Glassy Matrix Research Articles

Utilization of waste glass with natural pozzolan in the production of self-glazed glass-ceramic materials

Abstract Significant self-glazed glass-ceramic was obtained from a natural pozzolan and external glass cullet. Natural pozzolan with/without glass cullet was fused to glass melt that quenched in water to glass frits. The dried glass frits were pulverized (<0.083 mm) and then shaped in a stainless mold. The thermal behavior of the glasses shows a widening of the crystallization temperature with the incorporation of the glass cullet between ∼800 and 950°C. Sintering of the shaped glass powder at 1,050°C/2 h lead to the crystallization of augite, enstatite, cristobalite, and hematite. The microcrystalline structure shows massive texture with pores in-between; however, at high magnification regular euhedral to subhedral crystals in submicron to nearly submicron size was developed in the glassy matrix and their microanalysis indicates the dominant augite. The density of the glass-ceramic samples decreases from 2,706 to 2,539 kg/m3 with the incorporation of glass wastes. The sample surfaces show, through force electron microscopy, the fineness and smoothness of the grains with the incorporation of the glassy portion. The microhardness values were between 6.43 and 6.11 GPa. The coefficient of thermal expansion increased from 32.87 (25–300°C) to 66.89 (25–500°C) × 10−7°C−1. The chemical resistance of samples in water (0.0002–0.0016) is better than in an acidic medium (0.0011–0.0017). These glass-ceramic enjoy good density, hardness, and thermal expansion and can be used in the ceramic industry and cladding walls and floors.

Influence of Pr[formula omitted] ions on the structural properties of Er[formula omitted]-doped tellurite-tungsten glasses

An understanding of the optical, thermal and structural properties of tellurite glasses is necessary for the development of new technological applications. Previous works have already been published studying the properties mentioned above, however, the mechanism of modification of the glassy structure due to the addition of rare earth ions is still an open topic in materials science. In this paper, we report the mechanisms of structural modification of the Er3+ and Pr3+-doped glass tellurite-tungsten system through a systematic study. TeO2–ZnO–WO3–GeO2 glasses codoped with Er2O3 and varying the content of Pr2O3, was prepared by the conventional melt-quenching technique and studies of its structural, thermal and spectroscopic properties were carried out. The direct and indirect bandgap energies and the Urbach energy evidence an increase in the structural disorder of the glassy matrix due to the deformation of the TeO linkages by the insertion of Pr3+ ions in the sample can be suggested. Raman spectroscopy results showed an increase in TeO3+1 and TeO3 compared to TeO4 when the Pr2O3 doping was increased, modifying the structural coordination in TeO2, generating non-bridging oxygens. Raman spectroscopy in low-frequencies shows the Boson peak changed with the increase in the concentration of Pr3+. Furthermore, was obtained that transverse modes predominate in low Raman frequencies. This work suggests that the presence of Pr3+ ions influences the optical and thermal properties, in addition to altering the local glassy structure, generating a change in the coordination of network formers such as TeO2.

INTERPRETATION OF THE MAGMA CHAMBER PROCESSES USING MICRO-TEXTURE AND ZONING STYLES IN PLAGIOCLASE CRYSTALS: EVIDENCE FROM THE ANDESITIC ROCKS IN SABZEVAR ZONE (NE IRAN)

Investigation of variations in the micro-texture and chemical composition of plagioclases (core to rim) allows the sequencing of the magma chamber processes and helps interprete and associate textures to specific processes. In this contribution, the micro-textures and chemical zoning of the plagioclases, significant recorder of magma chamber processes, from the west of Torbat-e-Heydariyeh andesitic rocks (WTHAR) are considered to decipher the physical and chemical parameters of magma evolution. The rocks are cropped out in the northern branch of Neotethyan magmatic belt and considered as the products of Eocene magmatic activities of the Sabzevar zone (N-NE Iran). The rocks show vitrorphyric and vitroglomeroporphyric textures with main phenocrysts, plagioclase (andesine, labradorite, and bytownite), clinopyroxene (augite), orthopyroxene and magnetite scattered in a glassy matrix. The recognized micro-textures of the WTHA plagioclases can be divided into two categories: (i) growth- related textures in the form of coarse-sieved (CS), fine-sieved (FS), core sieved and intact margin (CSIM), core intact and sieved margin (CISM) and entirely sieved (ES) morphologies, oscillatory zoning (OZ), rounded zone corner (RZC) and resorption surfaces (RS) formed due to the changes in temperature, melt H2O content, pressure, composition of the melt, equilibrium at the crystal-melt interface and (ii) morphological textures such as glomerocrysts (GLO), synneusis (SY), swallow-tail (ST) crystals, broken crystals (BC), formed by the effect of dynamic behavior of the crystallizing magma (convection, degassing, etc.) and magmatic differentiation. Also, the occurrence of these changes can be related to the self-mixing process in the magma chamber. The self-mixing with recharge event can be the reason for the dynamic activities in the magma chamber.

Mineralogy, geochemistry, and genesis of lithium-bearing argillaceous sediments associated with the Neogene Bigadiç borate deposits, Balıkesir, western Anatolia, Türkiye

The Li-bearing claystone and carbonate are sedimentary rocks deposited in the lacustrine environment hosting the Bigadiç borate deposits in western Anatolia. The purpose of this paper is to explain the mineralogical, geochemical, stable isotope characterizations and formation of Li-rich claystone (hectorite, saponite), and have strategic, technological, and economic importance for the country's economy, which have not been sufficiently studied previously. In the rhyolitic and dacitic tuffs, sanidine and plagioclase crystals were altered, biotite and hornblende, Fe-oxidized, locally opaque, and chloritized in a sericitized, Fe-oxidized, argillized, calcified, and zeolitized glassy matrix. The claystone consists mainly of smectite and minor illite, volcanogenic quartz, feldspar, mica, hornblende, and occasionally calcite, aragonite, dolomite, and gypsum/anhydrite. Hectorite and saponite were determined based on the expansion of their basal peaks following heating at 500 °C and solvation with ethylen-glycol; additionally, hectorite expanded, and saponite was not affected after glycerine-saturated Cs-smectite and heating at 100 °C for 20 h. Smectite shows webby to crenulated forms, and coexist with feldspar, volcanic glass, rhomboidal calcite, blocky gypsum/anhydrite, and Fe-oxide phases. The Li values increase up to 2650 ppm in the smectite-rich claystone and marl, and up to 449 ppm in the volcanic rocks. The positive correlation of REE with each of SiO2, Al2O3, and K2O; positive correlation of MgO vs. Li, and increase of MgO + CaO, Sr, Li, LREE relative to MREE and HREE; negative Eu anomaly and high values of As and S suggest that the feldspar, mica, and hornblende alteration originating from the Miocene volcanic and pyroclastic materials and presence of gypsum/anhydrite during the hydrothermal alteration activities were the sources for the smectite formation. The high negative δ18O values of calcite, the δD and δ18O values of smectite and δ34S‰ and δ18O‰ values of gypsum, and the 87Sr/86Sr isotope ratios range of calcite and gypsum suggest the contribution of mixing meteoric and hydrothermal environmental conditions during the depositional and diagenetic process(es) in the playa lake environment.

Generation and Characterization of a Tetraradical Embedded in a Curved Cyclic Paraphenylene Unit.

Unique spin-spin (magnetic) interactions, ring-size effects on ground-state spin multiplicity, and in-plane aromaticity has been found in localized 1,3-diradicals embedded in curved benzene structures such as cycloparaphenylene (CPP). In this study, we characterized the magnetic interactions in a tetraradical consisting of two localized 1,3-diradical units connected by p-quaterphenyl within a curved CPP skeleton by electron paramagnetic resonance (EPR) spectroscopy and quantum chemical calculations. Persistent triplet species with zero-field splitting parameters similar to those of a triplet 1,3-diphenylcyclopentane-1,3-diyl diradical were observed by continuous wave (CW) or pulsed X-band EPR measurements. The quintet state derived from the ferromagnetic interaction between the two triplet diradical moieties was not detected at 20 K under glassy matrix conditions. At the B3LYP/6-31G(d) level of theory, the singlet state was lower in energy than the triplet and quintet states. These findings will aid in the development of open-shell species for material science application.

Revealing the Individual Effects of Firing Temperature and Chemical Composition on Raman Parameters of Celadon Glaze

The Raman polymerization index (or IP value) is often used as a positive indicator of the firing temperature of the glazes of ancient ceramics. Previous studies have also reported that the IP value was negatively correlated with the chemical composition of the glaze. However, these findings were derived from data on the potential integrative effects of temperature and composition. To explore their individual effects, we prepared celadon glaze samples with controlled composition and firing temperatures. Particularly, according to the typical content of K2O and CaO in celadon glaze, four categories, or, in total, fifteen compositional formulations, were designed, and each formulation was fired at multiple temperatures (from 1180 to 1250 °C by 10 °C). The chemical compositions and the glassy matrix of samples were analyzed by an energy-dispersive X-ray fluorescence spectrometer and Raman spectroscopy, respectively. A positive correlation between firing temperature and IP value (correlation coefficient = 0.56) was detected only in the samples with low contents of K2O and CaO. However, no significant correlation was found when combining the samples with broad variation in chemical composition. Additionally, both the K2O content and CaO content were negatively related to the IP value, with regression coefficients of −9.645 and −5.332, respectively. Our results help to clarify the technology of ancient ceramic production and to improve its preservation.

Stabilization of a flavoprotein for solid-state photo-CIDNP MAS NMR at room temperature by embedding in a glassy sugar matrix

Hyperpolarization via the solid-state photochemically induced dynamic nuclear polarization (photo-CIDNP) effect can be detected in frozen solutions of electron transfer proteins generating a radical-pair upon illumination. The effect has been observed in various natural photosynthetic reaction centers and in light-oxygen-voltage (LOV) sensing domains incorporating a flavin mononucleotide (FMN) as chromophore. In LOV domains, where a highly conserved cysteine is mutated to a flavin to interrupt its natural photochemistry, a radical-pair is generated by electron transfer from a nearby tryptophan to the photoexcited triplet state of FMN. During the photocycle, both the LOV domain and the chromophore are photochemically degraded, e.g., by the formation of singlet oxygen. This limits the time for collection of hyperpolarized nuclear magnetic resonance (NMR) data. We show that embedding of the protein into a trehalose sugar glass matrix stabilizes the protein for 13C solid-state photo-CIDNP NMR experiments which can be conducted at room temperature in a powder sample. Additionally, this preparation allows for incorporation of high amounts of protein further boosting the intensity of the detected signals from FMN and tryptophan at natural abundance. Signal assignment is aided by quantum chemical calculations of absolute shieldings. The underlying mechanism for the surprising absorption-only signal pattern is not yet understood. Comparison to calculated isotropic hyperfine couplings imply that the enhancement is not due to the classical radical-pair mechanism (RPM). Analysis of the anisotropic hyperfine couplings associated with solid-state photo-CIDNP mechanisms also show no simple correlation, suggesting a more complex underlying mechanism.

Disentangling the Li-Ion transport and Boundary Phase Transition Processes in Li10 GeP2 S12 Electrolyte by In-Operando High-Pressure and High-Resolution NMR Spectroscopy.

Li-ion transport and phase transition of solid electrolytes are critical and fundamental issues governing the rate and cycling performances of solid-state batteries. In this work, in-operando high-pressure nuclear magnetic resonance (NMR) spectroscopy for the solid-state battery is developed and applied, in combination with 6 Li-tracer NMR and high-resolution NMR spectroscopy, to investigate the Li10 GeP2 S12 electrolyte under true-to-life operation conditions. The results reveal that the Li10 GeP2 S12 phase may become more disordered and a large amount of conductive metastable β-Li3 PS4 as the glassy matrix in the electrolyte transforms into less conductive phases, mainly γ-Li3 PS4 , when high current densities (e.g., ≥0.5mA cm-2 ) are applied to the electrolyte. The overall Li-transport also varies and shows a tendency of boundary phases and Li10 GeP2 S12 synergistic dominant conduction at high currents. Accordingly, a mechanism of structural change induced by stress variation due to the drastic morphological change during Li-In alloying at high currents, and the local Li+ diffusion coefficient discrepancy is proposed. These new findings of Li-ion transport and boundary phase transition in Li10 GeP2 S12 solid electrolyte under high-pressure and high current density are first reported and will help provide previously lacking insights into the relationship of structure and performance of Li10 GeP2 S12 .

Mechanism of the Thermolysis of Magnesium Perylenetetracarboxylates

Black-red and orange magnesium perylene-3,4,9,10-tetracarboxylate species are synthesized in the ion-exchange reaction at room temperature and by boiling an aqueous solution, respectively. Upon heating the two species to 500°C in argon, they reversibly lose 19–27 wt % of their crystallization water, and the products become black. X-ray diffraction analysis results show the preservation of the layered structure upon heating, which is confirmed via transmission electron microscopy. Exposure to a humid atmosphere rehydrates and restores the original structure. Thermolysis to 1000°С in argon produces a composite of MgO nanoparticles in a porous glassy carbon matrix. The stability of perylenetetracarboxylates up to 500°C makes them a promising candidate for synthesizing metal–organic frameworks.

Heterogeneity of microstructures in a Cu–Zr based amorphous alloy composite reinforced by crystalline phases

Amorphous alloy composites (AACs) comprising reinforcing crystalline phases exhibit far better mechanical properties than their base amorphous alloy counterparts, and Cu–Zr based alloys consisting of B2 phase particles embedded in an amorphous matrix are well-researched AACs in this respect. Traditionally, the B2 particles in Cu–Zr based AACs may appear to be homogeneously crystalline (without any amorphous phase inside), the glassy matrix homogeneously amorphous, and their interfaces atomically sharp. Yet, such a picture would pose difficulties in understanding how crystallization can happen in the glassy matrix, since the crystallized product is denser than but iso-stoichiometric with the matrix. The present work provides insights into this puzzle, by using electron microscopy, nanoindentation and molecular dynamics (MD) simulations to investigate the structures and mechanical properties of the crystalline and amorphous phases, and their interfaces in a Cu62Zr34.5Al3Nb0.5 AAC. Surprisingly, in this AAC, the superficially crystalline particles with tens to hundreds of microns large are found to be heterogeneous at the sub-micron scale, comprising nano-crystallites embedded in a glassy matrix, and the amorphous phase outside also exhibits a gradient in free volume content towards the interface. Smaller particles containing only B2 nano-crystallites are found to be softer than the amorphous matrix, while larger particles are harder than the amorphous phase due to martensitic transformation into the B19’ phase. MD simulations indicate that the B2 phase is marginally more stable than the glassy state, and on crystallization the densification leads to free-volume generation in the surrounding glassy matrix as observed experimentally. Mechanics analysis indicates that the strain energy in the glassy matrix associated with free-volume generation scales with the volume of the crystallization, as would be the crystallization energy itself. Hence, crystallization in the AAC leading to a two-phase structure is a spontaneous but kinetically limiting process arising from the net energy difference between the crystallization energy and free-volume energy produced in the glassy matrix. This work provides a detailed understanding of the heterogeneity in the microstructures in Cu–Zr based AACs, to shed light on the crystallization of the iso-stoichiometric B2 phase from the amorphous phase.

METALLIZED GLAZES FOR THE DECORATION OF PORCELAIN STONEWARE USING RAW MATERIALS OF THE REPUBLIC OF BELARUS

The aim of this research was to study the possibility of obtaining metallic (metallized) raw glazes for porcelain stoneware using the raw materials of the Republic of Belarus. Fusible clay, quartz sand, dolomite, kaolin and copper oxide were used to prepare the glazes. The glazed porcelain stoneware obtained under the industrial conditions of Berezastroimaterialy JSC had dark grey surface with a metallic appearance. The research on the physico-chemical properties of the synthesized samples was carried out under the requirements of existing international standards. The temperature coefficient of linear expansion of glazes was (65.9–73.4)∙10–7 K–1, resistance to surface abrasion (PEI) – 1–2, resistance to thermal shock – 150±5 °C. The structure of glaze coatings was characterized by X-ray diffraction analysis and scanning electron microscopy. The glassy matrix was established to be the predominant phase. Anorthite and tenorite were the crystalline components. Their amount varied depending on the glaze composition. Due to the crystalline phases, glazed porcelain stoneware has a relatively high degree of resistance to surface abrasion. A hot-stage microscope and differential scanning calorimeter were used to study the melting behavior of the experimental glazes. The characteristic temperatures (sintering, sphere, half-sphere, fusion), as well as the contact angle and shrinkage of glazes in the temperature range of 500–1400 ℃ were determined. It was found that an increase in the content of copper oxide from 12.5 to 22.5 % contributes to a decrease in the sintering temperature by 10–50 ℃. However, the prevailing influence on the surface tension of the glazes at temperatures 1050–1200 °C had the percentage of dolomite. For citation: Shymanskaya H.M., Popov R.Yu., Pospelov A.V. Metallized glazes for the decoration of porcelain stoneware using raw materials of the Republic of Belarus. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 6. P. 69-75. DOI: 10.6060/ivkkt.20236606.6808.

Modification of the Bridging Unit in Luminescent Pt(II) Complexes Bearing C^N*N and C^N*N^C Ligands

In this work, we explored the synthesis and characterization of Pt(II) complexes bearing different tri- and tetradentate luminophores acting as C^N*N- and C^N*N^C-chelators. Thus, we investigated diverse substitution patterns in order to improve their processability and assessed the effects of structural variations on their excited state properties. Hence, a detailed analysis of the different synthetic pathways is presented; the photophysical properties were studied by using steady-state and time-resolved photoluminescence spectroscopy. We determined the absorption and emission spectra, the photoluminescence efficiencies, and the excited state lifetimes of the complexes in fluid solutions at room temperature and frozen glassy matrices at 77 K. Finally, a structure–property relationship was established, showing that the decoration of the bridging unit on the tridentate luminophores only marginally affects the excited state properties, whereas the double cyclometallation related to the tetradentate chelator prolongs the excited state lifetime and increases the photoluminescence quantum yield.

Efficient Treatment of Oily Sludge via Fast Microwave-Assisted Pyrolysis, Followed by Thermal Plasma Vitrification.

Oily sludge, as a critical hazardous waste, requires appropriate treatment for resource recovery and harmfulness reduction. Here, fast microwave-assisted pyrolysis (MAP) of oily sludge was conducted for oil removal and fuel production. The results indicated the priority of the fast MAP compared with the MAP under premixing mode, with the oil content in solid residues after pyrolysis reaching below 0.2%. The effects of pyrolysis temperature and time on product distribution and compositions were examined. In addition, pyrolysis kinetics can be well described using the Kissinger-Akahira-Sunose (KAS) and the Flynn-Wall-Ozawa (FWO) methods, with the activation energy being 169.7-319.1 kJ/mol in the feedstock conversional fraction range of 0.2-0.7. Subsequently, the pyrolysis residues were further treated by thermal plasma vitrification to immobilize the existing heavy metals. The amorphous phase and the glassy matrix were formed in the molten slags, resulting in bonding and, hence, immobilization of heavy metals. Operating parameters, including working current and melting time, were optimized to reduce the leaching concentrations of heavy metals, as well as to decrease their volatilization during vitrification.

Structural and thermal characteristics of Ge30−xSbxTe10Se60 (0 ≤ x ≤ 20) glasses for electronic devices

Thermal characterization of different compositions of Ge30−xSbxTe10Se60 (x = 0, 5, 10, 15, 20 at.%) glassy materials has been investigated through differential scanning calorimetry (DSC). The tested glasses have been synthesized by melt-quench technique. Glassy materials display compositional phase separation at x = 0, 5, 10, 15 at.%. For additional increase in Sb content at x = 20 at.%, the separation of phases combines in the glass matrix. The glass transition temperature (Tg), initial temperature of crystallization (Tc), peak crystallization temperature (Tp) and melting temperature (Tm) were found to be affected by both heating rate and composition. It is noticed that the increasing of antimony mass percentage in the glassy matrix is leading to decrease in Tg, Tc, Tp and Tm values. The melting temperature (Tm) of these glasses was found in the range 733–746 K for the first phase and in the range 740–792 K for the second phase. The activation energy of glass transition (Eg), activation energy for crystallization (Ec), Avrami index (n) and fragility index (Fi) were calculated using these specific temperatures. Eg decreases with increasing Sb content in all studied samples, but Eg is increasing in the sample with Sb content of 20%, and hence, it varies between 102.7 and 110.6 kJ approximately, whereas (Ec) decreases with the increase in the Sb content in all the tested samples and varies between 283 and 339 kJ. The fragility index varies between 10 and 26 indicating that the melts of these glasses are strong, and the fragility is minimum. The results were discussed in terms of the average coordination number NC and chemical bond approach.

High temperature and water stable CaF2:Eu2+ glass ceramic for high resolution X-ray detection

The rising requirement for radiation detection materials for practical applications has inspired to burgeoning investigation of scintillator materials. High performance X-ray detection require high spatial resolution and long-term stability, particularly for targeted objects at extreme conditions. Here, the CaF2:Eu2+ glass ceramic (GC), in which the CaF2:Eu2+ nanoparticles are wrapped by the glassy matrix, is successfully obtained the melting method. The as-obtained CaF2:Eu2+ GC manifests bright blue radioluminescence (RL) emission peaked at 470 nm thanks to the effective 5d-4f transition of Eu2+ ions. In addition, the as-obtained CaF2:Eu2+ GC presents high transmittance of 84.2% and visible light, contributing an excellent spatial resolution of 15 lp/mm at room temperature. Importantly, the as-obtained CaF2:Eu2+ GC exhibits high robustness at water conditions and high thermal stability with X-ray resolution of 12.1 lp/mm at 473 K. Our work demonstrates that CaF2:Eu2+ GC scintillators provide an excellent visualization tool for high-resolution scintillators X-ray images in harsh conditions.

Enhanced mechanical properties of Zr-Cu-Al-Ni bulk amorphous alloys by Ag and O doping

The microstructure and properties of amorphous alloys are very sensitive to oxygen content, so the extremely stringent atmospheric condition is required for their production, which also significantly increases the production costs. In this work, the strength and plasticity of Zr52Cu23Ni10.5Al14.5 amorphous alloy rods with a diameter of 2 mm are severely deteriorated after the addition of 0.15 at% O due to the formation of micrometer scale crystalline phases in glassy matrix. In contrast, the combined addition of 1 at% Ag and 0.15 at% O can substantially improve its fracture strength and plasticity. This synergy effect is mainly attributed to the fact that minor Ag addition can enhance the uniform distribution of nanocrystalline phases and refine their sizes. The present results can provide ideas for the industrial production and large-scale commercial applications of amorphous alloys in the future.

Improving the Corrosion Resistance of NiNb-Based Bulk Metallic Glass through the Hot Compression

This paper aims to study and evaluate the corrosion resistance of Ni55Nb45 and Ni55Nb35Co5Zr5 bulk metallic glasses (BMGs) in an environment similar to proton exchange membrane fuel cells. Moreover, the hot compression process was carried out to find the effects of a thermomechanical treatment on the corrosion resistance. The X-ray diffraction (XRD) test indicated that the hot compression process led to formation of crystalline species in both samples; however, it was more pronounced in the Ni55Nb35Co5Zr5 alloy. It is suggested that the minor addition of Zr and Co facilitated the crystallization in the material. The polarization test unveiled that the hot compression deteriorated the corrosion resistance of the Ni55Nb45 alloy through the introduction of anomalous chemical interfaces. On the other hand, the hot deformation affected the Ni55Nb35Co5Zr5 alloy in a positive way, so that the corrosion behavior improved compared with its fully glassy state. It is suggested that the hot deformation induces some NiNb crystalline constituencies in the microstructure of Ni55Nb35Co5Zr5 BMG, leading to the enrichment of glassy matrix from Zr/Co constituencies and the enhancement of corrosion resistance.

Frustrated crystallization behavior under hierarchical confinement in electrospun fibers of poly(styrene)/poly(ethylene oxide)/poly(l‐lactide) ternary mixtures

AbstractThe crystallization behavior of binary crystalline mixtures composed of poly(ethylene oxide) (PEO) and poly(l‐lactide) (PLLA) was investigated in the electrospun nanofibers fabricated by the ternary blends of polystyrene (PS), PEO, and PLLA. The weight fraction of PEO/PLLA mixture was kept at ≤0.2 such that PS formed the matrix phase. The preferred mixing of PEO and PLLA resulted in the formation of mixed PEO/PLLA dispersed domains in the PS matrix. The small diameter of the electrospun nanofibers restricted the size of dispersed domain. During cooling from melt, PLLA crystallized first resulting in crystallization induced phase separation and entrapment of PEO within the intracrystalline regions of PLLA crystals. Hence, whereas the PLLA crystallized within the soft PS matrix, the crystallization of PEO occurred within the hierarchical confinement imposed by the PLLA crystals as well as the glassy PS matrix. Interestingly, it was found that the confinement favored the formation of α crystals phase in PLLA even at very low crystallization temperatures. Furthermore, due to plausible entrapment of PEO segments within the PLLA crystals, significant depression in PLLA melting temperature was observed. Moreover, the PEO melting temperature also depressed by more than 30°C due to the frustrated crystallization within the hierarchical confinement.

Intrinsic Anti-Freezing and Unique Phosphorescence of Glassy Hydrogels with Ultrahigh Stiffness and Toughness at Low Temperatures.

Most hydrogels become frozen at subzero temperatures, leading to degraded properties and limited applications. Cryoprotectants are massively employed to improve anti-freezing property of hydrogels; however, there are accompanied disadvantages, such as varied networks, reduced mechanical properties, and the risk of cryoprotectant leakage in aqueous conditions. Reported here is the glassy hydrogel having intrinsic anti-freezing capacity and excellent optical and mechanical properties at ultra-low temperatures. Supramolecular hydrogel of poly(acrylamide-co-methacrylic acid) with moderate water content (≈50 wt.%) and dense hydrogen-bond associations is in a glassy state at room temperature. Since hydrogen bonds become strengthened as the temperature decreases, this gel becomes stronger and stiffer, yet still ductile, with Young's modulus of 900MPa, tensile strength of 30MPa, and breaking strain of 35% at -45°C. This gel retains high transparency even in liquid nitrogen. It also exhibits unique phosphorescence due to presence of carbonyl clusters, which is further enhanced at subzero temperatures. Further investigations elucidate that the intrinsic anti-freezing property is related to a fact that most water molecules are tightly bound and confined in the glassy matrix and become non-freezable. This correlation, as validated in several systems, provides a roadmap to develop intrinsic anti-freezing hydrogels for widespread applications at extreme conditions.

Monitoring of alpha-decay radiation damage in a 241Am-doped glass-ceramic material

The evolution under alpha-decay radiation of a 241Am doped aluminoborosilicate glass-ceramic was investigated in hot cells DHA-ATALANTE facility in CEA. The cumulative La2O3 - Am2O3 solubility limit was voluntarily exceeded, leading to the formation of apatite-like silicate crystals. The crystals, with a hexagonal-shaped morphology, that is characteristic of apatite crystals, have a composition and a cell parameter close to those expected for an apatite phase of stoichiometric composition Ca2(La,Am)8(SiO4)6O2. Structural and microstructural evolutions under alpha self-irradiation were followed for 8 years by regularly analyzing the crystals and the residual glassy matrix. The evolution of the X-Ray Diffraction (XRD) patterns is the result of a progressive radiation-induced amorphization in apatite crystals. The fully amorphous state is reached at an alpha-decay dose of around 3 × 1018 α/g. Raman analyses suggest a modification of the connectivity of the SiO4 tetrahedra of apatite crystals, with a transition from isolated SiO4 units in the crystalline state to connected SiO4 units in the metamict state. The crystalline-to-amorphous transformation is accompanied by an increase in macroscopic volume (swelling), highlighted by RAMAN imaging. This macroscopic dimensional change is also associated to a decohesion of the crystals from the glassy matrix, observed by Scanning Electron Microscopy (SEM). However, optical and SEM images of the glass-ceramic surface do not reveal any significant cracks in the residual glass under alpha self-irradiation, thus showing a quite good stability of this glass-ceramic material.