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Integrated simulation of manufacturing plants plays crucial role in development of sustainable processes and optimized products. However, no investigation has been reported for the whole process chain of porcelain stoneware manufacturing. In this contribution, semi-empirical models of porcelain stoneware processing steps have been developed and implemented into Dyssol framework. By validation based on industrial and lab-scale experiments, the simulation has been applied for modeling and sensitivity analysis of the entire process. The simulation results are in a good agreement with experiments showing that the proposed modeling strategy has high potential to be used for future digital transformation in this sector.

An original discrete element model for coupling thermo-mechanics with sintering is presented to disclose the thermo-micromechanical behavior of particulate systems and their densification process under rapid firing. This paper focuses on the numerical model formulation and application on the fast firing of Al2O3, including its verification with literature. Particular emphasis is given to the evolution of thermal and densification gradients over sintering conditions and sample length, zeroing in on the shrinkage evolution and the characteristic densification phenomena. Relationships between defects, microstructure, and sintering parameters are also explored. Finally, the time-dependent change of material microstructure concerning coordination number evolution, cohesive neck size distribution, gradients of temperature, and sample length are analyzed. The numerical results present good agreement with experimental data from the literature.

In the present work, laminar ceramic structures formed by layers of alumina and partially stabilized zirconia were fabricated by water-based tape casting. Rheological, physical and mechanical properties of slurries and laminates were evaluated. The laminates consisted of stacked alumina and zirconia green tapes produced by thermopressing. Pyrolysis was carried out at 450 °C and sintering at 1500 °C. The alumina/zirconia laminates were studied for a better understanding of the formation behavior and crack propagation at the laminate interface. The flexural strength values of laminates depend on the stress state on their surface. The laminates with the highest amount of zirconia layers presented low strength values (6.7 MPa), while the laminates with more alumina layers had a higher strength level (57.7 MPa). This is because these laminates have alumina layers on the surface which are in a state of residual compressive stress.

A study on the strength of ceramic fiber bundles based on experimental and computational procedures is presented. Tests were performed on single filaments and bundles composed of two fibers with different nominal fiber counts. A method based on fiber rupture signals was developed to estimate the amount of filament rupture during the test. Through this method, the fiber bundle true strength was determined and its variation with the initial fiber count observed. By using different load-sharing models and the single filament data as input parameter, simulations were also developed to verify this behavior. Through different approaches between experiments and simulations, it was noted that the fiber bundle true strength increased with the fiber count. Moreover, a variation of the fibers&rsquo, final proportion in the bundles relative to the initial amount was verified in both approaches. Finally, discussions on the influence of different load-sharing models on the results are presented.

To substitute conventional pigments, which often are toxic or suffer from fading in ultraviolet light, non-iridescent structural colors should demonstrate high spectral selectivity, while being also mechanically stable. However, conventional photonic glass (PhG) shows low color saturation due to the gradual transition in the reflection spectrum and low mechanical stability due to weak interparticle attachment. Here, a PhG with sharp spectral transition in comparison with the conventional full sphere PhG is designed by a conformal coating via atomic layer deposition (ALD) onto an organic PhG template. The ALD deposition allows to control the film thickness precisely for the highly saturated color. This structure can be described by hollow particle motifs with the effective size larger than the interparticle distance. Such unusual PhG is motivated by the achievable features in the spatial Fourier transform of a disordered assembly of such motifs. The surface-templated inverse PhG shows much higher color saturation than the direct PhG from full spheres. Moreover, the dense and solid connected shell will be beneficial for mechanical stability. These results pave the way for highly saturated structural colors. The demonstrated sharp spectral selection feature can be also considered for many related applications such as sunscreens, photovoltaics and radiative cooling by adjusting the reflection transition to the required wavelength. This can be achieved by proportionally scaling the motif and lattice dimensions as well as the film thickness.

A composite-laminate formed by thick layers (~ 320 µm) of zirconia-toughened alumina (ZTA) with thin (~ 50 µm) interlayers of zirconia partially stabilized (Y-PSZ) has been fabricated by tape casting and pressureless sintering. Fracture behavior and strength has been investigated and compared to a “monolithic” reference, e.g. a stack of zirconia-toughened alumina (ZTA) without interlayers. The fracture behavior has been analysed using stable crack growth in V-notched specimens loaded in 3-point bending. The ZTA+Y-PSZ composite laminate presented a rising crack resistance with maximum values between 6 and 14 MPa m1/2. In contrast, the “monolithic” ZTA laminate shows a plateau R-curve behavior at 2.7 MPa m1/2. Several toughening mechanisms were identified in the ZTA+Y-PSZ composite laminate, such as, crack arrest/slow down, micro cracking and bifurcation. These toughening mechanisms are most likely caused by high tensile residual stresses that were estimated theoretically.

A process for generating highly porous α-Al 2 O 3 ceramics has been developed. In this paper, a combination of self-assembly and atomic layer deposition is demonstrated as a means to fabricate inverse alumina opals, which have their structures transformed via sintering. The resulting highly porous structure is stable even after a 4 h dwell time at 1400 °C, in contrast to structures generated by conventional powder metallurgy, sol-gel or colloidal powder suspension infiltration methods. TEM analysis reveals that the structure consists of single grain domains of up to 3 µm, each containing a randomly interconnected network of alumina ligaments that share a common crystalline orientation, suggesting a different mechanism of grain boundary migration during sintering. These highly porous α-alumina ceramics are considered to be ideal for filtration or catalysis applications.

The influence of preexisting defects and the generation of new ones during flash sintering was studied in 3YSZ. Weibull statistics was used to analyse mechanical testing data from flash and conventionally sintered specimens with equal densification. The obtained values for Weibull modulus and characteristic strength are 6.09 and 371 MPa for the conventionally sintered samples, respectively, and 5.92 and 506 MPa for the flash sintered samples. It can be inferred that flash sintering does not alter significantly the defect distribution on the studied material. Preexisting defects were manufactured with rice starch as a pore forming agent, in 5, 10 and 15 vol%. Those samples were flash sintered in isothermal and constant heating rate experiments. The experiments show that there is no noticeable difference on the incubation time and the onset temperature for flash sintering.

The production of self-lubricating composites containing second phase particles is one of the most promising choices for controlling friction and wear in energy efficient modern systems. To gain a better understanding of the wear behaviour of such materials, Fe-Si-C matrix composites containing solid lubricants added during the mixing step were studied in this work. The samples were produced using powder metallurgy route, with total contents of 5, 7.5 and 10% in terms of volume of hexagonal boron nitride (hBN) and graphite mixtures as the solid lubricants. The composite's tribological properties were evaluated under reciprocating sliding conditions and their mechanical properties were tested using tensile tests. Additionally, after interruptions at different stages of the reciprocating tests, the wear scars were characterised by Raman spectroscopy and scanning electronic microscopy, to evaluate the evolution of the wear with test time. Higher total solid lubricant contents greatly increased the scuffing resistance of the composites, but decreased the mechanical properties. Furthermore, increasing the hBN content reduced both properties. Among the composites studied, the samples containing 1% vol hBN and 9% vol graphite showed the best combination of mechanical and tribological properties.

Zirconia nanoceramics are interesting materials for numerous high-temperature applications. Because their beneficial properties are mainly governed by the crystal and microstructure, it is essential to understand and control these features. The use of co-stabilizing agents in the sol-gel synthesis of zirconia submicro-particles should provide an effective tool for adjusting the particles’ size and shape. Furthermore, alumina-doping is expected to enhance the particles’ size and shape persistence at high temperatures, similar to what is observed in corresponding bulk ceramics. Dispersed alumina should inhibit grain growth by forming diffusion barriers, additionally impeding the martensitic phase transformation in zirconia grains. Here, alumina-doped zirconia particles with sphere-like shape and average diameters of ∼ 300 n m were synthesized using a modified sol-gel route employing icosanoic acid and hydroxypropyl cellulose as stabilizing agents. The particles were annealed at temperatures between 800 and 1200 ∘ C and characterized by electron microscopy, elemental analysis, and X-ray diffraction. Complementary elemental analyses confirmed the precise control over the alumina content (0−50 mol%) in the final product. Annealed alumina-doped particles showed more pronounced shape persistence after annealing at 1000 ∘ C than undoped particles. Quantitative phase analyses revealed an increased stabilization of the tetragonal/cubic zirconia phase and a reduced grain growth with increasing alumina content. Elemental mapping indicated pronounced alumina segregation near the grain boundaries during annealing.

Metal–ceramic composite materials are used in several fields of industrial applications. Most of the composites are particulate composites, where metal is the matrix and ceramic the reinforcing particulate material. Oxide dispersion strengthened alloys show increased temperature stability compared to the pure alloy. Theoretical models describing the densification evolution during sintering are only available for particle reinforced materials, but there are no models developed for interpenetrating structures, when both phases are sintering. We present a modelling approach based on the discrete element method, which can be used to investigate the sintering behavior on the whole range of powder metallurgical producible composites. The discrete element method takes the particulate structure of the powder compact into account and allows one to perform detailed modelling of each contact separately. In this paper the metal fraction was varied between 100 and 0 vol.% and the densification was analyzed by the contact radius evolution.

A strategy for stacking multiple ceramic 3D photonic crystals is developed. Periodically structured porous films are produced by vertical convective self-assembly of polystyrene (PS) microspheres. After infiltration of the opaline templates by atomic layer deposition (ALD) of titania and thermal decomposition of the polystyrene matrix, a ceramic 3D photonic crystal is formed. Further layers with different sizes of pores are deposited subsequently by repetition of the process. The influence of process parameters on morphology and photonic properties of double and triple stacks is systematically studied. Prolonged contact of amorphous titania films with warm water during self-assembly of the successive templates is found to result in exaggerated roughness of the surfaces re-exposed to ALD. Random scattering on rough internal surfaces disrupts ballistic transport of incident photons into deeper layers of the multistacks. Substantially smoother interfaces are obtained by calcination of the structure after each infiltration, which converts amorphous titania into the crystalline anatase before resuming the ALD infiltration. High quality triple stacks consisting of anatase inverse opals with different pore sizes are demonstrated for the first time. The elaborated fabrication method shows promise for various applications demanding broadband dielectric reflectors or titania photonic crystals with a long mean free path of photons.

Zirconia-based ceramics cover a huge variety of applications, including refractories, electro- and bioceramics, fuel cells, catalysts, and many more. For various photonic applications considered for energy systems and heat management, zirconia microspheres are interesting building blocks due to their high refractive index, as well as their chemical and mechanical robustness. However, instabilities caused by thermally-induced phase transitions and grain growth at temperatures above ∼1000 °C preclude high-temperature applications of pure zirconia particles. Here, we present a synthetic route for yttria-stabilized zirconia microparticles with significantly improved thermal stability. With these particles we conducted the first study on their thermal stability as a function of the yttrium content and at temperatures up to 1500 °C. Using X-ray diffraction and scanning electron microscopy, the optimum Y content was determined to be 8–10%, which was marked by stabilization of the tetragonal or cubic phase and significantly attenuated grain growth. Furthermore, with diameters ranging from 2 to 5 μm, the particles covered a size range perfectly suited for photonic applications in the IR spectral range. To demonstrate this, photonic glass coatings were prepared with these particles and their IR reflectivity and microstructural stability was studied after subjecting them to various heating cycles. While heating beyond 1200 °C led to failure and delamination of undoped particle films, films doped with 6 and 10% Y displayed quite stable broadband IR reflection of up to 80% in the wavelength range from 1–5 μm, even after prolonged heating at 1400 °C. A detailed analysis of the X-ray diffraction patterns revealed that prolonged heating at 1400 °C resulted in phase decomposition due to Y segregation into Y-lean and Y-rich domains, confirming the presence of the solute-drag effect.

The mechanical behavior of bundles of ceramic fibers exhibits a characteristic rupture process when subjected to tensile known as avalanche failure. This process is related to the load sharing among fiber bundles once some of the elements begin to fail. Mechanical tests were performed with bundles and Weibull statistics was used to interpret the results of the maximum stress supported by the bundles before the avalanche failure. A computational simulation was originally adapted introducing load sharing models. The simulations were compared with experimental results. Finally, the newly proposed load model was considered to be a better approach for the understanding of the rupture avalanche effect.

Understanding the sintering behavior of tailored porosity in thin-film ceramics is essential for applications in photonics, thermal coatings, catalysis, and electrodes. Alumina films exhibiting a random distribution of templated pores with monodisperse size were produced by spin coating from suspensions of alumina powder and polystyrene microspheres. The microstructural evolution, grain size, pore size, and their respective distributions were determined as a function of the initial volume fraction of templated pores, sintering temperature, and time. The behavior between grains and pores at the surface and in the bulk was evaluated and compared to other disordered and ordered porous alumina systems. Above a pore fraction threshold of ∼9 vol%, increasing pore fractions retarded grain growth, with smaller grains observed between close pores. While the average bulk pore size did not change with sintering temperature, time, or pore fraction, it did produce a broader pore size distribution with different pore geometries.

A library of ceramic compounds based on the lead-free (KxNa1−x)1−yLiy(Nb1−zTaz)O3 solid solution has been synthesized and characterized using high-throughput experimentation (HTE) method. The phase space previously reported by Saito and Takao has been expanded to {{x, 0.1, 1.0}, {y, 0, 0.1}, {z, 0, 0.2}}, and new phase boundaries are observed. The relative density values show that with the appropriate sintering temperature, ∼92% of the theoretical density can be reached. The relative permittivity values show that with increasing amount of K+ and Ta5+, the dielectric constant values increase. The effect of density on the dielectric constant values is however minimal. Resistivity values ranging from 109 to 1013 Ω·cm are obtained for the samples. The piezoelectric charge coefficient values for selected compositions show that higher values are obtained close to the phase boundaries rather than away from them. The properties for the ceramic library using the HTE method are generally 15%–20% less than from the conventional method. This method is therefore more suited for screening of sample compositions than for producing samples with high piezoelectric properties.

The applications and processing of nanostructured materials at high temperatures require stability of their morphology. However, in such environments (>1000 °C), these structures are prone to significant undesired microstructural changes that result in a loss of functional properties. The thermal stability of titania inverse opal films, prepared from self-assembled templates of monodisperse polystyrene spheres by infiltration utilizing atomic layer deposition and subsequent calcination, was assessed. Resistance to grain growth and a shift in the anatase-to-rutile transformation to higher temperatures was observed, with dramatic stability under vacuum. Vacuum annealed samples retained the anatase phase and exhibited minimal grain growth even after 3 h at 1300 °C. Photonic properties were retained until the transformation onset. The remarkable resistance was attributed to inhibition of surface diffusion and structure-substrate constraints. In addition to being technologically enabling, the results provide further insight into the titania system and its phase transformation mechanism.

Flash sintering is a nonlinear phenomenon characterized by a sharp increase in the conductivity of the sample and concomitant rapid densification under an electric field in low temperatures in a matter of seconds. Since it is a transient phenomenon, the power dissipation on the sample is not uniform during the process. Thus, a transient analysis is needed to estimate the temperature of the sample during flash sintering due to Joule heating. In this work, the Finite Element Method on a coupled electrothermal nonlinear analysis was used in order to obtain the specimen temperature of 8YSZ after 5 s of flashing. The results agree with the experimental data obtained by the flashing of dense samples and with previous literature.

All-oxide ceramic matrix composites produced by a novel route based on the lamination of thermoplastic prepregs are investigated. This route allows for the production of composites with very homogeneous microstructures and a reduced amount of matrix cracks. NextelTM 610 alumina woven fabric is used here to reinforce a porous oxide matrix composed of 80 vol% Al2O3 and 20 vol% ZrO2. The mechanical behavior of composites submitted to different heat treatments is investigated under 4-point bending and short beam shear. Results show that composites with low interlaminar shear strength present a graceful failure under 4-point bending, characterized by a stepwise stress reduction upon straining beyond the peak stress. The fracture of such composites is accompanied by a series of interfacial delamination events, which enhance energy dissipation during failure. An increase of the interlaminar shear strength due to matrix densification causes a loss of the stepped stress–strain behavior. Nevertheless, fiber-related toughening mechanisms such as crack deflection and bridging still ensure inelastic deformation up to failure of these composites.

Three-dimensionally ordered macroporous (3DOM) ceramic materials are considered for a variety of applications. One of its many subclasses, inverse opals, is constituted by the ordered arrangement of the pores, resulting in the functionality of a photonic crystal and leading to strong reflection of incident electromagnetic radiation. Exposing these porous structures to high temperatures, however, can lead to sintering of the desired structure and loss of functionality. Therefore, discrete element method (DEM) simulations are performed on inverse opal structures with random homogenous distributed alumina particles forming the struts and nodes. Grain-boundary diffusion as well as surface diffusion are modeled via respective parameters of a contact model applied in MUSEN-DEM. Furthermore, the void to particle size ratio is varied to simulate fine and coarse grained 3DOM ceramics. Results indicate that nodes densify at higher rates and to a larger extent when compared to struts. An increase in the void to particle size ratio results in similar trends but with lower densification rates. This behavior is observed regardless whether surface or grain-boundary diffusion is considered as the dominant transport mechanism, with the latter giving higher densification rates. Variations in particle coordination due to the initial random packing favor local desintering, thereby causing the formation of defects/crack nuclei.

Properties of the fiber/matrix interface in monoclinic ZrO2-coated alumina fiber-reinforced composites were investigated using model composites with dense alumina matrix and single alumina fibers. The fiber-matrix porous interface was produced via dip-coating single fibers in monoclinic ZrO2 suspensions and two different particle sizes were used in order to vary the coating porosity. The interfacial sliding stress was determined via fiber pushin test; crack deflection behavior was analyzed from cracks created via Vickers indentation and via fracture surface. Fracture toughness and elastic modulus of interface, matrix and fibers were evaluated and used to predict the crack deflection behavior using the model of He and Hutchinson. Results showed that monoclinic zirconia interfaces are suitable for dense alumina composites, due to the low fiber/interface chemical interaction. A uniform coating can be produced via dip coating and tailored with using different monoclinic zirconia particle sizes. The sliding stress values obtained with the pushin test were about 120 MPa.

Powder metallurgy is a growing sector in industrial production, as it offers outstanding energy, cost and material savings in comparison with established processing routes such as casting. Hot work toll steels are usually produced by ingot metallurgy, but also by powder metallurgy, namely hot isostatic pressing and powder forging routes. In this paper we investigate the possibility of production of a hot work tool steel (AISI H13) by conventional (die compaction and pressureless sintering) and metal injection molding routes, aiming to reduce cost and production time. The sintering behavior was studied from 1250 °C until 1430 °C and the resulting parts were compared in terms of microstructure, hardness and tensile strength. The results showed that both shaping routes together with pressureless sintering are suitable to produce this alloy. By combining the best shaping approach and a tailored sintering cycle, it was possible to produce samples with 400 HV10 as well as tensile strength of 1 GPa, which are comparable to the ones obtained by powder forging.

This work compares values of Young׳s modulus and fracture toughness of amorphous albite measured from different experimental techniques. Sodium feldspar powder was used to synthesize the albite glass. After quenching, the microstructure of the amorphous solid was analyzed via scanning electron microscopy and X-ray diffraction. Several nanoindentations on albite samples were carried out with two purposes: determination of Young׳s modulus by continuous stiffness measurement, and critical stress intensity factor by crack size evaluation. Concurrently, impulse excitation technique and three point bending single-edge notched test were adopted for providing the comparison of elasticity and toughness, respectively. Young׳s modulus measured by continuous stiffness yielded a value of 71.8±0.9 GPa, which was in agreement with the value obtained by impulse excitation (72.5±1.3 GPa). The fracture toughness determined by nanoindentation was slightly higher (0.86±0.06 MPa m1/2) than that (0.78±0.06 MPa m1/2) obtained by single-edge notched beam.

Electrical conductivity, thermal expansion and redox behavior of Y- and Al-substituted SrVO3 were evaluated for potential use in solid oxide fuel cell anodes. Sr1-xYxV1-yAlyO3-delta (x = 0-0.4, y = 0-0.2) ceramics were prepared by solid state reaction route and sintered in hydrogen-containing atmosphere. Solid solubility limits of yttrium and aluminum cations in SrVO3 perovskite lattice were found close to similar to 25% of strontium sublattice and 8-10% of vanadium sublattice, respectively. Under reducing conditions, all ceramics exhibit nearly p(O-2)-independent metallic-like electrical conductivity slightly decreasing with substitution level. Undoped SrVO3-delta is characterized with unfavorably high thermal expansion coefficient (TEC = 21.6 x 10(-6) K-1 at 823-1273 K) impeding thermomechanical compatibility with common solid electrolytes. Substitutions with yttrium and aluminum suppress to some extent oxygen nonstoichiometry variations and thermal expansion decreasing average TEC values down to (14.5-15.1) x 10(-6) K-1 at 300-1273 K. Substitutions extend also phase stability domain of perovskite phase, enabling processing of Sr(Y)V(Al)O3-delta electrodes in inert atmosphere with p(O-2) similar to 5 x 10(-5) atm. Slow decomposition into Y5+-based phases is observed however at slightly higher oxygen pressure of similar to 10(-4) atm. Oxidative decomposition into Sr2V2O7 and YVO4 phases on heating in air results in significant bulk dimensional changes, contributed by progressive sintering of Sr2V2O7 phase fraction. (C) 2013 Elsevier B.V. All rights reserved.

WOS: 000309016600005, The aim of this work is the optimization of ultrasonic methods in the non-destructive testing of sintered porcelain tiles containing defects. For this reason, a silicon nitride ball, carbon black and PMMA (Polymethylmethacrylate) were imbedded in porcelain tile granules before pressing to make special defects in tiles. After sintering at 1220 degrees C, the time of flight of the ultrasonic waves and ultrasonic signal amplitudes through the sintered porcelain tiles were measured by a contact ultrasonic transducer operating on pulse-echo mode. This method can allow for defect detection using the A-scan. The results of the test showed that the amplitude of the received peak for a defective part is smaller than for a part which has no defects. Depending on the size, shape and position of the defect, its peak can be detected. Additionally, an immersion pulse-echo C-scan method was also used to differentiate between defects in porcelain tiles. By using this technique, it is possible to determine the place and shape of defects. To support the results of the ultrasonic investigation, a SEM characterization was also made., Anadolu University Scientific Research Project [080210], The financial support from the Anadolu University Scientific Research Project, project 080210, is gratefully acknowledged. The authors would like to thank Research Assistant Sukru Gorgulu from Anadolu University, Dipl. -Ing. Wilfried Liebig and Prof. Dr. Karl Schulte from the Technische Universitat Hamburg-Harburg.

Ceramic matrix composites (CMCs) were developed to overcome the intrinsic brittleness and lack of reliability of monolithic ceramics. Their major advantages include high temperature capability, light weight, corrosion resistance and adequate damage tolerance. All-oxide Ceramic Matrix Composites (OCMCs) offer essential advantages with respect to long time stability in oxidizing atmospheres, when compared to their non-oxide counterparts. Nevertheless, there is at present almost no production concept which meets the requirements in view of cost and performance for these materials. This work aims at producing OCMCs by means of a more flexible production route. This is achieved by integrating well-known powder metallurgy routes with the prepreg technique, used at present for producing commercial high performance polymer matrix composites. The processing consists of the following steps: (a) infiltration of commercial alumina fiber fabrics (3M NextelTM610) with a liquid suspension of the matrix material; (b) lamination of the pre-infiltrated fiber textiles with a paraffin-based suspension for the formation of prepregs; (c) layup of prepregs; (d) warm-pressing for the consolidation of the green body; (e) debinding and (f) reaction bonding and/or sintering for synthesis of the oxide matrix. Pure alumina or Reaction Bonded Aluminum Oxide (RBAO) can be used as matrix materials and damage tolerance is achieved by the porous, weak-matrix approach. Microstructural analysis of a pure alumina composite fabricated by this route show good infiltration of fiber bundles and proves the good adhesion of prepregs during processing. Average strength value of 199 MPa in fiber direction is in good agreement with values presented in the literature for OCMCs produced by other techniques.

s common knowledge that for bundles of fibers, that the bundle strength is always less than the sum of the fiber strengths. This behavior can be explained by load-sharing models. So even when the weakest fiber fails, the remaining fibers share the load, and thus increase the effective stress in these fibers. At this work, different load sharing models were implemented on a simulated tensile test of ceramic oxide fibers using Matlab. The results are in agreement with the theoretical predictions and are a powerful tool for design of composites.

The feasibility of stacking of thin ceramic inverse opals with incommensurable periodicity constants was investigated. Inverse opals with photonic stopgaps in the infrared range were prepared by the vertical convective self-assembly from aqueous suspensions of monodisperse polystyrene (PS) particles with the sizes of 476, 608, and 756 nm. The opal templates were infiltrated with TiO2 by a low-temperature atomic layer deposition process using titanium isopropoxide and water as precursors. The second PS template could be deposited on top of the infiltrated opal layer after exposing the latter to the UV-light, which rendered its surface hydrophilic. Finally, the sacrificial PS templates were removed by calcination at 500°C. It is shown that smoothness of the surface of the inverse opals is crucial for the photonic performance of the heterostructures. Two well-defined stopgaps could be observed in the spectra of reflectance of the stacked inverse opals with improved surface morphology.

In the present study, fiber-matrix compatibility in an all-oxide ceramic composite is examined. Reaction-bonding aluminum oxide is used as porous matrix to ensure weak interfaces with fibers. Matrix cracks have been deflected around the interface for sintering temperatures up to 1300°C, due to the effectiveness of porous matrix in enabling damage tolerance. Above 1300°C, densification of the matrix resulted in brittle fracture of the samples, with matrix cracks going through the fibers. Observation of fracture surfaces confirmed the fiber pull-out phenomenon up to processing temperatures of 1300°C. The well-known He and Hutchinson criteria for crack deflection was used to predict debonding behavior at the fiber-matrix interface as a function of matrix porosity. Furthermore, evaluation of the microstructure evolution of Nextel™ 610 alumina fibers showed a pronounced grain coarsening at sintering temperatures above 1300°C. Changes in crack deflection behavior and fiber microstructure of a composite sample aged for 100 h are also presented.

This work reports on different approaches to predict the pressure drop in capillary structures for two phase heat transfer devices (TPHTD). For this purpose, several porous wick structures were produced by slip casting and characterized concerning their porosity, critical pore diameter, capillary pressure and permeability. The wick structures exhibited porosity in the range of 48–58%, pore diameter ranging from 1 μm to 4 μm, with capillary pressure of 80 and 22 kPa, respectively. Two expressions were developed to simulate the pressure drop permeabilities as a function of the heat load applied to the TPHTD evaporator. The prime target of this work is to evaluate the differences in predicting pressure drop just by using the Darcyan constant, k 1 , and both by using Darcyan and non-Darcyan constant, k 1 and k 2 . When k 1 was used only it was considered as Darcyan approach and when both constants were taken into account it was considered as Forchheimer approach. Additionally, ceramic wick structures have been tested as capillary evaporator in a TPHTD. The startup was successful after 20 min the inlet and outlet evaporator temperatures remain constant. It confirms that all applied heat load was transported to the condenser.

High-density alumina was produced by fast firing (5 min, temperatures ≤1550°C). Most of densification occurred under nonisothermal conditions. High densification rates observed are related to a change in the internal structure of the compact. The formation of a dense outer alumina layer controlled the heat flux to the interior of the compact, and increased the amount of energy available for sintering. Sintering in fast firing occurred as a densification front moving from the outer surface toward the sample center. As long as the rate of heat transfer is enough to sustain its advance, no differential densification occurs.

Purpose Bioresorbable materials have been developed in the hope that the body will replace them with newly formed tissue. The first step of this remodeling process in bone is the bioresorption of the material by osteoclasts. The aim of this study was to analyze osteoclastic resorption of biomaterials in vitro using the commonly used two-dimensional methods of light-microscopy (LM) and scanning electron microscopy (SEM) in comparison with infinite focus microscopy (IFM), a recently developed imaging method allowing for three-dimensional surface analysis. Methods Human hematopoietic stem cells were cultivated in the presence of the cytokines M-CSF and RANK-L for 4 weeks directly on dentin and a calcium phosphate cement. Osteoclast development was surveyed with standard techniques. After removal of the cells, resorption was characterized and quantified by LM, SEM and IFM. Results Osteoclast cultures on the biomaterials presented the typical osteoclast-specific markers. On dentin samples LM, SEM as well as IFM allowed for discrimination of resorption. Quantification of the resorbed area showed a linear correlation between the results (LM vs. SEM: r=0.996, p=0.004; SEM vs. IFM: r=0.989, p=0.011; IFM vs. LM: r=0.995). It was not possible to demarcate resorption pits on GB14 using LM or SEM. With IFM, resorption on GB14 could be visualized and quantified two- and three-dimensionally. Conclusions In this paper we introduce IFM as a technology for three-dimensional visualization and quantification of resorption of biomaterials. Better understanding of the bioresorption of biomaterials may help in the design of better materials and might therefore constitute an important step on the avenue to the development of artificial bone.

A high-throughput experimental (HTE) approach starting from dry, fine-grained powders was used to synthesize bulk samples in the system (KxNa1−x)1−yLiy(Nb1−zTaz)O3, a doped variant of the piezoelectric (K0.5Na0.5)NbO3 (KNN). Starting from the system (K0.5Na0.5)1−yLiy(Nb1−zTaz)O3 known from the works of Saito et al. an effort was made to establish a higher order phase diagram. Special emphasis was put on expanding the known morphotropic phase boundary that constitutes a region of special interest for electroceramic materials as it features maximum piezoelectric properties. Analyses were performed using a HTE-compatible technique, namely automated powder X-ray diffraction (XRD).

A high-throughput experimental (HTE) setup using conventional powders as raw materials was developed to synthesize and characterize ceramic bulk samples avoiding the customary liquid- or vapor-phase synthesis routes. Its functionality was verified using the well-known binary material system ZrO2-Y2O3. Libraries of 0.5 mol % yttria resolution were prepared using varying boundary systems as well as a number of liquid mixing aids. Automated powder X-ray diffraction (XRD) was applied to check the monoclinic phase content retained after heat-treatment on various positions for each sample. This phase information was used for comparison with a reference library comprising conventionally prepared samples by means of a regression analysis and mean deviation of monoclinic phase percentage. Out of the eight HTE libraries, three showed a significant comparability to the reference library.

Affordable manufacturing of components with complex shapes is still the most essential shortcoming with respect to successful commercial use of advanced ceramics. This holds particularly for components with high demands of geometric precision and mechanical reliability at the same time. Two routes are considered here which offer a high potential for fast and cost-effective manufacturing of reliable components: (I) reactive-based processing exhibiting often low shrinkage and/or advanced shapability (and sometimes savings in raw material and processing costs) and (II) recently developed advanced shaping techniques suitable for CAD/CAM without labor intense tooling optimization. Recent developments in both areas are briefly highlighted.

Particle & particle systems characterization 33(9), 645 - 655(2016). doi:10.1002/ppsc.201600069, Zirconia microspheres synthesized by a wet-chemical sol–gel process arepromising building blocks for various photonic applications considered forheat management and energy systems, including highly effi cient refl ectivethermal barrier coatings and absorbers/emitters used in thermophotovoltaicsystems. As previously shown, pure zirconia microparticles deteriorate atworking temperatures of ≥1000 °C. While the addition of yttrium as a dopanthas been shown to improve their phase stability, pronounced grain growthat temperatures of ≥1000 °C compromises the photonic structure of theassembled microspheres. Here, a new approach for the fabrication of highlystable ceramic microparticles by doping with lanthanum, gadolinium, and acombination of those with yttrium is introduced. The morphological changesof the particles are monitored by scanning electron microscopy, ex situX-ray diffraction (XRD), and in situ high-energy XRD as a function of dopantconcentration up to 1500 °C. While the addition of lanthanum or gadoliniumhas a strong grain growth attenuating effect, it alone is insuffi cient to avoida destructive tetragonal-to-monoclinic phase transformation occurring afterheating to >850 °C. However, combining lanthanum or gadolinium withyttrium leads to particles with both effi cient phase stabilization and attenuatedgrain growth. Thus, ceramic microspheres are yielded that remainextremely stable after heating to 1200 °C., Published by Wiley-VCH, Weinheim