calculated using both Kissinger and Ozawa methods, decreases from about 500 kJ/mol to about 330 kJ/mol. Further increase of Cu addition to 1 at. pct promotes the concomitant crystallization of several phases, as α-Fe, FeB, Fe3C, and Fe2P. In order to understand the crystallization behavior of the alloys as a function of Cu content, the Avrami exponent n, evaluated from the Johnson–Mehl–Avrami equation, was in details analyzed. The current study reveals that the minor Cu addition plays a crucial role at the initial stage of the crystallization. Among the studied alloys, the glassy samples with 0.5 at. pct Cu addition have the optimum compositional condition for the single α-Fe formation with a high nucleation rate.

Vitreous and Crystalline Phosphates : elaboration and electrical properties

Interest in mixed metals titanium phosphates, both in glass and crystalline forms, for their properties as ionic conductors or non-linear optical materials, has led to large number of studies of these materials [1-3]. Our investigation of Na2O – Li2O – CaO – TiO2 – P2O5 system led to the discovery of NaxLiyCazTit(PO4)3 solid solutions which exist in both glassy and crystalline forms. Here the preparation of NaxLiyCazTit(PO4)3 will be described. The compounds were structurally characterized by PXRD, and their chemical and physical characterization were completed using DTA, XRD, UV-visible, Raman spectroscopy and ionic conductivity measurements. NaxLiyCazTit(PO4)3 glasses have been prepared by heating stochiometric amounts of Na2CO3, Li2CO3, CaCO3, TiO2 and NH4H2PO4 in a platinum crucible at 10500C. The microcrystalline samples were obtained by crystallization of the corresponding glasses at 6400C or by standard solid state preparation at 7000C. The values of the characteristic temperatures Tg (glass transition), Tc (crystallization) and Tf (fusion) of the glasses are found in the following ranges: 400 – 5000C for Tg, 440 – 6500C for Tc and 780 – 8300C for Tf. Rietveld refinements of powder X ray diffraction data collected on crystalline samples of NaxLiyCazTit(PO4)3 shows the existence of a solid solution in the domain 0 ≤ X ≤ 0.5 and the presence of a mixture of phases in the domain 0.5 &lt; X ≤ 1.5. The crystalline phases belong to the Nasicon family, space group R32. Their structure, determined from refinement of powder diffraction patterns , consists of a 3D network of AO6 (A = Ti, Na, Li, and Ca) octahedra and PO4 tetrahedra linked by corners. Sodium atoms fully occupy the M(1) sites and partially the M(2) sites.

Polymorphism and polyamorphism in bilayer water confined to slit nanopore under high pressure.

A distinctive physical property of bulk water is its rich solid-state phase behavior, which includes 15 crystalline (ice I-ice XIV) and at least 3 glassy forms of water, namely, low-density amorphous, high-density amorphous, and very-high-density amorphous (VHDA). Nanoscale confinement adds a new physical variable that can result in a wealth of new quasi-2D phases of ice and amorphous ice. Previous computer simulations have revealed that when water is confined between two flat hydrophobic plates about 7-9 Å apart, numerous bilayer (BL) ices (or polymorphs) can arise [e.g., BL-hexagonal ice (BL-ice I)]. Indeed, growth of the BL-ice I through vapor deposition on graphene/Pt(111) substrate has been achieved experimentally. Herein, we report computer simulation evidence of pressure-induced amorphization from BL-ice I to BL-amorphous and then to BL-VHDA(2) at 250 K and 3 GPa. In particular, BL-VHDA(2) can transform into BL-VHDA(1) via decompression from 3 to 1.5 GPa at 250 K. This phenomenon of 2D polyamorphic transition is akin to the pressure-induced amorphization in 3D ice (e.g., from hexagonal ice to HDA and then to VHDA via isobaric annealing). Moreover, when the BL-ice I is compressed instantly to 6 GPa, a new very-high-density BL ice is formed. This new phase of BL ice can be viewed as an array of square ice nanotubes. Insights obtained from pressure-induced amorphization and crystallization of confined water offer a guide with which to seek a thermodynamic path to grow a new form of methane clathrate whose BL ice framework exhibits the Archimedean 4⋅8(2) (square-octagon) pattern.

Strongly Nonlinear Optical Glass Fibers from Noncentrosymmetric Phase-Change Chalcogenide Materials

We report that the one-dimensional polar selenophosphate compounds APSe(6) (A = K, Rb), which show crystal-glass phase-change behavior, exhibit strong second harmonic generation (SHG) response in both crystal and glassy forms. The crystalline materials are type-I phase-matchable with SHG coefficients chi((2)) of 151.3 and 149.4 pm V(-1) for K(+) and Rb(+) salts, respectively, which is the highest among phase-matchable nonlinear optical (NLO) materials with band gaps over 1.0 eV. The glass of APSe(6) exhibits comparable SHG intensities to the top infrared NLO material AgGaSe(2) without any poling treatments. APSe(6) exhibit excellent mid-IR transparency. We demonstrate that starting from noncentrosymmetric phase-change materials such as APSe(6) (A = K, Rb), we can obtain optical glass fibers with strong, intrinsic, and temporally stable second-order nonlinear optical (NLO) response. The as-prepared glass fibers exhibit SHG and difference frequency generation (DFG) responses over a wide range of wavelengths. Raman spectroscopy and pair distribution function (PDF) analyses provide further understanding of the local structure in amorphous state of KPSe(6) bulk glass and glass fiber. We propose that this approach can be widely applied to prepare permanent NLO glass from materials that undergo a phase-change process.