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This paper explores the hydrothermal treatment of α-Al2O3 powders to improve the binding in ceramic parts produced via a chemical bonding of ceramic powders combining a phosphate binder and infrared (IR) curing. Alumina powders are pre-treated in hydrothermal conditions with both water and phosphoric acid solution before slurry preparation and infrared irradiation. The effects of hydrothermal treatments on the powder's chemical reactions and the composite's final microstructure are assessed upon IR irradiation. While the water treatment does not induce any chemical changes, the presence of phosphoric acid leads to the appearance of phosphate phases Al(PO3)3 and AlPO4. Hydrothermal treatments in water and in phosphoric acid solution are found to drive faster and more intense phosphate condensation reactions at lower temperatures, with a stronger effect in the presence of H3PO4 (condensation temperature of 150 °C for the H3PO4-hydrothermal treated powder compared to 165 °C for the untreated powder). This improved reactivity of hydrothermal treatment α-Al2O3 powders, especially in the presence of H3PO4, leads to a general decrease of porosity for 3D printed parts compared to untreated alumina (for both top surfaces and cross-sections). While further optimization is needed to reduce the final porosity, it is possible to rapidly print 3D parts using this method, demonstrating a possible pathway to a single-step additive manufacturing (AM) process for ceramics. [ABSTRACT FROM AUTHOR]

This paper presents a method for joining Si3N4 and 7A52 aluminum alloy using femtosecond laser surface modification of Si3N4 ceramics. This study investigated the impact of laser scanning speed on the morphology, chemical composition, and wettability of Si3N4 ceramic surfaces, as well as the mechanism behind the laser-assisted joining of Si3N4 and 7A52. After undergoing femtosecond laser processing, the ceramic material underwent modifications resulting in the creation of a periodic groove structure. This structure featured an ideal depth-to-width ratio that effectively increased the surface area for bonding with the solder. Furthermore, the surface of Si3N4 experienced thermal decomposition, which produced a recrystallized layer of 'Si.' This layer improved the solder's wetting effect on the ceramic surface, which led to a stronger diffusion of Al and Mg elements to the ceramic interface. The presence of the periodic groove structure also changed the fracture path of the joint, ultimately enhancing the strength of the brazed joint by approximately 52.4% when compared to the original joint. Notably, this significant improvement was achieved without the need for surface metallization. In summary, the femtosecond laser processing method significantly improved the strength of the ceramic–metal brazed joint through surface modifications, promoting a more reliable and robust bond. [ABSTRACT FROM AUTHOR]

Lipases are widely used in industry. Free lipases are difficult to recover and have poor stability under operational conditions. Herein, lipases are immobilized onto the methyltrimethoxysilane (MTMS)-modified ceramic membranes (~ 5 nm) with reverse filtration method, and further cross-linking by glutaraldehyde (GA) is used to improve the lipase stability. FTIR and XPS analyses demonstrate the successful immobilization of lipase. The immobilized lipases are used to hydrolyze glycerol triacetate (GT) to fatty acids and glycerol. Under the optimal immobilization conditions (MTMS concentration 0.1 M, lipase immobilization time 80 min, lipase concentration 3 mg/mL, and GA concentration 2%), the loading of lipases reaches 0.24 mg/g. Under the optimal operational conditions (temperature 45 °C, pH 7, pressure 0.2 MPa, GT concentration 0.05 M), the immobilized lipases have the highest catalytic activity of 25 U/mg. Moreover, the thermal and pH stabilities of immobilized lipases are found to be higher than those of the free lipases. In the long-term runs, the immobilized lipases still have 64% of the initial activity after 7 cycles, indicating good reusability. This paper provides a simple process for immobilizing lipase on ceramic membranes. The immobilized lipases have better stability at high temperature and basic environments (pH 7–9), which would have broad applications in lipase-catalyzed reactions. [ABSTRACT FROM AUTHOR]

This paper reports enhanced high-temperature piezoelectric properties of Bi(Zn0.5Ti0.5)O3-modified BiFeO3-BaTiO3 (BF–BT-xBZT) ceramics prepared by two-step sintering method. The resultant ceramics show a symmetrical transition from a rhombohedral–pseudo-cubic (R-PC) phase coexistence to main PC phase with the increase of x, whose R-PC fraction (CR/CPC) is 53.3/46.7, 52.9/47.1, 50.2/49.8, 27.4/72.6, 15.3/84.7 when x = 0, 0.005, 0.01, 0.03, 0.05, respectively. The modification of BZT inhibits the grain growth, reduces the leakage current and gradually drives ferroelectric to relaxor transition. Optimal piezoelectric properties: d33 = 193 pC N−1, Pr = 20.6 μC cm−2, TC = 503 °C and kp = 36% achieved at x = 0.01 composition, which is due to the synergistic effect of an appropriate CR/CPC ratio, improved insulation and good polarization performance. In addition, the depolarization temperature Td is close 280–312 °C, and the high-temperature d33 further increases to 286–347 pC N−1, which shows a good application prospect of lead-free piezoceramics at high temperature. Our work also confirms that the addition of (Zn0.5Ti0.5)3+ and two-step sintering method are an effective and convenient strategy to improve the high-temperature electrical performance of BiFeO3–BaTiO3 based lead-free ceramics. [ABSTRACT FROM AUTHOR]

To meet the polarization adaptation in communication systems, it is necessary to improve the performance of polarization converters. Microwave dielectric materials are very promising to optimize the response speed, operating frequency, conversion efficiency, and transmission stability of polarization converters, which puts higher demands on ceramic materials. In this paper, the microwave dielectric properties of Ca5Mn4(VO4)6 ceramics are improved by using Cu2+ instead of Mn2+. The effects of Cu2+ substitution and sintering temperature on microwave dielectric properties are also investigated. The substituted ceramics have excellent microwave dielectric properties of εr = 11.4, Q × f = 42709 GHz, and τf = − 65 ppm/°C. As a concept demonstration, a new 5G polarization converter between linear polarization and left-handed circularly polarized (LCP) waves is designed by using this ceramic substrate. By observing the surface electric field and surface current, it can be judged that the principle of the polarization converter is the difference in the electric dipole resonance absorption between the LCP and the right-handed circularly polarized (RCP) waves. The simulation results of normalized reflectivity and far-field (electric field and phase) show good performance of the polarization converter. [ABSTRACT FROM AUTHOR]

This paper presents the experimental investigation of the effect of Nb2O5 content on the phase composition, microstructure, and physical and mechanical performance of the zirconia-toughened alumina (ZTA) ceramics, aimed to optimize the additional amount of Nb2O5, refine the ceramic grains, and improve the densification, hardness and fracture toughness. ZTA ceramics with various Nb2O5 contents were prepared using the spark plasma sintering method. The addition of trace amounts of Nb2O5 did not produce a new Nb-rich phase; the Nb atoms were dissolved in the ZrO2 grains. The addition of trace amounts of Nb2O5 led to grain refinement and an increase in density, but the addition of excessive Nb2O5 resulted in grain growth and a decrease in relative density. Furthermore, the addition of Nb2O5 promoted uniformity of the microstructure. The sample with 0.25 wt.% Nb2O5 had the maximum Vickers hardness and indentation fracture toughness, which were 1228.40 HV and 9.17 MPa √m, respectively. Mechanical properties of the composite mainly depended on the grain size, which was influenced to some extent by the relative density. [ABSTRACT FROM AUTHOR]

In this paper, 50 ... 680 nm thick AlN-Al2O3 coatings are deposited by magnetron sputtering on the surface of a steel substrate and a piece of copper is melted on top of the ceramic. Upon heating the ceramic layer is cracked, and the phase inversion of the two top phases from steel/ceramic/copper configuration to the steel/copper/ceramic configuration takes place within 30 s of liquid time of copper. This phase inversion process is accompanied by a Gibbs energy change of about − 1.78 J/m2, due to good wettability of solid deoxidized steel by liquid copper in contrary to poor wettability of the ceramic by the copper. When copper is melted on AlN-Al2O3 coating with its thicknesses smaller than a critical value of about 170 ± 60 nm, liquid copper droplets hanging down into the cracks within the ceramic reach the solid steel surface at the bottom of the cracks, thus the flow of Cu down along the cracks is enabled. However, when copper is melted on AlN-Al2O3 with its thickness larger than the critical value of 170 ± 60 nm, Cu first forms a non-wetting droplet on top of the ceramics, and only after a certain incubation time it starts flowing down the cracks. This incubation time was found to depend linearly on the thickness of the ceramic, as cracks are filled from the bottom upwards by liquid copper via the evaporation–condensation mechanism. By the end of the process, the steel/copper/ceramic configuration is further stabilized by gravity. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present a novel negative temperature coefficient (NTC) thermistor based on A2Zr2O7 (A = Nd, Sm, Gd, Yb) zirconate ceramics with pyrochlore-type structure for high-temperature application. The zirconate ceramics were synthesized via a solid-state reaction method where rare-earth oxides and ZrO2 were used as starting materials. The physical structures were characterized by X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. It was confirmed that Nd2Zr2O7 and Sm2Zr2O7 are pyrochlore phases, while Yb2Zr2O7 and Gd2Zr2O7 are defect fluorite phases. The electrical property investigated by using resistance–temperature measurements demonstrated that the prepared A2Zr2O7 zirconate ceramics exhibit a typical characteristic of NTC over a wide temperature range between 673 and 1273 K. Particularly, A2Zr2O7, in addition to having high activation energy to ensure better sensitivity, can still maintain higher resistivity under high-temperature environments. Furthermore, the resistivity of A2Zr2O7 is almost independent of the change in oxygen partial pressure. These properties are superior to the classical spinel-type or perovskite-type NTC thermistor, providing valuable information to explore new NTC thermistor for high-temperature applications. [ABSTRACT FROM AUTHOR]

While mullite is a significant oxide ceramic material, its current preparation process has many limitations such as complicated process, low efficiency, and high cost. In this paper, directed laser deposition (DLD) was used to prepare mullite ceramics directly using α-Al2O3 and SiO2 powder as raw materials. The phase composition, microstructure, and primary defects of prepared samples were investigated by XRD, Raman spectroscopy, and SEM/EDS. Vickers indentation and three-point bending experiments were used to evaluate mechanical properties. The results showed that microstructure was mainly composed of a mullite crystal phase and Si-rich glass phase. It is shown that mullite ceramics were successfully synthesized in situ during the DLD process with the use of Al2O3 and SiO2 powder. Morphology of mullite crystal inside cylindrical sample was particular "tabular cellular," which transformed into "rod cellular" at the edge. Two mullite crystals were arranged along deposition direction basically, surrounded by the Si-rich glass phase. The defects included pores with various sizes and crack, in which large pores were mainly distributed at the edge of the sample, and small pores were throughout the section. The crack was distributed in the center of the sample and spread to the edge. Mechanical properties test showed flexural strength, microhardness, and fracture toughness were 62.8 ± 30.3 MPa, 12.7 ± 0.34 GPa, and 1.84 ± 0.14 MPa·m1/2, respectively. It is considered that pores and crack were responsible for poor mechanical properties. This research is expected to provide a new option for the rapid preparation of mullite ceramics. [ABSTRACT FROM AUTHOR]

This paper proposed a method for preparing subtle and complex lattice structure Al2O3 ceramic via digital light processing (DLP) 3D printing technology. The solid-phase mass fraction of Al2O3 ceramic slurry and the porosity of the green body reached 52% and 83%, respectively. According to the TG-DSC curve and two-way analysis of variance, the optimum technological parameters for debinding and sintering of Al2O3 ceramic green body were determined. The same shrinkage of Al2O3 ceramic prepared by pressureless sintering in all directions was confirmed. The density of sintered lattice structure Al2O3 ceramic was 95%, and the diameter of the lattice structure strut was about 170 μm. XRD and Raman spectrum showed that the crystal phase of the sintered Al2O3 ceramic was α-phase, which has a good crystal quality. SEM results revealed a high density without significant pores and cracks sintered ceramic. The strict complex structure Al2O3 ceramic prepared by DLP technology had a compact microstructure and similar to the mechanical strength of Al2O3 prepared via the conventional shaping method, thereby providing an effective method for fabricating large specific surface area ceramic radiators and fine ceramic components in other fields. [ABSTRACT FROM AUTHOR]

This paper reports that Cu acceptor substitution at the Ti site has significant effects on structure and electrical properties of Aurivillius-phase Bi4Ti3O12 polycrystalline ceramics. Phase purity, microstructure and defect chemistry of Bi4Ti3−xCuxO12−x (BiT–100xCu, x = 0–0.12) are characterized by XRD, SEM, EDS and EPR measurements. Neutron diffraction refinement indicates that BiT–8Cu has an orthorhombic symmetry [space group: B2cb; lattice parameters: a = 5.4116(1) Å, b = 32.833(1) Å, c = 5.4479(1) Å and V = 967.98(5) Å3]. Impedance spectra of BiT–100xCu were measured under variable oxygen partial pressure (pO2). Bi4Ti3O12 shows mixed electronic (hole) and ionic conduction owing to the existence of oxygen vacancies ( V O · · ) arising from the loss of Bi2O3 during sintering. Interestingly, bulk conductivity in Cu-substituted Bi4Ti3O12 ceramics is predominately ionic due to the fact that there are considerably additional oxygen vacancies introduced into the perovskite lattices. The optimum composition of BiT–8Cu shows high ionic conductivity in the bulk with a value of ~ 0.007 S/cm at 650 °C. [ABSTRACT FROM AUTHOR]

Powellite ceramic represents a waste form matrix material to immobilize minor actinides and Mo from reprocessed UMo nuclear fuel. In this paper, the Ca1−xLix/2Gdx/2MoO4 (0 ≤ x ≤ 1) series is prepared by solid-state reaction using Gd3+ as trivalent minor actinide (Cm3+) surrogate, and the structure/microstructure is characterized by XRD, HRTEM, Raman spectroscopy and SEM. Rietveld refinements show that the couple (Gd3+ and Li+) enters into the eightfold coordinated Ca site of the powellite structure. With the increase in the contents of Gd and Li, Raman bands broaden due to the distortion of MoO4 tetrahedra and disordered arrangements of Gd3+ and Li+. The chemical durability analyzed by the PCT-B indicates that the leaching behaviors of Gd and Mo are related to the interfacial dissolution–reprecipitation mechanism. For the Ca0.5Li0.25Gd0.25MoO4 ceramic, 7-day NLGd and NLMo are shown in the order of ~ 10−4 and ~ 10−4 g m−2, respectively. Thus, our initial results of the structure and chemical durability will provide insights to design new single- or multiphase waste forms for the Mo-rich HLW conditioning. [ABSTRACT FROM AUTHOR]

In this paper, the (In0.5Nb0.5)xTi1−xO2 (with x = 0, 0.005, 0.01, 0.02, 0.05, and 0.1) ceramics were prepared by solid-state reaction. To investigate the humidity sensitive properties, capacitance was measured as a function of relative humidity (RH). Our results reveal that the capacitance increases with the increase in RH and doping level. The best humidity sensitivity of 229.22 pF/%RH was achieved in the sample with x = 10. The humidity sensing mechanism was ascribed to the defects of oxygen vacancies and Nb Ti · ions. Besides, the humidity shows remarkable influence on the dielectric properties of the co-doped samples via the surface-layer effect, which leads to a Maxwell–Wagner relaxation near room temperature. This work underscores that the (In + Nb) co-doped samples are sensitive to the environment moisture. The processing conditions should be optimized for superior dielectric behavior in (In + Nb) co-doped TiO2 ceramics. [ABSTRACT FROM AUTHOR]

Directionally aligned prismatic and lamellar porous alumina scaffolds with a high strength-to-density ratio were fabricated from submicron Al2O3 powders and a tiny quantity of nanoscale TiO2 sintering aids by freeze casting using TBA and water as solvents. Both freezing temperature (− 10 °C, − 50 °C, − 90 °C) and sintering temperature (1300 °C, 1350 °C, 1400 °C) were varied to adjust pore parameters while a low solid loading (15 vol%) was maintained to ensure high porosity. This paper describes and compares the microstructures, porosity, pore size, wall thickness and compressive behavior of the scaffolds with two typical pore morphologies (lamella and honeycomb), which help to identify their scope of application and to unveil the relationship between pore morphology and mechanical property to optimize the material performance. The failure modes of these two types of scaffolds under compression were simulated. The TBA-based 1 wt% TiO2-containing alumina scaffolds with dense ceramic walls that were freeze-cast at − 90 °C and sintered at 1400 °C exhibited a compressive strength of 160 MPa with a porosity of 59%, indicating lightweight and high-strength characteristics. [ABSTRACT FROM AUTHOR]

Optimizing thermal and mechanical properties of clay block masonry requires detailed knowledge on the microstructure of fired clays. We here identify the macro- and microporosity stemming from the use of three different pore-forming agents (expanded polystyrene, sawdust, and paper sludge) in different concentrations. Micro-CT measurements provided access to volume, shape, and orientation of macropores, and in combination with X-ray attenuation averaging and statistical analysis, also to voxel-specific microporosities. Finally, the sum of micro- and macroporosity was compared to corresponding data gained from two statistically and physically independent methods (namely from chemical analysis in combination with weighing, and from mercury intrusion porosimetry). Satisfactory agreement of all these independently gained experimental data renders our new concept for identifying the pore spaces of fired clay as a very promising tool supporting the further optimization of clay blocks. [ABSTRACT FROM AUTHOR]

A novel processing route for fabricating cellular and microcellular ceramics with controllable open-cell content has been developed. The proposed strategy for producing cellular and microcellular ceramics involves: (i) development of desired foamable polysiloxane–polyolefin blends by using a compounder element, in which the polyolefin phase is uniformly dispersed in the polysiloxane matrix, (ii) foaming the obtained blends by implementing the thermodynamic instability principle to produce a cellular or microcellular ceramic precursor structure, and (iii) completing the organic–inorganic transition without sacrificing the obtained cellular or microcellular structure and inducing open-channels in the cell walls by burning out the sacrificial dispersed polyolefin phase at elevated temperatures. By controlling the viscosity of the dispersed polyolefin phase, the polyolefin concentration and compounding parameters, the polysiloxane–polyolefin blend morphology can be varied. Furthermore, plus a deliberate control of foaming and pyrolyzing parameters, the foam morphology and open-cell content of produced cellular and microcellular ceramics can be adjusted. In this paper, the technique to get a desired cellular and microcellular ceramic precursor structure is demonstrated. The deliberate pyrolysis technique to complete the organic–inorganic transition and the mechanical properties of the obtained microcellular ceramics will be discussed in another paper. [ABSTRACT FROM AUTHOR]

The paper reviews the wear behaviour of oxide ceramics. Wear maps are considered and consequently mild and severe wear are defined. Since the use of ceramics in engineering applications require operation in the mild wear regime, the paper concentrates on mild wear mechanisms, but also considers factors which control the transition to severe wear. Within the mild wear regime, the formation of tribofilms are discussed and the manner in which dislocation activity leads to the wear transition is considered. The wear of so-called ceramic nanocomposites, for which no time dependent wear transition has yet been observed, is considered and the reasons for enhanced performance discussed. The role of transformation toughening in zirconia ceramics is considered in detail, and reasons for the generally poor wear response of these materials defined. [ABSTRACT FROM AUTHOR]

In a companion paper, a ceramic formulation based on CaZrO3 was developed to decrease the sintering temperature of this oxide. We achieved in obtaining a low sintering temperature ceramic fireable below the copper melting point while maintaining attractive properties whatever the atmosphere used (oxidising or reductive). The present paper deals with the fabrication of the copper electrodes multilayer ceramic capacitors (MLCC) and their optimisation. Several points have been tested to enhance the characteristics of the components. They are based on the precursors origin and the manufacturing process optimisation. These studies result in NPO components with good properties (C ∼ 30 pF/5 active layers; τℇ = -45 ppm/K; ESR ∼ 20 mΩ at 30 MHz; tgδ < 10 × 10-4; ρi > 1012 Ω · cm). [ABSTRACT FROM AUTHOR]

This paper presents the micro-shot peening of zirconia (ZrO)-advanced ceramics applicable for bio-medical, dental, automotive and aerospace sectors. A ZrO-advanced ceramic was micro-shot blasted with selected parameters as a first-step investigation focused on the topography, microstructure, surface hardness and the surface fracture toughness ( K) characteristics. A new technique of micro-blasting was conducted using a portable shot blaster. A white-light interferometer, scanning electron microscopy and Vickers indentation technique were employed for the analysis. This was followed by determining the K using an empirical equation. Surface roughness was improved by 34 % after micro-shot blasting treatment. No surface cracking was present which generally exists due to the brittle nature of the ceramic. The hardness, however, reduced by 5.6 % with a reduction in the Vickers crack length of 9 %. This improved the K by 3 % when comparing the micro-shot peened surface to the original, as-received surface. It is difficult to conclude if the ZrO-advanced ceramic has undergone plastic deformation and the movement of dislocations increased to strengthen the ZrO ceramic at this stage. However, based on the results, it can be predicted that a level of surface compression was induced beneath the micro-shot peened layer as indicated from the result of the surface topography and integrity. This would justify the hardness modification and the enhancement in K. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to describe the five-parameter grain boundary character distribution (GBCD) of polycrystalline silicon and compare it to distributions measured in metals and ceramics. The GBCD was determined from the stereological analysis of electron backscatter diffraction maps. The distribution of grain boundary disorientations is non-random and has peaks at 36°, 39°, 45°, 51°, and 60°. The axis-angle distribution reveals that most of the grain boundaries have misorientations around the [111], [110], and [100] axes. The most common grain boundary type (30 % number fraction) has a 60° misorientation around [111] and of these boundaries, the majority are twist boundaries. For other common boundaries, symmetric tilt configurations are preferred. The grain boundary character distribution of Si is distinct from those previously observed for metals and ceramics. The measured grain boundary populations are inversely correlated to calculated grain boundary energies available in the literature. [ABSTRACT FROM AUTHOR]

The renewed interest in transition metals diborides, classified as ultra high temperature ceramics, for applications at high temperature or in highly aggressive environments has given rise in recent years to an increasing number of research projects particularly devoted to the study of their interfacial characteristics when placed in contact with liquid metals and alloys, which complement and upgrade the limited number of older investigations. This paper critically reviews these systematic studies, addressing both basic (wettability, interfacial tension and phase equilibria determination) and application (joining by brazing) aspects. Particular reference is made to studies aimed at elucidating the role that dissolution, chemical reactions, additions of active metal elements to the molten matrix have in the wetting process and on the solid-liquid adhesion in relation to the mechanical characteristics of brazed joints. [ABSTRACT FROM AUTHOR]

The purpose of this review is to present the recent developments in silicon nitride (SiN) ceramics and to examine the achievements regarding our understanding of the relationship between processing conditions, chemical composition, microstructure and mechanical properties of SiN. SiN is one of the most important structural ceramics because it possesses a combination of advanced properties such as good wear and corrosive resistance, high flexural strength, good fracture resistance, good creep resistance and relatively high hardness. These properties are obtained through the processing method involving liquid phase sintering in which a tailored microstructure, with high aspect ratio grains and chemistry of intergranular phase, triggers the toughening and strengthening mechanisms leading to the development of high fracture toughness and fracture strength. However, despite high fracture toughness and strength, SiN ceramic materials still break catastrophically, and the fracture behaviour of this ceramic is considered to be the major obstacle for its wider use as a structural material. In addition to the macrostructure-mechanical properties relationship, this paper also reviews new designs involving laminates possessing no plane of weakness and some theoretical developments involving crack opening displacement. Proposals of how to improve the fracture resistance were also discussed. [ABSTRACT FROM AUTHOR]

Wave-transparent materials used at high temperature environment generated by high supersonic and hypersonic speeds must possess excellent mechanical property. In this paper, porous Si3N4 ceramics with high strength were fabricated by low molding pressure (10 MPa) and pressureless sintering process, without any other pore forming agents. The sintering behavior and the effect of porosity on the mechanical strength and dielectric properties were investigated. The flexural strength of porous Si3N4 ceramics was up to 57–176 MPa with porosity of 45–60%, dielectric constant of 2.35–3.39, and dielectric loss of 1.6–3.5 × 10−3 in the frequency range of 8–18 GHz, at room temperature. With the increase of porosity, the flexural strength, dielectric constant, and dielectric loss all decreased. [ABSTRACT FROM AUTHOR]

In this paper, we have examined and analyzed the effects of systematic intercalation of the lead ions on vanadate–tellurate glass ceramics with interesting results. The structural properties of the lead–vanadate–tellurate glass ceramics of compositions xPbO·(100 − x)[6TeO2·4V2O5], x = 0 − 100 mol%, are reported for the first time. It has been shown by X-ray diffraction that single-phase homogeneous glasses with a random network structure can be obtained in this system. Among these unconventional lead–vanadate–tellurate glass ceramics, we found that network formers are good host material for lead ions and are capable to intercalate a variety of species such as Te2V2 5+O9, Pb3(V5+O4)2, Pb2V2 5+O7, and V2O5-rich amorphous phase. On the other hand, these glass ceramics contain V4+ and V5+ ions necessary for the electrical conduction. Based on these experimental results, we propose that the V4+=O bonds are created by two different mechanisms: the first of reduction of V5+ ions to V4+ ions and thus of creation of V4+=O bonds. [ABSTRACT FROM AUTHOR]

In this paper, the densification of a ceramic powder matrix that contained large macropores of the size much larger than the average grain size of the matrix was studied. The grain-boundary diffusion controlled sintering models of ceramic matrix contained large macropores were first established. A sintering potential associated with the macropores was also verified and introduced into the models. The experimental data were collected for the sintering of porous 8 mol% yttria-stabilized zirconia system with 20 vol% large pores. The predictions of the model were found in good agreement with experimental data. [ABSTRACT FROM AUTHOR]

This paper describes some technical limitations encountered in joining ceramics–ceramics or ceramics–metals, and how, to some extent, they have been practically overcome. The effect of the residual stresses on the strength of joints fabricated between alumina–alumina or alumina and the nickel base alloy HAYNES® 214™ using a solid-state bonding technique with Ni interlayer was studied. Finite element analyses (FEA) for the elastic–plastic and elastic–plastic–creep behavior have also been used to better design the joints and to predict their performance. It was found that the residual stresses caused by the thermal expansion mismatch between alumina (Al2O3) and the Ni-based superalloy (HAYNES® 214™) have severely deteriorated the joints compared to Al2O3–Al2O3 joint fabricated with the same solid-state bonding parameters. The high residual stresses zones obtained through the FEA simulation fitted well with the fractographic observations of the Al2O3/Ni/HAYNES® 214™ joints. Also, in order to use the joint material as a structural material, the study about the effect of geometrical parameters has been performed. Optimal geometries have been determined. [ABSTRACT FROM AUTHOR]

A model that was proposed originally to account for optimal superplasticity in metals and alloys with grain size in the micrometer range and later extended in a few subsequent papers to cover optimal superplastic deformation in ceramics, sub-micrometer-grained and nanostructured materials and intermetallics is described, with an emphasis on the current ideas used in this model and the mathematical procedure used at present (yet to be published in detail) for validating the proposals. The central assumption is that the rate controlling deformation process is confined to high-angle grain/interphase boundary regions that are essential for grain boundary sliding developing to a mesoscopic scale (defined to be of the order of a grain diameter or more) and for superplastic flow setting in. The strain rate equation was validated against experimental observations concerning metals, alloys and ceramics of micrometer- and sub-micrometer grain sizes, nanostructured materials and intermetallics. [ABSTRACT FROM AUTHOR]

This paper highlights the dielectric, pyroelectric, and resistivity studies of Ba1.45Sr2.4Dy0.1Li xNa2− xNb10O30 ( x = 0 ≤ x ≤ 1.0) tungsten–bronze-structured ceramics. X-ray diffraction studies indicated single orthorhombic ( mm2) phase supported by tolerance factor and average electronegativity difference. The lattice parameters, unit cell volume, axial ratio, and densities are calculated from XRD studies. The experimental densities obtained are about 95% to that of theoretical values. It is found that the unit cell volume enhanced up to Li0.8. The effect of Li modification and Dy doping on εRT, $$ \varepsilon_{{{\text{T}}_{\text{c}} }}, $$ and Tc in BSNN system are discussed. D.C. resistivity studies indicated the positive temperature coefficient of resistivity (PTCR) response in these compositions. [ABSTRACT FROM AUTHOR]

Pore size has been found to strongly depend on the sintering program in the preparation of porous ceramic membranes. In this paper, a model was developed to predict the variation in pore size and porosity of membranes during the sintering process. A comparison of shrinkage characteristics was made between the sintering processes of supported membranes and unsupported membranes. For supported membranes, the effect of restriction coming from a rigid substrate on the sintering behavior has been taken into account in the calculation. It is predicted that the pore size increases in supported membranes and decreases in unsupported membranes as the sintering temperature is increased. Calculations also showed that the loss of porosity in the supported membranes was less than that in the unsupported membranes. In order to verify reliability of this model, unsupported and supported membranes were prepared with α-Al2O3 powders at the sintering temperatures ranging from 1125 °C to 1325 °C. The pore size and porosity were measured by gas permeation technique and Archimedes’s method. The experimental results for the unsupported and supported α-Al2O3 membranes showed a good agreement with those calculated from the model. Therefore, this model provides an effective tool in predicting the porosity and the pore size of ceramic membranes at the different sintering temperatures. [ABSTRACT FROM AUTHOR]

This paper has clarified the anelasticity of 8Y-FSZ/α-alumina composites wherein the 8Y-FSZ phases are dispersed like islands. The amount of anelastic strain generated and the manner of anelastic deformation were compared to those of monolithic 8Y-FSZ. The anelastic strains of six kinds of 8Y-FSZ/α-alumina, as well as of monolithic 8Y-FSZ and monolithic α-alumina, were measured. The results showed that the anelastic strain was produced even in the composite where 8Y-FSZ phases existed as islands, and that the more the anelastic strain produced, the higher the volume fraction of 8Y-FSZ. In addition, the composition with a fully densified alumina phase had the effect of inhibiting anelastic strain in the 8Y-FSZ phase. [ABSTRACT FROM AUTHOR]

The processing of yttria-stabilised zirconia (Y-ZrO2)-based ceramic nanocomposites by means of pulsed electric current sintering (PECS) is described. A nanometer-sized electrically conductive secondary TiCN phase was added to the insulating zirconia matrix in order to make the composite electrically conductive. The paper focuses on the importance of processing conditions and highlights the benefits of the PECS method as compared to more traditional hot pressing. The mechanical and microstructural properties of the ZrO2–TiCN composites have been determined, and the benefits of using an electrical current to densify these composites were explained in terms of the evolution of the electrical properties of the densifying powder compact. [ABSTRACT FROM AUTHOR]

Designing tissue engineering scaffolds with the required mechanical properties and favourable microstructure to promote cell attachment, growth and new tissue formation is one of the key challenges facing the tissue engineering field. An important class of scaffolds for bone tissue engineering is based on bioceramics and bioactive glasses, including: hydroxyapatite, bioactive glass (e.g. Bioglass®), alumina, TiO2 and calcium phosphates. The primary disadvantage of these materials is their low resistance to fracture under loads and their high brittleness. These drawbacks are exacerbated by the fact that optimal scaffolds must be highly porous (>90% porosity). Several approaches are being explored to enhance the structural integrity, fracture strength and toughness of bioceramic scaffolds. This paper reviews recent proposed approaches based on developing bioactive composites by introducing polymer coatings or by forming interpenetrating polymer-bioceramic microstructures which mimic the composite structure of bone. Several systems are analysed and scaffold fabrication processes, microstructure development and mechanical properties are discussed. The analysis of the literature suggests that the scaffolds reviewed here might represent the optimal solution and be the scaffolds of choice for bone regeneration strategies. [ABSTRACT FROM AUTHOR]

Composite laminates on the nanoscale have unique properties, such as high strength, high wear resistance, and biocompatibility. In this paper we report on the nanoindentation behavior of a model metal–ceramic nanolaminate consisting of alternating layers of aluminum and silicon carbide (Al/SiC) processed by PVD on a Si substrate. Composites with different layer thicknesses were fabricated and the effect of layer thickness on Young’s modulus and hardness was quantified. The effect of indentation depth on modulus and hardness was studied. The damage that took place during nanoindentation was examined by cross-sectioning the samples by focused ion beam (FIB) technique and imaging the surface using scanning electron microscopy (SEM). Finite element modeling (FEM) of nanoindentation of nanolaminates was conducted. The damage patterns observed in experiments were qualitatively supported by the numerical simulations. [ABSTRACT FROM AUTHOR]

Using pressure-pulsed chemical vapor infiltration (PCVI) method, TiN was partially infiltrated at 850 °C from gas system of TiCl4 (1%)–N2 (10%)–H2 into the highly porous carbon substrates prepared by the carbonization of cotton-wool, filter paper, and wood at 1,000 °C in Ar for 4 h. After 10,000 pulses of PCVI, electro-conductive porous ceramics having the three-dimensionally continuous current paths were obtained, which had the porosity of 80% and more, the resistivity of 10−5–10−6 Ω m, and the average pore sizes of 10–40 μm. The geometric surface area per unit volume of the sample was higher than that of the conventional foil-type current collector for lithium-ion battery. The surface area showed the highest value for the sample obtained from carbonized wood substrate. [ABSTRACT FROM AUTHOR]

A study of the structural characteristics of the composites [Pb(Fe0.5Nb0.5)O3(PFN)] x -[Cr0.75Fe1.25O3(CRFO)]100− x ( x = 0 (CRFO100), 10, 50, 90, 100) was performed in this work. The compounds PFN100 and CRFO100 were prepared by conventional solid-state method and investigated by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and 57Fe Mössbauer Spectroscopy techniques. The X-ray analysis shows that PFN100 is tetragonal and the CRFO100 phase has a trigonal symmetry. The refinement of all the composites was also performed and discussed in this paper. The Mössbauer spectrum for the composite samples shows a paramagnetic doublet and a sextet probably assigned to a magnetic phase associated to Fe+3. For the sample PFN100, only a magnetic field of 49.5 T (isomer shift (δ) = 0.21 mm/s) was detected. For the composite sample, the δ and Δ are typical of Fe ions at sites of octahedral coordination. [ABSTRACT FROM AUTHOR]

High current characterization of SnO2-based varistors have been carried out and the results obtained have been compared with those ZnO-based commercial surge arresters. It is shown that for a high temperature sintering (1350 °C), the leakage current, breakdown voltage and the saturation at high current density are similar between both types of surge arresters. The paper shows, for the first time, that the high breakdown voltage observed with tin dioxide cannot be easily maintained since the saturation of the ceramics is reached for current densities of several amperes per square centimetre. [ABSTRACT FROM AUTHOR]

Gd3+ was chosen as a substitute for Bi3+ in BiNbO4 ceramics, and the substitution effects on the sintering performance and microwave dielectric properties were studied in this paper. The high temperature triclinic phase was observed only in the Bi0.98Gd0.02NbO4 ceramics when sintered at 920 °C. Both bulk densities and dielectric constant (εr) increased with the sintering temperature, while decreased with the Gd content. The quality factor ( Q) exhibited a correlation to the Gd content and the microstructures of Bi1− x Gd x NbO4 ceramics. At the sintering temperature of 900 °C, Bi0.992Gd0.008NbO4 ceramics exhibited microwave dielectric properties of εr ∼ 43.87, Q × f ∼ 16,852 GHz (at 4.3 GHz), and its temperature coefficient of resonant frequency (τf) was found to be near-to-zero. [ABSTRACT FROM AUTHOR]

This paper introduces the Dual Electro/Piezo Property (DEPP) gradient technique via Micro-Fabrication through Co-eXtrusion (MFCX) which pairs a high displacement lead zirconate titanate (PZT) piezoceramic with a high permittivity barium titanate (BT) dielectric. By grading with this material combination spatially across an actuator, the electric field is concentrated in the more active region for improved efficiency, higher displacements, and complex motions. To aid in synthesis and analysis of any gradient profile, compositional maps are provided for key material properties (density, stiffness, permittivity, and piezoelectric coefficients). The DEPP technique was validated, independent of the MFCX process, by powder pressing a conventional bimodal gradient beam which demonstrated through experiments high displacement capabilities at lower driving potentials than comparable functionally graded piezoceramic actuators. For more complex gradients, the MFCX process was adapted to the DEPP gradient technique and illustrated by the fabrication of a linearly graded prototype whose monolithic nature and gradual material variation significantly reduces internal stresses, improves reliability, and extends service lifetime. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated ac conductivity, dielectric losses, permittivity of Ba x Sr1− x Fe0.8Co0.2O3−δ ( x = 0, 0.5, 1) ceramics. It has been observed that increase in barium content decreases activation energy (i.e. conductivity increases) in the higher temperature region (550–770 K). In the lower temperature region system with x = 0 shows metallic conductor behavior and system with x = 1 shows thermally activated behavior. The ferroelectric peak temperatures are observed at 700, 750 and 723 K for x = 0, 0.5 and 1, respectively. This peak temperature can be attributed to the oxygen-vacancy-related dielectric relaxation. With the increase of barium content the dielectric dispersion tend to diminishes. Partial substitution of strontium with barium (for x = 0.5) reduces dielectric losses by 50%. [ABSTRACT FROM AUTHOR]

The paper deals with elastic thermal stresses in an isotropic multi-particle-matrix system consisted of periodically distributed spherical particles in an infinite matrix, imaginarily divided into cubic cells containing a central spherical particle. Originating during a cooling process as a consequence of the difference in thermal expansion coefficients between the matrix and the particle, and investigated within the cubic cell, the thermal stresses, as functions of the particle volume fraction v, being transformed for v = 0 to those of an isotropic one-particle-matrix system, are maximal at the critical particle volume fraction, representing a considerable value related to maximal resistance of the thermal-stress strengthened multi-particle-matrix system against mechanical loading. The thermal stresses are derived for such temperature range within which the multi-particle-matrix system exhibits elastic deformations, considering the yield stress and the particle-matrix boundary adhesion strength. With regard to a curve integral of the thermal-stress induced elastic energy density, critical particle radii related to crack initiation in ideal-brittle particle and matrix, functions describing crack shapes in a plane perpendicular to the direction of crack formation in the particle and in the matrix, and consequently dimensions of a crack in the particle and in the matrix are derived along with the condition concerning the direction of the crack formation. Additionally, derived by two equivalent mathematical techniques, the elastic energy gradient within the cubic cell, representing a surface integral of the thermal-stress induced elastic energy density, is presented to derive the thermal-stress induced strengthening in the spherical particle and in the cubic cell matrix. The former parameters for v = 0 are derived using the model of a spherical cell with the radius $${R_c\rightarrow\infty}$$ . Derived formulae are applied to the SiC–Si3N4 multi-particle-matrix system, and calculated values of investigated parameters are in a good agreement with those from published experimental results. [ABSTRACT FROM AUTHOR]

A significant weight loss of copper plate was observed after copper-water vapor interaction near critical point. This leads to the acceleration of the ceramic layer formation on SUS surface during granite-water vapor interaction in the presence of copper. In this paper, we have determined the chemical state of copper at which the mass transfer takes place through reaction with H2 and O2+N2 gas mixture at the different O2 amount. Obtained results indicate that the weight loss of copper plate occurs at Cu2O (+1) state due to a complex processes. The morphology of copper species on the surface of mesh and granite suggests that the Cu2O was dissolved in water vapor and recrystallized on the surface of mesh and granite. Copper species were characterized by X-ray diffraction(XRD), scanning electron microscopy (SEM) equipped with an energy dispersive X-ray (EDX). [ABSTRACT FROM AUTHOR]

This paper deals with the effects of preparation methods on the texture development and densification in textured SrBi4Ti4O15 (SBT) ceramics. The specimens were prepared by the oriented consolidation of anisotropic particles (OCAP), templated grain growth (TGG) and reactive templated grain growth (RTGG) methods. The specimens with extensive texture were obtained by all methods except for TGG with small template and large matrix particles. The origin of extensive texture development was the growth of aligned platelike particles. A characteristic of microstructure was the formation of colonies, in which platelike grains contacted face-to-face. The size of colonies was dependent on the preparation method, and determined the size of pores between colonies, which had a large effect on the sintered density. The OCAP and RTGG methods gave the green compacts composed of only platelike particles and large colonies and pores formed during sintering. The TGG method gave the green compacts composed of platelike and equiaxed particles and prevented the formation of large colonies and pores during sintering. Thus, the dense, highly-textured SBT ceramics were obtained by the TGG method. [ABSTRACT FROM AUTHOR]

Achieving a stable dispersion with high solid loading is pre-requisite in many conventional/emerging ceramic forming processes. Hence, assessing the quality of dispersion is one of the critical aspects to be considered during forming process to ensure the final product quality. There are several direct/indirect techniques to assess the quality of dispersion. Many are optical methods, which generally require dilution of the suspension, with consequent alteration of the equilibria. This complicates the system unless particular care is taken to compensate for the dilution process. Many times it has been observed that a dispersant, that provides good dispersion at low solids concentration will not necessarily provide good dispersion at high solids concentration. This paper compares two indirect techniques, namely, particle charge detector (PCD) using the principle of `Streaming Potential' and capillary suction time (CST) apparatus based on the principle of capillary suction pressure to study the effectiveness of a dispersant for maximum dispersibility. [ABSTRACT FROM AUTHOR]

Due to high deposition rates and the avoidance of inflammable, often hazardous organic solvents EPD from aqueous suspensions is a fast and low-cost shaping technique for ceramics and glasses. Since the deposition rate is independent of particle size EPD has an outstanding ability for the shaping of nano-particles. In this paper the shaping of complex silica glass and zirconia components, like tubes or structured parts by means of the membrane method is shown. Three-dimensional shaped porous polymer moulds were used as ion-permeable deposition surface. To enable near-shape manufacturing, mixtures of nanosized and microsized particles were electrophoretically deposited. No size-dependent separation was observed. Due to the very high green density of these green bodies (up to 84% of the theoretical value) shrinkage could be reduced to 4.7%. Not only oxide ceramics but also silicon carbide was deposited from aqueous suspensions. Apart from bulk SiC, protective coatings with a thickness of app. 60 μm were applied on top of CFC substrates by EPD. Good adhesion was observed and no cracking occurred. Furthermore, electrophoretic impregnation was used for the modification of porous green bodies. Thus silica glasses with graded density and pore size as well as functionally graded composites were prepared. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cells are currently constructed using a yttria stabilised zirconia electrolyte membrane. However, zirconia has a number of disadvantages associated with its use, such as the high operational temperatures required for it to exhibit acceptable levels of ionic conductivity. Alternative ceramics such as doped cerium oxide show promise as electrolytes capable of operating at reduced temperatures, but introduce additional problems such as electronic conduction and inferior mechanical properties. This paper describes the manufacture and characterisation of a number of prototype electrolytes consisting of a mixture of yttria stabilised zirconia and gadolinium doped ceria. Traditional ceramic processing techniques were used to produce the samples, which were then examined using dilatometry, impedance spectroscopy and X-ray diffraction. Results show a lowering of the ionic conductivity of zirconia with the addition of doped ceria. X-ray diffraction patterns obtained from the samples suggested that this effect could be attributed to the formation of a solid solution of ceria in zirconia. [ABSTRACT FROM AUTHOR]

In a bending load test for brittle materials, such as ceramics for spacecraft and aircraft, decreasing the number of test specimens required is a crucial problem. This paper discusses the effectiveness of using the information of both fracture stress and fracture location to decrease the number of specimens required to obtain the same precision as the Weibull estimator. The following results were obtained: It was found that by adding the fracture location information, the precision of the Weibull parameter estimation under the optimal design became 1.5–1.9 times better compared with the case of using only the fracture stresses. This means the number of samples necessary to attain the same precision becomes 1/1.5–1/1.9. Tables and figures which give information on the number of samples necessary to attain the required precision are given. [ABSTRACT FROM AUTHOR]

Zirconium titanates are widely used in electrical (common microwave dielectrics) and optical devices as well as in bifunctional catalysis and structural ceramics. In this paper, ultrafine amorphous solid microsphere precursor particles of zirconium titanate (ZrxTi1 - xO2) with possibly tailored intraparticle nanostructure (i.e., nanosized pores) were synthesized by a “dielectric-tuning” solution coprecipitation method, in which inorganic salts were dissolved in a simple water-alcohol mixture and homogeneous nucleation and growth of particles were then induced by heating at temperatures below 100°C. Near-monodispersed particles were obtained. Particle sizes (nanometers to a few micrometers in diameter) were controlled by adjusting the process parameters such as salt concentration, alcohol-to-water volume ratio, temperature, and heating time. Nanosphere particles were produced with a rapid microwave heating nucleation-control scheme. Transmission electron microscopic analysis of each individual microsphere indicates that uniform nanostructures (a few nanometers in pore size) as well as compositional homogeneity (in terms of the Zr/Ti ratio) have been obtained inside each amorphous microsphere. In situ high-temperature X-ray diffraction data show that no phase segregation was observed in as-preprared microspheres and the transition from amorphous to the single-crystalline ZrTiO4 phase occurred around 650°C for a composition of Zr/Ti = 1. Interestingly, thermal analysis (DTA/TGA) data indicate that the solution synthesis condition seems to affect the crystallization activation energy and onset temperature, which varies from 530 to 680°C. [ABSTRACT FROM AUTHOR]

The paper discusses the material removal process in refractory ceramics eroded by hydro-abrasive jets. In particular, bauxite, sintered magnesia, and magnesia chromite are eroded. The influence of abrasive particle velocity, local exposure time, abrasive mass-flow rate, and abrasive type is investigated. Erosion depth, specific erosion rate, and geometry of the generated cavities are measured and analysed. For particle velocity as well as for local exposure time, threshold conditions are identified. At low erosion intensity, target material properties and abrasive type do not affect the material removal process notably. From optical and SEM-microscopy it is further found that the material removal mode changes with the progression of the erosion process. In the upper region of the eroded kerf, the dominating material removal mode is the simultaneous cutting of matrix and inclusion grains (transgranular). In the lower range, the erosion process is characterised by the removal of the binding matrix followed by washing off the inclusion grains (intergranular). The balance between both modes depends on the energy delivered to the erosion site. These observations are explained by assuming a continuous loss in kinetic energy of the abrasive particles during HAE. Some features of non-linear fracture are noticed and suggestions are made how to use non-linear fracture parameters to evaluate erosion resistance. [ABSTRACT FROM AUTHOR]

In this paper, we describe the fabrication of Li2O-Al2O3-SiO2 (LAS) crystallized preforms with suitable drawing formability, and the characteristics of drawn LAS glass-ceramic capillaries. It was found that addition of K2O to the LAS glasses reduces crystallinity of the crystallized preforms and forms low-viscosity glass matrices. It was confirmed that, by using a parallel plate viscometer, such crystallized preforms show suitable viscosity for drawing below the melting temperatures of the crystalline phase. We also proved that the addition of K2O is effective in stabilizing the preforms by preferential precipitation of stable β-spodumene solid solution (s.s.), which is essential in preventing the deposition of coarse surface crystals during the drawing. The LAS glass-ceramic capillaries drawn from the crystallized preform containing 50 mass% β-spodumene s.s. showed a dimensional accuracy within sub-micrometers. It was confirmed that the glass-ceramic capillaries have a low thermal expansion coefficient (25 × 10-7/K) and excellent mechanical and chemical durability, making them promising candidate components of fiber-optic devices. [ABSTRACT FROM AUTHOR]

This article focuses on a study related to formation of an alumina-silicon carbide nanocomposite. Alumina-silicon carbide ceramics have been increasingly studied in the past few years as the combination should provide a novel ceramic with chemical and oxidation resistance at high temperatures. The properties of sub-micron grained composites are generally superior to those manufactured from larger particles and the importance of nanostructured materials will increase. In this paper high intensity ball milling of a mixture of silicon dioxide, aluminum and graphite powders is examined to determine whether the formation of a composite of alumina and silicon carbide can be achieved at a low temperature.