Glassy Matrix Research Articles

Effect of the Content and Ordering of the sp2 Free Carbon Phase on the Charge Carrier Transport in Polymer-Derived Silicon Oxycarbides.

The present work elaborates on the correlation between the amount and ordering of the free carbon phase in silicon oxycarbides and their charge carrier transport behavior. Thus, silicon oxycarbides possessing free carbon contents from 0 to ca. 58 vol.% (SiOC/C) were synthesized and exposed to temperatures from 1100 to 1800 °C. The prepared samples were extensively analyzed concerning the thermal evolution of the sp2 carbon phase by means of Raman spectroscopy. Additionally, electrical conductivity and Hall measurements were performed and correlated with the structural information obtained from the Raman spectroscopic investigation. It is shown that the percolation threshold in SiOC/C samples depends on the temperature of their thermal treatment, varying from ca. 20 vol.% in the samples prepared at 1100 °C to ca. 6 vol.% for the samples annealed at 1600 °C. Moreover, three different conduction regimes are identified in SiOC/C, depending on its sp2 carbon content: (i) at low carbon contents (i.e., <1 vol.%), the silicon oxycarbide glassy matrix dominates the charge carrier transport, which exhibits an activation energy of ca. 1 eV and occurs within localized states, presumably dangling bonds; (ii) near the percolation threshold, tunneling or hopping of charge carriers between spatially separated sp2 carbon precipitates appear to be responsible for the electrical conductivity; (iii) whereas above the percolation threshold, the charge carrier transport is only weakly activated (Ea = 0.03 eV) and is realized through the (continuous) carbon phase. Hall measurements on SiOC/C samples above the percolation threshold indicate p-type carriers mainly contributing to conduction. Their density is shown to vary with the sp2 carbon content in the range from 1014 to 1019 cm−3; whereas their mobility (ca. 3 cm2/V) seems to not depend on the sp2 carbon content.

Characterization of Pseudotachylite and Fault Gouges in Drill Cores from Andong, Korea and Its Implications for Paleo-Earthquakes

Pseudotachylite and fault gouges were observed in core samples of Precambrian granitic gneiss drilled from depths as great as 1000 m in Andong, Korea. Fault gouges were found in the upper parts of the borehole, whereas pseudotachylites developed in the lower parts. Pseudotachylite with widths varying from a few mm to 10 cm sharply contacted or were interlayered with the host rock. The quartz-rich portion of the granitic gneiss remained unaffected, but the mafic portion was melted preferentially. The glassy surface of pseudotachylite is characterized by a smooth, glassy matrix with an amorphous phase and silicate beads with diameters of ~200 nm, together with slickenlines. Slickenlines composed of parallel grooves showed a wavelength of 4–7 μm and an amplitude &lt; 1–2 μm. Residual or surviving grains have rounded corners and edges, indicating that those grains experienced abrasion, possibly from grain rotation or shear stress. Both melting and crushing contribute to the formation of pseudotachylite. Fe was always enriched in the glassy matrix, indicating that the pseudotachylite matrix originated from mafic minerals. The occurrence of pseudotachylite related to paleo-earthquake events showed that crystalline rocks in this area are unsatisfactory candidates for deep-disposal sites for high-level nuclear waste.

Applications of Raman spectroscopy in art and archaeology

Applications of Raman spectroscopy in art and archaeology

Comparative analysis of lithiated silica glasses by laser-induced breakdown spectroscopy and raman spectroscopy

Composition and bonding configuration of silicate glasses with different lithium content was studied by laser induced breakdown spectroscopy and Raman spectroscopy. The lithium content of the formed glass matrix has been determined by using laser induced breakdown spectroscopy with high precision. Analysis of the Raman spectra implied on the complex character of lithium incorporation into the glassy matrix with lithium content. It was found that the addition of lithium results in more depolymerized SiO4 structures and, in general, increases the disorder of the structure. However, at certain concentrations lithium has an ordering effect due to more homogeneous size distribution of structural units of the glass matrix.

Effect of the application technique on the colorimetric coordinates for a ceramic enamel

In ceramic tiles production processes for ornamental purposes, the industry uses enamel as raw materials that support the pigments that give coloration and tonal constancy in a glassy matrix. These parameters are of great interest in the acceptance of the final product by the consumer. Due to the increasing number of complaints related to variations in tone in ceramic enamel of the tiles produced by a ceramic company in northeastern Colombia, this work studied the enamel approval methodology’s effect on the final tone of the ceramic pieces. A ceramic enamel was prepared and applied by the enameling pad technique on tiles manufactured by dry pressing. By applying the spectrophotocolorimetric technique, the colorimetric parameters were determined. The Tukey test’s statistical results did not show statistical significance in the tile samples’ tonal variation.

Investigation of two-body wear behavior of zirconia-reinforced lithium silicate glass-ceramic for biomedical applications; in vitro chewing simulation

The aim of this work was to the investigate two-body wear behavior of zirconia-reinforced lithium silicate glass-ceramic and composite resins through in vitro chewing simulation. Two types of glass-ceramics (IPS e.max CAD; lithium disilicate, Vita Suprinity; zirconia-reinforced lithium silicate) and two types of composite resins (Filtek Supreme; nano-filled, Ivoclar Vivadent Heliomolar; micro-filled) were used. All specimens were exposed to two-body wear tests using a dual-axis computer-controlled chewing simulation. Each chewing simulation test procedure, Al2O3 ball with a diameter of 6 mm, was used as antagonist material. The mean volume loss and wear depth of all specimens after the chewing tests were determined with use non-contact 3 D profilometer. Zirconia-reinforced lithium silicate Vita Suprinity had significantly higher two-body wear resistance than lithium disilicate IPS e.max CAD glass-ceramic and other composite resins after chewing tests. While Vita Suprinity exhibited a homogeneous crystal microstructure, IPS e.max CAD glass-ceramic exhibited a structure with needle-shaped fine-grained crystals embedded in a glassy matrix. As a result, the homogeneous distribution of zirconia particles into the ceramic material will increase the two-body wear resistance through chewing simulation tests.

Immobilisation of heavy metals in hazardous waste incineration residue using SiO2–Al2O3–Fe2O3–CaO glass-ceramic

Hazardous waste incineration residue (HWIR) is categorised as hazardous waste due to the presence of heavy metals such as Zn, Cu, and Cr. Based on the abundant components of silica, aluminium oxide, iron oxide, and calcium oxide in a HWIR from an environmental protection corporation in China, a 100% HWIR was used to prepare SiO2–Al2O3–Fe2O3–CaO glass-ceramic samples. The results showed that Zn, Cu, and Cr present in the glass-ceramic samples were effectively immobilised through the melting–sintering process. Among the four parameters of heat treatment, crystallisation temperature played the most significant role. The glass-ceramic that was formed under optimal conditions contained haematite, pseudobrookite, and anorthite, and exhibited a superior compressive strength, volume density, and water absorption of 204.84 MPa, 2.80 g/cm3, and 1.20%, respectively. Compared with the raw HWIR sample, the leaching concentrations of Zn, Cu, and Cr from the prepared glass-ceramic samples decreased significantly, and their immobilisation efficiencies exceeded 99%. Physical encapsulation in the glass-ceramic samples along with ion exchange in the amorphous glassy matrix and iron-rich crystalline phases were the main immobilisation mechanisms of Zn, Cu, and Cr.

Low Cost Ceramic Product Based on Mixing Granodiorite and Talc from Eastern Desert, Egypt.

The Abu Ziran area is easily accessible following the Quseir-Qift asphaltic road in the Central Eastern Desert of Egypt. Microscopically and geochemically, the granodiorite rock represents a good source for the major oxides that are contained in its mineral components: quartz, oligoclase, orthoclase, microcline, biotite and hornblende as its essential minerals; besides sphene, zircon, apatite and magnetite as its accessory minerals. These minerals represent suitable raw materials in the formulation of the low cost ceramic product. The low cost ceramic materials were prepared from mixing wastes of granodiorite and talc quaries in the Eastern Desert, Egypt. Four samples were prepared in the 70:30, 60:40, 50:50 and 40:60 ratios of granodiorite:talc. After sintering process of the green ceramic samples up to 1300 C, aluminum enstatite, kyanite, pyrope and cristobalite were developed. The microstructure of the sintered samples show rod-like crystals in micron and submicron size oriented or disoriented in glassy matrix. The samples enjoy good densities between 1.65 and 2.21 g/cm3 and porosity ratio between 18.01 and 39.27 %. This low cost ceramic product can be used in insulation for heat and sound.

Structural evolution of zinc selenite nanocomposite system with molybdenum trioxide as modifier studied by positron annihilation and allied experimental methods

The successful synthesis of the metal oxide nanocomposite xMoO3–(1-x)(0.5SeO2–0.5ZnO) for x = 0.0, 0.1, 0.2, …, 0.9 by mixing and melt-quenching of the stoichiometric ratios of the metal oxides is reported in this work. X-ray diffraction patterns and transmission electron microscopy images confirmed the formation of the nanocomposites and their evolution to the amorphous glassy phase and newer nanocrystallites as x increased from 0–0.3, 0.3–0.7 and 0.7–0.9 respectively. The findings from Brunauer–Emmett–Teller isotherms also supported these observations, as one observed a significant enhancement in the pore volume and total pore surface area when the nanocomposites evolved from x = 0.3 to 0.9. The optical bandgap energy was another physical quantity that showed a steady decrease with increase in x and is attributed to the generation of additional electronic defect levels towards the conduction band within the bandgap. An important step that was taken up in this study was to characterize the defects in the composites by positron annihilation studies. Positron lifetimes and intensities pointed out the presence of vacancy-type defects within the nanocomposites, porous defects within the glassy amorphous phase and interfacial defects between the latter and the newer nanocrystallites formed. Coincidence Doppler broadened spectra revealed the decrease of positron trapping in cationic vacancies as x increased, showing that the annihilations within vacancy type defects decreased and in interfacial defects and nanocrystallite surfaces increased, confirming the formation of the newer nanocrystallites and their uniform dispersion in the glassy amorphous matrices.

Ravishing blue emission from Ce3+ activated lithium borate glasses for photonic applications

Lithium borate glasses activated with specific concentrations of Ce3+ ions have been processed by melt quenching technique. X-ray diffraction and SEM with EDAX carried out structural and surface morphology with elemental confirmation respectively. The nebulous nature of glassy matrices have been affirmatively confirmed by XRD and it was corroborated with SEM analysis. A distinguished absorption band is noticed in the ultraviolet region and the photoluminescence spectra displays a broad and intense blue emission band in the region from 395 nm to 570 nm which is centered at 447 nm (5d→4f) by exciting with 350 nm in Ce3+: LBZ glassy matrices. The dazzling blue emission intensity was significantly ameliorated by improving the addition of Ce3+ ion concentration in the glass matrix. The blue emission intensity has been found to be decreased at higher concentrations due to concentration quenching and the optimal concentration of Ce3+ ions is estimated to be 0.5 mol%. The fluorescence decay time has been evaluated as 0.86 ms from the decay profile of 0.5 mol% Ce3+: LBZ glass. Chromaticity coordinates were determined from the luminescence spectra, which are found to be falls in the bright blue region. The obtained blue emission CIE coordinates are close to standard EBU and NTSC coordinates for blue illumination. In view of these spectral features, 0.5 mol% Ce3+: LBZ glass could be recommended as promising candidate for the applications of blue emissive photonic devices.

Spray‐Dried TiO2(B)‐Containing Photocatalytic Glass‐Ceramic Nanobeads

AbstractGlass‐ceramic nanospheres of molar composition 0.83 SiO2 · 0.17 TiO2 are produced by the sol‐gel spray‐drying method followed by controlled heat treatments up to 1200 °C. TiO2(B) and anatase nanocrystals are precipitated in the glassy matrix: the latter phase gradually predominates with increasing ceramization temperature and time, in parallel to an overall increase in crystal sizes. The nanospheres exhibit evident photocatalytic activity under UV‐A irradiation, especially at annealing stages involving a comparatively higher amount of TiO2(B) and smaller crystals. The occurrence of TiO2(B) in this simplified binary glass‐ceramic material underlines the key role of this phase in the dynamics of crystallizing TiO2‐bearing silicate melts.

Modern magnetic resonance approaches for characterizing rare-earth containing glasses and glass ceramics

Rare-earth containing glasses are important materials with technologically relevant combinations of mechanical and optical properties. For developing their functional materials potential it is important to understand the local environment and spatial distribution of the rare-earth ions and their influence upon the structural organization of the glassy matrix. Nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) can furnish crucial information about these aspects. In this review we describe the relevant theoretical foundations with a particular focus on rare-earth containing systems. Important experimental approaches covered include dipolar NMR, paramagnetically perturbed NMR, EPR, and hyperfine interaction spectroscopies. These are illustrated in the context of various case studies, including (1) structural features of rare-earth aluminosilicate glasses, (2) spatial distribution and clustering of rare-earth dopants, (3) rare-earth ligand distributions in fluoride phosphate glasses, and structural changes along the glass-to-ceramic transformation in (4) aluminoborate and (5) oxyfluoride glasses.

Persistent room temperature blue phosphorescence from racemic crystals of 1,1-diphenylmethanol derivatives

Among the six alkyldiphenylmethanol derivatives assessed in this study, five showed persistent room temperature phosphorescence (pRTP), whereas the original diphenylmethanol (DPhHOH) did not. pRTP is a unique luminescence phenomenon that appears only in the crystalline state and is different from the luminescence produced by dispersed molecules, such as those in a glassy solvent matrix at 77 K or a polymeric matrix. The data also suggest that pRTP appears in conjunction with a specific crystal structure. The present work demonstrates that various crystal structures show pRTP regardless of the presence or absence of weak hydrogen bonds. However, nonradiative deactivation is suppressed by both intermolecular interactions and steric regulation in the crystal, such that the emission quantum yield is dependent on the crystal structure. In addition, although the molecular structure in the crystalline state necessary for the appearance of pRTP was not fully elucidated, intermolecular interactions between face-to-face and face-to-edge benzene rings appear to play a major role. Density functional theory calculations indicate that intersystem crossing is promoted in the crystalline state because the number of paths that allow this intersystem crossing is greater in a structure having weak interactions between molecules as compared to a dispersed state. DPhHOH did not show pRTP and is considered to have a structure based on the column-like stacking of multiple molecules. In contrast, the crystals that exhibited pRTP had pseudo racemic conformation in their crystals even though each molecule was achiral. In these racemic crystals, the interactions between pairs of molecules were important to the generation of pRTP.

Two ratiometric thermometry methods based on the interplay between Eu[formula omitted] and Eu[formula omitted] and single Eu[formula omitted] emissions on OH[formula omitted]-free low-silica calcium aluminosilicate glass

The constant demand to accurately measure the temperature sheds light on luminescent materials that have dependence on their thermodynamic quantities. Several materials have been applied as sensors to measure temperature for different applications, however, very few showed high precision and sensitivity. This work reports the Eu2+/Eu3+-doped low-silica calcium aluminosilicate glass as a potential candidate for high sensitive ratiometric thermometer. The glass was analyzed close to the physiological temperature range, between 288.15 – 333.15 K. Since this glassy matrix provides the presence of two europium valences, two different approaches are presented. The first takes into account the temperature dependence of 5D0→7F4 emission for two different excitation wavelengths, and the second one is based on the interplay between Eu2+ and Eu3+ emissions. Both ratiometric approaches presented high reproducibility and relative sensitivity values, from 1.2 to 1.6 %/K and from 0.75 to 0.95 %/K, for the first and second approach, respectively.

Effective sensitization of Eu3+ ions on Eu3+/Nd3+ co-doped multicomponent borosilicate glasses for visible and NIR luminescence applications

Eu3+/Nd3+ co-doped multicomponent borosilicate glasses (ND1E: 10BaO +10ZnF2+10K2O +20SiO2+(49-x) B2O3+1Nd2O3+xEu2O3) were prepared by conventional melting and rapid quench technique to evaluate the effect of Eu3+ ions in the Nd3+ doped glasses. Thermal stability, structural and spectroscopic characteristics of the ND1E glasses were investigated by using DSC, XRD, FTIR, Optical absorption, excitation and emission measurements. The Judd – Ofelt (JO) analysis is implemented to the absorption spectrum of the prepared glassy matrix in order to identify their potential applicability in lasing devices. Enhancement of 7F0 → 5L6 band (394 nm) with the increasing concentration of Eu3+ ion in the Nd3+ excitation spectra (λemi = 1060 nm) reveals the possibility of obtaining the characteristic fluorescence spectra of Nd3+ ion with the typical excitation wavelengths (Nd3+ = 584 nm and Eu3+ = 394 nm) of both rare earth ions and it is further verified from the emission spectrum. This interesting luminescence effect of showing excellent visible and NIR emission under 394 nm excitation mainly attributes the energy transfer mechanism between the RE3+ ions and the reason underlying this effect is discussed in detail with the help of partial energy level diagram. Energy transfer efficiency between the Eu3+ and Nd3+ ions were evaluated by using the radiative lifetimes of the prepared glasses. Also, a comparison of radiative properties and lasing characteristics of Eu3+/Nd3+ co-doped glasses with other Nd3+ glasses are reported. The emission intensities were characterized using CIE chromaticity diagram and the observed CIE coordinates shows a shift towards reddish – orange region with the increase in Eu3+ concentration. The quantum efficiency of the prepared glasses was determined experimentally. The obtained results suggest that the ND1E glassy system can be considered as a potential candidate for visible and NIR luminescence applications.

Work-hardenable TiZr-based multilayered bulk metallic glass composites through the solid solution strengthening in ex-situ Ti layers

To circumvent the trade-off with plasticity and strength, a series of TiZr-based controllable multilayered bulk metallic glass composites (ML-BMGCs), with ex-situ Ti layers and glassy matrix containing precipitated dendrites distribution in an alternate, was fabricated by the hybrid strategy with in-situ and ex-situ. ML-BMGCs exhibit not only enhanced plasticity from 1±0.2% to 8.4±0.2% but also improved the fracture strength from 1643±15 MPa to 1956±20 MPa under compression. The improved strength is attributed to that the solid solution strengthen of Zr in the ex-situ Ti layers by Zr element diffusion from glassy matrix to them is increasing with Zr addition. Ti layers and the in-situ dendrites create a strong barrier for the shear band propagation and generate multiplies of the shear band after solid solution strengthening, thereby which together with the pronouncedly plastic deformation of Ti layers, greatly improves the plastic deformation capacity.

Molecular Mobility and Crystal Growth in Amorphous Binary Drug Delivery Systems: Effects of Low-Concentration Poly(Ethylene Oxide).

Polymer additives have been widely reported to affect the crystallization of amorphous drugs, while the underlying mechanism is poorly understood. The present study aims to investigate the relationship between the crystal growth and the molecular mobility of amorphous nifedipine (NIF) in the presence and absence of low-concentration poly(ethylene oxide) (PEO). The addition of 3% w/w PEO yields approximately a 5-fold increase in the crystal growth rate of NIF in the glassy matrix and a 10-fold increase in the supercooled liquid. Broadband dielectric spectroscopy is performed to investigate the molecular mobility of amorphous pure NIF system and NIF doped with low-concentration PEO. With 3% w/w PEO, the structural relaxation time τα of amorphous NIF significantly decreases, indicating an increase in the global molecular mobility. However, the increase of the molecular mobility is insufficient to explain the 5- to 10-fold increase of the crystal growth rate at the same τα scale. Moreover, we compare the accelerating effect of PEO in NIF-PEO systems to other PEO-doped systems. The accelerating effect of low-concentration PEO on the crystal growth of amorphous drugs is found to be independent of the Flory-Huggins interaction, Tg of the drug, or the increase of the global molecular mobility. These findings suggest that an in-depth understanding regarding the effects of polymer additives on the crystallization of drugs should consider the localized mobility of the host molecules near the crystal-liquid interface.

Negative thermal expansion in porous glass-ceramics based on Mg2Al2B2Si5O18 prepared from Saudi raw materials

A porous glass-ceramic enjoyed very low and negative thermal expansion was prepared. A glass of the base molar composition, 2 MgO·2 Al2O3·2 B2O3·5 SiO2 with the addition of 1.61 ma% TiO2, was melted from kaolin, magnesite, silica sand and boric acid. The composition is based on cordierite where 50 % Al2O3 were replaced by an equimolar concentration of B2O3. The glass was crashed and powdered, subsequently plastified, uniaxially pressed and finally sintered at temperatures in the range from 1100 to 1300 °C. X-ray diffraction of sintered samples gave evidence of a cordierite like crystalline phase. Scanning electron microscopy and electron dispersive microanalysis of samples prepared at 1300 °C showed crystals with hexagonal shape doped by TiO2, B2O3 and Fe2O3 embedded in a glassy matrix. With increasing crystallization temperature, the porosity of the glass-ceramics increased from 8.99 % (at 1200 °C for 3 min) to 56.42 % (at 1300 °C for 3 min). This led to a decrease of the specimen density from 1.9880 to 1.1278 g/cm3 whereas the skeletal density increased from 2.1303 g/cm3 to 2.5878 g/cm3. The microhardnesses were in the 5.60 and 6.00 GPa range. The coefficient of thermal expansion was between −3.26 and −2.27×10−6 K−1 from room temperature up to 300 oC and −0.45 and 1.89×10−6 K−1 from room temperature up to 500 °C. For the first time, to the best of our knowledge, a porous cordierite glass-ceramic with negative thermal expansion is reported. The partial replacement of Al2O3 by B2O3 enables to apply lower melting temperature which is advantageous for the production process.

Paper-based nanosensors to evaluate community-wide illicit drug use for wastewater-based epidemiology

Wastewater-based epidemiology (WBE) is a powerful technique for monitoring illicit drugs of abuse in the community. Here, we report upon a surface-enhanced Raman spectroscopy (SERS) sensor for the sensitive and selective detection of methamphetamine based upon the assembly of noble metal core-shell nanoparticles on a bespoke glassy nanofibrous electrospun paper matrix. The hierarchical structure of the fibrous paper, modified with the synthesized Au@Ag core-shells (Au@Ag) gave strong SERS signalling, enabling us to evaluate the community-wide prevalence of methamphetamine in wastewater treatment plants within Beijing. We show that, when normalized for the daily flow of the wastewater treatment plants and for population density, higher mass loads of drugs are generally found in sewage influent from urban areas, implying greater local methamphetamine usage than that in less populated areas. The user-friendly and disposable paper sensors demonstrate the applicability of rapid on-site illicit drug detection, illustrating the application to wastewater-based epidemiology, which has the potential to inform government agencies regarding societal interventions.

Role of amorphous silica gel in B2O3-Bi2O3-ZnO-SiO2 to immobilize iodine waste

The treatment of radioactive iodine waste is particularly difficult because of its volatilization issues. In this study, amorphous silica gel was used to gradually replace crystalline SiO2 in B2O3-Bi2O3-ZnO-SiO2 based materials aimed to investigate the effects on iodine waste immobilization. Samples with different silica gel replacements (0, 20, 40, 60, 80, and 100%) were characterized by XRD, FT-IR, and SEM-EDS. The results showed that silica gel had a benefit in the immobilization of iodine waste at low-sintering temperatures (500, 550, and 600 °C). At 550 °C, AgI was immobilized in the pure glassy matrix and elements (Ag and I) distributed uniformly on the matrix surface. FT-IR analysis presented the tetrahedral SiO4 units in the sintered samples that were mainly in the form of sheets. Our work revealed the potential application of silica gel in the field of iodine waste immobilization.