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Tape casting is a flexible technique for manufacturing scalable ceramic sheets. This study fabricated La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF6428) tapes using water‐based tape casting. A high molecular weight plasticizer, polyethylene glycol 4000, was chosen to balance flexibility and mechanical strength. Adjusting the plasticizer‐to‐binder ratio (R‐value) and increasing relative humidity during drying led to crack‐free and flawless green tapes of 330 µm. The uniform polymer matrix improved homogeneity and consistency as well. An applicable suspension formulation was developed for the water‐based fabrication of LSCF tapes for continuous production. [ABSTRACT FROM AUTHOR]

Three-dimensional printing allows accurate geometries to be obtained across a wide range of applications and it is now also moving into the architecture and construction industry. In the present work, a unique binary mix composed of ordinary Portland cement (OPC) and quick-setting cement (QSC) was combined with silica sand aggregate in different proportions for a customized binder jetting 3D printing (BJ3DP) process. Specimens were printed using the blended dry powders and deionized water to determine the impact of the processing variables on the properties of the realized specimens. The results show that the properties are influenced by the binary mix proportions and the layer thickness. The investigation found significant improvement in mechanical performance on increasing the proportion of OPC and optimal conditions were identified with proportions of 35 wt% OPC and 5 wt% QSC. Notable enhancements were also observed as the layer thickness was reduced. [ABSTRACT FROM AUTHOR]

Purpose: Recent advances in 3D printing construction elements have focused on ordinary Portland cement (OPC) concrete using polymeric binders; herein, this study aims to produce the same using pure water. Design/methodology/approach: A binder jet printer prototype was used to fabricate specimens that are used to assess geometric and mechanical properties. Two distinct water-based binder formulations, compatible with OPC chemistry and piezoelectric jetting device, were used: pure water and water-polyvinyl alcohol (98:2 w/w) solution. Findings: This study examines the effect of binder flow rate on dimensional accuracy. Furthermore, the changes in the mechanical properties over time with hydration have been investigated. Practical implications: Results indicate that the increase in mechanical strength of Portland cement concrete with pure water was consistent; however, it was delayed by the water: PVA (98:2 w/w) solution. Post-curing by water vapor hardened the structure with the removal of layering native to 3DP and decreased infilling porosity by diffusion mechanism. Originality/value: This paper has used pure water jetting for BJT of Portland cement-containing bodies. [ABSTRACT FROM AUTHOR]

Since its first introduction in 2016, cold sintering process (CSP) has gained worldwide interest from the scientific community as green and innovative fabrication route due to the dramatic reduction of processing time, energy, and costs. Cold sintering resembles the geological formation of rocks where a ceramic powder is densified with the aid of a liquid phase under an intense external pressure and limited heating conditions (below 350 °C). Up to date, tens of different materials, including composites, have been successfully processed through CSP and extraordinary results in terms of densification, microstructure and final properties have been achieved. In the present review, processing features and variables, possible densification mechanisms and issues also for the realization of ceramic-based composites are explored. Advantages with respect to existing techniques are analysed and current challenges are described to lay the ground for new processing opportunities to be faced in the near future. [ABSTRACT FROM AUTHOR]

Electric forces acting on crystallographic defects generated at the flash onset or due to the surface polarization of the dielectric surrounding pores have been claimed to interact with the sintering kinetics upon flash processes. Herein, we estimated the magnitude of the external field-induced forces pointing out that the surface polarization does not play significant role on sintering. Moreover, the electric forces acting on charged defects are negligible when compared with the sintering stresses in the majority of flash experiments, only becoming comparable with the capillarity pressures when the external field is in the order of 103 V cm−1. Therefore, they can be of some relevance during flash sintering of resistive compounds like alumina or silicate glasses, they remaining normally not relevant otherwise. [ABSTRACT FROM AUTHOR]

Purpose: Three-dimensional (3D) printing technology allows geometric complexity and customization with a significant reduction in the structural environmental impact. Nevertheless, it poses a serious threat to the environment when organic binders are used. Binder jet printing of alkali-activated geopolymer precursor can represent a successful and environmental-friendly alternative. Design/methodology/approach: The present work reports about the successful 3D printing of metakaolin-based alkali-activated concrete, with dimensional integrity and valuable mechanical behavior. Findings: The geometric behavior was studied as a function of alkali activator flow rate, and the minimum geometric deviation with complete saturation was recorded at 103 mg/s. The printed specimen is characterized by a modulus of rupture as high as 4.4 MPa at 135 mg/s. Practical implications: The 3D printed geopolymer-based concrete can be potentially used in a wide range of structural applications from construction to thermal insulation elements. Originality/value: The analysis of the 3D geopolymer-based concrete printing system and material conducted in this paper is original. [ABSTRACT FROM AUTHOR]

The broad and far-reaching (beyond sintering) implications of flash processes are critically assessed. Different mass transport-based flash-like technologies are currently emerging: synthesis, pyrolysis, joining, plastic and viscous shaping. These could be used to develop new high entropy materials, to change wetting properties in ceramic-metals joints, to shape ceramics by plastic deformation. Moreover, the flash can change the chemistry of oxides thus introducing far-from-equilibrium crystallographic and/or electronic features. The development of predictive models to determine the field-current-material interactions and the produced defects could represent a new tool to design and engineer ceramics in the next future. [ABSTRACT FROM AUTHOR]

Commercial soda-lime silicate float glasses are chemically strengthened at 450 °C for 4 and 24 h in molten potassium nitrate containing small but controlled amount of NaNO 3. The ion-exchange efficiency is determined from the measurement of surface compressive stress, potassium penetration and flexural strength. Chemical strengthening remains efficient also for NaNO 3 additions up to 0.5 wt% (equivalent to ~1350 ppm Na) and the glass performance being identical to those obtained in pure KNO 3 , with no significative difference between "tin" and "air" side. For larger Na contamination residual stress and strength are reduced by an amount of about 25%. • Contamination of KNO 3 up to ~1350 ppm Na has no effect on ion-exchange efficiency. • Larger contamination reduces residual stress and strength by about 25%. • No significative difference between tin and air side of glass are revealed. [ABSTRACT FROM AUTHOR]

Abstract Calcium-phosphate glass optical fiber and capillaries (with composition identical to the core and the cladding of the fiber) were fabricated and subjected to mechanical characterization. Tensile tests were carried out to determine the strength distribution, the fatigue behavior and the elastic modulus of fibers and capillaries. The tests were performed without the application of any coating, in order to assess the behavior in bare conditions, just like in the provisional application as bio-resorbable elements. Strength ranging from 200 to 350 MPa was measured for both fiber and capillaries, the Weibull's modulus being around 3 to 6, thus revealing quite scattered distributions associated to the presence of variable surface flaws. The elastic modulus of the two glasses was shown to depend on the specific composition, the presence of MgO being responsible for a stiffer material. An evident sub-critical crack growth was also pointed out in the presence of water. Highlights • Resorbable phosphate glass optical fibers and capillaries are mechanically characterized. • The tensile strength of bare fibers ranges from 200 to 350 MPa. • The elastic modulus of the glasses scales with the MgO content. • Evident sub-critical crack growth is pointed out in the presence of water. [ABSTRACT FROM AUTHOR]

Abstract Flash sintering is a novel densification technology for ceramics, which allows a dramatic reduction of processing time and temperature. It represents a promising sintering route to reduce economic, energetic and environmental costs associated to firing. Moreover, it allows to develop peculiar and out-of-equilibrium microstructures. The flash process is complex and unusual, including different simultaneous physical and chemical phenomena and their understanding, explanation and implementation require an interdisciplinary approach from physics, to chemistry and engineering. In spite of the intensive work of several researchers, there is still a wide debate as for the predominant mechanisms responsible for flash sintering process. In the present review, the most significant and appealing mechanisms proposed for explaining the "flash" event are analyzed and discussed, with the aim to point out the level of knowledge reached so far and identify, at least, possible shared theories useful to propose future scientific activities and potential technological implementations. [ABSTRACT FROM AUTHOR]

Abstract Flash sintering represents an innovative electric field-assisted sintering technology which allows a drastic reduction of the consolidation time and temperature of many ceramics. It is still under debate whether and how the electric field and current boost the densification process. In this work, we investigate the impact of microstructural temperature gradients, associated to an overheating of the interparticle contact points, on mass transport in the different stages of flash sintering of yttria-stabilized zirconia (YSZ). Although the temperature difference between grain bulk and boundary is limited, it is associated to extremely high gradients as a result of the small particle size. In such conditions, a temperature gradient-driven atom flux can be activated. The calculations point out that thermodiffusion can significantly accelerate densification of micrometric YSZ powder upon flash sintering if the thermal gradients exceed 106 K m−1. [ABSTRACT FROM AUTHOR]

ZrB 2 is one of the most promising materials for extreme environment applications, especially in the aerospace field, due to the combination of superior thermophysical properties and low density. Nevertheless, pure ZrB 2 is intrinsically hard to sinter, requiring either the application of intense external pressure or the use of sintering aids. In the present work, the feasibility of ultrafast high-temperature sintering (UHS) for the densification of commercial ZrB 2 was explored. Thanks to the addition of B 4 C as a sintering aid, Densities up to 92–98% could be obtained in just 2 min. Hardness of 16.3–17.8 GPa was obtained for the UHS ZrB 2 -based ceramics, similar to what is reported in the literature using slower, more sophisticated and energy-consuming sintering approaches like spark plasma sintering. These first results show that UHS could provide a quick and simple way to produce high-performance ZrB 2 -based components with just a few minutes of processing time in pressure-less conditions. [ABSTRACT FROM AUTHOR]

Purpose: Particles bed binding by selective cement activation (SCA) method is a computer-aided manufacturing (CAM) technique used to produce cementitious elements. A computer-aided design file is sliced to generate G-codes before printing. This paper aims to study the effect of key input parameters for slicer software on the final properties of printed products. Design/methodology/approach: The one factor at a time (OFAT) methodology is used to investigate the impact of selected parameters on the final properties of printed specimens, and the causes for the variations in outcomes of each variable are discussed. Findings: Finer aggregates can generate a more compact layer, resulting in a denser product with higher strength. Fluid pressure is directly determined by voxel rate (rV); however, high pressures enable better fluid penetration control for fortified products; for extreme rVs, residual voids in the interfaces between successive layers and single-line primitives impair mechanical strength. It was understood that printhead movement along the orientation of the parts in the powder bed improved the mechanical properties. Originality/value: The design of experiment (DOE) method assesses the influence of process parameters on various input printing variables at the same time. As the resources are limited, a fractional factorial plan is carried out on a subset of a full factorial design; hence, providing physical interpretation behind changes in each factor is difficult. OFAT aids in analyzing the effect of a change in one factor on output while all other parameters are kept constant. The results assist engineers in properly considering the influence of variable variations for future DOE designs. [ABSTRACT FROM AUTHOR]

An electrical current upon flash sintering experiments modifies the defect chemistry of corundum and causes the formation of color centers (F-centers), consisting of discharged oxygen vacancies. This phenomenon interacts with the diffusion kinetics in the anodic region and promotes abnormal growth of some grains which reach several hundreds of micrometers in just few minutes, the grains being strongly oriented orthogonally to the current flow. [ABSTRACT FROM AUTHOR]

The effect of MnCo 2 O 4 on the electric field assisted flash sintering of CeO 2 is demonstrated. CeO 2 being a refractory material sinters, conventionally, at very high temperature (∼1500 °C) and with the assistance of 120–150 V/cm at 890–962 °C. A conducting MnCo 2 O 4 which is flash sintered at lower temperatures (200–230 °C), by utilizing fields in the range of 12.5–15.0 V/cm is added to ceria to reduce its sintering processing parameters. MnCo 2 O 4 percentage in the composite is varied to understand the significance of the constituent phases during the flash sintering. The extent of sintering along with the phase distribution in the composites is evaluated on the basis of scanning electron microscopy study in backscattered electron mode. Role of the two phases in the flash-effect is emphasized by the measurement of flash threshold parameters, I–V characteristics and specimen temperature during flash sintering. [ABSTRACT FROM AUTHOR]

Tricalcium phosphate (β-TCP) bioceramic was consolidated by flash sintering in the present work. TCP powders were synthesized by solid-state route, starting from calcium carbonate and ammonium phosphate, and shaped into cylindrical pellets of different height by uniaxial pressing. Sintering was performed within an on purpose modified dilatometer working under constant heating rate and monitoring shrinkage and electrical parameters (current and field), simultaneously. The obtained TCP bodies exhibit well densified microstructure, maintaining the β-TCP composition. A power balance model, based on a thermal runaway mechanism and considering the contribution of the contact resistance on the voltage actually applied on TCP material, is shown to successfully predict the flash phenomenon. The achieved results, although preliminary, show the possibility to employ flash sintering to obtained dense β-TCP products at lower furnace temperature and in shorter time with respect to the conventional process, avoiding the undesirable expansion related to the β–α transition. [ABSTRACT FROM AUTHOR]

In this work, we try to point out the influence of annealing prior to chemical strengthening on the mechanical strength of thin ion exchangeable alkali borosilicate glass. The effect of annealing at 425 °C on density, hardness and cracking behaviour were investigated. Then, as-received and annealed samples were subjected to ion exchange in a molten potassium nitrate bath at the same temperature for 4 h and the generation of compressive stress in glass was analyzed as well as the bending strength. Annealing makes the glass denser, improves hardness and enhances the compressive stress build-up. However, bending strength of as-received and annealed glass after ion-exchange is substantially the same, this being probably attributed to the limited case depth if compared to surface flaws. Annealing before ion exchange does not appear to be a crucial factor in improving chemical strengthening efficiency in thin borosilicate glass. [ABSTRACT FROM AUTHOR]

Two different ceramic laminates composed of porous alumina and alumina/zirconia layers were designed and produced in the present work. The two symmetrical architectures were selected whose fundamental difference is the presence on the surface of a porous layer in the first and a compact alumina/zirconia composite layer in the second. The residual stress profile and corresponding fracture toughness were tailored to promote the stable growth of surface defects prior to final failure to increase the mechanical reliability of the material. The laminates were realized by stacking together different green laminae (containing specific pore former content) in a specific order, thermo-compression and co-sintering. The results point out an important reduction of the strength scatter and a clear insensitivity to surface damage. It is also shown that the mechanical performances are strictly related to the specific architecture of the laminate, this allowing to tailor a priori the mechanical performances of the composite. [ABSTRACT FROM AUTHOR]

Soda lime silicate float glass was ion exchanged in potassium nitrate baths systematically contaminated with calcium nitrate up to 0.01 mol%. The results show that surface compression and flexural strength are dramatically depressed if the treatment is carried out in salt containing calcium nitrate in excess of 0.0015 mol%, this being related to more limited sodium-potassium exchange on the surface. The presence of calcium in the salt accounts for a “blocking” effect of the conventional Na-K exchange which is shown to be thermodynamically less favoured than Na-Ca one, especially at higher temperature. [ABSTRACT FROM AUTHOR]

Magnesia silicate glass-containing alumina was flash sintered using an E-Field in the 500–1500 V/cm range. The addition of glass allows to reduce the current needed for densification and improves the shrinkage obtained during field-assisted sintering process. This behaviour is related to the different sintering mechanisms involved in the two materials, i.e. solid state sintering for pure alumina and liquid phase sintering for glass-containing alumina. The estimated activation energy for conduction during flash sintering is compatible with ionic diffusion in silicate melt. Moreover, evidence of magnesium diffusion toward the cathode is recorded. The estimated sample temperature is in almost all cases lower than 1355 °C, which is the temperature at which the first liquid is formed in the ternary system MgO-SiO 2 -Al 2 O 3 . Finally, it is shown that the application of an E-Field accounts for efficient liquid phase sintering at temperatures at which it cannot be reproduced conventionally. [ABSTRACT FROM AUTHOR]

Two alkali borosilicate glass tubes, as used in pharmaceutical packaging, were subjected to chemical strengthening in four potassium nitrate salts, these mainly characterized by differing sodium and calcium content. The heat treatment was at 450 °C and 465 °C for 4 h. The mechanical strength of the tubes was measured by 4-point bending tests. The compressive stress build-up at the glass surface was checked by Vickers indentations. The composition of the glass surface after ion-exchange was studied by EDS analyses. The results show that treatment increases the strength to twice the initial value, and that this is similar in the two glasses. A greater sodium content in the salt slightly decreases the exchanged layer depth and, consequently, the bending strength. Conversely, even a very low calcium content in the salt dramatically decreases the efficiency of chemical strengthening: it is shown that calcium blocks the sodium-potassium exchange, this being attributed to the thermodynamically favoured Na-Ca exchange on the glass surface with respect to the expected Na-K. [ABSTRACT FROM AUTHOR]

• The application of an electric field provides beneficial effects to ion exchange in terms of processing time and temperature respect to the conventional process. • The ion-exchange rate is also determined by the chemical composition of the glass. • During multi-steps EF-IE processes, the potassium penetrated on one side can limit the exchange rate during the treatment on the opposite side although being only partially reversible. Electric field-assisted ion exchange process was carried out on an innovative soda magnesia silicate float glass by using a specifically realized equipment which allows to change the applied voltage and the polarity and to measure the flowing current. Parameters such as surface K/Na exchange rate, potassium penetration, inter-diffusion coefficient, residual stress and case depth were measured and correlated with the processing conditions. The results revealed a high propensity of the considered glass to be chemically strengthened and a beneficial effect of the applied electric field in terms of time and temperature. For treatment carried out at 410 °C potassium penetration depth in excess to 10 μm can be achieved in less than 5 min. By alternating the polarity, both sides can be homogeneously reinforced. When the duration of each single cycle at a certain polarity is increased, the potassium penetration depth increases although cycles longer than 10 min can be detrimental. [ABSTRACT FROM AUTHOR]

Nearly pure α-alumina samples produced by uniaxial pressing were flash sintered under electrical fields ranging from 500 V/cm to 1500 V/cm in experiments at constant heating rate. Sintering temperature significantly decreased with the applied E-field even down to ≈900 °C at 1500 V/cm. The onset temperature for flash sintering can be successfully modelled as a function of the applied voltage. The sintering temperature is also shown to be strongly affected by the electrode materials used during the treatment: using silver or carbon electrodes the sintering temperature is about 300 °C lower than when using platinum electrodes. In addition, the bulk density and porosity of the sintered alumina ceramic correlate strongly with the imposed current limit. Power dissipation was analysed before and during flash sintering; the activation energy for conduction was calculated in both cases, indicating that the process is based on ionic diffusion phenomena. Finally, we showed that during flash sintering the activation energy for conduction decreases, suggesting the occurrence of physical or structural modifications induced by current localization at the grain boundaries. [ABSTRACT FROM AUTHOR]

Different Thermo-Reactive Diffusion and Deposition (TRD) treatments have been analysed in the present work. The processes were carried out on UNI 42CrMoS4 (AISI 4140) steel both in the nitrided and bare state at temperatures of 825, 900 and 1000 °C, the samples being quenched in water afterwards. Hard, compact and adherent vanadium and chromium carbide and vanadium nitride coatings, mainly consisting of Cr 7 C 3 , V 6 C 5 and VN, were obtained using different processing conditions. Biphasic layers composed by two different carbides were also obtained. The average micro-hardness of the coatings ranged from 1717 ± 170 to 2451 ± 236 HV 0.02 whereas R a values between 0.2 and 1.2 μm were measured. The kinetics of the coating growth was also studied on the basis of SEM observations. It was demonstrated that the layer thickness is related to the time by a parabolic law and to the temperature by an Arrhenius-like behaviour. [ABSTRACT FROM AUTHOR]

The effect of Al doping on Ni- YSZ anode sintering in metal-supported solid oxide fuel cell ( MS- SOFC) was studied in the current work.The electrical conductivity of the Al-doped anode was found to increase considerably. Such result may be attributed to the inhibited sintering of insulating YSZ caused by the segragation of Al2O3 at grain boundaries. It was found that the addition of Al to the anode accounts for a finer grained YSZ matrix, thus coating the conducting Ni grains to a lesser extent. 5 wt% Al-doped NiO used for Ni- YSZ anode material gave the finest microstucture and the highest electrical conductivity at room temperature although it showed the lowest bulk density. Overall, Al-doped Ni- YSZ anode material was found to be a suitable material for the anode in MS- SOFC produced by cosintering. [ABSTRACT FROM AUTHOR]

Sintering of composites constituted by two nonstoichiometric phases (La0.6Sr0.4)(Co0.2Fe0.8)O3 (LSCF) and Gd0.1Ce0.9O2 (GDC) under constant electric field in constant heating rate experiment is studied in this work. The requirements of field and temperature for composite systematically increase with GDC amounts this indicating the importance of material conductivity. Sintering/grain growth rate is higher in the composite compared to pure LSCF phase. Flash-sintering phenomenon in the composite is explained on the basis of three factors: (1) large and continuous increase in conductivity of LSCF acts as source of defects, (2) maintenance of sufficient local temperature because of GDC during continuous conductivity increase facilitates the cationic diffusion, and (3) reduction reactions of LSCF, during polaron hopping conduction, and of GDC phase at higher temperature activate the sintering process. [ABSTRACT FROM AUTHOR]

Six slightly different KNO3 baths were considered in this work, for the chemical strengthening of soda lime silicate glass. Five of these were commercially available pure KNO3 salts for industrial or laboratory use and one was a salt from an unknown source that had been already used for at least 1000 h in Na-K ion exchange. Various amounts of sodium - the main impurity - calcium, and magnesium were measured in the six salts together with other more limited contaminants. Different strengthening effects associated with clearly dissimilar ion exchange efficiency were measured on glass treated in the different melts. The presence of Na - major impurity - in the salt was revealed to be not a critical aspect, at least up to concentration of about 0.5 wt%. Instead, the "blocking" effect caused by the presence of Ca and Mg in the KNO3 bath (also in amounts of few tens of ppm) is shown to be a major issue. [ABSTRACT FROM AUTHOR]

In the present work the effect of Mg 2+ ion doping (1–14 mol%) on the solid state synthesis of beta-tricalcium phosphate (β-TCP) powder and its thermal behaviour is investigated. The powders are synthesized at temperatures between 1000 and 1300 °C for 2 h, starting from brushite (hydrated calcium hydrogen phosphate—CaHPO 4 ·2H 2 O) and calcium carbonate (Ca CO 3 ). The maximum substitution of Mg 2+ ion in β-TCP lattice decreases from >14 mol% to less than 8 mol% as the synthesis temperature increases from 1000 to 1300 °C. It is also found that already in 1 mol% MgO doped powders the β-TCP phase is stabilized at temperatures higher than 1500 °C. [ABSTRACT FROM AUTHOR]

In the present work, the control of a ceramic colloidal process is aimed to fabricate NiO-YSZ composite with specific microstructure and porosity for anode-supported solid oxide fuel cell applications. The optimization of dispersant and solid concentration in anode slurries provides a reduction in their viscosity, shear stress and yield stress; concurrently, solvent evaporation and hysteresis in flow behaviour are minimized, thus improving the suspension stability. The corresponding sintered compacts produced from the optimized slurry demonstrated uniform microstructure with specific porosity distribution. It is shown that the residual porosity can be tailored in the range of 12–23% exclusively by controlling the conditions of drying, burn-out and sintering process; the lower limit allows effective gas permeation during anode reduction owing to an interconnected pore structure obtained already at 12–14% porosity. This indicates a stable pore structure derived from the burn-out of pore former even for sintering temperature as high as 1400 °C. [ABSTRACT FROM AUTHOR]

Abstract: We show that a two-phase 50vol% 3YSZ-alumina ceramic flash-sinters at a furnace temperature of 1060°C under an electrical field of 150Vcm−1. In contrast undoped, single-phase alumina remains immune to field assisted sintering at fields up to 1000Vcm−1, although single-phase 3YSZ flash sinters at 750°C (furnace temperature). The mechanisms of field assisted sintering are divided into two regimes. At low fields the sintering rate increases gradually (FAST), while at high fields sintering occurs abruptly (FLASH). Interestingly, alumina/zirconia composites show a hybrid behavior such that early sintering occurs in FAST mode, which is then followed by flash-sintering. The specimens held in the flashed state, after they had sintered to near full density, show much higher rate of grain growth than in conventional experiments. These results are in contrast to earlier work where the rate of grain growth had been shown to be slower under weak electrical fields. [Copyright &y& Elsevier]

The flash-sintering behavior of manganese cobaltite spinel (MnCo2O4) is analyzed in the present work. It is shown that the MnCo2O4 is flash-sintered at 120–150°C under 15.0–17.5Vcm−1, which is substantially lower than the conventional-sintering temperatures of 1080°C and more. We have also demonstrated that the flash-sintering is a transient phenomenon, where the power dissipation rises quickly at first and then results to Joule heating. The extent of sintering is confirmed through SEM, where a dense and pore-free morphology is observed for the well-sintered samples. The growth of secondary phase as a function of sintering temperature in both conventional and flash processes is monitored by XRD. Consistent changes in I–V curves observed at 200–700°C, suggest that the rapid increase of the conductivity during flash-effect follows the hopping mechanism of usual conductivity phenomenon. On the basis of correlation between the conductivity, phase-stability and microstructure, a mechanism for flash-sintering has been proposed. [ABSTRACT FROM AUTHOR]

In this work, step-index 40/125 μm diameter optical fibers produced from two slightly different lithium phosphate glasses were subjected to mechanical characterization. Tensile tests were carried out on fibers with gage length from 10 to 150 mm, allowing for the determination of the failure stress (ranging from ≈200 to 400 MPa) and the elastic modulus (60 GPa). Some tests were also performed with the fiber 'immersed' in water; an important subcritical crack growth effect was pointed out, and a fatigue susceptibility parameter ( n) equal to 11.4 was determined. The analysis of fracture mirror allows an estimated fracture toughness equal to 0.5 MPa m0.5. [ABSTRACT FROM AUTHOR]

In this work, an innovative compliant current collector-supported microtubular solid oxide fuel cell has been designed and produced. A nickel wire is coiled around carbon-composite rods to fabricate the cells support, and dip coating technique is used to deposit the anode and the electrolyte from ceramic slurries containing NiO/yttria-stabilized zirconia (YSZ) and YSZ, respectively. Pyrolizable materials are eliminated by heat treatment in air at 800°C; the half-cell is then sintered in Ar at 1380°C to avoid the oxidation of the Ni wire whose compliance allows to minimize stresses generated during heat treatments. The cathode consists of two layers made by lanthanum strontium manganate-YSZ mixture and pure lanthanum strontium manganate co-sintered at 1150°C. Electrochemical I-V characterization of single microtubular solid oxide fuel cells points out great potentiality of the innovative architecture demonstrated by the maximum power output of ~200 mW/cm2 at 800°C under a wet H2 fuel flow. [ABSTRACT FROM AUTHOR]

Hardening behaviour and strength of oxychloride cement strongly depend on the formation of Phase 3 and Phase 5 from MgO and magnesium chloride water solution, and the initial composition can be chosen accordingly within the corresponding phase diagram. A certain number of reactions occur before the final formation of P5 or P3 crystals, and several parameters influence the transformations kinetic, such as MgO reactivity and temperature. Several articles deal with the first aspect, while no indications can be found with regard to the curing temperature's effect on the formation of noble phases. In this article the evolution of magnesium oxychloride cement pastes is analysed at various curing temperatures between 5 and 40 °C. The study is carried out to simulate typical industrial processing conditions and indicate optimal conditions for the production of high chemical and mechanical resistance oxychloride cement. It is shown that at low temperature, Phase 3 is produced in place of Phase 5, and a certain amount of MgO remains non-reacted. The corresponding cement is characterised by lower mechanical strength and higher water solubility. [ABSTRACT FROM AUTHOR]

Anode-supported solid oxide fuel cells have been produced by water base sequential tape casting and cosintering. The curvature developed upon cosintering was monitored in situ. By tailoring the green microstructure, it was possible to reduce the curvature rate and to produce flat cells avoiding the need for a creep-flattening treatment. The power density at 800°C and 0.7 V was 751.7 mW/cm. [ABSTRACT FROM AUTHOR]

Abstract: A novel method is proposed for the determination of the uniaxial viscosity of porous ceramic layers upon sintering. This approach is based on the application of a continuous but very low tensile stress to the densifying powder compact whose deformation is continuously monitored by an optical system. The viscosity of the system can be determined as a function of temperature and density from the sintering rate differences measured between loaded and unloaded samples. The uniaxial viscosity of porous Y2O3 doped ZrO2 (YSZ) and NiO–YSZ composites was measured using the proposed approach. The results were used to predict the curvature evolution of bilayers used in solid oxide fuel cell applications, obtaining a fairly good agreement between the model and the data recorded experimentally. [ABSTRACT FROM AUTHOR]

Ceramic laminates composed of alumina/silicon carbide composite layers were produced by spark plasma sintering (SPS). Monolithic composite disks containing up to 30 vol% of silicon carbide were fabricated by stacking together and cosintering by SPS green layers prepared by tape casting water-based suspensions. An engineered laminate with a specific layer combination that is able to promote the stable growth of surface defects before final failure was also designed and produced. Fully dense materials with an optimum adhesion between the constituting layers and a homogeneous distribution of the two phases were obtained after SPS. Monolithic composites showed an increasing strength with SiC load, and biaxial strength values as high as 700 MPa were observed for a SiC content of 30 vol%. The engineered laminate showed a peculiar crack propagation that is responsible for the high strength value of about 600 MPa and for the evident insensitivity to surface defects. [ABSTRACT FROM AUTHOR]

Abstract: Important features of the ESP (engineered stress profile) glasses are the crack arrest and multiple cracking phenomena that occur even in an unstable stress field. In this work a detailed “in situ” observation of crack observation and analysis was performed with the aim to examine crack propagation in detail and relate it to the residual stress field produced by ion exchange and to the final mechanical performances of the material. The results showed that the peculiar residual stress field with a maximum below the surface is responsible for the formation of a multitude of stable cracks on the tensile surface of the glass that evolved into through-thickness flaws. The propagation within the material is limited by the increasing compressive residual stress, which also leads to kinking of the cracks in a direction parallel to the surface. The observed fracture phenomena are also responsible for a shielding effect that makes the measured failure resistance of ESP glass larger than predicted by simplistic single crack models. [Copyright &y& Elsevier]

Abstract: A design and processing approach for high failure resistance and increased damage tolerance in laminated ceramic structures is presented. Layers of different compositions are stacked in order to develop a specific residual stress profile by the sintering process. The fracture toughness of the laminate is related to the residual stress. The fracture toughness behaviour can be tailored so that surface defects are forced to grow in a stable way before becoming critical. In this way a ceramic with a unique value of fracture strength is obtained. Laminates composed of alumina/mullite and alumina/zirconia layers have been designed and fabricated. These materials possess a strength of 700MPa with a standard deviation of <4%. The strength is insensitive to surface damage and in good agreement with the design value. [Copyright &y& Elsevier]

Abstract: A procedure for designing innovative ceramic laminates characterized by high mechanical reliability is proposed in this work. A fracture mechanics approach has been considered to define the stacking sequence, thickness and composition of the different laminae on the basis of the requested strength and of the defect size distribution. Once the different laminae are stacked together a residual stress profile is generated upon cooling after sintering because of the differential thermal expansion coefficient. Such residual stress profile is conceived in order to allow stable growth of surface defects upon bending and guarantee limited strength scatter. As an example, the proposed approach is used to design and produce ceramic laminates in the alumina–zirconia and alumina–mullite system. Mechanical performances of the produced materials are discussed in terms of the generated residual stress profile and compared to parent monolithic ceramics. [Copyright &y& Elsevier]

In this paper, we report a study on the thermal shock resistance (TSR) of MoSi2/SiCO ceramic composites obtained through controlled pyrolysis of a gel-derived precursor. MoSi2-filled gel is prepared by casting a sol obtained from MoSi2 powder dispersed in methyltriethoxysilane. The pyrolysis product can be described as a porous ceramic composite formed by a SiCO matrix with a dispersion of MoSi2 particles. Mechanical characterization is performed on bar samples by four-point bending. The TSR is investigated either by evaluating the R parameter (associated with strength, elastic modulus, and thermal expansion coefficient), or with the conventional water quenching technique. In both cases, the results suggest that the studied ceramic material displays a good TSR, which makes it a candidate for high-temperature application. [ABSTRACT FROM AUTHOR]

A design and processing approach to fabricate ceramic laminates with high mechanical reliability, i.e., high failure resistance, limited strength scatter, and increased damage tolerance is presented in this paper. Different ceramic layers are stacked together to develop a specific residual stress profile after sintering. By changing the composition of the laminae and the composite architecture it is possible to produce a material with predefined failure stress which can be evaluated from the fracture toughness curve correlated to the residual stresses. In addition, by tailoring the fracture toughness curve, surface defects can be forced to grow in a stable way before reaching the critical condition, thus obtaining a unique-value strength ceramic material. Laminates composed of alumina/mullite composite layers are designed and created in this work by the implementation of the proposed approach. The material obtained shows a “constant” strength of 456 MPa (standard deviation <7%) even when large surface damage is produced by Vickers indentation. [ABSTRACT FROM AUTHOR]

Abstract: A procedure is presented for the measurement of residual stress profile in regular geometry bodies such as plates and disks. The experimental work is based on the sole measurement of the sample curvature deriving from progressively etching one of its surfaces. A relationship is obtained to correlate curvature data as function of etching depth to the original residual stress profile. The sensitivity of the method and the influence of possible experimental errors are analyzed. The technique is then applied to strengthened glass samples produced by both thermal tempering and ion exchange and obtained results are compared to data obtained by available alternative technique to demonstrate the validity of the proposed approach. [Copyright &y& Elsevier]

The introduction of a compressive residual stress with a maximum below the glass surface can promote the stable growth of surface flaws and result in high strength value with limited scatter. Such approach has been reduced to practice in recent years using a double ion-exchange process. Obtained glasses have been named as engineered stress profile (ESP) glasses to emphasize the engineering design approach. In the present work, an alternative production technique, based on physical processes to obtain the specific residual stress profile in soda-lime silicate glass is presented.The proposed technique consists of a conventional physical tempering followed by a fast heating treatment necessary to relax the compressive stress on the surface only. Such relaxation is produced by rapid treatment in a fused tin bath. ESP glasses produced in this manner are compared in terms of residual stress profile, mechanical strength and failure behaviour. [Copyright &y& Elsevier]

Borosilicate glasses, together with silica glass, are commonly considered as ‘anomalous’ glasses. This definition regards the occurrence of Hertzian-like cone cracks during Vickers indentation. Such a particular behavior can be related to anelastic densification processes occurring in the highly stressed region beneath the indenter. Conversely, glasses defined as ‘normal’ show mainly a median/radial crack system and plastic deformation is accounted for shear faulting. Quite surprisingly, in this work both median and conical crack systems were observed in soda–borosilicate glasses under Vickers indentation. Three glasses, with different composition mainly related to the network-modifier content, were considered. The surface and in-depth crack morphology was analyzed as a function of chemical composition, test environment and indenter geometry and the influence of the experimental conditions on the actual glass behavior was discussed. [Copyright &y& Elsevier]

Fatigue behavior of borosilicate glasses was studied using the analysis of subcritical propagation of Vickers indentation cracks. Glasses containing various amounts of glass-network modifiers, mainly soda, were considered. Cone and median/ radial crack systems were observed, depending on glass composition, indenter geometry, and test environment. Indentation tests were performed in water, holding the maximum load for durations ranging from 15 s to 6 d. The analysis of the crack length as a function of dwell time allowed evaluation of the subcritical growth parameters and fatigue limit at crack arrest. The influence of composition on fatigue parameters and fatigue limit was discussed in terms of fourfold-coordinated boron atoms fraction compared with the content of glassnetwork modifier ions. [ABSTRACT FROM AUTHOR]

Identifies techniques used to stabilize crack growth of polycrystalline ceramics. Consideration on the toughness and residual stress profile of the material; Determination of stable growth range and strengthening; Selection of required stress profile or toughness curve.

Develops a ion-exchange process on strengthening and multiple cracking of glasses. Importance of first ion-exchange step in determining the degree of strengthening; Effect of second step control duration on the extent of crack stability; Causes of multiple cracking.

Doped-zirconia finds several applications as strucutral material and in different electrochemical devices; moreover, it is considered a model ceramic system. The consolidation of 3 mol% Y 2 O 3 stabilized ZrO 2 (3YSZ) by rapid sintering (flash processes) has yielded unusual properties like higher hardness and thinner electrochemical grain boundaries. To explore the effect of high heating rate and distinguish it from field-induced phenomena, we investigated and compared UHS (Ultrafast high-temperature sintering) with conventional heating with and without an electric field. The results show that: i) UHS allows ultra-rapid consolidation (<30 s) of YSZ nanopowders (≈20 nm) with a densification pathway different from conventional sintering in terms of microstructural evolution (UHS allows a grain size reduction by more than 60% at a fixed desnity level); ii) the electric field plays a minor role in sintering, microstructure evolution, and properties; iii) UHS does not affect the hardness and the grain boundary electrochemical properties of the sintered bodies. Whereas similarities can be pointed out between UHS and flash-related techniques in terms of accelerated densification and microstructure, the final properties are rather different with UHS YSZ being more similar to conventional sintering. [ABSTRACT FROM AUTHOR]

Direct ink writing (DIW) is an attractive additive manufacturing (AM) technology because of its simplicity, production speed, and feedstock flexibility; in addition, the use of a limited amount of binder makes the subsequent thermal debinding process easy. Nevertheless, the conventional approach to debind and sinter AMed components remains extremely slow, representing a bottleneck in the manufacturing process. In order to address such limitation, we explored different rapid sintering strategies: ultrafast high‐temperature sintering (UHS), pressureless spark plasma sintering (P‐SPS), and fast firing (FF), for the densification of BaTiO3 components fabricated by DIW, one of the widely used lead‐free piezoceramics. All sintering technologies allow debinding and sintering of crack‐free components in a few minutes instead of several hours. The final density and microstructure are strongly dependent on the sintering atmosphere (inert for UHS and P‐SPS, air for FF) and a maximum relative density of only ≈72% was obtained when firing occurred in an inert environment, irrespective of the sintering technique (UHS and P‐SPS). An undesired phase transition from tetragonal to hexagonal BaTiO3 was also observed upon UHS and ‐PSPS. On the contrary, FF in air yielded a density of about 95% in a few minutes while maintaining the desired tetragonal polymorph. The results provide proof of feasibility for rapid processing of BaTiO3 components obtained by DIW. [ABSTRACT FROM AUTHOR]