Glassy Layer Research Articles

UV-driven efficient white light generation by Ag nanoclusters dispersed in glass host

In this work we present an alternative new method for generation of warm to cool white light by Ag nanoclusters dispersed in oxyfloride glass. White light of high colour rendering properties comparable to that of commercial sources and quantum yield (QY) exceeding 20% at room temperature is generated upon 250–400nm UV excitation of microwatt power. The QY increases with increasing ratio of oxide to fluoride components and also with lowering the temperature. The spectral width of the white light luminescence of Ag nanoclusters dispersed in this glass is most likely due to a broad distribution of Ag nanoclusters sizes and their surroundings. This material can be used as a tube material for luminescent lamps, in flexible displays, as a phosphor for light emitting diodes and as down-conversion glassy layers in enhanced solar cells.

Oxidation behaviour of matrix modified carbon/carbon composites by novel solvothermal process

In order to investigate the oxidation behaviour and oxidative mechanism of the as modified carbon/carbon (C/C) composites at the temperature range of 600–800°C, C/C composites were modified by a novel solvothermal process using tributyl borate, absolute alcohol, acetic acid and B2O3 powders as raw materials. The phase compositions and microstructures of the modified C/C composites were characterised by X-ray diffraction, laser Raman spectra, SEM and energy dispersive spectroscopy analyses. Results show that after modification, the surface and internal defects of C/C composites are covered and occupied by a glassy B2O3 layer and B2O3 crystallites; the oxidation resistance of C/C composites is effectively improved. After oxidation at 650°C for 22 h, the mass loss of the composites is only 3·34%. In comparison with the non-modified composites, the oxidative mechanism of modified composites is changed, and the corresponding oxidation activation energy of composites is obviously enhanced.

Densification and oxidation behavior of a novel TiB2–MoSi2–CrB2 composite

Titanium diboride (TiB2) composite with MoSi2 and CrB2 has been prepared and tested to possess excellent oxidation resistance. Dense composite pellets were fabricated by hot pressing of powder mixtures. Microstructural characterization was carried out by XRD and SEM. Hardness and fracture toughness values were measured. Extensive oxidation studies of the composites were also carried out. Density of ≥96% ρth was obtained by hot pressing at 1800°C under a pressure of 35MPa for 1h. Hardness and fracture toughness were in the range of 18–24GPa and 3.5–4MPa·m1/2 respectively. Crack branching, deflection and bridging mechanisms were observed in the crack propagation paths. Isothermal and continuous oxidation studies of these composites up to 1000°C showed improved oxidation resistance with the formation of protective glassy layer. TiO2, Cr2O3 and SiO2 phases were identified on the oxidized surface. Diffusion controlled mechanism of oxidation was observed in the composites.

Conductivity of Se95As5 chalcogenide glassy semiconductor layers containing the EuF3 rare-earth impurity in high electric fields

By investigating the I–V characteristics of an Al-Se95As5:EuF3-Te structure, it is established that, upon the application of a positive potential to Te, the current flows in it by the mechanism of space-charge-limited currents (SCLCs) of unipolar-injection, and the N-type I-V characteristic is observed for the opposite polarity. It is shown that these are processes of the thermal-field ionization of neutral and negatively charged U− centers, which play a dominant role in the current-flow mechanism in the investigated structures upon the application of an electric field with intensities exceeding 105 V/cm. These are also processes of the electron-hole recombination and capture of charge carriers at U− centers. The energy position and concentration of the local states, which correspond to the indicated centers and characterize the effect of the electric field—activation length are determined. It is established that it is the EuF3 impurities that predominantly affect the local-state concentration.

Mechanical Properties and Cross-Link Density of Styrene–Butadiene Model Composites Containing Fillers with Bimodal Particle Size Distribution

Mechanical properties and cross-link density of model composites being solution styrene–butadiene rubbers filled with different amounts of nanosized silica particles or mixtures of nanosized silica particles and micrometer-sized borosilicate glass particles are studied. The cross-link density of the rubber matrix is measured based on a double-quantum NMR spectroscopy method. Shear data show that reinforcement and dissipation G″ in the rubber plateau range depend systematically on the total surface area of the filler per unit composite. Different contributions to reinforcement due to hydrodynamic effects, “filler network”, glassy polymer layer, and “occluded rubber” are quantified based on a comparison of linear response measurements with strain sweeps performed at different temperatures. The results show a percolation threshold at silica volume fractions of about 0.15. The load-carrying capacity of the “filler network” decreases significantly with temperature. This may indicate the existence of a glassy polymer layer on the surface of the filler particles which softens several ten degrees above the bulk Tg of the rubber matrix. Two regimes are found in the dissipation above Tg which both depend systematically on the surface area of the filler system: A strongly frequency-dependent dissipation regime with power-law behavior is observed in G″(ω) at temperatures up to 70 K above the bulk Tg, and a nearly frequency-independent G″ regime dominates at higher temperatures. The molecular nature and importance of this finding for tire applications are discussed.

Pigments and enamelling/gilding technology of Mamluk mosque lamps and bottle

On‐site Raman spectroscopy is used to investigate four mosque lamps and a bottle dating back to the 13–14th centuries (Syria and/or Egypt, Mamluk period) from the Department of Islamic Art, Musée du Louvre, Paris. The pigments and the enamelled glass matrix have been identified in order to discuss their technology. A comparison is made with one masterpiece from the 19th century made by Brocard. The results obtained for blue (lapis lazuli or Co‐coloured glass), yellow (Naples yellows or zinc/chrome yellow), green (mixture of the aforementioned blue and yellow pigments or lead chromate for restorated foot) red (hematite), white (cassiterite or arsenate) and pink (hematite and cassiterite) pigments are presented. The consistency of the pigments period of use/technology with the datation proposed for each artefact is evaluated. For one lamp, the detection of quartz in some places of the hematite‐rich glassy layer supporting the gold is related to the search of a physical bonding with the artefact body. Carbon residues in such enamel are consistent with the use of an organic medium to place the enamel powder before the firing. Copyright © 2012 John Wiley & Sons, Ltd.

Physical and mechanical properties keramsite obtained with added glauconite

This paper presents the assessment of the physical and mechanical properties lightweight of aggregate obtained from the addition of expanded clay mineral clay – glauconite and clay from the bed, “Buda Mszczonowska”. Crushed plastic was prepared by firing at a temperature of over 1170 ° C. Evaluation of physical parameters was based on parameters such as density, bulk density and bulk density, tightness, porosity, water absorption. The study of mechanical properties was carried out on the basis of aggregate hardiness, resistance to crushing, abrasion in the drum Los Angeles. In addition, the compounds were determined in the aggregate coloring. Use glauconite in the lightweight of aggregate is beneficial for the texture of the sinter resulting in the formation of a glassy layer on the surface of the granules, and by increasing their porosity. Investigated the properties indicate that the resulting lightweight of aggregate with glauconite meets the basic requirements for materials used in construction.

Calcium bodies of Titanethes albus (Crustacea: Isopoda): Molt-related structural dynamics and calcified matrix-associated bacteria

Crustaceans form a variety of calcium deposits in which they store calcium necessary for the mineralization of their exoskeletons. Calcium bodies, organs containing large amounts of calcium, have been reported in some terrestrial isopod crustaceans, but have not yet been extensively studied. We analyzed the architecture of these organs during the molt cycle in the isopod Titanethes albus. Two pairs of calcium bodies are positioned ventrolaterally in posterior pereonites of T. albus. Individual organs are epithelial sacs that contain material arranged in concentric layers delimited by thin laminae. As demonstrated by electron microscopy and fluorescence in situ hybridization, abundant bacteria are present within the calcium bodies. Regardless of the molt cycle stage, crystalline concretions are present in the central areas of the calcium bodies. Energy dispersive X-ray spectrometry of the concretions demonstrated that they are composed predominantly of calcium and phosphorus and selected area electron diffraction indicated the presence of hydroxyapatite. In molting animals, a glassy layer of mineralized matrix is formed between the envelope and the outermost lamina of the calcium body. This layer consists of an amorphous calcium mineral which contains less phosphorus than the central concretions and is resorbed after molt. Since changes in the mineralized matrix are synchronized with the molt cycle, the calcium bodies likely function as a storage compartment that complements sternal deposits as a source of calcium for the mineralization of the exoskeleton. Bacteria associated with the mineralized matrix of calcium bodies are evidently involved in calcium dynamics.

C/SiC/Si-Mo-Cr multilayer coating for carbon/carbon composites for oxidation protection

To improve the oxidation resistance of carbon/carbon (C/C) composites at high temperature, the C/C composites were first slurry-coated by carbon, then pack cemented by mixtures of Si and graphite powder (60-80:10-25 wt/wt), followed by heat treatment to form C/C composites coated with a C/SiC layer, and finally a Si-Mo-Cr oxidation protective coating was prepared on the surface of the these composites by pack cementation. Scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy were used to characterize the compositions and microstructure of the coating. The oxidation behavior of the coated C/C composites at 1873 and 1 973 K in air was investigated. The coating showed excellent oxidation resistance at 1 873 K due to the formation of a glassy layer of SiO2 and Cr2O3 during the oxidation test, which could effectively protect C/C composites from oxidation for 135 h. The coating failed after oxidation for 30 h at 1973 K because the protective glass layer was disrupted.

SiC/HfC/SiC ablation resistant coating for carbon/carbon composites

To improve the ablative resistance of carbon/carbon (C/C) composites, a SiC/HfC/SiC coating was prepared by a multi-step technique of diffusing reaction and chemical vapor deposition. The microstructure and morphology of the coatings were characterized by Scanning Electron Microscopy, X-ray diffraction. The coated C/C exhibits good ablation resistance. A compact glassy HfO2 layer was obtained on the coating surface after ablation, which can efficiently prevent C/C composites from ablation. Meanwhile, the outer SiC coating provides positive protection; Weight loss of the coated samples is only 2.3% after oxidation at 1500°C for 66h. HfSiO4 was formed during oxidation and characterized by a stable glassy phase which could protect C/C composites from oxidation.

A Global Glassy Layer on BaAl2B2O7 Crystals Formed during Surface Crystallization of BaO·Al2O3·B2O3 Glass

A glass with the composition BaO·Al2O3·B2O3 was thermally annealed at temperatures from 700 to 780 °C for 1–8 h. This resulted in the crystallization of [0001]-oriented rhombohedral BaAl2B2O7 at the surface of the glass. The crystals grow fastest perpendicular to their c-axes (parallel to the surface) and cannot circumvent barriers in the surface. The surface of samples encapsulated in alumina ceramics during annealing was covered by a thin layer of glass, indicating nucleation occurred below the surface. If the samples were not encapsulated in alumina, around 85% of the surface was glass covered. This was the result of surface contaminations such as cubic BaSO4 detected on these samples. Crystal growth occurs toward the surface until the enrichment of impurities in the glassy layer is large enough to inhibit further crystal growth. The coinciding enrichment of impurities on the bulk side of the oriented surface crystals probably initiates the secondary nucleation, leading to the second layer of oriented ...

Oxidation behaviors of Nb–Si–B ternary alloys at 1100 °C under ambient atmosphere

Oxidation behaviors of the Nb-based two phase alloys comprising the Nb(Si, B) solid solution and Nb5(Si, B)3 phases have been evaluated based on the microstructural characterizations of isothermally oxidized samples at 1100 °C under ambient atmosphere. The oxide products were identified as β-Nb2O5, NbO2 and 3Nb2O5·B2O3, while the existence of Si/B rich crystalline oxide or glassy oxide layers could not be confirmed from the microstructural analysis results. The critical oxidation sequences with respect to the selected alloy compositions are discussed in terms of microstructural evolutions during oxidation exposure.

Glass transition and crystallization of low-temperature amorphous condensates of the water-propane mixture

Interest in gas hydrates stems from the existence of vast reserves of hydrocarbons on the earth in the form of gas hydrates, prospects for using them as a fuel source, and the possibility of storage and transporta� tion of gas in the gas hydrate state. The known meth� ods of production of gas hydrates are based on rela� tively small deviations from the equilibrium condi� tions of gas dissolution. They require the use of high pressures in laboratory or manufacturing equipment. For example, the pressure corresponding to the for� mation conditions of methane hydrate at temperatures near 0°С amounts to tens of bars. In addition, forma� tion of the crystal hydrate requires dispersion of water, which is afforded by longterm and vigorous stirring of the water-gas mixture. In this work, we have proposed another approach implying that hydrates are formed under conditions far from thermodynamic equilibrium. The approach is based on lowtemperature molecularbeam deposi� tion in a vacuum onto a surface cooled by liquid nitro� gen. During this process, amorphous (glassy) layers of the water-gas mixture are initially formed, which are stabilized by high viscosity. Heating of the amorphous layers is accompanied by avalanchetype nucleation and growth of gas hydrate crystallization sites. This method requires neither high pressures nor stirring of the water-gas system. Its advantage is that it is univer� sal and can be used for producing various gas hydrates. This work deals with studying the glass transition and crystallization of amorphous condensates of the binary water-propane system obtained by lowtem� perature condensation to determine the conditions of crystal hydrate formation. Amorphous solid (glassy) layers of lowmolecular� weight substances can be obtained by molecularbeam deposition onto a cooled surface. At low temperatures, the amorphous state of these substances is stabilized by the high viscosity. Molecularbeam deposition onto a copper substrate cooled by liquid nitrogen affords amorphous layers of water and simple molecular com� pounds (1), as well as of aqueous solutions of organic liquids (2). Cooling rates under these conditions are as high as 10 5 -10 7 K/s. On heating, the condensates undergo glass transition (softening) and subsequent spontaneous crystallization. In the course of the latter, a decisive role for phase transformation is played by homogeneous nucleation. The crystallization of amorphous water-gas condensates can result in the formation of gas hydrates (3-5). Hydrate formation is facilitated by the low chemical affinity of the hydrate� forming substance, as well as by the size and shape of its molecules corresponding to the geometry of cavi� ties in the arising clathrate framework. Among such substances, there are light hydrocarbons of the meth� ane series. Experiments with lowtemperature con� densates of the water-methane mixture showed the possibility of producing massive samples of crystal hydrates with high gas content capable of sustained burning (5).

Solid particles in an elastomer matrix: impact of colloid dispersion and polymer mobility modification on the mechanical properties

The reinforcement of elastomers by inorganic fillers, a concept of very high technological importance, is commonly understood to result from the presence of a mechanical network of partially aggregated filler particles. The non-linear mechanical properties, in particular the decrease of the modulus at high strain (Payne effect), are further interpreted to be a consequence of the breakdown of this filler network. There are, however, many open questions concerning the actual nature of the interparticle connections, where a modified polymer layer forming “glassy bridges” constitutes one possibility. In this work, we address this issue with a suitable silica-filled model elastomer, where we characterize the silica dispersion by SANS in combination with reverse Monte-Carlo modeling, and the mobility modification of the polymer by low-field proton NMR spectroscopy. In our samples, we identify a glassy layer as well as a region of intermediate mobility (possibly modified Rouse modes). Based on the structural information from SANS, we are able to quantify the amount of interparticle connections, and correlate it with the magnitude of the Payne effect taken from shear rheology. This works only if we assume that these connections comprise both, the glassy layer as well as the region of intermediate mobility. The amount of glassy immobilized polymer only does not suffice to explain the mechanical properties.

Temporal stability of blue phosphorescent organic light-emitting diodes affected by thermal annealing of emitting layers

Emitting layers were thermally annealed at 20 to 100 °C for varying durations without causing phase transformation in the rest of the PhOLEDs. Heating EMLs above their Tgs with a free surface created pinholes filled by the underlying TAPC melt with concurrent interlayer mixing to emit satellite peaks accompanying FIrpic's phosphorescence. With a robust glassy TmPyPB layer on top of the EML, pinholes and fortuitous fluorescence could be prevented. Annealing of mCP:SiPh4:FIrpic induced crystallization in 1 h, while mCP--PhSiPh3:FIrpic consistently resisted crystallization under all conditions. Crystallization or pinhole formation diminished EQE and driving voltage at the same time. Without incurring pinhole formation in the absence of a free surface presented by the EML, annealing of mCP:SiPh4:FIrpic at 60 °C for 1 h led to about 50% loss in EQE. In contrast, the pristine device's EQE persisted with mCP--PhSiPh3:FIrpic annealed at 60 °C for up to 24 h, beyond which other sources of device failure took over. The concept of bipolar hybrids holds promise for mitigating morphological instability as part of the challenge to the PhOLED device lifetime.

Wrinkling of a nanometric glassy skin/crust induced by drying in poly(vinyl alcohol) gels

During drying of a chemically crosslinked poly(vinyl alcohol) gel, we observed, by atomic force microscopy (AFM) and scanning electronic microscopy, micron-order wrinkling which remains until the end of drying. We show that while at high humidity drying is homogeneous and no surface instability is observed, fast drying at low humidity induces the formation of a glassy skin layer on the soft bulk that wrinkles because the skin is compressed as the bulk contracts. The role of the glass transition is not only to create a mismatch of the elasticity with the bulk but also to remove the in-plane tensile tension which stretches the skin before drying. We proved experimentally the presence of this thin glassy skin on the wet bulk by approach–retract curve measurements in AFM. We also comment on the effect of mechanical restraint and the observation of hierarchical wrinkling over different length scales.

Oxidation of ultra-high temperature transition metal diboride ceramics

The oxidation behaviour of transition metal diboride ceramics is reviewed with emphasis on the performance of zirconium diboride and hafnium diboride. First, the oxidation behaviour of nominally pure diborides is discussed, focusing on the transition to linear mass gain kinetics at temperatures above ∼1100°C. Next, the use of SiC and other additives that produce silica based scales when oxidised is reviewed. These additives improve oxidation protection due to the formation/stability of the outer layer of borosilicate glass that acts as a barrier to diffusion of oxygen to the substrate. However, elevated temperatures (>1650°C) and/or the combination of aerodynamic flow, high heat flux and reactive atmosphere associated with hypersonic flight destabilises the outer oxide and decreases oxidation protection. Other additives that affect the composition and structure of the crystalline oxide scale without forming an outer glassy layer are a promising approach to improving oxidation behaviour of diborides. These additives require further research to understand the mechanisms of improved protection and further optimise the protective behaviour. While the oxidation of ultra-high temperature diborides has been studied for many years, several possible areas for future research are identified.

Composite Layers with Ceramic Matrix Modified with Glassy Carbon Destined for Oil-Less Sliding Pairings

Composite Layers with Ceramic Matrix Modified with Glassy Carbon Destined for Oil-Less Sliding Pairings The paper presents basic knowledge about producing and some results of tribological and metallographical research on composite layers with porous, anodic hard coating matrix which were modified with glassy carbon nanotubes. These composite layers were formed as surface layers of machine parts operating under conditions of sparse lubrication (limited lubrication) and friction in air. The layers were tested at sliding mating with EN-GJL-350 cast iron used for piston rings in combustion engines and air compressors. On the basis of the metallographical tests was the structure of the composite layer described. It was fount that on the surface of the oxide is a glassy carbon layer and in the pores of oxide are regullary carbon nanotubes. On the basis of the obtained results of tribological tests it was found that glassy carbon layer on the oxide surface shorts the wering-in time, and the glassy carbon nanotubes formed inside the pores of anodic hard coating upon EN-AW-6061 aluminum alloy prove to be effective solid lubricants and complement lubrication function of the graphite in cast iron. Consequently the coefficient of friction was lower than in case of nanotubes-free oxide layers.

Effect of CrSi2 and HfB2 addition on densification and properties of ZrB2

Effect of CrSi2 and HfB2 addition on densification and properties of ZrB2 has been investigated. Dense samples of ZrB2+10%CrSi2 and ZrB2+10%CrSi2+10%HfB2 were prepared by hot pressing. Addition of CrSi2 assisted in densification of ZrB2 at lower hot pressing temperature (1650°C) and pressure (20MPa). During sintering, formation of ZrSi2 took place which helps in densification by liquid phase sintering. Hardness of ZrB2 with silicide was measured to be lower than the monolithic ceramic, but the fracture toughness was higher. CrSi2 addition improved the oxidation resistance of ZrB2 in the temperature range of 800–1000°C due the formation of silica based glassy layer on the surface. Addition of HfB2 to this composite has been found to increase the hardness. Oxidation resistance of the composite containing 10%HfB2 was found superior compared to other samples. Thus a composite having a higher fracture toughness and better oxidation properties than monolithic ZrB2 has been developed with the addition of CrSi2 and HfB2.

Melt crystallization of syndiotactic polypropylene in nanolayer confinement impacting structure

Layer multiplying coextrusion technique was used to fabricate films with hundreds of alternating layers of a crystallizable polymer, syndiotactic polypropylene (sPP), and an amorphous polymer, polycarbonate (PC). Atomic force microscopy and wide-angle X-ray scattering revealed the absence of any oriented crystal morphology of sPP in the extruded layered films. An approach of isothermal melt recrystallization of sPP nanolayers revealed the formation of oriented lamellae under the rigid confinement of hard glassy PC layers. X-ray scattering data showed that sPP crystallized as stacks of single crystal lamellae oriented parallel to the layers at high crystallization temperatures. As the crystallization temperature decreased, on-edge lamellar orientation was preferred. Formation of in-plane lamellae was attributed to heterogeneous bulk nucleation, while nucleation of on-edge lamellae was initiated at substrate interface. It was observed that as the layers thickness reduced, the orientations of both in-plane and on-edge lamellae became sharper. Detailed analysis of crystal orientations in 30 and 120 nm sPP layers was carried out. Melt recrystallization of 30 nm layers revealed formation of in-plane lamellae above 90 °C and mainly on-edge lamellae below 70 °C. At intermediate temperatures, formation of mixed crystals was reported. In 120 nm layers, crystallization temperature of 100 °C was required to form in-plane crystals, while on-edge lamellae were formed below 90 °C. We also investigated crystallization onset for on-edge and in-plane lamellar nucleation. Although, the two crystal fractions were significantly affected as a function of crystallization temperature, it was noticeable that both crystal habits were initiated at the same time. The results suggested that the relative growth rates of in-plane and on-edge crystal orientations was responsible for different fractions of the two crystal orientations at a given crystallization temperature. Oxygen transport properties of melt recrystallized sPP layers were measured. When the melt recrystallization temperature increased from 85 to 105 °C in 120 nm sPP layers, at least one order of magnitude enhancement in the barrier properties was observed. It was evident from the X-ray data that the amount of in-plane crystal fraction increased with increasing crystallization temperature. In-plane crystals acted as impermeable platelets to oxygen flux resulting in improved gas barrier properties. A similar effect was observed in 30 nm sPP layers over a temperature range of 60–105 °C. A correlation between in-plane crystal fraction and the oxygen permeability was obtained from X-ray and oxygen transport data analysis. It was shown that the permeability decreased exponentially with increasing in-plane crystal fraction.