Self‐Healing Behavior of Barium–Lanthanum–Borosilicate Glass and Its Reactivity with Different Electrolytes for SOFC Applications

The diffusion couples of lanthanum‐based barium borosilicate glass with high‐ and low‐temperature electrolytes have been heat‐treated at 850°C and 800°C, respectively, for 5, 100 and 750 h. These prepared diffusion couples have been characterized using various techniques like X‐ray diffraction (XRD), scanning electron microscopy (SEM), X‐ray dot mapping, and electron probe microanalysis (EPMA). The thermodynamic parameters like frequency factor, crystallization constants, free volume, and bulk thermal expansion coefficients have been calculated to understand the behavior of glass. Interestingly, glass revealed self‐healing tendency with heat treatment duration.     

Interaction Study of Yttria‐Based Glasses with High‐Temperature Electrolyte for SOFC

The chemical interaction study of AO–SiO₂–B₂O₃–Y₂O₃ (A = Ba, Sr) (BaY, SrY) glass with high‐temperature electrolyte yttria‐stabilized zirconia (YSZ 8 mol%) is reported as a function of different heat treatment durations. The as‐prepared glass with 10 mol% of yttria shows limited amount of crystallization at 800 °C. Due to this yttria‐based glasses BaY and SrY have been chosen to make diffusion couples with high‐temperature electrolyte and interconnect material. These diffusion couples have been heat treated at 850 °C, for 100, 200, and 500 h. The heat‐treated diffusion couples have been characterized using X‐ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). Microstructural analysis of diffusion couples shows absence of any undesired oxides and detrimental reaction products at the interface. The glass has shown good bonding characteristics and absence of cracks, pores, or any kind of delamination from YSZ. Apart from this, SrY and BaY glass seals have also shown good adhesion characteristics with Crofer 22 APU, even after 500 h at 850 °C. The morphology and microstructure of the glass matrix suggest limited amount of devitrification in the glass.     

Effect of Thermal Treatment on Chemical Interaction Between Yttrium Borosilicate Glass Sealants and YSZ for Planar Solid Oxide Fuel Cells

This article is to address the bonding and sealing capability of two yttrium borosilicate glasses. These glass seals have been tested with AISI 441 steel and high-temperature solid electrolyte that is yttria-stabilized zirconia (YSZ), as a function of different heating durations for planar solid oxide fuel cell applications in air atmosphere. The diffusion couples were prepared by slurry coating and then subjected to heat-treatment for different time durations of 1, 100, and 500 h at 850°C. In addition to this, the diffusion couples with YSZ were also thermally cycled between room temperature and 850°C. These prepared diffusion couples have been characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive spectroscopy (EDS). XRD indicated surface crystallization of the coating glass/YSZ diffusion couple. MgY glass sample shows less devitrification than the CaY glass. The overall analysis of the resulting microstructure by SEM/EDS revealed improvement in adhesion with increase in time duration of heat treatment as well as thermally cycled sample without any detrimental phase formation. The diffusion couples with AISI 441 steel have shown good adhesion with crack-free interface.     

Palladium Migration Through a Zirconium Carbide Coating in TRISO‐Coated Fuel Particles

Reaction of ZrC with Pd at temperatures up to 1500°C was examined using ZrC/Pd composite, Pd/ZrC‐coated TRISO particles, and Pd/ZrC bulk diffusion couples experiments. Intermetallic phase (Pd₃Zr) and amorphous carbon at the ZrC–Pd interfaces were identified by X‐ray diffraction (XRD), Raman and scanning electron microscope (SEM). Moreover, thicknesses of Pd₃Zr layers were measured by energy‐dispersive X‐ray spectrometry (EDS). The validity of the reaction was proved by thermodynamic calculation. The reaction kinetics parameters, i.e., the activation energy (208.2–266.5 kJ/mol) and the reaction order (3.38–3.78) for Pd attacking through a ZrC coating in TRISO particles were determined based on both the DSC curves and the growth of the Pd₃Zr layer.     

Phase Evolution of SiO2–Al2O3–ZnO–CaO–ZrO2–TiO2‐Based Glass with Added Y‐PSZ Particles

Yttria partially stabilized zirconia Y‐PSZ/glass‐ceramic composites were prepared by reaction sintering using powder mixtures of a SiO₂–Al₂O₃–ZnO–CaO–ZrO₂–TiO₂‐based glass and yttria partially stabilized zirconia (Y‐PSZ). The glass crystallized during sintering at temperatures of 1173, 1273, and 1373 K to give a glass‐ceramic matrix for high‐temperature protecting coatings. With the increasing firing time, the added zirconia reacted with the base glass and a glass‐ceramic material with dispersed zircon particles was prepared in situ. Furthermore, the added zirconia changed the crystallization behavior of the base glass, affecting the shape, amount, and distribution of zircon in the microstructure. The bipyramid‐like zircon grains with imbedded residual zirconia particles turned out to have two growth mechanisms: the inward growth and the outward growth, and its rapid growth was mainly dominated by the later one. For comparison, the referenced glass‐ceramic was prepared by sintering using exclusive glass granules and its crystallization behavior at 1173–1373 K was examined as well. Scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDS), transmission electron microscopy (TEM), and X‐ray diffraction (XRD) were used to characterize the crystallization behavior of the base glass and the phase evolution of the Y‐PSZ/glass‐ceramic composites.     

Nanocomposite materials based on zinc sulfide nanoparticles reinforced chlorinated styrene butadiene rubber

The effect of zinc sulfide (ZnS) nanoparticles in chlorinated styrene‐butadiene rubber (Cl‐SBR) was analyzed by X‐ray diffraction analysis (XRD), scanning electron microscopy (SEM), Differential Scanning Calorimetry, and impedance analyzer. The cure time, mechanical properties, and solvent transport of petroleum fuels through the Cl‐SBR/ZnS nanocomposites at different temperatures were evaluated. XRD and SEM studies showed that ZnS nanoparticles were well‐placed in the polymeric structure of Cl‐SBR. The increased glass transition temperature of the composite with the loading of nanoparticles indicated the increased molecular rigidity. Rheometric torque, alternating current conductivity, dielectric property, tensile strength, tear resistance, modulus, hardness, abrasion resistance, heat build‐up, and compression set were increased with the loading of nanoparticles, however, cure and scorch time, elongation at break, and resilience were reduced with the loading of nanoparticles. The diffusion results have been explained in terms of the size of liquid molecules and the diffusion mechanism was found to follow the anomalous trend. The activation energy for diffusion, sorption and permeation process was evaluated. These activation energy parameters were increased with the size of the penetrant molecules and also with the loading of nanoparticles. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46538.     

Chemical Expansion and Change in Lattice Constant of Y‐Doped BaZrO3 by Hydration/Dehydration Reaction and Final Heat‐Treating Temperature

Knowledge of thermal behavior of electrolyte is important for fuel cell fabrication. In this study, using high‐temperature X‐ray diffraction analysis (HT‐XRD) and thermo‐mechanical analysis (TMA), a systematic investigation of lattice constants was performed on Y‐doped BaZrO₃, which is a promising candidate for electrolyte in protonic ceramic fuel cells. The results revealed that a chemical expansion was observed between 300°C and 450°C during the heating process in HT‐XRD, and was attributed to the dehydration of BZY. Furthermore, it was found that the lattice constants of the samples doped with Y, Sm, Eu, and Dy were larger for the ones finally heat‐treated at 1600°C for sintering than those heat‐treated at 1300°C for synthesizing. The similar behavior was not observed in Sc‐doped samples.     

Rare‐earth‐doped SiO2‐CaF2 glass ceramic nano‐particle with upconversion properties

Rare‐earth‐doped upconversion nano‐phosphor shows new possibilities in the field of bioimaging because of its unique properties like higher penetration depth, low signal to noise ratio (SNR), good photo stability, and zero auto fluorescence. The oxyfluoride glass system is the combination of both fluoride and oxide where fluoride host offers high optical transparency due to low phonon energy and oxide network offers high physical stability. Thus, in the present work, an attempt has been made to synthesize 1 mol% Er³⁺ doped SiO₂‐CaF₂ glass ceramic nano‐particles through sol‐gel route. The synthesized glass ceramic particles were heat treated at 4 different temperatures starting from 600°C to 900°C.The X‐ray diffraction (XRD) analysis and Transmission electron microscopy (TEM) analysis confirmed the formation of CaF₂ nano‐crystals in the matrix which is 20‐30 nm in size. The vibrational spectroscopic analysis of the glass ceramics sample has been investigated by Fourier transform infrared (FTIR) spectroscopy. The UV‐Visible‐NIR spectroscopy analysis was carried out to analyze the absorption intensity in the near infrared region. Upon 980 nm excitation, the sample shows red emission corresponds to ⁴F_9/2→⁴I_15/2 energy level transition. The prepared nano‐particles showed excellent biocompatibility when tasted on MG‐63 osteoblast cells.     

In Situ X‐Ray Diffraction and Stress Analysis of Solid Oxide Fuel Cells

To increase the long term stability and performance of solid oxide fuel cell (SOFC) materials, it is important to understand the main degradation processes in their functional layers. In this work, the interface between electrolyte and anode material was investigated by in situ X‐ray diffraction (XRD) stress and phase analysis. It has been found that the determining process for the initial degradation of SOFC is the reduction of the anode material with hydrogen. During this process a tensile strength of 600–700 MPa is measured. These stresses are induced in the electrolyte material and produce crack networks. The reduction from nickel oxide to pure nickel was monitored by in situ phase analysis. This reaction induces tensile stress at the interface between electrolyte and anode. The stress produced in the electrolyte material was also confirmed by the observation of crack networks detected using scanning electron microscopy (SEM). Finally, the reducing process was optimized using different process gases, decreasing the destructive tensile stress level.     

Infrared to Visible Up‐Conversion Emission in Er3+/Yb3+ Codoped Fluoro–Phosphate Glass–Ceramics

Erbium Er³⁺ and ytterbium Yb³⁺ codoped fluoro‐phosphate glasses belonging to the system NaPO₃–YF₃–BaF₂–CaF₂ have been prepared by the classical melt‐quenching technique. Glasses containing up to 10 wt% of erbium and ytterbium fluorides have been obtained and characterized using differential scanning calorimetry (DSC) and UV–visible and near‐infrared spectroscopy. Transparent and homogeneous glass–ceramics have been then reproducibly synthetized by appropriate heat treatment above glass transition temperature of a selected parent glass. Structural investigations of the crystallization performed through X‐ray diffractometry (XRD) and scanning electron microscopy (SEM) have evidenced the formation of fluorite‐type cubic crystals based during the devitrification process. Finally, infrared to visible up‐conversion emission upon excitation at 975 nm has been studied on the Er³⁺ and Yb³⁺ codoped glass–ceramics as a function of thermal treatment time. A large enhancement of intensity of the up‐conversion emissions–about 150 times‐ has been observed in the glass–ceramics if compared to the parent glass one, suggesting an incorporation of the rare‐earth ions (REI) into the crystalline phase.     

Ethylene–octene copolymer (engage)–clay nanocomposites: Preparation and characterization

In this work, preparation and properties of nanoclay modified by organic amine (octadecyl amine, a primary amine) and Engage (ethylene–octene copolymer)–clay nanocomposites are reported. The clay and rubber nanocomposites have been characterized with the help of Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X‐ray diffraction (XRD). The X‐ray results suggest that the intergallery spacing of pristine clay increases with the incorporation of the amine. The XRD peak observed in the range of 3–10° for the modified clay also disappears in the rubber nanocomposites at low loading. TEM photographs show exfoliation of the clays in the range of 10–30 nm in Engage. In the FTIR spectra of the nanocomposite, there are common peaks for the virgin rubber as well as those for the clay. Excellent improvement in mechanical properties, like tensile strength, elongation at break, and modulus, is observed on incorporation of the nanoclay in Engage. The storage modulus increases, tan δ peak decreases, and the glass transition temperature is shifted to higher temperature. The results could be explained with the help of morphology, dispersion of the nanofiller, and its interaction with the rubber. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 603–610, 2006     

An improved basis for characterizing the suitability of fly ash as a cement replacement agent

Fly ash is a critical material for partial replacement of ordinary portland cement (OPC) in the binder fraction of a concrete mixture. However, significant compositional variability currently limits fly ash use. For example, the performance of OPC‐fly ash blends cannot be estimated a priori using current characterization standards (eg, ASTM C618). In this study, fly ashes spanning a wide compositional range are characterized in terms of glassy and crystalline phases using a combination of X‐ray fluorescence (XRF), X‐ray diffraction (XRD), and scanning electron microscopy with X‐ray energy‐dispersive spectroscopy (SEM‐EDS) techniques. The compositional data are distilled to a unitless parameter, the network ratio (N_r), which represents the network behavior of atoms that form alkali/alkaline earth‐aluminosilicate glasses that make up fly ashes. N_r is correlated with known composition‐dependent features, including the glass transition temperature and amorphous XRD peak (“hump”) position. Analysis of heat release data and compressive strengths are used to evaluate the impact of fly ash compositions on reaction kinetics and on the engineering properties of cement‐fly ash blends. It is shown that fly ashes hosting glasses with a high network ratio (ie, having a less stable glass structure) are more reactive than others.     

Determining the Crystal Volume Fraction of BS2 Glass by Differential Scanning Calorimetry and Optical Microscopy

In this work, the crystal volume fraction, α(t), of a barium disilicate (BS₂) glass‐ceramic was carefully investigated by optical microscopy (OM) and differential scanning calorimetry (DSC). X‐ray diffraction experiment revealed that the reflected peaks of the glass‐ceramic, which was prepared by heat treatment at 1000°C for 12 h, were indexed as the low‐temperature orthorhombic sanbornite mineral phase. This result was confirmed by the refinement of the crystal structure parameters. Bulk samples were then heat‐treated in the range of 760°C to 830°C. In each case, the α(t) values obtained by DSC were higher than those determined by OM due to surface crystallization and the formation of new nuclei during the heating/cooling steps in the DSC experiments. OM and DSC techniques were also used to estimate the number of preexisting nuclei, N_q, in a set of samples heat‐treated at 790°C directly in the DSC furnace. At this temperature, it was found that the N_q obtained directly by OM measurements were in reasonable agreement with those calculated from the combination of overall crystallization with crystal growth kinetics.     

Anomalous enhancement of photoluminescence intensity of sintered YAG:Ce particles‐embedded glasses

For high‐power white LED applications, YAG:Ce‐based yellow phosphors were embedded in a low‐T_g Bi₂O₃–B₂O₅–ZnO–Sb₂O₅ glass by sintering route. Effects of sintering temperature (325‐390°C) on the microstructure and photoluminescence properties were investigated. X‐ray diffraction was used to measure the retained fraction of YAG:Ce phase after sintering. Scanning electron microscope and transmission electron microscope, equipped with energy‐dispersive X‐ray spectrometry, were used to examine the microstructure, including the element distribution across the phosphor–glass interface. Photoluminescence properties of the samples before and after sintering were compared. With the increasing sintering temperature, the retained fraction of YAG:Ce decreased from 83.3% to 82%. This effect tends to reduce the luminescence intensity of the samples after sintering. The increasing sintering temperature also enhances the diffusion of cations (esp. Bi) from glass matrix to YAG:Ce. This effect tends to increase the luminescence intensity of the YAG:Ce particles after sintering. When the sintering temperature was lower (325°C), the effect of YAG:Ce loss was dominant, thus the luminescence intensity was reduced after sintering. When the sintering temperature was higher (350‐390°C), the effect of solute dissolution was dominant, resulting in luminescence intensity anomalously higher than that before sintering. Similar result has not been reported in literatures. The maximum luminescence intensity of the sintered samples is 1.57 times as high as that of the samples before sintering.     

Influence of portlandite on Pyrex glass dissolution and the formation of alkali‐silica chemical reaction products

The dissolution behavior of Pyrex glass in a model system consisting of 1‐M NaOH with varying amounts of portlandite, representing the glass dissolution in alkaline environment and alkali‐silica reaction (ASR) in cementitious materials, is studied. The Pyrex glass dissolution and the reaction products were characterized using X‐ray diffraction (XRD), ²⁹Si nuclear magnetic resonance (²⁹Si‐NMR), and scanning electron microscopy with energy dispersive X‐ray (SEM/EDX), and the silica and calcium concentrations in the liquid phase were determined using inductively coupled plasma atomic emission spectroscopy (ICP‐AES). The experimental results show that the dissolution of the Pyrex glass continued until it consumed the portlandite and then reached a constant rate, with a linear relationship with the amount of portlandite. The absence of calcium and reduction of silica concentration in the liquid phase with the increase in portlandite indicate the formation of high‐reaction products with portlandite, confirmed by XRD and ²⁹Si‐NMR. The calcium sodium silicate hydrate (C–N–S–H) and sodium silicate hydrate (N–S–H) are the main ASR products; their composition and proportions strongly depend on the reaction time and the amount of portlandite added. A thermodynamic model, which couples geochemical code (PHREEQC) and the experimental silica dissolution rate, was used to predict ASR products and the remaining portlandite. The simulation results predicted the experimental data fairly well for different portlandite additions. The mechanism for Pyrex glass dissolution in the presence of varying portlandite additions is discussed with regard to experimental data and simulation results.     

Reactions between Strontium-Substituted Lanthanum Manganite and Yttria-Stabilized Zirconia: II, Diffusion Couples

Formation of secondary phases and diffusion of cations in diffusion couples of yttria-stabilized zirconia and lanthanum manganite substituted with 0 to 60 mol% strontium have been studied by scanning electron microscopy and energy dispersive X-ray spectroscopy. Only the primary phases were observed after 120 h at 1200°C, while formation of secondary phases was identified already after 1 h heat treatment at 1350°C. The phase composition of the reaction layer altered from La₂Zr₂O₇ to SrZrO₃ at increasing Sr content in La _x Sr_{1- x} MnO₃. The thickness of the reaction layer was increasing with heat treatment time. In diffusion couples of La_0.4Sr_0.6MnO₃ formation of manganese oxide was observed in the perovskite layer after 1 h heat treatment at 1350°C, while isolated grains of SrZrO₃ relatively deep inside the zirconia were observed after longer heat treatment time. Diffusion of Mn into zirconia was observed preferenced along grain boundaries in the early stage of the interface reaction.     

X‐ray Absorption Spectroscopy Studies of the Room‐Temperature Ferromagnetic Fe‐Doped 6H–BaTiO3

We investigated the effect of annealing temperature on magnetic properties of 2% and 10% Fe‐doped BaTiO₃. To understand the possible structural differences between samples treated at different annealing temperatures, and to correlate them with the magnetic properties, several characterization techniques, such as X‐ray diffraction and X‐ray absorption spectroscopic methods (XANES and EXAFS) were employed. We found that the 2% Fe‐doped BaTiO₃ pseudocubic perovskite is paramagnetic regardless of the heat‐treatment conditions. Initially paramagnetic 10% Fe‐doped 6H–BaTiO₃, treated at 1250°C, became ferromagnetic after additional annealing at higher temperature. We have crystalographically characterized the cation ordering processes in the 6H–BaTiO₃ that occurred during the high‐temperature annealing. The ferromagnetism that is induced in this stage is most probably associated with the observed diffusion processes but it extrinsic character still cannot be fully disregarded.     

Zirconia Nanostructures: Novel Facile Surfactant‐Free Preparation and Characterization

Zirconia nanostructures have been prepared via a facile precipitation route using Zirconium (IV) oxynitrate hydrate and tetraethylenepentamine (TEPA). Here, TEPA was used as novel precipitator to fabricate zirconia nanostructures. The influence of reaction time, dosage of TEPA, and solvent was also examined to control the shape and particle size. Results of this work indicate that these reaction parameters have important impact on the control of shape and grain size of the zirconia. To characterize the as‐synthesized nanostructures, techniques such as X‐ray diffraction (XRD), ultraviolet–visible (UV–vis) spectroscopy, energy dispersive X‐ray microanalysis (EDX), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FT‐IR) spectroscopy, and photoluminescence (PL) spectroscopy were applied. In addition, the formation mechanism of zirconia nanostructures was discussed.     

Sol–Gel Synthesis of Bioactive Glass‐Ceramic 45S5 and its in vitro Dissolution and Mineralization Behavior

Amorphous bioactive glasses such as 45S5 have been successfully used in bone‐filling therapy in non‐load bearing biomedical applications for decades. In this study, we challenge the predilection to amorphous over crystalline ceramics by investigating the effect of synthesis route on surface texture, in vitro dissolution, and mineral formation on powders produced by sol–gel and glass melt‐casting methods. Many reports have indicated bulk crystalline bioactive glass‐ceramics to be less bioactive than their amorphous counterparts as measured by the onset time for mineral formation. Bioactive glass 45S5 was synthesized using the sol–gel method followed by heat treatment to produce a semi‐crystalline structure and was compared against commercially available amorphous melt‐cast 45S5 powder. Gel‐derived samples were stabilized at 700°C making more than 80% of the structure crystalline. Dissolution of 45S5 glass‐ceramic in powder form(particle diameter 12 μm) was studied by in vitro immersion in simulated body fluid solution for various periods of time. The immersed powders were then analyzed through X‐ray diffraction (XRD), Scanning electron microscopy (SEM), energy dispersive X‐ray analysis (EDS), Differential scanning calorimetry (DSC), and thermogravimetric analysis (DSC/TGA), and Fourier transform infrared spectroscopy (FTIR) to determine the onset time for surface mineralization, and were compared with the melt‐cast powder as a control. The rates of dissolution and onset time for mineral formation were similar for the gel‐derived powder as compared with the melt‐cast control; it is proposed that the higher surface area of the sol–gel powder overcame the penalty usually associated with lower dissolution rates of crystalline materials, implicating surface texture as a much more important determinant of dissolution and mineralization behavior than mere crystallinity.     

Fire Behavior of Natural Rubber Filled with Intumescent Flame Retardant Containing Graphite

Melamine salt of pentaerythritol phosphate/graphite (MPP‐G) mixture was prepared by dispersing graphite flakes in MPP during its synthesis. The chemical structure of MPP‐G was characterized by proton nuclear magnetic resonance, fourier‐transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), and scanning electron microscope. MPP‐G was blended with natural rubber (NR) at different loading levels and its effect on the thermal stability and flammability properties of NR was studied. The cone calorimeter results exhibited that the addition of MPP‐G to NR decreased the peak of heat release rate, mean heat release rate, total heat release, mean mass loss rate, mean effective heat of combustion, and maximum average rate of heat emission. Moreover, fire growth rate index and fire performance index values showed that NR/MPP‐G composites are safer than NR. The digital photographs of char formed after cone calorimeter test indicated the formation of a coherent char. The mechanism of flame retardation was studied based on FTIR, energy‐dispersive X‐ray spectrometry, and XRD analysis of char residue. J. VINYL ADDIT. TECHNOL., 26:155–164, 2020. © 2019 Society of Plastics Engineers