Flexural strength of glass–ceramic for structural applications

In order to characterise the design strength of an innovative type of glass–ceramic with a view to structural applications, 4-point-bending and Ring-on-Ring biaxial bending tests have been performed. Strength is comparable with that of tempered glass but remarkably, the material breaks into large pieces like annealed glass. Interpreted through Weibull-type probability distributions, the data show much lower dispersion with respect to glass. Additional tests performed at different load rates have allowed an evaluation of the effects of static fatigue. Using a phenomenological model of equivalent-crack growth, a method is presented to calculate the decay of strength with loading time. As expected, this material is proven to be less sensitive than glass to this type of degradation.     

A high ionic conductive glass fiber-based ceramic electrolyte system for magnesium‒ion battery application

The rechargeable magnesium-ion batteries are one of the emerging alternatives of lithium-ion batteries as it has a high volumetric capacity, non-toxic nature and a divalent charge of Mg-ions. The design of an excellent performing magnesium-ion battery requires a stable electrolyte system with high ionic conductivity. However, there is a lack of understanding of how different materials affect the properties of separators in terms of ionic conductivity and stability. In the present study, an attempt has been made to compare the physical and electrochemical characteristics of glass-ceramic and polypropylene membranes as separators in the magnesium-ion battery, using magnesium bis(trifluoromethanesulfonimide) and propylene carbonate as an organic electrolyte. The characterization like X-ray diffraction, field emission electron microscopy, electrolyte uptake, ionic conductivity, voltage stability, thermal stability and transference number are thoroughly examined for both the membranes. The glass-ceramic electrolyte system showed significantly higher ionic conductivity of 9.22 mS cm⁻¹ at room temperature as compared to the polypropylene membrane. Additionally, the glass-ceramic electrolyte system showed higher thermal and voltage stability.     

New glass and glass–ceramic sealants for planar solid oxide fuel cells

This work describes the design of three new glass and glass ceramic compositions to join the ceramic electrolyte (YSZ wafer) to the metallic interconnect (Crofer22APU) in planar SOFC stacks. The designed sealants are low-sodium, barium free and boron-oxide free silica-based glasses.The sealing process was optimized for the most promising composition and joined Crofer22APU/glass–ceramic sealant/YSZ samples were morphologically characterized and tested for 300 h in humidified hydrogen atmosphere at the fuel cell operating temperature of 800 °C. The study showed that the use of the glass–ceramic was successful in joining the YSZ ceramic electrolyte to the Crofer22APU metallic interconnect and in preventing severe corrosion effects at the Crofer22APU/glass–ceramic interface after static treatments in humidified hydrogen at 800 °C for 300 h.     

A computational analysis of a ZrO2–SiO2 scale for a ZrB2–ZrC–Zr ultrahigh temperature ceramic composite system

The success of a ceramic composite for ultrahigh temperatures (i.e., >1873 K) in an oxidizing atmosphere resides in the protective characteristics of a scale to limit oxygen ingress or to control the oxygen reaction into the substrate. With temperature changes from room temperature to ultrahigh temperatures, the mechanics of the scale and its reactivity becomes critical for ceramic composites to operate under extreme environments. A study was pursued to design computationally a SiO₂–ZrO₂ scale for a ZrB₂/ZrC/Zr–Si composite by using conventional finite element analysis, which was used as a baseline microstructure for the extended finite element method. The model of the Zr boride/carbide composite with a SiO₂/ZrO₂/ZrSi_x scale simulates the development of local strain energetics under a thermal load from 300 to 1700 K. The computational analysis determined that the size of the SiO₂ and ZrSi_x precipitates does not appreciably influence the durability of the microstructure. A simulated annealing optimization algorithm was also developed for an extended finite element program (called XMicro) with the purpose of optimizing the auto re-meshing of XMicro and thus minimizing its combinatorial selection of a composite's reinforcement architecture. After correcting for the overlapping of ZrO₂ precipitates within a matrix, XMicro determined that 1.96 μm as the optimal spacing of precipitates within a cluster and 20 μm between clusters within a silica matrix of the scale interphase. The strategic experimentation determined that porosity developed during oxidation should be incorporated into the simulation of a ceramic composite. To probe into the efficacy of the silica layer for the scale, oxidizing experiments were performed at 1973 K, as well as microstructural analysis of the scale interphase. The computational mechanics coupled with consideration of the thermodynamic stability of phases for the Zr–Si–O system to set the oxygen potentials between layers can design a scale interphase for an ultrahigh-temperature, ceramic composite system. The processing challenge would be to attain the optimal configuration of the microstructure, for example, silicide precipitates developed with the appropriate spacing along a scale/matrix interface or ZrO₂ clusters within a silicate phase.     

Effect of silicon carbide whisker reinforcement on CaO–ZrO2–SiO2 glass–ceramic system

Abstract

An industrial frit formulated in the new CaO–ZrO₂–SiO₂ glass–ceramic system was studied as a matrix for whisker reinforced composites. The frit was ball milled in acetone and wet ultrasonically mixed with 5, 10, 20, and 30 vol.-% SiC whiskers in order to overcome whisker agglomeration and obtain intimate mixing of the two phases. The samples were hot pressed at 14 MPa in graphite dies, using a N₂ atmosphere, for 2 h at 1280°C. In order to investigate the effect of whiskers as a reinforcement, flexural strength as well as crack configuration and propagation were taken into consideration. Whisker orientation perpendicular to the hot pressing direction was found by SEM observation, and no carbon layer at the whisker/matrix interface was detected by EPMA. Further characterisation of the specimens involved physical (density, elastic modulus) and microstructural properties (XRD, SEM, TEM). The result of glass devitrification was inter locked wollastonite crystals.     

Preparation of structured meso–macroporous silica materials: influence of composition variables on material characteristics

Meso–macroporous silica materials with a well-ordered array of mesopores were prepared from oil-in-water emulsions. The influence of the following three composition variables on material characteristics was studied: the dispersed phase fraction of the emulsion, the concentration of silica used and the concentration of surfactant. The obtained materials were characterized via small-angle X-ray diffraction scattering, scanning electron microscopy, transmission electron microscopy, Hg intrusion porosimetry and nitrogen adsorption–desorption isotherms. A network of structured mesopores was obtained even when using a highly concentrated emulsion (volume of the disperse phase, ? ≥ 0.75). The mesopores network presented a hexagonal arrangement, with mesopore diameters between 4 and 7 nm. Non-ordered macropores, with diameters between 50 nm and 10–15 μm were also present, depending on composition variables. The isotherms were of type IV, typical of mesoporous materials, but at high p/p₀ they were the usual shape for the macroporous materials. The possibility of tailoring mesopore and macropore structures by altering in composition variables could extend the application of these materials.     

Ionic conductivity behavior by activated hopping conductivity (AHC) of barium aluminoborosilicate glass–ceramic system designed for SOFC sealing

Non-conducting BaO-B₂O₃-Al₂O₃-SiO₂ parent glasses designed for solid oxide fuel cell (SOFC) sealing applications were prepared using the melt-quenching technique. The glass formation region was determined according to phase equilibrium relations and was found to be in the composition range 70BaO-(x)Al₂O₃-(10−x)B₂O₃-20SiO₂ where 3.0 < x < 6.0 wt%. The conductivity values obtained conductivity ranged from 10⁻⁵ to 10⁻¹⁰ S/cm at temperatures between 600 and 850 °C. The batch compositions presented a threshold of dc conductivity near 70BaO wt% with a quasi linear behavior with the decrease of the BaO content. Different values of conduction activation energy were observed at temperatures above the glass transition temperature (T_g) (up to 700 °C), which were attributed to the thermal bond-breaking of non-bridging oxygen (NBO) defects. The experimental results of the electrochemical characterization by impedance spectroscopy of glass–ceramic interfaces with yttria-stabilized zirconia (YSZ) acting as solid ionic conductor electrolyte are presented and discussed.     

Sol–gel based fabrication and characterization of new bioactive glass–ceramic composites for dental applications

The fabrication of a new composite glass–ceramic with potential application in dental restoration was investigated. The developed material aims to modify the surface of dental ceramics creating bioactive surfaces able to improve material–cell interaction enhancing the bonding of the marginal gap between restoration and tooth. The application of the sol–gel method led to a microporous homogeneous glass–ceramic which can be applied as coating on commercial dental ceramic substrates. The microstructural, thermal, mechanical and biological properties of the fabricated coatings were studied and compared to the respective results of a previously investigated glass–ceramic composite. The material–cell interaction on these two sol–gel dental composites was studied in detail. The attachment and proliferation of both periodontal ligament and gingival fibroblast cells confirmed the bioactive behavior of the new materials and their ability to be potentially applied in dental restorations for soft tissue regeneration and sealing of the marginal gap.     

Effect of iron oxide content on the crystallisation of a diopside glass–ceramic glaze

The effect of iron oxide content on the crystallisation of a diopside glass–ceramic glaze was investigated using a glass–ceramic frit in the K₂O–ZnO–MgO–CaO–Al₂O₃–SiO₂ system and a granite waste glass. Measurements by X-ray diffraction (XRD) combined with scanning electron microscopy (SEM) and EDX microanalysis showed that the distribution of Fe³⁺ ions among different crystalline phases such as franklinite (ZnFe₂O₄) and hematite Fe₂O₃ depends on the iron content in the original diopside mixture. Thus, the original glaze crystallises to franklinite or hematatite when iron content is greater than 2 and 15%, respectively.     

A biomimetic mesoporous silica–polymer composite scaffold for bone tissue engineering

A biomimetic organic–inorganic composite system comprising of microspheres fabricated from combination of a biodegradable polymer poly(lactide-co-glycolide) (PLGA) and bioactive mesoporous silica (SBA-15) has been developed through sintering technique for bone regeneration applications. The morphological and structural properties of the SBA-15/PLGA composite scaffold were evaluated using electron microscopy and fourier transform infrared spectroscopy and the results showed spherical morphology and composite nature. The presence of mesopores in the silica was confirmed through nitrogen adsorption–desorption isotherms. The surface area and pore size of mesoporous silica were found to be 792 m² g^?1 and 3.7 nm, respectively. The thermal characteristics of the SBA-15/PLGA composites studied using thermogravimetry analysis shows a weight loss of around 80% with the degradation occurring at 324?°C. The prepared scaffold is also found to support the adhesion and proliferation of osteoblast cells. The expression of specific bone markers is significantly enhanced in the SBA-15/PLGA composite scaffold when compared with the pristine polymeric scaffold indicating the positive effect of mesoporous silica. Hence, these SBA-15/PLGA composite scaffolds can be explored further for bone regeneration applications.     

A novel polyborosilazane for high-temperature amorphous Si–B–N–C ceramic fibres

Polyborosilazane synthesised from BCl₃, HMeSiCl₂, and Me₃SiNHSiMe₃ is easy to cross-link for dehydrogenation of Si–H and N–H, which limits its practical applications for Si–B–N–C fibres on an industrial scale. Therefore, in this context, MeSiCl₃ was used instead of HMeSiCl₂ to synthesise a novel polyborosilazane with limited cross-linking density to fabricate Si–B–N–C fibres. The polyborosilazane synthesised from BCl₃, MeSiCl₃, and Me₃SiNHSiMe₃ exhibits good melt-processability and 1 km long polyborosilazane fibre can be obtained by melt spinning. Prior to pyrolysis, chemical curing with vapour HSiCl₃ at 80 °C was utilised to make the λ green fibres infusible. The as-cured fibres were subsequently pyrolyzed at 1200 °C in nitrogen atmospheres to provide Si–B–N–C ceramic fibres with ca. 1.5 GPa in tensile strength, ca. 160 GPa in Young's modulus, ca. 12 μm in diameter and keeping amorphous up to 1700 °C, which makes them to be promising reinforcements in ceramic matrix composites for high temperature applications.     

logmip: a disjunctive 0–1 non-linear optimizer for process system models

Discrete-continuous non-linear optimization models are frequently used to formulate problems in process system engineering. Major modeling alternatives and solution algorithms include generalized disjunctive programming and mixed integer non-linear programming (MINLP). Both have advantages and drawbacks depending on the problem they are dealing with. In this work, we describe the theory behind logmip, a new computer code for disjunctive programming and MINLP. We discuss a hybrid modeling framework that combines both approaches, allowing binary variables and disjunctions for expressing discrete choices. An extension of the logic-based outer approximation (OA) algorithm has been implemented to solve the proposed hybrid model. Computational experience is reported on several examples, which are solved using disjunctive, MINLP and hybrid formulations.     

Sn-based glass–graphite-composite as a high capacity anode for lithium-ion batteries

Sn-based anode has been widely studied because of its high theoretical specific capacity. However, the capacity of Sn-based anode decreases sharply during the cycle, which hinders its application in commercial batteries. In this paper, Sn-based glass was successfully obtained by melt quenching method. Sn-based glass and graphite were combined by the ball milling method as anode materials. The Sn-based glass–graphite-composite anode can still maintain the capacity of 700 mA h g⁻¹ after 500 cycles at 500 mA g⁻¹, which is about 2.7 times that of the Sn glass anode (260 mA h g⁻¹) under the same test conditions. The addition of graphite can effectively inhibit the accumulation of Sn particles in the discharge process of Sn-based glass anode, which improves the capacity of Sn-based glass anode, and the addition of graphite can effectively reduce the resistance of Sn-based glass anode. Therefore, the Sn-based glass–graphite-composite anode has excellent Li⁺ ions storage properties.     

Lewis and Brønsted acid catalysis with AlMCM-41 and AlMMS: dependence on exchange cation

Mesoporous solid acid catalysts based on AlMCM-41 and AlMMS have been prepared. The two catalysts exhibit similar unidimensional pore structures with hexagonal symmetries. AlMMS shows less long-range order than AlMCM-41 but is considerably easier to synthesise. The catalytic activities have been measured and compared in the Lewis-acid-catalysed alkylation of toluene with benzyl chloride, and the Brønsted-acid-catalysed alkylation of toluene with benzyl alcohol. Activities have been measured for catalysts ion-exchanged with H⁺, Fe³⁺, Al³⁺ and Na⁺, and following thermal activation at temperatures of 150–350°C. They have also been compared with K10, a mesoporous acid-treated clay catalyst. Results show that the acid-treated clay is the most active of the three catalysts in both reactions. For all catalysts, the Fe³⁺ forms exhibit the highest Lewis acid catalytic activities, and the Al³⁺ and H⁺ forms show higher Brønsted acid activities. Infrared spectra of adsorbed pyridine show relative concentrations of Lewis and Brønsted acid sites consistent with this. Differences in the dependence of catalytic activities on thermal activation temperature are interpreted in terms of the hydration properties of the catalysts.     

Asymmetric ceramic membranes from Langmuir–Blodgett deposition precursors: deposition of fatty acid salts on porous ceramic substrates

Nanoporous 7930 Vycor silica tubes and mesoporous and macroporous Anopore anodic alumina discs are examined as substrates for the multilayer Langmuir–Blodgett (LB) deposition of Cd, Mg, Zn and Ca salts of the arachidic and stearic fatty acids. Conditions for successful deposition are reported. Under appropriate conditions both mesoporous and macroporous Anopore aluminas allow for a full substrate coverage (maximum degree of deposition, D_d,max→1), while a Vycor substrate imposes a D_d,max⩽0.7 and a mechanism explaining the observed D_d,max values is presented. The produced ceramic oxide–LB film composites are prototype precursors for gas-separating all-ceramic asymmetric membranes, following the application of an oxidative plasma treatment.     

Efficient multiscale strategy for toughening HfB2 ceramics: A heterogeneous ceramic–metal layered architecture

A multiscale structural design was innovatively adopted herein to increase the toughness of monolithic HfB₂ ceramics. SiC whiskers (SiC_w) and graphene oxide (GO) were used as fillers for the HfB₂ matrix, whereas a ductile W foil was introduced as an interlayer to synthesize laminated HfB₂-SiC_w-rGO/W ceramics. Monolithic HfB₂-SiC_p (particulate) and laminated HfB₂-SiC_p/W ceramics were prepared using the same routes and used as controls. Following tape casting and spark plasma sintering at 1800°C, the toughness of the prepared laminated HfB₂-SiC_w-rGO/W samples was increased to 14.2 ± 0.6 MPa·m^1/2, with minimal sacrifice in flexural strength (421 ± 16 MPa). Morphological analysis of the fracture surface revealed the synergistic effects of micro-toughening (including bridging and pullout of whiskers and rGO) and macro-toughening (including crack deflection, bifurcation, and delamination) mechanisms responsible for improving the fracture toughness of the laminated HfB₂-SiC_w-rGO/W composites.     

A rat–human scale-up procedure for the endocrine system

The main contribution of this work is to present a detailed scale-up procedure between human and rats models to more accurately predict what would happen in human beings, based on the experimental results obtained from rats. This procedure begins using the human model, given by Sorensen (1985). The proposed scale-up technique required to establish some assumptions, to do an intensive search in the literature about organs volumes and flow rates of body rats and a dedicated experimental work in the laboratory with these animals. Even though it is mainly focused on studying the endocrine system behavior to obtain a proper in in silico healthy rat it can be extended to study another body regions. Several simulation results with the obtained rat model are included and confronted with experimental data of ten healthy rats. The analogy between human and rat dynamic behavior after equivalent meal intakes are also discussed.